Area Forecast Discussion
Issued by NWS Tucson, AZ

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150
FXUS65 KTWC 020416
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
916 PM MST Thu Dec 1 2016

.SYNOPSIS...Temperatures will remain below normal through the
upcoming weekend. A storm system will move across the region late
Friday and Saturday, resulting in a chance of valley rain and
mountain snow. Dry conditions return Sunday and Monday. Another
system will then brush the state on Tuesday of next week which will
result in a slight chance valley rain and mountain snow mainly to
areas east of Tucson.

&&

.DISCUSSION...Satellite imagery continued to show a trend in
increasing cloudiness late this evening as a weather system moves
closer to the area. Latest models showed this system deepening over
southern Arizona tomorrow with precipitation chances increasing by
Friday evening. The current forecast still looked in good shape with
the trends, so no updates necessary this evening. Please refer to
the additional sections for more details.

&&

.AVIATION...Valid through 03/06Z.
SCT cirrus clouds above 20k ft AGL and surface wind less than 12 kts
thru the forecast period. Aviation discussion not updated for TAF
amendments.

&&

.FIRE WEATHER...Another low pressure system will move into the
region Friday night and Saturday, resulting in a chance of valley
rain and mountain snow, especially over Cochise county. This system
may also produce some gusty east winds. Dry conditions are expected
behind the system Sunday and Monday. Another system may impact the
region Tuesday of next week.

&&

.PREV DISCUSSION...High clouds continue to move across the forecast
area in response to a disturbance moving southward through southern
California. This disturbance will move southeast to near Yuma this
evening and then consolidate with another impulse diving southward
through the Great Basin on Friday. A closed low then develops over
far southwest Arizona late Friday afternoon. This system will deepen
as it sinks south into northern Sonora, Mexico by early Saturday.
This will result in a slight chance of mainly mountain showers late
Friday afternoon. Slight chance to even high end chance pops exists
Friday night, with a very sharp precipitation gradient across the
forecast area from northwest to southeast (with the highest pops
over Santa Cruz and especially Cochise county).

The low continues to move southeast on Saturday into far southeast
Sonora by Saturday night...pushing east of the region by early
Sunday morning. Again, this will result in a steep precipitation
gradient on Saturday, with the highest precipitation chances
southeast of a line from Nogales to Safford, although the Tucson
Metro area will still have a slight chance of showers. Precipitation
rapidly winds down from northwest to southeast across the forecast
area Saturday night as the upper low moves away from the region.

Although there are differences between the GFS/ECMWF in regards to
the strength and timing of system ejecting eastward (with the GFS
being deeper and slower), overall trends between the two models are
more similar on the latest run. Therefore, have bumped up pops
considerably south/southeast of Tucson on this forecast package. The
southern mountain ranges (Chiricahuas and Huachucas) will have the
best chances for appreciable snowfall with the passage of this
system, with 1-2 inches possible in the Huachucas and 2-4 inches in
the Chiricahuas. Snow levels will start out around 7000 feet Friday
evening...lowering to around 6000 feet early Saturday.

A couple of degrees of warming will then occur Sunday as the system
moves east, with more substantial warming on Monday. Temperatures
will warm to near normal on Monday. Another storm system will then
drop into far eastern Arizona/western New Mexico on Tuesday of next
week, which will result in a slight chance of valley rain and
mountain snow mainly to areas east of Tucson next Tuesday.

&&

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

&&

$$

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