Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 191658

Area Forecast Discussion
National Weather Service Tucson AZ
958 AM MST Mon Mar 19 2018

.SYNOPSIS...High pressure will bring a strong warming trend the
first half of the week. Another system will brush by mainly north of
the area later in the week for a few degrees of cooling and gusty
winds, with the best chance of showers remaining north of the


.DISCUSSION...A cool morning with below average overnight lows,
but the 12Z KTWC sounding tells the story with 6 to 7 degrees of
warming working it`s way down the temperature column. The
deepening boundary layer will easily mix this to the surface this
afternoon, and is handled well by the current forecast. Pretty dry
as a ridge builds in from the west, with precipitable water
measured at 1/4 of an inch and surface dew points in the teens and
20s (down 10 to 15 degrees over the past 24 hours). No updates
this morning with fairly typical transition season weather in
store. Please see sections below for additional details.


.AVIATION...Valid through 20/18Z.
SCT cloud layers above 15k ft AGL. SFC winds this morning
variable less than 10 kts, becoming WLY/NWLY 8-15 kts this
afternoon, diminishing to less than 10 kts this evening.

Aviation discussion not updated for TAF amendments.


.FIRE WEATHER...Dry with a warming trend through Thursday. A Pacific
storm system will bring a slight chance of showers mainly north of
Tucson Thursday night into Friday, as well as cooler temperatures on
Friday. Highs next weekend will be at or slightly above normal. 20-
foot winds will mainly be less than 15 mph today into Wednesday.
Some gusty southwest afternoon winds Thursday into Saturday.


.CLIMATE...A strong ridge of high pressure aloft by mid-week will
bring record or near record highs on Thursday for portions of
southeast Arizona. Not everyone will be near record highs. However,
the Tucson International Airport forecast high temperature of 89
degrees for Thursday, March 22, is within one degree of the record
high of 90 degrees set in 1990. The historical average first 90
degree date of the year in Tucson is April 9. The average date since
1980 has been April 1 while in the 21st century the average first 90
degree occurrence has been March 25.


.PREV DISCUSSION...Upper ridge axis was just west of the
California coast early this morning. Meanwhile, a deep upper low
pressure system was further west of the ridge axis, or centered
near 34N/140W. The upper ridge will move eastward into the
southwestern CONUS by Wednesday as the upper low phases with a
deep trough closer to the Pacific Northwest coast. This pattern
will yield dry conditions across southeast Arizona, as well as
varying amounts of cirriform clouds, and a strong warming trend.

The upper ridge axis is progged via the 19/00Z GFS/ECMWF/CMC to move
east of the area Thursday as a trough deepens close to the
California coast. These solutions depict measurable precip to be
well west to northwest of this forecast area, or generally across
much of California northeastward into the Great Basin. Per
coordination with neighboring WFO`s, have opted for continued precip-
free conditions Thursday.

The models then depict deeper moisture associated with a shortwave
trough will move eastward across the Intermountain West and into the
central Rockies Thursday night and Friday. These solutions have
continued previous model depictions of trending the deeper moisture
gradually northward or away from this forecast area. This translates
into gradually reduced precip chances versus model solutions from
about 48 hours or longer ago.

At any rate, have opted for a slight chance of showers Thursday
night into Friday morning mainly west to north of Tucson. A slight
chance of showers continues Friday north to northeast of Tucson, and
especially across the White Mountains. At this time, appears that
snow levels will primarily remain above mountain tops. Dry
conditions will then prevail Friday night into next Sunday under
generally westerly flow aloft.

As mentioned earlier, a strong warming trend will exist through
Thursday which will likely be the warmest day during this forecast
period. Based on the 19/00Z guidance as well as local thickness
studies, have adjusted forecast highs Thursday upward either a few
to several degrees depending upon location. Forecast confidence is
quite high that the Tucson International Airport official high
temp will be quite close to a record high temp for March 22. Please
refer to the climate section for additional detail. Cooler temps
will occur Friday followed by very little daily high temp changes
Saturday and Sunday.






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