Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 230927
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
226 AM MST Wed Jun 23 2021

.SYNOPSIS...A moisture increase from the south will bring a
chance of showers and thunderstorms through tonight. Thereafter, the
heat will return for the upcoming weekend. The heat will not be as
hot or prolonged as the recent record breaking heat wave. This will
be due to an increase in deeper moisture across the area starting
late in the weekend and continuing through the middle of next week.
This moisture increase will moderate temperatures and result in
areawide isolated to scattered showers and thunderstorms next week.

&&

.DISCUSSION...KEMX radar indicates spotty light showers across
portions of southeast Arizona early this morning. These showers were
pushing to the north-northeast at around 15 mph. Very little in the
way of measurable precipitation was noted with these showers,
generally trace amounts to a couple of hundredths. But, these
showers continues to moisten up the atmosphere.

Overall, most factors point to a bigger day, precipitation wise,
today and this evening. A weak inverted trough lifting north across
the region, favorable steering flow between the upper low to the
west and high pressure aloft to the east, PWATs between 1-1.25
inches and an outflow boundary pushing northwest across southeast
Arizona from the convection in northern Sonora. The latest model
guidance pops are up across the board for today/tonight with the
deterministic GFS well into the likely category (70 percent pops).

One limiting factor that could come into play for the development of
widespread heavier showers and/or thunderstorms across southeast
Arizona today will be the amount of cloud cover. Satellite blended
total precipitable water imagery indicate higher PWAT values of
between 1.25-1.50 inches residing across northern Sonora. Both the
NAEFS and the ECMWF ensemble mean precipitable water show these
higher values moving northward across the forecast area today. In
short, where there is some clearing today, the potential exists for
heavier and stronger convection. If the clouds stay widespread
today, expect lighter precipitation, with isolated thunderstorms.
Either way, the chance for precipitation across southeast Arizona
will be higher than we have seen in quite some time. Otherwise, with
the cloud cover and precipitation chances, high temperatures this
afternoon will be 3-6 degrees below normal for late June.

By Thursday, the ensembles favor a drying trend into the upcoming
weekend as westerly flow aloft develops. At the same time, high
pressure aloft shifts back westward, with a flat ridge across the
desert southwest and a highly amplitude ridge developing across the
northern portion of the western United States and the upper high
centered in the Pacific Northwest by late this weekend. This will
result in hotter temperatures across southeast Arizona Saturday and
Sunday. This position of the upper high will eventually favor an
influx of moisture from the east and southeast, as a surface cold
front dropping south through the Plains pushes westward into eastern
Arizona. The timing of this feature and subsequent moisture
advection still remained somewhat uncertain but ensembles point to
Sunday night or next Monday for the start. Once this moisture
advances into eastern sections, daily shower and thunderstorm
activity should be on the increase and spread farther west during
the week. Overall, the prospects of rain showers and thunderstorms
look to be on the increase next week.

&&

.AVIATION...Valid through 24/12Z.
SCT-BKN clouds 8k-13k ft AGL today with scattered -SHRA/-TSRA. Some
areas may briefly see TSRA/+TSRA. Slight chance of very brief MVFR
with the best chance west of KTUS late morning and east of KTUS by
afternoon. Surface winds generally westerly at 8-14 kts with a few
gusts to near 25 kts this afternoon. Localized gusts from
thunderstorm outflow winds to 45 kts are possible. Winds decrease
light and variable at other times. Aviation discussion not updated
for TAF amendments.

&&

.FIRE WEATHER...A brief period of increased moisture will last
through today, returning again Sunday into early next week resulting
in scattered shower and thunderstorm activity. Any thunderstorms
that do develop may result in gusty outflow winds in excess of 45
mph. Minimum relative humidity values will generally be in the 10-20
percent range in the valleys and 15-30 percent in the mountains.
Expect excellent RH recoveries Thursday morning with good recoveries
Friday morning. Recoveries briefly dip back into the 20-30% range
Saturday and Sunday morning, before widespread 50-75% returns
thereafter. 20-ft winds will be less than 15 mph, with typical
afternoon gustiness due to strong surface heating.

&&

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

&&

$$

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