007
FXUS65 KPSR 090835
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
135 AM MST Mon Sep 9 2024

.SYNOPSIS...
Drier air will spread through the region early this week as high
pressure still remains dominant, helping to keep temperatures
above normal for a few more days. A pattern change will then take
place during the latter half of the week as a weather system
slowly moves across the Western U.S. This system is likely to
bring breezy conditions to our region on Wednesday and Thursday
followed by noticeably cooler temperatures by the coming weekend.

&&

.DISCUSSION...
The brief period of increased moisture resulting in mostly higher
terrain shower and thunderstorm activity over the past few days
has come to an end as drier air continues to spread northwestward
through the region. The high pressure ridge is still the dominant
feature across the Southwestern U.S. and is expected to stay that
way through Tuesday. With H5 heights of 586-590dm over the region
over the next few days, the above normal temperatures will
persist. NBM forecast highs for today and Tuesday show readings
from 105-110 degrees across the south-central Arizona lower
deserts to 107-112 degrees across the western deserts with
localized Major HeatRisk mainly relegated to the Lower CO River
Valley.

By Wednesday, the weather pattern will begin to shift as a strong
upper level trough is forecast to dive southeastward into the
Pacific Northwest, displacing the ridge to well off the coast of
southern California. Heights aloft over our region will drop
quite quickly Wednesday into Thursday, but the noticeably cooler
air will mostly hold off until Thursday over the western deserts
and Friday over the rest of the area. As the upper trough swings
into the Great Basin on Wednesday, we will begin to see increased
westerly winds across southeast California, potentially near
advisory level Wednesday evening/night across portions of Imperial
County. The center of the trough will pass well to our north on
Thursday, but the large trough will extend its influence over all
of the Desert Southwest as H5 heights lower to between 582-585dm.
Gusty winds are likely to impact much of Arizona on Thursday, but
as of now they should easily stay below advisory level with
afternoon gusts approaching 30-35 mph over the higher terrain.
Forecast highs are seen lowering to around 100 degree across the
western deserts on Thursday and then across the rest of the lower
deserts starting Friday. Models have been trending a bit more
shallow with trough over the past several runs, so temperatures
have bumped up a couple degrees, but they should at least make it
into the normal range.

By next weekend, we should fall under the influence of either
broad troughing or weak ridging temporarily with little change in
temperatures before yet another trough nears the region by next
Monday. Additionally, guidance continues to suggest a tropical
system somewhere near southern Baja will help to direct moisture
northward into portions of our region over the weekend. There is
still a great deal of model uncertainty given the amount of
potential moisture, timing, and the influence of the Pacific
trough coming in from the northwest. For now it looks like we may
see rain chances as early as Saturday night extending into early
next week depending on the evolution of the Pacific system, but it
is still nearly a week away and could easily change.

&&

.AVIATION...Updated at 0530Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation weather concerns are expected through the forecast
period under mostly clear skies. Winds will continue out of the
E-SE overnight with speeds remaining around 6-8 kts. Easterly flow
will increase around sunrise Monday with intermittent gusts up to
18-20 kts developing at all terminals. Gusts will subside by the
early afternoon with a more typical diurnal pattern taking hold
thereafter. A late westerly shift is anticipated at KPHX by 23Z.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation concerns are expected through the forecast
period. Winds will generally be N-NW at KBLH and KIPL overnight
with periods of calm and vrb. Winds will return out of the SE at
KIPL early Monday morning and S at KBLH by Monday afternoon. Skies
will remain mostly clear with the exception of a FEW passing high
clouds.

&&

.FIRE WEATHER...
Drier air will continue to spread through the region over the next
couple of days as high pressure remains dominant across the
region. As a result, rain chances have virtually ended areawide
and temperatures will stay above normal into mid-week. Generally
persistent easterly winds are expected again today before winds
become more diurnally driven and lighter on Tuesday. Humidities
will trend slightly lower over the next couple of days with MinRHs
around 10% across the lower elevations to 15-20% over higher
elevation areas. The weather pattern will then shift during the
latter half of the week as an upper level trough moves into the
Western U.S. This will keep dry air in place initially, but it
will result in breezy to possibly locally windy conditions across
the western districts Wednesday and over the eastern districts on
Thursday. Temperatures should eventually drop to around or
slightly below normal by Friday.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Tuesday for AZZ530-532.

CA...Excessive Heat Warning until 8 PM PDT Tuesday for CAZ569.

&&

$$

DISCUSSION...Kuhlman
AVIATION...Salerno
FIRE WEATHER...Kuhlman