Severe Thunderstorm Warning 92, NWS Flagstaff, AZ

Area Forecast Discussion
National Weather Service Flagstaff AZ
919 AM MST Tue Sep 13 2022

.SYNOPSIS...Isolated to scattered thunderstorm activity will
continue into the morning hours then become more numerous this
afternoon. For Wednesday, storm coverage is expected to decrease
and become focused mainly from the Mogollon Rim northward. On
Thursday and over the coming weekend drier air will arrive,
mostly putting an end to the thunderstorm threat. Look for a
gradual warming trend through the period.

&&

.UPDATE...Only minor updates this morning to account for current
trends and latest CAMs, as the going forecast is on track. Expect
an active day across the CWA similar to yesterday, but with less
shear. Storms most numerous around and NW of the Flagstaff area,
and over the White Mountains. In addition to our typical
thunderstorm threats (hail, strong winds), training storms will
have the potential for locally heavy rainfall.

&&

.PREV DISCUSSION /330 AM MST/...A trough just to the west, and
southerly flow aloft have kept scattered showers and a few strong
thunderstorms going overnight with the highest coverage along the
I-17 corridor and into NW Gila County. Other isolated storms
persist in much of Coconino and NW Yavapai counties as of 230 AM.
This trough will not move much today, and after a lull in the
activity later this morning, scattered to numerous showers and
storms are forecast to redevelop this afternoon and into at least
early evening. The highest coverage of precipitation this
afternoon is expected over Coconino County and along the Mogollon
Rim into the White Mountains. HREF neighborhood probabilities of
3-hr QPF hitting 1" or greater are around 30% from Flagstaff
northwest to the Grand Canyon and Kaibab Plateau, and also near
the White Mountains. So there will still be a risk of localized
flash flooding today, especially in these areas. This threat will
linger into the evening and possibly overnight in northwest
Arizona including Grand Canyon and vicinity. However, don't think
the expected coverage is high enough to warrant extending the
current Flash Flood Watch so we will let it expire this morning
at 5 AM. For Wednesday, the trough weakens and shifts eastward.
Highest shower and storm coverage is forecast in NW Coconino
County, with mostly isolated activity elsewhere. The heavy rain
threat decreases significantly on Wednesday. High temperatures
today and Wednesday will be 5-8 degrees cooler than normal for
this time of year.

Thursday through the weekend - drier westerly flow develops over
the region, ending the chance of storms. Daytime temperatures will
warm back up to near normal, with seasonably cool nights. By later
in the weekend, a trough developing over the western US may get
close enough to our area for increasing southwest winds in the
20-30 mph range, something we haven't seen in a couple months.
Models differ on how deep the trough will be when in moves
through, but in any case it should knock temperatures down a bit
below normal. GFS even tries to pull some moisture up ahead of the
trough, though most other guidance does not. Blended guidance is
used in our forecast this far out, and includes a 20-30% chance of
rain for next Monday and Tuesday.

&&

.AVIATION...For the 18Z TAF package...Mainly VFR conditions persist
for the next 24 hours with SCT to BKN cloud cover. Expect scattered
SHRA/TSRA developing after 20Z with greatest coverage across
northwest Coconino County and along/northeast of the Mogollon Rim.
Anticipate activity to decrease after 05Z Wed with storms continuing
across northwest Coconino County and northeast Arizona overnight.
Gusty winds, minor turbulence, and brief MVFR/IFR conditions,
resulting in mountain obscuration at times, will be possible in and
around any storms. South/southwest winds 10-15 kts are otherwise
expected in the afternoon. Aviation discussion not updated for TAF
amendments.

&&

.FIRE WEATHER...Expect scattered to widespread showers and
thunderstorms across northern Arizona this afternoon and evening,
with scattered storms along and north of the Mogollon Rim on
Wednesday. Temperatures will be cooler than normal with southwest
winds around 10 to 20 mph.

Thursday through Saturday...Dry weather is forecast with breezy
conditions in the afternoon. Daytime temperatures warming a bit.

&&&

.FGZ WATCHES/WARNINGS/ADVISORIES...NONE.
&&

PUBLIC...BAK/JJ
AVIATION...LaGuardia
FIRE WEATHER...BAK

For Northern Arizona weather information visit
weather.gov/flagstaff

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