Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 211159

Area Forecast Discussion
National Weather Service Phoenix AZ
459 AM MST Mon May 21 2018

.UPDATE...Updated Aviation discussion.


A seasonably warm and dry weather pattern will continue through the
middle of the week along with clear to mostly clear skies. Expect
warm daytime temperatures near to slightly below seasonal normals
through Wednesday with breezy to windy conditions today and
Tuesday. The latter part of the week will see a noticeable
warming trend as high temperatures climb back above 100 and
continuing into the weekend.


A deepening upper level low currently centered across central
California will settle across southern California later today
before weakening and lifting to the northeast on Tuesday. As
typical for this time of year, the system is mostly moisture
starved with only some modest high level moisture and cloudiness
moving in from the northwest. The main impact for today will be
the stronger winds, especially across western Imperial County
where gusts will approach Wind Advisory at times. Elsewhere, winds
will gust to around 25 mph this afternoon and early evening,
falling well short of advisory level. The breezy and dry
conditions today will bring an enhanced fire danger threat, but
winds will fall short of Red Flag criteria.

As the low sits just to our west today and to the northwest
on Tuesday, it will bring slightly cooler air to the region. Highs
today will still reach near normal for south-central Arizona, but
cool into the lower 90s for the deserts west of Phoenix. Highs for
Tuesday should be in the lower 90s across all the lower deserts
before temperatures begin to climb starting Wednesday.

Another deep trough is forecast to develop well off the West Coast
on Wednesday allowing ridging to amplify over the Western U.S.
The low should eventually drift eastward toward the West Coast by
Friday, but 500mb heights will settle in between 584-588dm across
the Desert Southwest. Under clear to mostly clear skies,
temperatures will rise under the amplified ridge later this week.
Highs will warm into the upper 90s by Thursday and then just over
100 degrees starting Friday. Model spread increases starting
Friday as the low moves into central California and even more
into the weekend. The GFS is a bit more aggressive pushing the low
further inland before lifting northeast through Nevada while the
European tracks the low further north. Either solution is a bit
cooler than our previous Friday through Sunday forecast, so
temperatures have been lowered slightly each day. However,
temperatures should still easily end up 3-6 degrees above
normals through the Memorial Day weekend.


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

Breezy conditions will develop later this afternoon ahead of a low
pressure system in southern California. Initially, a period of
southerly crosswinds is likely at KPHX, before veering to west-
southwesterly later this afternoon. Gusts as high as 20-25 kt will
be possible during the late afternoon, before subsiding during the
early evening. A return to the typical downslope flow is expected,
though its onset may delayed a few hours at both KIWA and KPHX.

Southeast California/Southwest Arizona including KIPL and KBLH:

Westerly component to the flow will continue to increase ahead of
a low pressure system in southern California. Gusts to 25-30 kt
are likely later this afternoon and early this evening at KIPL,
while winds will be somewhat weaker at KBLH. There is also the
possibility of patchy blowing dust at KIPL late this afternoon,
though significant reductions in visibility are not anticipated.


Wednesday through Sunday:
Temperatures will rise significantly with highs across the lower
deserts rising from the low to mid 90s on Wednesday to near the
100 to 105 range by Friday and remaining near that range through
the weekend. Conditions will remain dry through the period with
minimum humidities mainly in the single digits and overnight
recoveries becoming poor to fair by the weekend. Winds will follow
normal diurnal headings with some afternoon breeziness up to 20
to 25 mph.


Spotter activation will not be needed.




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