Area Forecast Discussion
Issued by NWS Tucson, AZ
FXUS65 KTWC 290419
Area Forecast Discussion
National Weather Service Tucson AZ
919 PM MST WED SEP 28 2016
.SYNOPSIS...An area of low pressure aloft will provide periods of
showers and thunderstorms through Thursday. Then dry conditions
will prevail this weekend. A trough will bring cooler air and a
chance of showers back to the area late Monday or Tuesday.
.DISCUSSION...The synoptic pattern remains virtually unchanged from
this time yesterday, with a large high pressure system centered over
extreme southern Texas/northeast Mexico and a low pressure system to
our northwest that extends from southern Nevada into southern
California and the eastern Pacific waters west of the central Baja
peninsula. With strong south to southwest flow aloft over Arizona
between these two features, moisture remains high with the 29/00Z
KTWC sounding revealing a PW of 1.31 inches, which is about two
tenths of an inch wetter than 24 hours ago. A disturbance aloft from
the southwest moved across the region earlier this afternoon which
helped trigger some decent showers and storms, mainly across parts
of Santa Cruz county and also central and eastern portions of Pima
county, including the Tucson metro and eastern Pinal county. Some
respectable rain amounts this afternoon, with the highest report
from an automated gauge in Pima county near Corona De Tucson that
picked up 0.75 inches. A trained spotter in that area also reported
nearly an inch in about a half hour, which was the highest reported
amount from around the region.
IR satellite imagery shows lingering cloudiness that extends from
central Baja through western Sonora and the eastern two thirds of
Arizona and the western half of New Mexico. Radar mosaic from around
the state shows very little activity over southeast Arizona, with
the bulk of continued shower and thunderstorm activity north of the
Mogollon Rim and moving quickly north. With the CIRA LPW Total
Imagery showing high values remaining to our south over much of the
Baja Peninsula, the Gulf of California and much of Sonora, we will
continue to be threatened by a slight potential for convection
throughout the overnight hours, with a significant threat once again
Thursday afternoon and into the early evening hours, especially east
of Tucson toward the New Mexico border. The POP forecast for the
rest of tonight seems reasonable and blends well with surrounding
offices, so no changes are planned at this time.
As of 04Z (9 PM MST), temperatures ranged from the mid 60s to the
upper 70s, with the Tucson Intl Airport reporting a temp of 73 degs,
after achieving an afternoon high of 90 degrees, which was 1 degree
below normal for this date. Will make some minor adjustments to
account for ongoing temperature trends, otherwise overnight lows
seem to be on track.
See previous discussion below for details beyond tonight.
.AVIATION...Valid through 30/06Z.
Isol`d to sct -TSRA/-SHRA thru the period with the best chances E
to SE of KTUS. SCT to BKN clouds around 8-12k ft AGL with brief MVFR
conditions and higher terrain obscurations possible, especially
Thursday afternoon. SFC wind ELY/SELY at 8-12 kts with higher gusts
at times during the afternoon/evening hours. Terrain driven wind at
less than 10 kts overnight. Aviation discussion not updated for TAF
.FIRE WEATHER...Isolated to scattered showers and thunderstorms
will occur area-wide through Thursday evening, with a slight chance
of showers and thunderstorms continuing Friday mainly east of Tucson.
Dry conditions will then prevail Saturday into the middle of next
week. 20-ft winds will be easterly to southeasterly through Thursday
at less than 15 mph, with normal diurnal wind trends occurring
Friday into early next week.
.PREV DISCUSSION...Thursday looks more and more interesting as the
final fragment from Roslyn is absorbed ahead of the deepening trough
and helps to create another day with decent thunderstorm potential.
Dry southwesterly flow over the weekend with temperatures above
Model resolutions on that next low are progressively deeper for
Monday and Tuesday, however the operational GFS is still a bit too
far north for a significant impact for our area other than gusty
winds and cooler air. ECMWF is a little deeper with more robust
moisture fields from the south. We might be a tad under done on our
precip chances Monday night. Either way, temperatures will drop back
to around 6 to 8 degrees below average by Tuesday.
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