Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 02/02/21
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
301 PM AKST Mon Feb 1 2021
.SHORT TERM.../Monday and Tuesday/ A very complex and dynamic
winter storm continues to unfold across Southeast Alaska this
afternoon as a developing area of low pressure moves SE out of the
northern gulf. Heavy bands of snow continue to move through the
northern half of the Panhandle this evening as seen on satellite
and radar imagery. Lower resolution models struggle with
identifying mesoscale features and their evolution through time;
making forecasting bands of heavy snow very difficult more than a
few hours out. Guidance over the past few days has been indicating
a convergence zone setting up over the Central Panhandle where a
heavy snow band would likely develop; however lower confidence
existed on the exact location it would form. Guidance last night
trended the placement of this band further west and model runs
today continued that trend. What looked to be a Kake snow event
yesterday has turned into a Juneau to Angoon to Little Port Walter
snow storm as the narrow band of heavy snow has set up right over
this area. 12z RAOB soundings and recent MDCRS soundings indicate
a stable boundary layer with NE winds keeping cold air at the
surface with a very unstable layer above 850mb and into the DGZ.
Mid and upper level lapse rates exceeding 8.5C/km and a fully
saturated column indicate efficient snowflake production in the
DGZ, high snow to liquid ratios, and the possibility for
impressive snowfall rates of 1-2" per hour.
This morning, Yakutat received 8-10 inches of snow within a 10
hour period with only 0.25 inches of liquid, yielding snow ratios
upwards of 40:1! With the banded and showery nature of the snow,
snow accumulations will greatly vary from one town to the next.
Under the heavy snow band across the north central Panhandle,
expect an additional 3-6 inches through this evening with snowfall
rates exceeding 1" per hour. The Winter Weather Advisory for
Juneau and Angoon has been upgraded to a Winter Storm Warning as
total snow accumulations through tonight will be upwards of 4 to
9+ inches. Lower, sub advisory snow amounts expected around
Haines, Gustavus, Pelican, and across the southern half of the
As the area of low pressure moves SE along the coast, expect
precipitation to pivot and sag southward along the Outer Coast.
Guidance has also trended a tad further west with the position of
the low, keeping the heaviest snow slightly offshore of POW
Island. Kept slight chance to chance wording for POW Island as a
few snow showers will still be possible through Tuesday morning.
A northerly outflow event begins as this system departs tonight
and into Tuesday. Storm force northerlies develop in Lynn Canal
with small crafts in the Central Inner Channels on Tuesday. Expect
gusty winds to 50 mph in Skagway during this time frame as well.
Mountain Wave guidance indicates marginal conditions for Taku Wind
development late tonight through Tuesday morning. Currently do
not expect a full Taku to develop; however with a strong northerly
gradient, gusts to 40-50 mph are still possible in Downtown
Juneau and Douglas. Along the Northeast Gulf coast, expect gale
force winds blowing out of interior passes.
Confidence is only around average for the short term as the main
challenge will continue to be pin pointing exactly where smaller
snow bands set up Monday evening.
.LONG TERM.../Wednesday through Monday night/...Extended forecast
period begins with a broad ridge to the south. Northwesterly flow
will be in place behind a low that has departed to the southeast
and will promptly be replaced by another low and associated
frontal system. A very tight pressure gradient through the
northern inner channels will be slackening at the beginning of the
forecast period as well. Overall, the region should be cold enough
for the predominant precip type at the onset for this Wednesday
system to be snow, however, flow will switch around to the south
and should see a transition to rain early for most coastal areas
and the southern inner channels. Through the inner channels, early
indications are that this warm push should be able to transition
precip over to liquid as far north as Hoonah before the end of the
day. Precip associated with this system should linger through
Thursday for many areas and by the end of day two, may see the
change over to rain reach Gustavus and Juneau. Snowfall totals
from this system look to be mostly unimpressive for southeast with
the exception being the interior location of Hyder which remains
cold enough for snow and gets the added benefit of the highest
precip totals being in the southern panhandle.
Any break that we get from precip should be short lived as the
pattern remains active with yet another front poised to impact the
region from the southwest Friday into Saturday. Noticeably warmer
air can be expected with this front. How far this can actually
drive the rain/snow line north is still up for a great amount of
scrutiny, but what is becoming increasingly evident is that Haines
and Skagway do not look likely to see much of that warm up and
with the amount of moisture that could be accompanying this front,
a decent snow event may be in the works.
For the duration of the forecast, a sizable break in
precipitation does not appear to be in the cards as the Fri/Sat
front is projected to trough out over the region before being
absorbed into yet another frontal system late in the period. By
this point, enough "warmer" air may have crept into the region,
and with persistent cloud cover, diurnals may not be in play which
could lead to less likelihood for snow for many areas, or the
alternative of temperatures fluctuating right around the freezing
mark. Still have plenty of time for future analysis regarding such
things, but for now, optimistically wishing for the warm up.
