Flash Flood in Utah, September 1, 2015

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
1008 AM MDT TUE SEP 1 2015

.SYNOPSIS...AN UPPER LEVEL TROUGH DEVELOPING OVER WESTERN CANADA
WILL SETTLE SOUTH INTO THE PACIFIC NORTHWEST MIDWEEK. A MOSTLY DRY
AND WARM SOUTHWEST FLOW ALOFT WILL FORM ACROSS THE GREAT BASIN...
FOLLOWED BY COOLER FALL LIKE TEMPERATURES SPREADING ACROSS THE
REGION OVER THE WEEKEND.

&&

.DISCUSSION...SOUTHWESTERLY FLOW ALOFT PREVAILS ACROSS THE
INTERIOR WEST THIS MORNING...DOWNSTREAM FROM A DEEPENING UPPER
TROUGH SITUATED ALONG THE PACIFIC NORTHWEST COASTLINE. THIS
TROUGH IS DEEPENING IN RESPONSE TO AN EMBEDDED LOW DIGGING ALONG
THE BRITCOL COASTLINE. A WEAK WAVE NOTED IN WV IMAGERY IS LIFTING
THROUGH SOUTHERN AND CENTRAL UT THIS MORNING...HELPING TO DRIVE
ISOLATED SHOWERS AND THUNDERSTORMS ACROSS CENTRAL UT. A WEAK
DEFORMATION AXIS ALONG WITH THIS WAVE APPEARS TO BE ALSO ENHANCING
A MID LEVEL CLOUD DECK ACROSS NORTHERN UT.

GOES DERIVED PW IMAGERY AND REGIONAL 12Z SOUNDINGS INDICATE
DEEPER MOISTURE PRESENT ACROSS AZ NORTHWARD INTO EASTERN
UT...WHILE THE BOUNDARY LAYER ACROSS THE EASTERN GREAT BASIN
REMAINS DRIER WITH PW VALUES LARGELY BELOW 0.5 INCHES. THE
EXCEPTION IS A PLUME OF MID LEVEL MOISTURE WHICH HAS LIFTED INTO
NORTHERN UT THIS MORNING ASSOCIATED WITH THE AFOREMENTIONED WAVE.

AS THIS WAVE CONTINUES NORTHWARD TODAY AND IS COUPLED WITH DAYTIME
HEATING ON THE HIGHER TERRAIN...ANTICIPATE SCATTERED CONVECTION
ALONG THE TERRAIN AND POTENTIALLY SPREAD INTO THE EASTERN VALLEYS.
GIVEN THE AXIS OF MID LEVEL MOISTURE AND WEAK FORCING...COULD
POTENTIALLY SEE SOME OF THIS ACTIVITY SPREAD INTO THE WASATCH
FRONT THIS AFTERNOON...ALTHOUGH MOST RECENT HI-RES CONVECTIVE
ALLOWING MODELS ARE NOT VERY AMBITIOUS WITH THE WESTWARD EXTEND OF
CONVECTION...LARGELY KEEPING ANY ACTIVITY CONFINED TO THE EASTERN
HALF OF THE FORECAST AREA. THIS IS REFLECTED IN THE CURRENT
FORECAST AND WILL HOLD OFF ON UPDATING FOR NOW...BUT KEEP A CLOSE
EYE ON SATELLITE/RADAR TRENDS INTO THE AFTERNOON HOURS.

&&

.AVIATION...VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD AT
KSLC...WITH GUSTY SOUTHERLY WINDS PREVAILING THROUGH THE DAY.
THERE IS A 40 PERCENT CHANCE WIND GUSTS EXCEED 26 KTS AT
TIMES THROUGH THE AFTERNOON...AND A 20 PERCENT CHANCE OF A WIND
SHIFT TO THE NORTHWEST BETWEEN 22-01Z. THERE IS ALSO A 10 PERCENT
CHANCE OF A THUNDERSTORM DEVELOPING OFF THE OQUIRRHS AFTER 19Z AND
IMPACTING THE TERMINAL...WITH THE MAIN THREAT BEING GUSTY ERRATIC
WINDS.

&&

.FIRE WEATHER...A WEAK WEATHER DISTURBANCE CROSSING THE AREA TODAY
WILL SERVE AS A FOCUS FOR SHOWERS AND THUNDERSTORMS ACROSS THE
EASTERN HALF OF UTAH THIS AFTERNOON AND EVENING. A DEVELOPING
TROUGH ALONG THE WEST COAST WILL RESULT IN AN INCREASE IN
SOUTHWESTERLY FLOW THROUGH THURSDAY...RESULTING IN GUSTY SOUTHERLY
WINDS DURING THE AFTERNOON...PARTICULARLY ACROSS WESTERN UTAH.
WHICH COULD RESULT IN LOCAL CRITICAL FIRE WEATHER CONDITIONS IF
FUELS BECOME SUFFICIENTLY DRY.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...NONE.
WY...&&

SEAMAN

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

FOR FREQUENTLY ASKED QUESTIONS ABOUT THE AREA FORECAST DISCUSSION
VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY/GENERAL/AFD_FAQS.PHP (ALL LOWER CASE)