051
FXUS65 KPSR 182334
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
434 PM MST Wed Sep 18 2024

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

&&

.SYNOPSIS...
A passing low pressure system late this week and early this
weekend will bring regionally breezy conditions, some higher
terrain light showers, and keep temperatures near or below normal.
Following this system heading into next week, temperatures are
expected to warm back up above normal, primarily with the
afternoon highs. Lower desert high temperatures are forecast to
return to or above 100 degrees by Sunday or Monday.

&&

.DISCUSSION...
The cooler temperatures the past couple of days, relative to the
last few months, have certainly been pleasant, especially the 60
and 70 degree mornings across the lower deserts. While the high
temperatures are forecast to warm back up by next week, the
morning low temperatures at least look to remain on the cooler,
more seasonal, side. Current objective analysis shows the low
pressure that brought our initial cooldown now near the Canadian
border, while another follow-on low is making its way down the CA
coast. This puts the Desert Southwest under dry southwesterly
flow. Slight warming, by a few degrees on the afternoon highs, is
expected through tomorrow ahead of the next low, but still with
temperatures near to below normal.

A brief cooldown/moderation on temperatures is expected once the
current coastal low traverses through the region. Latest global
models push the central low circulation through AZ on Friday and
Saturday. In addition to moderating the temperatures, this low is
expected to lead to some breezy conditions, mainly Thursday and
Friday. Most areas will see afternoon and evening gusts into the
20-30 mph range, while mountain and valley winds in Imperial
County CA, particularly the southwest part of the county, will see
potential for evening gusts over 30 mph. Latest HREF has up to an
80% chance for advisory level wind gusts (40+ mph) in this area
Thursday evening. Additionally, the colder air aloft with the low
and a small increase in mid-level moisture around the low could
bring some weak elevated showers to the lower deserts Friday, but
shower odds are better in the higher terrain of northern AZ, and
more specifically near and north of the center of the low
circulation. NBM PoPs for nearly all southern AZ and southeast CA
are under 10%.

The upper level trough will eject northeast of the Desert Southwest
by the end of the day Saturday, allowing H5 heights to rebound to
584-587 dam by Sunday. A high amplitude ridge then sets up just
off the West Coast and gradually shifts east early next week. With
the increase in heights aloft, temperatures, primarily high
temperatures, will trend up over the weekend back to near normal
range on Sunday and likely a few to several degrees above normal
early next week. Highs are forecast to rise back above 100F for
the lower deserts and bring HeatRisk levels back up to Moderate.
Global ensemble cluster analysis still reveals a fair amount of
uncertainty as to the overall amplitude of the pattern next week
and whether there will be any cutoff low circulations. Overall,
the long-term forecast is currently calling for above normal
temperatures and continued dry conditions.

&&

.AVIATION...Updated at 2330Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT and
Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation concerns are expected through the TAF period.
Winds will continue to exhibit the typical diurnal tendencies,
although there will likely be an extended period Thursday
afternoon of southerly winds across the Phoenix TAF sites before
eventually switching to a westerly component. Wind speeds will
generally remain aob 10 kts. Mostly clear skies will be favored
throughout the period with just a FEW cumulus clouds expected at
times.

&&

.FIRE WEATHER...
A drier and cooler airmass encompassing the region will make for
below normal temperatures through Saturday. Winds will follow
generally light and diurnal patterns today, with typical upslope
gusts to 15-20 mph during the afternoon. Slightly stronger
southerly to southwesterly afternoon gusts to 20-25 mph can be
expected tomorrow and Friday. Afternoon Min RHs in the teens will
be common in lower elevations and closer to a 20-30% range across
higher terrain today, whereas Min RHs will be in the upper teens
up to around 25% areawide Thursday and Friday. Overnight recovery
will range widely from fair to good at 30-70%. As temperatures
warm closer to normal over this weekend and into early next week,
humidity levels will decrease further, with single digit readings
more likely in lower desert communities by Sunday.

&&

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

$$

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