National Weather Service Raw Text Product

791 
FXUS63 KFSD 092332
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
532 PM CST WED JAN 9 2013

.DISCUSSION.../ISSUED AT 328 PM CST/
A DEEP TROUGH OF LOW PRESSURE DIGGING ONTO THE WEST COAST WILL 
SPREAD INTO THE NORTHERN ROCKIES BY TOMORROW. THIS WILL ALLOW LOW 
PRESSURE OVER TEXAS TO LIFT NORTHWARD WHICH WILL AFFECT THE AREA ON 
THURSDAY. HIGH PRESSURE AT THE SURFACE WILL SHIFT EAST TONIGHT WHICH 
WILL ALLOW A STRONG SOUTHERLY GRADIENT TO DEVELOP. THE COOLEST 
OVERNIGHT LOWS WILL BE ACROSS NORTHWEST IOWA...BUT EVEN HERE LOWS 
WILL LIKELY STILL BE IN THE 20 TO 25 DEGREE RANGE. IN CENTRAL SOUTH 
DAKOTA WHERE SOUTHERLY WINDS WILL BE STRONGEST LONGEST LOWS WILL BE 
CLOSER TO 30 TO 35 DEGREES. HIGH CLOUDS WILL BE ON THE INCREASE FROM 
THE SOUTH THROUGH THE NIGHT BUT THE DEEPEST MOISTURE AND CLOUD COVER 
WILL HOLD OFF UNTIL THURSDAY MORNING AND AFTERNOON. SOME PATCHY FOG 
WILL BE POSSIBLE IN LOWER SPOTS OF MAINLY NORTHWEST IOWA BUT WITH 
THE STRONG SOUTHERLY GRADIENT DO NOT EXPECT ANY MAJOR PROBLEMS. 

THIS LEADS INTO THURSDAY WHICH WILL SEE SOME PRECIPITATION ISSUES 
THROUGH THE DAY. WILL BE TOSSING OUT THE NAM SURFACE CONDITIONS 
RIGHT OFF THE BAT AS IT CONTINUES TO SUFFER FROM SNOW COVER 
ISSUES...MAINLY REMAINING TOO COLD. ALOFT ALL THE MODELS ARE FAIRLY 
AGREEABLE ALTHOUGH THE COLDER NAM SEEMS TO EXTEND UP TO ABOUT 925MB. 
EXPECT STRONG MOISTURE ADVECTION FROM SOUTH TO NORTH FROM ABOUT 15Z 
THURSDAY THROUGH 0Z FRIDAY. THIS IS WHERE A PERIOD OF RAIN SHOULD 
DEVELOP AND LIFT NORTH AND POSSIBLY POSE THE BIGGEST PROBLEM OF THE 
DAY. TEMPERATURES WILL BE FAIRLY CLOSE TO 32 DEGREES WHILE THIS RAIN 
IS FALLING SO THERE WILL BE A THREAT FOR A LITTLE OF THIS RAIN TO 
FREEZE ON EXPOSED SURFACES. HOWEVER...AT THIS TIME LEANING TOWARD 
TEMPERATURES AT THE SURFACE CLOSER TO 33 TO 35 DEGREES WHICH WOULD 
SUGGEST LITTLE OR NO FREEZING AT THE SURFACE. AFTER THIS BAND OF 
FORCING PRESSES THROUGH THE MID LEVELS REALLY DRY OUT AND SATURATION 
DOES NOT OCCUR AT TEMPERATURES COLDER THAN -10 DEGREES C...SO LIKELY 
TRANSITION TO DRIZZLE THROUGH THE AFTERNOON. HIGHS TOMORROW SHOULD 
RANGE FROM AROUND 40 IN CENTRAL SOUTH DAKOTA TO THE MID 30S EAST OF 
THE JAMES RIVER VALLEY. THE BIGGEST POTENTIAL CHANGES TO THE 
FORECAST WILL BE IF CONFIDENCE INCREASES THAT SURFACE TEMPERATURES 
WILL BE BELOW FREEZING DURING THE DAY...BUT AT THIS TIME THAT DOES 
NOT LOOK LIKELY. /08

ON THURSDAY NIGHT MUCH OF ANY MEASURABLE PRECIPITATION WILL SHUT 
DOWN WITH THE MID LEVELS CONTINUING TO DRY OUT ACROSS THE AREA. 
HOWEVER...LOW LEVELS REMAIN SATURATED WITH JUST ENOUGH LIFT TO 
PRODUCE DRIZZLE AND AREAS OF FOG ACROSS MUCH OF THE AREA OVERNIGHT. 
PRECIP TYPE IS AGAIN TRICKY DEPENDENT ON WHAT SURFACE TEMPERATURES 
DO...AND SOME LOCALES IN OUR FAR NORTH AND WEST COULD DIP TO 
FREEZING VERY LATE THURSDAY NIGHT...RESULTING IN SOME VERY LIGHT 
FREEZING RAIN/FREEZING DRIZZLE WHICH COULD COAT UNTREATED SURFACES. 
EVEN SO...QPF AMOUNTS WOULD BE VERY LIGHT WITH ONLY MINIMAL ICE 
ACCUMULATIONS EXPECTED AT THIS TIME.

