Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 220256

Area Forecast Discussion
National Weather Service Tucson AZ
756 PM MST Wed Feb 21 2018

.SYNOPSIS...A passing system will bring gusty winds Friday with a
slight chance of showers north of Tucson. Otherwise, dry conditions
with below normal temperatures through Sunday. A warming trend will
occur early next week, then another system will bring a slight
chance of showers to much of the area next Wednesday.


.DISCUSSION...Latest models continued to indicate a few showers in
the White Mountains tonight as a disturbance passes through the
region. This scenario looked reasonable as regional radars were
detecting some light showers across the eastern Rim into the White
Mountains this evening. Models track this disturbance east of the
area tomorrow morning with another one lined up in its wake. Current
forecast looked on track so no updates necessary at this time.
Please refer to the additional sections for more details.


.AVIATION...Valid thru 23/06Z.
A few -SHSN may occur near the White Mountains northeast of KSAD
tonight. Otherwise, expect a few to occasionally broken clouds at 5k-
9k ft AGL and broken clouds mainly above 15k ft AGL tonight. Clouds
to decrease from west to east late tonight/early Thursday morning,
then mainly few to scattered clouds above 10k ft AGL Thursday
afternoon. Surface wind Thursday afternoon swly/ sly 8-16 kts with
gusts near 25 kts. Surface wind variable in direction mainly less
than 10 kts at other times. Aviation discussion not updated for TAF


.FIRE WEATHER...Dry conditions continuing through Thursday. A
weather system will bring a slight chance of showers north to
northeast of Tucson Friday afternoon and Friday night. Dry
conditions will then prevail Saturday into Tuesday. A stronger
system may bring at least a slight chance of showers to much of the
area next Wednesday. Expect gusty southwest to northwest winds
Friday afternoon and evening, as well as next Wednesday. Otherwise,
20-foot winds will generally be less than 15 mph.


.PREV DISCUSSION...A highly amplified upper pattern continues this
afternoon with strong high pressure aloft centered well west of the
Pacific Northwest near 45N/150W, and a strong upper high just east
of the eastern seaboard. Between these systems, a deep upper trough
was over the western CONUS. A series of disturbances embedded within
the upper trough will bring a couple of precipitation chances and
gusty winds at times this forecast period, or through next Wednesday.

A digging system remains progged to move southeast across the Great
Basin Friday, then eastward into the Four Corners region Friday
night. The 21/12Z NAM12 and GFS have trended downward on precip
chances associated with this system, and the official forecast was
adjusted accordingly.

Thus, a slight chance of showers exists from southern Pinal County
northeastward to the White Mountains Friday afternoon and evening
with dry conditions elsewhere. A few lingering snow showers may
continue late Friday night across the White Mountains. A tight mid-
level gradient will support gusty southwest to west winds across
much of the area Friday afternoon. Winds will decrease starting
Friday evening as the mid-level trough axis moves east of the area.
Expect less wind Saturday as dry conditions commence, then dry
conditions will prevail Sunday through Monday.

Thereafter, the focus of attention will likely turn toward a
potentially deeper/stronger upper low that is progged via the 21/12Z
and 21/18Z GFS to be centered midday Tuesday near the central
California Coast. This system is progged to remain progressive but
eventually fill while moving eastward into the southwestern CONUS
next Wednesday. Still appears that dry conditions will continue
Tuesday, then have opted for a slight chance of showers across much
of the area next Wednesday. Although next Wednesday is at the end of
this forecast period, forecast confidence regarding precip detail is
low at this time. However, this appears to be a system to be

Daytime temperatures Thursday through Sunday will remain generally
10-15 degrees or so below normal. A warming trend is on tap Sunday
into Tuesday, and high temps Tuesday should be quite close to
seasonal normals. Cooler temps likely next Wednesday associated with
the aforementioned deeper upper system.





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