Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 202225
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
325 PM MST Mon Mar 20 2017

.SYNOPSIS...Remaining dry with unseasonably warm daytime
temperatures through Wednesday. A storm system will then bring a
chance of showers Wednesday night into Thursday. This system will
also bring gusty winds Wednesday afternoon and Wednesday night
followed by much cooler temperatures Thursday. Dry conditions with
warmer temperatures will prevail across much of the area Friday into
early next week.

&&

.DISCUSSION...Visible satellite imagery and surface observations
depicted scattered high-based cumuloform clouds from the Tucson
metro area eastward to the New Mexico border this afternoon.
Meanwhile, mostly clear skies prevailed west of Tucson with just
some thin cirriform clouds across that area. The bulk of the
cirriform clouds should dissipate with the loss of daytime heating
this evening. Locally gusty southwest winds will diminish as well.
Thus, expect mostly clear skies later tonight along with light winds.

The 20/12Z NAM/GFS/ECMWF/CMC remained similar versus their
respective solutions regarding the evolution of an upper trough
presently over the eastern Pacific, and the subsequent progression
of this trough into the southwestern CONUS by Wednesday night and
Thursday. The GFS continued to be markedly more moist versus the
ECMWF/CMC, and the official forecast received only minor
modifications for this issuance.

Thus, dry conditions will continue ahead of this approaching system
into Wednesday morning, and most likely for much of the area into
Wednesday afternoon. The exception may occur across far western Pima
County late Wednesday afternoon when a slight chance of showers and
thunderstorms exists. Low pressure aloft is progged to be centered
over Utah midday Thursday with the trough axis extending southward
into southern Arizona.

The period for the most widespread precip associated with this
system to occur appears to be from about 06Z-18Z Thursday. Before
this time, there is a chance of showers and a slight chance of
thunderstorms Wednesday evening mostly west-to-northwest of Tucson.
There is a chance of showers across much of the area late Wednesday
night into Thursday morning. Precip chances will decrease from west-
to-east Thursday afternoon, then a slight chance of snow showers
continues Thursday night across the White Mountains northeast of
Safford.

Gusty southwest winds will also occur with this system beginning
Wednesday afternoon and continuing into Wednesday night. Favored
southwest wind-prone locales such as Sierra Vista may briefly
experience wind advisory criteria Wednesday night. Gusty west winds
will continue into Thursday as the mid-level trough axis moves
eastward across the area. The system should be cool enough to
support snow accumulations up to three inches or so across the White
Mountains above 7500 feet.

Dry conditions return Friday as a shortwave ridge moves eastward
across the area, then two shortwave troughs are progged to move
mainly north of this forecast area Saturday into Monday. These
systems will bring some gusty afternoon winds and will remain
generally dry. However, there appears to be enough moisture to
support a slight chance of showers across the White Mountains next
Monday.

Although some minor cooling is on tap Tuesday and Wednesday, high
temps both days will remain well above seasonal normals. Expect much
cooler temperatures Thursday followed by a warming trend Friday into
Saturday. Daytime temperatures Sunday and Monday will return closer
to seasonal normals.

&&

.AVIATION...Valid through 22/00Z.
Expect FEW-SCT clouds around 10k-15k ft AGL into this evening, then
FEW-BKN clouds above 20k ft AGL late tonight into Tuesday afternoon.
Surface wind into early this evening and Tuesday afternoon sly/swly
5-15 kts with gusts of 20-25 kts. Surface wind variable in direction
less than 12 kts at other times. Aviation discussion not updated for
TAF amendments.

&&

.FIRE WEATHER...Expect dry conditions into Wednesday. A Pacific
storm system will then bring a chance of showers to most sections
Wednesday night followed by a chance of showers mainly northeast of
Tucson Thursday. A few snow showers may occur across the White
Mountains northeast of Safford Thursday night. Dry conditions will
then prevail Friday into Sunday. There is a slight chance of showers
across the White Mountains next Monday.

The Pacific storm system will also bring gusty mainly southwest
winds Wednesday afternoon into Wednesday night. The combination of
strong and gusty southwest winds and low relative humidity may
create critical fire weather conditions Wednesday afternoon across
the southern one-third of Fire Zone 152.

There will be some gusty west to northwest winds Thursday, then less
wind Friday into Saturday. Some gusty afternoon west winds are
forecast to return Sunday and next Monday.

&&

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

&&

$$

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

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