AN UPPER LEVEL LOW BEGINS TO LIFT OUT OF THE CENTRAL ROCKIES ON 
FRIDAY...AS A SURFACE INVERTED TROUGH NUDGES INTO OUR WEST DURING 
THE DAY. MIDLEVELS REMAIN DRY ACROSS MOST OF THE AREA 
HOWEVER...PRODUCING MAINLY DRIZZLE OR FREEZING DRIZZLE DEPENDENT ON 
TEMPERATURES...WITH THE BETTER CHANCE OF PRECIPITATION BEING HELD TO 
OUR FAR WEST AND NORTH WHERE DEEPER MOISTURE AND OPTIMAL LIFT WITH 
AFOREMENTIONED WAVE WILL RESIDE. MODELS IN FAIRLY DECENT AGREEMENT 
ON SUB ZERO C 850 MB TEMPERATURES SLOWLY CREEPING EASTWARD THROUGH 
THE DAY BEHIND THE INVERTED TROUGH...BEING POSITIONED SOMEWHERE 
ALONG THE INTERSTATE 29 CORRIDOR BY LATE AFTERNOON...RESULTING IN 
ANY PRECIPITATION OVER THAT AREA TRANSITIONING TO LIGHT SNOW. A 
STRONG SOUTHERLY FLOW OUT AHEAD OF THE SYSTEM WILL BRING RELATIVELY 
MILD TEMPERATURES IN OUR SOUTHEAST WITH HIGHS NEAR 40 THROUGH MUCH 
OF NORTHWESTERN IOWA. IN OUR FAR WEST...TEMPERATURES WILL SLIDE INTO 
THE MID 20S BY AFTERNOON. LIKELY CHANCE OF LIGHT SNOW IN OUR FAR 
NORTHWEST/NORTH ON FRIDAY EVENING AS THE UPPER LEVEL LOW TRACKS JUST 
TO OUR NORTH AND WEST...WITH ANY LIGHTER PRECIPITATION TO THE SOUTH 
AND EAST TRANSITIONING TO SNOW AS MUCH COLDER AIR PLUNGES INTO THE 
AREA BEHIND THE EXITING INVERTED TROUGH. TOTAL SNOWFALL AMOUNTS FROM 
THE ENTIRE EVENT WILL BE LIGHT...AVERAGING AROUND 2 INCHES FROM THE 
CHAMBERLAIN TO HURON CORRIDOR TO LESS THAN HALF AN INCH SOUTH AND 
EAST OF LAKE ANDES TO MITCHELL TO BROOKINGS. LOWS ON FRIDAY NIGHT 
WILL RANGE FROM THE SINGLE DIGITS NORTHWEST TO MID TEENS SOUTHEAST. 
IN ADDITION TO THE VERY COLD TEMPERATURES...WITH THE STRONG COLD AIR 
ADVECTION/TIGHTENING GRADIENT BEHIND THE SYSTEM...GUSTY 
NORTHWESTERLY WINDS WILL DEVELOP OVERNIGHT AND PERSIST INTO 
SATURDAY. ANY LINGERING LIGHT SNOW WILL PULL OFF TO THE NORTH BY 
SATURDAY MORNING...WITH HIGHS IN THE AFTERNOON ONLY REACHING THE 
TEENS.

IN THE EXTENDED...SUNDAY THROUGH WEDNESDAY OF NEXT WEEK...MODELS IN 
DECENT AGREEMENT ON KEEPING UPPER LEVEL TROUGHING ACROSS THE REGION. 
THIS WILL RESULT IN TEMPERATURES AT OR JUST BELOW NORMAL INTO 
TUESDAY...WITH POSSIBLE WARMING BY THE MIDDLE OF NEXT WEEK. IN TERMS 
OF PRECIPITATION...NO SIGNS OF ANY SIGNIFICANT SYSTEM THROUGH THE 
PERIOD.

&&

.AVIATION.../FOR THE 00Z TAF ISSUANCE/
FIRST 12 TO 15 HOURS OF THE FORECASTS WILL MAINTAIN VFR CONDITIONS. 
HOWEVER...APPROACH OF UPPER LEVEL WAVE FROM THE SOUTHERN PLAINS WILL
SPREAD LOWERING CEILINGS NORTHWARD. SHOULD BE A FAIRLY RAPID 
TRANSITION FROM VFR TO MVFR/IFR CEILINGS AND VISIBILITIES AS BAND OF 
LIGHT RAINFALL WORKS NORTHWARD THURSDAY MORNING AND EARLY AFTERNOON.
AFTER MAIN BAND LIFTS NORTH...LIKELY WILL LEAVE BEHIND SOME LOWER 
MVFR TO IFR CEILINGS AND VISIBILITIES WITH PRECIPITATION INTENSITY 
DROPPING OFF TO DRIZZLE WITH FOG. AS OF NOW...DO NOT SEE MECHANISM 
TO HOLD LOW LEVEL COLD AIR IN AT LOW LEVELS TO PRESENT ANY FREEZING 
RAIN THREAT. WILL ALSO SEE THE WINDS INCREASING THIS EVENING FOR 
KHON AND A BIT LATER FOR KFSD. MARGINAL CONDITIONS TO MENTION LOW 
LEVEL WIND SHEAR AT HURON...AS LONG AS SURFACE WINDS RESPOND TO 
INCREASING GRADIENT...WITH A FEW GUSTS AROUND 25 KNOTS EXPECTED.
/CHAPMAN

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
MN...NONE.
NE...NONE.
SD...NONE.

&&

$$