Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/17/16
Area Forecast Discussion
National Weather Service Louisville KY
855 PM EST Fri Dec 16 2016
Issued at 855 PM EST Fri Dec 16 2016
The forecast is in good shape.
A recent AMDAR sounding out of Louisville shows above-freezing
temperatures through a deep layer of the atmosphere several thousand
feet thick, with the exception of a very brief dip slightly below 0C
around 1500 feet. Dual pol data are suggesting that the echoes
showing up over southern Indiana are liquid drops at beam heights
around two to four thousand feet. In the few spots with the best
signal-to-noise ratio CC is showing strong homogeneity among the
This all agrees with the forecast calling for mainly rain tonight.
Still, with cold surface temperatures some brief, very light
freezing rain (little more than sprinkles) isn`t out of the question
for about an hour at onset. The best chance of any very light
freezing sprinkles is between 10pm and midnight in southern Indiana.
So far, however, the bone dry air at the surface has been doing a
good job of evaporating those hydrometeors before they make it to
the ground. Regional mesoanalysis shows warmer dew points to our
south have been steadily advecting northward for the past several
hours. Dew points are already approaching 40F in western Kentucky.
These higher dew points will continue to push aggressively to the
north and northeast, with all of central Kentucky and central
southern Indiana possessing dew points at or above freezing by 2am.
So, rain will indeed eventually make it to the ground tonight. It
will be light, though, with amounts less than 0.20" through daybreak.
.Short Term (Now through Sunday)...
Issued at 255 PM EST Fri Dec 16 2016
...Wintry Precip Likely Late Saturday Night Into Sunday Morning...
Cold and still dry air mass remains in place over the Ohio Valley as
high pressure is now retreating off the mid-Atlantic coast. Enough
warm advection in the SE low-level flow that temps are now just
either side of freezing, even in the face of a thick cirrostratus
ceiling. Surface low just about ready to pull ENE out of the OK/TX
Low-level jet will crank up this evening, with 900mb winds expected
to increase to 50 kt after sunset. Isentropic lift on the nose of
this jet will develop a precip shield, but quite a bit will be lost
to evaporative cooling in this very dry environment. Expect the
onset of light precip late this evening, and given the evap cooling,
precip type could be an issue at least initially. Have included
mention of freezing rain, mainly along and north of I-64. This does
not appear to be a sleet scenario given the expected lack of ice
crystals. Any mixed precip will be too short-lived to have
substantial impact, as temps will rise sharply through the 30s and
40s after midnight.
Rain will get more patchy in the morning once the initial wave of
isentropic lift pushes through. POPs for Saturday are quite high,
but it does not look like a washout as hi-res models show
substantial breaks, especially in the morning. Coverage and QPF
will increase through the afternoon as the surface low scoots from
STL to YYZ, pushing a cold front into the Ohio Valley. After the
mild start, max temps will top out in the lower/mid 60s.
Heaviest rainfall will be Saturday night with the strong surface
cold front, and a few embedded T-storms are also possible.
Instability is quite limited, but wind fields are dynamic enough
that we can`t rule out a marginally severe wind gust here or there.
Front pushes through after midnight Sat night, and temps will drop
like a rock behind it. The cold air does come in quickly enough to
undercut some decent QPF, and could present a precip type issue.
Still appears that the cold air arrives around the same time that we
lose ice crystals, but will be cold enough to support a period of
freezing rain late Saturday night into Sunday morning. QPF is
mercifully light by that point, but ice accumulations around a tenth
of an inch are possible. Even without freezing rain, we could still
see slick spots as any standing water freezes. Snow remains an
outside chance with the loss of ice crystals, but later in the day
as precip tapers off, the near-surface layer gets cold enough to
allow some fine snow grains. Either way, little or no snow
accumulation is expected. Temps generally in the 20s on Sunday
morning will remain there for most of the day under strong cold
.Long Term (Sunday night through Friday)...
