Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 021105
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
605 AM CDT TUE JUN 2 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 409 AM CDT TUE JUN 2 2015

QUITE A FEW WEATHER CONCERNS TODAY...FROM STRONG WINDS...TO
CONVECTION LATER TODAY AND TONIGHT. EARLY THIS MORNING...A PAIR OF
WAVES ARE EJECTING INTO THE PLAINS.  ONE WAVE IS LIFTING NE INTO
NORTH DAKOTA THIS MORNING...WITH A SECOND DRIVING SOUTHEAST ACROSS
NEBRASKA. IN BETWEEN...AN INCREASING LLJ IS TRYING TO DEVELOP LIGHT
PRECIPITATION ON THE NOSE OF A MORE SUBSTANCIAL LOW-LVL MOISTURE
AXIS ADVECTING NE. IN GENERAL...GIVEN THE SPLIT NATURE OF THE
FORCING...NOT ANTICIPATING ANY LARGE SCALE REDEVELOPMENT THROUGH
MORNING.

THE DAYTIME HOURS TODAY WILL FEATURE STRONG SOUTHEASTERLY
WINDS...ALONG WITH RISING DEW POINTS. SOUNDINGS SHOW A FAIRLY EARLY
DEVELOPMENT TO GUSTY SFC WINDS...AS WE QUICKLY MIX THROUGH 10AM.
WOULD ANTICIPATE FAIRLY PERSISTENT 20 KNOT WINDS THROUGH THE
DAY...BUT GIVEN THE UNIFORM NATURE OF THE WIND FIELD ALOFT...GUSTS
SHOULD STAY REASONABLE.

BY THIS AFTERNOON...WE WILL WATCH AN IMPRESSIVE CORRIDOR OF
INSTABILITY BUILD ACROSS CENTRAL SD/NE...WITH LATE AFTERNOON MLCAPE
VALUES PUSHING 2500 J/KG.  MOST OF THIS INSTABILITY WILL BUILD ALONG
AND AHEAD OF A N-S ORIENTATED SFC BOUNDARY ACROSS CENTRAL SD.   AT
THE SAME TIME...SOUNDINGS REVEAL A RATHER SIGNIFICANT AND THICK
CAPPING INVERSION AOA 750MB THROUGH THE MISSOURI RIVER VALLEY. THE
QUESTIONS FOR LATER THIS AFTERNOON WILL BE THE DEGREE OF COVERAGE OF
STORMS INITIALLY NEAR AND AHEAD OF THE BOUNDARY. MOST HIGH-RES
SOLUTIONS ONLY SHOW ISOLATED TO SCT COVERAGE OF STORMS ON THE
BOUNDARY INTO THE EARLY EVENING...WITH MORE SIGNIFICANT DEVELOPMENT
LATE IN THE EVENING AS STRONGER FORCING...COOLER LOW-LVL TEMPS...
AND THE NOCTURNAL LLJ BEGINS TO INTENSIFY.

WHILE EFFECTIVE SHEAR IS NOT ALL THAT STRONG...IT SHOULD BE STRONG
ENOUGH FOR STORMS WITH SUPERCELLULAR CHARACTERISTICS IN THE INITIAL
DEVELOPMENT...MAINLY WEST OF THE MO RIVER AND INTO NORTH CENTRAL NE
BY EVENING. INITIAL STORMS WILL BE VERY SLOW MOVING...SO WOULD NOT
ANTICIPATE A QUICK EASTWARD PROGRESSION INTO THE WESTERN CWA UNTIL
NEAR OR AFTER 00Z.  THICK CAPE PROFILES AND MODEST MID-LVL LAPSE
RATES WOULD SUPPORT A VERY LARGE HAIL RISK...GOLF BALL OR LARGER.
MORE CONCERNING IS THE SUBSTANCIAL DRY AIR INTRUSION ALOFT AND DEEP
SFC MIXING...WITH DCAPE VALUES AOA 1000 J/KG THROUGH THE EVENING
HOURS SUPPORTING DAMAGING WINDS.  AS THE EVENING GOES ON
PROBABILITIES INCREASE FOR A COUPLE WIND DRIVEN STORM CLUSTERS OR
EVEN A LARGER MCS GROWING INTO THE OVERNIGHT.

