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000
FXUS65 KTWC 250422
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
920 PM MST Sun Sep 24 2017

.SYNOPSIS...Dry conditions will prevail across much of the
area through Tuesday with a few record low temperatures for the
coldest valley locations southeast of Tucson. Expect scattered
showers and thunderstorms Wednesday, then isolated to scattered
storms mainly east of Tucson Thursday into Saturday.

&&

.DISCUSSION...Latest satellite imagery shows clear skies over all of
Arizona this evening. One must look all the way to the Great Basin
to find any significant cloud cover. Those clouds are associated
with a strong low pressure system moving through that region and
helping to maintain the trough that is currently in place over us.
The 00z KTWC sounding indicated that precipitable water values are
down to only 0.34 inches, which further explains the lack of clouds
today.

The pleasant daytime highs in the upper 70s/lower 80s will
transition into a relatively chilly night across our area as lows
will fall to a few degrees cooler than Saturday night. Expect lower
50`s for Tucson and areas west and lower to mid 40s for the southern
and eastern valleys. Some areas such as Tombstone, Douglas, and
Sierra Vista could approach or even surpass their record low
temperatures for tonight. Another quiet and seasonably cool day is
on tap for Monday. Look for clear skies and temperatures slightly
warmer than today, but still well below normal for this time of
year. Otherwise, the current forecast looks to be on track. Please
see the previous discussion for further details.

&&

.AVIATION...Valid thru 26/06Z.
Dry air will allow for SKC conditions to persist for all areas
through the entire TAF period. SFC winds Sunday night will be
terrain driven and variable below 10 kts. Winds will turn WLY to
NWLY after 25/19z and are expected to remain at or below 12 kts.
Aviation discussion not updated for TAF amendments.


&&

.FIRE WEATHER...A dry atmosphere will dominate the region through
Tuesday morning. A slight chance of isolated storms will exist
starting Tuesday evening into the overnight hours east of Tucson.
Then isolated to scattered thunderstorms will prevail Wednesday
through Friday mainly for areas from Tucson eastward. Some lingering
moisture will allow for a slight chance of storms Saturday. 20-foot
winds will be terrain driven less than 15 mph through Wednesday.
Thursday and Friday winds will shift to easterly with afternoon
gusts between 15-20 mph.


&&

.CLIMATE...The current low temperature forecast at Tucson
International Airport for Monday morning is 54 degrees. That would
be the coolest low temperature in September since 2004 when 54
degrees occurred on the 22nd. The last time Tucson recorded a low of
53 degrees (which may occur Monday morning) in September was in 1988
on the 23rd.

&&

.PREV DISCUSSION...Our weather is currently dominated by a relatively
strong early season lower pressure system through the Great Basin
and the Rockies. We`re on the southern periphery, but still seeing
gusty winds at times this afternoon as well as daytime highs several
degrees below average. Another cool night in store with temperatures
generally in the 40s in cooler eastern valleys, to 50s from Tucson
into the lower deserts. Not bad for late September after all those
100 degree days. As a matter of fact, it could approach record lows
in a few colder locations such as Douglas and Tombstone.

We`ll keep some energy sagging back to maintain a weakness in the
flow even as a large scale ridge of high pressure starts to build in
from the west the first half of the week. It will serve to slow our
warming trend and wrap some moisture from New Mexico and Chihuahua
into mainly eastern areas around mid week for a chance of showers
and thunderstorms by Wednesday. The weak cut-off will slowly fill
and lift into the front side of the ridge late in the week before it
shears back into higher latitude support next weekend.

At that point we`ll have to see if the eastern Pacific ridge becomes
dominant, or if the storm track continues to keep it upstream and
out of the picture. One means near record highs in early October,
and the other windy and relatively cool.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

Discussion...JKP
Prev Discussion...Meyer/Zell/Hardin

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