Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
322 PM MST SAT DEC 20 2014

.SHORT TERM...THIS EVENING THROUGH SUNDAY NIGHT
ISSUED AT 319 PM MST SAT DEC 20 2014

CURRENT SURFACE ANALYSIS SHOWS WARM FRONT JUST TO THE EAST OF THE
FORECAST AREA. UPPER LEVEL ANALYSIS DEPICTS NEAR ZONAL FLOW ACROSS
THE REGION...WITH A STRONG STORM SYSTEM AND UPPER JET PUSHING
ACROSS THE PACIFIC NW. WATER VAPOR IMAGERY SHOWS A WEAK SHORTWAVE
HAS MOVED EAST OF THE AREA...WITH PARTLY CLOUDY SKIES BEHIND IT.
TEMPS RANGE FROM THE UPPER 30S ACROSS FAR SOUTH CENTRAL SD TO NEAR
50 IN THE RAPID CITY AREA. WINDS ARE MOSTLY ON THE LIGHT SIDE FROM
THE WEST AND NORTHWEST.

A UNSETTLED PATTERN WILL TAKE SHAPE FOR THE END OF THE WEEKEND AND 
INTO EARLY NEXT WEEK AS A DEVELOPING LOW PRESSURE SYSTEM MOVES 
SOUTHEAST ACROSS THE REGION. HOWEVER...IT WILL REMAIN MILD INTO 
SUNDAY BEFORE THIS SYSTEM PUSHES IN. THE STORM WILL BRING AT LEAST 
SOME LIGHT RAIN AND SNOW TO MOST AREAS...ALONG WITH STRONG NORTHWEST 
WINDS EARLY NEXT WEEK. 

FOR TONIGHT...SKIES WILL REMAIN PARTLY CLOUDY IN GENERAL AS WEST TO 
SOUTHWEST WINDS DEVELOP. THE WINDS WILL BECOME BREEZY OVERNIGHT OVER 
PORTIONS OF NORTHEAST WY...ESPECIALLY CAMPBELL CO. RELATIVELY MILD 
TEMPS CAN BE EXPECTED...WITH LOWS IN THE 20S AND LOWER 30S...A BIT 
WARMER ACROSS THE EASTERN SLOPES OF THE BLACK HILLS. 

CLOUDS WILL BEGIN TO INCREASE FROM THE WEST SUNDAY MORNING...WITH 
SKIES BECOMING MOSTLY CLOUDY ACROSS THE ENTIRE AREA BY MID 
AFTERNOON. MILDER AIR WILL REMAIN ACROSS THE REGION THROUGH MUCH OF 
THE DAY...WITH HIGHS IN THE 40S AND LOWER 50S...WARMEST AGAIN ACROSS 
THE EASTERN SLOPES OF THE BLACK HILLS AND ADJACENT PLAINS. 
DEVELOPING LOW PRESSURE WILL MOVE ACROSS NORTHERN MT DURING THE DAY 
AND INTO ND/NORTHERN SD SUNDAY NIGHT...DRAGGING A COLD FRONT ACROSS 
THE CWA DURING THE AFTERNOON AND EVENING HOURS. RAIN SHOWERS WILL 
DEVELOP ALONG AND BEHIND THE COLD FRONT...MOSTLY DURING THE 
AFTERNOON...AS UPPER LEVEL ENERGY ACCOMPANIES THE FRONT. THE BEST 
CHANCES DURING THE AFTERNOON LOOK TO BE ACROSS FAR NORTHEAST 
WY...SOUTHEAST MT...FAR NORTHWEST SD...AND EVENTUALLY THE NORTHERN 
BLACK HILLS AREA. NORTHWESTERLY WINDS WILL INCREASE BEHIND THE FRONT 
LATE SUNDAY AND SUNDAY NIGHT...BECOMING BREEZY TO WINDY IN MANY 
AREAS OVERNIGHT.  

