Weather Service Report


264 
FXUS65 KPSR 261449
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
750 AM MST Wed Apr 26 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 will
likely bring windy conditions and has the potential to produce a 
slight chance of afternoon showers over the eastern Arizona 
mountains. 

&&

.DISCUSSION...

Dry northwest flow aloft providing mostly clear skies and warmer 
afternoons are forecast today and Thursday in the aftermath of 
Tuesdays windy cold front. Another windy episode is expected Friday, 
details below. Otherwise current forecasts look ok. No short term 
updates necessary.


.PREVIOUS DISCUSSION...555 AM MST...

An upper level trough axis has shifted well into New Mexico early
this morning with increasing subsidence and modest warming aloft 
over SE California and Arizona. The warming aloft will lead to 
highs increasing a few degrees over Tuesday's readings with the 
Phoenix area reaching near 90 degrees and the SE California and SW
Arizona lower desert locations reaching into the lower 90s. Winds
will again be breezy today, but gusts should mostly remain below 
25 mph. Similar conditions are expected for Thursday as dry 
northwest flow continues.

Much better model agreement is now shown for the next low 
pressure trough bringing a closed low southward through eastern
Utah into the Four Corners area Friday night. This will bring a
cold frontal boundary southward through Arizona Friday afternoon
through early Friday night. Some limited mid level moisture ahead
of the front will likely result in some scattered showers and a
very remote chance of a thunderstorm over the high terrain north
and east of Phoenix. Can't completely rule out a shower or two
making it off the high terrain into the south-central Arizona
deserts, but a very dry sub-cloud layer should only result in 
virga or sprinkles. Very dry air will usher in behind the cold 
front with surface dew points likely crashing into the single 
digits late Friday afternoon and evening. Another windy day is 
likely on Friday with a high likelihood of some areas being under 
Wind Advisory. The strong winds and lowering humidities on Friday 
will likely bring dangerous fire weather conditions once again.

Ahead of the cold front on Friday, highs should reach into the 
upper 80s across the deserts. Cooler air ushering in behind the
cold front will allow for a fairly mild but breezy day on 
Saturday as highs should only top out between 80-85 degrees. 
Rapidly building heights and warming aloft will take place 
Saturday night into Sunday as the upper level trough shifts 
eastward into the Southern Plains. This will return temperatures 
back to near normals on Sunday and a few degrees above normal for 
Monday. 

Considerable model spread exists after Monday with potential for 
yet another upper level trough digging southward through the Great
Basin and Four Corners area. The operational GFS is on the 
extreme side bringing a closed low through eastern Arizona while 
the operational European keeps it much farther north and east,
essentially showing ridging over the Desert Southwest. The GFS 
and European ensemble means are somewhere in between the 
operational solutions. For now we are keeping our forecast mainly 
based on the ensemble means calling for near normal temperatures 
with continued dry and breezy conditions.

&&

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

We can expect another breezy day today, but we should see much less 
wind that what occurred yesterday. Still, we can expect afternoon 
and early evening breezes favoring the west at the TAF sites. Winds 
at KPHX may have a hard time returning to the east for any 
significant time this morning, possibly just going light/variable 
for a few hours before picking up again from the southwest to west. 
Winds likely to remain out of the west (or a westerly component) 
past midnight tonight before exhibiting some typical diurnal trends. 
No aviation concerns for sky, just some variable mainly thin high 
clouds with SCT to BKN decks at times.

Southeast California/Southwest Arizona Including KIPL and KBLH: 

Less wind expected today as compared to yesterday with speeds mostly 
below 12kt next 24 hours. Winds to favor the north at KBLH this 
morning before swinging back to the south/southwest by early 
afternoon. Winds rather light/variable at KIPL this morning then 
likely turning southeast during the afternoon. Expect winds to 
become breezy from the west again after 01z this evening and 
possibly gusty at times for much of the night with peak gusts over 
25kt possible. No sky issues, just variable amounts of mainly thin 
cirrus at times.

Aviation discussion not updated for amended TAFs.

&& 

.FIRE WEATHER...
Friday through Tuesday:

A sharp cooling trend will settle into the region as a mostly dry 
storm system sweeps through the Great Basin and down through the 
Southwest Friday into Saturday. Very strong and gusty winds will 
develop across the area Friday with gusts over 40 mph likely over 
much of the area, especially south-central Arizona. Humidity levels 
will fall sharply during the day as a cold front sweeps across the 
area and given the high fire danger, we will likely see widespread 
dangerous fire weather conditions across most of the area by 
afternoon. Critical thresholds may well be reached from the far 
southeast California deserts into the higher terrain of southern 
Gila County. Less wind is expected Saturday but breezy conditions 
from the north will persist over the western deserts and with 
minimum RH values to stay mostly below 10 percent area-wide, we can 
expect continued dangerous fire weather conditions out west during 
the afternoon hours.

Dry and warmer conditions are expected Sunday into Monday as high 
pressure builds into the area from the west. By MOnday high 
temperatures over the deserts will climb into the mid 90s for the 
most part with minimum RH values to stay mostly in the single 
digits. Less wind is expected although we should see continued 
afternoon and early evening breezes across much of the area, 
favoring the west. It will continue to be dry and warm Tuesday 
although there is the chance for an increase in wind especially 
across south central Arizona where gusts in excess of 30 mph are 
likely for much of the afternoon.

&& 

.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...Vasquez/Kuhlman
AVIATION...CB
FIRE WEATHER...Hernandez/CB

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Western Regional Climate Center, wrcc@dri.edu