Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 171026

Area Forecast Discussion
National Weather Service Tucson AZ
325 AM MST Mon Feb 17 2020

.SYNOPSIS...Dry with high temperatures several degrees above average
through Friday. A storm system will bring a chance of showers
especially on Saturday. Drier conditions to return next Sunday.


.DISCUSSION...IR satellite imagery and surface observations depict
clear skies across much of southeast Arizona early this morning.
However, a few to scattered cirriform clouds were noted especially
across Cochise and Santa Cruz Counties southeast-to-south of Tucson.
Quasi-zonal flow ongoing across the area will prevail into midweek,
then upper ridge amplification to occur Thursday ahead of a
deepening low pressure system near the California coast. This
pattern will maintain precip-free conditions at least into Thursday
night, and most likely into Friday morning as well.

Thereafter, the various 17/00Z models depict a 554-556 dm low will
be centered adjacent the central California coast Friday afternoon.
Ahead of this system, a few showers may develop Friday afternoon
east of Tucson, and especially near the New Mexico state line.
However, any rainfall amounts will be negligible. Precipitation
chances will improve Friday night and especially Saturday as the
aforementioned upper low weakens while moving eastward into the
southwest CONUS.

Have noted timing difference between the GFS/GEFS and the ECMWF/
ECENS regarding the start/end timing of rainfall and higher
elevation snow, and the model projected liquid amounts and snow
accumulations. In essence, the ECMWF/ECENS was generally 6-12 hours
faster versus the GFS/GEFS, and the ECMWF/ECENS amounts were
somewhat higher versus the GFS/GEFS. However, these models were
generally anemic with precipitation amounts overall.

At any rate, the official forecast continues with scattered to
numerous valley rain and higher elevation mountain snow showers on
Saturday. Precipitation chances decrease Saturday night as the
filling upper low ejects eastward into the southern Rockies. Dry
conditions will return to much of the area next Sunday. However, a
few lingering rain/snow showers may continue mainly across the White

Very preliminary event total rainfall amounts are forecast to
generally range under about 0.30 inch. However, amounts approaching
0.60 inch may ultimately be achieved across the White Mountains.
Event total snowfall amounts appear at this time will range from
2-4 inches above 8000 feet. These amounts will be subject to change
with subsequent forecast issuances.

High temperatures today through Friday will be several degrees above
normal. Expect some cooling on Saturday with high temperatures next
Sunday trending quite close to seasonal normals.


.AVIATION...Valid through 18/12Z.
FEW-SCT cirrus into this evening before mainly clear skies later
tonight into Monday morning. Surface wind variable in direction
under 12 kts. Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Dry conditions through Friday morning. A few showers
may develop as early as Friday afternoon, though more likely Friday
night followed by widespread showers on Saturday. Precipitation
chances decrease Saturday night, then a few lingering showers next
Sunday should be confined to the White Mountains. 20-foot winds will
be terrain driven under 15 mph through Thursday. Some gusty east
to southeast winds should occur Friday, then gusty southwest winds
Saturday associated with a storm system over the desert southwest.
Expect less wind Sunday as the storm system departs the area.






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