Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 241815

Area Forecast Discussion
National Weather Service Phoenix AZ
1115 AM MST Sat Mar 24 2018

.UPDATE...Updated Aviation discussion.


A cooling trend will continue through the weekend with high
temperatures dropping into mid 70s by Sunday. A fairly dry
weather system will bring another slight chance of showers early
next week for the higher terrain east of Phoenix while keeping
temperatures well below normal. Drier and warmer weather return
during the latter portion of next week.


At 2 am this morning, dry southwest flow aloft was present across
the area, with Arizona and far SE California on the far southeast
flank of a large upper trof taking shape along the Pacific NW coast.
Latest 00z plot and raob data showed the dry SW flow, with PWAT just
0.19 inches at Flagstaff. Surface dewpoints over the central deserts
ranged from the mid 20s to mid 30s and were down 3-12 degrees from
24 hours ago. Current IR imagery showed variable amounts of high
cloudiness embedded in the flow aloft with skies ranging from clear
to partly cloudy. Little change in the pattern is expected today,
and with 500mb heights not changing much we can expect high
temperatures similar to yesterday, running from the upper 70s to low
80s over the warmer lower deserts. With low level gradients tight,
it will be quite breezy or even windy over much of the lower deserts
in far southeast California, especially favored wind prone areas
such as the Imperial Valley and the I-8 corridor west of El Centro.
We have added patchy blowing dust to the forecast out west this

Model guidance remains in very good agreement in calling for a large
upper trof to slowly develop over the western CONUS; it will remain
open-wave through Monday afternoon with 500mb heights dropping to
around 552dm over portions of south-central Arizona. With an inland
trajectory, this will be a dry trof and no precipitation is
expected; we can expect a marked cooling trend which will drop high
temperatures into the lower 70s over the deserts by Monday. Latest
model trends are keeping this trof a bit drier and not quite as deep
so Phoenix may stay in the 70s and not reach into the upper 60s with
this trof passage.

Starting Monday night, a closed low develops with this trof and sets
up initially over northern Arizona; Tuesday into Wednesday the
closed low quickly dives south then southeast and is well into New
Mexico by Wednesday afternoon leaving a dry northerly flow in place
in its wake. Again, moisture will be limited and surface dewpoints
over the central deserts fall into the teens by Tuesday afternoon.
With colder air aloft, there will be just enough instability and
cooler temps will allow for a slight chance of higher terrain
showers Tuesday into Wednesday afternoon. The shower threat should
remain well east of the greater Phoenix area. By Wednesday evening,
the drier northerly flow will scour out remaining moisture and
pretty much end any threat of showers across the area. Expect skies
to be mostly sunny from Phoenix westward by Wednesday afternoon. We
will also see quite breezy to windy conditions Tuesday afternoon
over the deserts west of Phoenix; gusty north winds may reach to
near 40 mph at times and could stir up some blowing dust. Patchy
blowing dust has been added to the forecast for Tuesday afternoon.

For Thursday into Friday, strong high pressure aloft will build into
the area from the west, giving sunny days and generally clear nights
along with a strong warming trend. High temperatures will rise into
the middle 80s Thursday and then into the upper 80s to near 90 by


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

Expect light to moderate southeasterly to southerly winds at 5-8kt
through midday. Then by 19-20Z breezy to very breezy westerly winds
will develop at 10-15kt with gusts of 17-22kt through the early
evening. For tonight through Sunday morning a generally light,
diurnal wind pattern is anticipated. Otherwise skies will be partly
to mostly cloudy with high cloud CIGS this afternoon, and then
scatter out from late afternoon to early evening.

Southeast California/Southwest Arizona including KIPL and KBLH:

Expect breezy to windy westerly winds to predominate during the
period with gusts of 22-30kt expected at KIPL and 17-22kt at KBLH
this afternoon and evening. The winds at KBLH should become light
and variable by later tonight. Skies will be partly cloudy with FEW-
BKN high clouds passing across the region.

Aviation Discussion not updated for amended TAFs.


Monday through Friday...
A large area of low pressure will affect the Desert Southwest
early next week, but overall dry conditions will prevail. The low
will usher in cooler air with temperatures falling to below normal
levels through Tuesday. Breezy to windy conditions will also be an
issue during this time leading to increased fire danger conditions
mainly across southeast California and southwest Arizona as
afternoon humidities drop below 15% both days. High pressure will
then build back into the region during the latter part of next
week bringing much warmer conditions starting Thursday. Winds will
diminish on Wednesday and become fairly light starting Thursday.
Minimum RH values of 10-20% are likely through the end of the


Spotters should follow standard reporting procedures.




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