Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/20/22

Area Forecast Discussion

National Weather Service Phoenix AZ

 347 PM MST Tue Jul 19 2022

.UPDATE...UPDATED 00z AVIATION DISCUSSION.

&&

.SYNOPSIS...
Chances for showers and thunderstorms over the next several days
are likely to be confined to the high terrain across eastern
Arizona as drier air filters into the area. Above normal
temperatures will prevail through at least Friday with high
temperatures across the lower deserts mainly in a 110 to 113
degree range. Starting Saturday, moisture is likely to increase
across the region resulting in a return of shower and thunderstorm
chances across the Arizona deserts, and the start of a cooling
trend.

&&

.DISCUSSION...
Latest WV satellite imagery is showing a large MCV moving e-ward
across central baja. Mid/high-level clouds from this MCV are
currently streaming n-ward over much of AZ. An outflow from this
feature has moved into SW AZ, bring gusty southerly winds to the I-8
corridor all the way from Yuma to Gila Bend at this hour. Winds have
been strong enough to produce localized blowing dust to the region.
Current 88-D radar is showing the development of -SHRA/TS across the
Rim/White Mountains, just outside of our CWA.

Latest Phoenix ACARS aircraft soundings are showing some decent mid-
level moisture, with a PWAT value of 1.47 inch. Although the
sounding is also showing some good instability (MUCAPE 1450 J/kg),
it appears that warming aloft has allowed a couple of caps/warm
layers to develop (around 850mb and 400-500mb). Winds aloft have
also become quite light and unfavorable for propagation of storms
from the higher terrain. Thus, the current thinking is that the
lower deserts will remain quiet t-storm wise, with just a bit
greater chance for outflows from distant storms (10-30% chance of
winds >30 kts). Storm development looks more likely over southern
Gila County as that area has a better chance for enough lift from
the Rim/White mtn storms to trigger storms over that region.
Although storm coverage will likely remain in the isolated-scattered
range over southern Gila County, the slow storm motion does increase
the risk a bit for localized flooding, especially over/near burn
scars and enhanced risk for locally strong winds. Current HRRR/FV3
hi-res models solidly support that idea, with WPC including southern
Gila County in a MRGL risk area for excessive rainfall and SPC
including the same area in a MRGL risk for severe T-storms.

The upper level ridge center is expected to shift westward across
the region with the center eventually settling over central Arizona
late tomorrow into Thursday. The upper level ridge will remain quite
strong through Friday with H5 heights hovering between 595-597dm, or
mostly between 90-97% of climo for the period. The main forecast
concern over the next several days will be the hot temperatures as
forecast H8 temperatures increase from 28C yesterday to 30-31C today
before peaking around 32C on Friday. NBM forecast high temperatures
warm to 109-112 degrees over most of the lower deserts today before
peaking on Thursday and/or Friday at 110-113 degrees, or 3-6 degrees
above normal. Even warmer temps are forecast for parts of the lower
Colorado River/Imperial valleys, with highs rising into the 112-116
degree range out there. Overnight lows will also be several degrees
above normal through at least Friday, mostly ranging between 84-90
degrees. The temperature forecasts for south-central AZ are on the
high end of Moderate HeatRisk to even very localized High HeatRisk,
with lower Colorado River/Imperial valleys likely seeing more
widespread HeatRisk values in the High-Very High range. Needless to
say, these hot temperatures will pose an increased risk to those
most vulnerable to the heat and an Excessive Heat Watch has been
issued for the lower Colorado River/Imperial valleys for Thu/Fri.

The boundary layer will continue to dry out on Wednesday before
reaching its driest point on Thursday. Forecast afternoon surface
dew points are seen dropping from the mid 50s today to 45-50 degrees
on Thursday and Friday. This drier air and less favorable conditions
aloft should limit any convection to areas over the eastern Arizona
high terrain Wednesday through Friday. Daily chances for afternoon
showers and thunderstorms will be seen over the high terrain with
NBM PoPs anywhere from 10-30%, with gusty winds and heavy downpours
continuing to be the main concerns. A subtle mid level disturbance
is advertised for Wednesday, just clipping southeast Arizona. This
may be enough to provide a bit more organization to afternoon
convection, but for now this is likely to mainly be focused across
far southeast Arizona. High terrain storms over the next few days
may also be enough to send storm outflow winds westward toward the
lower deserts, but per the 00Z HREF there is only around 10%
probability of 35+ mph winds reaching eastern portions of Phoenix.

Starting over the weekend, we are likely to see a return of good
quality monsoonal moisture as the upper level high center again
retreats back over the Four Corners area. Models continue to favor
a dramatic increase in PWATs as early as Saturday, possibly
peaking near 2" Sunday into Monday. There are also indications of
at least one inverted trough providing upper level support for
convection over the weekend with an even larger scale easterly
wave possible early next week. Both the GEFS and EPS show good
potential for rainfall during this time, at least extending
westward through the south-central Arizona lower deserts. The
specific details such as timing of showers and thunderstorms and
their potential impacts are still uncertain, but models have been
consistent in showing these chances over the past several days.
The current scenario shown by some of the model ensemble members
suggests heavy rainfall and flooding are likely to be a concern.
Temperatures are also shown to cool off starting this weekend as
moisture and rainfall chances increase over the region. NBM
guidance shows highs dropping back to around normal as early as
Sunday.

&&

.AVIATION...2250Z Update.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Westerly winds will persist through the evening with gusts to
around 18-25 kts. Shower and thunderstorm activity should remain
northeast of the area with only a 10% chance of an outflow
reaching any of the terminals. Winds will remain slightly elevated
and westerly overnight, becoming variable near daybreak. Breezy
westerly winds resume once again Wednesday mid morning. Skies will
features few to sct coverage near 12-15 kft with high clouds
continuing as well.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds at KIPL will transition from SE to favor the W to SW,
gusting upwards of 20-25 kts this evening, before transitioning
back to a light SE component after midnight. At KBLH, winds will
favor a southerly component, gusting to around 20 kts at times
this afternoon/evening. FEW-SCT clouds aoa 15 kft are expected
through the period, becoming BKN at times.

&&

.FIRE WEATHER...
An upper level high pressure system and drier air settling
over Arizona should limit storm chances to the eastern Arizona
high terrain through Friday. Daily storm chances across southern
Gila County will mainly fall between 10-30% with gusty outflow
winds and heavy downpours the biggest threats. Temperatures will
remain above normal through the period with lower desert readings
at or a few degrees above 110 degrees. MinRH values across the
lower deserts will mostly be in the teens each day to 20-25% over
the high terrain. Moisture is likely to improve over the coming
weekend with storm chances increasing and expanding into the lower
deserts. Winds will remain fairly light most of the time, with
the exception being some enhanced afternoon upslope breeziness as
well as any thunderstorm activity resulting in strong and erratic
winds.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Watch from Thursday morning through Friday
     evening for AZZ530.

CA...Excessive Heat Watch from Thursday morning through Friday
     evening for CAZ567-569.

&&

$$

DISCUSSION...Percha/Kuhlman
AVIATION...Hodges/Smith
FIRE WEATHER...Kuhlman