Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 211120

Area Forecast Discussion
National Weather Service Tucson AZ
420 AM MST Wed Mar 21 2018

.SYNOPSIS...Expect a strong warming trend into Thursday when near
record temperatures will occur, especially from Tucson eastward. A
weather system will then bring a slight chance of showers Friday
north of Tucson. Cooler temperatures and gusty winds will also
occur. Dry conditions will prevail Saturday through Monday, then a
slight chance exists next Tuesday across the White Mountains. High
temperatures will cool below seasonal normals early next week.


.DISCUSSION...A broad upper ridge was over the western CONUS early
this morning with the ridge axis extending from southern California
northward into Idaho. A deepening upper trough was also west of the
Pacific Northwest coast and extended southwestward to near 30N/140W.
The upper ridge axis will move eastward across southeast Arizona
today, and continue eastward across the Rockies Thursday. Meanwhile,
the upper trough will continue to deepen closer to the California

Dry conditions will continue into Thursday along with increasing mid
and high-level clouds. A strong warming trend will also occur, with
forecast high temps Thursday approaching or perhaps exceeding record
values particularly from Tucson eastward to the New Mexico state
line. Fairly strong southwesterly flow aloft Thursday night is
progged to veer toward more westerly flow Friday. The 21/00Z
deterministic GFS/ECMWF/CMC trended the area of model-generated
liquid precip amounts somewhat further north and away from this
forecast area versus solutions of 24 hours or longer ago.

Thus, have opted for dry conditions area-wide Thursday night. Per
coordination with neighboring WFO`s, have maintained a slight chance
of showers Friday morning from south central Pinal County
northeastward to the White Mountains with dry conditions elsewhere.
A slight chance of showers continues Friday afternoon across the
White Mountains, then dry conditions area-wide Friday night.

The upper flow Saturday will become southwesterly again as the next
upper trough deepens adjacent the West Coast. The GFS/ECMWF were
fairly similar with depicting a 531-535 dm low Saturday afternoon to
be centered just west of the northern California coast. The GFS/
ECMWF then depict a digging upper trough Sunday over the Great
Basin. This upper trough is progged to deepen further over the
southwestern CONUS, and a 549-550 dm upper low depicted via the
GFS/ECMWF to be centered near Las Vegas, Nevada midday next Tuesday.

For this forecast issuance and per coordination with neighboring
WFO`s, have maintained dry conditions area-wide Saturday through
Monday night. A slight chance of rain/snow showers then exists
across the White Mountains next Tuesday with dry conditions
elsewhere. These solutions suggest a somewhat better for more
widespread valley rain/mountain snow showers next Tuesday night and
Wednesday. However, this period is beyond the scope of this forecast

A pronounced cooling trend is on tap Friday into early next week. At
this time appears that high temperature next Monday and Tuesday will
generally be about 15-20 degrees cooler versus Thursday`s
unseasonably warm temperatures.


.AVIATION...Valid through 22/12Z.
SCT-BKN clouds above 20k ft AGL will remain through the forecast
period. Light and variable surface winds this morning settle WLY-
NWLY this afternoon, holding predominantly below 10 kts. Aviation
discussion not updated for TAF amendments.


.FIRE WEATHER...Temperatures continue to climb today and by
Thursday, highs should reach near record heat across a large portion
of southeast Arizona. However, a passing weather system knocks
temperatures back down on Friday with a slight chance for showers
developing north of Tucson. Winds become breezy Thursday with a
general westerly component that picks up each afternoon into Monday
next week, especially for areas east of Tucson. By late Tuesday,
another developing system reintroduces the slight chance for showers
along the White Mountains.






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