Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 211015
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
315 AM MST Mon Aug 21 2017

.SYNOPSIS...Expect isolated to scattered mainly afternoon and
evening thunderstorms into next weekend. The greatest coverage of
thunderstorms should occur Wednesday into Thursday. Otherwise, the
bulk of thunderstorms will likely remain east to south of Tucson.

&&

.DISCUSSION...IR satellite imagery has depicted a very gradual
decrease in the mid-level clouds across southeast Arizona during the
past several hours. The sky condition at this time ranged from
mostly clear mainly near the international border to mostly cloudy
near the New Mexico border and across the White Mountains. For the
solar eclipse later this morning, expect mostly clear skies to
partly cloudy skies across southeast Arizona.

Weak low pressure aloft was centered near Los Angeles early this
morning, and a high pressure ridge extended from the southeast CONUS
southwestward into Chihuahua Mexico. Water vapor satellite imagery
depicted a drier regime versus 24 hours ago, and blended total
precip water values ranged from around 1.0 inch across the White
Mountains upward to around 1.30 inches near the international border.

For this forecast issuance, Probability of Precip (PoP) values
through Tuesday were lowered considerably generally from Tucson
westward versus previous forecasts. Various 21/00Z Numerical Weather
Prediction (NWP) models have trended toward a drier scenario versus
previous solutions, and this is mostly attributed toward a more
southwesterly mid-level flow to occur.

Thus, isolated to scattered showers/tstms east-to-south of Tucson
this afternoon and evening. The bulk of any showers/tstms should end
by midnight, though have maintained a slight chance of showers/tstms
mainly near the New Mexico border. Less coverage of showers/tstms is
expected Tuesday, with slight chance category PoPs mostly near the
New Mexico border.

The mid-level steering flow is progged to become more southeasterly
Wednesday into Thursday. The deterministic GFS/ECMWF have been
fairly consistent with suggesting that Wednesday into Thursday
should have greater coverage of showers/tstms, with the bulk of this
activity to occur east of Tucson. Only minor PoP changes were made
this period, and the official forecast continues with scattered
showers/tstms mainly east of Tucson during the afternoon/evening
hours, and less coverage of showers/tstms late Wed night/early
Thursday morning. The best chance (albeit just slight chance) of
showers/tstms to occur west of Tucson is Wed afternoon into Thursday
morning.

Thereafter, high pressure aloft is progged to strengthen over the
Great Basin by next Sunday. The mid-level generally northeasterly
flow regime next weekend appears to suggest another decrease in the
coverage of showers/tstms is on tap. Thus, isolated to scattered
showers/tstms mainly east of Tucson Friday into next Sunday with dry
conditions elsewhere.

Daytime high temps today into next Sunday will be quite close to
seasonal normals, or trend a few degrees above normal depending upon
location.

&&

.AVIATION...Valid thru 22/12Z.
SCT to locally BKN clouds 8-12k ft with isolated to scattered
TSRA/SHRA 21/18Z through 22/05Z, mainly east and south of KTUS.
Surface wind variable in direction mainly less than 12 kts, although
brief gusts to near 35 kts in vicinity of TSRA are possible.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Expect isolated to scattered thunderstorms mainly
east and south of Tucson today then even fewer on Tuesday.
Thunderstorm chances increasing again Wednesday onward. Normal
diurnal wind trends will occur through Wednesday then the flow will
become mostly easterly thereafter. Locally strong and gusty winds
expected in the vicinity of thunderstorms. Daytime temperatures will
be warmer than normal through the week into next weekend with
typical humidity levels.

&&

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

&&

$$

DISCUSSION...Francis
AVIATION...Cerniglia
FIRE WEATHER...Cerniglia

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