Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 200450
AFDTWC

Area Forecast Discussion
National Weather Service Tucson AZ
950 PM MST Sun Feb 19 2017

.SYNOPSIS...Isolated valley rain and mountain snow showers ending
tonight. Dry conditions will prevail through next Saturday except
for a few snow showers near the White Mountains Thursday. A strong
warming trend will also occur through Wednesday before cooler
temperatures return late this week. The next system will then bring
a slight chance of valley rain and mountain snow early next week.

&&

.DISCUSSION...A few showers lingering mostly across eastern and
southern portions of the Tucson metro area at this time. Otherwise,
mostly cloudy skies prevailed across southeast Arizona, with low-
level clouds most sections. However, cirriform clouds were noted
across western Pima County.

20/00Z NAM/GFS and several HRRR solutions were similar with
maintaining a few valley rain and higher elevation snow showers
through much of the rest of tonight. Any rainfall amounts or snow
accumulations will be quite minimal, however. The official forecast
was updated to include patchy fog through about 15Z Monday for
locales south-to-southeast of Tucson. Expect clouds to very
gradually erode into Monday, then mostly clear skies should prevail
Monday evening. Warmer temperatures are on tap Monday followed by
additional daily warming Tuesday into Wednesday.

Please refer to the additional sections for further detail.

&&

.AVIATION...Valid through 21/06Z.
Isolated -SHRA and mountain -SHSN ending tonight. Otherwise, cloud
decks mostly 4k-8k ft AGL into Monday morning, then decreasing
clouds Monday afternoon. A FEW-SCT clouds around 6k-10k ft AGL
Monday evening. Patchy fog late tonight through about 15Z Monday
especially vicinity KOLS. Surface wind variable in direction less
than 12 kts. Aviation discussion not updated for TAF amendments.

&&

.FIRE WEATHER...Scattered showers will come to an end tonight with
dry and warmer weather returning Monday through Wednesday. A storm
system passing across northern Arizona will bring breezy conditions
late Wednesday through Thursday with cooler temperatures Thursday
onward. There is a slight chance of snow showers across the White
Mountains Thursday. Seasonal conditions return Friday and Saturday.
Another weather system will bring a slight chance of valley rain and
mountain snow showers early next week.

&&

.PREV DISCUSSION /235 PM MST/...Partly sunny to mostly cloudy
conditions this afternoon across the CWA with scattered valley rain
and mountain snow showers. Cool surface temperatures as of 19/21z
with values around 7 to 10 degs below normal. WSW products continue
to be in effect until 20/00z this evening for elevations above 7500
ft as some of the remaining precip could produce an additional
couple inches of snowfall this afternoon. Additional liquid amounts
will generally remain less than 0.15".

This storm system will continue to lift off to the northeast
overnight into Monday. We will see precip dwindle this evening and
end from southwest to northeast, with dry conditions occurring
tomorrow. Strong ridging setting up behind the low will cue a sharp
warming trend into Tuesday and Wednesday, when daytime high temps
will reach 7 to 10 degs above normal. Thereafter, models continue to
show varying forms of a shortwave trough digging south out of the
Pac NW and through the Great Basin. The latest operational solutions
indicate just a glancing blow for southeast AZ, as the trough axis
passes through the northern half of the state Wednesday night into
Thursday. With a tight pressure gradient aloft, expect to have some
gusty west winds Thursday afternoon, especially near the AZ/NM
border. Have also opted to continue with a slight chance for a rain
or snow shower across the White Mountains Wednesday night and
Thursday.

That system is a quick one, and will be out of here Thursday night.
Zonal flow sets up Friday into Saturday with daytime temps hovering
within a couple degrees of normal. In the extended, there are early
indications of another disturbance pushing through the region Sunday
and Monday. However, significant differences remain in timing and
intensity between the GFS/ECMWF, with the GFS stronger/wetter and
the ECMWF almost totally dry. Another situation where we will have
to wait and see what subsequent model runs have to say, but for now
have included at least a slight chance of precip for most areas
Sunday and Sunday night.

&&

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

&&

$$

DISCUSSION...Francis
PREV DISCUSSION...French

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