Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 122205
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
305 PM MST Sun Nov 12 2017

.SYNOPSIS...Dry conditions with passing high clouds into next
weekend. Expect near record daytime temperatures into Tuesday. A
system moving north of the area will bring cooler temperatures late
in the week, but above normal temperatures to continue next weekend.

&&

.DISCUSSION...A broad area of high pressure aloft remains anchored
south of this forecast area this afternoon, and water vapor
satellite imagery places the anticyclonic pivot point over the
southern Gulf of California. Meanwhile, a deep upper trough was
located near the Pacific Northwest coast. Although clouds have
thickened somewhat at times over southeast Arizona during the past
12-24 hours, IR/water vapor satellite imagery depict markedly
thicker clouds arcing from well west of the Baja California spur
northeastward into the Great Basin.

Expect partly cloudy to mostly cloudy skies tonight into Monday.
Despite the potential for more cloudiness Monday versus today,
increased heights/thicknesses support another 1-3 degrees of warming
on Monday. Thus, record or near-record high temperatures for at
least some locales appears likely on Monday. The upper high is
progged to flatten starting Tuesday, and this will translate into a
few degrees of cooling. However, forecast highs Tuesday will remain
close to record or near-record levels, especially east of Tucson.

The 11/12Z GFS/ECMWF/CMC remain consistent with keeping the upper
high centered over southern Baja California Wednesday into Thursday.
However, a progressive upper trough is progged to move into the
Pacific Northwest Wednesday night, then continue to advance eastward
across the Great Basin and eventually into the northern/central
Rockies by Friday. At least, according to the 11/12Z GFS.

The 11/12Z ECMWF deviated from several previous ECMWF solutions
regarding the progression of this system north of this forecast
area. As such, there were fairly distinct timing differences between
the 11/12Z GFS/ECMWF solutions by the latter part of the week. In
essence, the GFS was faster with the eastward movement of this upper
trough versus the ECMWF. Forecast confidence remains very high that
any measurable precip associated with this system will be well north
of this forecast area. Forecast high temps were raised a few degrees
Thursday versus the previous forecast. Thus, more noticeable cooling
now appears to occur Friday, although high temps will still be
several degrees above normal.

Thereafter, the progged upper pattern differences between the GFS/
ECMWF become more distinct next weekend and early next week. The GFS
was similar to previous GFS solutions, as well as ECMWF solutions
prior to 11/12Z, with depicting an amplifying ridge over the area.
However, the 11/12Z ECMWF now depicts a fairly vigorous shortwave
trough to dig into the Great Basin/Desert Southwest late next
Sunday. Assuming this system to be reality, the main impact will be
for cooler temperatures to potentially occur.

However, for this forecast issuance, have opted for no significant
change in daytime temps Friday into next Sunday. A quick glance at
the ECMWF EPS suggest that the deterministic ECMWF may be an outlier
solution. Appears that heights would rebound quickly after the
passage of the aforementioned shortwave trough and thus any cooling
would be short-lived.

&&

.AVIATION...Valid thru 14/00Z.
Expect broken to overcast clouds above 20k ft AGL into Monday
afternoon. A few clouds as low as 12k-15k ft AGL may occur Monday
afternoon. Surface wind will be variable in direction mainly less
than 10 kts. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Dry conditions with periods of mainly high level
cloudiness to prevail into next weekend. 20-foot winds will mainly
be less than 10 mph as well, although some gusts to near 20 mph may
occur during the afternoon hours. Unseasonably warm daytime
temperatures will continue into midweek before cooler temperatures
arrive Friday into next Sunday.

&&

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

&&

$$

Francis

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