Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 062130

Area Forecast Discussion
National Weather Service Tucson AZ
230 PM MST Fri Dec 6 2019

.SYNOPSIS...Dry conditions with warmer than normal daytime
temperatures into Saturday. Another weather system will bring valley
rain and high elevation snow Sunday into Monday. Dry conditions with
seasonable temperatures will prevail next Tuesday into Friday.


.DISCUSSION...Shortwave ridge overhead today resulting in warmer
high temperatures versus yesterday, under partly cloudy conditions.
The mid-level deck that moved over eastern Pima county this
afternoon did have some virga.

Satellite imagery this afternoon showed a large upper level low
off Oregon/northern California coast with lots of mid-high level
clouds extending from southern California/northern Baja southwest
extending southwest to 25N/125W. Under this cloud deck are PW
values over 1". Thus higher PW values will gradually overspread
the area this weekend. Models pretty consistent on bringing a
chance of showers, as early as Saturday evening, but mainly
overnight in Sunday morning NW of a Arivaca to Clifton line. As
the upper level trof approaches the area Sunday there will be
scattered to numerous showers which will continue into Sunday
night, although can see a break out west of Tucson. Latest model
runs are now showing that the tail end of this upper level trof
will close off briefly on Monday. Models also are coming in slower
versus previous runs. Increased PoPs late Sunday night into Monday
across most of the area. As cold pool aloft comes through on
Monday can see a few thunderstorms, but at this time the chances
are low thus left them out of the forecast. Later shifts will be
evaluating the chances for thunder.

Storm total QPF was heavily weighted toward WPC guidance which is
in line with ensemble guidance from ECWMF/CMC/GFS. The NBM was not
considered as it was woefully light on QPF. Valley totals from
0.10" to 0.50" with 0.50" to 1.25" in the mountains. Could see
isolated totals of 1.50" to 2" at the highest mountain elevations.

Snow amounts, as usual, will be tricky. Snow levels for most of
the mountain ranges will remain above the tips through Sunday
evening. The exception will be across the Whites where snow will
start to accumulate Sunday. Snow levels falling between 7000 and
7500 feet on Monday. At this time going with snow amounts above
7000 feet in the 3 to 7 inch range with localized amounts up to
10" at the highest elevations. These totals will likely change
over the next 24-48 hours.

Lingering showers eastern sections late Monday into early Tuesday
otherwise drier weather settles in Tuesday through the end of
next week. An upper level trof moves across the area on Wednesday
but it will be dry for the area.

Temperatures will remain above normal Saturday then be at or
slightly below normal Sunday through Tuesday then turning slightly
warmer the rest of next week.


.AVIATION...Valid through 08/00Z.
SCT-BKN cirrus clouds above 20k ft MSL persisting through the
forecast period. FEW-SCT clouds increasing 10-15k ft MSL Saturday
afternoon. SFC wind generally ELY/SELY less than 10 kts this
afternoon. Winds will then be light and variable overnight into
Saturday morning, becoming SWLY to NWLY in the afternoon at mainly
less than 10 kts. Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Minimal fire weather concerns. Dry conditions
through Saturday. A weather system is expected to impact the area
starting late Saturday night through Monday night with a chance of
valley rain and mountain snow. The best chance for precipitation
will be from central Pima County eastward and northward, and
particularly across the higher elevations. Dry conditions return
Tuesday afternoon and continue through the end of the work week.
20-ft winds will generally remain less than 15 mph through the
forecast period.





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