Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 051139
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
639 AM CDT SAT SEP 5 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 310 AM CDT SAT SEP 5 2015

ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS CONTINUE TO DEVELOP
OFF AND ON IN SOUTHWEST MN AND NORTHWEST IA...WELL EAST OF I 29. A
VERY WEAK MID LEVEL SHORT WAVE IS MOVING ACROSS THAT AREA AT THIS
TIME...AND COUPLED WITH A HUMID LOW LEVEL AIR MASS AND A BRISK 30 TO
40 KNOT LOW LEVEL JET...IT DOES NOT TAKE MUCH ASCENT TO SPARK THIS
ACTIVITY. THESE ZONES DISPLAY A DECENT AMOUNT OF MOISTURE IN THE 850-
700MB LAYER WHICH OTHER LOCATIONS IN OUR FORECAST AREA ARE LACKING.
NOW THIS WAVE EXITS BY AROUND 12Z...SO AM NOT EXPECTING THE
CONVECTION TO LAST PAST THE PRE DAWN HOURS IN OUR FAR EASTERN ZONES.
OUR ATTENTION THEN SHIFTS TO OUR FAR WESTERN ZONES BETWEEN 12Z AND
18Z WHERE ANOTHER SHORT WAVE MOVING FROM NORTHEAST COLORADO TO SOUTH
CENTRAL SD MAY EXERT ITS INFLUENCE. MID LEVEL MOISTURE IN THE 700-
500MB LAYER IS VERY ABUNDANT...SO WOULD NOT RULE OUT MORE ISOLATED
TO SCATTERED CONVECTION IN OUR WESTERN ZONES THIS MORNING...
DEVELOPING EASTWARD IN THE AFTERNOON TO ENCOMPASS MOST OF OUR SOUTH
DAKOTA ZONES. STILL...WOULD NOT PEG THE CHANCES ANY BETTER THAN
ABOUT 40 PERCENT TODAY FOR OUR WESTERN ZONES DUE TO THE LACK OF LOW
LEVEL FOCUS...DRIVEN PURELY BY THE MID LEVEL SHORT WAVE AND BUOYANCY.

ONE THING LIMITING INSTABILITY IS THE HIGH AMOUNT OF 700-500MB
MOISTURE WHICH MOVES FROM WEST TO EAST THROUGHOUT THE DAY TODAY. IF
THESE CLOUDS BEGIN TO COOL OFF OUR TEMPERATURES MORE THAN
FORECAST...THEN INHIBITION WILL BE EVEN STRONGER LEADING INTO THIS
EVENING. THIS IS THE ONE BIG CHALLENGE IN CONVECTIVE FORECASTING FOR
TONIGHT. FOR THIS REASON...STILL HAVE LIKELY POPS IN A SWATH FOR
MANY OF OUR SD ZONES THIS EVENING. BUT TAILED THEM DOWN TO LOWER END
LIKELYS AS MANY MODELS ARE FRIGHTENINGLY DRY TONIGHT IN OUR FORECAST
AREA...LIKELY AN ARTIFACT OF CAPPING STRENGTH. THE NAM WAS THE MOST
BULLISH FOR PRECIP CHANCES IN OUR FORECAST AREA AND WAS GENERALLY
FOLLOWED AS THE AFOREMENTIONED WAVE LIFTING NORTHEASTWARD LATE THIS
AFTERNOON AND EVENING ACROSS EAST CENTRAL SD IS FAIRLY STRONG. AFTER
MIDNIGHT...THE WAVE WILL BE NORTH OF OUR AREA AND AGAIN WITH A LACK
OF A LOW LEVEL FOCUS...DRIVEN ONLY BY LOW LEVEL JET STRENGTH SIMILAR
TO RIGHT NOW...THE RAIN CHANCES WILL BEGIN TO BECOME MORE SCATTERED
AS THE CONVECTION TRIES TO HEAD INTO OUR EASTERN ZONES. SO ALL
SAID...AGREE WITH SPC IN ONLY A MARGINAL SEVERE OUTLOOK FOR SOME OF
OUR SD ZONES THIS EVENING...FAVORING EAST CENTRAL SD.

CONCERNING TEMPERATURES...HIGHS TODAY ARE TRICKY DUE TO THE AMOUNT
OF MID CLOUDS MENTIONED ABOVE. FOR NOW...HEDGED TOWARD THE COOLER
BIAS CORRECTED READINGS WHICH ARE STILL VERY WARM FOR THIS TIME OF
YEAR. BUT RIGHT NOW...DO NOT SEE WIDESPREAD LOWER 90S WHICH THE NON
BIAS VALUES WERE GIVING US. ANOTHER VERY WARM NIGHT TONIGHT WITH
SIMILAR TEMPERATURES TO WHAT WE ARE SEEING RIGHT NOW.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 310 AM CDT SAT SEP 5 2015

CONTINUED MOVEMENT OF THE COLD FRONT WILL BRING A GENERALLY
DECREASING THREAT OF STORMS TO THE EAST/SOUTHEAST PART OF THE
FORECAST AREA SUNDAY. HOWEVER...A LATE AFTERNOON INCREASE IN
STORMS WILL AFFECT MAINLY NORTHWEST IOWA. THESE STORMS WILL BE SLOW
TO DECREASE SUNDAY NIGHT DUE TO THE SLOWING OF THE FRONT WITH THE
WEAKENING DRY PUSH BEHIND IT. MODELS STILL SHOW THAT THERE WILL BE
ENOUGH OF A DRY PUSH TO AFFECT EVEN THE SOUTHEAST PART OF THE AREA
AND MOVE THE STORMS TO THE SOUTHEAST BY THE END OF SUNDAY NIGHT.

