000
FXUS65 KPSR 300544
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1044 PM MST Sun Jan 29 2023

.Update... Updated Aviation...

The High Wind Warning for SW Imperial County has been canceled
early. We did have an observation over 60 MPH early this evening,
but since that time winds have weakened significantly and should
remain lighter overnight.

Surface and low-level moisture continue to lift off the Gulf of
California, in advance of the approaching H5 low across
California. Clouds will attempt to fill in overnight across much
of the area as the lower troposphere tries to saturate.
Temperatures will be held up some overnight as we introduce this
moisture: expect widespread low/mid 40s by morning over the
desert floor.

High-res guidance (HRRR/HREF members) indicate that at least
20-30% coverage of showers is on the table by mid/late morning,
even around Metro Phoenix. Amounts would be very light if
measurable at all with this initial activity. More details on this
and additional shower opportunities later Monday into Tuesday
will be refined in the overnight forecast package.

&&

.SYNOPSIS...
A low pressure system moving through the Southwest early this week
will result in scattered showers and isolated breezy conditions.
The passage of this system will also allow temperatures to retreat
from near normal levels into a below normal category through the
middle of the week. Dry weather will return during the latter half
of the week with temperatures climbing back to seasonal normals.

&&

.DISCUSSION...
Clear skies abound across the Desert Southwest today. Further
upstream, a positively-tilted trough is evident on water vapor
imagery across northern California. Ahead of this trough,
southwesterly flow is helping to boost temperatures across the
region. High temperatures are expected to reach the upper 60s this
afternoon across the lower deserts, which will likely be the
warmest readings in over two weeks, though this will still be a
few degrees below normal. The warmer conditions will result in
somewhat stronger winds mixing down to the surface later this
afternoon and evening, resulting in areas of breezy conditions.
The most anomalous ECMWF EFI wind values are situated across
portions of southeastern California and southwestern Maricopa
County, where gusts of 30 mph are anticipated. However, even
across the Phoenix area, wind gusts up to 20 mph are possible
later this afternoon, before subsiding in the evening.

A return to cooler and wetter conditions is expected early this
week as the trough moves slowly towards San Diego Monday and to
Yuma by Tuesday. Latest NBM indicates high temperatures will again
struggle to reach the 60 degree mark in Phoenix both days.
Meanwhile, some precipitation is expected though the multi-model
mean has trended drier. Model clusters are more or less stratified
by each ensemble system, with the ECMWF indicating a deeper low
and consequently more rainfall, while the GEFS and CMC are
noticeably drier. Timing of the precipitation is more certain than
the intensity and the best chance appears to be Monday night and
Tuesday, when vorticity and jet-forced ascent is maximized ahead
of the low pressure system. Despite the favorable lift, weak IVT
will generally limit rainfall amounts. Most likely rainfall totals
range from around a tenth of an inch in the Phoenix area, up to
roughly a third of an inch across the Imperial Valley in
southeastern California. However, a few ECMWF members still
suggest a slight (10 percent) chance of considerably more
precipitation above three quarters of an inch.

Latest model consensus indicates the aforementioned low will
drift slowly into northern Sonora Wednesday. A drier northerly
flow will develop behind this system, resulting in a continuation
of the below normal temperatures but an end to the rain chances.
Thereafter, a steady warming trend is likely as a broad ridge
migrates eastward through the intermountain West late in the week.
A return to the 70 degree mark is likely by Friday in Phoenix,
and there is a 30 percent chance temperatures could even reach the
mid 70s by next Sunday.

&&

.AVIATION...Updated at 0540Z.

South-Central Arizona including KPHX, KIWA, KSDL, KDVT:
The main aviation concern will be low ceilings over the forecast
area beginning at or before daybreak. FEW050 will begin to filter
in over the area over the next few hours. Starting early this
morning, BKN030-040 will prevail through most of the forecast
period starting around 12-13Z. There is a 40-50% chance of MVFR
CIGS developing around 13Z and continuing into midday with the
highest chances developing at KDVT and KSDL. Mountain obscuration
is possible in association with lower CIGS. E-SE winds will last
through tomorrow afternoon. Wind speeds will be primarily below
10kt, a few gusts are possible late tomorrow morning. A few
showers are possible in the morning, but higher chances (40-50%
chance) exist at the end of the TAF period.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will continue to diminish this evening. W-SW winds will
become light and variable in the morning and last through the
early afternoon. FEW-SCT050 clouds are expected through tonight
until tomorrow morning before becoming BKN050 from 15Z on. A
60-70% chance of showers at both terminals early tomorrow
afternoon.

&&

.FIRE WEATHER...
Ahead of a weather disturbance moving through the region early this
week, locally gusty winds will develop this afternoon for a brief
period across much of the area. The best opportunity for wetting
rainfall will occur Monday and Tuesday through western districts as
temperatures return into a below normal range through the middle of
the week. Afternoon minimum humidity levels will increase into a 30-
50% range with the passage of this weather system with overnight
recovery will be excellent in a 60-100% range. Conditions will
rapidly dry during the latter half of the week as minimum humidity
levels fall closer to 25-40% and temperature warm back closer to the
seasonal normal providing a good opportunity for prescribed burning.

&&

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

$$

UPDATE...Heil
DISCUSSION...Hirsch
AVIATION...Worley
FIRE WEATHER...18

NWS PSR Office Area Forecast Discussion