Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 031144
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
444 AM MST Wed Mar 3 2021

.UPDATE... Aviation discussion update.

&&

.SYNOPSIS...
A Pacific low pressure system will move through the region today
bringing widespread windy conditions this afternoon and elevated
fire weather concerns across much of Arizona. There will also be a
chance of showers by this evening into tonight, but best chances
will be focused over the central Arizona high terrain. After a
brief cool down on Thursday, a return to above normal temperatures
is expected starting Friday, lasting through the weekend. A more
unsettled weather pattern will be possible into next week, but
rain chances on any particular day remain fairly low.

&&

.DISCUSSION...
A vigorous upper level low continues to track eastward toward the
southern California coast early this morning with southerly flow
beginning to increase across much of our region. Forecast thinking
has changed very little since the afternoon forecast package as
the main impacts with the incoming system should be strong winds
and increased fire weather concerns. As the center of the closed
low nears San Diego early this afternoon, much stronger boundary
layer winds should begin mixing down to the surface, especially
from the CO River to as far east of the Phoenix area. A Wind
Advisory and Red Flag Warning remain in effect for southwest and
much of south-central Arizona this afternoon with wind gusts
reaching 30-40 mph and likely higher at times, especially in a
corridor between Yuma and Phoenix. Blowing dust may also become a
concern, but any dense blowing dust is likely to be very
localized.

Rain chances today still look somewhat limited due to an overall
lack of decent moisture associated with this strong system and
partially due to the low center tracking across far western
Arizona this evening into northern Arizona tonight. Guidance
mainly points toward scattered showers developing late this
afternoon across southeast California into western Arizona before
moving across central and northern Arizona from the middle part of
this evening through much of tonight. Light QPF amounts generally
less than 0.1" of an inch is expected across lower desert areas
to as much as 0.25-0.50" across the high terrain north and
northeast of Phoenix. For the Phoenix area, rain chances should
definitely favor areas across north Phoenix. Could also see a few
isolated thunderstorms, but HREF MUCAPE only shows minimal
instability this evening across northern Maricopa County.

The colder air will work through the region tonight, while the
upper level low quickly exits into northern New Mexico and
Colorado by late Thursday morning. Upper level ridging and
subsidence aloft will filter in behind the exiting low on Thursday
leaving clearing skies, but high temperatures are forecast to top
out a few degrees below normal readings. Starting Friday, the
high amplitude ridge will give a big boost to temperatures as
highs warm into the lower 80s. Very similar conditions will be
seen over the weekend with a bit higher potential for a few spots
hitting 85 degrees. Models have backed off on a potential trough
suppressing upper level heights for late Saturday into Sunday, so
forecast highs have been nudged upward 3-5 degrees on Sunday.

For at least the first half of next week, the model ensemble
cluster analysis shows a high likelihood of a deep trough setting
up across the eastern Pacific/far Western U.S. Initially as the
trough digs southward, southwesterly flow is likely to increase
again over our region potentially bringing up a sub-tropical
moisture plume into northern Mexico and maybe as far north as
southern Arizona. For now it seems this may just lead to a period
of thick mid level clouds on Monday, but there is at least some
model evidence for some rain chances across the high terrain east
of Phoenix. Unfortunately, if this moisture even does make its way
northward into our area, the only vertically forced ascent seen
would be in the form of upslope flow. Minimal rain chances may
also be possible Tuesday into Wednesday as at least one shortwave
trough looks to potentially swing through our region within the
larger scale trough that will likely remain situated across the
Western U.S. for much of next week. Temperatures should begin to
trend downward early next week with the increase in cloud cover
and lowering heights aloft, but there is much higher spread in
temperature guidance starting Monday.

&&

.AVIATION...Updated at 0549Z.

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

Easterly winds across the Phoenix area will gradually turn to the
southeast then south along with increasing speeds and gusts through
the late morning hours. A period of gusty south/crosswinds is
expected around 21Z as winds continue to swing to the southwest by
later in the afternoon. Some lofted dust may develop across the
region by late in the afternoon, impacting slantwise visibility.
Anticipating some showers developing, mainly along the northern
and eastern fringes of the metro area, after the evening push
(after 03-04Z).

Southeast California/Southwest Arizona including KIPL and KBLH:

Southerly winds will gradually increase through the rest of this
morning, becoming gusty by 17-18Z. A switch to the southwest and
brief uptick in speeds is expected mid afternoon as a front moves
across the area, along with a few showers. Some blowing dust will
be possible through the day.

&&

.FIRE WEATHER...
Friday through Tuesday:
Increasing high pressure early in the period will result in
continued dry conditions and warming temperatures. Highs will
quickly warm from slightly below normal on Thursday to into the
lower 80s Friday into the weekend. After minimum humidities in a
20-30% on Thursday, readings will fall into the teens starting
Friday. Winds will be fairly light for much of the period, but
some increased breeziness is likely on Saturday and Monday.
Despite a couple weak weather disturbances passing by or through
the region, no wetting rains are expected.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Red Flag Warning from 11 AM this morning to 6 PM MST this
     evening for AZZ132.

     Wind Advisory from 11 AM this morning to 6 PM MST this evening
     for AZZ531-533>541-545-559.

CA...Wind Advisory from noon today to 10 PM PST this evening for
     CAZ562.

&&

$$

DISCUSSION...Kuhlman
AVIATION...Iniguez
FIRE WEATHER...Kuhlman



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