677
FXUS65 KTWC 180935
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
235 AM MST Tue Jun 18 2024

.SYNOPSIS...After a mild decrease in temperatures today, high
temperatures heat back up again Thursday and Friday. Moisture
should begin to increase late this week which would bring the
potential for thunderstorms late in the week into the weekend.

&&

.DISCUSSION...The upper air pattern is characterized by a longwave
trough over the western portion of the U.S. and strong high
pressure over the eastern U.S. This will put Arizona under dry
westerly flow through the middle of the week with temperatures
around normal today and a few degrees above normal Wednesday.
Winds will also be elevated today, especially along the
international border.

By Thursday the area of high pressure over the eastern CONUS
begins to build back into the Southwest shunting the trough into
Canada. Shortwave troughing will be present to the west over
California. This will bring temperatures back into the moderate
and major heat categories for portions of southeast Arizona
Thursday and Friday. Tucson will make another run at 110 degrees
with the NBM giving a 60 percent chance to hit 110 Thursday and
26 percent chance Friday. Because of this an Excessive Heat Watch
is in effect both days.

Along with the heat the position of the high will help turn the
mid-level flow to the east southeast. This easterly flow will
extend all the way to the surface thanks to surface high pressure
over the plains creating a fairly strong east-west pressure
gradient. This will lead to fairly strong winds Thursday,
especially in the Gila River Valley where sustained winds of 20
to 30 mph will be possible. This will lead to fairly strong
moisture advection from the Gulf of Mexico, aided by a possible
tropical system hugging the Texas coastline. Moisture arrives
Thursday afternoon mainly along the AZ/NM border where there will
be a 15-20 percent chance of mainly dry thunderstorms. Friday into
the weekend moisture increases with mean ensemble PWAT values
ranging from 1.2 to 1.5 inches by Saturday. Surface dew points
also look to reach the mid 50s from Tucson eastward Friday into
the weekend. This surface moisture will likely be aided by
outflows generated from convection in New Mexico Wednesday and
Thursday. By Friday into the weekend expect isolated to scattered
thunderstorms each afternoon and evening mainly from Tucson south
and eastward. The main threats will likely be strong outflow winds
and lightning, with possibly localized and brief heavy rain if
the boundary layer has moistened enough later in the weekend.
Temperatures moderate some over the weekend thanks to the
moisture.

Early next week the moisture looks to stick around with continued
afternoon and evening thunderstorms with high pressure centered
over Arizona.

&&

.AVIATION...Valid through 19/12Z.
SKC through the forecast period. Surface winds less than 10 kts
this morning becoming southwesterly 10-15 kts with gusts to 25
kts this afternoon and early evening. Winds decease again below 10
kts a couple hours after sunset. Aviation discussion not updated
for TAF amendments.

&&

.FIRE WEATHER...Temperatures are expected to heat back up by
Thursday and Friday after the brief few degrees of cooling today
and tomorrow. Through Wednesday expect minimum relative humidities
of 8 to 15 percent with overnight recoveries between 25 to 40
percent. Afternoon breeziness out of the southwest can be expected
through Wednesday with gusts to around 20 to 25 mph. Starting
Thursday, surface winds turn to the south to southeast, which also
begins to open the door for increasing low and mid-level
moisture. The Gila River Valley could see sustained southeast
winds of 20 to 30 mph Thursday and 15 to 25 mph Friday. Chances
for mainly dry thunderstorms east of Tucson arrive on Thursday and
then as far west as Tucson by Friday into the weekend. Min RH
values will also increase to 15 to 30 percent.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Watch from Thursday morning through Friday
evening for AZZ501>506.

&&

$$

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