Special Weather Statement, NWS Salt Lake City, UT

Area Forecast Discussion
National Weather Service Salt Lake City UT
409 PM MDT Wed Sep 21 2016

.SYNOPSIS...A strong cold and moist storm system will impact most
of the region through the end of the week.

&&

.SHORT TERM (Through 00z Saturday)...Weather will become
increasingly active across the area over the next 48 plus hours.
Set up moving forward combines anomalously high low/mid level
moisture from the subtropics that is poised to merge with the
advancement and passage of a strong early winter type storm system
overhead. Impacts from Flash Flooding across the south are
possible, widespread heavy rain across the north is expected, as
are much colder temps and accumulating snow above 7000ft during
this period.

Afternoon water vapor and H5 analysis indicate continued east-
southeast advancement of this positively tilted trough stretching
from southern Britcol to NorCal. Downstream a strengthening
southwesterly flow aloft continues to tap this low/mid level
moisture remnant from what was Tropical storm Paine, with said
moisture advecting north from the desert southwest into southern
Utah. Widespread light to moderate rain has been experienced
across the south already today, as this moisture has interacted
with shearing vorticity stretching across the south remnant from
an old closed Low that was over Baja. Convection has, for the time
being, remained largely non existent due to a lack of instability,
but that will change over the next 12 hours as well.

The aforementioned trough will continue to translate east-
southeast tonight with the center of the cold core low poised to
move into Nevada. As that occurs increasing diffluence aloft will
begin to drive large scale forcing across the southwest by
daybreak, and all areas by the afternoon. Slight cooling at the
midlevels as this occurs will aid steeper lapse rates, and
formation of modest instability across the southwest by morning
and all areas by the afternoon. As such, areal coverage and
significance of precip is expected to increase and become more
convective, rapidly expanding south to north during the day. Due
to the anomalous nature of the moisture coupled with the strength
of the upper level trough, opted to issue a Flash Flood Watch for
much of southern/eastern Utah through early Friday morning when
convective potential wanes, as locally heavy rain aided by a deep
warm cloud layer is expected.

Strong deep layer shear coupled with this instability and moisture
(and some mid level drying ahead of the approaching cold front)
will allow for the potential of convective organization on
Thursday. Severe thunderstorms are possible, with hail and
damaging winds possible impacts from any organized cores. SPC
currently has the forecast area under a marginal risk for this
potential.

The attendant cold front of the upper trough will largely stall to
our west through tomorrow, then push east across the area
tomorrow evening into the overnight hours bringing much colder
temperatures by Friday morning. Steadier precip will begin to
focus across the northern half of the area as the cold core
settles in, with a trowal forming overhead. Combining the duration
of precip potential and presence of the deep layer moisture,
anticipating in excess of an inch of rainfall along the Wasatch
Front, with mountain areas potentially seeing 2 to 3 inches of
liquid by Friday night. H7 temps forecast to bottom out in the -3
to -4 C range will allow for snow levels to lower to around 7000ft
Friday, with accumulating snow expected elevations above, and
focused across the northern mountains. Anticipating need for a
Winter Weather Advisory for these higher mountain areas Thursday
night/Friday, with impacts largely relegated over 8000ft.

&&

.LONG TERM (after 00Z Saturday)...The cold upper low is forecast
to be lifting into nrn WY at the start of the long term period
with wrap around precip in nw flow remaining in place across nrn
UT orographically enhanced into the Wasatch mtns.

This should taper off overnight with a few lingering showers over
the nrn mtns on Sat morning pretty much ending in the afternoon.

The upstream ridge remains centered off the coast thru Sun with a
cool dry northerly flow over the CWA. Clearing skies Sat night
should allow temps to dip to near or below freezing in the
normally colder valleys.

Dry conditions persist Sun thru Wed as the upstream ridge slowly
progresses into the Great Basin and brings a warming trend to the
CWA. Expect temps to return to near seasonal normals by Tue and
warm a little more Wed.

&&

.AVIATION...VFR conditions will continue at the SLC terminal
through the night. Cigs will remain above 6000 ft AGL until about
06-08z after which they could dip below that at times in passing
rain showers. Winds will remain southerly overnight and will be
occasionally gusty. Outflow from passing rain showers could send
stronger erratic gusts across the airfield at times through the
night.

&&

.FIRE WEATHER...Deep moisture moving north from a remnant tropical
system will combine with a strong early winter type storm system
late tonight through Friday before gradually tapering over
northern portions of the district Saturday. Currently this
moisture is producing widespread wetting rains across the
southwest and surface RH has reached levels not seen for some
time. As the storm system carves into eastern Nevada tonight this
moisture and associated rainfall/thunderstorm potential is
expected to spread north encompassing much of the area tomorrow. A
strong cold front will work west to east across the district
Thursday evening into the overnight hours maintaining widespread
precip, and likely making it more steady across the north through
Friday before tapering Saturday. Snow levels by Friday morning
will lower to near 7000ft, with accumulating snow expected to
focus over the higher mountain areas in northern Utah.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...Flash Flood Watch through late Thursday night for UTZ012-013-
     019>021-518.

