Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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989
FXUS63 KFSD 071723
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1123 AM CST SUN FEB 7 2016

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 406 AM CST SUN FEB 7 2016

INTERESTING...BUT COMPLEX...SYSTEM SET TO AFFECT THE REGION OVER THE
NEXT 24-36 HOURS. POTENT UPPER LEVEL WAVE MOVING THROUGH THE RED
RIVER VALLEY INTO NORTHERN MINNESOTA AT THIS HOUR...WITH ANOTHER
TRAILING WAVE DROPPING INTO THE WESTERN DAKOTAS OUT OF SASKATCHEWAN.
TEMPERATURES IN WESTERLY FLOW EARLY THIS MORNING ARE VERY MILD...
WITH READINGS IN THE MID 30S TO AROUND 40 IN MOST LOCATIONS AS OF
3AM. DAYTIME HIGHS LIKELY TO BE NEAR THESE READINGS...WITH STEADY TO
FALLING TEMPERATURES EXPECTED AS THIS WAVE SWINGS SOUTHEAST INTO OUR
FORECAST AREA IN THE LATE MORNING AND AFTERNOON. ASSOCIATED COLD
ADVECTION WILL NOT ONLY BRING IN THE COOLER AIR...BUT ALSO ALLOW FOR
BETTER COUPLING BETWEEN THE SURFACE AND MUCH STRONGER WINDS ALOFT.
LATEST MODEL SOUNDINGS INDICATE THIS COUPLING MAY HOLD OFF UNTIL A
BIT AFTER SUNRISE FOR OUR WESTERN AREAS...SO HAVE DELAYED THE START
OF OUR HIGH WIND WARNING AND JAMES VALLEY WIND ADVISORY UNTIL 15Z.
DISTRIBUTION OF WIND HEADLINES STILL LOOKS GOOD THOUGH...WITH THE
STRONGEST GUSTS EXPECTED TO IMPACT OUR FAR SOUTHWEST CORNER...WHILE
THE JAMES VALLEY IS MORE IN THE REALM OF HIGH-END ADVISORY.

START OF SNOW SHOWERS MOVING INTO OUR NORTHERN AREAS ALSO SLIGHTLY
DELAYED FROM PREVIOUS FORECAST...BUT AS THE WAVE DIGS SOUTHEAST
THROUGH THE AFTERNOON...THE STRONG COLD ADVECTION LEADS TO THE LOWER
ATMOSPHERE BECOMING SLIGHTLY UNSTABLE...AND EXPECT DEVELOPMENT OF
SNOW-STREETS...OR BANDS OF SNOW SHOWERS ORIENTED PARALLEL TO THE
NORTHWESTERLY LOW LEVEL FLOW. HIGH-RES MODELS HAVE BEEN LATCHING ON
TO THIS IDEA FOR PAST SEVERAL RUNS...WITH MOST SHOWING STRIPES OF
HIGHER QPF ACROSS THE AREA. DIFFICULTY IS DETERMINING EXACTLY WHERE
THE BANDS WILL LINE UP AND HAVE BROADENED OUT THE POPS/QPF MORE THAN
THESE HIGH-RES MODELS WOULD INDICATE. AS A RESULT...IT IS CERTAINLY
POSSIBLE THAT SOME AREAS WILL SEE SLIGHTLY HIGHER SNOWFALL AMOUNTS
THAN CURRENTLY FORECAST...WHILE OTHERS WILL SEE LESS. AT ANY RATE...
ANTICIPATE SCATTERED TO NUMEROUS SNOW SHOWERS OVER MUCH OF THE CWA
DURING THE AFTERNOON...BUT AS WE LOSE ANY DIURNAL HEATING...FOCUS
WILL SHIFT TO THE EASTERN CWA WHERE LINGERING CYCLONIC CURVATURE
ALONG WITH A REINFORCING SHOT OF COLD ADVECTION...WILL CAUSE THE
SNOW SHOWERS TO BECOME CONCENTRATED EAST OF THE I-29 CORRIDOR. PER
COORDINATION WITH OFFICES TO OUR EAST...BUMPED POPS FOR THESE AREAS
INTO CATEGORICAL RANGE...WITH EXPECTATION OF SEEING FREQUENT SNOW
SHOWERS WITH PERIODS OF RELATIVE QUIET. GREATER COVERAGE SHOULD LEAD
TO MORE WIDESPREAD 1-2 INCH SNOWFALL ACCUMULATIONS EAST OF BROOKINGS
TO LUVERNE TO IDA GROVE...WHILE AMOUNTS TAPER TO LESS THAN A HALF
INCH IN THE JAMES RIVER VALLEY. THIS AREA OF GREATER SNOWFALL ALSO
LIKELY TO SEE STRONGEST WIND GUSTS TONIGHT THANKS TO THE REINFORCING
PUSH OF COLD ADVECTION...AND THIS COMBINATION SUPPORTIVE OF KEEPING
BLIZZARD HEADLINES FOR OUR EASTERN CWA FROM LATE THIS AFTERNOON INTO
MONDAY.

