Debris Flows and Damaging Wind in Arizona, July 15, 2020

Area Forecast Discussion
National Weather Service Tucson AZ
930 AM MST Wed Jul 15 2020

.SYNOPSIS...Scattered showers and thunderstorms are expected each
afternoon and evening across southeast Arizona from the Tohono
O'odham nation eastward today through the weekend. Each day will
there will be a favored area and some days there will be fewer
storms than others. Temperatures will continue to be warmer than
normal the rest of the week, dropping to near normal this weekend.

&&

.DISCUSSION...Inherited official forecast of scattered showers and
thunderstorms from Tucson eastward/southward this afternoon and
evening appears to be in great shape via various high-res models.
15/12Z KTWC sounding precip water value of 1.35 inches was virtually
unchanged versus 24 hours ago. Storm motions should favor a more-
northerly component today versus the northeasterly component
exhibited Tuesday afternoon/evening. Isolated showers/tstms are
forecast continue late tonight (i.e. 06Z-12Z Thursday) mainly east
of Tucson. Several high-res models as well as global models depict a
westward expansion of showers/tstms Thursday afternoon/evening to
include all but western Pima County with at least a slight chance of
showers/tstms.

Please refer to the additional sections in this product for further
detail.

&&

.AVIATION...Valid through 16/18Z.
FEW-SCT clouds 10-15k ft MSL and SCT-BKN clouds 20k-25k ft MSL
through much of the period. Isolated to scattered -SHRA/-TSRA
expected this afternoon into this evening mainly from KTUS/KOLS
eastward. Gusty outflow winds around 40 kts will be possible
near -TSRA. Outside of gusty outflows, SFC winds will be WLY/SWLY
8-12 kts with a few gusts around 20 kts this afternoon. Winds
diminish after sunset becoming variable less than 10 kts into
Thursday morning. Aviation discussion not updated for TAF
amendments.

&&

.FIRE WEATHER...Expect isolated to scattered showers and
thunderstorms each afternoon/evening through the forecast period.
Activity today looks best for areas from Tucson eastward. Thursday
into early next week, expect isolated to scattered storms for most of
southeast Arizona. Temperatures will ease back to slightly above
normal levels by Friday. Daytime relative humidities will be 15-30
percent through the week with generally good overnight recoveries.
20-ft winds generally remain less than 15 mph with some afternoon
gustiness, although any thunderstorms will be capable of producing
gusts of 45 mph or higher.

&&

.PREV DISCUSSION (227 AM MST)...The upper level flow is finally
becoming more consistently conducive to advecting moisture over the
area and at the same time not capping off the convection with overly
warm mid-level temperatures. What that means is from this afternoon
onward we will see scattered convection developing each afternoon
into the early evening hours then diminish during the overnight
hours. There will be a few nights, especially later on in the
forecast period, where the convection will continue well into the
nighttime hours.

That said, in true monsoon flow fashion, that doesn't mean every
location will see showers or storms each day, but rather they will
occur each day somewhere and there will be favored areas from one
day to the next, and those favored areas will move around. More
often than not those favored locations will be determined by the
activity the previous day or night meaning it won't be apparent
until the day of. Overall this is good news for the fires around the
region as wetting rains will raise humidity levels and start the
greenup process, decreasing the fire threat. The possible exception
being the Bighorn fire scar as it is vulnerable to heavy rains
potentially resulting in floods and/or mud flows. In that case, a
little rain is good, a lot is not.

The other aspect of the more favorable monsoon pattern is the
gradual reduction in the afternoon high temperatures moving forward.
The next couple of days we will still be a few degrees warmer than
normal, however this weekend highs will be near normal and
potentially a bit lower than average by early next week. These
cooler temperatures will be partially offset by the increase in
humidity, but at least the very hot temps will be a thing of the
past for little while.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None.

&&

DISCUSSION...Francis
AVIATION...Carpenter
FIRE WEATHER...Carpenter
PREVIOUS DISCUSSION...Cerniglia

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