Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 242120

Area Forecast Discussion
National Weather Service Tucson AZ
220 PM MST Sun Mar 24 2019

.SYNOPSIS...Strong high pressure aloft will bring warmer
temperatures early this week, with daytime highs peaking on Tuesday.
Temperatures will approach the 90 degree mark from Tucson westward
into the western deserts. A gradual cooling trend will begin
Wednesday with highs returning closer to seasonal normals later
this week. Dry conditions to persist through Saturday.


.DISCUSSION...Upper ridge axis extended from the Lower Colorado
River Valley northwestward into the Pacific Northwest this
afternoon. The upper ridge will amplify Monday while moving eastward
into the Intermountain West and southwest CONUS. Some cirrus clouds
will also move across southeast Arizona, but these will generally be
of little consequence. The main influence from the upper ridge
on Monday will be warmer temperatures across the area.

The flow aloft on Tuesday will become increasingly southwesterly as
the upper ridge axis moves well east of this forecast area. Given
this flow regime, increasing mainly cirriform clouds should be
sufficient for partly cloudy skies. Various 24/12Z models suggest
the warming trend will peak Tuesday, and the increased high clouds
should have minimal effect on the daytime temps. Thus, high temps
Tuesday should encroach upon the 90 degree mark from the Tucson
metro area westward into the western deserts. For this forecast
issuance, have maintained a forecast high temp of 89 degrees Tuesday
at Tucson International Airport.

Dry conditions will continue Wednesday through Friday as southwest
flow aloft initially transitions to generally westerly flow aloft
Thursday into Friday. The bulk of mainly cirriform clouds will
depart Wednesday night followed by clear skies or some passing
mostly thin cirrus clouds Thursday into Friday. A cooling trend will
occur later this week, with high temps by Friday returning closer to
seasonal normals.

Thereafter, there were marked differences between the 24/12Z
GFS/GEFS and the ECMWF/EPS regarding the upper pattern over the
southwestern CONUS next weekend. The deterministic GFS depicted a
557 dm low to be centered near the Four Corners region midday
Saturday. Meanwhile, the ECMWF depicted northwesterly flow aloft
across the area, and maintained wly/nwly flow into Sunday.

However, the GFS moved the upper low southward to the White
Mountains Saturday night, with the upper low moving southeastward to
near El Paso late next Sunday afternoon. The differences in these
solutions essentially results in precip-free conditions continuing
area-wide as depicted via the ECMWF; or, perhaps chance-category
PoPs east of Tucson Saturday night into Sunday.

For this forecast issuance, have maintained precip-free conditions
area-wide Saturday into Sunday morning (neighboring WFO`s have
slight chance PoPs near the White Mountains). Have opted for a
slight chance of showers Sunday afternoon across the White Mountains
with dry conditions elsewhere. The scenario described is essentially
24 hours later versus the official forecast issued Saturday
afternoon (i.e. slight chance of showers Sunday versus Saturday).
High temps next weekend should remain close to seasonal normals for
late March.


.AVIATION...Valid through 26/00Z.
SFC winds generally less than 12 kts through the period. VFR
conditions with FEW-SCT clouds above 20k ft MSL. Aviation discussion
not updated for TAF amendments.


.FIRE WEATHER...Dry conditions persist until next Sunday when a
slight chance of showers develops across the White Mountains. 20-
foot winds remain fairly light until Wednesday through Friday when
stronger westerly breezes reach 10-20 mph each afternoon, especially
east of Tucson. Well above normal daytime temperatures Monday
through Wednesday will cool to near normal later in the work week.






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