Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 190426
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1026 PM CST TUE NOV 18 2014

.UPDATE...
ISSUED AT 957 PM CST TUE NOV 18 2014

GOOD WARM SURGE OCCURRING JUST AHEAD OF VERY STRONG COLD FRONT
PLOWING INTO THE NORTHWESTERN CWA AT THE PRESENT TIME. IN FACT...
HAS MIXED TO THE LOWER TO MID 30S SOUTHWEST OF A K9V9 TO KYKN
LINE...AND THIS WILL THREATEN TO END THE BELOW FREEZING STREAK FOR
KSUX AS WE GO THROUGH THE NEXT FEW HOURS. PRESSURE RISES OF
3-4HPA/3H WILL MEAN A SHARP INCREASE TO NORTHWEST WINDS...AND HAVE
INCREASED BOTH SUSTAINED AND GUSTS FOR SEVERAL HOURS AFTER FRONTAL
PASSAGE. ALSO SOME SIGNIFICANT CHANGES TO TEMPERATURE TRENDS
ACROSS THE CWA... BUT THERE IS NO GUIDANCE THAT DOES EVEN AN
ADEQUATE JOB OF CAPTURING THE PULSE OF MIXING WARMING NEAR THE
BOUNDARY. DID REMOVE PRACTICALLY ALL OF THE MEASURABLE
PRECIPITATION THREAT AS DEEPER FORCING HAS RACED EAST WITH DRY
AIRMASS LIMITING EFFECTIVENESS OF LIFT. BETTER THREAT FOR PRECIP
WILL COME IN FORM OF FLURRIES AS CLOUD LAYER TEMPS COOL INTO THE
MORE DENDRITIC FAVORED ZONE.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 325 PM CST TUE NOV 18 2014

CLOUDS ARE ON THE INCREASE ACROSS THE REGION AHEAD OF A COLD FRONT
THAT IS EXPECTED TO WORK THROUGH THE AREA TONIGHT.   AS OF 21Z...THE
COLD FRONT HAD WORKED INTO THE NORTHWEST CORNER OF THE STATE WITH
WINDS GUSTING OVER 40 KNOTS.  AM NOT EXPECTING WIND GUSTS TO BE AS
STRONG ACROSS THE FORECAST AREA...BUT STILL MAY CAUSE GUSTY WINDS AS
COLD AIR ADVECTION CONTINUES BEHIND THE FRONT.  COULD ALSO HAVE SOME
LIGHT SNOW WITH THE FRONT AS CLOUDS COINCIDES WITH THE DENDRITIC
LAYER...THOUGH LIFT AND MOISTURE ARE FAIRLY SHALLOW.  IN TERMS OF
TEMPERATURES...EXPECT FAIRLY STEADY TEMPERATURES THROUGH THE EARLY
EVENING HOURS AHEAD OF THE FRONT...THEN FALLING TEMPERATURES AS THE
WINDS INCREASE BEHIND THE FRONT.

BREEZY DAY EXPECTED ACROSS THE AREA ON WEDNESDAY.  CONTINUED THE
MENTION OF PATCHY BLOWING SNOW...BUT DO NOT EXPECT IT TO HAVE TOO
LARGE OF AN IMPACT AS MUCH OF THE SNOW COVER HAS SETTLED OVER THE
LAST FEW DAYS.  TEMPERATURES WILL STRUGGLE TO WARM SIGNIFICANTLY
THROUGHOUT THE DAY AS 925 MB TEMPS FALL TO NEAR -10C. SKIES WILL
GRADUALLY CLEAR THROUGHOUT THE DAY...BUT THE SNOW COVER AND LOW
SUN ANGLE WILL NOT HELP WITH MIXING.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 325 PM CST TUE NOV 18 2014

A SHIFT IN THE PATTERN WILL BEGIN ON WEDNESDAY NIGHT AND CONTINUE
THROUGH THE WEEKEND. EXCEPT FOR THE NAM BEING COOLER AT LOW LEVELS
THAN THE GFS OR ECMWF...THERE IS LITTLE DIFFERENCE BETWEEN MODELS
THROUGH FRIDAY.

