Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/06/21

Area Forecast Discussion

National Weather Service Phoenix AZ

 410 PM MST Mon Jul 5 2021

.UPDATE...
Updated Aviation

&&

.SYNOPSIS...
Drier conditions will settle into the area, likely persisting
through the majority of the week. Daily isolated storms will still
be likely across the eastern Arizona high terrain, while the lower
deserts will mostly remain dry. Temperatures will warm to a few
degrees above normal for much of the coming week with highs mostly
in a 109 to 112 degree range across the lower deserts. A slight
boost in moisture is likely later this week, but this alone is not
likely to be enough to bring back rain chances for the lower
deserts.

&&

.DISCUSSION...
Latest water vapor imagery reveals drier air aloft overspreading
the Desert Southwest, however conditions remain quite moist in the
lower levels with dewpoints in the 50s and even lower 60s. Total
PWATS are near 1.5 inches in Phoenix but are steadily decreasing.
Meanwhile, RAP streamline analysis indicates the Monsoon High has
taken up residence near the Four Corners, while the 700 mb ridge
is positioned across southwestern Arizona. This is resulting in a
weak north-northwesterly steering flow across the higher terrain
well east of Phoenix, where there is more instability and convection
is more likely to initiate. Consensus from the CAM ensemble
indicates only isolated storms will develop across Gila County this
afternoon, before drifting southward. There is also a very low
probability of an outflow boundary with gusty winds reaching the
Valley this evening.

NBM PoPs remain less than 5 percent across the Valley this evening,
owing to widespread convective inhibition. This is largely due to a
well-defined subsidence inversion around 800 mb evident on the
latest ACARS sounding. Latest HREF depicts debris clouds lingering
overnight, which will likely result in temperatures a few degrees
above normal.

&&

.PREVIOUS DISCUSSION...
Looking at the large scale pattern throughout the coming week, model
ensembles have shifted the positioning of the building ridge.
Currently, the upper level (250/300mb) ridge center is situated just
south of Arizona. There is now better agreement in this ridge slowly
shifting to the northwest late this week while strengthening,
becoming another anomalously strong ridge over the Western U.S.
Previous runs were fairly similar, but there was at least a strong
sign of a moist easterly return flow later in the week. This is
still somewhat true, but a likely stronger ridge and a subtle shift
in the winds will likely only give us a brief window of moisture
return, mostly involving shallow Gulf of California moisture surges
Wednesday into Thursday. After limited storm chances over the
eastern Arizona high terrain through Wednesday, Thursday could
possibly bring a few isolated storms to the south-central Arizona
deserts with the help of the GoC surge, but it is looking much less
likely due to the lack of deeper moisture. Friday is likely to be
similar to Thursday, but NBM PoPs continue to back off on rainfall
chances over the lower deserts (now at 10% for Phoenix, down from
20%). PoPs for next weekend are also considerably lower than the
previous few forecast packages as the shift in the high center to
our west northwest is likely to bring more pronounced northerly dry
flow. We will have to wait and see if the potential moisture return
later this week will be enough for a return of storm chances for
some of the lower deserts.

A warming trend is definitely on the way over the next couple days
as the boundary layer dries out. Highs are still forecast to warm
to around 110 degrees across the western deserts today and then over
the south-central Arizona deserts starting Tuesday. From Tuesday
through the coming weekend, NBM guidance shows little variability in
forecast highs mostly ranging from 109-111 degrees across the
Phoenix area to 110-113 degrees across the western deserts. As the
ridge strengthens later this week, these temperatures will mostly be
dependent on how much boundary layer moisture is present. If we end
up being drier than forecast, temperatures very well could reach
excessive heat levels in some areas. The highest probabilities of
this occurring looks to be during the Friday-Sunday time period when
the ridge is likely peaking in intensity.

&&

.AVIATION...Updated at 2310Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Westerly winds will weaken this evening with speeds falling below 10
kts. Guidance shows easterly winds struggling to take hold overnight.
Chances for convection in Phoenix this evening is low (< 10%) and
model guidance do not support outflows reaching the terminals. West
winds should return quickly be late Tuesday morning. FEW-SCT clouds
aoa 10 kft are forecast through the period.

Southeast California/Southwest Arizona including KIPL and KBLH:
Mostly clear skies are expected through the TAF period. South winds
will be expected at KBLH with NBM showing speeds as high as 12kt.
West winds at KIPL should become SE again Tuesday morning with NBM
showing a few gusts up to 20kt this evening.

&&

.FIRE WEATHER...
Thursday through Monday:
Somewhat drier than normal conditions will generally confine the
threat of storms to the higher terrain north and east of Phoenix.
Strong high pressure affecting the region will also result in
slightly above normal temperatures. Min RH values will generally be
in a 15-20% range over the lower deserts and 20-30% across the
eastern Arizona high terrain. Max RHs will recover into the 35-45%
range for lower deserts locations to 50-60% across the high terrain.
Wind patterns should follow diurnal patterns for much of the period
with daily afternoon gusts to around 20 mph likely.

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Excessive Heat Watch from Saturday morning through Sunday
     evening for CAZ560-561-570.

&&

DISCUSSION...Hirsch
PREVIOUS DISCUSSION...Kuhlman
AVIATION...Smith/18
FIRE WEATHER...Kuhlman/Hirsch