000
FXUS63 KUNR 092318
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
518 PM MDT SUN MAR 9 2014

.SHORT TERM...THIS EVENING THROUGH MONDAY NIGHT
ISSUED AT 248 PM MDT SUN MAR 9 2014

PAC AIRMASS IN PLACE WITH APPRECIABLE MID AND UPPER
LEVEL MOISTURE ADV ONGOING OVER THE REGION. ROCKIES AND LOCAL
BLKHLS DOWNSLOPING HAS SUPPORTED VERY MILD CONDITIONS OVER MOST OF
THE REGION...WITH 60S AND 70S COMMON. COOLER TEMPS PREVAIL OVER NE WY
WHERE THICK CLOUDS HAVE STRONGLY LIMITED INSOLATION. INITIAL
IMPULSE AND SFC LOW WILL PROGRESS ACROSS SOUTHERN SK/MB
TONIGHT...SHIFTING THE MAIN THERMAL RIDGE EAST OF THE FA...AS THE
PAC NW UPPER TROUGH SHIFTS EAST. THIS WILL SUPPORT A WEAK SFC
TROUGH INTO THE REGION BY MONDAY MORNING...WITH WINDS SHIFTING NE
AND CAA ENSUING NE AREAS. MEANWHILE THE PAC NW UPPER TROUGH WILL
PROGRESS EAST AND SUPPORT INCREASING CLOUD COVER AND LSA ACROSS THE
REGION...SUPPORTING THE DEVELOPMENT OF A FGEN BAND OF PRECIP ACROSS
NORTHERN AREAS BY MONDAY AFTERNOON. LSA AND LL MOISTURE
TRANSPORT/CONVERGENCE WILL INCREASE MONDAY EVENING SUPPORTING A
DESCENT PERIOD OF LIFT ACROSS THE AREA WITH SOME JET STREAK
INFLUENCED LIFT. PRECIP WILL START AS RAIN AND TRANSITION TO SNOW
MONDAY EVENING NORTH TO SOUTH. TIMING OF PRECIP SWITCH OVER WILL
COMPLICATE THE FORECAST AS THIS WILL DICTATE RESULTING SNOW ACCUMS.
CAA WILL DOMINANT TUES AS THE UPPER WAVE AND ASSOCIATED PRECIP EXITS
THE REGION TUES MORNING. CAA WITH PRESSURE RISES WILL SUPPORT A
WINDY DAY TUES WITH ADV OR NEAR ADV CONDITIONS ACROSS MOST OF THE SD
PLAINS...ESP IN THE LEE OF THE BH.

TONIGHT...WESTERLY DOWNSLOPE  FLOW WILL PERSIST THROUGH MOST OF THE
NIGHT WITH VERY MILD CONDITIONS EXPECTED MOST PLACES...ESP IN THE LEE
OF THE BH. HAVE RAISED MINS MOST PLACES ESP INVOF RAPID CITY.
CLOUDS WILL ALSO BE ON THE INCREASE AS MOISTURE ADV AND
MOUNTAIN GRAVITY WAVE INTERACTION PERSISTS.

MONDAY...SFC TROUGH AND ASSOCIATED COLD FRONT WILL 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 THE DEVELOPMENT OF A BAND OF
RAIN ACROSS THE NORTHERN ZONES BY AFTERNOON...WHICH IS EXPECTED TO
INTENSIFY AND SHIFT EAST THROUGH THE EVENING. FORECAST MODELS HAVE
BEEN AND REMAIN ADAMANT IN PROGGING APPRECIABLE STEEP MID LEVEL
LAPSE RATES THROUGH THE LAYER OF INCREASING FGEN ALOFT...SUPPORTING
GROWING CONDITIONAL INSTABILITY AND RESULTING IN A LIKELY CONVECTIVE
RESPONSE GIVEN THE AMOUNT OF PW /0.6-0.7/ AS PROGGED IN NAM/GFS
SOLUTIONS. THIS COUPLED WITH A PERIOD OF STRONG LSA AND POSSIBLE JET
STREAK ENTRANCE REGION ENHANCED LIFT...WITH NEARLY 315K AT H7...WILL
SUPPORT A PERIOD OF MODERATE TO HEAVY SNOW IN THE NORTHERN HALF OF
THE FA. THE QUESTION WILL BE HOW FAST WILL THE RAIN TO SNOW CHANGE
OVER OCCUR. CERTAINLY WILL BE EARLY ENOUGH IN THE NORTHERN BH TO
SUPPORT THE THREAT FOR WARNING SNOWS GIVEN AVAILABLE MOISTURE AND
FORCING. HAVE INTRODUCED COLD AIR IN THE AREA QUICKER EFFECTIVELY
DROPPING TEMPS...AND THIS PRODUCES SLIGHTLY HIGHER SNOW TOTALS.
ANOTHER IMPORTANT QUESTION THAT STILL REMAINS SEMI-ELUSIVE IS THE
PLACEMENT OF THE FGEN BAND. THE 12Z MODELS HAVE SHIFTED THIS BAND
FARTHER NORTH...WHICH COULD BE A SIGN OF CONVECTIVE FEEDBACK.
ALTHOUGH THE 18Z NAM REMAINS PERSISTENT WITH THIS GENERAL LOCATION
ACROSS THE NW SD ZONES. GIVEN ABOVE CONCERN WITH THE NORTHERN HILLS
SEEING THE BEST CHANCE FOR WARNING SNOWS...WILL ISSUE A WINTER STORM
WATCH THERE. ALREADY HAVE 5-6 INCHES IN THE GRIDS OVER SOUTHERN
LAWRENCE COUNTY/MOST FALLING IN A 6 HOUR PERIOD/ AND FEEL THE
POTENTIAL FOR HIGHER AMOUNTS IS THERE. MORE UNCERTAINTY WRT TO THE
SD PLAINS ATTM WITH RAIN LIKELY DOMINATING THROUGH EVENING THERE.

TUE...SNOW WILL SHIFT SOUTH OUT OF THE AREA TUE WITH SKIES CLEARING
AND WINDS INCREASING. ADV TO NEAR ADV WINDS EXPECTED ON THE SD
PLAINS...ESP IN THE LEE OF THE BH. HAVE ADJUSTED TEMPS WITH SLIGHTLY
COOLER READINGS EXPECTED. SNOW COVER WILL CERTAINLY DICTATE HIGHS
ALSO. COLDER CONDITIONS EXPECTED TUE NIGHT AND HAVE ADJUSTED LOWS DOWN
SOME.

&&

.LONG TERM...TUESDAY THROUGH SUNDAY
ISSUED AT 248 PM MDT SUN MAR 9 2014

UPPER RIDGING WILL BRING DRY CONDITIONS AND ABOVE
AVERAGE TEMPERATURES FOR THE SECOND HALF OF THE WEEK. THE NEXT WAVE
DIVES THRU THE NWRLY FLOW FOR THE UPCOMING WEEKEND BRINGING THE NEXT
CHANCES FOR RAIN/SNOW AND SLIGHTLY COOLER TEMPERATURES.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 517 PM MDT SUN MAR 9 2014

VFR CONDITIONS WILL CONTINUE THROUGH MONDAY AFTERNOON.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WATCH FROM MONDAY EVENING THROUGH TUESDAY MORNING
     FOR SDZ024-028.

WY...WINTER STORM WATCH FROM MONDAY EVENING THROUGH TUESDAY MORNING
     FOR WYZ057.

&&

$$

SHORT TERM...JC
LONG TERM...13
AVIATION...HELGESON