FXUS65 KTWC 210421
Area Forecast Discussion
National Weather Service Tucson AZ
920 PM MST Tue Feb 20 2018
.SYNOPSIS...A cool air mass will linger across southeast Arizona for
the next several days as a series of weak storm systems move across
the region. The next chance for rainfall will occur Friday into
Saturday, especially north and east of Tucson.
.DISCUSSION...Skies continued to clear late this evening across
southeast Arizona with mostly clear skies areawide by Wednesday
morning. Still looking at cold temperatures for lows tonight, with
the lower deserts from Tucson westward dropping to near freezing.
That said, the current forecast looked in good shape so no updates
necessary this evening. Please refer to the additional sections for
.AVIATION...Valid thru 22/06Z.
SCT-BKN 4 to 8 kft AGL south and east of KTUS will dissipate tonight
with SKC most areas Wednesday. Surface wind speeds generally less
than 12 kts. Aviation discussion not updated for TAF amendments.
.FIRE WEATHER... Dry conditions and well below normal temperatures
will occur into Sunday morning, except for a slight chance of
showers Friday into Saturday morning. 20-ft west to southwest winds
will occur through Thursday and generally remain less than 15 mph.
Slightly elevated west or southwest winds may then occur Friday with
less wind occurring this weekend.
.PREV DISCUSSION...The large-scale pattern will continue to favor
mean troughing across the Western CONUS, resulting in a series of
weak disturbances moving across the Southwest throughout the week.
Given the relative rapid frequency of systems, any substantial
moisture return is expected to remain limited, which will limit the
potential for widespread or substantial rainfall. The first system
is forecast to move across Arizona Wednesday/Thursday, but current
trends suggest only a glancing effect with low rainfall chances
across the White Mountains and points northward.
A better chance for rainfall will occur late Friday into Saturday in
association with a digging upper trough across the Great Basin
towards the Four Corners region. Still some timing/amplitude
differences amongst the deterministic model guidance, but general
model consensus brings the trough across early Saturday morning.
Should see associated precipitation chances increase during this
period, especially east of Tucson. Should not see much of an effect
on temperatures, with perhaps only a few degrees of cooling expected.
Into next week, a substantial warming trend closer to seasonal
normals is expected across midlevel height rises as the flow
temporarily becomes more quasi-zonal. However, the evolution at this
time period is more uncertain, and there is some potential for
another deepening storm system to affect the region during the early
parts of next week.
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