Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 050431

Area Forecast Discussion
National Weather Service Tucson AZ
930 PM MST Mon Dec 4 2017

.SYNOPSIS...A weather system will bring increasing cloudiness
through Wednesday along with a few showers, mainly in the mountains,
Tuesday afternoon into Wednesday. Dry conditions will return
Thursday into the weekend. Near normal daytime temperatures can be
anticipated through Friday with warmer temperatures this weekend.


.DISCUSSION...Satellite imagery this evening showed high cloudiness
continuing to stream across the area. This high cloud cover extends
to off the northern Baja CA where more mid-level clouds cover exits.
Precipitable water values across the area around the 0.50" to 0.60"
range with higher values over 0.75" over the northern Gulf of
California, which is captured by the 00z models. Some of this higher
PW is forecast to move across the area overnight into the Tuesday.
Now all we need is an upper level feature to work on this increase
in moisture and bring some light shower activity. And looking
upstream on the upper level charts there is an upper level trof that
extends from central NV to over the LA basin. Models are suggesting
that a weak upper level low will spin up in this trof axis during
the overnight hours as it moves to the east.

00z GFS a little aggressive in producing measurable rain north and
northeast of Tucson before sunrise while the 00z NAM/12z ECMWF and
12z Canadian hold off until after sunrise and mostly over the higher
terrain. With low levels still on the dry side, can see some very
light rain breaking out over the higher terrain Tuesday morning. As
this upper level low continues to move east across the state and the
atmosphere continues to moisten up from top down, expect isolated to
scattered showers late Tuesday afternoon into Wednesday morning,
mainly from Tucson east. Snow levels will remain rather high, above
8500 feet, and since we`ve been in this extended warm period, not
much will stick. Will run out a quick update for the overnight
period and Tuesday.


.AVIATION...Valid thru 06/00Z.
SCT-BKN clouds above 20k ft AGL through the period with gradual
lowering of mid level clouds after 05/15z. Isold -SHRA psbl NE of
KTUS after 05/15z. SFC winds will follow diurnal trends through
Tuesday afternoon at less than 12 kts. Aviation discussion not
updated for TAF amendments.


.FIRE WEATHER...Dry conditions and light winds will persist through
Tuesday afternoon. A passing disturbance will bring a chance of
isolated to scattered showers to the White Mountains late Tuesday
morning and then expanding to areas from Tucson eastward Tuesday
night into Wednesday. Any rainfall accumulations will remain light
at less than one-tenth of an inch. Dry conditions will return for
the remainder of the week. Gusty east winds will develop Tuesday
night and continue through Saturday, with the strongest winds
occurring Thursday.





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