Heat in Arizona, August 23, 2020

Area Forecast Discussion
National Weather Service Tucson AZ
255 AM MST Sun Aug 23 2020

.SYNOPSIS...A better chance of thunderstorms later today and this
evening. High pressure building back through Arizona will tend to
limit thunderstorm coverage and push temperatures back up this
week, although there will still be some storms around. Excessive
heat is expected with near record high temperatures Monday and
Tuesday.

&&

.DISCUSSION...Still seeing some debris cloud with embedded showers
from the earlier widespread thunderstorm activity. That will
continue to dissipate through the early morning with partial
clearing by sunrise.

A ridge of high pressure remains over the desert southwest, but
the high center has shifted to near the 4-corners region. The
resulting easterly steering flow for storms will enhance a little
today, with even better support for easterly outflows from the
higher terrain. Plenty of conditional instability to tap again
today, with modest convective inhibition to overcome in some
valley locations. That means mid afternoon development for
mountains and mid to late afternoon propagation of outflows
lifting storms through lower elevations. Organized outflows could
create blowing dust in the late afternoon and evening hours. We're
actually seeing a little drying in the lower levels, which would
enhance our prospects for damaging winds from storms. Still
plenty of moisture for locally heavy rainers.

High pressure will strengthen over the state Monday, with
excessive heat an issue for at least Monday and probably Tuesday
as well. Temperature records will once again be in jeopardy. Weak
subsidence will slow thunderstorm development each day, along
with a little dry air intrusion from the east. This makes lower
elevations vulnerable to storm outflows with time to take full
advantage of surface heating before storms try to push in. As far
as that's concerned, Tuesday looks interesting.

We'll maintain an overall easterly steering flow for storms as
the ridge largely stays in place the rest of the week as tropical
activity downstream stalls our pattern. That could end up keeping
excessive heat in the forecast into Thursday. We'll see how the
thunderstorm situation develops early in the week before extending
the current Excessive Heat Warning into those days.

&&

.AVIATION...Valid through 24/12Z.
FEW-BKN clouds 10k-14k ft MSL into Monday morning with periods of
SKC possible around midday today. ISOLD-SCT TSRA/SHRA redevelop this
afternoon and continue through this evening. Some +TSRA will be
possible with reductions in CIGS/VIS, MTN obscurations and wind
gusts over 40 kts. Otherwise, SFC winds generally less than 10 kts
this morning becoming WLY-NWLY 8-14 kts with gusts to 25 kts.
Strongest wind vicinity KSAD. Winds decrease overnight into Monday
morning. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Moisture remains in place with isolated to scattered
showers and thunderstorms this afternoon through this evening.
Minimum humidities 15-25 percent across the valleys and 30-45
percent in the mountains today along with good/excellent overnight
recoveries. 20-foot winds generally remain less than 15 mph outside
of any thunderstorm gusts which could reach 40+ mph. Drier
conditions and hotter temperatures in the next few days slightly
reduces shower/thunderstorm coverage and daytime humidity values by
5 to 10 percent. Monday and Tuesday should be the hottest days while
precip coverage looks to be the most limited on Thursday and Friday.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning from 10 AM Monday to 8 PM MST Tuesday for
AZZ501-502-504>506-509.

&&

Public...Meyer
Aviation...Carpenter
Fire Weather....Carpenter

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