Issued at 255 PM EST Fri Dec 16 2016
Arctic high pressure will settle in beginning Sunday night, and
modify as it remains draped over the southeastern CONUS through
midweek. Sunday night will be the coldest of the bunch,
with lows in the teens across Kentucky, single digits in southern
Indiana, and wind chills near zero. Highs on Monday will struggle to
reach 30 degrees. From there expect tranquil weather and slowly
moderating temps. GFS and ECMWF both show a disturbance swinging
through Wed night/Thu, but have significant differences in whether
it`s a northern or southern stream show. Have cut back on POPs in
that time frame, but will leave it up to the next shift whether to
.Aviation (00Z TAF Update)...
Issued at 643 PM EST Fri Dec 16 2016
Lots going on during this forecast period. Low pressure will ride
from END to STL tonight and on to CLE by this time on Saturday. It
will pull a warm front northward in the first few hours of the
period and swing a cold front through here in the SDF planning
Winds ahead of this system tonight will increase and become somewhat
gusty. With low level jetting developing plus a strong low level
inversion forming, will continue to carry LLWS tonight and into
Precipitation will break out late this evening. There is still a
possibility of about an hour of very light freezing rain at onset,
but plain rain is expected to be the dominant precip type.
Ceilings will lower as the atmosphere moistens, with MVFR cigs from
late this evening through the rest of the forecast.
Shower activity may wane a bit from late morning into early
afternoon Saturday, but then coverage should increase by afternoon
as the cold front approaches. Some thunder will be possible into the
evening hours, especially at BWG, but is not big enough of a concern
for inclusion in the TAFs quite yet.
In SDF`s planning period, cold air will sweep in behind the cold
front but precipitation should remain in the form of rain until the
very end of this TAF package.
Looking ahead to late Saturday night/early Sunday morning, beyond
this forecast period, there appears to be a threat of light
FZRA/FZDZ. Stay tuned.
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
835 PM CST Fri Dec 16 2016
833 PM CST
The main band of moderate to heavy snow, now over northeastern
Illinois, will abate by late evening as the band of frontogenesis
around 850 MB begins to shift out of the area. Before it ends, a
good 1 to 3 inches of fresh snow are likely over far northern
sections of the area. Once this band of snow ends, it appears the
main accumulating snowfall will be done for much of the area until
Saturday evening. However, intermittent light snow and or
freezing drizzle will be possible tonight into Saturday. Freezing
rain/drizzle may actually end up being the main P-type during
this period as drier air aloft moves over the area, resulting in
relatively warm cloud top temperatures at or above -10 C, which
favors a dearth of ice nuclei. We have therefore trended the
forecast for the remainder of the night in this direction.
While significant ice accumulations are not expected, some
glazing is likely, and this could make for hazardous travel,
especially on untreated roads. Given the likelihood of freezing
drizzle tonight into Saturday, followed by another period of
accumulating snow Saturday night, no changes are planned to the
current winter weather advisory.
The next concern will be the dangerously cold conditions expected
Sunday into Monday. We have opted to go ahead an issue a wind
chill advisory for Sunday through Monday morning for areas
generally along and north of I-80, though the entire area may end
up needing to be in the advisory. At the present time, areas in
the advisory are expected to have wind chills of 20 below to 30
below. There is a small potential that some areas could experience
wind chills in excess of 30 below over northern Illinois Sunday
night as actual air temperatures drop into the teens to low 20s
below zero. If wind chill values colder than 30 below appear more
likely, an upgrade to a wind chill warning may be needed for parts
of the area.
334 PM CST
Through Saturday Night...
After a prolonged top-down saturation process, the dry air is
finally losing out to the strong forcing for ascent based off
latest radar and aircraft sounding trends, with echoes indicative
of moderate rates developing over far northeast Illinois as of
this writing. The WAA process combined with the ascent stout mid-
level wave lifting northeast (noted by impressive cold cloud tops
on IR satellite) will bring the period of snow an impacts to the
evening commute. Have recently received a report of moderate to
heavy snow in Rockford area and snow quickly accumulating on
roadways. In a nod to the slightly longer saturation time than
earlier expected, did slightly lower QPF and forecast snow amounts
in this first round of snow to 1 to 4 inches, highest in the
Wisconsin border counties.
