Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 261150 AAA

Area Forecast Discussion...Updated
National Weather Service Phoenix AZ
450 AM MST Mon Oct 26 2020

.UPDATE...Updated aviation discussion.


As a strong fall weather system moves through the region today,
temperatures will hardly budge all day with highs 15 to 20
degrees below normal today and little improvement on Tuesday. The
potential for showers will remain mainly across Gila and Pinal
counties through this afternoon. Across southeast California and
southwest Arizona, strong northerly winds will last much of the
day, likely leading to localized areas of blowing dust. Dry and
warmer conditions are expected during the latter half of the week
as high pressure settles in across the region.


A strong and cold upper level trough continues to surge southward
into the region early this morning. A surface cold front has also
punched its way through the Lower CO River Valley since midnight
bringing very strong winds and wind gusts of 40-45 mph in some
spots. Farther to the east, scattered showers with some occasional
embedded thunder are ongoing across the high terrain in central
and eastern Arizona. This activity is within a focused area of jet
forced ascent and southwesterly low level upslope flow. Low
levels of moisture will continue to be the main limiting factor
for rain chances today as HREF members mostly show just scattered
activity across Gila Co. through this afternoon while rainfall
amounts are likely to remain fairly light.

As the upper low tracks southward today, the impressive pressure
gradient will remain conducive for very strong northerly winds
across southeast California and southwest Arizona. As a result,
wind gusts of 35-50 mph will be possible through this afternoon.
Very dry air will also follow behind the cold front as surface dew
points drop into the single digits and likely to below zero. The
combination of very low RHs and strong winds will result in an
elevated fire risk for today. A Red Flag Warning is currently in
effect for the Lower CO River Valley and JTNP, while a Wind
Advisory covers much of southeast California and southwest

Temperatures today will actually not change all that much from the
current 60s readings as highs are likely to only top out in the
middle 60s in most places. This evening should turn out to be
quite chilly with temperatures falling into the 50s and breezy
conditions in most areas. Tuesday morning`s low temperatures are
also of concern as the full force of the incoming cold air mass
will be felt. Current forecast lows are generally in the 40s
throughout the lower deserts with more sheltered desert areas
likely seeing some upper 30s. Winds will remain breezy across our
western deserts and this should keep lows mostly in the mid 40s to
lower 50s. Areas across south-central and eastern Arizona are
however more likely to see lighter winds and less mixing resulting
in colder temperatures. A Freeze Warning has been issued for
Tuesday morning for the bulk of southern Gila Co., including the
Globe area.

As the low exits to the east southeast during the day Tuesday,
winds will remain somewhat breezy, but some warming will begin to
take place allowing highs mostly in the lower 70s in southeast
California to the mid to upper 60s in the Phoenix area. Tuesday
night and Wednesday morning will again be quite chilly, possibly
colder in some spots due to calmer winds and more efficient
cooling effects. Widespread lows in the low to mid 40s are
forecast for Wednesday morning for the lower deserts with the
coldest deserts likely dipping into the upper 30s.

Models are now leaning more toward a bigger warm up for the latter
half of the week as a fairly strong ridge seems likely to build
over our region late in the week. This will keep us under dry
conditions while highs warm back to around normal by Thursday and
then potentially back to around 90 degrees again for the upcoming


.AVIATION...Updated at 1150Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Winds will be the primary weather impact and forecast challenge
through tonight. FEW-SCT decks in a 070-110 AGL layer will be common
into the morning hours with considerable clearing from the west by
17z. Southwest winds should prevail through the afternoon hours
although there is the potential for directions to briefly go back
towards a SE direction at times this morning through about 15z, as
winds back ahead of an approaching low (albeit likely not truly
going back to an easterly direction).

Confidence is good that SW gusts 20-25 kt will resume by late this
morning with a tendency for directions to veer from SW to NW through
the day and across the metro area. While BLDU at the ground is not
expected, lofted dust from western AZ may create slantwise
visibility issues throughout the day. Forecast confidence remains
lower late in the afternoon and evening as there may be a period of
gusty northerly cross runway winds surging south through Phoenix in
association with a steep cold front. Speeds may be strong enough to
impact arrival rates with these cross winds before a tendency for
weakening tonight. After 03z tonight, winds should favor north to
northeast, especially KSDL and KDVT with sustained speeds genly 15kt
or less.

Southeast California/Southwest Arizona including KIPL and KBLH:
Unusually strong winds and categorical MVFR (and potentially periods
of IFR) BLDU will be the main weather hazards through this evening
under mostly clear skies. A strong cold front will surge south
creating very intense northerly winds throughout much of the day
Monday, especially at KBLH. KIPL winds should veer to northerly
closer to sunrise with gusts approaching 30kt through the day. Have
left out any BLDU at KIPL as northerly trajectories are generally
not favorable, but lofted dust and poor slantwise visibilities are
likely. At KBLH, even stronger 40-45kt winds will persist off and on
for much of the day with periods of MVFR/IFR BLDU possible. Due to
lowered confidence about the lower vis values (dropping into IFR),
will only go with 5SM in the TAF as predominant vis, knowing that it
could drop much lower for brief periods off an on during the day.
Expect less wind after sunset due to the lack of mixing.

At KBLH, following sunset and as minimal decoupling occurs, there is
potential for LLWS at the terminal for much of the overnight as
strong winds over 40kt persist around 2k feet. Despite continued
elevated surface winds, shear potential exists and LLWS has been
added into the TAF.


Wednesday through Sunday:
Below normal temperatures will persist Wednesday, but while also
steadily warming. Above normal temperatures are then expected by
Friday with lower desert highs warming into the lower 90s late in
the period. Min RH will remain quite low through the period near
10-15%, and in the single digits across western districts
Wednesday. Overnight recoveries will be around 25-40%. Winds will
be relatively light each day with typical afternoon breezes and
favoring typical diurnal tendencies.


Spotters should follow standard reporting procedures.


AZ...Freeze Warning from 9 PM this evening to 9 AM MST Tuesday for

     Blowing Dust Advisory until 3 pm MST this afternoon for AZZ532.

     Red Flag Warning until 9 PM MST this evening for AZZ131.

     Wind Advisory until 9 PM MST this evening for AZZ530>533-535-536.

CA...Blowing Dust Advisory until 3 pm PDT this afternoon for CAZ564-

     Red Flag Warning until 9 PM PDT this evening for CAZ230-231.

     Wind Advisory until 9 PM PDT this evening for CAZ561-564-565-569-

     High Wind Warning until 9 PM PDT this evening for CAZ560-568.



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