Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 230413
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
913 PM MST Sun Jul 22 2018

.SYNOPSIS...Strong high pressure will bring hotter than normal
temperatures through midweek, with record highs for some locations.
Isolated to scattered thunderstorms through Wednesday will mainly be
limited near mountains east to south of Tucson. Thunderstorm chances
increase as temperatures moderate late this week and next weekend.

&&

.DISCUSSION...Convection this evening was quite limited with a few
smaller storms over the White Mountains and Cochise and Santa Cruz
counties. With a less favorable convective environment and a lack of
upper level support the storms quickly died off after sunset and all
we are left with are the high debris clouds that will gradually
dissipate overnight. This is well covered in the current forecast
therefore no updates are needed at this time. Looking beyond tonight,
well hot is the word and that is highlighted well in the previous
discussion below.

&&

.AVIATION...Valid through 24/00Z.
SCT-BKN clouds above 12k ft gradually clearing overnight with isolated
TSRA/-SHRA developing near mountains east to south of KTUS, again
Monday afternoon mainly across the White Mountains northeast of KSAD.
Surface wind variable less than 12 kts tonight through Monday
afternoon. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Isolated to scattered thunderstorms into midweek
will mainly be confined to locales east to south of Tucson. A more
favorable flow regime will increase thunderstorm chances especially
Friday into next Sunday. Aside from gusty thunderstorm outflows, 20-
foot winds will be terrain driven and generally under 15 mph. An
exception is Monday afternoon and evening when occasional gusts to 25
mph should occur across the Upper Gila River Valley (including
Safford).

&&

.PREV DISCUSSION...
The various 22/12Z numerical weather prediction models were
consistent versus solutions from 24 hours ago regarding the overall
scenario Monday and continuing into next weekend. Strong high
pressure aloft during the early portion of the work week will prevail
across the Great Basin, central/southern Rockies, and southwestern
CONUS. The deterministic GFS/ECMWF and associated ensembles depict a
598-600 dm high to briefly become centered on Tuesday over southeast
Arizona. The upper high center is then progged to migrate northwest
into west central Arizona by midday Wednesday.

The main concern regarding this strong high pressure system is heat
impacts Monday through Wednesday. The inherited official forecast
included an Excessive Heat Warning that was in effect from 10 a.m.
Monday to 8 p.m. MST Tuesday for AZZ501>509, or the forecast zones
below 5000 feet elevation. Based on the various 22/12Z guidance,
opted to extend the Excessive Heat Warning to 8 p.m. MST Wednesday
for the same area, or the forecast zones below 5000 feet.

Regarding precip chances Monday through Wednesday, any showers/tstms
Monday afternoon/evening should be confined to the White Mountains
northeast of Safford. The models suggest and the official forecast
continues with isolated to scattered afternoon/evening showers/tstms
Tuesday from Tucson eastward to the New Mexico state line, and
southward to the international border from near Nogales to Douglas.

The 22/12Z models provided mixed scenarios regarding Wednesday
afternoon/evening. The GFS was more robust versus ECMWF regarding
precip coverage, essentially as far west to include the Tucson metro
area by evening. Given these model differences, opted to make no
changes to the inherited PoP/Weather grids for Wednesday afternoon/
evening. Thus, expect isolated to scattered afternoon/evening
showers/tstms Wednesday essentially east of a Hannagan Meadow-Mount
Graham-Sierra Vista line.

Starting Thursday and continuing into next weekend, the models
depict the upper high center to generally become positioned over the
Great Basin weekend by next weekend. A more favorable generally ely
flow regime should ensue across southeast Arizona, and this regime
should result in a potentially significant increase in shower and
thunderstorm coverage, especially Friday into next Sunday. In the
meantime, daytime temps Friday into next Sunday will moderate closer
to seasonal normals.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning from 10 AM Monday to 8 PM MST Wednesday
for AZZ501>509.

&&

$$

PUBLIC...CernigliaFrancis
AVIATION....CernigliaFrancis
FIRE WEATHER...Francis

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