Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Tucson Arizona
255 PM MST Monday Sep 22 2014
Synopsis...expect reduced coverage of showers and thunderstorms by
midweek. The chances for showers and thunderstorms will then
increase Thursday through Saturday followed by much drier
conditions early next week. A gradual warming trend will occur
through Wednesday followed by cooler temperatures this weekend.
Discussion...scattered showers and thunderstorms were occurring
east and south of Tucson at this time. Meanwhile...sunny skies
prevailed across western Pima County and south central Pinal County.
Moisture will remain sufficient for scattered showers/thunderstorms this
evening across Greenlee...Graham and Cochise counties. There is the
potential for locally heavy rainfall to occur with the stronger
thunderstorms. Isolated showers/thunderstorms will be possible this evening for the
Tucson metropolitan area and Santa Cruz County...and dry conditions will
continue further west across western/central Pima County. A slight
chance of showers/thunderstorms will continue late tonight mainly near the
New Mexico border with dry conditions elsewhere.
High pressure aloft centered over the northern Gulf of California Tuesday is
prognosticated to amplify over the southwestern Continental U.S. Wednesday. Warmer middle-level temperatures
in combination with decreased moisture will translate into markedly
reduced precipitation chances Tue-Wed. Isolated showers and thunderstorms
Wednesday afternoon/evening should only be confined to near the mountains
east and south of Tucson.
Lower and middle-level moisture is prognosticated to increase Thursday-Sat ahead
of a deepening upper trough over the western Continental U.S.. there remained some
differences between the 22/12z GFS/European model (ecmwf) regarding the evolution of
this trough by this weekend. Although the GFS continued to depict a
somewhat more-progressive system versus the European model (ecmwf)...these solutions
were actually fairly similar with the middle/upper level pattern and
associated quantitative precipitation forecast/S for this weekend.
At any rate...isolated showers/thunderstorms Thursday should increase to
scattered coverage of showers/thunderstorms by Sat. The presence of a
negatively-tilted trough axis and strong diffluence aloft may
enhance the potential for severe thunderstorms to occur Sat. Deeper moisture
is then prognosticated to be shunted eastward across much of New Mexico Sunday.
However...there should be enough residual moisture to maintain
isolated showers/thunderstorms sun mainly from Tucson eastward to the New
Mexico border. Thereafter...GFS/ECMWF were quite similar with
depicting a much drier westerly/northwesterly flow aloft regime. Thus...have opted
for precipitation-free conditions area-wide by Monday afternoon.
Expect a degree-or-two of daily warming Tue-Wed. Daytime temperatures will
then fall to below seasonal normals this weekend.
Aviation...valid through 24/00z.
Expect scattered -shra/-tsra from ktus vicinity east and south this
this evening. MVFR conditions and brief wind gusts to around 35 kts
will occur with the stronger thunderstorms. Isolated -shra/-tsra
will then be confined mainly near the New Mexico border late tonight
into Tuesday morning. Isolated -shra/-tsra will then prevail Tuesday
afternoon mainly near the higher terrain east of ktus to the New
Mexico border. Otherwise...surface wind will be mainly less than 10
kts through Tuesday afternoon. Aviation discussion not updated for taf
Fire weather...scattered showers and thunderstorms will occur
mainly from Tucson eastward and southward this evening. Drier
conditions will produce much less coverage of showers and
thunderstorms Tuesday and Wednesday. Increasing chances for showers
and thunderstorms will then prevail 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 this week.
Hydrology...pretty extensive area of rainfall this morning from
central Greenlee County east into western Grant County in New
Mexico. Doppler radar indicated that over two and a half inches had
fallen east of Clifton with a couple of gauges near and northwest of Virden
New Mexico recording between 1"-2". Runoff from these heavy rains
flowed into the San Francisco and Gila rivers this morning. As a
result...the Gila River near Clifton gauge...which is approximately
6 miles south of the town of Clifton...indicated a rise to 17.1 feet
earlier this morning with a flow of just under 11,000 cfs. Since
that time the stage has fallen to 8.96 feet as of 1 PM MST...with a
flow of just under 3000 cfs. This flow will continue down the Gila
River and will affect the Solomon...Safford and Pima areas this
afternoon and/or early this evening. As of 115 PM MST...the stage
was 12.9 feet...with a flow of nearly 9,000 cfs. As the water
continues to rise in the Solomon...Safford and Pima areas....some of
the approaches to bridges may be affected by the rising water.
Therefore...a hydrologic advisory in the form of a small stream
Flood Advisory was issued through 830 PM MST this evening. In
addition...water flowing through the Gila River in New Mexico toward
Arizona and is expected to result in a rise on the Gila at Duncan
with the crest occurring early Tuesday morning. However...it is
expected to crest a foot or so below bankfull.
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