Severe Thunderstorm Warning 1, NWS Tucson, AZ

Area Forecast Discussion
National Weather Service Tucson AZ
136 PM MST Thu Jun 20 2024

.SYNOPSIS...Hot temperatures this afternoon with an Excessive Heat
Warning in effect for portions of southeast Arizona. Increased
moisture will result in the potential for thunderstorms each day
into next week week. Storms this afternoon into evening could
produce strong winds and blowing dust mainly from Nogales to Tucson
and into Pinal County. Windy conditions are also expected into
Friday. The added moisture will also result in temperatures dropping
back down close to seasonable levels through the weekend.

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.DISCUSSION...Plenty of active weather to talk about today as a more
monsoonal pattern/moisture regime is developing. East to southeast
winds are ongoing, mainly from points Tucson eastward with a
southerly to southwesterly flow elsewhere. Given the strong surface
pressure gradient, we've seen wind gusts between 40 and 50 mph for
portions of Graham and Cochise County where a Wind Advisory remains
in effect until 5 AM Friday. Moisture levels have increased
considerably with PWAT values of 1 to 1.25 inches from Tucson
eastward, but still between 0.5 inch to 1 inch west of Tucson where
the moisture hasn't made it quiet yet. For this afternoon, we're
particularly focused on the potential for a north-south line of
showers and thunderstorms developing across Eastern Pima/Eastern
Santa Cruz/Eastern Pinal/Western Graham/Western Cochise Counties.
This north-south line of showers and thunderstorms is forming along
the western edge of the moisture push (pseudo dry line) with the mid
to upper level flow generally pushing the storms that do develop
towards the east to northeast. MLCAPE values this afternoon per the
RAP are around 500-1000 J/KG in this favored zone with DCAPE values
nearly 2000 J/KG. Given this profile, the main concern with any
thunderstorms will be strong/gusty outflow winds producing areas of
blowing dust. With that said, a Blowing Dust Advisory remains in
place between 3 PM and 8 PM this evening. Not a lot of rain with
these storms with dry lightning potential in spots as well.

Convective activity will diminish after sunset this evening, and
then the focus overnight into Friday morning will continue to be the
larger scale east to southeast winds. The normally more susceptible
spots for east to southeast winds (including the south and east
portions of the Tucson Metro) will especially see the winds kick up
tonight into Friday morning. A few locales will see sustained winds
approaching advisory levels (30 mph). We didn't expand any wind
headlines on this forecast cycle but this is something we'll
continue to monitor this evening and overnight. HREF probabilities
for wind gusts over 45 mph are over 50 percent in these localized
most favored spots so the winds will certainly be noticeable
overnight into Friday morning for many folks.

For Friday, wind speeds will gradually diminish as the day
progresses with the main focus turning to the deeper moisture and
convective potential. With the increased moisture, temperatures will
drop about 3 to 6 degrees for most locales compared to today. PWAT
values Friday will increase to around 1 to 1.5 inches and these
values range from 150% to 225% of normal so it's certainly
anomalous to have this much moisture early in the monsoon.
HREF/CAMS are showing isolated to scattered showers and
thunderstorms across most of southeast Arizona Friday afternoon into
evening. Main concerns will continue to be gusty winds with brief
localized downpours with the strongest storms.

For this weekend, additional moisture makes its way into the region
with PWAT values increasing to between 1.25 inches near the NM
border to nearly 2 inches for the western deserts. These values are
2 to 3 standard deviations above normal for this time of year. With
that said, the mid/upper high will be just to our north and east
with warm temperatures aloft that will partially mitigate
convection. However, given the deep moisture, we'll certainly see
scattered mainly afternoon and evening showers and thunderstorms
this weekend.

The ensembles are showing a slight meander early to mid next week of
the mid/upper level high to the south and west as it strengthens
slightly. This type of regime would result in thunderstorm chances
shifting to locales generally from Tucson south and eastward. With
the high increasing in strength, temperatures bump back up during
this timeframe to about 3 to 5 degrees above normal.

&&

.AVIATION...Valid through 22/00Z.
SCT-BKN clouds 10-14k ft AGL KTUS/KOLS eastward. Convergence along a
surface boundary will likely lead to isolated to scattered -SHRA/-
TSRA starting around 21/21Z through about 22/03Z. Main terminals
affected will be KTUS and KOLS. Storms will be capable of winds 35-
45 kts with a 10-30 percent chance for winds in excess of 50 kts.
Outside of storms SFC winds become SELY at 15-25 kts with gusts to
30-40 kts across much of the forecast area. The strongest winds are
expected at KDUG and KSAD terminals. Aviation discussion not updated
for TAF amendments.

&&

.FIRE WEATHER...Temperatures are expected to peak today from
Tucson westward, then more seasonable temperatures thereafter.
Surface winds currently east to southeast from Tucson eastward and
west to southwest areas west of Tucson. The strongest winds will be
in the Upper Gila River Valley near Safford as well as near Douglas
along the International and NM borders. The increased moisture with
min RH values in these locales currently 20-30 percent. So while the
winds are at critical levels, RH values will remain just above
critical levels but certainly still elevated fire weather conditions
due to the strong winds and dry fuels Thursday. Breezy to windy
conditions continue Friday, though increased moisture will have
overspread more of the forecast area. A mixture of dry/wet isolated
to scattered storms are expected this afternoon from Tucson eastward
and then to include the remainder of southeast Arizona Friday. As
moisture remains this weekend, isolated to scattered thunderstorms
will continue each day through the weekend into early next week with
a low to mid grade monsoon pattern in place.

&&

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.TWC WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning through 8 PM MST this evening for AZZ501>506.

Blowing Dust Advisory from 3 PM this afternoon to 8 PM MST this
evening for AZZ502-504>506.

Wind Advisory through 5 AM MST Friday for AZZ508-509.

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