Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 231227

Area Forecast Discussion
National Weather Service Phoenix AZ
527 AM MST Fri Mar 23 2018

.UPDATE...Updated Aviation and Fire Weather Discussions...


A weak weather system will move off to the east today with just a
few lingering morning showers expected over the higher terrain east
of Phoenix. A cool down is in store starting today; desert highs
will fall to around 80 and then fall into the lower 70s by Sunday. A
fairly dry weather system will bring another slight chance of
showers early next week while keeping temperatures well below normal.


At 2 am this morning, a fast moving and progressive open wave trof
continued to push east across Arizona with the cold front moving
through the central deserts. This has been a very dry system for
southern Arizona; radar returns at the 0.5 degree cut have been weak
with values mostly below 30dBZ. Cloud bases have been high and as
such most precip has fallen as virga. The latest 6 hourly rainfall
map from the flood control district did not have one gage reporting
0.04 or higher. This wave is forecast to quickly push east and out
of the area this morning, bringing in cooler, drier and more
subsident air. There will be a slight chance of lingering morning
showers over the higher terrain east of Phoenix otherwise expect
skies becoming mostly sunny by afternoon from Phoenix westward.
Highs today will drop into the low 80s over the warmer lower deserts.

Dry southwest flow aloft will set up over the area Saturday with
some embedded high cloud giving partly sunny skies, and high
temperatures will change little as 500mb heights remain below 570DM
over the lower deserts.

Model guidance, including operational runs of the GFS and ECMWF and
GEFS ensemble guidance, continue to be consistent in their depiction
of the weather pattern across the desert southwest Sunday into the
early part of next week. They continue to forecast a deep, cool but
relatively dry upper trof to set up and deepen over the desert
southwest Sunday into next Monday. The trof remains open wave and
with a mostly overland trajectory very little moisture is entrained
into this system. Thus no rain is in the forecast through Monday; we
can expect mostly sunny to partly cloudy skies along with a sharp
cooling trend. HIgh temperatures over the lower deserts will drop
both days, bottoming out in the upper 60s to low 70s by Monday.

For Monday night through Wednesday, the trof forms a closed upper
low that gradually spins up and moves steadily southeast across the
area. Again, this is a dry low but there looks to be sufficient
moisture to allow for a few light showers mainly over higher terrain
areas north and east of Phoenix Tuesday through Wednesday night. By
Wednesday night the upper low center is forecast to move into New
Mexico leaving a dry northerly flow behind in its wake. High temps
will stay cool on Tuesday then start to warm Wednesday as skies
clear. Most of the warming Wednesday will be over the western
deserts where 500mb heights climb the most and skies are sunniest.
Look for central desert highs to stay below normal and int the mid
70s Wednesday with warmer western deserts rising into the low 80s.

Stronger high pressure aloft will build into the desert southwest
Thursday for sunny skies and high temperatures climbing back into the
low to mid 80s.


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

Weak cold front currently moving through the area will bring a few
isolated light showers mainly north of Phoenix. Skies will
gradually scatter out later this morning with only some high
clouds affecting the area through the rest of today. West winds
behind the front will be periodically breezy today before
diminishing this evening.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation impacts through at least Saturday morning. Winds will
be a bit breezy this afternoon with some occasional gusts into the
teens. Winds will diminish somewhat tonight, but again become
breezy at times on Saturday.

Aviation Discussion not updated for amended TAFs.


Sunday through Thursday...
A large area of low pressure will build across the desert
southwest Sunday into early next week, but overall dry conditions
will prevail. The low will usher in a cooling trend with high
temperatures falling into the upper 60s to low 70s across the
deserts by Monday. Slight warming will then take place through
Wednesday but highs will stay below normal and in the 70s. Some
moisture will sneak into south- central Arizona and by Tuesday
afternoon there will be a slight chance of light showers across
higher terrain areas north and east of Phoenix. For the most part
minimum RH values will stay a bit low and mostly in the teens
each day, reaching into the mid 20s over the higher terrain areas
east of Phoenix. We can expect breezy conditions each day during
the afternoon hours, favoring the west to northwest over the
deserts with slightly higher values across ridgetops and over
favored higher terrain locations.


Spotters should follow standard reporting procedures.




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