285
FXUS65 KTWC 182127
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
227 PM MST Tue Jun 18 2024

.SYNOPSIS...After a mild decrease in temperatures today, high
temperatures heat back up again Thursday and Friday. Moisture
will increase starting Thursday and result in the potential for
thunderstorms late in the week and through the weekend.

&&

.DISCUSSION...A relative lull in hot temperatures today across the
forecast area as highs this afternoon drop back down to seasonable
levels. This is due to broad troughing across the western US. The
normal high for Tucson is 102 degrees today.

Wednesday: Broad troughing continues, though heights/thickness
values nudge upward which will result in a few degrees of warming.

Thursday: A very interesting weather pattern starts Thursday as the
pattern aloft begins to shift. While heights remains elevated with a
ridge axis just to our southeast, a strong low level east push, at
least partially attributed to what is now the Potential Tropical
Cyclone One in the western Gulf of Mexico, will move into Arizona
from the east. A very tight surface pressure gradient will ramp up
winds considerably, but most notably near the NM border and in the
Upper Gila River Valley. These strong east to southeast surface
winds are quite anomalous per the ECMWF EFI and we`ve ramped up the
wind forecast east of Tucson Thursday. Some locales, but especially
the Upper Gila River Valley may need wind headlines
Thursday into Friday, especially if these trends continue. The
strong east push will bring with it increased moisture as PWAT
values jump to the 1" to 1.25" range Thursday. The western edge
of this east push will make it to around the Tucson area Thursday
afternoon with a pseudo dry-line/convergence setting up. Still some
differences in the ensembles with the GEFS/GEPS pushing the moisture
farther west than the ECMWF EPS. This boundary may help to initiate
a few mainly dry thunderstorms with little rain but strong and
gusty outflow winds (in addition to the background synoptic scale
gusty winds). Meanwhile, an Excessive Heat Watch remains in effect
from Tucson westward Thursday. Temperature trends have dropped back
slightly so will continue to monitor.

Friday: The moisture and east push will have made it all the way
to the western deserts with ensemble mean PW values ranging from
about 1 inch to 1.5 inches across the forecast area. The wind speeds
and gradient will remain strong on Friday with continued
breezy to windy across the forecast area. Even
with the increased moisture, as the high aloft will be nearly
overhead with warm mid level temperatures, that will help to limit
widespread convection. With that said, still expect at least
isolated mainly dry thunderstorms. An Excessive Heat Watch is also
in effect Friday but this will need to be re-evaluated over the next
day or two as the moisture may help keep temperatures below high
heat risk levels, especially for areas near Tucson. Hotter
temperatures more likely west of Tucson.

Saturday into next week: Once the moisture comes in, it doesn`t
appear to be going anywhere per ensemble guidance. That means from a
moisture perspective, we are in the monsoon. However, with the
mid/upper level high nearby, that will certainly be a mitigating
factor. Depending on the strength/location of the high each day,
that will drive convective trends but at least a low grade monsoon
pattern is expected during this time frame with temperatures a few
degrees above normal.

&&

.AVIATION...Valid through 20/00Z.
SKC through the forecast period. Surface winds SWLY 10-15 kts with
gusts to 25 thru 19/03Z. Thereafter, sfc winds decrease to 10 kts or
less into Wednesday morning. Aft 19/18Z, sfc winds become SLY/SWLY
10-15 kts with gusts to 25 kts thru the end of the forecast period.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Temperatures are expected to heat back up by
Thursday from Tucson westward after the brief few degrees of cooling
through Wednesday. Minimum relative humidity values through
Wednesday will be 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 east to southeast and
become stronger, especially across Graham/Greenlee/Cochise Counties
where sustained 20-ft winds of 20 to 35 mph are expected with
stronger gusts. The strongest of these winds will be in the Upper
Gila River Valley near Safford. With these east to southeast winds,
there will be increased moisture with min RH values in these
locales around 20 percent Thursday. 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. Some isolated mainly dry
thunderstorms are expected starting Thursday from Tucson eastward
and then to include the remainder of southeast Arizona Friday. As
moisture remains this weekend, isolated thunderstorms will continue
each day through the weekend into early next week with a low grade
monsoon pattern in place.

&&

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

&&

$$

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