Winter Storm Warning 11, NWS Salt Lake City, UT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
746 PM MDT SAT OCT 23 2010

.SYNOPSIS...THE MOIST WESTERLY FLOW ALOFT ACROSS THE PACIFIC WILL
BRING A SERIES OF INCREASINGLY COLD AND ENERGETIC WEATHER
DISTURBANCES TO UTAH THROUGH THE MIDDLE OF NEXT WEEK. HIGH PRESSURE
IS EXPECTED TO RETURN BRIEFLY THURSDAY BEFORE ANOTHER STORM SYSTEM
AFFECTS THE AREA NEXT WEEKEND.

&&

.DISCUSSION...WATER VAPOR LOOP SHOWS A SHEARED WAVE PROGRESSING
ACROSS NORTHERN UTAH. THE NEXT STORM SYSTEM WAS LOCATED AROUND
45N/130W. ACARS 400-250MB WIND OBSERVATIONS INDICATE A 100-125KT
ANTICYCLONICALLY CURVED JET IS OVER THE PACIFIC NORTHWEST AND
WESTERN GREAT BASIN. 00Z 700MB ANALYSIS PLACES A CYCLONE ACROSS
THE PLAINS WITH THE NEXT STORM OFF THE PACIFIC NORTHWEST. LITTLE
THERMAL CHANGE WAS OCCURRING LOCALLY WITH -2C REPORTED AT SLC
UPSTREAM AT KLKN. 00Z KSLC RAOB SHOWS 5C OF COOLING IN THE LOWER
LEVELS WITH 1-3C OF COOLING ALOFT DURING THE PAST 24 HOURS. THE
PROFILE WAS SATURATED EARLIER THIS EVENING.

GOES SOUNDER/RUC AND GPS PRECIPITABLE WATER SENSORS INDICATE VALUES
RANGE FROM A HALF INCH TO THREE QUARTERS OF AN INCH.

SENT OUT AN UPDATE EARLIER THIS EVENING TO ACCOUNT FOR RAPID
DECREASE IN PRECIPITATION COVERAGE ACROSS NORTHERN UTAH WITH THE
PASSAGE OF THE SHEARED WAVE. CHANGED WORDING TO CONVECTIVE SHOWERS
IN THE REMAINING COLD ADVECTION. AREA OF FOCUS IS ACROSS CENTRAL
UTAH THIS EVENING. PER IR SATELLITE IMAGERY...TOPS ARE WARMING THERE
AS WELL. WILL LIKELY REVISE THINGS AGAIN LATER THIS EVENING AND
LOWER THE ADVISORY CURRENTLY IN PLACE FOR THE NORTHERN AND CENTRAL
MOUNTAINS.

KEPT MENTION OF THUNDER ACROSS CENTRAL UTAH PER OBSERVATIONS AND
SHORT RANGE ENSEMBLE INSTABILITY FORECASTS THIS EVENING. THIS IS A
SHORT TERM THREAT FOR THE NEXT HOUR OR TWO.

THINGS STILL LOOK ON TRACK FOR WARM ADVECTION TO GET GOING
TOMORROW...PROVIDING STRATIFORM PRECIPITATION ACROSS NORTHERN
UTAH...AND GUSTY SOUTHWEST WINDS ACROSS THE WESTERN VALLEYS. FEEL
SOME OF THE MOMENTUM TRANSPORT WILL BE LIMITED BY CLOUD COVER ACROSS
THE NORTH...DESPITE STRONG PRESSURE FALLS ACROSS NORTHWEST UTAH AND
STRENGTHENING FLOW ALOFT. WILL ALLOW MIDNIGHT SHIFT TO RAISE ANY
HEADLINES AFTER GLANCE AT OVERNIGHT SATELLITE IMAGERY AND 00Z
GUIDANCE.

OTHERWISE...JUST SOME MINOR TWEAKS TO SKY/TEMPERATURES BASED ON
CURRENT OBSERVATIONAL TRENDS AND LATEST MODEL DATA.

PREVIOUS DISCUSSION FOLLOWS...
AS THE INITIAL SHORTWAVE EXITS LATE TONIGHT/EARLY TOMORROW...THE
AREA SHOULD SEE A BRIEF BREAK IN PRECIP. HOWEVER...AS STRONG WARM
ADVECTION DEVELOPS AHEAD OF THE NEXT APPROACHING SYSTEM...PRECIP
WILL BEGIN AGAIN IN THE AREA OF BEST LIFT OVER NORTHERN UTAH.
SOUTHWEST FLOW IS PROGGED TO INCREASE QUITE A BIT BY LATE IN THE DAY
SUNDAY...WHICH COULD PRODUCE SOME SIGNIFICANT WINDS OVER WESTERN
UTAH. EXPECT SOME HIGHLIGHTS MIGHT BE NEEDED...BUT WILL LET THE
MIDNIGHT SHIFT MAKE THE FINAL DECISION.

