Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 231720

Area Forecast Discussion
National Weather Service Tucson AZ
1020 AM MST Fri Mar 23 2018

.SYNOPSIS...Generally dry conditions with a cooling trend and
gusty winds at times into early next week. A low pressure system
will bring a chance of valley rain and mountain snow mainly east of
Tucson by the middle of next week.


.DISCUSSION...Clouds continued to decrease late this morning in the
wake of an exiting system passing north of the area. This system had
ushered in a cooler air mass, with projected highs today about 8 to
10 degrees lower than observed yesterday. Current forecast looked on
track, so no updates necessary this morning. Please refer to the
additional sections for more details.


.AVIATION...Valid through 24/18Z.
SCT clouds above 20k ft AGL with FEW-SCT clouds 8-12k ft AGL. High-
level clouds gradually increasing in coverage tonight. SWLY-WLY 12-
18 kts with gusts near 25 kts, easing after sunset. Aviation
discussion not updated for TAF amendments.


.FIRE WEATHER...Dry and breezy weather is expected for the next few
days, lasting into Monday next week. Isolated areas may briefly
flirt with critical fire conditions each afternoon, especially east
to south of Tucson. 20-ft winds reach 15 to 20 mph, locally up to 25
mph, decreasing during the nighttime hours. Conditions abate on
Tuesday with the arrival of a developing weather system that brings
a slight chance of showers into part of Thursday.


.PREV DISCUSSION...Latest IR/WV satellite imagery shows the
shortwave trough pushing across the lower Colorado River Valley with
the mid/upper level moisture plume moving across the region. Given
that we`re on the tail end of the system as it pushes to the
northeast, we`re not expecting precipitation across the area today
with the exception of the White Mtns where there is a slight chance
of a shower. Otherwise, generally decreasing cloud coverage today
and temperatures about 5 to 9 degrees cooler than yesterday

Heading into this weekend, broad west to southwesterly flow aloft
will continue as height and thickness values gradually drop. A
fairly tight pressure gradient will result in some gusty afternoon
winds, especially south and east of Tucson Saturday and Sunday
afternoon. Meanwhile, a weak subtropical disturbance will mainly
clip Cochise County Saturday afternoon and evening. We`ve gone ahead
and introduced a slight chance of a shower in the Douglas vicinity
but we`re not expecting much as the sub cloud layer remains fairly
dry with mostly some virga expected. Dry conditions return area-wide
on Sunday with daytime temperatures close to seasonal normals.

The medium range guidance is in agreement regarding an upper level
trough dropping southward with an overland trajectory from the Great
Basin on Monday into the Desert Southwest on Tuesday as an upper low
closes off. While this system will be moisture starved, we can`t
rule out a few showers mainly from Tucson eastward on Tuesday. The
upper low and trough axis will be slow to push away from the region
keeping a slight chance of showers for eastern areas Wednesday and
even into Thursday right along the New Mexico border. Perhaps the
most notable thing this system will do is drop our daytime
temperatures on Tuesday to about 10 to 13 degrees below normal with
a gradual moderating in temperatures thereafter.





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