Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 221646

Area Forecast Discussion
National Weather Service Tucson AZ
945 AM MST Mon May 22 2017

.SYNOPSIS...Dry conditions will prevail into next weekend. Daytime
temperatures through midweek will be several degrees above normal
followed by moderating temperatures late week. Some breeziness will
occur Thursday and Friday.


.DISCUSSION...Clear skies prevail across much of southeast Arizona
at this time. The exception was across the White Mountains were some
cumuloform clouds had developed. Dewpoints at lower elevations valid
9 AM MST ranged from the upper teens-20s, and these temps were 2-8
degrees higher versus 24 hours ago. Surface temps were generally 2-5
degrees warmer versus this time Sunday morning. 22/12Z KTWC sounding
precip water value of 0.38 inch was nearly identical to 24 hours

22/12Z upper air plots depicted deep low pressure centered near the
Great Lakes with a 500 mb trough axis extending southwestward into
the Four Corners regions. Meanwhile, strong high pressure aloft was
centered off the northern California coast with weak low pressure
aloft centered well west of the Baja California Spur near 24N/13W.
Moderate to strong westerly flow aloft above 500 mb prevailed across
southeast Arizona.

The main forecast concern into early this evening is the potential
development of showers/thunderstorms across the White Mountains.
Some cumuloform clouds have already developed, especially just north
of this forecast area. A very shallow moisture layer appears to
exist (700-600 mb) via the 22/06Z GFS, and the aforementioned mid-
level trough axis will move southeastward across the White Mountains
by daybreak Tuesday. Have noted that the NAM12 and GFS depict a
hundredth of an inch of rainfall near the New Mexico border adjacent
the White Mountains by this evening. For now, believe that precip-
free conditions will occur, but will monitor for potential forecast

Otherwise, abundant sunshine will boost into the 90s for most lower
elevation locales, and afternoon temperatures appear likely to
exceed the century mark across some western deserts such as western
Pima County. Gusty northwest winds will occur this afternoon east of
Tucson, and especially across the Upper Gila River Valley including

There are no updates planned at this time. Please refer to the
additional sections for further detail.


.AVIATION...Valid thru 23/18Z.
Expect a FEW to perhaps BKN clouds around 8k-12k ft AGL KSAD
vicinity northeastward to the White Mountains into early this
evening. Otherwise clear skies into Tuesday morning. Surface wind
east of KTUS this afternoon and early this evening nwly 12-25 kts
with gusts up to 35 kts. Otherwise and elsewhere, surface wind
terrain driven mainly less than 12 kts. Aviation discussion not
updated for TAF amendments.


.FIRE WEATHER...Dry conditions will prevail into next weekend. 20-
foot winds through midweek will mostly be terrain driven and
generally less than 15 mph. Expect occasional afternoon gusts due to
daytime heating, and stronger winds will also occur in Graham County
including the Safford area. Thereafter, stronger winds are forecast
to occur across more of the area Thursday and Friday. Critical fire
weather conditions may happen especially during the afternoon hours.


.PREV DISCUSSION /300 AM MST/...IR satellite imagery this morning
showed clear skies over southeast Arizona. Surface temperatures were
running 5-10 degs warmer than 24 hours ago after daytime highs
reached into the mid and upper 90s for many valley locations Sunday
afternoon. A weak shortwave passing across the area today may
produce a few afternoon buildups across the White Mountains, but the
bulk of moisture and any precipitation should remain east of the
AZ/NM border.

Dry NW flow aloft will dominate into mid-week as ridging builds in
from the west. This will result in mostly clear skies and above
normal temperatures, with Wednesday being the warmest as the ridge
axis passes overhead. The upper flow becomes westerly on Thursday as
the high breaks down ahead of another trough. Temperatures will
moderate by a few degrees in conjunction with an uptick in southwest
winds. The main concern here is the potential for critical fire
weather conditions to occur Thursday and Friday afternoons. Please
see the fire weather section below for more information.

As the aforementioned trough swings through the Great Basin and Four
Corners region Friday into this weekend, high temperatures may drop
to near seasonal averages. Though the GFS/ECMWF are coming into
better agreement with the evolution of this system, some differences
remain and the finer details will need to be ironed out in
subsequent forecast issuances. Regardless, this system looks to be a
dry one with precip remaining north of the area and zonal flow
keeping temperatures within a couple degrees of average through





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