Severe Thunderstorm Warning 27, NWS Salt Lake City, UT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
408 PM MDT WED JUN 9 2010

.SYNOPSIS...A LARGE COOL PACIFIC TROUGH WILL CONTINUE MOVING
INLAND THIS EVENING...WITH WARM SOUTHERLY FLOW AHEAD OF IT. THE
TROUGH WILL GRADUALLY MOVE FARTHER INLAND AND CLOSE OFF OVER THE
GREAT BASIN THURSDAY THROUGH FRIDAY. THIS LOW WILL THEN REMAIN IN
PLACE THROUGH THE WEEKEND.

&&

.DISCUSSION...THE ONLY SHOWERS ACROSS THE CWA THIS AFTERNOON ARE
IN FAR NORTHERN UTAH...WITH MOST OF THE CONVECTIVE ACTIVITY
REMAINING SUPPRESSED BY THE EXTENSIVE CLOUD COVER ACROSS THE
NORTHERN HALF OF THE CWA. THESE CLOUDS...ALONG WITH A SLIGHT
NORTHERLY GRADIENT...HAVE KEPT TEMPERATURES ALONG THE WASATCH
FRONT SLIGHTLY COOLER THAN FORECAST...BUT STILL WARMER THAN THE
LAST COUPLE DAYS IN MOST LOCATIONS.

THE PRECIPITATION IS EXPECTED TO INCREASE IN BOTH AREA AND
INTENSITY OVERNIGHT AND INTO THURSDAY MORNING...AS GOOD JET
DYNAMICS ASSOCIATED WITH THE INCOMING TROUGH MOVE OVER THE AREA.
THIS SHOULD SET UP A BAND OF PRECIP...WITH THE MODELS CURRENTLY
PLACING THAT BAND FROM DELTA TO EVANSTON WY AND INTO CENTRAL
WYOMING...PEAKING ON THURSDAY MORNING AND PERHAPS LINGERING INTO
THE AFTERNOON HOURS. AFTER THAT JET STREAK MOVES OFF TO THE
NORTHEAST...THE AREA MAY SEE A BREAK IN THE PRECIP ON THURSDAY
EVENING AND FRIDAY MORNING AS THE TROUGH DIGS SOUTHWARD INTO
NEVADA. THIS BREAK WILL BE SHORT-LIVED...AS PRECIP FILLS BACK IN
LATE FRIDAY AND INTO SATURDAY AS THE TROUGH MIGRATES SLOWLY
EASTWARD. WITH SOMEWHAT INCREASED CONFIDENCE AND GOOD MODEL
AGREEMENT IN THIS PERIOD...HAVE INCREASED POPS A BIT ON EITHER
SIDE OF THE PERCEIVED BREAK ON THURSDAY/FRIDAY.

BEYOND SATURDAY...THE FORECAST BECOMES SIGNIFICANTLY MORE
UNCERTAIN...AS THE GFS AND ECMWF BEGIN TO DIVERGE. AS THE ECMWF
HAS BEEN MORE CONSISTENT RECENTLY AND HAS BETTER SUPPORT FROM THE
CANADIAN MODEL...HAVE LEANED MORE TOWARD THE EC IN THE EXTENDED.
THIS MEANS A SOMEWHAT COOLER AND WETTER FORECAST...WITH THE LOW
LINGERING OVER THE GREAT BASIN INTO EARLY MONDAY. AS THE FORECAST
WAS ALREADY TILTED TOWARD THE EC...NOT MANY CHANGES HAD TO BE MADE
IN THIS TIMEFRAME. EITHER WAY...BOTH THE GFS AND EC ADVERTISE SOME
WARMING FOR TUESDAY AND WEDNESDAY AFTER THE UNSEASONABLY COOL
AIRMASS LEAVES THE REGION.

&&

.HYDROLOGY...FLOODING CONTINUES ALONG THE WEBER RIVER NEAR
OAKLEY...WHILE LITTLE COTTONWOOD CREEK REMAINS JUST BELOW
BANKFULL. LITTLE COTTONWOOD IS FORECAST TO REMAIN BELOW FLOOD
STAGE THROUGH TODAY...BUT A WATCH IS STILL IN EFFECT FOR THE
CHANCE THAT RAINFALL COULD RAISE THE CREEK ONCE AGAIN. ALONG THE
WEBER RIVER...FLOODING IS EXPECTED TO CONTINUE THROUGH AT LEAST
THIS EVENING AS WARMER TEMPERATURES CONTINUE TO FEED SNOWMELT INTO
THE RIVER.

&&

.AVIATION...THE COMBINATION OF SHOWERS TO THE NORTH OF THE SLC
TERMINAL AND A NORTHERLY SURFACE PRESSURE GRADIENT WILL KEEP
NORTHERLY WINDS AT THE SLC TERMINAL THROUGH TONIGHT AND THURSDAY.
THERE IS ABOUT A 50 PERCENT CHANCE OF SHOWERS AFFECTING THE SLC
TERMINAL BETWEEN 12 AND 19Z THURSDAY WITH A 20 PERCENT CHANCE OF
CIGS TEMPORARILY LOWERING TO MVFR LEVELS.

&&

.FIRE WEATHER...GUSTY SOUTHWEST WINDS AND LOW RELATIVE HUMIDITIES
WILL PERSIST ACROSS SOUTHERN UTAH THROUGH THURSDAY. A RED FLAG
WARNING REMAINS IN EFFECT ACROSS ZONES 439 AND 440 BELOW 6500 FEET
WHERE FUELS ARE CRITICAL. OTHERWISE A COLD FRONT WILL PUSH INTO
NORTHERN UTAH THURSDAY...THEN THROUGH THE REMAINDER OF THE STATE
THURSDAY NIGHT INTO EARLY FRIDAY. THE ASSOCIATED STORM SYSTEM IS
EXPECTED TO STALL ACROSS THE REGION THROUGH THE WEEKEND AND INTO
EARLY NEXT WEEK. THIS WILL BRING MUCH COOLER AND WETTER CONDITIONS
TO THE AREA.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...RED FLAG WARNING UNTIL 9 PM MDT THURSDAY BELOW 7000 FEET FOR
     UTZ439 AND 440.

     FLOOD WATCH THROUGH THURSDAY MORNING FOR UTZ003-008.

WY...NONE.
&&

PUBLIC...SCHOENING
FIRE WEATHER...SEAMAN
AVIATION...STRUTHWOLF
HYDROLOGY...SCHOENING

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)