Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 260446
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
946 PM MST Tue Apr 25 2017

.SYNOPSIS...
A series of mainly dry Pacific weather disturbances will move across
the western states through early next week. These systems will keep
afternoon temperatures near or slightly below normal, along breezy
afternoons and evenings. One stronger disturbance on Friday has the
potential to produce a slight chance of afternoon showers over the
eastern Arizona mountains.

&&

.DISCUSSION...
Winds have decreased substantially across much of the forecast
area with the loss of daytime heating and mixing. However,
observations still showing some locations with sustained speeds of
15-20 mph, primarily from Phoenix eastward. Winds should continue
weakening overnight at most locations as a shortwave trough
continues to quickly advance eastward across the Southern Plains.
Transient and brief midlevel ridging will build over the region
through Wednesday morning, ahead of another weak upper-level
disturbance. A rather tight geopotential height gradient aloft
will be maintained within this pattern, and the combination of
strong boundary-layer mixing and a modest surface pressure
gradient should result in breezy westerly winds once again
tomorrow afternoon. Temperatures will remain nearly identical to
today, near seasonal normals. Only very minor adjustments were
made to the forecast for this evening and early tomorrow morning.

&&

.PREVIOUS DISCUSSION...

A cold front from Nevada was moving through central AZ at 2 PM MST
and just about through Phoenix.  This system is dry but has a good
wind punch. Gusty west to northwest winds across the south central
AZ deserts and mountains, including Phoenix, are still expected this
afternoon/evening in the 25 to 35 mph range, with gusts to 45 mph in
southern Gila County to the east. A Wind Advisory and Red Flag
warning is posted for much of south central AZ through 7 pm MST.

Gusty north winds are expected to diminish overnight becoming north
8 to 14 mph most areas after midnight. Clear skies are also forecast
tonight.

Wednesday through Tuesday...

Dry northwest flow aloft will continue over our forecast area,
southeast CA to south central AZ, into the weekend. Several fast
moving disturbances will continue in this flow pattern, keeping
afternoon temperatures near or slightly below normal under mostly
clear skies. However one strong disturbance will deepen
significantly over eastern AZ on Friday, moving from northwest to
southeast, producing another episode of gusty afternoon and evening
winds. A slight chance of a shower or thunderstorm is also forecast
over the mountains of southern Gila County zone 24. Modeled
soundings forecast a short window of afternoon C.A.P.E for a threat
of instability showers.  A trend toward above normal temperatures
are expected early next week.

&&

.AVIATION...
South-Central Arizona Including KPHX, KIWA, and KSDL:

Wind gusts have become less frequent this evening, but westerly
winds around 15 kt are persisting across Phoenix area terminals.
Should expect to see a continued weakening trend into early
Wednesday morning, with an eventual shift to an easterly direction
occurring after 12Z. Westerly winds will strengthen once again
Wednesday afternoon, but will be weaker than Tuesday, around 8-14
kt at the surface. Cloud cover will also decrease through
Wednesday morning, remaining above 25 thousand feet.

Southeast California/Southwest Arizona Including KIPL and KBLH:

Westerly winds around 10 kts should persist through much of the
next 24 hrs across KIPL and KBLH, with only a modest strengthening
expected Wednesday afternoon. Little to no cloud cover is
anticipated.

Aviation discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Friday through Tuesday:

Temperatures will continue to hold at or above seasonal averages
today, with minimum RH values mostly below 15 percent as dry
northwest flow aloft persists over the area. Expect afternoon
westerly breezes especially over south central Arizona. A cooling
trend will settle into the region as mostly dry storm systems sweep
through the Great Basin and down through the Southwest. Outside of a
slight chance at some light showers over high terrain of Gila County
Friday into Saturday, widespread dry weather will cover the
districts. Dry afternoons with 5-10% will be common with overnight
humidities varying between mostly fair to good. Active storm track
through the West will keep afternoons breezy for the district, with
upslope west winds and occasional gusts possible through week`s end.

There continues to be potential for widespread dangerous fire
weather conditions Friday into Saturday as windy conditions develop
across most of the area - especially south-central Arizona on Friday
- and minimum RH values drop into the single digits across much of
the lower desert. The cooling trend may help mitigate some of the
fire danger potential however but this is something to keep our eyes
on as we move towards the latter part of the week.

&&

.SPOTTER INFORMATION STATEMENT...
Spotter activation will not be needed through the middle of next
week.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

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DISCUSSION...Rogers
PREVIOUS DISCUSSION...Vasquez
AVIATION...Rogers
FIRE WEATHER...Hernandez


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