HIGH PRESSURE WILL MOVE OVER THE EASTERN DAKOTAS ON WEDNESDAY
NIGHT. WINDS ARE EXPECTED DECREASE FAIRLY RAPIDLY WEST OF
INTERSTATE 29 WHILE NORTHWEST WINDS WILL REMAIN AT OR ABOVE 10 MPH
IN SW MN MUCH OF THE EVENING. BUT EVEN IN SW MN WINDS ARE
EXPECTED TO SLOWLY DECREASE AFTER MIDNIGHT. WITH A FAIRLY FRESH
SNOW COVER...LIGHT WINDS...AND CLEAR SKIES...TEMPERATURES SHOULD
DROP RAPIDLY AND EXPECT MOST OF SOUTHEAST SD AND SW MN TO FALL
BELOW ZERO OVERNIGHT WITH TEMPERATURES FROM 0 TO 5 ABOVE IN NW IA
AND EXTREME NORTHEAST NEBRASKA. THE HIGH WILL MOVE INTO MINNESOTA
AND IOWA ON THURSDAY. BUT WITH LIGHT WINDS...TEMPERATURES WILL
STRUGGLE TO RISE A LOT EAST OF THE JAMES RIVER WITH HIGHS IN THE
TEENS INTO THE LOWER 20S. WEST OF THE JAMES A GRADUAL INCREASE IN
SOUTHERLY WINDS WILL ALLOW FOR WARMER AIR TO MOVE NORTH AND BIT
MORE MIXING SO HIGHS WILL RISE INTO THE MID 20S.

SOUTHERLY FLOW WILL INCREASE ACROSS THE AREA THROUGH THURSDAY
NIGHT. WITH THE SOUTH WINDS WILL BE AN INCREASE IN MOISTURE
THROUGH THE NIGHT. EXPECT LOW CLOUDS TO DEVELOP OVER CENTRAL
NEBRASKA AND SPREAD NORTH AND NORTHEAST THROUGH THE
NIGHT...REACHING I-29 PRIOR TO SUNRISE. WITH THE CLOUDS AND
MOISTURE INCREASING...EXPECT TEMPERATURES TO FALL QUICKLY IN MOST
AREAS...ESPECIALLY AROUND SPENCER IOWA WHERE LOWS LOOK TO BE NEAR
ZERO. BUT AS WINDS AND CLOUDS INCREASE...TEMPERATURES WILL RISE
MUCH OF THE NIGHT.

FRIDAY LOOKS TO BE CLOUDY ACROSS THE ENTIRE AREA. THERE IS FAIRLY
STRONG WARM ADVECTION AND WEAK LIFT BELOW THE INVERSION. THIS DOES
SIGNAL THE POTENTIAL FOR FREEZING DRIZZLE AS THE DAY GOES ON. IN
FACT...THE NAM PRODUCES SEVERAL HOURS OF TRACE TO 0.01 IN.
PRECIPITATION. HOWEVER...WITH THE POTENTIAL 3 DAYS OUT AND SOME
UNCERTAINTY AS TO HOW DEEP THE MOISTURE WILL BE...DECIDED TO NOT
INCLUDE FREEZING DRIZZLE AT THIS TIME. TEMPERATURES WILL BE MUCH
WARMER THAN RECENT DAYS WITH HIGHS FROM THE UPPER 20S IN SW MN TO
THE MID 30S IN SOUTH CENTRAL SD.

IN THE EXTENDED...FRIDAY NIGHT THROUGH TUESDAY...MODEL DIFFERENCES
INCREASE OVER TIME. THE ISSUE IS HOW DIFFERENT MODELS HANDLE
PHASING BETWEEN THE NORTHERN STREAM WAVE NEAR THE CANADIAN BORDER
AND THE STRONG SOUTHERN STREAM WAVE MOVING INTO THE MISSISSIPPI
VALLEY ON SUNDAY. ALL MODELS SHOW PHASING BUT THE GFS AND CANADIAN MODEL
BOTH SHOW THIS OCCURRING EAST OF THE AREA WHICH KEEPS THE HIGHEST
POTENTIAL FOR MEASURABLE SNOW PRIMARILY ALONG AND EAST OF I35. THE
ECMWF HAS THIS NORTHERN STORM WAVE DROP SOUTHWARD INTO CENTRAL SD
WITH A BAND OF MODERATE SNOW. THIS SOLUTION IS AN OUTLIER FROM THE
PREVIOUS RUN AS WELL AS BOTH THE GFS AND NAM. SO DID NOT INCREASE
THE CHANCE OF SNOW ANYWHERE AT THIS TIME.

