052
FXUS63 KFSD 210241
AFDFSD
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
830 PM CST FRI NOV 20 2009
DISCUSSION
TEMPERATURES DROPPING OFF QUICKLY IN OUR EAST THIS EVENING WITH
WINDS NEARLY CALM...AND HAD TO DROP MINS A COUPLE OF DEGREES IN THE
LOWEST ELEVATIONS. EXPECT TEMPERATURES TO STEADY OUT OR EVEN A RISE
A BIT OVERNIGHT WITH WINDS PICKING UP IN A TIGHTENING GRADIENT...AND
HIGH TO MID CLOUDS ROUNDING THE CENTRAL U.S. RIDGE. MINOR UPDATES
OUT WITH NO CHANGE TO ZFP. /JM
PREV DISCUSSION
QUIET NIGHT ACROSS THE AREA AS WINDS GRADUALLY SWING AROUND TO THE
SOUTH AND SOUTHEAST AND INCREASE...ESPECIALLY OVER THE WEST. WENT
WITH NON DIURNAL TEMPERATURES ALONG AND WEST OF THE JAMES RIVER AS
WINDS BEGIN TO INCREASE MORE STEADILY. EVEN HAVE TEMPERATURES RISING
A LITTLE TOWARDS 12Z IN THE FAR EAST. OTHERWISE...DECREASED LOWS A
LITTLE FROM ABOUT INTERSTATE 29 EAST WITH LIGHT FLOW AND CLEAR SKIES
THROUGH MUCH OF THE NIGHT. LOWS SHOULD RANGE FROM THE MID TO UPPER
20S EAST OF INTERSTATE 29 TO THE LOWER 30S WEST OF THE JAMES RIVER.
SATURDAY SHOULD PROVE TO BE A MILD BUT BREEZY DAY AS WINDS INCREASE
TO SOMETHING AROUND 20 TO 30 MPH ON A STRONG SOUTHERLY GRADIENT.
MOISTURE ALSO SET TO INCREASE ALONG INCOMING LLJ SO HAVE PARTLY TO
MOSTLY CLOUDY SKIES IN THE EAST DURING THE AFTERNOON. QUIET A BIT OF
MOISTURE RETURN JUST OFF THE SFC AND THIS LOOKS REASONABLE GIVEN
HIGHER DEW POINT AIR IN EASTERN OKLAHOMA. HIGHS MAINLY IN THE 50S.
SATURDAY NIGHT WILL SEE A WIND SHIFT WORK INTO THE AREA AHEAD OF AN
ENTRANCE REGION TO A RELATIVELY WEAK UPPER LEVEL JET STREAK. MAY BE
JUST ENOUGH LIFT ALOFT AND JUST ENOUGH MOISTURE CONVERGENCE IN THE
LOW TO MID LEVELS TO SUPPORT A LITTLE LIGHT RAIN OVER THE EASTERN
CWA...BUT WILL HOLD OFF ON BETTER CHANCES UNTIL SUNDAY. EXPECT
CLOUDS TO ALSO INCREASE DURING THIS TIME AS THE UPPER WAVE
APPROACHES THE DECENT LOW TO MID LEVEL MOISTURE. LOWS WILL BE
MILD...ESPECIALLY IN THE EAST WHERE THE STRONGER SOUTHERLY FLOW
REMAINS IN PLACE...AND SHOULD RANGE FROM THE LOWER 40S IN NW IA TO
30 TO 35 IN CENTRAL SD.
AS STATED EARLIER...WILL MAINTAIN SOME LOWER END POPS IN THE EAST
FOR A FEW RAIN SHOWERS WITH INCOMING WEAK ENTRANCE REGION AND WEAK
MID TO LOW LEVEL MOISTURE CONVERGENCE. THIS SHOULD KEEP CLOUD COVER
IN PLACE MUCH OF THE DAY...BUT DECREASE SLOWLY FROM WEST TO EAST. A
LITTLE COOLER BUT A LOT LESS WIND SO STILL MILD...WITH HIGHS FROM
THE UPPER 40S TO LOWER 50S. /08
HEADING INTO SUNDAY NIGHT...AFTER SOME HINT OF A DYNAMIC DOWNTIME
AFTER WAVE SHEARS BY TO THE NORTHEAST...THE TRAILING SYSTEM STARTS
TO INCREASE LOW LVL FLOW AGAIN WITH ISENTROPIC TRANSPORT INCREASING
THRU THE CWA FROM S TO N. A LITTLE LOWER TO MID LVL CONVERGENCE
AXIS LOOKS TO SET UP FROM SW TO NE ACRS THE AREA LIFTING SLOWLY
NE...AND ENOUGH TO PERHAPS FOCUS A SMALL POP LATER IN THE NIGHT.
