Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 202010
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
310 PM CDT MON APR 20 2015

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 308 PM CDT MON APR 20 2015

A CORRIDOR OF VERY DRY AIR HAS MIXED DOWN THIS AFTERNOON ACROSS THE
CWA...WITH EARLY AFTERNOON DEW POINTS AS LOW AS 4 DEGREES. LARGE
UPPER TROUGH OVER THE WESTERN GREAT LAKES CONTINUES TO DEEPEN...WITH
WINDS GUSTING ABOVE 40 KNOTS.

FOR THE OVERNIGHT HOURS...WINDS WILL GRADUALLY WEAKEN AND
DECOUPLE...BUT REMAIN RATHER MIXY OVERNIGHT.  TEMPERATURES WILL FALL
NEAR THE 30-32 DEGREE MARK BRIEFLY...BUT NOT ANTICIPATING ANY
FROST/FREEZE HEADLINES.

TUESDAY PRESENTS ANOTHER INTERESTING FORECASTING CHALLENGE.  MODELS
SUGGESTING A SPOKE OF ENERGY ROTATING AROUND THE UPPER
TROUGH...BRINGING A WEAK BACKDOOR COLD FRONT THROUGH THE AREA EARLY
IN THE DAY. NAM/GEM ONLY MODEL SUGGESTING ENOUGH MOISTURE TO PRODUCE
LIGHT QPF...HOWEVER SUB-CLOUD LAYER REMAINS VERY DRY...AND ANYTHING
THAT DOES FALL MAY JUST BE SPRINKLES.

MECHANICAL MIXING WILL AGAIN DROP DEW POINTS LOWER THAN MODELS
SUGGEST IN THE AFTERNOON HOURS...WITH RH VALUES NEAR 20 DEGREES
AGAIN.  STRATO-CU MAY CLIP THE EASTERN ZONES IN THE AFTERNOON AND
HAVE LOWERED TEMPERATURES A COUPLE DEGREES.

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 308 PM CDT MON APR 20 2015

FOCUS IN THE MEDIUM RANGE CONTINUES TO BE THE DRY CONDITIONS LEADING
TO AN ELEVATED FIRE WEATHER DANGER...AND THE SUB-FREEZING
TEMPERATURES AT NIGHT.  CLEAR SKIES AND DECREASING WINDS WILL LEAD
TO GOOD RADIATIVE CONDITIONS ACROSS THE AREA BOTH TUESDAY AND
WEDNESDAY NIGHT.  WITH DEW POINTS TUMBLING WELL INTO THE TEENS
DURING THE DAY...TEMPERATURES HAVE A LONG WAYS TO FALL IN THE DRY
AIR.  WINDS WILL STAY UP ON BUFFALO RIDGE MORE TUESDAY NIGHT THAN
WEDNESDAY NIGHT...BUT WITH 925 HPA TEMPS NEAR 0...EXPECT LOWS TO
MAINLY BE IN THE 20S.  AM NOT ANTICIPATING FROST GIVEN THE DRY
NATURE OF THE ATMOSPHERE...BUT LOWS IN THE 20S COULD IMPACT EARLY
BUDDING PLANT ACROSS THE REGION.  CERTAINLY THE POTENTIAL FOR
WIDESPREAD FREEZE HEADLIGHT TUESDAY NIGHT...AND POTENTIALLY ONE
NORTH OF I-90 WEDNESDAY NIGHT.

SURFACE RIDGE SHIFTS EAST AND SOUTHERLY WINDS BEGIN TO DEVELOP ON
THURSDAY.  ACROSS THE EAST...MAY HANG ON TO MORE OF A NORTHWESTERLY
FLOW AS MOMENTUM DRAWN FROM ALOFT OVERCOMES WEAK SURFACE GRADIENT.
LITTLE MOISTURE RETURN INITIALLY WITH SOUTHERLY FLOW...WHICH WILL
LEAD TO ELEVATED FIRE WEATHER CONDITIONS CONTINUING.  THE SAVING
GRACE IS THAT SHORT GRASSES ARE STARTING TO GREEN UP.  WITH LACK OF
MOISTURE...HAVE CUT BACK POPS WITH WAVE MOVING ACROSS THE CENTRAL
PLAINS LATE IN THE WEEK.  BULK OF THE FORCING REMAINS SOUTH OF THE
FORECAST AREA ANYWAY...BUT WITH LITTLE MOISTURE TO WORK WITH...IT
WILL LIKELY BE TOUGH TO GET MEASURABLE PRECIP.