CURRENTLY HAVE A WIND ADVISORY IMMEDIATELY WEST OF THE BLIZZARD
WARNING...AND GAVE SOME CONSIDERATION TO BUFFERING THE BLIZZARD
WARNING WITH A WINTER WEATHER ADVISORY...IN AREA WHERE PROJECTED
SNOWFALL AMOUNTS COULD TOP A HALF INCH. HOWEVER...HAVE UNCERTAINTY
REGARDING HOW EXTENSIVE THE COVERAGE OF SNOW SHOWERS WILL BE...OR
HOW LONG THEY WILL PERSIST IN THAT AREA BEYOND SUNSET. WITH MILD
TEMPERATURES OVER THE PAST 24 HOURS FIRMING UP THE EXISTING SNOW
PACK...WILL NEED NEW SNOW TO CREATE POTENTIAL FOR SIGNIFICANT ISSUES
DUE TO BLOWING SNOW...SO OPTED TO STICK WITH THE WIND ADVISORY AND
CONTINUE A MENTION OF AREAS OF BLOWING SNOW IN THE ADVISORY.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 406 AM CST SUN FEB 7 2016

A CONTINUATION OF DETERIORATED CONDITIONS ACROSS THE EAST TO
START ON MONDAY... AS STRONG CORE OF LOW LEVEL WINDS REMAIN...
ONLY GRADUALLY DIMINISHING AS WRAPPED UP LOW ACROSS THE WESTERN
GREAT LAKES STARTS TO DRIFT EASTWARD. AGAIN...WILL LIKELY NOT BE A
PERSISTENT AND WIDESPREAD DEGRADATION TO VISIBILITY...BUT WHEN IT
IS BAD AROUND SNOW SHOWERS...VISIBILITY WILL BE QUITE BAD AS WINDS
WILL REMAIN FROM 25 TO 35 MPH WITH GUSTS TO 45 TO 50 MPH DURING
THE MORNING. HIGHEST SNOW CHANCES EARLY IN THE DAY MAINLY EAST OF
HIGHWAY 59... WITH LINGERING 850-700 HPA DIV Q FORCING AND
FAVORABLE THERMAL PROFILES SUGGESTING CONTINUED STREAKS OF MAINLY
LIGHT SNOW SHOWERS. COVERAGE OF SNOW SHOWERS WILL WANE THROUGH THE
MORNING...WITH LITTLE LEFT EVEN IN THE FAR EAST BY AFTERNOON.
WHILE WINDS DO START TO EASE A BIT AS WELL...LIKELY TO STILL FIND
SOME AREAS OF BLOWING SNOW MAINLY NEAR/EAST OF I-29 THROUGH MUCH
OF THE AFTERNOON. MAY VERY WELL END UP WITH AN EXTENSION OF WINTER
HIGHLIGHTS FOR THESE AREAS OF BLOWING SNOW THROUGH MONDAY
AFTERNOON...BUT NOT EXPECTING ENOUGH QUARTER MILE OR LESS
VISIBILITY EITHER SPATIALLY OR TEMPORALLY TO WARRANT A LONGER
BLIZZARD WARNING AT THIS TIME.