Later this evening and overnight, the best forcing will lift
northeast of the area except perhaps far north, but we will remain
in broad synoptic ascent. Attention turns to the potential for
freezing drizzle in roughly the I-80 to I-88 corridor area, as
guidance indicates to varying degrees the loss of saturation in
the snow growth zone and subsequent loss of ice crystals. Thus,
freezing drizzle or a "snizzle" (snow/freezing drizzle mix) could
cause a glaze of ice and additional travel issues overnight into
Farther south across our central Illinois counties and across
northwest Indiana south of the Kankakee River, concern has greatly
increased for freezing rain and ice accumulations. Guidance came
into better agreement on a slightly farther south low pressure
track (from STL to near/south of LAF), which will prevent much in
the way of boundary layer warming as a strong warm nose surges in
aloft. Overnight into Saturday morning, exit region of the upper
jet and continued isentropic ascent will cause an uptick in
precipitation just ahead of surface low path across area of
Forecast soundings are strongly supportive of freezing rain in
this timeframe, with full melting of hydrometeors. Given that
there is now expected to be a longer duration of temperatures at
or below freezing, ice accumulation could end up slightly upwards
of 1/10" in spots. With trend toward colder boundary layer in
guidance, lowered high temperatures to the low-mid 30s in the far
southeast CWA. If these temperatures are too warm as well, then
that would prolong icing concern. Even if readings creep just
above freezing, the very cold road temperatures could still result
in freezing on contact of liquid precip. Thus issued the Winter
Weather Advisory for Ford, Iroquois, Newton, Jasper and Benton
counties, in effect starting at 9pm this evening.
From mid Saturday morning through mid day, there is uncertainty
on the guidance regarding whether saturation returns to the snow
growth zone north of I-80. Overall lowered qpf and snow amounts
during this period, so will need to closely monitor trends.
Maintained mention of freezing drizzle potential in the grids, so
if occurring and not a full lull, this will continue to pose a
travel hazard on its own. With possibility that ice crystals will
be lacking, it could be that sleet will not be much of an issue
north of the heightened freezing rain concern area, but left
mention in grids for now.
Most recent guidance continues to be in better agreement of the
synoptic pattern Saturday afternoon into Saturday evening. The
mid-upper trough marking the leading edge of the incredibly cold
air mass in store for Sunday will be pivoting southeast, with some
sheared out short waves ahead of it. Associated large scale ascent
in deformation axis will cause a solid area of precipitation to
break out as thermal profiles rapidly cool with arrival of Arctic
air. Most of this will be snow as it shifts from northwest to
southeast across the area, except perhaps lingering mix changing
to snow southeast of I-57. Up to an inch of snow is possible
across far northern Illinois by sunset in this next round.
As the system deformation and upper trough move across the area
Saturday evening, forecast soundings show very steep lapse rates
above 600 mb. Thus, with this and good lift through the snow
growth zone, could see moderate to even briefly heavy snowfall
rates. 1 to 3 inches of snow could fall by the late evening area
wide. In addition, northwest winds will be gusting to 30-35 mph as
the bitterly cold air pours in, likely resulting in blowing and
drifting snow issues, particularly where the higher snow accums
occur tonight through tomorrow evening.
Also concerned with flash freezing of any liquid on road surfaces
in southeast CWA. With temperatures falling to the single digits
above and below zero after midnight, wind chill values will plunge
to 15 to 30 below zero. Will need a Wind Chill Advisory after the
end time of the Winter Weather Advisory (6am Sunday). Finally,
favorable lake effect parameters could enhance totals a bit into
Porter County, and will also need to monitor trends Sunday morning
there for a possible advisory extension. Overall, made no other
changes to the headlines that were already in effect, and very
little change to going forecast snow amounts due to expectation of
more snow Saturday evening than in previous forecast.
109 PM CST
Sunday through Friday...
The last big surge of cold air during this arctic outbreak will
arrive on Sunday. Strong and expansive high pressure will extend
through the nation`s heartland. While precipitation will be largely
finished, there is still enough of a pressure gradient between
the departing low to create blowing and drifting snow concerns in
the morning hours. Lighter lake effect snow may still be ongoing
across Porter County, IN, but the focus should shift east of the
area as the high moves east on Sunday.
