Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 282212
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
312 PM MST Thu Mar 28 2024

.SYNOPSIS...
A strong low pressure system will bring windy conditions and
excellent rain chances to the Desert Southwest this weekend through
early next week. Winds will ramp up across SE California tonight
and Friday with stronger winds overspreading the entire forecast
area on Saturday. A cold front will progress through the region
Saturday night into Sunday morning, resulting in widespread
showers and isolated thunderstorms. Moderate to brief heavy
rainfall will be possible. Scattered showers will persist Sunday
through Monday with accumulating rainfall totals between 0.50"-1.50"
possible across southcentral AZ. Temperatures will peak in the
low to mid 80s Friday and Saturday before falling well below
normal Sunday and Monday.

&&

.DISCUSSION...
An active weather pattern will set up across the Desert Southwest
this weekend into early next week. The main impacts ahead of the
approaching storm system will be strong gradient winds Friday and
Saturday followed by a potential robust line of showers/storms late
Saturday night through early Sunday. On/off showers and storms will
be possible through at least Monday until the system progresses
east of our region.

Before all the action begins, we will end the workweek with mostly
sunny skies and dry conditions area-wide. A deep upper level low,
which will be our big weather maker, is now located just off the
Pac NW coast. This low will begin to deepen and track swd over
the next 24 hrs. As this occurs, we will see increasing W-SW flow
aloft. Latest deterministic models show a tightening 500-700 hpa
height gradient over SE California beginning tonight and persisting
through much of the day on Friday. In response, wind speeds will
ramp up, especially across western Imperial County as early as
this evening. Latest NAM 12 cross-section analysis reveals a
prominent mountain wave signature developing over SW Imperial
County around 00Z tonight and persisting into early Friday
morning. Winds will begin to gust across the higher terrain and
spread ewd into the Imperial Valley tonight. Therefore, a Wind
Advisory has been issued for W Imperial County including El Centro
through 2 AM PDT Friday. Gusty winds should subside across most
of Imperial County early Friday morning, but will redevelop again
Friday afternoon as a stout mid-lvl jet becoming positioned over
SE California. Thus, the Wind Advisory will expand after 21Z
Friday to include all of Imperial, E Riverside County, and the CO
River Valley where gusts could reach 40- 45 mph.

The main story will continue to be wind as we head into Saturday.
Deep southwesterly flow aloft will overspread the entire forecast
area by Saturday afternoon with an unseasonably strong 500 mb jet
approaching 60-70 kts situated over southcentral AZ. Another Wind
Advisory is almost a sure bet to be issued Saturday afternoon for
the central deserts of AZ including the Phoenix Metro area where
gusts will likely (60-70%) exceed 40 mph. Blowing dust may also
become an issue in the most dust prone areas of N Pinal and S
Maricopa Counties.

.PREVIOUS DISCUSSION...
Our attention will then turn to a cold front associated with the
main leading shortwave ahead of the approaching upper low. Mid-
level moisture will continue to increase throughout Saturday
evening with PWATs peaking around 0.8-0.9". As the cold front
begins to migrate ewd Saturday night, a line of showers,
potentially evolving into a broken squall line with embedded
thunderstorms, is expected to develop across southeast CA and push
ewd overnight. The main concern associated with these showers
will be strong to severe wind gusts, and brief heavy rainfall.
For the rest of Sunday, the cold core portion of the upper low
will move east over our region with additional showers expected
later in the afternoon and through the evening. There also very
well could be a few isolated thunderstorms later on Sunday as
lapse rates improve and some weak instability develops mainly from
Phoenix and areas west of Phoenix. There is also model evidence
showing good shower potential lasting through the overnight hours
Sunday night across south-central Arizona. As the cold core low
remains in place over much of the region through Monday, shower
chances should persist. Depending on how much insolation can be
realized during the daytime hours Monday, its very possible some
areas could see some low-topped convective thunderstorms Monday
afternoon with small hail and brief heavy downpours the most
likely impacts.

As far as expected rainfall amounts, ample moisture will be present
this weekend, especially along and just ahead of the front when
there will be the most widespread rainfall. The  additional shower
and potential thunderstorm activity later on Sunday and Monday
should also add a decent amount to the rainfall totals from Maricopa
County and areas to the east. The latest storm total forecast
rainfall amounts are calling for between 0.10-0.25" for areas west
of the Colorado River to 0.50-1.00" in the Phoenix area. Higher
terrain areas northeast of Phoenix could receive as much as 1.5" in
a few spots. This rainfall is likely to be spread out across a 2-day
period, so at this point we are not anticipating much if any of a
localized flood threat.

Temperatures this weekend will also be something to take note of as
high temperatures Saturday will drop roughly 20 degrees to Sunday`s
daytime highs. Given the timing of the cold front during the early
morning hours Sunday, much of south-central Arizona is likely to see
highs reached just after midnight in the mid to upper 60s with
temperatures falling well into the 50s by sunrise Sunday morning.
Daytime temperatures will recover somewhat by the afternoon, but
depending on the cloud cover some areas Sunday afternoon may
struggle to get into the lower 60s.

For early next week as the weakening upper low is trying to linger
over eastern portions of the region, temperatures will be slow to
moderate. Forecast highs for Monday are 10-13 degrees below normals
with highs still in the 60s in Phoenix before likely improving into
the mid 70s on Tuesday. Ensemble guidance heavy favors a ridge to
begin building into the region by next Wednesday and this should
briefly push highs back into the 80s for 2-3 days later next week.

&&

.AVIATION...Updated at 1720Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

No aviation concerns are expected during the TAF period. Winds
will follow typical diurnal tendencies with speeds generally aob
10 kts. High clouds will continue to stream over the region before
gradually clearing by Friday morning.

Southeast California/Southwest Arizona including KIPL and KBLH:

Breezy to windy conditions will be the main aviation concern
during the period. W`rly gusts 25-35 kts will be common this
evening at IPL with elevated gusts potentially lasting through
Friday morning. These enhanced winds will be capable of producing
areas of of blowing dust leading to periods of reduced
visibilities. At BLH, S/SW`rly gusts 20-25 kts will commence this
evening before speeds calm through the early tonight. SCT high
clouds can be expected through tonight before clearing out by
tomorrow morning.

&&

.FIRE WEATHER...
Seasonably warm and dry conditions will persist through Friday,
but with increasing winds each day. Winds today will be light
across the eastern districts, but breezy to locally windy across
portions of southeast CA this afternoon and evening. Winds Friday
will increase further across the entire area with afternoon wind
gusts between 30-40 mph across the western districts to around 25
mph over the eastern districts. MinRHs both days are likely to
reach into the mid teens across the lower deserts to 20-25% over
higher terrain areas. Friday afternoon may bring a brief period
of elevated fire weather conditions within the Lower CO River
Valley. By the weekend, a strong low pressure system will be
moving in from the west bringing widespread windy conditions
during the daytime Saturday, fairly widespread wetting rains
Saturday night into Sunday, and cooler temperatures starting
Sunday.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Wind Advisory from 2 PM to 11 PM MST Friday for AZZ530.

CA...Wind Advisory from 2 PM to 11 PM PDT Friday for CAZ560-561-
     563>570.

     Wind Advisory until 11 PM PDT Friday for CAZ562.

     Wind Advisory until 2 AM PDT Friday for CAZ563-566-567.

&&

$$

DISCUSSION...Salerno/Kuhlman
AVIATION...RW
FIRE WEATHER...Kuhlman


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