Winter Storm Warning 2, NWS Rapid City, SD

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
301 PM MDT MON MAR 10 2014

.SHORT TERM...THIS EVENING THROUGH TUESDAY NIGHT
ISSUED AT 235 PM MDT MON MAR 10 2014

NW CONUS UPPER TROUGH ADVANCING EAST WITH PAC MOISTURE
ADVECTING OVER THE REGION AHEAD OF THIS FEATURE. THIS UPPER TROUGH
WILL SPLIT OVER THE CENTRAL ROCKIES WITH THE NORTHERN VORT LOBE
ADVANCING ACROSS THE FA TONIGHT AND SUPPORTING RAIN AND SNOW.
IMPRESSIVE COMPACT SHORTWAVE TROUGH EXPECTED INTO THE AREA
TONIGHT...WITH STEEP MID LAPSE RATES AND STRONG MOISTURE CONVERGENCE
AND LIFT. PREVIOUS FORECAST PRETTY MUCH ON TRACK WITH THE BIGGEST
ISSUE PER THIS SYSTEM BEING THE TIMING OF WHEN PRECIP WILL SWITCH TO
SNOW. A PERIOD OF COMBINED STRONG LSA AND LL CONVERGENCE IS EXPECTED
SUPPORTING A PERIOD OF DECENT SNOW ACCUMS...ESP IN THE NORTHERN
BLACK HILLS. NORTHERN STREAM UPPER TROUGH WILL DROP SE EAST OF THE
FA SUPPORTING A SECONDARY COLD FRONT INTO THE REGION TUES AFTERNOON.
THIS SYSTEM WILL ALSO BRING GUSTY NW WINDS TO THE SD PLAINS.

TONIGHT...PRIMARY SFC COLD FRONT CONTINUES TO SAG SOUTH IN THE
REGION. HELPING TO ESTABLISHED AN ELEVATED FGEN LAYER ACROSS THE
NORTHERN ZONES AS THE PAC NW COMPACT IMPULSE ADVANCES TOWARD THE
REGION. INCREASING LSA WITH ONGOING MOISTURE ADV ALOFT COUPLED WITH
INCREASED FGEN FORCING WILL LEAD TO EXPANSION OF THE THE RAIN BAND
ACROSS MT INTO NW SD BY EVENING. COLUMNS WILL COOL THROUGH THE
EVENING WITH THE FGEN BAND SLOWLY DRIFTING SOUTH THROUGH THE NIGHT.
DECENT UPGLIDE SIGNAL NOTED IN ISENTROPIC CHARTS WITH 30 KNOTS OF
CROSS ISOBARIC FLOW INDICATED. KEY TO THE SETUP WILL BE STEEP MID
LEVEL LAPSE RATES WITH 7C/KM PROGGED IN THE NAM...STARTING AT THE
BASE OF THE FRONTAL INVERISON AND EXTENDING THROUGH THE DGZ. 50 MB
DEEP DGZ NOTED IN FORECAST MODELS WHICH SHOULD SUPPORT MODERATE
SNOWFALL RATES FOR A PERIOD OF TIME...ESP IN THE 09-12Z PERIOD
ACROSS THE NORTHERN HILLS...GIVEN PW VALUES IN THE 0.6-0.7 INCH
RANGE. TIMING OF PRECIP SWITCH OVER IS AND REMAINS DIFFICULT WITH A
SLIGHTLY EARLY SWITCH OVER FORECAST GIVEN CONCERNS ON STRONG DYNAMIC
LIFT/COOLING. NE PORTIONS OF THE BH AROUND THE LEAD/DEADWOOD AREA
WILL BE IN A PRIME LOCATION FOR UPSLOPE ENHANCEMENT GIVEN DEEP NE
FLOW EVENTUALLY EXTENDING INTO THE DGZ BY EARLY MORNING WITH COLUMN
COOLING. THIS COUPLED WITH EARLIER SWITCH OVER /PER ELEVATION/IS
EXPECTED TO SUPPORT WARNING SNOWS THERE...EXTENDING NW INTO THE BEAR
LODGE MOUNTAINS. WILL UPGRADE TO A WARNING THERE. DECIDED TO ISSUE
AN WW ADV OVER NE WY INTO THE SD PLAINS FOR 2-4 INCHES OF SNOW
WHERE AN FGEN BAND WILL SUPPORT A PERIOD OF MODERATE SNOWFALL
RATES.. WILL ALSO ISSUE A WW ADV FOR 2-4 INCHES ACROSS THE CENTRAL
BLACK HILLS WHERE ELEVATION WILL WILL ALLOW HIGHER SNOW TOTALS.
GUSTY NORTHERLY WINDS ARE ALSO EXPECTED ON THE WY PLAINS GIVEN A
SHARP PRESSURE RISE SIGNAL EARLY TUE MORNING. THIS MAY LEAD TO SOME
DRIFTING BLOWING/DRIFTING FOR A PERIOD TIME.

SNOW WILL CONTINUE INTO TUE MORNING...ENDING BY LATE MORNING AS THE
SYSTEM QUICKLY EXITS THE REGION. TEMPS ARE EXPECTED TO RISE INTO THE
30 AND LOWER 40S MOST PLACES GIVEN STRONG BL MIXING PER CAA/STEEP LL
LAPSE RATES AND A SECONDARY COLD FRONT. HAVE ADJUSTED WINDS FOR
THIS. WINDS ARE NOT EXPECTED TO CAUSE ANY BLOWING SNOW CONCERNS TUE
GIVEN FAIRLY WARM BL TEMPS. GENERALLY COLD CONDITIONS EXPECTED TUE
NIGHT ALTHOUGH WINDS WILL REMAIN UP THROUGH THE NIGHT MOST PLACES
AND ARE EXPECTED TO MODERATE TEMPS TO A DEGREE. SMALL ADJUSTMENT MADE
TO TEMPS.

&&

.LONG TERM...WEDNESDAY THROUGH MONDAY
ISSUED AT 235 PM MDT MON MAR 10 2014

UPPER RIDGING ACROSS THE WESTERN CONUS WILL BRING DRY
CONDITIONS AND ABOVE AVERAGE TEMPERATURES THROUGH FRIDAY. THE NEXT
SHORTWAVE DIVES THRU THE NORTHERN PLAINS IN NWRLY FLOW FOR FRIDAY
NIGHT AND THE UPCOMING WEEKEND...BRINGING CHANCES FOR RAIN/SNOW AND
SLIGHTLY COOLER TEMPERATURES.

&&

.AVIATION...FOR THE 18Z TAFS THROUGH 18Z TUESDAY
ISSUED AT 235 PM MDT MON MAR 10 2014

VFR CONDITIONS WILL CONTINUE THROUGH THIS AFTERNOON.
CONDITIONS WILL DETERIORATE QUICKLY TONIGHT AS RAIN MOVES IN AND
CHANGES OVER TO SNOW FROM NORTH TO SOUTH BRINGING WIDESPREAD LIFR
CIGS/VIS AFTER 03Z ACROSS NORTHWEST SOUTH DAKOTA...AND BY 06Z ACROSS
THE REMAINDER OF THE AREA. THESE CONDITIONS WILL PERSIST THROUGH 18Z
ON TUESDAY.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO NOON MDT TUESDAY
     FOR SDZ024-025.

     WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO NOON MDT
     TUESDAY FOR SDZ001-002-012>014-028-072-073.

WY...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO NOON MDT TUESDAY
     FOR WYZ057.

     WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO NOON MDT
     TUESDAY FOR WYZ054-056-071.

&&

SHORT TERM...JC
LONG TERM...15
AVIATION...15

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