Red Flag Warning 21, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
242 AM MST Mon Jun 21 2021

.SYNOPSIS...Several degrees of relief from the heat this week, but
still above late June averages. We have just enough moisture for
isolated thunderstorms favoring eastern mountains to start the
week. A moisture increase from the south over the next 2 days
will bring a little better chance of showers and thunderstorms by
late Tuesday or Wednesday. We'll probably lose some of that by
this weekend as high pressure rebuilds and temperatures climb again.

&&

.DISCUSSION...Satellite imagery shows a decaying thunderstorm
complex over northern Sonora early this morning. GOES-16 CH-14 also
shows that the last area of development near Cananea, Mexico has
thrown off an outflow (moisture) boundary pushing northwestward into
Santa Cruz county. Dewpoints have increased into the mid 50s to mid
60s along the International Boundary from southwest Cochise county
into Santa Cruz county. However, with the center of the high parked
right between Douglas and Safford and northwest/north flow through
the entire column (as depicted on the KTWC 210621/00Z sounding), it
will be very difficult to get more than a low level moisture
intrusion and expect most of the deeper moisture to remain across
northern Mexico, or wash out with daytime heating today until the
high moves into a more favorable position for moisture transport
northward.

High temperatures today will be 4-5 degrees lower compared to
yesterday, but still above June normals. Also expect elevated
northwest winds again this afternoon and early evening, especially
in the upper Gila River Valley where speeds will once again exceed
critical fire weather thresholds. Given the wind speeds that were
observed yesterday and the two on-going fires near this area
(Pinnacle and Walnut Fires), will go ahead and issue a Red Flag
Warning from 11 AM to 7 PM MST today for portions of Graham,
Cochise, far eastern Pinal and southern Greenlee counties. Please
refer to the PHXRFWTWC product and the Fire Weather section below
for more information on the Red Flag Warning.

Otherwise, not much change in the Tuesday through Thursday time
frame, with the ensembles/cluster analysis indicating the upper high
shifts eastward into Texas, while a trough develops along the west
coast. This will allow for deeper moisture transport northward from
Mexico, with model guidance numbers trending up for pops in the
Tuesday night through Thursday time frame across the forecast area.
ECMWF ensemble mean precipitable water values during this stretch go
over 1.25 inches across southern portions of the forecast area and
1.50 inches was noted just south of the International Border. The
NAEFS mean PW was similar to the ECMWF, albeit a little more robust.
Near normal temperatures are expected Tuesday through Thursday due
to the increased cloud cover/moisture.

By Friday into the upcoming weekend the upper high shifts back
westward and PW values fall back to between 0.75-1.0 inches. That
means a return to warmer temperatures and less shower/thunderstorm
activity.

&&

.AVIATION...Valid through 22/12Z.
SKC-FEW clouds above 20k ft MSL through the forecast period, though
some lower level clouds may start to develop early Tuesday morning.
Minor VSBY reduction due to wildfire smoke and haze, particularly
E/NE of KTUS. SFC wind increasing this afternoon, NWLY 12-16 kts
with gusts to 25 kts. Slightly stronger speeds at KSAD, generally 20-
25 kts and gusts to 35 kts. Otherwise, SFC wind generally less than
12 kts at other times. Aviation discussion not updated for TAF
amendments.

&&

.FIRE WEATHER...Dry today with a Red Flag Warning in effect 11 am
through 7 pm for Southern Graham and Greenlee Counties, along with
northern Cochise and extreme eastern Pinal Counties. Gusty northwest
winds 15-25 mph and gusts to 35 mph combined with minimum RH of 8-13
percent is expected to lead to critical fire weather conditions.

Otherwise, above normal temperatures continue this week. Minimum
relative humidity values generally 10-15 percent, though values
along the International Border and in the mountains may be 15-25
percent. More substantial moisture will increase shower and
thunderstorms chances Tuesday through Thursday and potentially for
the upcoming weekend. Any thunderstorms which develop may result in
gusty outflow winds up to 40 mph and dry lightning strikes. After
today, 20-ft winds will generally be less than 15 mph, with typical
afternoon gustiness due to strong surface heating.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 11 AM to 7 PM MST today for AZZ151-152-154.

&&

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