THE TORNADIC POTENTIAL IS NOT ONE TO DISCOUNT EVEN THROUGH THE LATE
EVENING...WITH NAM/GFS SOUNDINGS SHOWING LONG LOOPED HODOGRAPHS
PRIMARILY WEST OF THE JAMES RIVER LATE THIS AFTN AND EVENING. ONCE
THE NOCTURNAL LLJ KICKS IN...0-1 KM HELICITY FURTHER
INCREASES...LCLS BEGIN TO FALL...AND THE BOUNDARY LAYER REMAINS ONLY
WEAKLY DECOUPLED IN THIS ZONE.

TIMING...CAPPING LIKELY LIMITS DEVELOPMENT TO ISO-SCT THROUGH
00Z...BUT MORE EXPANSIVE DEVELOPMENT WILL PICK UP BY 03Z AND EXPAND
AS STORMS CONGEAL AND MOVE EASTWARD THROUGH 9Z...REACHING THE I-29
CORRIDOR EITHER SIDE OF 06Z.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 409 AM CDT TUE JUN 2 2015

OUTFLOW DOMINANT CONVECTIVE CLUSTER WILL BE PRESSING EAST/SOUTHEAST
ACROSS THE EASTERN CWA EARLY WEDNESDAY MORNING...AS STRONG MID LEVEL
WAVE PUSHES THROUGH AREAS EAST OF I-29.  LOW LEVEL JET WILL HAVE
DEFLECTED TOWARD THE SOUTHWEST BY EARLY WEDNESDAY...BUT STILL ENOUGH
CONVERGENCE FOR SOME DECENT RAINFALL AMOUNTS FOR THE FAR
EAST/SOUTHEAST. NAM CONTINUES AMONG THE MOST AGGRESSIVE ON THE
BOUNDARY PUSH...AND MAY NOT BE A BAD IDEA TO FOLLOW GIVEN THE
CONVECTIVE IMPACT ON BOUNDARY. WILL BE IMPORTANT TO FOLLOW...AS
WOULD MOST CERTAINLY BE THE NARROW ZONE FOR ANY MINOR SEVERE THREAT
ON WEDNESDAY. SEVERAL MODELS CONTINUE TO SUGGEST SOME SOLID
AFTERNOON REDEVELOPMENT ALONG THE FRONTAL AXIS...BUT AT THIS TIME AM
SIDING MORE TOWARD THE EARLIER CONVECTION MESSING UP THIS
CONVERGENCE TO A GREAT ENOUGH DEGREE TO LIMIT COVERAGE AND THUS POP
AROUND MID CHANCE LEVEL FOR LATER AFTERNOON ACROSS THE SOUTHEAST
THIRD.

AFTER A GOOD 12 TO 18 HOURS OF CONVECTIVE PROGRESSION...THE REST OF
THE FORECAST CONTAINS A LOT OF WHAT IF...GIVEN LARGE IMPACT THE DAY
TO DAY CONVECTION WILL HAVE ON FUTURE DEVELOPMENT. SHORT WAVE
RIDGING BEHIND THE EARLY WEDNESDAY WAVE CERTAINLY SUGGESTS THAT THE
OVERALL TREND WILL BE TO MINIMIZE THE CONVECTION FOR A PERIOD FROM
LATER WEDNESDAY INTO WEDNESDAY NIGHT...ESPECIALLY NORTH OF THE
BOUNDARY FROM AT LEAST AROUND I 90 AND NORTHWARD.  SOME DIFFERENCE
IN TIMING...BUT ANOTHER WAVE WILL MOVE OUT INTO THE HIGH PLAINS
LATER WED NIGHT...AND MOVE VERY SLOWLY THROUGH THE RIDGE THROUGH
THURSDAY NIGHT.  IF ACTIVITY FROM WEDNESDAY NIGHT TAKES OFF TOWARD
THE BETTER INSTABILITY SOUTH...AND FURTHER DRIVES THE BOUNDARY
SOUTHWARD...POTENTIAL IS FOR VERY LIMITED CONVECTION THROUGH THE END
OF THE WEEK. AT THIS POINT...SEE ENOUGH EVIDENCE THAT LOW LEVEL JET
WILL REACT FAVORABLY EVEN WITH MORE SOUTHERN CONVECTION ON WED NIGHT
TO ALLOW A DECENT COVERAGE OF PRECIPITATION NORTH OF THE BOUNDARY
ACROSS MAINLY AREAS OF NORTHEAST NEBRASKA AND NORTHWEST IOWA. THIS
PRECIPITATION COULD BE FAIRLY EFFICIENT...WITH HIGH MOISTURE VALUES
AND WARM CLOUD DEPTH TO PRODUCE SOME POTENTIALLY HEAVIER
PRECIPITATION AMOUNTS.