ON MONDAY NIGHT...SURFACE RIDGE WILL BEGIN TO NOSE INTO AREAS WEST
OF I-29...WITH GRADIENT REMAINING OVER THE EASTERN CWA BUT
CONTINUING TO DIMINISH. WITH SOME 25 TO 35 MPH GUSTS AT LEAST EARLY
EVENING...HAVE MAINTAINED PATCHY BLOWING SNOW ALONG AND EAST OF THE
BUFFALO RIDGE AND SOUTHWARD ALONG HIGHWAY 71. OUT WEST...THE
LINGERING LOWER TO MID LEVEL BAROCLINIC ZONE WILL KEEP CLOUDS MORE
PERSISTENT...THICKENING UP MORE LATE AS WAVE BEGINS TO SLIDE
SOUTHEAST OUT OF CANADA. WAVE SHOULD INDUCE A PERIOD OF CROSS
FRONTAL FLOW THROUGH TUESDAY ACROSS THE WESTERN CWA...BEFORE
BOUNDARY COLLAPSES IN WAKE BACK TOWARD THE WEST...WARRANTING AT
LEAST A SMALL POP MENTION. ANOTHER PERTURBATION TOWARD WEDNESDAY
COULD AGAIN BRING A SMALL SNOW CHANCE TO THE WESTERN CWA TOWARD
DAYBREAK WEDNESDAY.

OVERALL...AGREEMENT HAS BEEN FAIRLY LACKING IN DETAILS OF BEHAVIOR
OF THE THERMAL GRADIENT WITH DIFFERENCES IN OPERATIONAL MODELS AND
ENSEMBLES ON EXTENT OF BREAKING DOWN THE WESTERN RIDGE/EASTERN
TROUGH PATTERN...ALONG WITH TIMING/STRENGTH OF WAVES IN THE FEATURE.
AT THIS POINT...HARD TO STICK WITH ANYTHING MORE THAN A GENERALITY
TO TEMPS FAVORING MUCH WARMER WEST THAN EAST...AND BEST OVERALL TO
KEEP MOST PRECIPITATION OUT OF THE FORECAST. HAVE MAINTAINED A LOW
CHANCE POP ON THURSDAY NIGHT AND FRIDAY TO ACKNOWLEDGE ECMWF AND
MORE WESTWARD LOCATION OF BAND...WHICH FITS A GREATER DEGREE OF
ENSEMBLE IDEA. MAY BE TOO AGGRESSIVE THOUGH...AS THE ECMWF HAS MUCH
STRONGER WAVE AND RESULTANT PUSH OF COLDER AIR INTO THE EASTERN TWO
THIRDS OF THE REGION THROUGH SATURDAY...WHILE GFS NOTABLY WEAKER AND
MORE RIDGY ALOFT...AND AS MUCH AS 15-20C WARMER AT 850 HPA.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1118 AM CST SUN FEB 7 2016

LIGHT SNOW SHOWERS ARE BEGINNING TO DEVELOP ACROSS THE AREA...AND
DETERIORATING CONDITIONS ARE EXPECTED TO CONTINUE TO OVERSPREAD
THE AREA AND PERSIST INTO LATE TONIGHT INTO EARLY MONDAY. SNOW
SHOWERS WILL NOT BE CONTINUOUS HOWEVER...BEING SCATTERED IN
NATURE...AND THERE WILL BE LOCALIZED VARIATION IN VISIBILITIES
THROUGH THE PERIOD DEPENDENT ON WHEN SNOW IS FALLING.
NORTHWESTERLY WINDS WILL CONTINUE TO BE VERY STRONG...CONTRIBUTING
TO BLOWING SNOW...MORE SO WHEN SNOW IS ACTUALLY OCCURRING.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...WIND ADVISORY UNTIL NOON CST MONDAY FOR SDZ039-054>056-060>062-
     065>071.

     WIND ADVISORY UNTIL NOON CST MONDAY FOR SDZ038-052-053-058-059-
     064.

     BLIZZARD WARNING UNTIL NOON CST MONDAY FOR SDZ040.

     HIGH WIND WARNING UNTIL 9 PM CST THIS EVENING FOR SDZ050-057-063.

MN...WIND ADVISORY UNTIL NOON CST MONDAY FOR MNZ098.

     BLIZZARD WARNING UNTIL NOON CST MONDAY FOR MNZ071-072-080-097.

     BLIZZARD WARNING FROM 4 PM THIS AFTERNOON TO NOON CST MONDAY FOR
     MNZ081-089-090.

IA...WIND ADVISORY UNTIL NOON CST MONDAY FOR IAZ001-012-020-031.

     BLIZZARD WARNING FROM 4 PM THIS AFTERNOON TO NOON CST MONDAY FOR
     IAZ002-003-013-014-021-022-032.

NE...WIND ADVISORY UNTIL NOON CST MONDAY FOR NEZ013-014.

&&

$$

SHORT TERM...JH
LONG TERM...CHAPMAN
AVIATION...JM



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