Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 03/13/21
Area Forecast Discussion
National Weather Service Phoenix AZ
509 PM MST Fri Mar 12 2021
Updated 00Z aviation discussion.
A slow moving weather disturbance will impact the region through the
first part of Saturday evening with periods of scattered showers,
locally gusty winds, and the possibility of an isolated
thunderstorm. Precipitation amounts are not expected to be very
heavy with the greatest chances and highest accumulations over
elevated terrain areas of south-central Arizona. Temperatures will
hover around 10 to 15 degrees below normal before moderating
starting Sunday. A separate, faster moving weather system may create
a period of breezy to locally windy conditions on Monday. Warming
conditions are likely for the latter half of next week with above
normal temperatures likely by next Thursday.
The upper air pattern depicts pronounced southwesterly
flow aloft with an H5 jetstreak along a slightly dryer slot axis.
This pattern was just ahead of the slow-moving Pacific low pressure
circulation centered over S CA and NW AZ as seen on afternoon WV
imagery. The low pressure system is maintaining elevated WV levels
and clusters of PVA anomalies/vort lobes rotating around it. The
overnight radar loop depicted an area of scattered showers that
moved east across Maricopa county and the Phoenix metro before
moving exiting the metro and tapering off earlier this morning.
Rainfall totals so far have been more on the modest side, ranging
from 0.04-0.08 in the west valley to 0.01-0.3 in the N and NE
valley, and mostly about 0.04-0.12 in N Pinal cty and south of
Phoenix. Sky Harbor picked up a total of 0.12" since Thursday night
with most of that amount falling in the pre-dawn hours. Clearing
skies by early to mid morning to the w-sw-nw of Phoenix allowed for
some extra heating, the development of a morning cu field and the
resumption of isolated to scattered showers and and an isolated
thunderstorm by early afternoon. The latest afternoon radar was
depicted a pronounced area of light to moderate showers extending
from near Gila Bend to s-central to E and NE Metro valley. There
were also some isolate showers in SE CA/E Riverside Cty.
CAMs and HREF members indicate periods of scattered to isolated
showers this afternoon and again late tonight across S-Cent AZ and
the Phoenix Metro. The latest ACARS sounding showed an increase PW
from 0.40 to 0.57 due to and increase in BL and mid-level moisture,
although there was a stable and dry layer near H5. SBCAPE had also
increased to the low 300sj/kg. range. Valley convective outflow
boundaries combined with PVA forced ascent and weak instability
will help maintain on-and-off shower activity for the next several
hours, again tonight with mostly modest rainfall amounts
On Saturday as the low pressure center and cold core slowly moves
across N-Central AZ and the region, CAMS are in good agreement on
another round of isolated to scattered showers with the E Valley
and higher terrain areas to east favored. Snow levels are
expected to fall to near 5Kft tonight and 3.5K ft on Saturday so
accumulations of 1-3 in. are possible for those higher terrain
Temperatures through Saturday will be unseasonably cool with highs
10-15 degrees below normal, but increasing high pressure beginning
Sunday should bring temperatures back to near normal. After a brief
upper level ridge Sunday into early Monday, models generally agree
in a deepening, but progressive upper level trough affecting the
region Monday into early Tuesday. The consensus track of the system
brings the low center mostly along the Arizona/Utah state line and
any potential precipitation chances remaining across northern
Arizona. The main forecast concern for this next system will be
strong westerly winds Monday afternoon affecting much of the area,
particularly southeast California. Advisory level winds definitely
seem possible across at least across Imperial County.
After a brief cool down on Tuesday resulting in highs slightly below
normal, gradual warming is expected through the rest of next week as
the bulk of the ensemble members show a large ridge forming across
the western U.S. Median NBM temperature guidance currently shows
highs topping 80 degrees by next Thursday and potentially reaching
into the 85-90 degree range for the following weekend.
.AVIATION...Updated at 0008Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Periodic rain showers and associated low ceilings and erratic
winds will be the main aviation weather impacts through Saturday.
Although East Valley terminals and KPHX should experience a brief
lull in shower activity through about 02-03Z, showers will likely
persist at West Valley terminals and KDVT through the evening
hours. More scattered to widespread shower activity affecting all
terminals should occur between 03-07Z as the upper level low moves
overhead before gradually tapering off overnight. Another round of
convection is expected Saturday morning, but confidence on timing
is low so only VCSH was included at this time. Very isolated
thunderstorms capable of producing small hail and lightning will
be possible at any time, though chances are too low to include
VCTS in the TAFs at any time. Winds will generally be westerly
this evening and southerly overnight through the morning hours
before becoming westerly again tomorrow afternoon. Isolated gusts
up to 20 knots are possible with shower activity through Saturday
morning, with widespread gusts up to 20 knots Saturday afternoon.
Southeast California/Southwest Arizona including KIPL and KBLH:
Aside from gusty westerly winds on Saturday afternoon, minimal
aviation concerns are expected through the TAF period. Isolated
showers will be possible through early evening, particularly at
KIPL where VCSH is expected through 02-03Z. Otherwise, shower
activity will be ending from west to east as the upper level low
pushes east of the region during the evening and overnight hours.
Winds will generally favor westerly components at 10-15 knots
through Saturday morning before gusting up to 20-25 knots during
the afternoon hours. A brief period of marginal low-level wind
shear is also possible at KIPL just prior to sunrise, but
confidence is too low to include it in the TAFs at this time as
W-NW winds aloft will probably remain below 30 knots with winds
near 10 knots at the surface.
Sunday through Thursday:
High pressure will be dominant through most of the period with one
mostly dry weather system tracking across northern Arizona late
Monday into early Tuesday. Near normal temperatures early in the
period will quickly warm starting Wednesday with highs reaching the
lower 80s by Thursday. After modest daytime breezes on Sunday,
stronger winds are expected on Monday with gusts approaching 25
mph across south-central Arizona to 30-35 mph across the western
deserts. Minimum afternoon humidity levels in a 15-25% range are
expected for Sunday and Monday, lowering to 10-15% starting Tuesday.
Overnight recoveries early in the period will mostly reach 40-55%,
before dropping to 30-40% by the middle of next week.
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
CA...Wind Advisory from 9 PM this evening to 10 PM PST Saturday for