SOME PRECIP COULD LINGER EARLY FRIDAY IN THE SOUTH AND EAST...BUT
FOR THE MOST PART THE BUILDING HEIGHTS AND INFLUX OF MORE STABLE
AIRFLOW FROM THE EAST AND NORTHEAST WILL CUT OFF PRECIPITATION FOR A
24-30 HOUR PERIOD. AIRMASS IS NOT EXACTLY CHILLY...BUT COOLER MIXING
POTENTIAL TOWARD THE LOWER TO MID 70S.

LITTLE BETTER NORTHERN STREAM WAVE WILL FLATTEN RIDGE HEADING
THROUGH SATURDAY AND SATURDAY NIGHT...INTERACTING WITH YET ANOTHER
SOUTHERN STREAM IMPULSE...WHEN MOST LIKELY WILL FIND THE NEXT CHANCE
OF PRECIPITATION. DEEPER INSTABILITY WILL RETURN AS BOUNDARY MOVES
ACROSS THE AREA...SO EXPECT THUNDERSTORMS...AND STRONGER MID LEVEL
WINDS PRESENT A BIT BETTER THREAT FOR SEVERE WEATHER...SOMEWHAT AT
ODDS WITH LESSER SURFACE BASED INSTABILITY OVER EASTERN SOUTH DAKOTA
VERSUS THE WEST.

ON LARGER HARD TIME SEEING MUCH NEED FOR A PRECIP THREAT ON SUNDAY
PAST ANY SMALLER LINGERING THREAT IN THE EAST. WILL BE WORKING ON
DRYING OUT THE LOWER LAYERS BEHIND THE FRONT ON SUNDAY...BUT EVEN
THEN AIRMASS REMAINS FAIRLY WARM. IN FACT...RAISED HIGHS BY SEVERAL
DEGREES SUNDAY AND ESPECIALLY MONDAY OVER THE INITIALIZATION
GRIDS...AND AM FAIRLY CONFIDENT THAT WILL SEE TEMPERATURES RAISED
EVEN MORE IF MIXY NORTHWEST FLOW CONTINUES TO BE ADVERTISED FOR THE
SUNDAY AND MONDAY TIME FRAME.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 603 AM CDT TUE JUN 2 2015

SEEING A BIT OF STRATUS CREEP UP THE MISSOURI RIVER BASIN THIS
MORNING AS LOW LVL MOISTURE SURGES NORTHWARD. FOR MUCH OF THE DAY
WE WILL HAVE VFR CONDITIONS ACROSS THE TERMINALS.

SOUTHEASTERLY WINDS WILL TURN RATHER BREEZY BY EARLY
MORNING...SUSTAINED GUSTS MAY APPROACH 15 TO 20 KNOTS WITH GUSTS
NEAR 30 KNOTS. CONVECTION LATER TODAY REMAINS HIGHLY
QUESTIONABLE...BOTH IN AERIAL COVERAGE AND TIMING. WILL INCLUDE A
VCTS TO HINT AT POTENTIAL AND ALLOW LATER SHIFTS TO REFINE TIMING
AS NEEDED.

&&

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

$$

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


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