Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 270428

Area Forecast Discussion
National Weather Service Tucson AZ
925 PM MST Wed Apr 26 2017

.SYNOPSIS...Another system north of our area will bring increasing
winds Thursday afternoon followed by a return of strong and gusty
winds Friday into Saturday. A few showers or thunderstorms are
possible northeast of Tucson. Cooler on Saturday followed by dry
conditions with a warming trend next week. Another round of strong
winds are possible next Tuesday or Wednesday.


.DISCUSSION...Well, April is typically the windiest month on average
across the southwest and this week is living up to that.  Today was
relatively quiet with fairly typical winds this afternoon for this
time of year but it is the lull between systems.

We are current under a longwave NW flow pattern with a with
shortwave currently over northern California/Southern Oregon headed
to the SE.  This feature will slide by just to the NE of the area
and tighten up the midlevel gradient which will be enough to
increase the afternoon winds a bit above what we had Wednesday
afternoon. Just enough to case some fire weather concerns that are
highlighted below.

Then a stronger system, currently in the Gulf of Alaska will be
headed our way for Friday.  This system has been handled fairly
consistently by the models and will deepen as it drops southeast and
will settle over the 4-corners area Friday evening as a cutoff low.
This is expected to ramp up the winds Friday to speeds similar to
what we saw on Tuesday which brings up the potential of meeting wind
advisory criteria and generating areas of blowing dust. There is a
bit of moisture with this system so we have a chance of a few
showers and/or thunderstorms northeast of the Safford area.

Once it cuts off it will be slow to move east so eastern areas will
likely see windy conditions Saturday along with cooler and drier air
moving in on the back side of the storm.  It will be cooler than we
have experienced in a bit with highs in the mid 60s higher eastern
valleys to the mid 70s lower deserts.  Then Saturday night will be
the coolest we`ve seen in about 3 weeks, with 30s in valleys east
and south of Tucson, and 40s from Tucson westward. A few spots will
probably freeze Sunday morning in colder Cochise county valley

From Sunday onward the upper trough will gradually shift to the east
allowing the area to come under greater influence of the west coast
ridge to our west.  This will allow temperatures to rise each day
eventually to above normal levels again by Tuesday.


.AVIATION...Valid through 28/00Z.
SKC to SCT clouds above 20k ft AGL thru fcst pd. SFC wind light and
variable at less than 10 kts then SFC wind increasing again Thursday
afternoon to 15-20 kts with gusts to 30 kts. The strongest speeds
will be E of KTUS. Aviation discussion not updated for TAF


.FIRE WEATHER...Interesting few days coming up, at least through
Saturday.  Due to the recent fire behavior noted with the very dry
fuels we have leaned toward the side of caution with RFWs.  For
Thursday, winds will pick up in the afternoon and are expected reach
Red Flag criteria across much of zone 152 and some parts of SE zone
151 including the higher terrain of Whetstone Mtns near the Sawmill
Fire.  Feedback from the fire indicates that the Empire RAWS wind
speeds are lighter than the wind in the open (its slightly
sheltered), so based on that and coordinating with onsite IMET will
include the fire area in the Red Flag warning for Thursday for a
marginal event.

Then the attention turns to Friday where winds will be stronger and
likely very similar to what we saw Tuesday.  RH levels will be
elevated again like Tuesday and generally a bit above criteria, but
based on how the very dry fuels reacted to the wind, and
coordination with IMET, opted to issue a Fire Weather Watch for much
of zones 151 and 152.  Actually RH levels will be lower from Tucson
westward which will meet criteria based on the current forecast so
also have the watch in effect there.

Winds will remain rather elevated again Saturday eastern areas
coupled with lower humidity levels on the back side of the passing
system.  As a result we stand a good chance of seeing Critical fire
weather conditions again across much of zone 152 and SE 151, but
will let that go for now and focus on the near term.

Beyond that the wind generally settles down some but the air mass
will remain very dry with single digit min RHs each afternoon into
next week with another round of gusty winds possible Tuesday.


Red Flag Warning from noon to 7 PM MST Thursday for AZZ151-152.

Fire Weather Watch from Friday morning through Friday evening
for AZZ150>152.



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