Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 281045
Area Forecast Discussion
National Weather Service Salt Lake City UT
445 AM MDT Tue Mar 28 2017
.SYNOPSIS...A ridge builds in mid week with the next storm expected
late Thursday into Saturday.
.SHORT TERM (THROUGH 00Z FRIDAY)...
Closed low feature is seen propagating southeast across Arizona,
with the trough axis passing overhead. Flow veered quite northerly
which shut off snow prospects for the Wasatch early. Other
mountain ranges will likely see a little additional accumulation
though it appears to not be as high of an impact. Therefore, have
cancelled all going winter weather advisories.
Remaining snow showers in the mountains will dissipate today as
flow aloft becomes more anticyclonic, height rises occur and
warming occurring aloft.
With 40kt of NNE flow at 700mb, decent cold advection and a
northwesterly pressure gradient, wind advisory across outlying
Dixie (not St. George) looks good. Many of the high resolution
models have solid advisory gusts through the morning. Will also
have to keep an eye on Fremont Junction.
After a warming trend thanks to a building ridge, the next storm
system develops a deep closed low over Nevada Thursday. Closed
lows are quite finicky to forecast for as a slight deviation of
track or intensity can shift the precipitation and wind shield to
a different part of the region. Global models tend to have a hard
time with these systems as well.
Good height falls begin Thursday with increasing clouds. Expecting
gusty south winds ahead of the cyclone with modestly strong
pressure gradient and pressure falls. Lowered PoPs from South Lake
southward during the day with south flow in place, but did raise
PoPs slightly across the far north.
.LONG TERM (AFTER 00Z FRIDAY)...
The next pacific trough in the series will continue to remain an
open wave across the northern Great Basin into Thursday night
prior to closing off over southern Nevada by Friday morning.
Upstream amplification of the ridge off the pacific coast will aid
Trends as of late in medium range guidance point towards a rapid
transition to a closed low over southern Nevada/SW Utah, and quite
energetic as it does so. Although IVT is not all that impressive,
PWAT remains a bit elevated for a trough this time of year (pushing
.50 inches). With trough evolution, upper diffluence originally
oriented over central/northern Utah late Thursday will transition
towards a focused moisture axis on the northwest/west periphery of
the low once again as it closes (Thursday night), though this time a
bit further west over western Utah vs. the last few. Trends in
medium range guidance point this way, and confidence is rather high
on this outcome due to the upstream ridge amplification. This said,
have lowered PoPs along the Wasatch Front and upped them along the
UT/NV border and the SW where the thermal gradient looks to remain
most focused into and through Friday.
Regarding P-type, beneath the cold core of the trough over SW Utah,
do expect a transition from rain to snow across the southwestern
valleys Friday. Further north, a sharp gradient in H7 temps trends
towards valley rain north of Utah county and becoming more showery
with latitude. Will continue to have to monitor the potential of
more of an easterly wind concern for the northern Wasatch Front
Friday night than that of precip. These details will continue to
fall out as model to model consistency locks in.
A rather progressive downstream translation does look to limit both
length of precip, and the window of wind threats Friday night into
Saturday. Still, will have to monitor potential for enhanced
easterlies continuing in the north, and gap winds in the Washington
County area into Saturday morning.
Globals do diverge on downstream evolution of this low slightly, and
thus wave amplification/track of the next pacific trough of the
train thereafter into the weekend. Have low confidence in this
evolution, and have largely trended grids towards or slightly below
Northerly winds will remain in place at the KSLC terminal through
today. Mid level cigs are expected to thin mid to late morning
maintaining VFR conditions. In large, operational weather concerns
will remain minimal at the KSLC terminal through the valid TAF
UT...Wind Advisory until noon MDT today for UTZ019.
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