Wildfire in Arizona, June 20 to 29, 2021

Area Forecast Discussion...Updated
National Weather Service Tucson AZ
506 AM MST Sun Jun 20 2021

...Updated for light showers over Cochise and eastern Santa Cruz
counties...

.SYNOPSIS...A strong ridge of high pressure will continue to result
in excessive heat today. Thereafter, we will see modest relief in
the heat, but high temperatures will generally remain above June
averages. Limited moisture with daytime heat will support isolated
or spotty light showers and mainly dry thunderstorms the next couple
of days. A little deeper moisture will move into southern Arizona
mid week for increasing chances of showers and thunderstorms.

&&

.UPDATE...A few light showers have developed during the early
morning hours over portions of Cochise and eastern Santa Cruz
counties. Automated gauges from this area indicate mainly trace or
zero precipitation amounts, so mainly virga attm. These showers
should diminish in coverage over the next couple of hours. Have
updated the corresponding grids/text products and sent those out.

&&

.DISCUSSION...The upper high has shifted southward from the Four
Corners into west central Arizona over the last 24 hours. This will
lead to another day of hot temperatures and excessive heat across
southeast Arizona. An Excessive Heat Warning remains in effect
through 9 PM MST this evening for much of the lower elevations of
our forecast area. Expect elevated west to northwest winds this
afternoon/early evening, especially in the upper Gila River Valley
where wind speeds will likely exceed critical fire weather
thresholds for portions of the afternoon hours. Given the small
areal extent of these strong wind speeds have elected not to issue a
Red Flag Warning, but instead highlight the gusty winds in the fire
weather section below as well as in the FWF product.

The models show the upper high will remain anchored across central
and southern Arizona through Monday, along with PW values between
0.80-1.00 inches. That is just enough moisture to continue the
slight chance of thunderstorms along the Mogollon Rim and White
Mountains and possibly over the mountains of Cochise and Graham
counties. The main threats from any storms that do develop will be
erratic gusty outflow winds and lightning, which could cause issues
with the on-going fires across the forecast area.

Tuesday through Thursday, the ensembles and cluster analysis
indicate the upper high shifts eastward and at the same time a
trough develops along the west coast. This will allow for deeper
moisture transport northward from Mexico, with some of the model
guidance numbers indicating increased pops in the Wednesday and
Thursday time frame. 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. Near normal to slightly above normal
temperatures are expected Tuesday through Thursday, which translates
to around 102 degrees for the Tucson Metro. By Friday into next
weekend the upper high shifts back westward and PW values fall back
to near 1 inch or less. That means a return to hot temperatures
and possibly excessive heat for southeast Arizona.

&&

.AVIATION...Valid through 21/12Z.
SKC-SCT clouds generally above 14k ft MSL thru much of the forecast
period. ISOLD -TSRA/-SHRA this afternoon/evening in the White
Mountains NE of KSAD. Minor VSBY reduction due to wildfire smoke and
haze, particularly E/NE of KTUS. SFC wind increasing this afternoon
WLY/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...Near record to record high temperatures once again
this afternoon. Minimum relative humidity values 10-15 percent
through at least mid-week, with the highest values particularly near
the International Border. There will be a slight chance of
afternoon/evening thunderstorms across the White Mountains this
afternoon, followed by dry conditions Monday. More substantial
moisture will increase shower and thunderstorms chances once again
Tuesday through the rest of the week. Any thunderstorms which
develop may result in gusty outflow winds up to 40 mph and dry
lightning strikes. Otherwise, 20-ft winds will generally be less
than 15 mph, with typical afternoon gustiness due to strong surface
heating. The exception will be today and Monday in the upper Gila
River Valley, as northwest winds increase to 15-20 mph with gusts to
35 mph and isolated critical fire weather conditions may develop.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 9 PM MST this evening for AZZ501>506-
509.

&&

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