000
FXUS65 KPSR 222100
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
200 PM MST Fri Jun 22 2018

.SYNOPSIS...
Somewhat cooler temperatures will spread over the Southwest through
the weekend as a weak low pressure system passes north of the
region. This period of more moderate temperatures will be brief as
by early next week, high temperatures in lower elevation communities
will once again be flirting with the 110 degree mark. There are
still no signs of rain through next week as deeper moisture remains
trapped south of the international border.

&&

.DISCUSSION...
A deep midtropospheric anti-cyclone has become depressed from
southern Arizona into the northern Gulf of California this afternoon
in response to shortwave energy and a modest jet streak digging
southeast into the Great Basin. Prior to this evolution, 12Z KTWC
sounding data sampled H5 heights at 595dm (near record levels for
the date) and thermal profiles nearly identical to Thursday. Not
surprisingly, surface temperatures were trending fairly close to 24
hours ago and eventual highs should be approaching and/or touching
the 110 degree threshold.

The aforementioned shortwave upper trough will evolve across the
northern Rockies this weekend leading to a decrease in midlevel
heights across most of the western CONUS, and correspondingly a
slight cooling trend Saturday and Sunday. Despite this seemingly
boring transition, there is very good evidence the combination of a
tightening pressure gradient and differential heating will result in
a shallow Gulf surge of moisture through far SW Arizona and SE
California Saturday morning. This surge is best identified by high
resolution models, but even consensus blends suggest temperatures
muted by this richer near surface moisture. However even with
afternoon highs nearly 10F cooler than today, mid 60 dewpoints in
cities like Yuma and El Centro may actually make it feel more
uncomfortable than the current dry environment.

This overall cooling trend will be short-lived as ridging and
heights near 594dm build back over Arizona and New Mexico early next
week. There is good model consensus that temperatures nearing 110
degrees will return to lower desert communities as early as Tuesday.
With the breadth of the ridge axis extending through the southern
tier of the Conus and the storm track remaining fairly active for
late June across the Pacific Northwest/northern tier, it will be
difficult for high pressure to become established in a more
favorable location necessary for moisture transport into the
forecast area. In fact, there is some signal for a seasonably strong
upper trough to develop late next week across the western CONUS,
which would bring another cool down to the Southwest and continue to
trap better quality moisture into central Mexico.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA, and KSDL:
No aviation concerns will exist through Saturday afternoon under
clear skies. Some afternoon westerly wind gusts around 20kt will be
likely around the Phoenix terminals, but otherwise timing of
directional changes will be similar to the past several days.

Southeast California/Southwest Arizona including KIPL and KBLH:
Under clear skies, increasingly gusty S/SE winds Saturday will be
the primary aviation concern. By mid morning, sustained winds 10-
15kt will be common with stronger gusts impacting the terminal sites
by noon. KBLH will experience the strongest winds well over 20kt
with only slightly weaker speeds at KIPL.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Monday through Friday:
A rapid warming trend will spread into the districts early next week
with temperatures easily climbing above seasonal normals by Tuesday.
By the middle of the week, conditions will be similar to the past
several days (i.e hot and dry). Minimum afternoon humidity values
will fall back mostly into the single digits with a return of poor
to fair overnight recovery. No strong winds are expected next week,
although typical afternoon upslope gustiness will be common around
terrain features. There are still no signs of rain through next
week.

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 9 PM MST this evening for AZZ532-
     536-537-539>546-548>551-553>556-560-562.

     Heat Advisory until 9 PM MST this evening for AZZ563.

CA...Excessive Heat Warning until 9 PM PDT this evening for CAZ561-
     566>568-570.

&&

$$

DISCUSSION...MO/Rogers
AVIATION...MO
FIRE WEATHER...MO

NWS PSR Office Area Forecast Discussion