Area forecast discussion
National Weather Service Salt Lake City Utah
830 PM MDT Tuesday may 21 2013
Synopsis...a low pressure system will remain over the Pacific
northwest through this week...keeping most of Utah and southwest
Wyoming in a dry southwest flow. A weak cold front will stall
across far northern and western Utah through the middle of the
week.
&&
Discussion...water vapor loop shows ridging quickly shifting to our
east with a large Pacific storm moving ashore. Acars 400-250mb wind
observations show a 60-105kt cyclonically curved jet over the
Pacific northwest...and a 50-75kt anticyclonic jet over the region.
Rap...GOES...GPS sensors...and 00z slc radiosonde observation indicate precipitable
water values in the 0.25"-0.80" range across the region.
Regional radar indicates that dry showers are affecting the west
desert as divergence aloft increases from west to east. Based on 00z
sounding...this activity poses more of a gusty wind threat than
measurable precipitation. Updated probability of precipitation to remove mention for the
Uinta Mountains and expand mention across the west.
Updated winds to reflect increasing gusty winds due to upstream
convective activity spreading into the Wasatch front overnight. This
is shown by both the hrrr-3km and local 4km WRF-arw.
Also slightly adjusted sky grids based on infrared satellite trends.
Otherwise very minor changes to temperatures overnight. Rest
unchanged.
Previous discussion follows...
a deepening trough continues to move inland over
the Pacific northwest this afternoon...leaving Utah and southwest
Wyoming in a warm southwest flow south and east of this trough.
Middle and high level clouds have moved into the County Warning Area out ahead of
this trough...helping keep afternoon temperatures a few degrees
cooler than they might otherwise be with the warming airmass and
southwest winds. Despite this additional moisture...conditions are
fairly stable across the area...with radar only picking up very
isolated light showers over northern Utah.
The combination of clouds and southwest winds will lead to a warm
evening...and overnight minimum temperatures should also be warmer
than climatological normals...despite most clouds forecast to
clear out after midnight. The afternoon maximum temperature forecast for
Wednesday is a tricky one across the northern third of the
County Warning Area...as a cold front associated with the aforementioned trough
will move into northwest Utah starting Wednesday morning. The GFS
and European model (ecmwf) have the front stalling right around Salt Lake City
through the afternoon. The NAM is more progressive with the cold
air...and therefore produces maximum temperatures 10-15 degrees fahrenheit
colder than the global models across much of the Wasatch front.
The current forecast is a bit of a compromise...though tilted
moreso toward the warmer solution of the global models. In the
southern and eastern portions of the state...another
dry...warm...and windy day will be in store for most locations.
The front is forecast to weaken but remain relatively stationary
through the day Thursday...keeping the northern and eastern
portions of the County Warning Area near climatological normals Thursday
afternoon. The cooler air then looks to push into the rest of the
County Warning Area in earnest on Thursday evening...as the southern lobe of the
low...still spinning over the Pacific northwest...swings through the
Great Basin. Throughout this entire period...the southern two
thirds of the County Warning Area keeps a dry airmass in place...while isolated
convection at best is expected across the northern third.
Any cooling from Thursday evening is short-lived...as warmer
southwesterly flow is forecast to return by Friday afternoon...and
remains in place through Saturday. The GFS and European model (ecmwf) begin to
diverge after Saturday in how they break down the Pacific trough.
The GFS drops another trough on the backside of the low...then
swings that trough through the Great Basin beginning Sunday. The
European model (ecmwf) keeps the storm track further north...leading to warmer and
drier conditions for the extended. For now...have kept the
forecast mostly aligned with the warmer ec solution.
&&
Aviation...the slc terminal will see VFR conditions through the taf
period. Moderate southeast winds will persist into late morning
Wednesday...with a good chance of gusts beginning 16-17z.
&&
Fire weather...high pressure aloft moves east through the eastern
Great Basin and will exit the area this evening. Behind the high
pressure an increasingly strong southwest flow will develop ahead
of the low pressure system settling into the Pacific northwest
this evening. Warm and breezy conditions will develop across the
western half of the state Wednesday ahead of the first of two cold
fronts moving through northern Utah Wednesday and Thursday. The
first front will be quite weak and should offer up little more
than a few showers and slightly cooler temperatures Wednesday. The second
front will produce a more substantial cooling across the northern
third of the state along with a little better threat of
showers/isolated thunderstorms. Southern Utah will see little in
the way of cooling and precipitation from these fronts...and will remain
breezy...warm and dry heading into the end of the week. Will not
be issuing any fire weather highlights this afternoon as fuels are
still not in the critical moisture range.
&&
Slc watches/warnings/advisories...
Utah...none.
Wyoming...none.
&&
$$
Public...rogowski/schoening
fire weather...Conger
aviation...verzella
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visit...
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