Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 181640

Area Forecast Discussion
National Weather Service Tucson AZ
940 AM MST Thu Jan 18 2018

.SYNOPSIS...Very warm afternoon temperatures and dry
conditions will persist through Friday. A storm system will then
move across the area this weekend, resulting in much cooler
temperatures, gusty winds and a chance of valley rain and mountain
snow. High pressure aloft will build back across the area next week
for a return to dry and warmer conditions.


.DISCUSSION...Upper level ridge axis extended from southern
California northeastward into the northern Rockies this morning. The
resultant northerly flow aloft ahead of this ridge axis, and per the
18/12Z KTWC sounding, was spreading some thin cirriform clouds
southward across southeast Arizona at this time. Surface temps valid
9 AM MST ranged from the lower 30s near Douglas to the lower 50s
from the Tucson metro area westward into western Pima County.
Surface winds were generally from the east at 5-10 mph.

The 18/12Z NAM12/GFS support the inherited official forecast
scenario for the rest of today, with some cirriform clouds to move
across the area as the upper ridge flattens. High temps later today
are forecast to be just a few degrees warmer from Tucson westward
versus Wednesday. However, highs across eastern sections later today
will be about 5-10 degrees warmer versus Wednesday. Surface winds
will mainly be less than 10 mph with a general easterly component.

There are no updates warranted at this time. Please refer to the
additional sections for further detail.


.AVIATION...Valid thru 19/18Z.
SKC-BKN clouds above 20k ft AGL into Friday morning. Surface wind
mainly under 12 kts with generally an east to southeast component.
Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Dry conditions through Friday. A storm system will
then move across the area Saturday, resulting in much cooler
temperatures, gusty southwest winds and a chance of valley rain and
mountain snow. Dry conditions will return Sunday and into next week.
Gusty northwest winds will impact the Upper Gila Valley, including
Safford, Sunday. Otherwise, terrain driven winds mainly less than 15
mph will occur early next week.


.PREV DISCUSSION /350 AM MST/...IR satellite imagery revealed mostly
clear conditions across most of Arizona with some scattered cirrus
beginning to stream in across western portions of the state. A ridge
of high pressure aloft will move into the region from the west
today, resulting in a brief warm up through Friday. Afternoon temps
on Friday are expected to top out 8-12 degrees above mid-January

The warm temperatures will be fleeting as a deep trough of low
pressure moves into the western CONUS Friday night. As the trough
progresses eastward, there will be a chance of valley rain and
mountain snow Saturday into Sunday morning along with gusty
southwest winds. In addition, much colder temperatures will occur
both Saturday and Sunday, generally a 15 to 20 degree drop compared
to high temperatures forecast to occur Friday. Much colder overnight
lows are anticipated as well, with freezing temperatures possible
across the Tucson metro Sunday and Monday mornings.

At this time, the fast moving system will be out of the state by
Sunday afternoon, and precip accumulations should remain fairly
light. Valley locations will generally see less than 0.10 inches,
while the mountains could see up to 0.25 inches of liquid,
especially in the White Mountains. Although snow levels are expected
to drop to around 3500 ft by Sunday morning, the majority of precip
should be over by then. Snowfall totals by Sunday afternoon in the
mountains will be up to 1 inch in the Catalina, Rincon and
Chiricahua`s, and up to 3 inches in the White Mountains.

Dry conditions and zonal flow advect into the region Monday with
temperatures returning to near average levels. The warmup will
continue into the middle of the week with ridging in control by
Wednesday with above average temperatures.






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