Don`t be fooled by the sunshine on Sunday, as the 850 thermal trough
will be centered over our area, it will not be a pleasant day
outside. Wind chill readings which will start the day near -30 in
the Rockford area to -20 in northwest Indiana only look to
recover to maybe -25 to -15, and highs will range from the
single digits southeast to the low to mid single digits below
The ridge of high pressure will be positioned across the Mississippi
Valley in the afternoon and then stretched out across the Fox
River valley and into central Illinois Friday evening. With the
weakening winds, very cold start point and the recent snowfall, a
rapid temperature drop will ensue during this time, with some
areas already reaching the double digits below zero by sunset. The
biggest temperature drop will occur during the evening area with
lows possibly bottoming out in the teens to lower 20s below zero.
Model 2m temperatures depict -15 to -20 readings in our western
outlying areas, with MEX and ECE MOS for one of our cold spots
ARR of -14 and -16, impressive even for a MOS product. Model
guidance does suggest some recoveries overnight and into Monday
morning as lower level warm advection begins with the high
departing to the east. Wind chills by daybreak will generally be
-5 to -15 in the far south/southeast CWA, with -15 to -25 along
and north of I-80, above -20 all areas by mid morning or so.
There is some good news in that this arctic air intrusion comes to
a close, and we will have several dry days with teens for highs
Monday, 20s to near 30 Tuesday, and in the lower 30s (mid 30s
south) Wednesday, which is more like normal for winter equinox.
The next chance for precipitation will be Wednesday into Thursday
as a pacific shortwave moves quickly across the country. Model
guidance develops some light precip with this wave and its
associated cold front which at this point appears to be snow. The
wave comes through in a clipper-like fashion with current guidance
favoring our northern half of our area, with some back side
lighter snow showers behind it.
109 PM CST
High temperatures on Sunday (Dec 18) are forecast to remain in the
single digits above to single digits below zero. This will likely
be the coldest day of 2016. The current coldest day of 2016 is
|. Chicago`s high that day: 7, Low: -4. Some
records will be threatened or broken.
Rockford: Daily Low: -17 in 1983.
Forecast Low: -16.
Chicago: Daily Low: -11 in 1983.
Forecast Low: -13.
Rockford: Daily Low: -21 in 1983
Chicago: Daily Low: -14 in 1983.
For the 00Z TAFs...
Steady snow is expected to persist at the Chicago terminals
through mid evening with ocnl LIFR vsby expected in the heavier
bursts of snow. Main axis of snow expected to shift north of the
Chicago terminals late evening and through the overnight, but
could continue later into the evening and perhaps overnight at
RFD. In the wake of the steadier accumulating snow this evening,
look for perhaps some very lift/fine snow or perhaps a little mist
or freezing drizzle overnight into early Sunday morning, but it
appears unlikely that this precipitation will amount to anything
of significance. CIGS should steadily build down to IFR tonight
and probably remain IFR or perhaps low end MVFR at times through
Sunday. A second round of IFR vsby and accumulating snow is
expected Sat evening with increasing northwest winds likely to
eventually lead to blowing/drifting snow as well.
150 PM CST
Main marine concerns in the near term focus on modestly gusty
south-southeast winds late this afternoon and evening across
far southern Lake Michigan, in a region of surface pressure falls
in association with an advancing area of low pressure lifting out
of the Central Plains. Winds gusting near 25 kts at times are
expected, with Small Craft Advisories already in place for the
IL/IN shores through this evening. Attention then turns to the
tightening gradient and strong low-level cold advection
developing later Saturday as the Plains low moves south of the
lake and pulls off to the east. Combined with a substantial push
of bitter cold arctic air, and strong high pressure building
across the Plains and into the Midwest through Sunday, north gales
are expected to develop From north to south across Lake Michigan
Saturday afternoon and continue through early Sunday morning. The
northern periphery of the arctic high will then move across the
lake late Sunday, allowing winds to diminish and back to the
Southwesterly gales will then be possible on northern Lake
Michigan Monday into Monday evening as an area of low pressure
passes north of the Lakes, and strong high pressure remains across
the Ohio Valley. With cold arctic air in place, these periods of
higher winds will also produce freezing spray.
IL...Winter Weather Advisory...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-
ILZ022-ILZ023-ILZ032-ILZ033-ILZ039 UNTIL 6 AM Sunday.
