Wildfire in Arizona, June 20 to 28, 2021

Area Forecast Discussion
National Weather Service Tucson AZ
951 AM MST Sun Jun 20 2021

.SYNOPSIS...As high pressure weakens and shifts east of the area
this week, our temperatures will fall back a few degrees even as
they remain above seasonal averages for late June. We have just
enough moisture for isolated thunderstorms favoring eastern
mountains to start the week. A moisture increase from the south
over the next few days will bring a little better chance of
showers and thunderstorms by mid week. We'll probably lose some
of that by next weekend as high pressure rebuilds and temperatures
climb once again.

&&

.DISCUSSION...As expected we saw 1 inch PW on the 12Z KTWC
sounding this morning and 50 degree dewpoints have reached the
border, with Nogales up to 53 this morning and mid to upper 40s
elsewhere. Our mid level flow this morning is recirculating
moisture from the north and northwest, some of which is making
the long trip around the high. We will see some storms over
mountains closer to the eastern border again today, however this
steering flow is generally unfavorable for much else. Some minor
tweaks accenting storm chances near and south of the Chiricahuas
this afternoon. A deeper low level push from the south tonight
should spread the 55 degree dewpoint line from northern Sonora
deep into our area. More on that this afternoon.

Please see the previous discussion below for additional details
beyond tonight.

&&

.AVIATION...Valid through 21/18Z.
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.

&&

.PREV 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.

&&

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

&&

Meyer

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