Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 081022

Area Forecast Discussion
National Weather Service Tucson AZ
322 AM MST Mon Mar 8 2021

.SYNOPSIS...High pressure and warm temperatures will give way to
an area of low pressure to our northwest this week. This will
result in gusty afternoon winds for much of the upcoming week
along with a cooling trend. A slight chance of mountain snow
showers and valley rain showers are also possible. However
significant precipitation is not anticipated.


.DISCUSSION...Expect another warm day with lower deserts around
80 degrees. Any breaks in clouds could allow for a degree or two
warmer this afternoon. Don`t be shocked with these passing clouds
to see some virga and/or sprinkles of rain hitting the windshield
on your morning commute. Unfortunately this system is too weak and
the atmosphere way too dry for anything beneficial.

An unsettled pattern is shaping up this week with much cooler
temps, breezy/windy conditions, patchy blowing dust downwind of
dust source regions, elevated fire weather, and a slight
chance/chance of valley rain showers and mtn snow showers. These
impacts will begin Tuesday and persist most of the week. The best
chance for precip will be later Thursday into Friday.

Confidence is high in regards to much cooler, breezy/windy
conditions, and elevated fire weather concerns. However
confidence is moderate for precip, timing, and amounts. Latest
guidance is wetter, but we use wetter cautiously. Even in a good
scenario, this storm will likely amount to only up to 0.25" of
valley rain and a couple inches of snow in the mtns. That
certainly could change as WPC clusters are beginning to support a
deeper/colder and slower system. This could allow for increased
chances of precip and amounts, but a couple more model suites are
needed to see if a trend is developing.

Another thing to watch with this system Thursday night into
Friday morning will be much colder air filtering in behind the
frontal passage. Would not be shocked to see at least a rain/snow
mix or brief changeover to snow to 5000ft, potentially down to
4000ft Friday morning. Probabilistic NBM guidance has around 20
percent chance of seeing a dusting of snow for many locales around
4000-5000ft south and east of Tucson. Impacts appear low at this
time. We will be watching these values to see if probabilities
increase. The mountains could see a couple inches, but should
stay below advisory criteria.

By next weekend, the storm will be pulling away. At this time,
there is uncertainty on the evolution of the exit. It could
linger keeping things cooler with wraparound showers. Even though
this system is quite chilly for this time of the year, a freeze
does not look likely for the Tucson Metro. However cold morning
lows will return for higher valleys south and east of Tucson in
the storms wake.


.AVIATION...Valid through 09/12Z.
BKN-OVC clouds generally AOA 15-18k ft MSL thru the end of the
forecast period. SFC wind less than 12 kts and variable in direction
thru 08/19Z. Aft 08/19Z, increasing SLY/SWLY SFC wind at 10-20 kts
and gusts up to 30 kts with the strongest winds east of Tucson.
Winds become variable and diminish to 12 kts or less after
09/03Z. Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Dry conditions are expected into the middle of this
week, with a slight chance of precipitation in the White Mountains
starting on Tuesday and then across the rest of southeast Arizona
Thursday and Friday. High temperatures will be 5-10 degrees above
normal through Tuesday, with much colder temperatures overspreading
southeast Arizona Thursday and Friday. Gusty 20-foot wind speeds
start to increase today and especially on Tuesday through Thursday.

There will be the possibility of localized critical fire weather
conditions being met during the afternoon and early evening hours in
areas south and east of Tucson Tuesday and Wednesday, with
borderline conditions hanging on over Cochise County Thursday as the
colder air overspreads the area and higher RH values follow.





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