Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
244 PM MDT Friday Aug 1 2014
Synopsis...high pressure aloft will strengthen across the
interior west over the first half of the upcoming weekend. A
stronger and significantly moister weather disturbance will lift
north through the Great Basin and impact much of Utah Sunday
through early next week.
Discussion...a ridge of high pressure remains centered over the
Great Basin this afternoon...with a somewhat moist airmass trapped
underneath it...as precipitable water values over Utah and
southwest Wyoming are hovering between 0.8 and 1.0 inches.
Showers and thunderstorms are initiating off the higher terrain of
central and southern Utah yet again this afternoon...with some of
these storms producing heavy rainfall. With relatively little
synoptic scale forcing...these storms are generally expected to
dissipate around sunset. One possible exception is in southwest
Utah...where the hrrr is producing scattered thunderstorms between
02z and 07z. That said...have kept probability of precipitation there in the slight chance
category after 00z Saturday...as the hrrr has been overdoing
convection some today.
Saturday should be fairly similar to today with the ridge
overhead...and should be the warmest day of the week in most
locations. Some additional convection is possible along the Nevada
and Arizona borders...but the best moisture should remain south
of the County Warning Area through 00z Sunday.
Models are still promoting a good shortwave trough moving through
the Great Basin on Sunday and Monday...with an impressive moisture
surge increasing precipitable water values to above an inch across much of the
region. Kept probability of precipitation and quantitative precipitation forecast values high for Sunday through
Tuesday...with significantly cooler temperatures. One concern
could be the possibility that the best forcing stays over
Nevada as shown in the 12z GFS...bringing Utah cloud cover but
less rain than expected...but most depictions over the past few
shifts have had a near direct hit for much of the County Warning Area.
The shortwave looks to push north and east of the area late
Tuesday or early Wednesday. Both global models keep the western
Continental U.S. Fairly active in the extended...so the forecast challenge
is timing the next major shortwave to pass through the County Warning Area. As of
the 12z runs...both the GFS and European model (ecmwf) have a trough moving through
the Great Basin on Thursday and Friday...so have elevated probability of precipitation
through this period...especially in the northern half of the
forecast area. Have also lowered temperatures a bit in the extended due
to the possibility of increased cloud cover most days in northern
Aviation...north winds will prevail at the slc terminal through 03-
04z before switching to the south. Otherwise...VFR conditions are
expected throughout the valid taf period.
Fire weather...high pressure aloft will remain across the region
into the day Saturday maintaining light winds...within lingering
moisture maintaining a threat for showers and thunderstorms mainly
over the higher terrain. A strong surge of monsoonal moisture will
spread north into southern Utah late Saturday though Sunday...then
northward across the remainder of the area Sunday night through
Monday. This surge of moisture will bring showers and thunderstorms
capable of producing heavy rainfall. Moisture will linger through
much of next week maintaining cooler temperatures...higher humidity
and a threat for showers and thunderstorms.
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