Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 240350
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1050 PM CDT SUN AUG 23 2015

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 331 PM CDT SUN AUG 23 2015

WILL CERTAINLY CONTINUE TO FEEL LIKE EARLY AUTUMN TONIGHT. SURFACE
RIDGE OF HIGH PRESSURE WILL EXTEND RIGHT DOWN THE PLAINS FROM CANADA
TO TEXAS. BY SUNSET...WINDS WILL BE LIGHT...AND COUPLED WITH CLEAR
SKIES AND DRY AIR...A CLASSIC RADIATIONAL COOLING NIGHT. CONTINUED
THE TREND OF THE PREVIOUS FORECAST WHICH HAS LOWS WELL BELOW MANY
CONSENSUS GUIDANCE READINGS. THE COLDEST LOWS TONIGHT WERE EXHIBITED
BY THE BIAS CORRECTED HIRES NAM...NMM AND ARW VALUES...AND MAY NOT
BE TOO BAD. RECORD LOWS FOR AUGUST 24 ARE IN GENERAL A COUPLE OF
DEGREES EITHER SIDE OF 40 DEGREES. OUR FORECAST TEMPERATURES ARE
CLOSE TO SOME OF THOSE READINGS...AND WITH A RECORD LOW OF 39 AT
HURON...IT IS THAT SITE THAT NEEDS WATCHED VERY CLOSELY FOR SETTING
A RECORD.

MONDAY WILL FEATURE A LOT LESS WIND AS HIGH PRESSURE CONTINUES TO
DOMINATE. HIGHS WILL MAINLY BE IN THE UPPER 60S TO MID 70S UNDER
PLENTY OF SUNSHINE.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 331 PM CDT SUN AUG 23 2015

QUIET WEATHER IS EXPECTED TO CONTINUE THROUGH WEDNESDAY. THE SURFACE
RIDGE WILL REMAIN OVER THE EASTERN DAKOTAS AND WESTERN MINNESOTA
ON MONDAY NIGHT AND TUESDAY. THIS WILL RESULT IN RELATIVELY LIGHT
WINDS AND CLEAR SKIES. SOUTHEASTERLY FLOW WILL BECOME ESTABLISHED
ALONG AND WEST OF THE JAMES RIVER BY TUESDAY WHICH WILL SLOWLY
BRING MORE MOISTURE INTO THE AREA. THIS WILL KEEP LOWS IN THE
LOWER 50S MONDAY NIGHT IN THE JAMES AND MISSOURI VALLEYS WHILE
LIGHT WINDS AND CLEAR SKIES RESULT IN LOWS IN THE 40S ELSEWHERE.
HIGHS ON TUESDAY WILL BE A FEW DEGREES WARMER THAN MONDAY...IN THE
70S TO AROUND 80 IN SOUTH CENTRAL SD. THE RIDGE WILL REMAIN EAST
OF I29 ON TUESDAY NIGHT KEEPING LOWS FROM THE UPPER 40S TO AROUND
50...WITH 50S EXPECTED ELSEWHERE

ON WEDNESDAY...WARMER AIR AND A LITTLE MORE MOISTURE WILL MOVE
NORTHWARD. 700 TO 500 MB LAPSE RATES WILL BE AROUND 8 C/KM AND THERE
WILL BE WEAK WARM ADVECTION AROUND 700 MB. IT WILL REMAIN FAIRLY DRY
BELOW 850 MB SO AT THIS POINT...EXPECT THE MAIN EFFECT OF THIS WILL
BE DEVELOPMENT OF ALTOCUMULUS...ESPECIALLY NORTH OF I90 IN SOUTHEAST
SOUTH DAKOTA. WHILE IT IS NOT IMPOSSIBLE THERE COULD BE A SHOWER OR
THUNDERSTORM DURING THE AFTERNOON IN THIS AREA...THE BETTER FORCING
FOR ASCENT AND GREATER INSTABILITY IS EXPECTED TO REMAIN WEST OF THE
MISSOURI RIVER THROUGH THE DAY. HIGHS ON WEDNESDAY WILL BE A COUPLE
OF DEGREES WARMER...FROM THE MID 70S TO LOWER 80S.

