Area Forecast Discussion
Issued by NWS Salt Lake City, UT

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FXUS65 KSLC 231607
AFDSLC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
907 AM MST MON FEB 23 2015

.SYNOPSIS...AN UPPER LEVEL LOW PRESSURE SYSTEM WILL INTENSIFY TO
THE WEST OF UTAH TODAY...THEN TRACK EAST SOUTHEAST ACROSS NORTHERN
ARIZONA ON TUESDAY. HIGH PRESSURE ALOFT WILL BRIEFLY RETURN TO
THE REGION TUESDAY NIGHT...FOLLOWED BY A COUPLE OF WEAK WEATHER
DISTURBANCES CROSSING THE REGION MIDWEEK.

&&

.DISCUSSION...WATER VAPOR LOOP SHOWS A CLOSED LOW OVER CENTRAL
CALIFORNIA. AMDAR 400-250MB WIND OBSERVATIONS INDICATE A CYCLONIC
JET OF 100-130KT JET AROUND THE CLOSED LOW...WITH THE LEFT EXIT
REGION NEAR THE FOUR CORNERS. GOES/GPS/RAP/12Z RAOB INDICATE THE
PRECIPITABLE WATER VALUE RANGES BETWEEN 0.05-0.10" FAR NORTH...TO
0.45-0.50" FAR SOUTH. BLENDED TOTAL PRECIPITABLE WATER PRODUCT
INDICATES A MOISTURE TAP INTO THE SOUTHWEST CONUS. THERE IS A
STRONG DELINEATION BETWEEN ABNORMALLY DRY AND MOIST AIRMASSES NEAR
INTERSTATE 70.

PRESSURE GRADIENT WILL SLACKEN AND RE-ORIENT ITSELF TOWARD NORTH-
SOUTH THROUGH THE DAY PER RAP. THUS...EXPECT EASTERLY
DOWNSLOPE/CANYON WINDS TO SLACKEN THROUGH THE DAY ALONG THE NORTHERN
WASATCH. KEPT WARNING GOING FOR LOCALIZED 60+ MPH AND MORE
WIDESPREAD 45-55 MPH GUSTS THAT ARE ONGOING. ANTICIPATE LETTING HIGH
WIND WARNING EXPIRE AT 11 AM.

SNOW RATES INCREASED LATE LAST NIGHT INTO THIS MORNING ACROSS
SOUTHERN UTAH. THIS WAS SUPPORTED BY INCREASING 700MB FRONTOGENESIS
DUE TO ARRIVAL OF LEFT EXIT OF THE UPPER LEVEL JET. DYNAMICAL
SUPPORT WILL SHIFT TOWARD THE EAST AS THE DAY PROGRESSES...WE
ANTICIPATE BEST SNOW RATES THIS AFTERNOON TO BE NEAR GREEN
RIVER...HANKSVILLE...BULLFROG. ISSUED A WINTER WEATHER ADVISORY FOR
DIXIE EARLIER DUE TO WINTER DRIVING CONDITIONS AS SEEN ON WEBCAMS.
THESE SHOULD ABATE QUICKLY THIS MORNING WITH SOLAR INSOLATION. WILL
KEEP THIS UP FOR A COUPLE MORE HOURS.

WILL ALSO ASSESS POSSIBILITY OF LOWERING WINTER STORM WARNING FOR
SANPETE/SEVIER VALLEYS IN A COUPLE OF HOURS BASED ON NEWER DATA.

PREVIOUS DISCUSSION FOLLOWS...

THE UPPER LOW CURRENTLY OVER CENTRAL CALIFORNIA BECOMING BETTER
ORGANIZED LATE TONIGHT. INCREASINGLY STRONG UPWARD MOTION EVIDENT IN
RAPIDLY COOLING CLOUD TOPS AND EXPANDING AREA OF PRECIP IN TO THE
EASTERN FLANK OF THE LOW AT THIS TIME. GOOD BAROCLINIC STRUCTURE AND
SOLID UPPER LEVEL DIVERGENCE SHOULD MAINTAIN STRONG LIFT ACROSS
SOUTHERN UTAH INTO THIS EVENING. THIS RATHER BROAD AREA OF SYNOPTIC-
SCALE LIFT WILL PRIMARILY IMPACT SOUTHWEST AND SOUTH-CENTRAL UTAH
THROUGH TONIGHT TODAY AS THE CENTER OF THE UPPER LOW HOLDS BACK
ACROSS CALIFORNIA.

PRECIP WILL EXPAND NORTH AND EAST TONIGHT AS THE CENTER OF THE UPPER
LOW MOVES INTO SOUTHERN NEVADA THIS EVENING...THEN EAST-SOUTHEAST
ACROSS NORTHERN ARIZONA LATE TONIGHT/TUESDAY. LOOKING AT A FAIRLY
SHARP LINE BETWEEN HEAVY PRECIP AND DRY CONDITIONS ACROSS CENTRAL
UTAH AS THE UPPER LOW DEVELOPS A TIGHTER CIRCULATION AS IT MOVES
INTO NORTHWEST ARIZONA. THIS LINE WILL DRIFT SOUTH WITH THE UPPER
LOW DURING THE DAY TUESDAY.

