Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 211045

Area Forecast Discussion
National Weather Service Tucson AZ
345 AM MST Wed Feb 21 2018

.SYNOPSIS...Below normal daytime temperatures will continue across
southeast Arizona into this weekend as a series of weak storm
systems move across the region. The next chance for rainfall will
occur Friday and Friday night, mainly north and east of Tucson.


.DISCUSSION...IR satellite imagery revealed mostly clear skies from
Tucson westward with partly cloudy skies to the east this morning. A
cooler and drier regime was in place at the surface, with
temperatures 6 to 12 degrees cooler and dewpoints down up to 10
degrees compared to 24 hours ago. The overall weather pattern was
defined by broad troughing across the western CONUS with ridging
along the eastern seaboard. Not much variation to this pattern is
expected over the next several days as troughing across the western
states will generally remain the rule. However, a series of quick-
hitting disturbances of differing strengths will move through the
region into next week. Since these storms are expected to pass
through fairly quickly, deeper moisture and therefore widespread
heavy rainfall is not anticipated.

The first system is forecast to move across Arizona today into
tomorrow. Continued low heights and thicknesses will allow
temperatures to remain quite cool CWA-wide and shallow moisture will
restrict slight chances of snow showers to across the White
Mountains tonight and early Thursday. Additionally, some elevated
southwest winds are likely mainly across Cochise County both today
and Thursday afternoons.

We`ll see a better chance for rainfall to include Tucson Friday and
Friday night as a slightly stronger upper trough develops across the
Great Basin and moves toward the Four Corners region. Expect another
round of gusty west to southwest winds especially Friday afternoon
ahead of valley rain and mountain snow showers developing Friday
evening into Saturday morning. The 21/00z GFS has backed off on
precip a bit compared to previous runs, so opted to limit PoPs to
slight chances mainly from Tucson northward and eastward except for
the White Mountains. Not much change in temperatures yet again, with
daytime highs holding steady around 8 to 12 degrees below normal
Friday and Saturday.

A third shortwave will blast through the Four Corners Sunday into
Monday with little impact on the southeast portion of the state as
of right now. A brief period of shortwave ridging is then expected
to follow, with temperatures rebounding to near-normal values for
Monday and Tuesday. The warm up may be short-lived though, as there
are hints that the active period will continue with another storm
system by the middle of next week. Confidence is low on this
occurrence at the current time as there remains ample disparity
between deterministic model solutions.


.AVIATION...Valid thru 22/12Z.
SCT-BKN clouds at 4k-8k ft AGL mainly east of KTUS thru 21/18Z. Aft
21/18Z, SCT-BKN clouds AOA 15k ft AGL overspreading the area from
west to east. Surface wind less than 12 kts til 21/19Z and then
again aft 22/03Z. Between 21/19Z and 22/03Z, SLY/SWLY surface wind
at 10-15 kts with some gusts to near 25 kts. Aviation discussion not
updated for TAF amendments.


.FIRE WEATHER... A series of storm systems will move across the
western United States through next week. The main bulk of these
systems will stay north of the area, although each will bring some
gusty winds to southeast Arizona, as well as a slight chance of
valley rain showers and mountain snow showers to areas mainly
northeast of Tucson. The first system will impact the White
Mountains tonight into early Thursday. The next system will occur
Friday into Saturday. Yet another system is slated for Tuesday into
Wednesday of next week. Some gusty 20-ft south to southwest winds
will occur this afternoon especially over eastern areas, with even
stronger southwest to west winds areawide on Friday. Otherwise, 20-
ft winds will generally be less than 15 mph into early next week.






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