Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Salt Lake City Utah
338 PM MDT Friday Oct 31 2014
Synopsis...a mild and increasingly strong southerly flow will
remain over the area through early Saturday. A vigorous Pacific
storm system will reach Utah Saturday. Cool and unsettled weather
will remain over the area Saturday night through early Monday.
Short term (through 12z monday)...
water vapor loop shows the ridge shifting east of The Rockies as
a trough develops along the West Coast. A weakening southern
Pacific system is currently lifting overhead. Amdar 400-250mb wind
observations reveal a cyclonic 100-135kt jet off the Pacific
northwest. GOES/GPS/rap/12z radiosonde observation indicate the precipitable water
value ranges between 0.15" mountains...to 0.40" valleys.
Thermal ridge in place ahead of the approaching cold front. Utilized
lamp guidance to aid temperature trend overnight...with forecast
lows overnight expected to be well above MOS guidance.
Southerly winds increase overnight in favored nocturnal areas
(western valleys...benches and mountains) in response to pressure
and height falls ahead of the trough. Modestly strong southeasterly
pressure gradient and southerly 700mb flow increasing to 40-50kt as
shown by the rap. This is the main reason wind and winter highlights
start at midnight.
Several cold frontal surges are expected in the short term. The
primary boundary propagates southwest to northeast across Utah
tomorrow. With and behind the cold front...expect strongest winds as
gradient will shift from the southwest coincident with good mixing
and 700mb flow remaining elevated. Strongest winds expected across
northwest Utah midday tomorrow through the afternoon as the northern
piece of the trough pivots overhead.
European coming into agreement with the GFS that a second cold front
moves into northern Utah from the northwest late Saturday night into
Sunday. This cold advection looks to provide more of a typical
distribution of light precipitation across the northern mountains
and benches due to orographics and building instability. Lake
enhancement possible Sunday with the water temperature near
+14c...though model thermal profiles adjusted for the lake in BUFKIT
indicate warming aloft may limit lake effect later Sunday night into
Synoptic thermal profiles and dynamics best support thunder during
the daytime Saturday. However if the Great Salt Lake contributes
more activity than currently anticipated...thunder will be possible
downstream of the lake Sunday into Sunday night.
Southern Utah becomes active again later Saturday night and Sunday
as the southern piece of the approaching trough begins to split
southwest. Jet dynamics should be in play here so show an increase
in areal extent of precipitation. With the surface boundary slowing
its southeastern progress...this feature may also present a focus
for precipitation during the second half of the weekend.
Long term (after 12z monday)...
the trough looks like it finally exits the forecast area during
the day Monday. Some lingering showers are expected Monday
morning...primarily over the higher terrain...but should decrease
in coverage during the afternoon hours.
Behind the exiting system...high pressure is prognosticated to return
beginning Monday night. The building ridge will result in dry
conditions with a steady warming trend in temperatures through
Thursday. Latest European model (ecmwf) indicates a system moving north of the area
that would bring a dry front into northern Utah...cooling
temperatures down just a bit. However...the GFS keeps high pressure
strongly over the area through next week.
Aviation...the slc terminal will see VFR conditions through the
evening with increasing high and middle level clouds. Winds will be
southerly through the overnight hours...with occasional gusts to or
above 30 miles per hour during the late afternoon and early evening.
Utah...Winter Weather Advisory from midnight tonight to 10 PM MDT
Saturday for utz007>010-517-518.
Wind Advisory from midnight tonight to 10 PM MDT Saturday for
High Wind Warning from midnight tonight to 10 PM MDT Saturday
For more information from National oceanic and atmospheric administration/S National Weather Service visit...
http://weather.Gov/saltlakecity (all lower case)
For frequently asked questions about the area forecast discussion
http://weather.Gov/saltlakecity/general/afd_faqs.Php (all lower case)