Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 202221

Area Forecast Discussion
National Weather Service Salt Lake City UT
421 PM MDT Fri Apr 20 2018

.SYNOPSIS...An upper level low pressure system will slowly make
its way across the southern and central portion of the region
today. High pressure will bring a warming and drying trend for the
upcoming weekend.


Antecedent Conditions...
Extreme Drought is occurring from Provo south to Cedar City and
to the southeast. Severe Drought is occurring surrounding the
Extreme Drought, in areas south of Ogden and Duchesne to the
Arizona border. Drought conditions scale down to Abnormally Dry
along the Idaho and Wyoming border.

Big Picture...
During the past 5 days, the amplified pattern over the Pacific has
shifted toward being more zonal as the magnitude of the jet has
significantly decreased. This is leading to a higher potential of
cutoff systems as opposed to consolidated troughs.

Water Vapor Satellite shows a deep closed low has progressed to
the central Rockies. 400-250 MDCARS wind observations show a
cyclonic 100-135kt jet over from eastern Nevada, across Arizona
into the southern Rockies.

Local Observations and Trends...
12Z KSLC RAOB shows steep lapse rates up to near 300mb above the
nocturnal inversion, with uniform east-northeast winds of
25-45kts in this layer. Very dry below 600mb, and moist above
this level. Precipitable Water values range from 0.10"-0.20"
mountains, to to 0.40"-0.65" most valleys.

The surface boundary has progressed out of the area, from
southwest Wyoming through central Colorado. In the wake of the
storm, gusty winds are mainly confined to the ridges. A 1017mb
high has formed over southwest Utah.

24 hour trends include 10-20F cooler south of Salt Lake City, 5F
warmer to the west and north. Dewpoints depression has decreased
(moistened) 25-45F except 5F higher (drier) across the northwest.

Strong height rises and mid level warming in the wake of the storm
will cause showers and thunderstorms to continue to decay in
coverage through the early evening hours.

A ridge builds in for the first half of the weekend providing
wonderful sunny and warm conditions Saturday. By Sunday afternoon
and early evening, isolated showers and storms may develop from
the Uinta mountains to Boulder Summit. Moistening return flow
provide for weak instability with steep 700-500mb lapse rates.

The next storm system mainly passes to our north. Height falls
develop Sunday evening across the northwest, spreading across
northern Utah and southwest Wyoming overnight. At the surface,
expect the attendant cold front to cross into northwest Utah
Sunday evening, clearing much of northern and central Utah along
with southwest Wyoming by mid morning Monday.

While this compact system is bundled up nicely, it passes well to
our north. The upper level jet aligns near the Idaho border Monday
morning. This suggests much of the sensible weather will be north
of Utah. Still, destabilization occurs Monday in the moistening
post frontal environment, bringing the chance for scattered
showers and thunderstorms across the north. The storm begins to
shear late Monday, with the better dynamics and cold pool shifting
east over the northern Rockies further from the local area. Will
have to watch for gusty post frontal winds Monday.

Behind the exiting grazing trough,
high pressure is expected to move back into the area, remaining the
dominant weather feature through day seven. This will result in a
warming trend with dry conditions and light winds. By day seven,
maxes are currently progged to run up to 15F above seasonal normals.


Northerly winds at the SLC terminal this afternoon are expected
to persist into early evening, although may become erratic and
variable for brief periods. Ceilings should remain above 7000 ft
through the period. The winds are expected to shift to the SE
between 07-09Z.




LONG TERM...Traphagan

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