POTENT STORM SYSTEM AND ASSOCIATED STRONG COLD FRONT ARE ON TRACK
TO PUSH THROUGH THE CWA LATE SUNDAY THROUGH MONDAY. WITH AMPLE
MOISTURE...GOOD DYNAMICS...AND SIGNIFICANT FGEN FORCING...THERE
SHOULD BE A PERIOD OF INTENSE PRECIPITATION WITH THE FRONT. STRONG
NORTHWEST WINDS WILL ALSO ACCOMPANY THE BOUNDARY. TEMPERATURES
WILL DROP RAPIDLY...ALLOWING FOR THE POSSIBILITY OF SNOW TO THE
NORTHERN UTAH VALLEY FLOORS BY MONDAY AFTERNOON...WITH SOME
ACCUMULATIONS IN BENCH LOCATIONS. MOISTURE AND COLD POOL RELATED
INSTABILITY WILL REMAIN THROUGH MONDAY EVENING...ALLOWING FOR
PRECIP TO CONTINUE...ESPECIALLY IN AREAS FAVORED BY NORTHWEST
FLOW. WITH SUCH A COLD AIRMASS MOVING IN...LAKE EFFECT SNOW IS A
POSSIBILITY MONDAY NIGHT AND TUESDAY. CLEARING SKIES IN VALLEY
LOCATIONS COULD RESULT IN A HARD FREEZE FOR SOME LOCATIONS MONDAY
NIGHT AND TUESDAY NIGHT.

RESIDUAL MOISTURE AND INSTABILITY SHOULD ALLOW PRECIP TO LINGER
ACROSS THE NORTHERN AND CENTRAL MOUNTAINS THROUGH AT LEAST TUESDAY
AND PERHAPS INTO WEDNESDAY BEFORE HIGH PRESSURE RETURNS ON
THURSDAY. BOTH THE EC AND GFS INDICATE ANOTHER TROUGH AFFECTING
THE REGION NEXT WEEKEND...BUT IN THE 12Z GFS THIS IS A FASTER
MOVING GRAZING NORTHERN UTAH FRIDAY AND SATURDAY...WHILE IN THE EC
THIS IS A SLOWER SYSTEM THAT IMPACTS THE ENTIRE STATE SATURDAY AND
SUNDAY. HAVE KEPT POPS ABOVE CLIMO FOR THE END OF THE FORECAST
PERIOD.

&&

.AVIATION...SOUTHEAST WINDS EXPECTED TO STRENGTHEN AT THE SLC
TERMINAL LATE TONIGHT. THERE IS A 20 PERCENT CHANCE OF A SHOWER
REDUCING CEILINGS TO MVFR WITH A TEMPORARY NORTHWEST WIND THROUGH
04Z.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER WEATHER ADVISORY UNTIL MIDNIGHT MDT TONIGHT ABOVE 8000
     FEET FOR UTZ007>010-517.

     WINTER STORM WATCH FROM SUNDAY EVENING THROUGH LATE TUESDAY
     NIGHT FOR UTZ007>010-517.

WY...NONE.
&&

PUBLIC...ROGOWSKI
AVIATION...ROGOWSKI

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)

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
657 PM MDT SAT OCT 23 2010

UTZ001>016-019>021-517-518-WYZ021-241200-
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-
657 PM MDT SAT OCT 23 2010

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

.DAY ONE...TONIGHT

PRECIPITATION WILL BECOME SHOWERY TONIGHT ACROSS NORTHERN
UTAH...WITH SNOW RATES DIMINISHING BEYOND THE LATE EVENING ACROSS
THE MOUNTAINS. SNOW WILL CONTINUE ACROSS THE CENTRAL UTAH
MOUNTAINS WITH ADDITIONAL LIGHT ACCUMULATIONS THROUGH MUCH OF THE
NIGHT. HIGH ELEVATION ROADWAYS WILL LIKELY BE SLICK AND SNOW
COVERED.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

A WARM FRONT WILL SWEEP ACROSS THE AREA LATE TONIGHT THROUGH
SUNDAY. MUCH WARMER TEMPERATURES AND STRONG WINDS ARE EXPECTED
ACROSS THE MOUNTAINS AND WESTERN VALLEYS SUNDAY AFTERNOON. AREAS
OF HEAVY PRECIPITATION ASSOCIATED WITH THE WARM FRONT ARE
EXPECTED...THOUGH MOST OF THIS ACTIVITY WILL BE CONFINED TO THE
FAR NORTHERN PORTIONS OF UTAH AND SOUTHWEST WYOMING.

A STRONG COLD FRONT WILL ENTER NORTHWEST UTAH LATE SUNDAY...THEN
SWEEP SOUTH THROUGH THE AREA BY MIDDAY MONDAY. MUCH COLDER
TEMPERATURES AND WIDESPREAD RAIN AND SNOW WILL EXIST ALONG AND
BEHIND THE FRONT...ESPECIALLY ACROSS THE NORTHERN HALF OF THE
STATE. A WINTER STORM WATCH IS IN EFFECT FOR SUNDAY NIGHT
THROUGH TUESDAY NIGHT FOR THE NORTHERN AND CENTRAL MOUNTAINS.
HEAVY SNOW...POSSIBLY IN EXCESS OF TWO FEET...IS POSSIBLE WITH
THIS STORM. VALLEY LOCATIONS ACROSS NORTHERN AND WESTERN UTAH WILL
SEE SNOW...WITH THE POTENTIAL FOR SIGNIFICANT ACCUMULATIONS IN
THE NORTHERN VALLEYS.

THE COLDEST AIR OF THE FALL SEASON WILL ACCOMPANY THIS SERIES OF
STORMS. TEMPERATURES BY WEDNESDAY WILL LIKELY BE 10 TO 20
DEGREES OR MORE BELOW LATE OCTOBER NORMS.

THIS COLDER AIRMASS WILL BRING A THREAT OF A HARD FREEZE TO THE
NORTHERN AND CENTRAL VALLEYS THAT CLEAR OUT TUESDAY NIGHT INTO
WEDNESDAY MORNING...AND TO ALL BUT THE LOWEST SOUTHERN VALLEYS
WEDNESDAY NIGHT AND THURSDAY MORNING.

.SPOTTER INFORMATION STATEMENT...

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

ROGOWSKI

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