Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 171041

Area Forecast Discussion
National Weather Service Salt Lake City UT
441 AM MDT Sun Sep 17 2017

.SYNOPSIS...A warming trend will develop today through Monday.
The next cold front will cross northern and central Utah Tuesday.
A warmer southwest flow will briefly return on Wednesday ahead of
a stronger cold front.


.SHORT TERM (Thru 00Z Wednesday)...A warmer southwest flow has
developed over the CWA today ahead of a weakening Pacific trof.
This wave will bring clouds and a few showers to the north with
the slight chance of an afternoon thunderstorm over the central
and nern mtns.

The airmass warms thru midday today then warming halts as the trof
axis passes this aftn. Still expect temps to rise 5 to 10 deg from

The flow backs on Mon and increases ahead of a cold but low
amplitude trof moving inland from the Pac. The airmass continues
to warm and highs should jump another 5 to 8 deg or so with low
80s possible at SLC.

This trof crosses the Great Basin and nrn Rockies on Tue sending
a cold front into UT early Tue. The main jet support and cold pool
aloft stay to our north with this wave so precip is not expected
to get very far south into the CWA and could be spotty and light.
The best chance will be in the morning from about SLC north. This
trof does send cooler air back into the state with highs Tuesday
falling back into the 60s across the north.

.LONG TERM (After 00Z Wednesday)...Heights will quickly rebound
in the wake of the Tuesday brush-by trough across northern Utah
and southwest Wyoming resulting in an end to any showers. Both the
GFS and EC show this rapid drying so have removed most PoPs for
the Tuesday night period.

The upstream trough will dig farther south and bring colder and
wetter weather with it Thursday. Have leaned towards the EC as
once again the 12Z GEFS ensemble mean is more in line with the EC
than the operational GFS. With the slightly slower EC forecast of
the cold front moving into the Wasatch Front Wednesday evening,
have boosted temps a few degrees from about Ogden southward for
Wednesday. The EC 700mb temps of plus 8C would support temps near
80 at SLC but held off on going that warm as gusty winds due to
deep mixing from aloft may cause temps to plateau in the afternoon
as cooler air aloft mixes downward.

Between 12Z Thursday and 18Z Thursday the EC shows frontogenetic
forcing from west of Milford NE to the northern Wasatch, while the
GFS is weaker with the 700mb baroclinic zone and displaced farther
eastward. The EC appears to have the better forecast so have gone
with the heavier and more widespread precip over western Utah into
northern Utah and SW Wyoming Thursday and Thursday night. Because
the EC is deeper with the trough it will be slower to move across
the region. Consequently, the cold and unstable air mass will
remain across the CWA through Saturday and across eastern and
northern mountains into Sunday. Have under cut MOS guidance temps
for Friday through Sunday, with temperatures remaining 15-20
degrees below normal.


.AVIATION...VFR conditions will prevail at the SLC terminal
through the TAF period. Light southeast winds will shift to
northwest about 18-19Z today and then back to southeast about 03Z.


.FIRE WEATHER...A mild southwesterly flow will develop today
bringing warming temperatures area wide along with a few showers
and thunderstorms over the north. The flow becomes stronger Monday
with temperatures continuing to warm and winds becoming gusty in
the afternoon. A cold front will cross northern and central Utah
on Tuesday with winds shifting to northwest and temperatures
cooling back down. There will also be a chance of rain over the
north with a little snow possible at the higher elevations.

Winds increase out of the south again on Wednesday and
temperatures warm up again ahead of the next cold front for
Thursday. This front will bring much cooler air along with fairly
widespread valley rain and mountain snow. Cool unsettled
conditions are expected to continue into the weekend.





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