Wildfire in Arizona, June 23 to 26, 2020

Area Forecast Discussion
National Weather Service Phoenix AZ
210 PM MST Tue Jun 23 2020

.SYNOPSIS...
High pressure will predominate across the Desert Southwest through
the end of the work week, resulting in above normal temperatures
into the weekend. By Sunday, a cooling trend will push temperatures
back to near normal readings followed by slightly below normal
temperatures early next week. Dry conditions will prevail through
early next week under clear to mostly clear skies.

&&

.DISCUSSION...
Strong high pressure aloft has developed across the desert
southwest, generally centered across central Arizona. 500mb heights
have climbed to around 592dm per the 12z plot data and very dry air
is in place across the lower deserts; central desert dewpoints
ranged from the mid 20s to low 30s as of noon today. IR imagery
showed generally clear skies area-wide early this afternoon. Model
guidance is clear and consistent in calling for the strong high
pressure to remain in place through at least Wednesday, with 500mb
heights in excess of 590dm. Look for sunny or mostly sunny days and
clear nights with desert highs around 110 across the hottest
locations each day.

Latest situational awareness data including NAEFS percentiles for
temperatures suggest that while high temperatures will remain above
seasonal normals for the work week, they will not be close to record
levels. In fact, 850mb percentiles suggest that temps will stay
under the 90th percentiles across our lower deserts. Heat risk data
for the lower elevations this week are mostly in the moderate range
and only a few pixels of high heat risk pop up at times in the
central deserts. As such, we will keep our forecast going with
hottest deserts around 110-111 but staying several degrees above
normal and we have no reason to consider WWA products such as
excessive heat watch/warnings at this time.

For Thursday into Friday, we will see an open wave upper trof dive
southeastward into the northwestern tier of states, eventually
passing by to the northeast of Phoenix; a weak upper low center
associated with the passing disturbance tracks through the 4 corners
area. This will be a very dry system and will only gradually erode
heights aloft. by Friday afternoon we will see 500mb heights drop to
around 586dm over south central Arizona. As such a gradual cooling
trend will develop lowering highs a couple degrees or so with time;
by Friday the forecast high in Phoenix will fall to around 109 which
is still a few degrees above seasonal normal.

As we move through the weekend and into early next week, a consensus
of various operational and ensemble forecast packages continue to
advertise the development of a large high amplitude upper level trof
across the western CONUS, with the trof axis setting up just inland
near the coast, but west of Arizona. As this occurs, 500mb heights
will fall off sharply and correspondingly we will see much cooler
temperatures develop in the boundary layer by early next week. In
addition to the cool-down, which will pull desert highs close to the
100 degree mark by next Monday, we can expect breezy to windy
conditions by Sunday with similar winds expected Monday. Favored
areas including high terrain locales across far southeast California
and southern Gila County may see peak wind gusts approaching 35 mph
at times during afternoon and evening hours. Of course, with
continue dry conditions and minimum RH values below 15 percent, the
gusty winds will combine to produce dangerous fire weather
conditions across much of the area. It's too early at this time to
consider fire weather products but they may be needed as we move
closer to the weekend. We will continue to message the increasing
winds late in the forecast as well as the heightened fire danger.

&&

.AVIATION...Updated at 1742Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Minimal aviation concerns are expected through Wednesday aside from
brief afternoon gusts each day. Light westerly winds at this hour to
pick up during the afternoon/early evening hours. with 15-20 knot
gusts expected during the late afternoon/early evening timeframe.
Although lofted smoke with reduced slantwise visibilities are
possible towards the far eastern and northern reaches of the
visual ranges of the Phoenix area terminals, smoke concentrations
continue to decrease. Thus, VFR conditions should persist with
some high cirrus through Wed.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns are expected as VFR conditions will
persist through the TAF period. Winds at KIPL will generally favor
southeasterly heading at 5-10 knots. Winds at KBLH to remain
southerly, with gusts to 15-20 knots expected this afternoon and
early evening.

&&

.FIRE WEATHER...
Friday through Tuesday:
Conditions will generally be hot and dry with afternoon breeziness
with gusts generally peaking at 20-25 mph. A few passing weather
disturbances during the weekend and early next week may support
occasionally stronger breezes especially on Sunday. Daytime RH
values will continue to drop below 15% for most areas. Overnight
recoveries will generally rise into the 20-40% range but may trend
higher towards next week. Gusty wind combined with the low humidly
will continue to promote elevated fire danger across the districts,
especially Sunday and Monday.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

DISCUSSION...CB
AVIATION...Percha/Hopper
FIRE WEATHER...AD/CB