Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Tucson Arizona
210 PM MST Tuesday Sep 23 2014
Synopsis...limited coverage of showers and thunderstorms today and
Wednesday...mainly near the mountains. The chances for showers and
thunderstorms will then increase Thursday through Saturday as a
front approaches the area from the northwest. Much drier and several
degrees cooler late this weekend into early next week.
Discussion...still decent moisture out there for late September
with 1.1 to 1.3 inches precipitable water...but the 12z sounding was
showing almost no flow and weak potential storm structure away from
terrain influences. As expected we have seen some mountain
thunderstorms with little inclination to move much. Coverage in
valley locations will be spotty at best and non existent in the
drier western areas. We will probably see a few mountain storms
around the area again Wednesday afternoon.
Nice early season trough for the weekend. Very strong low off the
coast of British Columbia will see several reinforcing pieces of
energy digging down the back side and deepening the trough down the
coast over the next 48 hours. As this is evolving...we should see a
modest moisture surge early Thursday assisted by thermal influences
and tropical activity but no direct tropical influence. Better
moisture Friday as we see deepening of a temporary southerly fetch
as the base of the trough digs and sharpens into the basin northwest
of our area.
Could see a few strong storms Saturday ahead of and with the trough
as decaying southern portion of frontal boundary will enhance shower
and thunderstorm activity...but best moisture/dynamics couplet will
be through northern and central Arizona. Several degrees of cooling
and drier behind the trough by late Sunday into Monday.
Aviation...valid through 25/00z.
Expect isolated rain showers/thunderstorms and rain from ktus eastward until 24/04z. Storms
will exhibit very slow movement and may have trouble moving off the
mountains. Thunderstorms and rain coverage will be less Wednesday and mainly east of a
line from ksad to kfhu. Surface wind generally less than 10 kts.
Aviation discussion not updated for taf amendments.
Fire weather...there is a slight chance of showers and
thunderstorms into this evening from Tucson eastward and mainly over
the mountains. On Wednesday...any storms that do develop should be
confined to mountains near the New Mexico border. Increasing chances
for showers and thunderstorms will then occur Thursday through
Saturday followed much drier conditions early next week. Brief gusty
outflows will occur with the stronger thunderstorms.
Otherwise...20-foot winds will generally be less than 15 miles per hour through
Friday but southwest winds closer to 20 miles per hour are forecast during the
afternoons this weekend as an upper trough influences Southeast Arizona weather.
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