AT THIS POINT THE GREATEST SNOW TOTALS WILL OCCUR ACROSS THE
SOUTHERN MOUNTAINS DUE TO THE LONGER DURATION CLOSER TO THE CENTER
OF THIS UPPER LOW. ADJACENT VALLEY LOCATIONS...ESPECIALLY THE HIGHER
VALLEY LOCATIONS OF SOUTHWEST AND SOUTH-CENTRAL UTAH WILL CONTINUE
TO RECEIVE PERIODS OF HEAVY SNOW THROUGH EARLY TUESDAY MORNING.

A PROGRESSIVE SHORTWAVE RIDGE TRAILING THE EXITING UPPER LOW WILL
SHIFT SOUTH ACROSS THE FORECAST AREA TONIGHT. BEHIND THIS UPPER
RIDGE A FAST-MOVING AND WEAK SHORTWAVE WILL CROSS UTAH WEDNESDAY.
THIS FEATURE COULD GENERATE SOME LIGHT PRECIP...BUT MORE LIKELY WILL
BRING CLOUDS AND KEEP TEMPS DOWN A BIT ACROSS THE NORTH AND EAST. A
SECOND SHORTWAVE SCHEDULED TO MOVE THROUGH WEDNESDAY NIGHT WILL
BRING ADDITIONAL LIGHT PRECIP...CLOUDS AND STILL COOLER AIR INTO THE
STATE FOR THURSDAY.

THE NEXT SHORTWAVE IN THE NORTHWESTERLY STORM TRAIN IS FORECAST TO
DROP INTO THE REGION THROUGH THE DAY THURSDAY. THE ECMWF AND GFS ARE
STILL IN DISAGREEMENT ABOUT EXACTLY HOW STRONG THIS WAVE WILL BE
WITH REGARDS TO PRECIPITATION...BUT BOTH PAINT AT LEAST SOME QPF
OVER NORTHERN UTAH...SO HAVE INCREASED POPS THROUGH THIS PERIOD.
THIS MOIST AND SLIGHTLY UNSTABLE NORTHWESTERLY FLOW LOOKS TO LINGER
OVER THE AREA THROUGH THURSDAY NIGHT AND INTO FRIDAY.

GLOBAL MODELS STILL BRING THE LONGWAVE TROUGH DOWN INTO THE WESTERN
CONUS FRIDAY NIGHT THROUGH SATURDAY...WITH A VERY LARGE AREA OF
COLDER TEMPERATURES AND INCREASED CHANCE OF PRECIPITATION. AS FAR AS
UTAH IS CONCERNED...THERE IS STILL SOME UNCERTAINTY ABOUT WHETHER
THE ENTIRE STATE WILL GET A DECENT PRECIPITATION EVENT. THE 00Z
MODELS ALLOWED THE BEST ENERGY TO DIG TO THE SOUTH...WITH PRIMARILY
THE SOUTHERN HALF OF THE STATE GETTING EXTENDED
PRECIPITATION...SIMILAR TO THE EVENT CURRENTLY ONGOING AS OF THIS
WRITING. HAVE KEPT POPS ELEVATED ACROSS THE ENTIRE CWA FRIDAY NIGHT
THROUGH SUNDAY...BUT INCREASED POPS A BIT MORE ACROSS THE SOUTH TO
ACCOUNT FOR THIS NEW SOLUTION.

HEADING INTO THE BEGINNING OF NEXT WEEK...THE LARGE TROUGH IS
PROGGED TO EXIT THE REGION ON MONDAY...BUT YET ANOTHER TROUGH COULD
ENTER THE GREAT BASIN ON TUESDAY AND WEDNESDAY.

&&

.AVIATION...EASTERLY WINDS ARE EXPECTED TO GRADUALLY SHIFT TO THE
NORTH AND DECREASE AT THE SLC TERMINAL BETWEEN 18 AND 20Z TODAY.
THERE IS A 40 PERCENT CHANCE THAT WINDS WILL SHIFT TEMPORARILY TO
SOUTHEAST OR SOUTHWEST DUE TO LOCAL EDDY EFFECTS FROM EASTERLY WINDS
OFF THE WASATCH MOUNTAINS. NO VSBY OR CIG ISSUES.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...WINTER STORM WARNING UNTIL 8 AM MST TUESDAY FOR UTZ013-014-016-
     020-021-517-518.

     WINTER WEATHER ADVISORY UNTIL NOON MST TODAY FOR UTZ019.

     HIGH WIND WARNING UNTIL 11 AM MST THIS MORNING FOR UTZ002-003.

WY...NONE.
&&

$$

PUBLIC...ROGOWSKI/CONGER/SCHOENING
AVIATION...STRUTHWOLF

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)



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