Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 071655
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
954 AM MST Thu Dec 7 2017

.SYNOPSIS...Much cooler temperatures with gusty winds today followed
by freezing temperatures for much of the area tonight. Dry
conditions with above normal temperatures will prevail this weekend
and into next week.

&&

.DISCUSSION...The main weather story last night was the gusty
northeast wind across the area. A few spots, mainly in Oro Valley
and Marana, experience wind gusts over 45 mph with some minor wind
damage reported in the foothills of the Tortolita mountains. Gusty
northeasterly winds will continue today but not as strong as last
night. The current Red Flag warning looked on track today. Wind
speeds will diminish this evening setting the stage of one of the
coldest night`s so far this season. Freeze warnings have been posted
tonight for areas around Tucson south to Nogales and eastward. That
said, no updates necessary this morning. Please refer to the
previous discussion for more details.

&&

.AVIATION...Valid thru 08/18Z.
Isolated -SHRA mainly near the New Mexico state line today.
Otherwise, clear skies KTUS vicinity westward into Friday morning.
East of KTUS scattered to overcast clouds generally 5k-10k ft AGL
into this afternoon, then clear or mostly clear skies by daybreak
Friday. Surface wind increasing from the northeast to east 12-25 kts
with gusts upward to 40 kts after 16Z and into this afternoon.
Surface wind this evening into Friday nely/ely 5-15 kts tonight.
Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...A Red Flag Warning is in effect until 4 PM MST this
afternoon for most of AZZ150 and for AZZ151 north of the Catalina
Mountains. The combination of strong and gusty northeast winds, low
relative humidity and a high fire danger will create critical fire
conditions.

Otherwise, isolated showers may occur near the New Mexico border
today followed by dry conditions tonight into next Wednesday. Strong
and gusty northeast to east winds today then winds diminishing this
evening. 20-foot winds will generally be easterly under 15 mph
Friday into next Wednesday.

&&

.PREV DISCUSSION...A highly amplified upper pattern continues across
the eastern Pacific and CONUS early this morning, with a north-to-
south ridge axis near the West Coast, and a broad trough east of the
Rockies. Water vapor imagery depicted a cyclonic twist representing
a vort max moving southward near the Four Corners region. There
still appears to be just enough moisture to support a slight chance
of showers near the New Mexico border today.

Otherwise, the main emphasis today will be regarding much cooler
temperatures and gusty northeast-to-east winds as northerly flow
aloft strengthens across the area. There is the potential for patchy
blowing dust, but have not opted to depict at this time with the
official forecast issuance with the notion that visibilities will
not be significantly reduced.

Clearing skies across eastern sections early this evening then clear
skies are expected area-wide later tonight. The combination of clear
or mostly clear skies and a very dry near-surface environment will
promote very cold temperatures from Tucson eastward. Although some
elevated wind speeds will likely occur, forecast confidence was
sufficiently high to have converted the inherited Freeze Watch to a
Freeze Warning from 10 PM this evening to 9 AM MST Friday. Please
refer to AWIPS product PHXNPWTWC /WMO header WWUS75 KTWC/ for
additional information.

Thereafter, the highly amplified upper pattern continues to be
progged by the 07/00Z GFS/GEFS and ECMWF/EPS Friday into the middle
of next week. These solutions remained quite close to previous
solutions from 24-48 hours ago. A Rex Block pattern is progged to
develop Saturday as strong high pressure aloft becomes centered over
the Pacific Northwest, and weak low pressure aloft develops west of
the Baja California spur.

The GFS/ECMWF then move the upper low northeastward to the northern
Baja California/northern Gulf of California area early next week.
Appears that precip-free conditions will continue with any moisture
of significance above about 600 mb. This moisture may be sufficient
for partly cloudy skies into Monday before clear skies or mostly
clear skies return Tuesday and Wednesday.

High temperatures this afternoon are forecast to be about 5-15
degrees cooler versus 24 hours ago. The greatest cooling will likely
occur from Tucson northward. Slightly warmer temperatures are on tap
Friday followed by more significant warming Saturday. Only minor
daily temperature changes Sunday and Monday with a few degrees of
additional warming by next Wednesday. Thus, below normal daytime
temperatures into Friday will be short-lived as above normal temps
are forecast to return Saturday and continue into the middle of next
week.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 4 PM MST this afternoon for AZZ150-151.

Freeze Warning from 10 PM this evening to 9 AM MST Friday morning
for AZZ503-504-506>509.

&&

$$

PREV DISCUSSION...Francis
AVIATION/FIRE WEATHER...Hardin

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