023
FXUS65 KPSR 170528
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1028 PM MST Tue Jul 16 2024

.UPDATE...Updated 06z Aviation Discussion.

&&

.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 0530Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Outflows emanating from recent shower/storm activity remains the
biggest uncertainty at this point, at least for KPHX and KIWA, due
to the rapid decay of the gust front as it moves southward. At
this point, expecting both terminals to remain out of the
southwest, with a chance of variable winds if the gust front
reaches either terminal. Otherwise, light and variable winds
expected to settle into the metro through the overnight hours,
with KIWA the highest chances of having a discernible
southeasterly wind develop going into tomorrow morning. Winds
will then go westerly with afternoon gusts 15-20 kts. Outflows
will again be a possibility tomorrow evening with convective
activity in the higher terrain. Best chances will be out of the
easterly or northeasterly direction, but probabilities are too low
to include in this TAF package. SCT-BKN into the overnight hours
will clear to FEW-SCT by tomorrow morning and remain this way
until the evening hours where skies will become more cloudy due to
convection nearing the metro.

Southeast California/Southwest Arizona including KIPL and KBLH:
Typical diurnal winds are expected to continue, with SE at KIPL
and S-SW at KBLH. Limited convective activity across the region
will only provide a very low (<10%) chance of an outflow reaching
either terminal through the forecast period. Skies will remain
FEW-SCT through the period.

&&

.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...Young
FIRE WEATHER...Berislavich/Lojero