Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 280005 AAA
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
505 PM MST Tue Sep 27 2022

.UPDATE...00Z Aviation Discussion.

.SYNOPSIS...
The return of moisture will bring on and off, slight chances of
showers and storms over the next few days and favor the high terrain
generally south and west of the Phoenix area. The very warm
temperatures will also begin to moderate some over the next few days
with readings dropping back closer to normal readings by Friday.

&&

.DISCUSSION...
First, we want to wish all the best to our colleagues in Florida
as they work vigilantly to protect lives and properties from
dangerous Hurricane Ian. Our thoughts will be with you over the
next couple of days.

The axis of the strong upper-level ridge that brought very warm
temperatures to our region will continue to get slowly nudged
eastward as another trough approaches the western CONUS. This will
lead to a gradual decrease in temperatures, with highs in the
upper 90s expected by the weekend. The EFI continues to signal
that temperatures today across western Imperial county are
unusually high for this time of year. Widespread moderate
HeatRisk and isolated high HeatRisk is also expected today in
that area and thus the Excessive Heat Warning will be in effect
for another day today. As for storms, easterly flow has helped to
advect drier air into northern and eastern Arizona, which will
limit instability and storm activity in those areas and across the
eastern half of our south-central Arizona forecast area this
afternoon and evening. The best moisture & instability will be in
areas west of Phoenix/Casa Grande metros towards the Colorado
River Valley, with isolated storms (chances <10%) favoring the
high terrain. HREF and associated members are also not very
optimistic about storms today and tonight and show less than a
10% chance of having 35 mph winds with any storm or outflow that
develops in our area. The chance of any of these isolated cells
producing more than a quarter inch of rainfall is near 0 percent.
So overall, today, impacts should be very minimal, but any of
these cells may produce lightning, brief gusty winds, and blowing
dust, especially in areas near and along the Colorado River
valley, where instability is greatest.

The overall limited moisture environment will continue into at
least Wednesday, while guidance suggests our region will fall
under a bit more favorable upper level ascent regime as the far
southern portion of the Pacific trough enters the Great Basin
area. This is reflected in the slightly better coverage of
convection seen within the latest 00Z HREF and more expansive
10-20% NBM PoPs Wednesday afternoon through the early morning
hours Thursday. Given the still limited atmospheric moisture and
instability, the main storm threats for Wednesday will be gusty
winds and the potential for localized blowing dust. Measurable
rainfall will be very sparse, but a few localized areas under any
stronger cells could see a half an inch or more of rain.

Model ensembles show the Pacific trough slowly tracking east
southeastward through the Northern Rockies and Great Basin later
this week and this will eventually shift our flow out of the west by
around Friday. Lingering moisture across our region should still
result in limited chances for showers and possibly isolated
thunderstorms on Thursday and maybe Friday, but eventually enough
dry air is expected to spread over our area that rain chances mostly
come to an end by the weekend.

Temperatures will slowly decrease later this week as the trough
bypasses our region to the north, but readings are likely to remain
at least 2-4 degrees above normals through the rest of the week.
Forecast highs in the upper 90s to just over 100 degrees are seen
across the lower deserts from Friday through early next week with
overall small spread in temperature guidance.

&&

.AVIATION...Updated 0005Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Periods of gusty east winds and lack of the traditional afternoon
westerly switch will be the primary weather issues through Wednesday
afternoon. FEW-SCT decks above 10K ft will be common, though any
SHRA/TSRA activity should remain well south towards the
international border this evening. Easterly winds to continue thru
the evening/overnight hours tonight and into early Wednesday
morning. Some increase in winds speeds is likely during the late
morning/early afternoon hours again on Wednesday.

As far as the forecast for Wednesday afternoon/evening is concerned,
expecting a bit more convective actively across the region as
moisture levels and winds aloft become more southerly. The main
impact to the Phoenix area terminals is to allow the winds to become
more southerly by late afternoon Wednesday. The bulk of the t-storm
activity is expected to remain to the south of the Phoenix area,
with only about a 10% chance of any t-storms actually impacting one
or more of the terminals. There is a greater chance (20-30%) that
outflows from distant storms produce wind gusts greater than 30 kt
and areas of blowing dust, but confidence is too low to include any
mention of stronger winds/blowing dust in the TAFs at this point.
Winds are then expected to revert back to more typical easterly
drainage winds around/shortly before midnight Wednesday night.

Southeast California/Southwest Arizona including KIPL and KBLH:
Only minimal weather issues will exist through Wednesday afternoon
with occasional SCT midlevel decks. Winds at KBLH should remain
mainly northerly tonight/early Wednesday, then become southerly
during the day on Wednesday. The potential still exists for an isold
shower and erratic wind directions is possible (though probabilities
too remote to include in TAF package). Southeasterly winds are
mostly likely at KIPL, with prolonged variable wind directions also
being a good possibility as well.

As far as the forecast for Wednesday afternoon/evening is concerned,
expecting a bit more convective actively across the region as
moisture levels and winds aloft become more southerly. There is only
about a 10% chance of any t-storms actually impacting one or more of
the terminals. There is a greater chance (20-30%) that outflows from
distant storms produce wind gusts greater than 30 kt and areas of
blowing dust, but confidence is too low to include any mention of
stronger winds/blowing dust in the TAFs at this point.

&&

.FIRE WEATHER...
Above normal temperatures will continue through at least mid week,
but with some gradual cooling bringing temperatures back closer to
normals late in the week. Modest moisture currently across much of
southern Arizona will shift westward starting today providing
chances for isolated showers and thunderstorms through at least
Wednesday focused more over higher terrain areas of western
districts. Drying conditions by the weekend will mostly end rain
chances across the majority of the area as high pressure rebuilds
across the region. Afternoon MinRHs through the end of the week will
mostly be between 15-25% each day. Enhanced easterly winds are
likely to prevail across much of southern Arizona through Wednesday
with morning gusts up to 25 mph today and Wednesday. Winds later
this week should shift back to a more typical diurnal pattern with
lighter winds speeds.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Excessive Heat Warning until 11 PM MST this evening for CAZ562-
     566-567.

&&

$$

DISCUSSION...Feldkircher/Kuhlman
AVIATION...Percha/18
FIRE WEATHER...Kuhlman


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