Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Tucson Arizona
935 PM MST Friday Dec 19 2014
Synopsis...a dry northwest flow pattern will result in some passing
high level clouds and near to slightly below temperatures this
weekend. Some areas of fog and freezing fog are expected again early
Saturday morning mainly across the valleys of Cochise and Graham
County. For early to middle next week...temperatures will rise to
above normal levels due to a passing upper level ridge. Unsettled
and cooler weather looks likely for the end of next week.
Discussion...main forecast concern tonight is development of fog
again mainly east of Tucson. Could see areas of dense fog again but at
this time don't believe that it will be widespread enough for an
advisory but observation will be monitored closely overnight into Saturday
morning. Otherwise satellite imagery showed high clouds over western Arizona
moving east. Partly cloudy forecast for tonight right on track. Clouds
may take an edge off low temperatures but overall it will still be
chilly to cold with areas of frost. Check previous discussion below
for additional forecast details for the weekend into next week.
Aviation...valid through 21/00z.
Eastern areas could see development of patchy fog or freezing fog
after 20/09z through 20/17z. Scattered to locally broken high clouds through
Saturday afternoon. Surface wind less than 10 kts will prevail
through the period. Aviation discussion not updated for taf
Fire weather...dry conditions will prevail today through Wednesday.
20-feet winds will generally be light and terrain driven through the
middle of next week. However...some northwest breezes will occur
Monday afternoon across the upper Gila River valley including
Safford. At this time confidence is low concerning the timing and
impacts of the next significant weather maker which may affect the
region late next week. Gusty winds and another chance for valley
rain and mountain snow are possible.
in the larger scale...weak shortwave ridging aloft is centered just
west of US at this time with some thin cirroform clouds across
western Arizona and more extensive middle and high level clouds across
the eastern Pacific pushing into Southern California. Considering
ample low level moisture remains tonight we think there will be some
areas of fog and freezing fog again early Saturday morning across
the valleys of Graham and Cochise County. The upper Gila River
valley will again have the best chance of seeing fog and freezing
fog. Some areas of frost will be possible as well for some of the
outlying areas of the Tucson metropolitan. There will be some thin
cirroform clouds overnight which could help mitigate low
temperatures and fog slightly but confidence is high enough to put
areas of fog in the forecast for the valleys east of Tucson.
A weak shortwave trough will skirt across mainly eastern sections of
the forecast area on Saturday with little sensible weather impact
other then some mainly high level clouds. Temperatures will warm a
few degrees on Saturday compared to today.
Thereafter...dry northwesterly flow aloft is expected from Sunday
through the middle of next week as ridging aloft is centered across
the eastern Pacific and troughiness is located over the plains.
Temperatures will be near normal Sunday and about 5 degrees above
normal Monday. There will be a weak cold front moving through from
the north-northeast early Tuesday but this will have little impact
on temperatures from Tucson westward with perhaps slight cooling for
eastern areas Tuesday into Wednesday.
By late next week...there remains considerable differences in the
global model guidance as another trough moves into the western US.
The 12z GFS keeps mainly zonal westerly flow this far south with the
12z Canadian and European model (ecmwf) more amplified with the trough late next
week. Will take a middle of the Road approach close to 12z gefs and
European model (ecmwf) ensemble means. Thus...have only made minor tweaks to the
ongoing forecast with slight chance probability of precipitation northeast of Tucson and
especially in the White Mountains Thursday and Friday. Temperatures
will drop back down to near normal values late next week.
Visit US on facebook...twitter...youtube...and at weather.Gov/Tucson