THE INCREASING SELY FLOW...CLOUDS...AND MOISTURE LKLY TO KEEP TMPS
WARM ENOUGH AT TIME OF PCPN THREAT FOR ALL RAIN...BUT ANY QUICKER
APPROACH WOULD PERHAPS BRING SOME LIGHT FREEZING RAIN TO THE MIX.
MONDAY GETS SOME BETTER DIV Q IN THE MIX ADVANCING OUT AHEAD OF THE
TROUGH DIGGING INTO THE CNTRL/SRN PLAINS. MAIN MID LVL
BNDRY/CONVERGENCE STARTS TO LOCK INTO THE NRN/SWRN CWA...AND WOULD
SEEM TO BE A SLIGHTLY BETTER FOCUS FOR MID TO HIGH CHC POPS. START
TO LIMIT DIURNAL RANGE SOMEWHAT MORE WITH HIGH AMT OF CLDS.
FOR THE EXTENDED RANGE /MON NIGHT THRU FRI/ ALMOST FUNNY HOW CHANGES
IN THE LONG RANGE GUIDANCE...ESPECIALLY AFFECTING THE START OF THE
PERIOD...WAS PREDICTABLE. FOR THE MOST PART THE VARIOUS CAMPS HAVE
NOT ABANDONED THEIR RESPECTIVE SLNS...WITH GFS CONTINUING AS THE
PROGRESSIVE POSTER CHILD...BUT THE CANADIAN/ECMWF/UKMET ALL ON THE
SLOW AND DIGGY SIDE...WITH 12Z RUNS OF THE FORMER PAIR EVEN MORESO.
ENCOURAGING WAS GFS HALF STEP BACK TOWARD MORE DIGGING. THEREFORE...
HARD TO DENY THAT THERE WILL NOT BE A PRECIPITATION EVENT IN THE
MONDAY NIGHT TO TUESDAY NIGHT WINDOW /ALTHOUGH LATEST GUIDANCE
TRENDS WOULD PERHAPS PUSH BACK A PERIOD OR SO FOR BEST FORCING/.
INTRODUCED SOME LKLY POPS THRU THE NWRN HALF OF THE CWA FOR THE
MOMENT...TAPERING OFF SLIGHTLY TOWARD THE FAR SE. WRAPPED UP LOWS
NOTORIOUS FOR SLOW PROGRESSION AND LOOKS TO BE ONE WHERE AN EVENTUAL
TROWAL STRUCTURE IS PROBABLE...ALONG WITH A HEALTHY INVERTED
TROUGH...FAVORING PCPN ALG/BEHIND. THESE TYPES OF SYSTEM ALSO SEEM
TO HAVE A TENDENCY TO BRING UP WARMER AND MOIST AIR...WRAPPING WELL
WESTWARD FOR A WHILE. CERTAINLY THE BETTER OF THE SNOW THREAT WOULD
BE BACK ALG/W OF THE INVERTED TROUGH...AND DO NOT HAVE SUGGESTIONS
OF A DRIER ELY TRAJECTORY TO HELP WET BULB THINGS. THEREFORE...KEPT
ANY SNOW MENTION LIMITED TO THE EXTREME WEST...WITH MIX TOWARD THE
JAMES VALLEY MONDAY NIGHT...THEN ON A BIT EASTWARD TUE...BEFORE
STARTING A WHOLE SCALE CHANGEOVER TUE NIGHT. SOME LINGERING POPS
CONTINUED THRU THE NE/E ON WEDNESDAY.
THE END OF THE WEEK IS FEATURED DRY AT THIS POINT AS RIDGING
REBOUNDS THRU THE NRN PLAINS. SFC RIDGE MOVING OVER THU INTO EARLY
FRI COULD LEAD TO SOME CHILLY LOWS...ESPLY IF WRN AREAS HAVE ANY
DECENT SNOWCOVER. SOME COLD AIR SC MAY BE AROUND ON THU THRU ERN
CWA...BUT MAINLY CLEAR TO MO CLR EXPECTED BY THU NIGHT/FRI. FOR
NOW...DID NOT FULLY ACCEPT THE RAPIDITY OF THE WARMUP ON FRIDAY...
BUT WL BE SOMETHING TO WATCH FOR ONCE THE EVOLUTION OF THE EARLY TO
MID WEEK SYSTEM IS DEFINED. /CHAPMAN
AVIATION
PRETTY MUCH VFR THROUGH 0Z SUNDAY. NOT OUT OF THE QUESTION TO SEE
SOME VALLEY FOG LATE TONIGHT...BUT COVERAGE SHOULD BE MINIMAL. WE
WILL SEE AN INFLUX OF MOISTURE ON SATURDAY AFTERNOON...WITH THE
POTENTIAL FOR HIGH END MVFR CEILINGS AT SUX...AND POSSIBLY FSD.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
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