Area Forecast Discussion

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.
Aviation/Fire Weather...Carpenter
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