Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 230431
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
930 PM MST Sat Apr 22 2017

.SYNOPSIS...Continued dry conditions with warmer than normal
daytime temperatures through Wednesday. Locally gusty east winds
will occur tonight into Sunday morning, then gusty mainly west
afternoon winds will prevail during the upcoming week. A weather
system north of the area is then expected to bring a chance of
showers with a few thunderstorms mainly to the White Mountains
Thursday and Friday.

&&

.DISCUSSION...Mostly clear skies across the area late this evening
with a few high clouds passing through overnight. Wind forecast
still calls for speeds increasing by daybreak Sunday morning in
response to a tightening surface pressure gradient. Otherwise,
daytime temperatures will peak Sunday with readings lowering a few
degrees for the upcoming work week. Current forecast remains on
track, so no updates necessary this evening. Please refer to the
additional sections for more details.

&&

.AVIATION...Valid through 24/06Z.
SKC continuing into Sunday afternoon. Surface wind into this evening
variable in direction generally less than 10 kts. Surface wind, KTUS
vicinity eastward to the New Mexico border, Sunday morning mainly
ely 10-20 kts with gusts of 20-30 kts. Surface wind Sunday afternoon
swly 10-18 kts with gusts to 25 kts. Aviation discussion not updated
for TAF amendments.

&&

.FIRE WEATHER...Dry conditions with warmer than normal daytime
temperatures will continue through Wednesday. Expect gusty east
winds from Tucson eastward to the New Mexico border tonight into
Sunday morning followed by occasionally gusty southwest winds Sunday
afternoon. Somewhat stronger southwest winds are expected Monday.

A Fire Weather Watch is in effect from Monday morning through Monday
evening for fire weather zones 151 and 152. The combination of
strong and gusty southwest winds, relative humidity in the single
digits to lower teens, and a high fire danger may create critical
fire weather conditions.

Critical fire weather conditions may also occur Tuesday into Friday,
especially during the afternoon and evening hours, and particularly
east of Tucson. Field crews are strongly encouraged to monitor
subsequent forecasts for additional Fire Weather Watch and/or Red
Flag Warning issuances.

A weather system north of the area may also bring a chance of
showers and a few thunderstorms to the White Mountains Thursday and
Friday. Dry conditions are forecast to return area-wide next
Saturday.

&&

.PREV DISCUSSION...A very dry regime continues across southeast
Arizona this afternoon as an upper ridge axis extends from southern
Arizona northward into the northern Rockies. A tight surface
pressure gradient also prevailed just east of this forecast area
across southwest New Mexico. The upper ridge axis will move eastward
into New Mexico Sunday. Meanwhile, the tight surface pressure
gradient will expand westward into far southeast Arizona later
tonight.

Clear skies will continue into Sunday. However, the tightening
surface pressure gradient will produce gusty mainly east winds
generally from Tucson eastward later tonight and into Sunday
morning. Expect winds to decrease late Sunday morning as the surface
pressure gradient loosens, then some gusty southwest winds should
occur Sunday afternoon.

The upper level pattern Monday into Wednesday will generally be
characterized with a strong high pressure system over eastern
Pacific, and a north-to-south trough axis across the central CONUS
Plains. The pattern will translate into a fairly tight northwest-to-
southeast oriented mid-level pressure gradient across the area. This
gradient should be sufficient to produce gusty mainly westerly winds
during the afternoon/evening hours. The combination of a continued
dry regime and gusty winds may produce critical fire conditions
during the upcoming week. Please refer to the Fire Weather section
in this product for additional information.

Thereafter, there were fairly distinct differences between the
deterministic 22/12Z GFS/ECMWF starting Thursday and continuing into
Friday. In essence, the GFS was much deeper with the evolution of an
upper trough over the Rockies versus the ECMWF. Thus, the GFS was
much more robust with precip potential (chances, amounts, etc.)
versus the ECMWF.

Per coordination with neighboring WFO`s, am inclined to believe that
reality will eventually be somewhere between these solutions. Thus,
have opted to maintain a chance of showers across the White
Mountains Thursday followed by dry conditions area-wide Thursday
night. There is a slight chance of showers and thunderstorms across
the White Mountains Friday with dry conditions elsewhere. Stronger
northwest flow aloft will likely translate into dry conditions area-
wide next Saturday.

High temperatures Sunday will be quite similar to temperatures
achieved this afternoon, or perhaps a few degrees warmer depending
upon location. A very minor cooling trend is forecast to occur
Monday into Tuesday followed by no significant change in high
temperatures Wednesday. A few degrees of daily cooling is on tap
Thursday into Friday, but daytime temperatures will likely remain at
least slightly above seasonal normals.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
    Fire Weather Watch from Monday morning through Monday evening
      for AZZ151-152.

&&

$$

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