Wind Chill Advisory...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
AM Sunday TO 10 AM Monday.
IN...Wind Chill Advisory...INZ001-INZ002...6 AM Sunday TO 10 AM
Winter Weather Advisory...INZ001-INZ002-INZ010-INZ011-INZ019
UNTIL 6 AM Sunday.
LM...Small Craft Advisory...NEARSHORE WATERS
UNTIL 10 PM Friday.
Gale Watch...LMZ743-LMZ744-LMZ745...9 PM Saturday TO 6 AM Sunday.
Gale Watch...LMZ777-LMZ779...6 PM Saturday TO 6 AM Sunday.
VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)
FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
Area Forecast Discussion
National Weather Service Mount Holly NJ
1012 PM EST Fri Dec 16 2016
High pressure will continue to move offshore tonight. Low pressure
moving from the mid-Mississippi to Saint Lawrence Valley will lead
to a warm frontal passage Saturday into Saturday night, followed
by a cold frontal passage on Sunday. A sprawling area of high
pressure will settle over the mid-Atlantic in the Monday thru
Wednesday time frame, prior to another storm system approaching
the region on Thursday.
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
10 PM: WSW and all fcst products reposted as well as updated
social media and emergency manager email update.
924 PM: we sent out a sample set of zones with higher ice
amounts. ice graphic has increased and should post by 930 PM.
Freezing rain rates may prevent a major problem but its a little
edgy for the higher terrain of se and e central PA where asos and
human observed radial amounts could exceed the 1/4 ice storm
warning threshold. We`ll try to have that resolved by 2 am. In the
meantime... plan on a very hazardous period of travel for a few
hours tomorrow morning and be very careful when stepping outside.
Leaving some snow on the ground and pavement might be a good idea
to allow the freezing rain to absorb into the snow instead of
transfer directly to a snow cleared frozen ground. Anti ice
treatments for pavement will be helpful and necessary top melt ice
tomorrow morning. Cant even promise 40s temps tomorrow since the
light and variable wind may turn light westerly midday off of the
colder snow covered se pa.
9 PM: will discuss adjustments at 945 PM. New 00z/17 NAM slower
and colder. Effectively will raise pops to near 100 pct after
09z. Will add .10 to the freezing rain ptns of se pa in the
morning. This fcst deserves only a few careful changes til we see
everything else from the 00z cycle. it has an 80 Kt 850 jet near
FDK MD tomorrow morning. Just seems too much. Biggest dump of
pcpn 11z-17z and the NCAR WRF ensembles for freezing rain look
very good fm the 00z/16 cycle.
No time to be sure about an ice storm warning for Berks W Chester
nw Mont and Bucks, specially higher terrain but we will add ice
amts in the 950 PM wsw and zones.
Thats it for now.
Remainder discussion below from earlier today.
Overrunning developing over the Mid-Atlantic region tonight as
warm, increasingly moist air is driven newd on a 60 kt sw 850 jet
whose center should be nosed over VA late tonight then deflects
eastward across the Delmarva after sunrise Saturday. This
deflection probably delays sfc subfreezing temperature erosion
and we will be monitoring for trends toward the significantly
colder 12z/16 GGEM solution. I prefer this colder solution though
its not mode for the plethora of warmer sfc temp solutions.
I kept it simple on start time. Virga loading next few hours should
eventually see a scattering of snow reports in PA MD by midnight
or 1 am and then a very rapid expansion in coverage around 3 or 4
We welcome your snow and ice amount reports..location and amount
and any other significant info you wish to share on
FB/Twitter/Skywarn and NWSchat accounts.
.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
Based analysis of the 12Z guidance, we trended faster with the
changeover from snow to freezing rain (with a couple hours of
sleet during the transition) as an impressive 70-80 kt (NAM) low-
level jet helps advance the warm nose aloft quickly northward
through the area during the morning. EC and GFS are decidedly east
and am concerned the NAM is too wrapped up inside.
0.25 to 1 inch qpf anticipated with max axis of rainfall probably
se PA and Southern or central NJ. Basically this event is done
around Noon with freezing drizzle or drizzle lagging and then
dealing with fog development later Saturday.
