Area Forecast Discussion
Issued by NWS Salt Lake City, UT
FXUS65 KSLC 172200
Area Forecast Discussion
National Weather Service Salt Lake City UT
400 PM MDT Mon Apr 17 2017
.SYNOPSIS...A weak cold front will stall across northern Utah
tonight. A stronger storm system will cross the area Tuesday
afternoon through Tuesday night. Another storm is possible late
Thursday into Friday.
.SHORT TERM (Thru 12Z Thursday)...The weak cold front that
crossed northern UT this morning has stalled across central UT
this aftn. The morning showers dissipated by midday with just a
few small showers this aftn along the ID border. Another small
area of showers has formed late this afternoon along the NV
border. No precip has been reported out of these altho a few
hundredths did fall at a station just over the ID border.
The cold front is forecast to retreat north across nrn UT tonight
but becomes active again as a warm front late tonight into Tue
morning. This is then pushed back south into the CWA as an active
cold front late Tue into Tue eve. The bulk of the precip stays
north of the GSL for most of the day then the central and srn
Wasatch front fills in late aftn thru the eve. Models continue to
advertise this will be a wet event for the nrn and central CWA
with half inch or more of water in the Wasatch Front valleys and
more in the mtns but the high snow levels will prevent much impact
from occurring on any of the well traveled routes, even as snow
levels fall after dark.
South winds pick up Tue aftn across the CWA as the front
strengthens across far nwrn UT, but do not reach advisory speeds.
The front pushes out of the area after midnight and the airmass
dries. Limited instability could keep a few showers going Wed but
these would be isolated at best and mainly over the north. The
next Pac trof begins to move into the Great Basin Wed night.
.LONG TERM (After 12Z Thursday)...Global models continue to remain
in good agreement regarding the approach of the next trough
Thursday morning, this riding the nose of a 100kt+ NW-SE oriented
upper jet impinging into the western CONUS. This trough is
relatively low amplitude and negatively tilted, but with solid
upper level jet support and a modest cold front, precip is
expected to become widespread across the northern half of the area
Thursday into the overnight hours.
Although decent cold advection will accompany the front, thermal
packing coincident with the mid level baroclinic zone is marginal
in H7 progs, as are lapse rates per BUFRs. Forcing should largely
remain tied to this thermal gradient, with precip becoming more
showery in the post frontal environment (though aided by the upper
jet and localized orographics). Cyclonic northwesterly flow
through mid level axis passage will allow for continued cold
advection Thursday night, with H7 temps nearly supporting valley
snowfall. This said, bulk of forcing/moisture will be shifting
east of the area as the upper trough quickly slides downstream
while deepening over the western plains. Do not see much of a snow
impact from this system, even in the mtns (2-4"), this due to
rapid downstream progression and only modest organization locally.
Short wave ridging will roll over the area Friday into the weekend
as the departing trough deepens downstream, with stable conditions
and warming trend temps anticipated. The ridge will flatten late
weekend as an ejecting lobe of the next weakening pacific trough
ejects inland. Confidence is low regarding evolution and track of
this feature attm, but the GFS does indicate a more amplified
solution with a short wave passage Sunday night. We`ll see.
.AVIATION...VFR conditions will persist for the SLC terminal
through the overnight period. Ceilings should remain above 6000
feet through the morning hours. Northerly winds will shift to the
southeast after 04z. There is a 30 percent chance this shift
happens later than expected.
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