Wildfire in Arizona, June 4 to 30, 2021

Area Forecast Discussion
National Weather Service Phoenix AZ
1102 AM MST Fri Jun 4 2021

.UPDATE...Updated Aviation Discussion.

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.SYNOPSIS...
The warmest temperatures so far this year will persist into the
weekend with readings 5 to 10 degrees above normal. This will result
in widespread moderate to localized high heat risk. Isolated showers
and thunderstorms are possible over elevated terrain of eastern
Arizona with just the remnant debris clouds drifting over lower
desert communities through Saturday. A subtle cooling trend is
possible early next week as low pressure nears the west coast,
however readings will still likely hover near the climatological
average.

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.DISCUSSION...
The pattern across the Southwest CONUS remains dominated by a
589-590dm high centered over the Great Basin. The weak upper low
which has been positioned south of the U.S. border has all but
fizzled out and a more well established upper low is seen near
the Big Bend of TX. The weakening of the low to the south and the
progression of an upstream trough through the Gulf of Alaska will
result in a gradual dampening of the high this weekend. Given the
general blocking nature of this setup, the pattern will be slow
to evolve and ensemble mean forecasts support a slight drift of
the high center to the southeast beginning today.

As a result, heat will remain the primary sensible weather impact
and likely peak today and possibly Saturday as the high drifts
closer to the local CWA. While not particularly unusual for
early-June, highs today and Saturday will range from 7-10F above
normal with magnitudes around 106-109F in south-central AZ to
108-113F in southeast CA. Daily records are around 114-117F and
not expected to be reached. Widespread moderate HeatRisk, with
locally high HeatRisk, is expected with these temperatures across
the lower deserts. Portions of the Phoenix metro area may even
reach locally high HeatRisk for a few hours in the afternoons.
Temperatures of this magnitude will equate to potential impacts
for sensitive groups, those reluctant to run their air
conditioner, or those not yet acclimated to the summer climate. An
Excessive Heat Warning remains in effect for portions of Imperial
and eastern Riverside counties through 9 PM PDT this evening.

Besides the heat, the past few overnights and mornings have
featured ACCAS/virga passing over AZ, including the lower deserts,
within the northeasterly flow. Which is the case again this
morning. A small shortwave/vorticty center, which helped enhance
ascent across the Four Corners region last afternoon, is still
seen on WV satellite early this morning pushing south through
west-central NM. With the current steering flow, the trajectory of
this feature will mostly remain too far east to have any
substantial impact on the local area. The next couple of
afternoons, the character and progression of mountain convection
will be the other weather hazard of concern. Steering flow will
tend to drive showers and storms from the Rim and White Mtns.
towards southern Gila County albeit probably in a decaying form
with very limited instability feeding deep convection. While
there's an outside chance (~10%) of storms within Gila County, the
most likely outcome is merely the decaying storms with erratic
winds, potentially a lingering lightning strike, but no
appreciable rainfall. Forecast BUFR soundings downstream into
lower elevations continue to support a very dry lower troposphere
and stable conditions.

As alluded to previously, early next week strong northern stream jet
energy will dampen and supplant anomalous ridging southeastward
leading to modest height falls and subtle cooling. However, the
entire CONUS blocking regime will remain largely intact shifting
eastward rather than being broken down entirely with highly
elongated troughing and deep negative height anomalies becoming
established over the NE Pacific basin. Ensemble cluster analysis
shows little variance in solutions through early next week with
the main uncertainty being the amplitude of the pattern. CMC mean
is notably more amplified and warmer than EPS and GEFS
membership. Nevertheless, there is relatively high confidence
that temperatures will be trimmed a few degrees, as well as an
increase breeziness, but the magnitude of these changes are more
uncertain. As expected with an increase to southwesterly flow
aloft, the vast majority of ensemble guidance is dry next week.

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.AVIATION...Updated at 1800Z.

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

Light and variable to light S crosswind component winds will
gradually veer to the southwest by early afternoon. Areas of
virga/sprinkles in the late morning to early afternoon may also
result in localized brief, erratic winds during that time. Winds
will increase this afternoon with gusts as high as 27 kt likely.
Occasional gusts to 30 kt may be possible early this evening
before the winds subside after 06z Saturday. Skies will be mostly
clear to partly cloudy with occasional FEW-SCT mid-high level
clouds.

Southeast California/Southwest Arizona including KIPL and KBLH:

Breezy southerly flow will develop early this afternoon at KBLH
with gusts of of 22-27 kt likely. Breezy conditions will also
develop at KIPL, but will likely hold off until the late afternoon
or evening. Winds will subside late in the evening, though
sustained winds of 5-10 kt will likely persist overnight.
Otherwise, skies will remain clear to mostly clear as high
pressure predominates across the Desert Southwest.

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.FIRE WEATHER...
Sunday through Thursday:
An elevated fire danger should be expected during the first half
of next week as afternoon humidity levels fall below 10%
coincident with wind gusts 20-30 mph and very dry fuels. Full
sunshine and temperatures near to slightly above the seasonal
average will only exacerbate the fire threat. While wind speeds
should relax somewhat during the latter half of the week, minimum
humidity levels will still fall into the single digits with
periodically gusty afternoon winds. Overnight recovery will be
poor to fair around a 20-40% range.

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

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.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Excessive Heat Warning until 9 PM PDT this evening for CAZ561-
     562-566-570.

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DISCUSSION...Benedict/MO
AVIATION...Sawtelle/Hirsch
FIRE WEATHER...MO