Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 252206

Area Forecast Discussion
National Weather Service Tucson AZ
306 PM MST Mon Sep 25 2017

.SYNOPSIS...Dry conditions across much of the area through
Tuesday with a few near record low temperatures for the coldest
valley locations southeast of Tucson. Expect scattered showers and
thunderstorms Wednesday, then isolated to scattered storms mainly
east of Tucson into Saturday. A gradual warming trend will push
temperatures back up to near and then above average over the next
several days.


.DISCUSSION...We have a strong ridge in the eastern Pacific and a
trough through the intermountain west, with a dry zonal flow under
the trough over our area. We`ve dried out quite a bit with
precipitable water values around 1/3 of an inch and surface dew
points in the 20s to lower 30s. Another night with temperatures
below average, but probably not quite as cool as last night.

Residual energy sagging into the back of the trough will stay
behind as the main trough lifts through the northern Plains and
into Canada over the next 48 hours. GFS ensemble/mean is very
similar to the ECMWF in handling the resulting cut-off low as it
wobbles around Arizona and southern Great Basin around the middle
of the week before filling and ejecting it northward later in the
week. The low should be in a position to tap into some of the
moisture to our southeast and east (through Chihuahua and New
Mexico), and draw enough into eastern areas for a chance of
showers and thunderstorms. As usual, Tucson will be on the edge of
things with the bulk of the activity east.

Temperatures will slowly climb back to near normal levels Tuesday
into Thursday, then above average by next weekend. Expect upper
90s in the lower deserts by next weekend, with middle 90s around
Tucson metro, and 80s east of Tucson as a little cooler air pooled
in New Mexico spills into eastern areas.

More transition season weather by early next week with weak
troughiness over the weekend hopefully keeping us from getting
nailed with a late season 100 at TIA.


.AVIATION...Valid thru 27/00Z.
Expect clear skies across the area through tomorrow morning with few
clouds at 15k-20k AGL forming tomorrow afternoon. Surface winds will
be westerly to northwesterly at 5-10 kts into the early evening
hours. Overnight and Tuesday morning surface winds variable below 10
kts then south/southwesterly at 5-10 kts tomorrow afternoon.
Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...A dry atmosphere will dominate the region through
tomorrow afternoon. Starting Tuesday evening into Wednesday morning
isolated to scattered storms will be possible east of Tucson. Storm
chances will then creep westward Wednesday with isolated storms in
Santa Cruz/eastern Pima Counties and scattered storms east of Tucson
through Friday afternoon. Some lingering moisture will allow for a
slight chance of storms Saturday. 20-foot winds will be terrain
driven less than 15 mph through Wednesday morning. Starting
Wednesday afternoon through Saturday winds will shift to the
east/southeast. Gusty winds will likely occur Wednesday and Friday
with gusts between 15-20 mph during the afternoon hours.






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