Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 241115
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
415 AM MST Tue Jan 24 2017

.SYNOPSIS...Scattered valley rain and mountain snow showers east of
Tucson this morning, then any snow showers limited to near the White
Mountains this afternoon and evening. Dry conditions will prevail
Wednesday into early next week. Expect widespread freezing
temperatures tonight and Wednesday night before a warming trend
occurs Thursday into early next week.

&&

.DISCUSSION...Scattered valley rain and mountain snow showers were
ongoing across Greenlee, Graham, Cochise and eastern Santa Cruz
Counties east-to-south of Tucson early this morning. These showers
were only producing light rain amounts and minimal snow
accumulations. Otherwise, IR satellite imagery and surface
observations depicted clear skies or mostly clear skies west-to-
northwest of Tucson, and partly cloudy to cloudy skies elsewhere.
Surface winds were generally from the west, and speeds had
diminished to less than 15 mph across much of southeast Arizona as
of 4 a.m. MST.

A broad and deep was over the western CONUS early this morning, and
a sharp ridge axis was west of the Pacific coast near 130W-135W.
Scattered valley rain/mountain snow showers will continue across
eastern sections this morning, then a drier mid-level wly flow
regime will limit any snow showers of significance this afternoon
and evening mainly to the White Mountains. Any additional rain
amounts and snow accumulations will remain minimal into this
evening. Occasionally gusty west-to-northwest winds will also occur
into this evening before winds diminish most sections this evening.

The 24/00Z GFS/ECMWF/CMC were similar with depicting the upper
trough to slowly move eastward into the central CONUS Wednesday as
the eastern Pacific upper ridge moves eastward into the Pacific
Northwest. The resultant northwesterly flow aloft will promote
precip-free conditions area-wide Wednesday into Thursday.

Thereafter, the GFS/ECMWF/CMC depicted an upper low to develop over
northern Arizona Friday as the upper ridge continues to amplify
adjacent the West coast. The position of this upper low is a sharp
departure of several previous GFS/ECMWF/CMC solutions which depicted
the development of this upper low to be much further south, or
generally over Sonora Mexico. The ECMWF in turn was more robust with
moisture associated with this system versus the drier GFS, and even
generated a few hundredths of an inch liquid accumulations across
far southeast sections late Friday night and Saturday.

For this forecast issuance and per coordination with neighboring
WFO`s, have maintained precip-free conditions Friday into Saturday.
Thereafter, the GFS/ECMWF/CMC were quite similar with moving the
upper low southward into central Sonora Mexico or the central Gulf
of California midday Sunday as high pressure aloft builds eastward
into the Great Basin region. A very dry regime should prevail across
southeast Arizona Sunday into Monday as the upper low becomes quasi-
stationary well south of the area, and a high pressure ridge remains
over the Great Basin.

High temps today will be nearly 10-20 degs cooler versus temps
achieved Monday. Expect no significant change in daytime temps
Wednesday, then highs Thursday will be about 5-10 degs warmer versus
Wednesday. The upper low will temper any warming of significance
Friday into Saturday before additional warming occurs Sunday into
next Monday.

&&

.AVIATION...Valid through 25/12Z.
Scattered -SHRA and mountain -SHSN this morning, then scattered
-SHSN mainly across the White Mountains northeast of KSAD this
afternoon and evening. Otherwise, cloud decks into this evening
generally 3k-7k ft AGL before clearing occurs by Wednesday morning.
Surface wind into this evening wly/nwly 8-18 kts with gusts to 25
kts. Surface wind variable in direction less than 12 kts after
25/06Z. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Scattered valley rain and mountain snow showers east
of Tucson this morning, then any snow showers will mainly be
confined to the White Mountains this afternoon and this evening. Dry
conditions will prevail area-wide Wednesday into early next week.
Expect occasionally gusty west to northwest winds today. 20-foot
winds will be terrain driven less than 15 mph Wednesday into Friday
followed by occasionally gusty east winds Saturday into Monday.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
    Freeze Warning from midnight tonight to 9 AM MST Wednesday
      for AZZ502-504>506.

&&

$$

Francis

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