Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Tucson Arizona
215 PM MST sun Jul 5 2015
Synopsis...Southeast Arizona will experience an upswing in showers
and thunderstorms today with locally heavy rainfall likely. Rain
chances will decrease as a low pressure system approaches central
California. Daytime temperatures will remain close to seasonal
Discussion...water vapor imagery and 05/12z upper-air plots show a
ridge centered over eastern New Mexico. Meanwhile...a Pacific low
pressure system is spinning well west of the Southern California
coast. A swath of dry middle to upper level air can be seen over the
eastern Pacific waters...the Baja California peninsula...northwestern Sonora
and across parts of Southern California and into western Arizona.
Meanwhile...visible and infrared satellite imagery and radar mosaic from
around the region show another mesoscale convective vortex that has developed as a result of
last nights convection...with the center of this feature just west
of Douglas in Cochise County.
Water vapor imagery shows a sharp demarcation between dry air to our
west and moist air to the east. In addition...this mornings ktwc
sounding revealed a precipitable water of 1.71 inches. The most recent satellite
derived blended total precipitable water imagery shows values of 1.4
inches over southwestern Arizona and 1.8 over the central part of my
forecast area...with values approaching 2 inches over the northern
Gulf of California. The thunderstorm activity fired along this
demarcation earlier today and the most recent radar mosaic show
scattered to numerous activity...mainly west of interstates 10 and
19 and south of Interstate 8. Radar rainfall estimates with these
storms have been quite healthy and with the high precipitable water value of this
mornings sounding...not to mention the latest satellite derived
estimates...it looks like heavy rain and the resultant stream
flooding/flooding of low lying areas will be the issue for the day.
The northern and eastern parts of the tohono o'odham nation is
currently taking the brunt of this heavy rain. A small stream Flood
Advisory has been issued to include central and western portions of
Pima County as well as southern portions of Pinal County until 345
PM MST. The 12z run of the u of a WRF/NAM seems to have captured the
ongoing radar scenario quite well.
After today...we should see a decrease in thunderstorm activity as
the upper low over the Pacific makes its way toward the West Coast
and eventually into the Great Basin by late in the work week. This
will result in southwesterly winds that will push moisture to the
Aviation...valid through 07/00z.
Scattered -tsra/-shra will occur this evening. Brief wind gusts of
30-40 kts may accompany the stronger thunderstorms and rain. Isolated to scattered
-tsra/-shra will then prevail late tonight into Monday morning.
Expect scattered coverage of -tsra/-shra Monday afternoon...with the
bulk of this precipitation to be from ktus eastward/southward to the
New Mexico/international borders. Otherwise...cloud decks will
mainly be at or above 6k feet above ground level and surface wind will generally be
less than 10 kts. Aviation discussion not updated for taf amendments.
Fire weather...scattered showers and thunderstorms will occur this
evening followed by isolated showers and thunderstorms late tonight
and Monday morning. Expect heavy rainfall and brief gusty winds
associated with the stronger thunderstorms. Scattered showers and
thunderstorms will return mainly from Tucson eastward and southward
Monday afternoon. Thereafter...somewhat reduced coverage of showers
and thunderstorms should prevail starting Tuesday and continuing
into next weekend. Otherwise...generally light terrain driven winds
will prevail outside of thunderstorm influences.
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