Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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571
FXUS65 KSLC 191155
AFDSLC

Area Forecast Discussion
National Weather Service Salt Lake City UT
555 AM MDT THU MAY 19 2016

.SYNOPSIS...High pressure will shift east today ahead of the next
Pacific storm. This system will stall over the Pacific Northwest
through the end of the week.

&&

.SHORT RANGE (Thru 18z Sunday)...A cool upper trof is closing
off into an upper low as it drops into the Pacific Northwest early
this morning. The axis of the downstream short wave ridge is over
UT and subsidence with this feature has brought mostly clear skies
to the CWA at this time.

The ridge shifts east this morning and high clouds out ahead of
the west coast low will spread into the CWA from the west. The
associated cold front arrives in nwrn UT this aftn and reaches SLC
around 00z.

Convection will form ahead of and along this front and this could
provide enough cold outflow to send the front surging thru nrn UT
with a brief period of strong gusty winds behind it. In addition,
given the dry subcloud environment expected ahead of the front,
any pre frontal thunderstorms will be capable of strong winds due
to microbursts. Kept the mention of gusty winds near thunderstorms
in the forecast for northwest UT this afternoon and evening.

The front retreats back north late Thu night into Fri then stalls
over far nwrn UT. Strong winds will develop over the western
valleys Fri aftn as a strong short wave drops down the back side
of the upper low and digs into nrn CA, ramping up the southerly
flow over UT. Models have been very consistent showing 35-40kt of
sustained surface winds over swrn UT Fri aftn with strong winds up
and down the west side of the CWA. Winds also increase over the
east Fri aftn but speeds look like they will be about 10kt
lighter.

Confidence was high enough to go ahead and upgrade the existing
high wind Watch to a Warning for the western valleys but just
don`t see where the winds get strong enough over the east for a
Warning so have issued an Advisory for the remaining areas that
were under the Watch. Also added some of the less wind prone areas
of the west to the advisory.

Showers Fri will be limited to the far nw CWA near the stalled
front but some convection could form over the nrn mtns. With the
strong flow aloft any winds from these mtn storms could be quite
strong.

The front gradually edges back east Fri night into Sat as the
upper low begins to shift east, with a little better chance of
convection along it. Winds will be gusty once again over the east
but with similar speeds to what is expected there on Fri.

The upper low continues to weaken on Sat and it shifts east Sat
aftn thru Sun bringing scattered showers.

.LONG RANGE (After 18z Sunday)...The broad long wave trough in
place will continue to encompass the western conus through much
of the long term period. Feature to note, largely agreed on in
guidance, is an upstream short wave amplifying the trough further
west over central/southern California Sunday into Monday. Said
amplification to the west will likely allow for subtle height
rises attempting to build over the forecast area through that
time, and likely minimizing precip potential from scattered across
the north to isolated by Monday...though diurnal trends will
continue to support increased development during the daytime hours
both days. Available moisture looks sparse, and is the deciding
factor for limited precip potential both days.

This wave will gradually translate east-southeast into AZ through
early next week continuing the trend of cyclonic flow and subtle
forcing, with limited moisture to act on. Have continued to opt for
highest PoPs diurnally and only scattered at best during the
afternoons.

&&

.FIRE WEATHER...ACTIVE PERIOD AHEAD IN THE SHORT TERM...WITH STRONG
THUNDERSTORM POTENTIAL ELEVATED ACROSS THE NORTHWEST THIS AFTERNOON
AND WIDESPREAD WINDY AND DRY CONDITIONS FRIDAY INTO SATURDAY. A COLD
FRONT WILL WORK INTO THE NORTHWEST THIS AFTERNOON PROVIDING FOCUS
FOR THE STORMS...BUT WILL RETREAT NORTH ALLOWING VERY STRONG WINDS
TO DEVELOP AREAWIDE FOR FRIDAY INTO SATURDAY. ALTHOUGH FUELS REMAIN
NON CRITICAL ACROSS THE AREA...CRITICAL FIRE WEATHER CONDITIONS WILL
BE WIDESPREAD ACROSS THE WESTERN/EASTERN VALLEYS WITH WIND GUSTS IN
EXCESS OF 55 MPH ACROSS THE WEST AND 45 MPH IN THE EAST EXPECTED.
THIS STORM SYSTEM WILL SLOWLY MOVE THROUGH AREA THROUGH EARLY NEXT
WEEK BRINGING SCATTERED SHOWERS AND ISOLATED STORMS TO THE NORTH
AND MORE ISOLATED PRECIP POTENTIAL TO THE SOUTHERN AREAS.

&&

.AVIATION...Southerly winds are expected to increase and become
gusty at the kslc terminal through this afternoon. An 80% chance
exists that these gusts will exceed 30mph in the 16-00z window.
A cold front is expected to push through the terminal between
00-02z today...and a 40% chance exists that strong outflow winds
or lightning will impact the terminal during that time and into
this evening.

&&

.SLC Watches/Warnings/Advisories...
UT...Wind Advisory from noon to 10 PM MDT Friday for UTZ002-004-013-
     014-019>021.

     High Wind Warning from noon to 10 PM MDT Friday for UTZ003-005-
     015-016.

WY...None.
&&

$$

wilensky/merrill

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