Warming at the surface will lag, especially as you get into the
higher terrain N/W of the Fall Line. There is a signal in the mass
fields from the models, showing an in-situ CAD ridge forming once
the precip begins, with the ridge axis oriented southwestward thru
NW NJ and interior portions of eastern PA. The warm front will
struggle to advance this far north during the morning, especially
with the potential for a weak wave of low pressure developing
along the front that could enhance northeasterly flow near the
surface across the northwestern third of the CWA.
The dry slot is expected to quickly advance northeastward through
the area during the afternoon. However, very light freezing rain
or freezing drizzle could persist across the higher elevations
from near I-78 northward through the late afternoon. Temperatures
may rise into the 40s southeast of the I-95 corridor and even 50s
toward southern DE during the afternoon. Concern is that the I95
corridor will not reach the 40s tomorrow as winds turn light west
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Active period shaping up with the potential for three systems to
impact the region. A long wave trough over the central conus
maintains a mean southwest flow aloft into early next week. A
shortwave moving this trough will lead to a cold frontal passage
late Sunday, with the potential for some heavier downpours. This
front will remain just to our south, due to the mid-level flow
paralleling it. A rather stout shortwave moving through the Ohio
Valley leads to low pressure development along the aforementioned
front late Tuesday into early Wednesday, with the potential for
renewed precipitation at least as far north as Delmarva. By mid-
week, the flow across the conus becomes more zonal, with the next
short wave progged to move across the area Thursday into Friday.
At this point, we expect low pressure to move through the Great
Lakes with the opportunity for secondary development off the east
coast, presenting yet another chance of precipitation.
Temperature-wise, after a warm Sunday with temperatures around 15F
above average, we return to within a few degrees of seasonal norms
through the remainder of the period.
Saturday night thru Sunday...
Ana-front-type cold front traverses the region Sunday afternoon.
From Sunday morning into the afternoon hours, an anomalous
southwesterly 850 hPa jet around 75 knots of about 3 Standard
Deviations (STD DEV) above average traverses the region. Likewise,
this aids in the pole ward transport of Precipitable Water (PW)
values up to around 1.5 inches across the area (up to around 4 STD
DEV above average). Model cross sections also indicate up to 20
micro bars (ub/s) of lift to the northwest of I-95. Thus, we have
high confidence for periods of heavy rainfall over this area
during the day on Sunday, with the potential for 1 to 1.5 inches
of precip. Although Flash Flood Guidance values are much higher
than this amount of rainfall, any leftover snow that clogs storm
drains could lead to localized, urban and poor drainage flooding.
Also, we are noting a low-level tongue of higher theta-e air in
advance of the front, with Dew Points modeled well into the 50s
moving north toward southern NJ. In addition, mid-level Lapse
Rates approach 6.5 C/km, along with sub-zero Showalter values up
to the I-95 corridor. Thus, a rumble of thunder south of the I-95
corridor is possible, but we kept it confined to far southern
Delmarva where the potential is greatest.
We also have high confidence for the formation of fog and drizzle
Saturday night into Sunday morning, particularly northwest of
I-95, where model sounding profiles are most favorable given the
low-level inversion/ lack of mixing. In addition, the fog may be
aided Sunday morning by the advection of higher Dew Points over
any existing snow cover.
Monday thru Tuesday...
Considerable uncertainty during this time frame leads to an
overall low confidence forecast. A dry Monday with increasing
chances for precip Monday night and primarily Tuesday. High
pressure over Atlantic Canada will ridge southward along the east
coast, while cyclogensis occurs along a stalled front just south
of the region. In general, the international models (EC/UKMET/Canadian)
bring the low further north, while the American models (NAM/GFS)
are at least 100 miles south. The primary reason for this is the
more robust shortwave shown by the international models. The EC
solution would bring precip to the I-95 corridor Tuesday,
predominantly in the form of rain showers, although its thermal
profile may be too warm. The GFS solution keeps the precip around
200 miles south (well offshore) and is much colder as a result.
These setups are tricky, and tend to favor locals closer to the
immediate coast for precip, given high pressure in place with a
dry, offshore, low-level flow. So for this forecast, we confined
PoPs to lower Delmarva, and within about 20 miles of the NJ coast.
