Severe Thunderstorm Warning 137, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
219 PM MST Tue Sep 12 2023

.SYNOPSIS...Moist westerly flow will result in cooler temperatures
and a chance for showers and thunderstorms through Wednesday,
including the nighttime periods. Thursday onward drier air will move
into the region bringing an end to the showers and thunderstorms with
temperatures running just a few degrees above normal.

&&

.DISCUSSION...Southeast Arizona temperatures are 10 to 20 degrees
cooler than yesterday at the same time. Thanks to morning showers,
a few embedded thunderstorms, and the mid-level cloud cover that has
tamped down the temperatures. A wild swing of temperatures since
last weekend. The upper level pattern has a general trough
forming along the Pacific Northwest with a High Pressure over
northern Mexico. The water vapor imagery has started to show the
presence of a shortwave tough moving through the region. The
latest mesoanalysis shows at least two short waves moving through
Southeastern Arizona which will help generate thunderstorms
especially with shear values of 20kts, PWATs still around 1.6
inches, and CAPE values 1500-2000 J/kg. With these ingredients and
conditions, thunderstorms will be building now and over the next
several hours with a general storm motion East-Northeast. The 12Z
HREF has highlighted strong gusty winds across the region with the
highest potential for the stronger end for Cochise County this
afternoon and evening. Overall, the main threats are strong gusty
winds, hail, and brief locally heavy rainfall.

Tomorrow, the trough will move eastward and it will advect more
dry air into Arizona. That dryer air will collide with the very
moist layer and it will enhance thunderstorm strength and also,
better chances for microbursts. The favorable locations for the
thunderstorms will be southern Pinal County to the White
Mountains. This set up will increase the rain efficiency due to
the cooler upper level layer, very moist atmosphere, and
orographic lift. Thus, the mountains will experience the heavier
side of the rainfall than the valley locations. As for winds, HREF
has large area east of Tucson that has over 70% chance of wind
gusts above 30kts with pockets of 50-55kts. This gives good
confidence of strong gusty winds and potential microbursts.

Later in the week, the chances for precipitation will decrease
with the dry air being over Arizona. The ensemble models show a
ridge building and boosting daytime temperatures slightly above
normal through the weekend.

&&

.AVIATION...Valid through 14/00Z.
SCT-BKN clouds at 7k-11k ft AGL and layered clouds above. ISOLD/SCT
SHRA/-TSRA thru the forecast period. SFC wind gusts with the TSRA
to 30-40 kts, as well as brief MVFR conditions, lowered
visibility in moderate/heavy rainfall and mountain obscurations.
Otherwise, SFC wind at most locations less than 12 kts, favoring a
SWLY thru NWLY direction during the afternoon/early evening hours
and variable in direction at other times. The exception will be
over Cochise County in the vicinity of KALK and KDUG, where SFC
wind aft 13/18Z will be WLY at 15-20 kts and gusts to 25-30 kts.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Isolated to scattered showers and thunderstorms will
continue through Wednesday, with Min RH values in the 25-35 percent
range in the valleys and 50-70 percent in the higher terrain. Dry
conditions then overspread most of southeast Arizona Thursday
onward, except for a slight chance of showers and thunderstorms in
the White Mountains Thursday and then along the New Mexico border
Sunday into early next week. High temperatures will top out within a
couple of degrees of normal into next week. With the significant
drying the second half of this week, Min RH values lower back into
the 10-20 percent range in the valleys and 20-30 percent in the
higher terrain by Friday.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
None.
&&

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