WAVE PROGRESSING EASTWARD LATE IN THE WEEKEND FROM THE PACIFIC
NORTHWEST WILL BE THE ONLY TRUE SHOT OF MOISTURE OVER THE NEXT WEEK.
LEFT GUIDANCE POPS IN THE FORECAST FOR SUNDAY INTO MONDAY FOR NOW.

&&

.FIRE WEATHER...

RED FLAG CONDITIONS CONTINUE OVER HALF OF THE AREA THIS AFTERNOON AS
DEW POINTS HAVE MIXED INTO THE SINGLE DIGITS AND WINDS HAVE GUSTED
AS HIGH AS 44 KNOTS. THESE CONDITIONS WILL CONTINUE THROUGH SUNSET
BEFORE MODEST IMPROVEMENT THIS EVENING. THE ONLY THING SAVING
PORTIONS OF IOWA FROM RFW WARNING CONDITIONS IS SATURDAYS
RAINFALL...AND A BIT MORE OF A GREENUP.

TUESDAY PRESENTS AN INTERESTING CHALLENGE FOR FIRE WEATHER. A WEAK
SFC FRONT WILL PASS THROUGH THE AREA EARLY IN THE DAY...HOWEVER WE
WILL BEGIN TO MIX QUICKLY BEHIND IT.  AGAIN...HAVE LOWERED DEW
POINTS BELOW GUIDANCE AND RESULTANT RH VALUES ARE AGAIN BELOW
CRITICAL LEVELS.  WINDS WILL MIX DOWN WEAKER THAN TODAY FOR
SUSTAINED WINDS...BUT FREQUENT GUSTS ABOVE 30 KNOTS ARE POSSIBLE.

WE WILL CERTAINLY BE NEAR OR AT RED FLAG CRITERIA IN MANY AREAS AND
PERHAPS FURTHER SOUTHEAST INTO WESTERN PORTIONS OF IOWA. STRONG
WINDS AND LOW HUMIDITY TODAY SHOULD FINALLY NEUTRALIZE ANY RAINFALL
THAT FELL NEAR THE MISSOURI RIVER ON SATURDAY.  LATER SHIFTS WILL
NEED TO WATCH FOR THE POTENTIAL OF A RED FLAG WARNING FOR
TUESDAY...WHICH FALLS IN LINE WITH SPC D2 FIRE WEATHER OUTLOOK.

CONDITIONS WILL LIKELY BE NEAR RED FLAG AGAIN WEDNESDAY AFTERNOON
ACROSS SOUTHWEST MINNESOTA AND ACROSS PORTIONS OF NORTHWEST IOWA.
RH VALUES ARE EXPECTED TO FALL INTO THE 15 TO 20 PERCENT RANGE
ACROSS THE AREA...KEEPING THE FIRE DANGER IN THE VERY HIGH TO
EXTREME RANGE.

WHILE WINDS WILL BE RELATIVELY LIGHT ON THURSDAY...MINIMUM RELATIVE
HUMIDITY VALUES WILL BE IN THE 15 TO 30 PERCENT RANGE.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 110 PM CDT MON APR 20 2015



VFR CONDITIONS EXPECTED INTO TUESDAY. NORTHWEST WINDS WILL
CONTINUE TO GUST ABOVE 35 KNOTS INTO THE AFTERNOON HOURS...BEFORE
WEAKENING OVERNIGHT. A WEAK SURFACE TROUGH WILL SWING THROUGH
EARLY TUESDAY MORNING...WITH WINDS AGAIN PICKING UP BY THE LATE
MORNING HOURS.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...RED FLAG WARNING UNTIL 8 PM CDT THIS EVENING FOR SDZ255>258.

     WIND ADVISORY UNTIL 7 PM CDT THIS EVENING FOR SDZ038>040-050-
     052>071.

MN...WIND ADVISORY UNTIL 7 PM CDT THIS EVENING FOR MNZ071-072-080-081-
     089-090-097-098.

IA...WIND ADVISORY UNTIL 7 PM CDT THIS EVENING FOR IAZ001>003-012>014-
     020>022-031-032.

NE...WIND ADVISORY UNTIL 7 PM CDT THIS EVENING FOR NEZ013-014.

&&

$$

SHORT TERM...DUX
LONG TERM...
AVIATION...DUX



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