Area Forecast Discussion
Issued by NWS Tucson, AZ
FXUS65 KTWC 202240
Area Forecast Discussion
National Weather Service Tucson AZ
340 PM MST SAT AUG 20 2016
.SYNOPSIS...Expect scattered afternoon and evening showers and
thunderstorms through Monday. A drying trend will then limit
thunderstorms to mainly near the New Mexico border by next Thursday.
High temperatures will generally be within a few degrees of normal
during the upcoming week.
.DISCUSSION...Scattered showers and thunderstorms were occurring
across much of the area at this time. The greatest coverage was
generally across the White Mountains and Graham County, and west of
Tucson across western/central Pima County. There were some fairly
pronounced differences between the 20/12Z Univ of AZ WRF-NAM and WRF-
GFS solutions regarding the next few hours. In essence, have leaned
toward the WRF-GFS which had the better depiction of showers/tstms
west of Tucson. The WRF-GFS was also more similar to the most recent
HRRR solution as well as the SPC SSEO.
At any rate, expect scattered showers/tstms this evening, then the
bulk of precip should end by around midnight tonight. For this
forecast issuance have maintained a slight chance of showers/tstms
for most sections late tonight. The evening shift may opt to trim
PoPs for the 06Z-12Z Sunday period as appropriate. Enough moisture
will then prevail for more scattered afternoon/evening showers/tstms
Thereafter, the 20/12Z GFS/ECMWF/CMC were quite similar with
depicting a pronounced drying trend from west-to-east across the
area Tue-Thur. This drying trend is due to somewhat stronger
westerly flow aloft which is in response to a longwave trough moving
eastward across the intermountain west.
Based on these solutions as well as per coord with neighboring
WFO`s, PoPs were lowered thru the Tue-Thur period. The expectation
by next Thur is for afternoon/evening showers/tstms to be confined
to near mountains east of Tucson, although would not be surprised
for this activity to be only limited to near the New Mexico border.
Some increase in progged moisture then justifies isolated to
scattered afternoon/evening showers/tstms area-wide Fri-Sat.
High temps during this forecast period will generally be within a
few degs of normal.
.AVIATION...VALID THRU 22/00Z.
Scattered -TSRA/-SHRA this evening, with the favored areas mainly
near mountains east of KTUS to the New Mexico border, and west to
southwest of KTUS. The bulk of -TSRA/-SHRA will end by 21/07Z, then
scattered -TSRA/-SHRA mostly east to south of KTUS Sunday afternoon.
Otherwise, cloud decks around 10k-15k ft msl and surface wind
generally less than 12 kts through Sunday afternoon. Aviation
discussion not updated for TAF amendments.
.FIRE WEATHER...Expect isolated to scattered mainly afternoon and
evening showers and thunderstorms through Monday. A drying trend
from west-to-east will then occur Tuesday through Thursday, with
only isolated thunderstorms mainly near mountains east of Tucson by
Thursday. Isolated to scattered thunderstorms will then prevail next
Friday and Saturday. Winds through the period will favor typical
upslope/downvalley diurnal trends except near thunderstorms.
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