Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 251028
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
328 AM MST Sun Feb 25 2018

.SYNOPSIS...A cool and dry weekend with a brief warming trend early
in the new week. A stronger winter storm system will pass through
the region later Tuesday into Wednesday. bringing a good chance
of valley rain and mountain snow. Dry and warmer to end the week.

&&

.DISCUSSION...We`re seeing a dry westerly flow overhead at the
base of a broad regional trough. Another impulse will push through
north of our area today. As for SE AZ, after a chilly morning
we`ll see another day with below average temperatures and plenty
of sunshine.

Our next weather maker is currently near northwest British
Columbia. Our current pattern gives this feature a clear shot to
dive quickly into the back of the large scale mean trough
position; carving back a little further westward as it does with
the positive orientation of the ridge in the eastern Pacific.

With a well defined pattern in place, we continue to see very
good operational and ensemble mean model agreement with this
storm. Trajectory and timing are holding well with the storm
bottoming out over southern California Tuesday morning before
kicking eastward and through Arizona Tuesday night into Wednesday.
We continue to have high confidences in increasing valley rain
and mountain snow chances, with late Tuesday night into early
Wednesday morning prime time for much of SE AZ. Valley rain
amounts between .1 and .25 inches, with mountain snow between 2
and 5 inches. Snow levels around 6k feet Tuesday evening,
bottoming out around 3500 feet Wednesday morning behind the front.
We could see some snow or rain/snow mix in Cochise county
valleys, but we`ll already be seeing drier air wrap into the
system through our area as this occurs. Thus, little or no
accumulation expected at lower elevations.

The cool air will knock temps back to around 15 degrees below
average Wednesday, with a shortwave ridge bringing a rapid warming
trend to end the new week. Another system should impact much of
the west next weekend, but may end up being a little too far north
to do much for our area.

&&

.AVIATION...Valid thru 26/12Z.
SKC conditions through the forecast period. SFC winds mainly less
than 12 kts through the forecast period, though a NWLY component
will develop this afternoon. Aviation discussion not updated for TAF
amendments.

&&

.FIRE WEATHER...Dry conditions will prevail through Monday night.
Scattered valley rain and mountain snow showers will over spread the
region from west to east Tuesday morning. The best chances of
precipitation will occur Tuesday night, with precip exiting to the
north and east Wednesday. Dry conditions will then occur into next
weekend. Expect west to southwest 20-ft winds Monday and especially
Tuesday around 15 to 25 mph. Elevated northwest winds will then
occur on Wednesday. Otherwise, winds will generally be terrain
driven at less than 15 mph through next Saturday.

&&

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

&&

$$

Meyer/Carpenter

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