Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 03/06/21

Area Forecast Discussion

National Weather Service Phoenix AZ

 600 PM MST Fri Mar 5 2021

.UPDATE...Updated Aviation discussion.

&&

.SYNOPSIS...
High pressure will lead to highs in the mid 80s through this
weekend, with a slight chance of reaching 90 degrees in Phoenix on
Sunday, though it will be considerably more cloudy on Sunday. A
more unsettled weather pattern and cooler temperatures are likely
by Wednesday, but rain chances on any particular day through the
end of next week remain somewhat low.

&&

.DISCUSSION...
Significant warming has occurred as a ridge has moved into the
Desert Southwest. The warming is most evident when comparing
aircraft soundings from now to 24 hours ago. Most areas eclipsed
their high temperature from yesterday before noon today.
Temperatures should top out in the low to mid 80s for the lower
deserts this afternoon.

Warming will continue this weekend, with the warmest temperatures
of the year so far expected. A weak shortwave is expected to
drift through the region Saturday, but with no more than some mid
level clouds in the morning. There will likely be some breezy
easterly to southeasterly winds Saturday morning as well for
south-central AZ, as a strong gradient develops between surface
high pressure in the Plains and an inverted trough through the
Sonoran Desert. HREF and EPS show potential wind gusts up to 20-30
mph for a few hours after sunrise in the valleys, with up to
40-50 mph winds a few thousand feet above the surface. The winds
are expected to decrease through the afternoon. The winds may help
with a more mild start to Saturday and the passing wave will have
little impact on afternoon temperatures, as mid 80s are
projected. NBM is favoring Sunday as the warmest day this weekend,
especially for south-central AZ. The latest forecast now has a
high of 88 degrees for Phoenix, with a 10% probability of reaching
90 degrees. The probability of reaching 90 is up to 20 to 30
percent for the east Valley and northwest Pinal county. Scattered
to broken high clouds Sunday, however, could inhibit heating
slightly in the afternoon. Regardless, upper-80s is enough for
low end heat impacts to occur, especially for the extremely
vulnerable.

By Sunday, flow will begin to turn southwesterly in response to a
deep Pacific trough sagging southward off the NW U.S. coast. This
shift in the upper level flow is expected to pull up an extensive
area of upper level moisture, resulting in the previously
mentioned high clouds. Ensemble trends do support a weak IVT axis
(200-300 kg/ms) setting up across northern Baja California,
Sonora, and southeast AZ by Monday and becoming nearly stationary
over this same area through Tuesday. So, the relatively cloudy
skies should persist through Tuesday, but with more of a focus
just southeast of our area. As the deep trough drifts further
south it will likely begin lowering heights aloft over our region,
lowering temperatures back into the mid 70s Tuesday.

Models are still in good agreement showing this deep Pacific
trough digging southeastward Tuesday into Wednesday with the low
center likely just off the California coast. Tuesday should
remain dry, but winds are expected to become breezy to locally
windy as the low approaches from the northwest. By Wednesday, some
notable spread with the depth and timing of the trough is seen
among the ensemble members, but model guidance overall remains in
decent agreement with the trough eventually tracking inland at
some point Wednesday into Thursday, possibly lingering into
Friday. Precipitation chances and QPF remain on the low side at
this time, as moisture looks to be a limiting factor. Sure there
is the aforementioned IVT axis and ensemble mean PWATs may rise up
to 0.4-0.6", but this richer moisture is shown to decrease before
the better dynamic/forcing with the core of the low fully reach
the region. Still, given the potential strength, colder air mass
associated with the trough, and extended resonance time, we can`t
rule out chances for precip at any point on Wednesday through
Saturday. Temperatures will continue to trend cooler into the
middle of next week with highs most likely dipping several degrees
below normal by Wednesday.

&&

.AVIATION...Updated at 0055Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Latest guidance indicates the pressure gradient will tighten
overnight as high pressure builds across the southern Rockies.
This will result in a stronger than normal downslope flow and
breezy conditions are likely after midnight and through Saturday
morning across the Valley. Gusts as high as 20-25 kt will be
possible through 17z. With easterly flow roughly around 35 kt at
2k ft, LLWS is expected to develop in areas where the winds drop
below 5 kt. Conditions will improve Saturday afternoon as the
pressure gradient weakens. However, a switch to westerly flow is
not anticipated.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns anticipated. Light, diurnal winds
and mostly clear skies will prevail at KIPL/KBLH through Saturday.

&&

.FIRE WEATHER...
Sunday through Thursday:
Well above normal temperatures with highs mostly above 80 degrees
will continue through Monday, but with fairly cloudy skies late
Sunday through much of Monday. A much more unsettled weather
pattern is expected starting Tuesday with gradual cooling
temperatures and a slight chance for wetting rains for Wednesday
into Thursday. Winds will be fairly breezy through much of the
period, particularly during the daytime hours when gusts to 25 mph
will be possible on most days. Minimum afternoon humidities in the
teens are likely through Tuesday with some slight improvement and
readings somewhat above 20% late in the period.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...Kuhlman
AVIATION...Hirsch
FIRE WEATHER...Kuhlman