FXUS65 KTWC 130933
Area Forecast Discussion
National Weather Service Tucson AZ
233 AM MST Wed Dec 13 2017
.SYNOPSIS...A weakening area of low pressure over the Gulf of
California will result in partly cloudy conditions along the
International border today. Two storm systems will then move south
from the northern Rockies and across New Mexico over the next couple
of days, bringing several degrees of cooling and breezy conditions
to southeast Arizona. The first system will move to our east
Thursday into Friday, with the second system expected on Sunday into
Monday. By Sunday, high temperatures will be right around average
levels. High pressure aloft will then build back across the desert
southwest next week for a return to well above average readings.
.DISCUSSION...The quasi-stationary upper low which has been parked
over the northern Gulf of California the last 36 hrs or so will
weaken and move slowly south today. There should be considerably
less cloud cover across southeast Arizona with this feature today,
with varying degrees of mid/high clouds along the International
border (for partly cloudy skies) and mostly sunny skies elsewhere.
Daytime temperatures will be up 2-4 degrees (versus yesterday), with
highs generally in the upper 60s to mid 70s across the valley
locations of southeast Arizona.
Otherwise, the highly amplified ridge pattern that has been across
the western United States will begin to shift westward into the
eastern Pacific Ocean. The overall position of this ridge will be
important for upcoming weather across southeast Arizona. At this
time, the ridge retreats just far enough west to allow a couple of
systems to dive south out of the northern rockies and across New
Mexico. This will result in several degrees of cooling across
southeast Arizona starting on Thursday and continuing into Sunday.
These systems will also bring breezy conditions to mainly eastern
areas Thursday and again on Sunday. With the current track of these
systems, any precipitation will be limited to areas east of our
forecast area, over New Mexico and points eastward. However, if the
ridge were to retreat a little further westward than anticipated,
we may end up with some precipitation along the New Mexico border.
This is something to keep an eye on going forward. The cooling trend
late this week into the upcoming weekend will lower daytime highs to
right around seasonal averages by Sunday.
Next week the ridge of high pressure shifts back eastward across the
southwestern United States. This will result in a return to well
above normal temperatures. High temperatures by mid next week are
expected to be 5-10 degrees above seasonal averages.
.AVIATION...Valid thru 14/12Z.
SKC to SCT clouds AOA 15k ft AGL through the period. Expect ELY/SELY
SFC winds 8-15 kts this morning to weaken to less than 12 kts and
become WLY/NWLY this afternoon. Terrain driven winds will then
prevail overnight tonight into Thursday morning. Aviation discussion
not updated for TAF amendments.
.FIRE WEATHER...Dry conditions through the forecast period. Elevated
20-foot winds from the east-southeast this morning will generally
diminish to less than 15 mph this afternoon with typical diurnal
trends returning. Some northwest breezes are then likely Thursday
afternoon followed by easterly winds on Friday as a storm system
passes east of the region. Another storm system looks to pass to the
east of our area again late this weekend bringing breezy
southwesterly winds to a few spots.
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