845
FXUS65 KPSR 121138
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
438 AM MST Wed Feb 12 2025

...Update...Updated Aviation Discussion

&&

.SYNOPSIS...
A large area of low pressure will remain over the region through
Friday with the main frontal boundary moving through Thursday
night and Friday. Cool and fairly cloudy conditions are expected
today and for much of Thursday before chances for showers spread
across much of southeast California by Thursday evening and then
into central Arizona Thursday night. Scattered showers are then
likely for south-central and eastern Arizona Friday morning into
the afternoon hours. High pressure will gradually settle back into
the region over the weekend bringing drier conditions and warming
temperatures.

&&

.DISCUSSION...
Broad troughing remains across the Western U.S. early this
morning with one shortwave trough exiting to the east into
Colorado and northern Mexico. A moisture plume is also pushing off
the Pacific into the Desert Southwest out ahead of a fairly
strong upper level low currently 1000 miles west of Oregon. For
today, we should mainly expect periods of somewhat thick clouds,
chilly temperatures with highs in the lower 60s, and maybe a few
light showers spilling over the interior mountains of southern
California into southeast California. The NBM continues to
struggle with our prolonged dry stretch as it keeps suggesting
unrealistically high PoPs for these weak disturbances. Hi-res CAMs
show a much more realistic picture of what we can expect for
today and Thursday with virtually no chance of showers today and
then increasing chances mainly across southeast California and
west-central Arizona by Thursday evening.

Now that we are getting closer to the late Thursday and Friday
weather event, it is becoming clearer that our precipitation
chances are going to be more limited. The main low center will
enter Oregon and northern California late Thursday as it continues
to weaken, but an additional shortwave trough will track across
southern California into central Arizona on Friday. A weak frontal
boundary will also accompany the shortwave trough, tracking
eastward through southern California Friday morning and across
southern and central Arizona Friday afternoon. Additional moisture
advection is also expected out ahead of the shortwave and frontal
boundary, boosting PWATs to around 200% of normal and low level
mixing ratios up to 6 g/kg. Despite adequate moisture, the lack of
strong forcing is expected to limit shower coverage Thursday
night and Friday. Forecast QPF has been coming down over the past
couple of days, with the latest guidance not showing much more
than a trace across southern Maricopa, Yuma, and much of Imperial
Counties. A few hundredths of an inch to up to around 0.1" are
now expected in the foothills areas across La Paz and Maricopa
Counties, to 0.2-0.5" in higher terrain areas northeast of
Phoenix. The highest amounts are likely to be seen across JTNP
where up to an inch will be possible by late Friday morning. By
Friday evening, much drier air will already be working into the
area from the west, largely ending rain chances across all but the
far eastern Arizona higher terrain.

Upper level ridging is then forecast to overtake the region from
the west Friday night and Saturday with skies clearing out. The
cooler air mass will however keep daytime highs near normal on
Saturday before the full warming of the ridge is realized
Sunday into Monday. NBM forecast temperatures show highs reaching
into the mid 70s Sunday and then into the upper 70s starting
Monday. Model uncertainty increases somewhat by the middle of
next week with some ensemble guidance showing a dry shortwave
trough diving into or just past our region. This feature may be
enough to provide some slight cooling, but at this point it looks
like guidance favors a continuation of the mid to upper 70s for
highs through at least the middle of next week.

&&

.AVIATION...Updated at 1137Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation concerns are expected during the TAF period.
Typical diurnal trends will prevail with a earlier than normal
switch to the W late this morning/early afternoon. BKN skies will
be present through much of the forecast. The lowest bases during
the forecast window will be around 4-5k ft, but most CIGs look to
remain AOA 7k ft.

Southeast California/Southwest Arizona including KIPL and KBLH:
Low CIGs, primarily at IPL, will be the main aviation concern
during the period. Bases there will drop to around 3-4k ft by mid
to late morning, with a 20-30% chance to see bases fall to MVFR
levels by tonight/early tomorrow morning. At BLH, CIGs will not
fall as far, but bases will still decrease to around 6-7k ft.
Winds through the forecast will generally be out of the W/NW at
both terminals, with gusty conditions (aob 30kts) expected to
prevail through the morning at IPL.


&&

.FIRE WEATHER...
Near to below normal temperatures and increasing humidities will
be seen over the next couple of days. Light showers will also
become possible by Thursday across the western districts and then
Thursday night and Friday for the eastern districts. Chances for
wetting rain is generally under 10% for the western districts to
upwards of 40-70% across the Arizona higher terrain. MinRHs will
gradually increase through Friday, ranging from 20-35% today to as
high as 30-50% Friday. Expect lighter winds today and Thursday,
but with some afternoon breeziness likely over the western
districts and across the Arizona higher terrain. Widespread
breezy conditions are likely for the daytime hours Friday.
High pressure will then push into the region over the weekend
leading to drier and warmer conditions, lasting through at least
early next week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Wind Advisory until 4 AM PST early this morning for CAZ562.

&&

$$

DISCUSSION...Kuhlman
AVIATION...Ryan
FIRE WEATHER...Kuhlman