Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 221056
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
355 AM MST Tue Aug 22 2017

.SYNOPSIS...A few thunderstorms may occur east to south of Tucson
this afternoon and evening. A favorable moisture and flow regime
exists for fairly widespread coverage of showers and thunderstorms
Wednesday into Thursday. Isolated to scattered thunderstorms will
then prevail mainly east and south of Tucson Friday into next
Monday.

&&

.DISCUSSION...Weak low pressure aloft remains centered just west of
the southern California coast early this morning, and strong high
pressure aloft was centered near El Paso Texas. Weak mid-level
diffluence was contributing to broken to overcast clouds across
central and southeast portions of this forecast area at this time.
Meanwhile, skies were clear at this time across western Pima County
and the White Mountains.

A relatively dry and stable environment will continue across
southeast Arizona into tonight as high pressure becomes centered
over northern Chihuahua, and the weak upper trough resides near the
southern California coast. There is just a slight chance of showers/
tstms this afternoon and evening mainly across the White Mountains,
and perhaps the Huachuca/Chiricahua Mountains southeast to east of
Tucson.

The 22/00Z GFS/ECMWF deterministic solutions as well as the high-
resolution Univ of AZ WRF-NAM and WRF-GFS were quite similar with
depicting considerably greater coverage of showers/tstms to occur
Wednesday into Thursday. The greatest coverage of showers/tstms
across this forecast area, including locales west of Tucson, appears
to be Wednesday afternoon into Thursday morning. The 700-500 mb flow
is progged to be more southeasterly during this period; a 700 mb
Theta-E ridge is progged to be oriented from western Chihuahua
northwestward into western Pima County; and a PV anomaly/vort lobe
is depicted to move southwest to northeast across the area.
Scattered showers/tstms should continue mainly east of Tucson
Thursday afternoon and Thursday night, with dry conditions across
the western deserts.

The upper high is progged to move northwestward into southeast
Arizona Friday, then continue to migrate northwestward into the
Great Basin by Sunday. Isolated to scattered showers/tstms Friday
into Sunday should be confined to locales east-to-south of Tucson
with precip-free conditions elsewhere. The official forecast was
modified add a slight chance of showers/tstms further west to
include the Nogales area Friday into Sunday.

The mid-level steering flow is progged to become more northeasterly
by Monday. Some models suggest that showers/tstms may propagate
southwestward from the Rim as early as Sunday afternoon, but will
likely not reach the Tucson metro area. However, the appears to be
better chances of showers/ tstms potentially reaching Tucson and
perhaps even farther westward Monday afternoon and evening.

High temps into next Monday for the most part will generally be a
few degrees above normal. Daytime temps Wed-Thur will be closer to
seasonal normals given the better precip chances.

&&

.AVIATION...Valid thru 23/12Z.
Mostly clear skies, then from 22/19Z through about 23/03Z SCT clouds
9-13k ft and Isold TSRA/SHRA developing mainly E and S 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 just a few thunderstorms east and south of
Tucson today. Thunderstorm chances increasing again Wednesday
through Thursday then decreasing over the weekend. 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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