Heat in Arizona, September 10 to 11, 2018

Area Forecast Discussion
National Weather Service Tucson AZ
940 AM MST Mon Sep 10 2018

.SYNOPSIS...Isolated thunderstorms continuing the first half of
the week, generally favoring the mountains and near the
International Border. Drier conditions possible by next weekend.
Daytime temperatures remain a few degrees above normal.

&&

.DISCUSSION...We might have just a little more moisture to work
with today as the 12Z KTWC sounding came in at 1.2 inches, and
surface dew points still range from the mid 50s to lower 60s.
We've also cooled back down a little in mid levels with the
sounding showing more convective potential and less convective
inhibition. We tweaked the precip forecast up for this afternoon
and early evening near the border, but it still should be below
average for a typical later monsoon day. Otherwise we expect our
low-grade monsoon forecast to continue. Please see the previous
discussion below for details beyond today.

&&

.AVIATION...Valid through 11/18Z.
Isolated -TSRA/-SHRA will develop this afternoon mainly east to
south of KTUS, quickly dissipating after sunset. Outside of that,
SKC-SCT clouds around 8k-12k ft AGL. Surface winds are light and
variable this morning, settling NWLY 8-12 kts this afternoon with
occasional gusts to 20 kts, returning light and variable in the
evening. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Isolated thunderstorms are expected to develop
today and again Wednesday during the typical afternoon timeframe.
The preferred areas will be east to south of Tucson, favoring the
mountains. Otherwise, dry conditions dominate the forecast for much
of the area with above normal temperatures. 20-foot winds remain
terrain driven mainly less than 15 mph, with the occasional
afternoon gustiness.

&&

.PREV DISCUSSION...A broad area of high pressure aloft continues
early this morning, with a ridge axis extending from the
southwestern CONUS westward into the eastern Pacific near
30N/140W. Meanwhile, an upper trough was near the Pacific
Northwest coast. Various 10/00Z numerical weather prediction
solutions remained quite consistent with their respective
solutions of 24-48 hours ago. As a result, the official forecast
remains quite consistent regarding the weather scenario for
southeast Arizona into next weekend.

As has been the case during about the past 2-3 days, isolated
showers and thunderstorms are expected to occur this afternoon and
early evening especially near mountains east of Tucson, and near the
International border southeast to south of Tucson. Any showers/tstms
of consequence should dissipate around or shortly after sunset. The
inherited PoPs for Tuesday were modified to depict precip-free
conditions area-wide as high pressure aloft becomes centered just
east of this forecast area, and the aforementioned upper trough
amplifies somewhat near the West Coast.

The models remained consistent for Wednesday with drawing
potentially slightly deeper moisture northward across this forecast
area as the mid-level flow transitions from a northerly to a
southerly component. The 10/00Z deterministic GFS continued to be
slightly more robust with precip potential versus the 10/00Z
deterministic ECMWF.

Thus, have maintained a slight chance of showers/tstms Wednesday
afternoon/evening generally from Tucson eastward to the New Mexico
state line, and southward to the International border. The models
suggest that enough moisture will continue Thursday to justify a
slight chance of afternoon showers/tstms mainly near the New Mexico
state line. Otherwise, precip-free conditions appear to occur
Thursday into next week with the synoptic pattern yielding an upper
trough near the West Coast, and high pressure aloft anchored over
the southern Rockies/southern Plains.

This official forecast issuance also continues with very minor daily
high temperature changes into next weekend, with daytime
temperatures averaging at least a few degrees above normal for mid-
September.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None.

&&

Meyer/Francis/Howlett

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