UPPER TROF AND DEVELOPING LOW PRESSURE SYSTEM WILL TRACK FROM MT ON 
SUNDAY TO SOMEWHERE OVER THE EASTERN DAKOTAS ON MONDAY MORNING. 
VARIOUS MODELS CONTINUE TO BE IN SOME DISAGREEMENT ON TRACK AND 
STRENGTH OF THIS SYSTEM. FOR SUNDAY NIGHT...WILL KEEP THE BEST 
CHANCES FOR PCPN OVER NORTHEASTERN PORTIONS OF THE CWA...AS WELL AS 
THE NORTHERN BLACK HILLS AREA. PCPN WILL GRADUALLY CHANGE OVER TO 
SNOW SUNDAY NIGHT...WITH THE QUICKEST CHANGE OVER THE BLACK HILLS. 
NOT EXPECTING MUCH IN THE WAY OF SNOW ACCUMULATION OVER THE PLAINS 
AS MOST OF THE PCPN WILL BE OUT OF THE AREA BY THE TIME TEMPS DROP 
OFF ENOUGH. HOWEVER...FORECAST SOUNDINGS AND FROUDE ANALYSIS SUGGEST 
FAVORABLE CONDITIONS FOR AT LEAST OCCASIONAL SNOW OVER THE NORTHERN 
BLACK HILLS SUNDAY NIGHT INTO MONDAY AS UPSLOPE NORTHWESTERLY FLOW 
INCREASES. HAVE RAISED POPS OVER THESE AREAS SUNDAY NIGHT AND HAVE 1 
TO 3 INCHES OF ACCUMULATION ACROSS THE HIGHER TERRAIN THROUGH EARLY 
MONDAY MORNING. LOWS SUNDAY NIGHT WILL BE IN THE MID 20S TO LOWER 
30S ACROSS THE FORECAST AREA.   

.LONG TERM...MONDAY THROUGH SATURDAY
ISSUED AT 321 PM MST SAT DEC 20 2014

UPPER TROF WILL DIG OVER THE DAKOTAS MONDAY AND REMAIN 
OVER THE UPPER MIDWEST THROUGH TUESDAY. WHILE MODELS INITIALLY HAVE 
A SIMILAR PLACEMENT WITH THE TROF AXIS OVER THE EASTERN DAKOTAS 
MONDAY MORNING...THEY ARE QUITE DIFFERENT WITH THE STRENGTH AS THE 
GFS CLOSES A LOW OVER SOUTHEASTERN SD WITH THE NAM FARTHER NORTH AND 
THE ECMWF ONLY A TROF...EVENTUALLY FORMING A CLOSED LOW BUT NOT AS 
STRONG. WITH 120-140KT JET COMING OVER WEST COAST RIDGE AND 
DIVING INTO THE UPPER TROF...THE STRONGER GFS WOULD BE A BETTER 
SOLUTION. DEEP VERTICALLY STACKED LOW WILL HAVE A STRONG PRESSURE 
GRADIENT ACROSS WESTERN SD...WITH GUSTS LIKELY TO REACH 50KT...AS 
FORECAST SOUNDINGS SHOW >50KT MOMENTUM TRANSFER. PRECIPITATION WILL 
SPREAD ACROSS FORECAST AREA MONDAY...COULD STILL SEE SOME RAIN/SNOW 
MIX EARLY BEFORE CHANGING TO SNOW. FROUDE NUMBER INCREASES TO MORE 
THAN 2 MONDAY MORNING...ALONG WITH 90-100 PERCENT RH AND STRONG 
WINDS...SO UPSLOPE SNOW IS LIKELY OVER THE NORTHERN BLACK 
HILLS...WHILE DOWNSLOPE WINDS WILL KEEP PRECIP TO A MINUMUM FROM 
RAPID CITY TO HOT SPRINGS AND EDGEMONT. DEPENDING ON THE AMOUNT OF 
PRECIPITATION...A WINTER WEATHER ADVISORY MAY BE MORE APPROPRIATE 
THAN A HIGH WIND WARNING AS BLOWING SNOW WOULD HAVE THE GREATER 
IMPACT. SNOW AND GUSTY WINDS MAY LINGER TUES AS A SECONDARY LOW 
ROTATES AROUND MAIN STORM CENTER. BRIEF RIDGE WILL BUILD ON 
WEDNESDAY BEFORE THE NEXT SYSTEM COMES ACROSS THE NORTHERN PLAINS ON 
CHRISTMAS DAY. MODELS IN GOOD AGREEMENT WITH A FAST-MOVING LONGWAVE 
TROF. CYCLONIC NORTHWEST FLOW REMAINS BEHIND THE TROF FRIDAY...WITH 
UPPER RIDGING SLOW TO BUILD TOWARD NEXT WEEKEND.

&&

.AVIATION...FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING
ISSUED AT 321 PM MST SAT DEC 20 2014

CLDS CONT TO CLR BEHIND A SHORT WAVE TROF CROSSING THE 
NRN PLNS...WITH HI CLDS ADVANCING FRM THE WEST. WNDS WL BE LGT THRU 
THE EVEN...THEN SW WNDS WL INCRS OVR NERN WY.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&

$$

SHORT TERM...26
LONG TERM...55
AVIATION...55





National Weather Service Glossary of Abbreviations