PUBLIC...Winter Storm Warning until 11 PM AKST this evening for AKZ024-
Strong Wind from 9 PM AKST this evening through Tuesday morning
Strong Wind until 6 PM AKST this evening for AKZ018-019.
Strong Wind from midnight AKST tonight through Tuesday afternoon
Winter Weather Advisory until midnight AKST tonight for AKZ021.
Strong Wind from late tonight through Tuesday afternoon for
Wind Chill Advisory from 3 AM Tuesday to 6 AM AKST Wednesday for
MARINE...Heavy Freezing Spray Warning for PKZ011-013.
Heavy Freezing Spray Warning for PKZ012.
Storm Warning for PKZ012-013.
Gale Warning for PKZ021-022-031-032-043-051.
Small Craft Advisory for PKZ011-033-034-041-042-052-053.
Visit us at http://www.weather.gov/Juneau
Area Forecast Discussion
National Weather Service Phoenix AZ
415 PM MST Mon Feb 1 2021
Strong high pressure developing across the region will allow for
continued warm temperatures through Wednesday, despite considerable
cloudiness. High temperatures across the lower deserts should top
out in the mid to upper 70s during this time. A weather system is
then expected to move through the region late Wednesday into
Thursday with the best chances for precipitation across the Arizona
higher terrain and only slight chances across the lower deserts.
After a brief cool down Thursday into Friday, temperatures are
likely to slowly warm back up.
Widespread and dense cloud cover has overspread the area due to
moist southwesterly flow. This is being driven by a deep trough off
the west coast which is slowly moving southeast. ACARS soundings
reveal a moist airmass above about 700 mb, but very dry and stable
air below that. Higher pressure to the northeast over the Great
Basin has resulted in breezy easterly conditions for portions of
Phoenix today as well. Meanwhile, a high amplitude ridge remains
over Arizona with very warm temperatures aloft. However, due to the
clouds and low level cooler air surface temperatures will remain
stable the next few days, with highs in the mid to upper 70s.
However, should the clouds be somewhat thinner than anticipated
temperatures could be a bit warmer. For instance, NBM temperature
probabilities show a 40-45% probability of reaching 80F on Tuesday,
and a 25-30% probability of reaching our daily record high of 82F.
This would reflect an outcome with lower than expected cloud cover.
The high amplitude ridge will begin to break down on Tuesday as
the previously mentioned trough moves into the area. As it does
so,the trough will split, with decent agreement that the southern
lobe will stall well southwest of the California coast for several
days. The northern branch of the trough will clip the four corners
region. WPC cluster analysis shows some variations in the amplitude
of the clipper system, which would result in cooler high
temperatures should the trough end up more amplified. Even in the
cases of the more amplified trough, very few ensemble members
produce any precipitation for Phoenix. If these wetter solutions
verify, total precipitation would still be negligible. As commonly
occurs with these systems, higher pressure will build north of the
area and result in breezy northerly winds Wednesday night through
Friday. The strongest of these winds will be in the Colorado River
Valley and along the foothills north and east of Phoenix.
For the upcoming weekend, the ensemble cluster analysis has
transitioned toward the high amplitude ridge building off the West
Coast late this week being more of a factor for our region by
Saturday or at the latest Sunday. This is now leading to higher
confidence in warming taking place during the weekend and possibly
into early next week. There is still a good amount of spread within
temperature guidance, but it is looking more likely we will be
seeing a return to above normal temperatures by early next week.
Rain chances will remain minimal through this period.
.AVIATION...Updated at 2315Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No significant weather issues will exist through Tuesday evening as
thick cigs varying in a 12K-20K ft range gradually break through the
period. While virga and perhaps a sprinkle will be common this
evening, no accumulating rainfall is expected. Otherwise, east winds
will prevail much of Tuesday with moderate confidence a light west
wind will develop through mid/late afternoon.
Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather issues will exist as thick 12K-15K ft cigs
eventually scatter throughout the day Tuesday. While a light N wind
will be preferred at KBLH and NW component at KIPL, extended periods
of light and variable winds will be common.
Wednesday through Sunday:
Wednesday will remain quite warm before an approaching weather
system brings a brief period of cooler temperatures late in the
week. The next weather system will bring chances for wetting rains
mainly be across higher terrain areas of eastern and central Arizona
late Wednesday into early Thursday. Generally dry conditions are
then expected Friday through the upcoming weekend. Winds early in
the period will be breezy at times, especially across the Lower CO
River Valley, while lighter winds are expected Friday through
Sunday. Minimum RHs on Wednesday and Thursday across Arizona will
mostly be around 25% before dropping into a 15-20% range by Friday.
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.