FXUS65 KTWC 192156
Area Forecast Discussion
National Weather Service Tucson AZ
256 PM MST Tue Jan 19 2021
.SYNOPSIS...A cooler and wetter weather pattern will bring periods
of elevated valley rain and mountain snow chances later Wednesday
into the early next week. Highest rain chances for Southeast
Arizona will be later Wednesday into Thursday. Best period for
mountain snow will be a pair of systems over the weekend and early
next week. Also expect gusty winds at times.
.DISCUSSION...A strong low has dropped into a position near and
offshore of northern Baja to our west. This system will spend the
next 36 hours tapping into a deep moisture fetch before filling
and lifting through the state on Thursday. Virga with a mid level
moisture increase will keep working on moistening things up with
upslope influences ahead of the low as early as Wednesday bringing
increasing rain chances. Our best rainfall period will be just
ahead of and with the system late Wednesday into Thursday, with
00Z to 15Z Thursday prime time. Snow levels will remain above 8000
feet through most of Thursday (starting out over 9000 feet), with
most precip expected to fall as rain in the mountains. 1/4 to 1
inch in valleys with over 2 inches in mountains, isolated higher
amounts possible in some mountain locations. Considering latest
trajectories, we may see higher amounts near the international
border as well.
Our high amplitude pattern will continue with ensembles keeping
low height anomalies well into next week. Another system will dig
into the area over the weekend, this one should be cooler but
have less time to pick up as much moisture. Snow levels as low as
5500 feet or so on Sunday.
An even stronger and cooler system is possible for next Tuesday
or Wednesday. We may keep a solid split in the eastern Pacific to
finish the month with an active pattern.
.AVIATION...Valid through 21/00Z.
BKN-OVC clouds at 11k-15k ft MSL, lowering aft 20/06Z to 7k-11k ft
MSL. Slight chance of -SHRA aft 20/01Z, then more widespread valley
-SHRA/mountain top -SHSN developing Wednesday afternoon into
Thursday. MVFR conditions and (and local IFR conditions) are
expected at that time. Otherwise, SFC winds SELY 15-25 kts with
higher gusts gradually diminishing aft 20/06Z to 10-15 kts. Aviation
discussion not updated for TAF amendments.
.FIRE WEATHER....Generally dry this afternoon with some localized
elevated fire weather conditions. 20-foot winds speeds of 15-25 mph
and gusts to 35-40 mph will gradually diminish this evening. A storm
system will then move into the region on Wednesday and across the
state on Thursday. This will result in cooler temperatures, higher
humidity levels and widespread valley rain and high elevation
mountain snow, generally above 8,000 feet. The highest precipitation
chances will be Wednesday afternoon through Thursday.
Another colder system moves in over the upcoming weekend, for a
continued chance of valley rain and much lower snow levels. Also
expect breezy winds Saturday into Monday with this second storm
Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson