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000
FXUS65 KTWC 061001
AFDTWC
Area Forecast Discussion
National Weather Service Tucson AZ
300 AM MST Fri Dec 6 2019
.SYNOPSIS...Dry conditions with warmer than normal daytime
temperatures into Saturday. Another weather system will bring valley
rain and high elevation snow Sunday into Monday. Dry conditions with
seasonable temperatures will prevail next Tuesday into Thursday.
&&
.DISCUSSION...Upper ridge axis extended from southeast Arizona
northwestward into the Pacific Northwest early this morning. This
ridge axis was ahead of deep low pressure centered west of the
northern California coast, or near 40N/135W. Generally zonal flow
aloft will prevail across this forecast area into Saturday as the
upper ridge flattens. This pattern will yield variable amounts of
mostly cirriform clouds into the first half of the weekend.
The 06/00Z GFS/GEFS and ECMWF/ECENS were quite similar with
depicting a progressive positive-tilted upper trough to move
eastward into the western CONUS Saturday night. A few showers
producing virga or very light rainfall may develop as early as
Saturday evening across western Pima County, but much of southeast
Arizona will remain precip-free Saturday evening. However, isolated
to scattered showers should occur late Saturday night mostly
northwest of a Safford-Tucson-Kitt Peak line.
Have noted that the 06/00Z deterministic ECMWF has trended away from
a closed upper low system depicted via the 05/12 ECMWF to move
eastward across the area early next week. As such, the 06/00Z ECMWF
was very similar to the GFS with the depiction of an eastward moving
positive-tilted upper trough to move eastward across southeast
Arizona Sunday into Monday. Despite the positive-tilted structure,
moisture will be sufficient to produce fairly widespread valley
rain. Snow levels by daybreak Sunday should be mostly above mountain
tops, but are forecast to fall to 7000-7500 feet midday Monday.
The mid/upper trough axis is progged to move well east of this
forecast area late Monday night. Given that the 06/00Z ECMWF has
trended away from a slower moving closed upper low system and is
very close to the GFS solution, precip chance were lowered Monday
night into Tuesday. Thus, a slight chance of valley rain and
mountain snow showers exists Monday night east of Tucson followed by
dry conditions area-wide Tuesday.
At this time, storm total rainfall amounts will generally range from
0.10 inch to 0.50 inch in the valleys, and from 0.25 inch to one
inch in the mountains. Storm total snowfall accumulations should
range from 1-5 inches across the highest peaks of the White
Mountains, Mount Graham, and the Catalina and Rincon Mountains near
Tucson. The bulk of precipitation should occur east of a Picacho
Peak to Kitt Peak line with little if any measurable precipitation
west of this line.
Although the models depict a shortwave trough will move eastward
across the area next Wednesday night, this system is not expected to
produce any measurable precip at this time. As a result, dry
conditions are forecast at this time to continue next Wednesday into
Thursday.
High temperatures today and Saturday will range about 3-7 degrees
above normal. A cooling trend is on tap Sunday into Monday, with
daytime temps Monday trending a few degrees below normal. High temps
Tuesday into Thursday will mostly be within a few degrees of
seasonal normals.
&&
.AVIATION...Valid through 07/12Z.
Expect SCT-BKN cirrus clouds above 20k ft MSL persisting through the
forecast period. Variable SFC wind less than 10 kts this morning.
Winds then become easterly less than 12 kts this afternoon turning
northwesterly at TUS and OLS in the evening. Winds will then be
light and variable tonight into Saturday morning. Aviation
discussion not updated for TAF amendments.
&&
.FIRE WEATHER...Dry conditions through Saturday. A weather system is
expected to impact the area early Sunday into Monday with a chance
of valley rain and mountain snow. The best chance for precipitation
will be from central Pima County eastward and northward, and
particularly across the higher elevations. A slight chance of
showers continues Monday night across eastern sections, with dry
conditions returning Tuesday and continuing through the end of the
work week. 20-ft winds will generally remain less than 15 mph
through the forecast period.
&&
.TWC WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
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