Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
1016 am MDT Friday Jul 31 2015
Synopsis...a ridge of high pressure will remain over the region
through Saturday...then shift eastward Sunday. An upper level
disturbance will cross the region Sunday and Sunday night.
Moisture will remain limited to southern Utah through
Saturday...then spread northward on Sunday.
Discussion...ridge axis remains oriented northwest to southeast
over the forecast area this morning...resulting in light flow
aloft. An area of moisture remains over southern Utah...with
satellite derived precipitable waters of 0.8 to 1.0 inch as far north as I-70.
Seeing some high and middle level cloudiness in association with this
moisture...and the possibility of isolated convection remains for
this afternoon and evening. However...given that most of this
moisture is at higher levels am not expecting much precipitation to hit
the ground. Updated the forecast earlier to expand slight chance
probability of precipitation a bit farther north this afternoon. No additional updates
By Saturday...the trough centered off the California coast near
130w is prognosticated to lift northward. This will shift the orientation
of the ridge axis eastward...allowing a more southwesterly flow to
develop over the forecast area by Saturday afternoon. This will
allow the moist airmass over southern Utah to spread northward.
Combined with a vorticity maximum that is expected to move up into the
Great Basin Sunday...coverage of showers and thunderstorms should
increase noticeably. Ec continues to remain more bullish with the
moisture surge and may be overdone. The passage of the wave is
expected to move the ridge eastward...resulting in a drier
westerly flow developing for the beginning of the work week.
Aviation...the slc terminal will see VFR conditions throughout
the day with mostly clear skies. Light winds are expected to
become prevailing northwesterly by 18z.
Fire weather...moisture has made little progress northward into
southern Utah during the past 12-18 hours as it continues to skirt
westward along the Arizona-Utah border. This moisture which is mainly
at high levels is expected to remain over the southern portions of
Utah today and only creep a little farther northward Saturday. There
is no organized feature to help generate convection so expect
isolated dry thunderstorms with gusty erratic winds to be the
main threat from about zone 496 southward today and possibly
spread northward into fire zones 495 and 493 Saturday.
A disturbance is expected to move northward across the fire
district Sunday bringing the best chance for convection but
because forecast models continue to show somewhat of a dry sub
cloud layer the chance for wetting rains will be minimal at best.
Therefore be alert for the possibility of dry thunderstorms
continuing through Sunday. In the wake of this Sunday
disturbance...a drier southwest flow is expected to develop Monday
through Wednesday with breezy southwest winds possible Tuesday and
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