Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 170412

Area Forecast Discussion
National Weather Service Tucson AZ
911 PM MST Tue Jan 16 2018

.SYNOPSIS...Gusty easterly winds and cooler temperatures will
continue on Wednesday. Otherwise, very warm mid-January afternoon
temperatures and generally dry conditions will persist through
Friday. A pattern change this weekend will bring much cooler
temperatures and the chance of valley rain and mountain snow


.DISCUSSION...A weak disturbance was passing through the area this
evening with considerable cloudiness associated with it. Recent
satellite imagery showed this feature starting to exit the area with
clearing skies to the west of Tucson. Winds from the east remained
elevated in speed late this evening, and will likely become more
gusty toward daybreak Wednesday. That said, the current forecast was
handling the trends nicely so no updates necessary this evening.
Please refer to the additional sections for more details.


.AVIATION...Valid thru 18/06Z.
BKN-OVC clouds AOA 20k ft AGL thru 17/08Z. Aft 17/08Z, SCT-BKN
clouds above 20k ft AGL. ELY/SELY SFC wind at 12-18 kts with gusts
to 22-27 kts aft 17/12z. Aviation discussion not updated for TAF


.FIRE WEATHER...A weak system passing north of the area will
result in a slight chance of showers mainly in the White Mountains
tonight into Wednesday. East to southeast winds will continue
through Wednesday. Dry conditions return on Thursday before another
storm system moves across the area starting late Friday night,
persisting into Sunday morning. This system will result in cooler
temperatures, breezy west/southwest winds and scattered valley rain
and mountain snow showers. Dry conditions and near normal high
temperatures return early next week.


.PREV DISCUSSION...Progressive shortwave ridging will move across
the area Thursday into early Friday ahead of a more significant
trough poised to move in just in time for the weekend. The ridging
will result in benign weather on Thursday with daytime temperatures
continuing to warm. Friday will start the transition with continued
mild temperatures and perhaps a few afternoon breezes.

Latest 12Z model guidance is fairly similar to previous model
guidance with the trough this weekend. 12Z ECMWF is still perhaps
about 6 hours slower than the GFS with a cold front sweeping across
the area on Saturday. This system will be rather moisture starved
given its progressive nature and trajectory. The biggest change will
be the sharply colder temperatures both Saturday and Sunday with a
freeze possible in Tucson Sunday morning. Regarding precipitation
chances, there will be a chance of a few valley rain and mountain
snow showers along with the cold front and then due to the trough
axis and instability later Saturday and into Saturday evening. QPF
amounts will be rather meager with most locales seeing less than
0.10". Snow levels could briefly get down to valley floors south and
east of Tucson Saturday evening before the moisture kicks out of
here but not expecting any impacts at this time. A few inches of
snow are possible in the mountains but this isn`t shaping up to be a
significant winter storm. A more zonal westerly flow is expected
early next week with temperatures warming up to about seasonably
normal levels on Monday and Tuesday.





Prev Discussion...GL
Aviation/Fire Weather...Zell

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