758
FXUS65 KTWC 071716
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
1016 AM MST Sun Jul 7 2024

.UPDATE...Today`s forecast focus continues to be centered around the
excessive heat. Despite attempts of overnight moisture rebounding
from Sonora/Chihuahua, afternoon dew points have been drying into the
upper 20s to lower 40s thanks to dry air mixing from aloft. At least
we are running a degree or two cooler than this time yesterday.
Nevertheless, today is shaping up to be a very hot desert day with
forecast highs running 3-7 degrees above normal across southeast
Arizona. In Tucson today, NBM probabilities for reaching 110 degrees
is 25 percent. An Excessive Heat Warning remains in effect through
Tuesday evening which still looks to be on track. Take plenty of
breaks from the sunshine indoors whenever possible and drink plenty
of water.

All the excessive heat is thanks to strong ridge of high pressure
building aloft over California. As the high stretches slightly
southeast today, we will see a slight warming of temperatures aloft
at 500 mb. When combined with surface drying, warmer mid-level
temperatures will choke off our available energy for thunderstorm
activity today for much of southeast Arizona. Thus, the most likely
scenario is some plumpy cloud buildups across the higher terrain as
mid-level warming battles it out with any remaining low-level
moisture. Although confidence is low, the exception to this will be
along the International border where just enough surface moisture
may be leftover in the afternoon.

&&

.PREV DISCUSSION... /issued 259 AM MST Sun Jul 7 2024/

.SYNOPSIS...Excessive heat continues through early this coming
week with high temperatures expected to approach record levels in
some locations. Drier air moving in from the north has reduced
thunderstorm chances, but returning moisture should begin to
increase chances again by the middle of the week.

&&

.DISCUSSION...In the upper levels, an impressive ridge remains
anchored over the west coast, while southeastern Arizona sits on
the southeastern periphery of the anomalous mid to upper level
heights. With this ridge axis position, climate sites in
southeastern Arizona should tease record highs over the next
several days. In Tucson, NBM probabilities for reaching 110
degrees rise from 25 percent today to 50-60 percent Monday through
Wednesday, an example of the period of elevated Heat Risk across
the region. The current Excessive Heat Warning remains in good
standing. There is a possibility it may need to be extended into
Wednesday at some point, however questions on the moisture
return`s impact on high temperatures lead to enough uncertainty
for now.

The atmospheric column this morning is about as dry as it`s been
since the monsoon season started, with the 00Z sounding measuring
0.74 inches of precipitable water. This, combined with warming
aloft, will keep the forecast today nearly dry outside of a very
low chance of a thunderstorm near the International Border. A
weak impulse running through the northwest flow aloft will
tighten the pressure gradient today, creating breezy conditions
this afternoon. The Safford area should see the strongest winds
with gusts up to 35 mph as the Gila River valley orientation will
be favorably aligned for the northwest flow setup.

Through the upcoming week, the center of the upper high will
slowly migrate east and gradually turn mean flow easterly by the
weekend. This process will bring moisture and thunderstorm
probabilities back into southeastern Arizona as early as Tuesday,
with ensemble probabilities for precipitable water exceeding one
inch becoming more widespread by Saturday.

&&

.AVIATION...Valid through 08/12Z.
Generally SKC across southeastern Arizona with FEW-SCT ceilings
10k-12k ft this afternoon. An isolated shower or thunderstorm near
KOLS-KDUG can`t be ruled out this afternoon. West to northwest
winds increase after 07/17Z with gusts up to 25 kts. Wind gusts to
around 30 kts possible at KSAD. Winds decrease after 08/02Z, but
may remain breezy in areas exposed to northwest winds. Aviation
discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Excessive heat continues through early this
coming week with highs 106-113 degrees from Tucson westward and in
the Gila River Valley, and in the upper 90s to 105 degrees across
Santa Cruz and Cochise counties. As moisture has pushed south of
the region, minimum relative humidities will lower into the 10-17%
range across the lower elevations and 14-25% range in the higher
elevations into the middle of the week. Monday should see the
driest conditions with the lowest relative humidity values falling
into the single digits. Winds today will be highest in the upper
Gila River valley near Safford where northwest winds of 20 to 25
mph and gusts to around 35 mph are expected. Otherwise, 20-foot
winds will generally be 15 mph or less each afternoon with
occasional gusts to 20-25 mph. Moisture begins to return Tuesday
onwards as well as chances for thunderstorms.

&&

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 8 PM MST Tuesday for AZZ501-502-
504>506-509.

&&

$$

DVS

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