879
FXUS65 KTWC 072157
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
257 PM 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. Substantially 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...Today`s immediate 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
down from aloft. At least we are running a degree or two cooler than
this time yesterday in Tucson. 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, the NBM
probability for reaching 110 degrees is 25 percent. Excessive Heat
Warning continues through Tuesday evening which still looks to be on
track.

All the excessive heat is thanks to a 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 leading to more overall stable conditions. When combined
with surface drying, the warmer mid-level temperatures have choked
off most of the available energy for thunderstorms today for much of
southeast Arizona. Thus, we are only seeing some plumpy cloud
buildups mostly favoring the higher terrain as mid-level warming
battles it out with dwindling low-level moisture.

A weak impulse running through the northwest flow aloft has
tightened the pressure gradient today along the AZ/NM border.
Combined with strong daytime heating, the gradient has led to breezy
to gusty northwest winds this afternoon for the Gila River Valley.
Gusts to around 35 mph can be expected through the afternoon with
breezy conditions continuing into the evening hours.

As we start the week,tomorrow will be a similar story with the
excessive heat, very limited storm chances, and desert breeziness as
the upper high dominates and mid-level warming continues. Tuesday
and beyond looks to be the start of a transition period with the
upper high becoming oriented into a more favorable setup to draw a
plume of moisture from the Gulf of Mexico and Gulf of California.
However, the orientation of the high on Tuesday will be such that we
see more northerly flow, keeping moisture and precipitation chances
mainly to areas east of Tucson with the highest storm chances along
the AZ/NM border.

Wednesday into Thursday appears to be the peak of the transition
period back into Monsoonal flow as the high becomes more positively
tilted resulting in northeasterly flow aloft. Surface moisture
deepens across all of southeast Arizona as well resulting in
elevated chances for storms and a more active weather period overall
through next weekend.

&&

.AVIATION...Valid through 09/00Z
Generally SKC conditions across southeast Arizona this afternoon
with FEW-SCT ceilings 10-12k ft AGL. SFC winds will be WLY to NWLY
through 08/04Z, with speeds of 10-15 kts and occasional gusts to 25
kts through 08/03Z diminishing thereafter. Peak winds will be in
the vicinity of KSAD with a few gusts to around 30 kts, with winds
remaining elevated and NWLY overnight. Winds pick up again and
become WLY to NWLY after 08/17Z. 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 this afternoon 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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