Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/01/23

Area Forecast Discussion

National Weather Service Phoenix AZ

 513 PM MST Mon Jul 31 2023

.UPDATE...Updated 00z Aviation Discussion...

&&

.SYNOPSIS...
An upper level weather disturbance will continue to impact the
region today with adequate monsoon moisture bringing higher than
normal chances for showers and thunderstorms across much of
southern Arizona. While strong gusty winds and dense blowing dust
will be the primary weather hazards, some locations could
experience heavy rainfall. This wetter pattern will be short lived
as abnormally dry conditions are expected to return during the
latter half of the week. After near normal temperatures through
Tuesday, the latter half of the week will see a modest warming
trend with highs once again topping 110 degrees over much of the
lower deserts by Friday.

&&

.DISCUSSION...
Light rain associated with last night’s MCS and residual MCV
continue to dissipate across southeastern California. Further east
across Arizona, skies are mostly sunny, but conditions are
several degrees cooler and more moist than 24 hours ago. With
surface dewpoints in the 60s, there is only a 10 percent chance
Sky Harbor Airport will reach 110 degrees. The historic streak of
110+ degree days stands at 31 days and that will likely end today.

Latest water vapor and RAP streamline analysis reveal the
inverted trough is lifting northward through Sonora. Meanwhile,
mesoanalysis indicates PWATs are running higher than normal,
generally between 1.3 and 1.7 inches. Unlike past days, latest
ACARS soundings from KPHX show 12+ g/kg mixing ratios extending
from the surface through 850 mb. MLCAPEs are also quite robust,
given the abundant moisture and well-below normal 500 mb
temperatures approaching -8 degrees C.

On the ascending side of the trough, convection has already
initiated across the favored areas of the higher terrain,
including the Mogollon Rim, White Mountains and the sky islands of
southeastern Arizona. A 20 kt east-southeasterly flow will
promote the propagation of these cells off the higher terrain and
into the lower deserts this afternoon.

Numerous CAMs within the HREF suggest the convection across
eastern and southeastern Arizona will migrate northwestward into
central Arizona this afternoon before increasing in coverage
across northwestern Maricopa County this evening, where moisture
convergence will be maximized. The official forecast reflects the
NBM, with PoPs of around 60-70 percent in the Valley. With above
normal PWATs, the strongest cells will be capable of producing
heavy rainfall and localized flooding. There is also a 70 percent
chance of wind gusts above 35 mph, which has the potential to
produce areas of blowing dust across portions of Pinal County and
the Phoenix Metro area. Although widespread damaging winds are not
anticipated, there is a marginal risk (5 to 10 percent) of severe
wind gusts across central and southern Arizona.

One caveat remains the potential for shower and thunderstorm
activity to skip over portions of the Valley, where CIN cannot be
eroded by outflow pushing northwestward through Pinal County.
Several runs of the HRRR have trended towards this scenario. On
the other end of the spectrum, the U of A WRF-GFS suggests little
inhibition with intense convection moving through central
Arizona.

&&

.PREVIOUS DISCUSSION...
Starting Tuesday, our region will fall under an increasingly dry
southwesterly flow with the sub-tropical high center positioned
over the Southern Plains. However, there should still be adequate
boundary layer moisture with MUCAPEs of around 500-750 J/kg in
place for isolated to possibly scattered afternoon showers and
thunderstorms focused more over higher terrain areas. The south
southwesterly steering flow on Tuesday is generally not favorable
for long-lasting outflows or widespread thunderstorm development,
so coverage over the lower deserts is likely to be fairly limited.
By Wednesday, low level mixing ratios are forecast to drop to
around 8 g/kg suggesting only fairly limited higher terrain
shower and thunderstorm potential.

For late this week and through the weekend, the sub-tropical high
is forecast to shift southward and become elongated stretching
from well west of Baja through the Southern Plains. This synoptic
set-up is very similar to the first week or two of July when it
was nearly impossible to get any meaningful monsoon moisture into
Arizona. Unfortunately, ensemble guidance is heavily favoring a
continued drying trend through the weekend as PWATs drop below 1"
across the entire Desert Southwest. This scenario should
essentially end any storm chances across the area by the weekend
with maybe only the highest peaks seeing any limited convection.
As of now, this dry weather pattern seems to take hold by the
weekend, potentially lasting through all of next week.

The near normal temperatures for today and Tuesday will steadily
climb higher during the latter half of the week with forecast
highs over much of the lower deserts again above 110 degrees by
Friday or Saturday. Ensemble guidance at least favors a more
active flow pattern across the northern and central U.S. starting
this weekend into next week, so it seems likely it will at least
limit the strength of the sub-tropical high as it keeps it
centered south of the region. For now, there looks to be some
localized areas of Major HeatRisk forming by the weekend but it
seems unlikely we will return to widespread Excessive Heat
Warnings under this pattern.

&&

.AVIATION...Updated at 0010Z.

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

The main aviation concern through this evening will be the
potential for gusty outflow winds emanating from thunderstorm
activity across southeast AZ. At this time, based on the latest
trends, it appears the outflow winds will be moving through the
terminals between 02-05z with winds switching out of the southeast
with gusts potentially exceeding 30 kts as well as reduced
visibilities due to BLDU. There is lower confidence, however, for
thunderstorm activity to directly affect the terminals so the
mention of VCTS have only been mentioned in the TAF at this time.
Conditions should improve after 06z with a return to the typical
nocturnal wind pattern. Much calmer conditions are expected for
Tuesday with the typical diurnal wind pattern expected along with
generally mostly clear skies with just a FEW mid to high-level
clouds.

Southeast California/Southwest Arizona including KIPL and KBLH:

At KIPL, winds will generally be from the southwest through this
evening into the overnight period, switching from the southeast by
the early morning hours with speeds generally near 10 kts. At
KBLH, winds will generally fluctuate from the south to south-
southwest with some gusts nearing 20 kts through early this
evening and once again for Tuesday afternoon. FEW-SCT mid to
high-level clouds will pass through the region during the period.

&&

.FIRE WEATHER...
The unsettled weather pattern will continue today with better
shower and thunderstorm chances across eastern and south-central
Arizona. Gusty erratic outflow winds are the greatest concern
with these storms, though some beneficial wetting rainfall is
likely for some areas. Drier conditions will begin to move in on
Tuesday, but lingering moisture should be enough for isolated to
scattered showers and thunderstorms. Minimum afternoon humidity
levels will fall into a 20-30% range through Tuesday, while
temperatures fall back closer to normal readings. For the latter
half of the week, gradual drying conditions will eventually end
storm chances across the lower deserts on Wednesday and even over
the high terrain by the coming weekend. Temperatures will once
again warm back to above normal readings starting Wednesday, while
minimum humidities on Wednesday dip back into a 10-20% range and
likely even into the single digits by Friday.

&&

.CLIMATE...

Active Streaks:

PHOENIX

1. Consecutive days of high temperatures 110F or greater: longest
   on record at 31 days (previous record: 18 days in June 1974)

2. Consecutive days of no measurable precipitation: 14th longest
on record at 130 days

YUMA

1. Consecutive days of low temperatures 85F or greater: Tied for
   longest on record at 20 days

&&

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

$$

DISCUSSION...Hirsch
PREVIOUS DISCUSSION...Kuhlman
AVIATION...Lojero
FIRE WEATHER...Kuhlman