Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 120348

Area Forecast Discussion
National Weather Service Tucson AZ
850 PM MST Sun Mar 11 2018

.SYNOPSIS...High pressure aloft will provide above normal
temperatures Monday through midweek. A series of disturbances will
then bring a chance of valley rain, mountain snow and cooler
temperatures Friday into Saturday. Remaining cool next Sunday with a
slight chance of showers especially east of Tucson.


.DISCUSSION...Current IR satellite imagery shows scattered cirrus
streaming in from the west with some residual lower level clouds in
southern Cochise County. At the surface dewpoints are still in the
mid to lowers 40`s across southern Arizona but midlevels have dried
out as can be seen in the KTWC 12/00Z sounding. This drying resulted
in a 0.22 inch drop in precipitable water for the 12/00Z compared to
the 11/12Z sounding.

Water vapor imagery shows a fetch of upper level moisture moving
around the periphery of a longwave trough situated off the western
coast of the U.S. This will likely result in some cirriform clouds
moving over Arizona tonight into Monday. The aforementioned trough
will not propagate very far east until later in the week leaving
Arizona under the influence of ridging through about midweek.
Because of this ridge temperatures will be above average for the
first part of the work week. Surface winds will be slightly elevated
tomorrow morning out of the east, but will start to weaken in the
afternoon. For more details please see previous discussion.


.AVIATION...Valid thru 13/06Z.
FEW-SCT clouds around 6k-10k ft AGL mainly around KDUG and SCT
clouds above 20k ft AGL late tonight into Monday afternoon for all
terminals. Surface wind variable in direction less than 12 kts
tonight then becoming ely/sely 5-15 kts with gusts to 20 kts around
12/14z until early afternoon. Monday afternoon surface winds will be
variable in direction less than 12 kts. Aviation discussion not
updated for TAF amendments.


.FIRE WEATHER...Dry conditions across much of the area late
tonight into Thursday. There is a slight chance of showers Friday,
then a chance of valley rain and mountain snow Friday into Saturday
night. Precipitation expected to decrease from west to east next
Sunday. Gusty east to southeast winds through midday Monday, then 20-
foot winds terrain driven mainly less than 15 mph late Monday into
Wednesday. Expect gusty southwest afternoon winds Thursday through


.PREV DISCUSSION...Isolated showers will continue mostly across the
White Mountains this evening, then any showers are expected to move
eastward into west central New Mexico late tonight. Otherwise,
scattered to broken cumuloform clouds across southeast Arizona at
this time will gradually dissipate with the loss of daytime heating
this evening. Mostly clear skies should occur by daybreak Monday
across western Pima County with partly cloudy to perhaps mostly
cloudy skies near the New Mexico state line.

A north-to-south upper level ridge axis is progged to amplify over
the southwestern CONUS Monday into Tuesday. Occasionally gusty east
to southeast winds Monday morning will diminish Monday afternoon.
The main impacts from the amplifying ridge will be dry conditions
with a fairly strong warming trend.

The flow aloft Wednesday will become increasingly southwesterly as
the upper ridge axis moves east into the central/southern Rockies,
and low pressure aloft deepens adjacent the West Coast. The 11/12Z
deterministic GFS/ECMWF suggest that isolated showers producing
light rain amounts may occur Wednesday into Thursday under fast
westerly/southwesterly flow aloft. However, per coordination with
neighboring WFO`s, have opted to maintain precip-free conditions
Wednesday into Thursday. Forecast confidence at this time is too low
to include a mention or depiction of measurable rainfall given the
progged upper level pattern.

The upper trough will continue to deepen near the California coast
Friday. The GFS also continues to favor a slower onset of potential
precip across southeast Arizona versus GFS solutions of 36-48 hours
ago. The GFS/ECMWF are depicting a series of impulses/speed maxes
embedded within the base of the long wave trough to move across the
southwestern CONUS late Friday through Saturday night. The GFS
remains consistent with producing more robust PoPs and rain/snow
amounts versus the ECMWF.

At any rate, the official forecast has a slight chance of showers
across much of the area Friday, then chance-category PoPs Friday
night into Saturday night. This precip event will almost assuredly
have markedly lower snow levels, and snow accumulations at least
above 7000 feet or so should ultimately occur. Given the potential
of brief negatively tilted upper trough late Saturday, would not be
surprised if thunderstorms also occur. Increasingly westerly flow
aloft next Sunday should translate into decreasing precip chances.
Have maintained a slight chance of valley rain/mountain snow showers
next Sunday from Tucson eastward, and precip-free conditions across
western sections.

The most pronounced warming Monday will occur from Tucson westward,
while eastern locales will have no significant temp changes versus
this afternoon. Expect well above normal temps Tuesday and Wednesday
before a cooling trend occurs Thursday into next weekend.





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