890
FXUS65 KTWC 031006
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
306 AM MST Mon Jun 3 2024

.SYNOPSIS...

Temperatures will increase mid-week and become potentially
dangerously hot Thursday and Friday. Sunny skies and
afternoon breeziness can be expected over the next few days. A
weather system moving into the area will bring a chance of
thunderstorms Friday and Saturday. These storms will produce
little if any rainfall, but will be capable of producing gusty and
erratic outflow winds.

&&

.DISCUSSION...

Benign upper level flow today will give way to rapid height rises
as a ridge builds across the western CONUS through Thursday.
Additionally, a weak rotation southwest of the southern
California coast this morning is forecast to close and sit off the
western Baja coast from Wednesday through at least Friday. This
pattern transition will act to warm highs 8 to 10 degrees from
today to Thursday, when upper level height anomalies are forecast
to cross the 99th percentile on NAEFS over the Four Corners. As
there will be active flow across the northern periphery of the
ridge through the Pacific Northwest and Northern Plains, there is
some subtle run to run variability in the ridge amplitude as
models attempt to handle shortwaves running atop the ridge. This
has caused NBM`s temperature probabilities to nudge down in recent
runs, with the current KTUS high probability of at least 105
degrees at 59 percent. The deterministic NBM along with MEX/ECM
MOS guidance continues to advertise well above normal temperatures
across the southeastern Arizona valleys, remaining in Excessive
Heat range for the ongoing watch on Thursday. For reasons
described here with the synoptic picture as well as described in
the previous discussion, the current forecast temperatures are
likely sitting on the higher end of the envelope of reasonable
possibilities while excessive heat still looks likely.
Additionally it`s looking likely that the strong height anomalies
continue into Friday, which would bring another day of higher
heat risk. While cloud cover associated with the approaching upper
level circulation may mitigate the highest temperature potential,
the increasing confidence from guidance was enough to at least
extend the watch through Friday.

As mentioned above, the Baja closed low should gradually move
northeastward into southern Arizona by the end of the weekend.
Modest mid-level moisture advection within the southerly-
southeasterly flow ahead of the upper low will combine with the
synoptic support to produce at least widespread virga, with some
chances for thunderstorms producing light rain. Non-zero
precipitation chances begin to come in as early as Thursday
evening, however real probabilities for measurable precipitation
hold off until Friday and Saturday. Sub-cloud layers will remain
very dry through this period which keeps forecast precipitation on
the light side with the main hazards with any thunderstorms being
lightning and gusty outflow winds.

The track of the upper level low through the end of the weekend
still remains uncertain as ensemble paths range from crossing the
western to eastern Arizona borders. The eastern track, as
depicted by the ECMWF ensemble mean, may linger precipitation
chances near the New Mexico border on Sunday. In comparison the
western track may be more quick to push dry air back into
southeastern Arizona. Either way, this low crossing the region
should bring temperatures back to near normal through the weekend.

&&

.AVIATION...Valid through 04/12Z.

Winds become west to southwesterly after 18Z and increase to
around 10 to 15 knots before diminishing after 02Z. Mostly SKC
with a few high clouds through the forecast period. Aviation
discussion not updated for TAF amendments.

&&

.FIRE WEATHER...

Dry conditions and high temperatures 2 to 5
degrees above normal the next few days, becoming 5 to 8 degrees
above normal the second half of the week. Dangerous heat is
anticipated across the valleys of Southeast Arizona Thursday and
possibly again Friday. Minimum relative humidity values 5-10% in
the lower elevations 8-15 percent in the mountains through the
week, along with poor overnight recoveries between 20-30%.

Breezy afternoon winds are expected again today with west to
southwest winds of 15 to 20 mph and gusts up to 30 mph. An
approaching weather system will result in the potential for dry
thunderstorms with gusty outflow winds Friday and Saturday.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Watch from Thursday morning through Friday
evening for AZZ501>509.

&&

$$

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Aviation...Edwards
Fire Weather....Edwards

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