Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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741
FXUS63 KFSD 192345
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
645 PM CDT TUE MAY 19 2015

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 331 PM CDT TUE MAY 19 2015

OVERALL FORECAST TO REMAIN VERY SIMILAR TO PREVIOUS BUT HAVE SLOWED
DOWN THE DEVELOPMENT OF THE LIGHT RAIN BY A FEW HOURS. LOW PRESSURE
ROTATING NORTHEAST RUNNING INTO DRY AIR IN THE LOWEST 12000 FEET OF
THE ATMOSPHERE SO WILL TAKE SOME TIME FOR LIFT TO SATURATE THE LOWER
LEVELS. THE BETTER CHANCES REMAIN SOUTH OF INTERSTATE 90 AND DID
INCREASE POPS TO 100 PERCENT CLOSER TO THE MISSOURI RIVER VALLEY
INTO NORTHWEST IOWA. STILL LOOKING LIKE A GOOD SHOT AT ABOUT A
QUARTER INCH ALONG THE MISSOURI RIVER QUICKLY DROPPING OFF TO LESS
THAN A TENTH OF AN INCH AROUND INTERSTATE 90. BETTER MOISTURE AND
MINOR INSTABILITY REMAIN BOTTLED UP IN SOUTHERN NEBRASKA WITH THIS
AREA MAINLY DEALING WITH MID LEVEL FORCING. TEMPERATURES NOT
EXPECTED TO FALL MUCH WITH CLOUDY SKIES SO LOWS MAINLY LOWER 40S.

ON WEDNESDAY THIS FORCING AND MOISTURE TO GRADUALLY DISSIPATE WITH
JUST A FEW SMALLER POPS IN THE SOUTHERN CWA. SOME WEAK INSTABILITY
IN AND JUST ABOVE THE MIXED LAYER ALONG WITH A LITTLE MOISTURE MAY
ALLOW FOR SOME SCATTERED SHOWERS TO DEVELOP. TEMPERATURES MOST
DIFFICULT IN SOUTHERN CWA WHERE CLOUDS MAY PLAY A BIGGER ROLE.
BASICALLY LOOKING AT HIGHS IN THE 50S EVERYWHERE WITH THE COOLEST
READINGS OVER PARTS OF NORTHWEST IOWA.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 331 PM CDT TUE MAY 19 2015

SURFACE HIGH PRESSURE WILL SETTLE SOUTHWARD ACROSS THE REGION ON
WEDNESDAY NIGHT AND THURSDAY. WITH THIS THERE WILL BE CLEARING
SKIES AND A LIGHT WEST/NORTHWESTERLY LOW LEVEL FLOW. WITH THE
CLEAR SKIES AND LIGHT WINDS...WEDNESDAY NIGHT WILL BE A LITTLE
COOLER WITH LOWS IN THE UPPER 30S TO AROUND 40. WITH THE EXCEPTION
OF A FEW CU ON THURSDAY IT WILL BE MOSTLY SUNNY...RESULTING IN
WARMER TEMPERATURES AND HIGHS INTO THE UPPER 60S TO AROUND 70.

ON THURSDAY NIGHT AND FRIDAY THE SURFACE RIDGE AXIS BEGINS TO SHIFT
OFF TO THE EAST. THIS WILL BRING A SOUTHERLY FLOW BACK TO THE
REGION...WITH LOWS ON THURSDAY NIGHT A LITTLE MILDER...IN THE MID
40S...AND HIGHS ON FRIDAY INTO THE LOWER 70S MOST PLACES. BY FRIDAY
EVENING A SHORTWAVE BEGINS TO LIFT OUT OF EASTERN COLORADO...AND OUT
AHEAD OF THIS...MIDLEVEL ISENTROPIC LIFT BEGINS TO OVERSPREAD OUR
AREA BRINGING INCREASING PRECIPITATION CHANCES FOR FRIDAY NIGHT INTO
EARLY SATURDAY. IT LOOKS TO BE STABLE ON FRIDAY NIGHT SO THINKING
MAINLY SHOWERS FOR ANY ACTIVITY THAT OCCURS...THEN CANNOT RULE OUT
SOME RUMBLES OF THUNDER ON SATURDAY WITH A LITTLE MORE INSTABILITY.
WITH THE CLOUDS AND SHOWERS SATURDAY LOOKS TO BE A LITTLE COOLER
WITH HIGHS MID AND UPPER 60S.

ON SATURDAY NIGHT AND SUNDAY CONVECTION CHANCES LOOK TO RAMP UP AS
ANOTHER SHORTWAVE LIFTS INTO THE REGION AND MOISTURE TRANSPORT
INCREASES WITH A STRENGTHENING LOW LEVEL JET ACROSS THE AREA. SEEING
MODEL DIFFERENCES WITH REGARD TO POSITION OF A SURFACE LOW/SURFACE
BOUNDARIES WITH THIS SYSTEM...AND ALTHOUGH INSTABILITY LOOKS TO
INCREASE DURING THIS TIME FRAME SEVERE WEATHER POTENTIAL IS
DIFFICULT TO PIN DOWN AT THIS POINT. BECAUSE OF THE MODEL
DIFFERENCES...TEMPERATURE DIFFERENCES ARE APPARENT ON
SUNDAY...THOUGH CONSENSUS PUTS HIGHS IN THE RANGE OF UPPER 60S TO
LOWER 70S.

MODELS CONTINUE TO DIVERGE THROUGH THE END OF THE EXTENDED...THOUGH
CONSENSUS WOULD SUGGEST THAT RAINFALL CHANCES WILL LINGER INTO
MONDAY...WITH DECREASING CHANCES LATER ON MONDAY INTO AT LEAST EARLY
ON TUESDAY. TEMPERATURE TRENDS DO APPEAR TO BE ON THE UPSWING FOR
THE BEGINNING OF NEXT WEEK.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 645 PM CDT TUE MAY 19 2015

UPPER AIR DISTURBANCE WILL USHER IN GOOD CHANCES FOR LIGHT
RAINFALL TONIGHT AND WEDNESDAY MORNING...PRIMARILY FOR AREAS ALONG
AND SOUTH OF THE INTERSTATE 90 CORRIDOR. LEFT THE MENTION OF
RAINFALL OUT OF THE KHON TAF SITE WHO IS DEEPER IN THE DRIER
AIR...AND ALSO KEPT THEM WITH VFR CONDITIONS THROUGH WEDNESDAY.
VARIOUS MODELS INCLUDING THE NAM...GFS AND RAP13 SHOW A GOOD
CHANCE FOR MVFR TO MOVE INTO THE KFSD AND KSUX TAF SITES AFTER
MIDNIGHT TONIGHT. IT IS PROGGED THAT KFSD WILL HAVE DRIER AIR
ENTRAIN IN BY 18Z WEDNESDAY ALLOWING FOR A RETURN TO VFR
CONDITIONS. BUT KSUX IS SUGGESTED TO STAY MVFR THROUGH THE ENTIRE
DAY WHICH LOOKS REASONABLE GIVEN THE MOISTURE PROFILES.

&&

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

$$

SHORT TERM...08
LONG TERM...JM
AVIATION...MJ



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