391
FXUS65 KPSR 162118
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
218 PM MST Tue Jul 16 2024

.SYNOPSIS...
Daily rain chances continue over the next several days, with most
activity remaining over the higher terrain areas. Moisture, along
with rain chances, start to increase over the lower deserts as we
approach the end of the workweek and through the weekend.
Temperatures will remain above normal with Friday and Saturday
expected to be the hottest days of the week. Widespread HeatRisk
will continue with increasing areas of Major HeatRisk across the
lower deserts on Friday and Saturday.

&&

.DISCUSSION...
Upon analysis of upper-level WV satellite imagery this afternoon,
the high pressure system is still centered over northern New Mexico.
This high pressure will slowly move westward through the week. As
the high pressure system moves over head, there will be increased
subsidence aloft leading to slight drying. However, there will still
be enough moisture to promote daily thunderstorm activity over the
Arizona higher terrain. The set up for today and tomorrow will be
fairly similar to yesterday. There will be marginal instability, and
the environment over the lower deserts is expected to remain capped.
Therefore as storms move off the higher terrain and into the lower
deserts they will weaken and fall apart. There is still a decent
amount of DCAPE in place, values in the 1500-2000 J/kg range.
This will support long traveling outflow boundaries, that could
impact lower elevations with some gusty winds. The HREF, shows a
10-30% chance of wind gusts over 35 mph getting into central
Maricopa and Pinal counties this evening.

As the high pressure migrates over Arizona and into eastern
Nevada late this week and into the weekend, global ensemble
members show an increase in PWATs to around 1.5". This will lead
to increasing thunderstorm chances across the lower deserts across
south-central Arizona, with PoPs around 20% Thursday-Saturday. In
addition to the rain and storm chances, temperatures will also be
on the rise through the week as the aforementioned high pressure
system migrates westward. The hottest days of the week are
expected to be on Friday and Saturday, with forecasted afternoon
high temperatures in the 110- 120 degree range and the hottest day
currently forecasted to be on Saturday. HeatRisk will also be on
the rise, with major HeatRisk becoming isolated across the lower
deserts on Friday and more widespread on Saturday. With the
increasing HeatRisk, excessive heat products may be needed.

As we head towards the end of the weekend and into next week, the
high pressure system will continue to migrate westward and looks to
eventually settle over Nevada. In addition there will also be a
trough pushing into the Planes. This will promote diffluence aloft,
and lead to an even more favorable synoptic pattern for increased
monsoon activity. This is reflected in the NBM guidance with PoPs
increasing to 40-50% across the south-central AZ lower deserts on
Sunday and Monday. The overall steering flow will be out of the
north/northeast, which will send storms that develop over the Rim
into the lower deserts. We will need to continue to monitor the
trend in the overall flow pattern, as historically, northeasterly
flow events have led to severe weather materializing across the
Phoenix area. So this will bear watching as we get closer to the
weekend once the overall mesoscale details start to become
clearer. In addition to these increasing rain chances,
temperatures will also cool slightly heading into next week as
that high pressure system settles over Nevada.

&&

.AVIATION...Updated at 1205Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
W to SW winds will prevail through this afternoon and evening at
all terminals with afternoon speeds up to 10-15 kts and gusts to
around 20 kts. Confidence in outflows passing through the
terminals is not as high as previous days. There is at least a low
chance for one from the E or NE this evening, after 3-4Z. An
outflow from the S may also coincide with an increase in low-level
SW winds closer to and just after midnight (7Z). Chances of
VCSH/VCTS are low this evening-tonight, 10% or less. Confidence in
a full E to SE wind shift Wednesday morning at all terminals is
low to moderate. If it does shift at KPHX, it may be for only a
few hours before shifting back W to SW by 16-17Z. FEW cumulus this
afternoon will be around 10-12K ft AGL, then SCT to occasional BKN
mid-level clouds around 14K ft will pass over the area this
evening- tonight.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will prevail out of the E-SE at KIPL, with potential for a
brief turn to the S-SW late this evening, and S-SW at KBLH through
the TAF. Speeds will remain around 10 kts or lower at KIPL while
KBLH see speeds around 10-15 kts, and gusts to around 20 kts at
times, through most of the TAF period. FEW to occasionally SCT mid
and high level clouds will pass over the area. There is a slight
chance (10-20%) of some spotty high-based convection passing
through the area Wednesday morning-midday.

&&

.FIRE WEATHER...
Sufficient moisture will remain in place to result in daily
thunderstorm activity through the next several days, with activity
mainly confined to the AZ high terrain through midweek. Thunderstorm
chances start expanding into the lower elevations by the latter half
of the week and through the upcoming weekend. Gusty, erratic winds
will be the biggest hazard with these thunderstorms, exacerbating
issues on any ongoing wildfires and new starts. Aside from the
thunderstorm winds, the typical afternoon upslope gustiness upwards
of 20-25 mph will be common. MinRHs during the next several days
will range between 10-30% with fair to good overnight recoveries
between 30-60%.

&&

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

$$

DISCUSSION...Berislavich
AVIATION...Benedict
FIRE WEATHER...Berislavich/Lojero