TEMPERATURES SUNDAY ARE SOMEWHAT UNCERTAIN DUE TO THE CLOUD COVER
AND STORMS EAST. IN THE WARM AIR IT WILL NOT TAKE MUCH BREAKAGE
IN THE CLOUD COVER TO GET TEMPERATURES BACK UP INTO THE
LOW TO MID 80S...WHILE CLEARING TO THE NORTHWEST WILL ALLOW
HEARING AND BRING SIMILAR HIGH TEMPERATURES AS DEW POINTS AND
HUMIDITY DECREASE. THE COOLER AIR WILL ALLOW TEMPERATURES TO
FALL INTO THE 50S BY EARLY MONDAY MORNING EXCEPT 60 OR SO FAR
SOUTHEAST.

OUR LONG CARRIED DRY AND COOLER LABOR DAY WILL BE BRIEF...LIKELY
WITH A LITTLE LESS COOLING THAT EARLIER EXPECTED. THE MAIN
DIFFERENCE THOUGH WILL BE THE NEXT APPROACHING SHORT WAVE AND
SECONDARY FRONT...ALL OF WHICH IS LOOKING A LITTLE STRONGER THAN
BEFORE. FOR NOW...WILL START WITH JUST A SLIGHT CHANCE OF STORMS
WEST IN THE AFTERNOON AND GO FOR MOST OF THE CONVECTION TO BE MONDAY
NIGHT. POPS MONDAY NIGHT WILL GO FROM LOW CHANCE NORTHWEST TO LIKELY
SOUTHEAST. THE NAM IN PARTICULAR IS QUICKLY RETURNING DECENT
INSTABILITY FROM THE SOUTH. WHILE THIS MODEL COULD BE OVERDOING THE
INSTABILITY RETURN...IT S A LOGICAL RESULT FOR A STRONGER WAVE THAN
EARLIER PROGGED. FORESEE THE THUNDERSTORM THREAT RETURNING
NORTH INTO MOST OF THE AREA BY MONDAY NIGHT.

TUESDAY THROUGH WEDNESDAY NIGHT WILL SEE A DECREASE AND
ENDING OF THIS BATCH OF STORMS FOLLOWED BY ANOTHER THREAT
WEDNESDAY AFTERNOON OR NIGHT AS STILL ANOTHER WAVE PASSES BY. THIS
WAVE WILL TURN THE UPPER FLOW MORE NORTHEASTERLY AND WITH ITS
STRENGTH BRING STRONGER COOLING AND DRYING BEHIND IT. THIS
SHOULD RESULT IN A DRY THURSDAY AND FRIDAY.

TEMPERATURES SHOULD SEE MODEST COOLING TUESDAY FROM LABOR
DAY...SLIGHT WARMING WEDNESDAY...THEN STRONGER COOLING LATE IN THE
WEEK WITH MID 60S TO LOW 70S HIGHS FOR FRIDAY.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 634 AM CDT SAT SEP 5 2015

DUE TO A STRONG LOW LEVEL JET...THERE CONTINUES TO BE SOME NON
CONVECTIVE LOW LEVEL WIND SHEAR ISSUES UNTIL ABOUT MID MORNING FOR
KFSD AND KSUX. THIS WILL ABATE A LITTLE LATER THIS MORNING AS THE
LOW LEVEL JET RELAXES. HOWEVER AFTER EVENING TONIGHT...THE LOW
LEVEL JET ONCE AGAIN BECOMES QUITE STRONG ACROSS THE ENTIRE
FORECAST AREA. THEREFORE INCLUDED LOW LEVEL WIND SHEAR AGAIN FOR
KHON AND KSUX. THESE TWO SITES ARE LIKELY TO HAVE SURFACE WINDS
DECOUPLE FROM THE STOUT LOW LEVEL JET...WHEREAS KFSD COULD REMAIN
FAIRLY MIXED ALL NIGHT DUE TO GRADIENT.

OTHERWISE IT IS ANTICIPATED THAT THE AREA WILL BE VFR TODAY AND
TONIGHT. THERE ARE CHANCES FOR TSRA HOWEVER...AND FINDING THE
HIRES MODEL SOLUTION FOR TIMING IS QUITE A CHALLENGE. FOR NOW
INCLUDED SOME TEMPO GROUPS FOR KHON...KFSD AND KSUX WHICH APPEAR
TO HAVE THE BEST CHANCE FOR TSRA ACTIVITY AT CERTAIN TIMES IN THIS
WAVY PATTERN PRIMARILY USING THE HIRES NAM SOLUTION.

&&

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

$$

SHORT TERM...MJ
LONG TERM...
AVIATION...MJ



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