WY...None.
&&

SHORT TERM/FIRE WEATHER...Merrill
LONG TERM/AVIATION...Wilensky

For more information from NOAA's National Weather Service visit...
http://weather.gov/saltlakecity

For frequently asked questions about the Area Forecast Discussion
visit...
http://weather.gov/saltlakecity/general/afd_faqs.php

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
407 AM MDT WED SEP 21 2016

UTZ001>016-019>021-517-518-WYZ021-221000-
CACHE VALLEY/UTAH PORTION-NORTHERN WASATCH FRONT-
SALT LAKE AND TOOELE VALLEYS-SOUTHERN WASATCH FRONT-
GREAT SALT LAKE DESERT AND MOUNTAINS-WASATCH MOUNTAIN VALLEYS-
WASATCH MOUNTAINS I-80 NORTH-WASATCH MOUNTAINS SOUTH OF I-80-
WESTERN UINTA MOUNTAINS-WASATCH PLATEAU/BOOK CLIFFS-
WESTERN UINTA BASIN-CASTLE COUNTRY-SAN RAFAEL SWELL-
SANPETE/SEVIER VALLEYS-WEST CENTRAL UTAH-SOUTHWEST UTAH-
UTAHS DIXIE AND ZION NATIONAL PARK-SOUTH CENTRAL UTAH-
GLEN CANYON RECREATION AREA/LAKE POWELL-CENTRAL MOUNTAINS-
SOUTHERN MOUNTAINS-SOUTHWEST WYOMING-
407 AM MDT WED SEP 21 2016

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE WESTERN TWO THIRDS OF
UTAH AND SOUTHWEST WYOMING.

.DAY ONE...TODAY AND TONIGHT

SCATTERED SHOWERS AND THUNDERSTORMS WILL AFFECT THE REGION.
RAINFALL WILL BE LOCALLY HEAVY...POSING THE THREAT FOR FLASH
FLOODING IN PRONE AREAS. STORMS MAY ALSO CONTAIN STRONG GUSTY
WINDS...ESPECIALLY NORTH OF INTERSTATE 70.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

A COLD WET POTENT STORM SYSTEM...WILL CONTINUE TO AFFECT THE
REGIONS WEATHER INTO THE WEEKEND...BRINGING A WIDESPREAD
PRECIPITATION EVENT TO THE REGION. WINDY CONDITIONS CAN ALSO BE
EXPECTED. SNOW LEVELS ARE FORECAST TO FALL FROM THE PEAKS TODAY
AND TOMORROW...TO SEVEN THOUSAND FEET BY FRIDAY.

FLOODING IS POSSIBLE DUE TO WIDESPREAD HEAVY PRECIPITATION
THURSDAY AND FRIDAY.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

ROGOWSKI/STRUTHWOLF

FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY/ (ALL LOWER CASE)

FOR INFORMATION ON POTENTIAL ROAD TRAVEL IMPACTS VISIT...
HTTP://WWW.UDOTTRAFFIC.UTAH.GOV/ROADWEATHERFORECAST.ASPX

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
708 PM MDT WED SEP 21 2016

UTZ002-005-220200-
GREAT SALT LAKE DESERT AND MOUNTAINS UT-NORTHERN WASATCH FRONT UT-
708 PM MDT WED SEP 21 2016

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN
WEBER...NORTHWESTERN DAVIS...NORTH CENTRAL TOOELE AND SOUTHEASTERN
BOX ELDER COUNTIES INCLUDING THE GREAT SALT LAKE UNTIL 800 PM MDT...

AT 706 PM MDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM 30 MILES SOUTH OF
PARK VALLEY TO 20 MILES NORTH OF KNOLLS...AND MOVING EAST AT 40 MPH.

WIND GUSTS OF 45 TO 55 MPH WILL BE POSSIBLE WITH THIS LINE.

LOCATIONS IMPACTED INCLUDE...
GUNNISON ISLAND...HAT ISLAND AND LAKESIDE.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

IF THREATENING WEATHER APPROACHES...TAKE SHELTER IN A STURDY
BUILDING.

IF ON OR NEAR THE GREAT SALT LAKE...GET OUT OF THE WATER AND MOVE
INDOORS OR INSIDE A VEHICLE. REMEMBER...LIGHTNING CAN STRIKE OUT TO
10 MILES FROM THE PARENT THUNDERSTORM. IF YOU CAN HEAR THUNDER...YOU
ARE CLOSE ENOUGH TO BE STRUCK BY LIGHTNING. MOVE TO SAFE SHELTER
NOW! DO NOT BE CAUGHT ON THE WATER IN A THUNDERSTORM.

&&

LAT...LON 4160 11234 4098 11222 4081 11333 4153 11322
TIME...MOT...LOC 0106Z 266DEG 37KT 4140 11313 4098 11321