IN THE EXTENDED...THURSDAY THROUGH SUNDAY...THE MAIN FOCUS WILL BE
ON THE CHANCE FOR RAIN BEGINNING LATE WEDNESDAY NIGHT AND
CONTINUING INTO FRIDAY. ON THE SYNOPTIC SCALE...ALL OF THE MODELS
SHOW FAIRLY SIMILAR EVOLUTION WITH A SHORT WAVE SLOWLY COMING
OVER THE TOP OF THE RIDGE ON THURSDAY AND THURSDAY NIGHT AND THEN
MOVING EAST BY FRIDAY NIGHT. THE GFS IS TYPICALLY FASTER WITH
PROGRESSION OF THE TROUGH COMPARED TO THE ECMWF AND CANADIAN GEM.
GIVEN THE RIDGE POSITION...THE SLOW EASTWARD PROGRESSION OF THE
ECMWF WILL BE FOLLOWED MORE CLOSELY FOR THIS FORECAST. THE OTHER
DIFFERENCE IS HOW FAR NORTH THE RAINFALL WILL GET LATE THIS
WEEKEND. THE GFS IS NOT ONLY THE SOUTHERN OUTLIER OF THE THREE
DETERMINISTIC MODELS BUT IT IS ALSO AN OUTLIER OF THE GFS ENSEMBLE
WITH THE ENSEMBLE MEAN SHOWING RAIN MOVING OVER MOST OF THE CWA
FROM THURSDAY THROUGH FRIDAY. WHILE THERE IS SOME CONCERN HOW FAR
NORTH OF I90 RAINFALL WILL GET...BOTH THE ECMWF AND CANADIAN SHOW
OVER 0.25 INCH OF RAINFALL ACROSS MOST OF THE AREA. WITH STRONG
UPPER LEVEL DYNAMICS AND WEAK INSTABILITY THIS DOES NOT SEEM
UNREASONABLE AND HAVE 30 TO 50 POPS FOCUSED ON THURSDAY NIGHT AND
FRIDAY. DRY WEATHER IS EXPECTED AFTERWARD. AS FOR TEMPS...THE
POTENTIAL FOR PRECIPITATION AND MORE CLOUDS ARE EXPECTED TO KEEP
TEMPERATURES BELOW NORMAL THROUGH FRIDAY. WITH SOME INDICATIONS
THERE COULD BE PARTIAL SUNSHINE ON THURSDAY...KEPT HIGHS IN THE
UPPER 70S TO LOWER 80S WITH TEMPS 3 TO 5 DEGREES COOLER FRIDAY
WITH MORE CLOUDS AND A BETTER CHANCE OF RAIN. SHOULD RAIN BE MORE
PERSISTENT PER THE CANADIAN GEM...TEMPS MAY STRUGGLE TO REACH
REACH THE LOWER 70S SO FAIRLY LARGE UNCERTAINTY FOR HIGHS ON
FRIDAY. AFTER FRIDAY TEMPS SHOULD GRADUALLY WARM TO NORMAL OR EVEN
ABOVE NORMAL BY LATE IN THE WEEKEND.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1050 PM CDT SUN AUG 23 2015

VFR WILL PREVAIL THROUGH MONDAY EVENING. LIGHT WESTERLY WINDS
OVERNIGHT WILL BECOME NORTHWEST AND COULD BECOME A LITTLE GUSTY
AGAIN MONDAY AFTERNOON. STRONGEST WINDS WILL BE FROM SOUTHWEST MN
INTO IOWA GREAT LAKES...WHERE GUSTS OF 20-25KT ARE POSSIBLE 17Z-22Z.
WINDS WILL QUICKLY DIMINISH TO LIGHT AND VARIABLE MONDAY EVENING.

&&

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

$$

SHORT TERM...MJ
LONG TERM...SCHUMACHER
AVIATION...JH


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