Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 162205

Area Forecast Discussion
National Weather Service Tucson AZ
305 PM MST Mon Oct 16 2017

.SYNOPSIS...Continued dry with unseasonably warm temperatures
through Wednesday. A fast moving disturbance will bring isolated
showers and thunderstorms Wednesday night into Thursday. Dry
conditions will then prevail Friday into early next week. Expect
some minor cooling Saturday, then very warm temperatures return
Sunday into Monday as high pressure builds over the area.


.DISCUSSION...Clear skies prevail across much of southeast Arizona
this afternoon. The exceptions were north of Tucson where a few thin
cirriform clouds were observed, and south of Tucson near the
International border where a few cumuloform clouds developed. Gusty
mainly east to southeast winds that occurred earlier today have
diminished somewhat, locally gusty winds continue as of 2 pm MST.
Expect clear skies tonight will occasionally gusty east to southeast
winds, especially in vicinity of KTUS.

A ridge of high pressure aloft over the southwest CONUS will flatten
Tuesday into Wednesday. Meanwhile, IR/water vapor satellite imagery
depicted a fairly large area of enhanced cloudiness west of central/
southern Baja California near 20-25N/120W. This moisture is progged
to move northward around the periphery of the upper high, then turn
eastward into the Desert Southwest by Wednesday night.

The 16/12Z GFS/NAM12 were fairly similar with the depiction of light
rainfall amounts to occur across portions of this forecast area
Wednesday night into Thursday. The deterministic 16/12Z ECMWF was
considerably drier versus the GFS/NAM12. However, per coordination
with neighboring WFO`s, opted for a slight chance of showers from
Tucson westward into western Pima County late Wednesday night.

A slight chance of showers then exists most sections Thursday
morning, and then opted for a slight chance of showers/tstms
Thursday afternoon. The bulk of deeper moisture associated with this
fast moving shortwave trough is progged to be east of this forecast
area Thursday night. The global models depict another mid-level
trough axis to move eastward across the area Friday night. This
system will initiate drier air to move into the area, and this very
dry regime will be maintained Saturday into next Friday as high
pressure aloft strengthens over southern California.

Expect no significant change in the unseasonably warm daytime
temperatures Tuesday through Friday, then only some very minor
cooling is on tap Saturday. Have noted that the 12Z guidance temps
for Saturday trended generally 3-5 degrees warmer versus the 16/00Z
guidance temps. Thus, warmer temps will return Sunday and next
Monday, with forecast highs at this time to approach record
thresholds for some locales.

The drier regime for late Saturday night/early Sunday morning and
for late Sunday night/early Monday morning will likely translate
into fairly cool morning low temps, especially for the colder
valleys east of Tucson. At this time, am not expecting a widespread
freeze to occur.

However, some areas within the Sulphur Springs Valley (among other
colder valleys east of Tucson) may experience temps near freezing
for a few hours early Sunday morning and again early Monday morning.


.AVIATION...Valid thru 18/00Z.
Expect clear skies or a few clouds above 20k ft AGL into Tuesday
afternoon. Surface wind into Tuesday morning generally ely/sely 5-15
kts with gusts near 20 kts. Surface wind Tuesday afternoon variable
in direction less than 12 kts. Aviation discussion not updated for
TAF amendments.


.FIRE WEATHER...A fast moving disturbance will bring isolated
showers and thunderstorms Wednesday night into Thursday. Otherwise,
dry conditions will prevail into early next week. Gusty east to
southeast winds will diminish early Tuesday followed by normal
diurnal wind trends during the latter part of the week and
into next week. Expect occasional afternoon gusts due to daytime






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