Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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149
FXUS63 KFSD 161750
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1250 PM CDT SAT MAY 16 2015

.UPDATE...
ISSUED AT 1059 AM CDT SAT MAY 16 2015

MESSY DAY AHEAD AS A SMALL MCS EXITS TO THE NORTH LEAVING BEHIND
EASTERLY FLOW IN THE FAR NORTHERN CWA. JET MAX LIFTING NORTH OVER
THE WESTERN HIGH PLAINS WILL SWING THROUGH THE ENTRANCE REGION
THIS AFTERNOON AND SOME EFFECTS OF THAT MAY ALREADY BE SHOWING UP.
A SMALL POSSIBLE MCV IS LIFTING NORTH INTO NORTH CENTRAL NEBRASKA
AND WILL LIFT THROUGH THE CWA EARLY THIS AFTERNOON. A HANDFUL OF
THE HIGH RESOLUTION MODELS INDICATING SCATTERED THUNDERSTORMS
POSSIBLE BETWEEN ABOUT THE JAMES RIVER AND INTERSTATE 29 AND
SUSPECT IT IS ASSOCIATED WITH THIS FEATURE. NOT SURE HOW MUCH TO
REALLY BITE ON THIS RIGHT NOW. IF THESE STORMS CAN DEVELOP AN
ISOLATED SEVERE STORM WOULD BE POSSIBLE BUT WITH CAPE VALUES
FAIRLY LOW...AROUND 1000 J/KG...MAINLY LOOKING AT QUARTERS AND 60
MPH WINDS.

IF THIS SMALL MCV FEATURE DOES NOT SET ANY ACTIVITY OFF THE FLOW
IS NOT REALLY CONVERGENT AT ALL AND WOULD EXPECT A BETTER CHANCE TO
THE WEST OF OUR AREA AND OF COURSE TO THE SOUTH. THE ACTIVITY TO
THE SOUTH WILL BE THE MOST IMPORTANT TO WATCH AS THAT WILL LIKELY
ADVECT/DEVELOP NORTH THROUGH THE EVENING. AGAIN...INSTABILITY
MARGINAL SO QUARTERS TO MAYBE HALF DOLLARS WILL BE THE MAIN
THREAT. WILL ALSO NEED TO WATCH FOR A SMALL CHANCE FOR SOME FLASH
FLOODING...ESPECIALLY FAR SOUTHEAST SD...NORTHWEST IA AND
SOUTHWEST MN WHERE HEAVY RAIN HAS FALLEN AS OF LATE AND OR THE
MODELS ARE HINTING AT SOME HIGHER RAINFALL POTENTIAL. THE 3 HOUR
FLASH FLOOD GUIDANCE IN THESE LOCATIONS RUNNING GENERALLY LESS
THAN 2 INCHES.

WILL PROBABLY DECREASE POPS A BIT THIS AFTERNOON AND FOCUS BEST
CHANCES AFTER ABOUT 2-4Z.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 340 AM CDT SAT MAY 16 2015

TRICKY FORECAST FOR TODAY...WITH UNSETTLED WEATHER CONDITIONS
PERSISTING FOR MUCH OF THE DAY AND INTO TONIGHT. MAIN CONCERN IS HOW
THE ONGOING THUNDERSTORM ACTIVITY WILL IMPACT TEMPERATURES AND
SEVERE STORM CHANCES LATER ON TODAY.

SURFACE LOW PRESSURE HAS DEEPENED OVER THE BLACK HILLS EARLY THIS
MORNING AND IS SLOWLY DRIFTING NORTHWARD. SEVERAL BANDS OF
THUNDERSTORMS ARE LIFTING NORTHWARD WITH THE ADVANCING WARM FRONT
NEAR THE NEBRASKA AND SOUTH DAKOTA BORDER. THE MOST RECENT RUNS OF
THE HRRR SEEM TO HAVE A GOOD HANDLE ON THIS ACTIVITY...WHICH SHOULD
CONTINUE LIFTING NORTHEAST THROUGH AROUND MID MORNING...LOSING
INTENSITY AS THE NIGHT PROGRESSES. THINK THAT IN GENERAL THERE WILL
BE A LULL IN PRECIPITATION ACTIVITY AROUND LATE MORNING AND MIDDAY
BEFORE SCATTERED STORMS IGNITE AGAIN IN THE AFTERNOON AS THE
STRONGER WAVE PIVOTS INTO THE MISSOURI VALLEY. DEWPOINTS SHOULD
REACH THE LOW TO MID 60S ACROSS THE REGION BUT THE QUESTION IS HOW
MUCH DESTABILIZATION WILL BE POSSIBLE WITH CLOUD DEBRIS FROM MORNING
CONVECTION AND HOW THIS WILL IMPACT TEMPERATURES. IF SOME CLEARING
AND DESTABILIZATION OCCURS...SEVERE STORMS WILL BECOME POSSIBLE.
COULD SEE CAPE VALUES AS HIGH AS 1000 TO 1500 J/KG WITH DECENT
SHEAR. MAIN SEVERE THREATS WILL BE HAIL TO HALF DOLLAR SIZE AND WIND
GUSTS TO 65 MPH. TORNADIC THREAT IS VERY LOW WITH THE WARM FRONT
LIKELY NORTH OF THE FORECAST AREA...BUT COULD BE LOCALIZED IF THE
FRONT LAGS AT STORM INITIALIZATION. AGAIN...IF WEAKER
DESTABILIZATION OCCURS...THE SEVERE THREAT WILL ALSO DIMINISH FOR
THIS AFTERNOON AND EVENING.