As for P-Type, an early estimate would be for precip to begin as
snow showers with a changeover to rain showers. Of course, this
will need further refinement in future forecast packages.
Transitory shortwave ridging over the region will promote weak
high pressure at the surface. Fair and dry weather is anticipated
Thursday and Friday...
The next storm system is expected to traverse the region, with
impacts expected primarily on Thursday, although timing at this
early juncture is subject to change. The pattern would favor a
progressive, inside runner with some opportunity for a secondary
low formation near the coast. This would favor a snow to rain
scenario, with the fast moving nature of the system limiting
precipitation amounts. If the timing of the system holds, fair
weather would make a return for Friday, aside for the possibility
of snow flurries across the higher terrain. Overall, below average
confidence during this period of the forecast.
.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Rest of tonight...VFR cigs lower to IFR in snow between 06z-09z.
Snow quickly changes to rain KMIV and KACY with spotty icing possible
for an hour or two prior to sunrise while sleet/freezing rain
develops vcnty KILG around 11z. Light wind. We have fcst LLWS
toward 11z in some TAFS but this is not a categorical fcst of
Saturday...IFR conds in snow, sleet and freezing rain changing to
drizzle/stratus/fog in the afternoon. Please see TAFS for details.
Significant travel delays expected Saturday morning, including
runway and aircraft deicing treatments. Light wind.
Saturday night and Sunday...Rain and fog across the terminals.
Predominantly IFR. Potential LLWS sw wind 60 kt at 2000 ft
Sunday morning. Otherwise, southwest surface winds becoming
northwest with gusts in the afternoon of 20-30 kt knots for an
hour or two with the cold frontal passage.
Sunday night thru Wednesday...Predominantly VFR conditions.
A SCA was issued for the waters. The SCA for the coastal waters
begins late tonight and continues into Saturday. For the DE Bay,
the start of the SCA is delayed until mid morning. SW winds will
increase over the waters during this time. There is a potential
for winds to approach gale force Saturday late morning and
afternoon as a strong low-level jet moves overhead. However,
confidence on these higher winds aloft mixing down to the surface
is low with warmer air moving atop the colder waters. Therefore,
held off on a GLW but mentioned the possibility of near gale force
gusts in the MWW and HWO.
Saturday night...All the available 16/12Z guidance indicates the
possibility of a marginal SCA (winds) across the ocean waters. A
limiting factor will be the departure of the low-level jet, and
formation of a weak inversion over the waters. For now, we held
off on a SCA, and will let the next shift re-evaluate.
Late Saturday night into Sunday...A return to SCA (winds) around
09Z Sunday, with the possibility of gales during a brief window
generally in the 12Z to 15Z time frame.
Monday thru Wednesday...SCA possible Mon...otherwise sub-SCA.
Checked our daily snowfall records for December 17.
Long shot we can approach at KABE, the 3.0 inches in 1919.
ILG would need 2.2 inches to equal the 1973 daily record and that
PA...Winter Weather Advisory until 2 PM EST Saturday for PAZ060>062-
Winter Weather Advisory until 11 AM EST Saturday for PAZ070-
Winter Weather Advisory until 6 PM EST Saturday for PAZ054-055.
NJ...Winter Weather Advisory until 2 PM EST Saturday for NJZ007>010.
Winter Weather Advisory until 9 AM EST Saturday for NJZ014-
Winter Weather Advisory until 11 AM EST Saturday for NJZ012-
Winter Weather Advisory until 6 PM EST Saturday for NJZ001.
DE...Winter Weather Advisory until 9 AM EST Saturday for DEZ002>004.
Winter Weather Advisory until 11 AM EST Saturday for DEZ001.
MD...Winter Weather Advisory until 9 AM EST Saturday for MDZ012-015-
Winter Weather Advisory until 11 AM EST Saturday for MDZ008.
MARINE...Small Craft Advisory from 3 AM to 6 PM EST Saturday for
Small Craft Advisory from 9 AM to 6 PM EST Saturday for ANZ430-
Near Term...Drag 1012P
Short Term...Drag/Klein 1012P