BOTH SATURDAY AND SUNDAY LOOK TO BE ABOVE FREEZING. AM CONCERNED
THAT CLOUDS WILL LINGER THROUGH SATURDAY EVENING EAST OF
I29...ESPECIALLY AS PRESSURES FALL OVER THE NRN ROCKIES ALLOW WINDS
TO BACK TO SOUTHEAST. AT THIS POINT...THERE SHOULD BE ENOUGH WARM
AIR IN THE CLOUD LAYER THAT TEMPERATURES WILL STILL WARM INTO THE
MID TO UPPER 30S EVEN WITH CLOUDY SKIES. IN SOUTH CENTRAL
SD...WHERE SOME SUN IS ANTICIPATED...LOWER 40S ARE EXPECTED. WITH
SOUTH WINDS AND PARTLY TO MOSTLY CLOUDY SKIES SATURDAY
NIGHT...TEMPERATURES WILL NOT DROP MUCH...REMAINING IN THE 20S
WHICH WOULD BE ABOVE NORMAL FOR MOST PLACES. THERE IS MORE
UNCERTAINTY ON TEMPERATURES ON SUNDAY DUE TO DIFFERENCES IN CLOUD
COVER AND TIMING OF THE COLD FRONT. FAVORED A SOLUTION CLOSER TO
THE GFS WHICH KEEPS HIGHS IN THE MID TO UPPER 30S. THE FRONT WILL
CERTAINLY COME THROUGH BY SUNDAY NIGHT AND THIS WILL BRING COLDER
AIR BACK INTO THE AREA. THIS COLDER AIR MAY BE ACCOMPANIED BY
LIGHT SNOW SUNDAY NIGHT AND MONDAY BUT...AS MENTIONED
ABOVE...AMOUNTS LOOK MINIMAL ALTHOUGH WILL NEED TO MONITOR THE
EVOLUTION OF THIS SYSTEM TO MAKE SURE THE PHASING OCCURS EAST OF
THE AREA. HIGHS ON MONDAY WILL BE BACK IN THE 20S. THERE WILL BE
A LITTLE WARMING ON TUESDAY...ESPECIALLY EAST OF I29...AS WARMER
AIR BEGINS TO MOVE BACK INTO THE AREA.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1022 PM CST TUE NOV 18 2014

FRONTAL BOUNDARY BEGINNING TO MOVE THROUGH THE TERMINALS LATE THIS
EVENING. EXPECTATIONS ARE FOR A BRIEF WINDOW OF 30 KNOT WINDS
BEHIND THIS BOUNDARY AND LOWERING CEILINGS INTO THE MVFR RANGE.
UPSTREAM OBSERVATIONS SHOW AN EXPANSIVE FIELD OF MVFR TO LOCALLY
IFR CEILINGS STREAMING SOUTHWARD AND MODEL GUIDANCE HINTS THAT
THESE LOWER CEILINGS MAY STICK AROUND FOR MUCH OF WEDNESDAY. GIVEN
MUCH OF THE CLOUD LAYER IS WITHIN THE -10 TO -20C RANGE...FLURRIES
WOULD BE POSSIBLE THROUGH WEDNESDAY. WINDS THROUGH WEDNESDAY WILL
REMAIN GUSTY FROM THE NORTHWEST.

WILL TREND MORE OPTIMISTIC BY THE END OF THE TAF AS CLOUDS TRY TO
SCATTER AND WINDS TURN LIGHT.

&&

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

$$

UPDATE...CHAPMAN
SHORT TERM...
LONG TERM...SCHUMACHER
AVIATION...DUX



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