EXPECT STORMS TO BECOME WIDESPREAD LATE AFTERNOON INTO THE
EVENING...WITH THE ARRIVAL OF THE JET MAX...FOLLOWED BY THE UPPER
LOW CENTER LIFTING INTO THE WESTERN FORECAST AREA OVERNIGHT. SEVERE
THREAT DIMINISHES LATE EVENING BUT WITH MULTIPLE CLUSTERS OF STORMS
LIFTING NORTH NORTHEAST THROUGH THE REGION...A GOOD SOAKING RAIN IS
EXPECTED FOR THE REGION. LOOKS LIKE AROUND A HALF INCH TO A LITTLE
OVER AN INCH IS POSSIBLE THROUGH TONIGHT.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 340 AM CDT SAT MAY 16 2015

STILL THINK THE NAM...LIKE A DAY AGO...IS A LITTLE TOO SLOW BRINGING
THE UPPER LOW NORTH ACROSS THE AREA. THE GFS AND EC LOOK BETTER BUT
THERE ARE DETAIL DIFFERENCES BETWEEN THESE MODELS ON PRECIPITATION
THREAT AS THE LOW MOVES NORTH. HAVE DECIDED TO KEEP A GENERAL
RAINFALL PATTERN FOCUSING ON OUR NORTHWEST EARLY WITH PRECIPITATION
THREAT AND AMOUNTS DECREASING SOUTH TO NORTH DURING THE DAY. THIS IS
NOT FAR FROM AN EC/GFS CONSENSUS. THE BIG QUESTION IS WILL THERE BE
A N/S BAND/LINE OF DECENT CONVECTION STILL GOING ON INTO THE MORNING
OVER THE EASTERN EDGE OF THE AREA...GOING WITH THE CONSENSUS THAT
MOST OF THIS WOULD BE DURING THE NIGHT AND BEGINNING TO MOVE NORTH
OF THE AREA.

AS FAR WEST AS THE LOW TRACK LOOKS...SURFACE WINDS WILL NOT BE GOING
WESTERLY UNTIL FAIRLY LATE IN THE DAY. TEMPERATURES SHOULD REACH THE
70S EAST TO THE 60S WEST.

THE SYSTEM SHOULD SLOWLY PULL OUT TO THE NORTHEAST SUNDAY NIGHT AND
HAVE A SHOWER THREAT DECREASING FROM SOUTHWEST TO NORTHEAST. IT DOES
LOOK WINDY RIGHT BEHIND THE LOW SUNDAY NIGHT. TEMPERATURES BY EARLY
MONDAY MORNING SHOULD DROP INTO THE UPPER 30S TO LOWER 40S.

MONDAY LOOKS COOL AND BREEZY TO WINDY. MODELS HINT AT A WEAK
SECONDARY SHORT WAVE DROPPING DOWN BEHIND THE MAIN SYSTEM. WITH COOL
AIR ALOFT A FEW LIGHT SHOWERS WOULD BE POSSIBLE AND LOW CLOUD COVER
SHOULD LINGER MUCH OF THE DAY ESPECIALLY NORTH. SUBSIDENCE BEHIND THE
LOW SHOULD COUNTER THIS AND MODEL INDICATIONS OF SOLID CLOUDS
LINGERING MOST OF THE DAY ARE PROBABLY OVERDONE. FOR THE SAME REASON
WILL LEAVE OUT ANY SHOWER OR SPRINKLE MENTION FOR NOW. DAYTIME HIGHS
WILL BE HELD TO THE MID 40S NORTHEAST TO THE MID 50S SOUTHWEST.

HIGH PRESSURE WILL BRING CLEARING BY MONDAY NIGHT AND A FAIRLY
BRIGHT DAY TUESDAY...THOUGH CLOUDS WILL BEGIN TO INCREASE FROM THE
SOUTHWEST BY LATE TUESDAY AS ONE IN A SERIES OF SHORT WAVES COMES UP
FROM THE SOUTHWESTERN USA TROUGH POSITION. THIS WILL BRING A THREAT
OF RAIN ESPECIALLY SOUTHWEST CENTERED ON WEDNESDAY...AND
TEMPERATURES WILL STILL BE COOL. AFTER A SHORT BREAK THURSDAY...A
CHANCE OF THUNDERSTORMS WILL DEVELOP AS THE WEEKEND APPROACHES AND A
STRONGER WAVE COMES UP. TEMPERATURES SHOULD BE WARMING A LITTLE BY
THE END OF THE WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1246 PM CDT SAT MAY 16 2015

MVFR CEILINGS WILL LIFT NORTH THROUGH THE AFTERNOON...BUT MAY
AGAIN REDEVELOP AFTER SUNSET AS MIXING DECREASES AND THE INVERSION
STRENGTHENS AGAIN. BACKED OFF ON THUNDERSTORM CHANCES THIS
AFTERNOON AND EVENING BUT WILL STILL BRING A GOOD CHANCES FOR
THUNDERSTORMS THROUGH FROM ABOUT 4Z THROUGH 12Z. AT THIS TIME NOT
EXPECTING MORE THAN ISOLATED SEVERE STORMS BUT THERE COULD BE
QUITE A FEW STORMS CAPABLE OF LIGHTNING...SMALL HAIL AND HEAVY
RAINFALL.

&&

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

$$

UPDATE...08
SHORT TERM...
LONG TERM...
AVIATION...08



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