Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 241706

Area Forecast Discussion
National Weather Service Salt Lake City UT
1106 AM MDT Wed May 24 2017

.SYNOPSIS...High pressure aloft will shift east of the region
this morning. This exiting high pressure will be followed by a
series of weather disturbances which will impact Utah late
Wednesday through the first half of the upcoming weekend.


.DISCUSSION...A low amplitude ridge axis overhead will remain in
place into the early afternoon prior to flattening and shifting
east in advance an approaching trough. Morning water vapor and H5
analysis place this primary trough of note over southern Britcol
with height falls advancing southeast across Idaho attm. Meanwhile
off the Cali coast a weak closed low with attendant southern
branch jet is advecting mid and upper moisture NE across the
central Great Basin that will arrive late day. A coupling of this
moisture and further advancement of the upstream trough and
attendant cold front will aid convective development over northern
(and portions of central Utah) by this evening.

BUFR profiles continue to exhibit a well mixed boundary layer with
inverted-v signature late this afternoon as modest
destabilization occurs (greatest along the UT/ID border). High
based convection is expected to develop this evening in the pre-
frontal environment over the northern half of the area with
erratic microburst winds the primary impact to note moving forward
with the more developed cells, but it will take time with slower
advancement of the cold front as noticed in last few runs of
guidance. Trimmed PoPs to isolated at best for late this
afternoon, with dry conditions now expected through at least 3pm
across the north. Window of best convection potential looks to
begin around 01z however.

Areal coverage of showers/convection is expected to increase
through the middle of the night tied closely to the area of best
baroclinicity shifting NW-SE across northern Utah/SW WY, prior to
slowly phasing away towards dawn over central portions as the
front stalls and trends more diffuse. No significant changes in
though there.

Outside of the above mentioned trimming of PoPs this afternoon,
also updated sky grids to follow latest and anticipated trends.
Namely, slight increases today across the north. Previous
discussion below...

PREVIOUS DISCUSSION...This boundary should remain across central
Utah tomorrow with the instability axis remaining in the warm
sector across south central Utah where isolated showers and
thunderstorms are possible tomorrow afternoon and evening. The
boundary lifts northward as a warm front tomorrow night, ahead of
a cold front which makes its way across northwest and west central
Utah by Friday morning. Focused shower activity along the Idaho
border region late tomorrow night as the right entrance region of
the polar jet propagates into northern Utah in advance of the next
storm system.

PoPs were increased a little bit this evening, and focused south
of Ogden to near Provo from north of Delta across southwest
Wyoming. This activity shifts east and a bit south overnight. Area
of PoPs reduced Thursday to just along the frontal zone and
Thursday night just along the Idaho border.

Went on the high side of guidance for today`s high temperatures
everywhere, and in the warm sector tomorrow. Tomorrow will be much
cooler across the north where I leaned more heavily on the cooler

The last wave from the trough is expected to cross northern Utah
and southwest Wyoming during the day Friday, likely resulting in
at least scattered convection over much of the northern half of
the forecast area. Most convection will tend to dissipate Friday
evening/overnight as the trough weakens and pulls away from the
area. However, enough instability will remain for isolated
convection into Saturday.

Behind the exiting wave, high pressure is expected to move back into
the forecast area, resulting in a warming and drying trend for the
latter portion of the Memorial Day weekend. Maxes by Monday are
expected to run at least 5F above seasonal normals with a bit more
warming through the middle of next week. Conditions remain mostly
dry for the majority of the extended period, though EC/GFS show the
ridge shifting east Wednesday with some instability moving in from
an approaching trough, so have added climo POPs for day seven.


.AVIATION...South winds will become increasingly gusty at the KSLC
terminal through 20-21z prior to veering to the northwest for the
afternoon hours. High based showers/storms are expected to work
in from the west after 00-01z this evening bringing an erratic and
gusty outflow threat to the terminal, with window of greatest
impact potential lasting through 02-03z. A cold front will cross
the terminal overnight maintaining a prevailing northwesterly wind
through much if not all night.




PREVIOUS DISCUSSION...Rogowski/Traphagan

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