Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 142200
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
300 PM MST Sat Oct 14 2017

.SYNOPSIS...Dry conditions with above normal daytime temperatures
will continue during the upcoming week. Gusty east to southeast
winds will also occur at times Sunday into early Tuesday. Expect
cooler temperatures with a slight chance of showers and
thunderstorms mainly near the White Mountains next Saturday.

&&

.DISCUSSION...Visible satellite imagery and surface observations
depicted a few cumuloform clouds over southern Cochise/eastern Santa
Cruz Counties this afternoon. Otherwise, clear skies were the rule
across southeast Arizona. The cumuloform clouds will dissipate with
the loss of daytime heating this evening allowing for clear skies
area wide later tonight.

High pressure aloft is progged to amplify over the Desert Southwest
Sunday into Monday. This system will maintain clear skies across
much of this forecast area. Meanwhile, a fairly tight surface
pressure gradient will also prevail as surface high pressure
strengthens over west Texas. This pattern will translate into gusty
east to southeast winds at times Sunday into Monday, and perhaps
into Tuesday morning.

High temperatures Sunday across eastern sections will be about 5-10
degrees cooler versus this afternoon, but a few degrees of warming
will likely occur Sunday from Tucson westward into the western
deserts due to the general downslope wind regime. Expect no
significant change in daytime temperatures Monday versus Sunday.
However, would not be surprised to see some haze due to the gusty
ely/sely winds. Any gusty ely/sely winds will abate by Tuesday
afternoon as the surface pressure gradient loosens.

A flat ridge aloft will maintain dry conditions Tuesday into
Thursday. Thereafter, there continued to be differences amongst
various extended global models and their respective ensembles
regarding the evolution and progression of an upper trough, or
closed upper low, into the Desert Southwest late next week and into
next weekend. As for a few examples amongst the myriad of solutions,
the 14/12Z deterministic GFS depicted a progressive long-wave upper
trough to approach California on Friday, then continue eastward into
Arizona next Saturday. This solution kept any measurable rainfall
west-to-north of this forecast area.

However, the 14/12Z ECMWF was slightly more robust with measurable
rainfall potential versus the GFS, basically yielding slight chance-
category PoPs across eastern sections next Saturday. Although beyond
the scope of this forecast package, noted the very aggressive ECMWF
fairly deep upper low to move from the Four Corners region next
Saturday southwestward to near Tucson next Sunday evening. This
solution was a distinct outlier versus the GFS and GFS ensembles.

At any rate, per coordination with neighboring WFO`s, thought the
prudent course-of-action was to maintain dry conditions Friday, then
have introduced a slight chance of showers and thunderstorms mainly
across the White Mountains next Saturday. The idea of some sort of
upper trough at least should translate into daytime temperatures
cooling closer to seasonal normals next weekend.

&&

.AVIATION...Valid thru 16/00Z.
A few clouds at 8k-12k ft AGL southeast of KTUS early this evening
and Sunday afternoon, otherwise clear skies. Surface wind into
tonight variable in direction mainly less than 12 kts. Surface wind
Sunday into Sunday evening ely/sely 8-18 kts with occasional gusts
to 25 kts. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Dry conditions will continue through Friday followed
by a slight chance of showers and thunderstorms mainly near the New
Mexico border next Saturday. Gusty east to southeast winds will
occur at times Sunday into early Tuesday. Normal diurnal wind trends
with occasional afternoon west to southwest gusts will then prevail
during the latter part of the week.

&&

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

&&

$$

Francis

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