Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 080803
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
303 AM CDT TUE JUL 8 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 303 AM CDT TUE JUL 8 2014

MAIN CONCERN IS THE CHANCE OF INSTABILITY SHOWERS AND THUNDERSTORMS
THIS AFTERNOON. ALL MODELS SHOW A WEAK SHORT WAVE MOVING ACROSS MN
IN THE NW FLOW AT 500 MB. THE NAM IS STRONGEST WITH THIS WAVE WHILE
THE 12Z ECMWF WAS WEAKEST. HOWEVER...ALL MODELS AGREE THAT WITH 700
MB TEMPS AROUND 2 C AND 850 MB TEMPS BLO 10C...FULL SUN RESULTS IN
RAPID DESTABILIZATION OF THE BOUNDARY LAYER BY EARLY AFTERNOON IN
THE VICINITY OF SW MN. AS A RESULT A 10-20 KFT LAYER OF WEAK
INSTABILITY DEVELOPS AND WITH CYCLONIC FLOW ALOFT AND SEE NO REASON
WHY THERE WILL NOT BE DEVELOPMENT OF ISOLATED SHOWERS AND
THUNDERSTORMS BY EARLY AFTERNOON. THERE IS A DEFINITE GRADIENT IN
THIS INSTABILITY AS WARMER TEMPERATURES ALOFT AND A DRIER BOUNDARY
LAYER RESULT IN LESS INSTABILITY AND CUMULUS AS ONE GOES WEST OF
I-29. THIS IS CONFIRMED BY HI-RES ARW AND NMM WHICH SHOW INSTABILITY
SHOWERS DEVELOPING SHORTLY AFTERNOON IN NE SD AND SPREADING
SOUTHEAST DURING THE AFTERNOON. AS A RESULT...ADDED A SLIGHT CHANCE
OF SHOWERS TO MUCH OF SW MN AND INTO EC SD WHERE INSTABILITY IS
GREATEST. CONSIDERED EXPANDING THE AREA OF SHOWERS FARTHER SW AND
GOING HIGHER POPS BUT ENOUGH UNCERTAINTY ON HOW DEEP AND WIDESPREAD
THE INSTABILITY IS THAT WILL FOCUS ON MOST CONFIDENT AREAS FOR NOW.
HOWEVER...EVEN WHERE IT RAINS...PCPN WILL LIKELY LAST LESS THAN AN
HOUR AND AMOUNT TO ONLY A FEW HUNDREDTHS. ANY SHOWERS SHOULD QUICKLY
DISSIPATE DURING THE EVENING WITH THE LOSS OF DIABATIC HEATING.
THAT WILL LEAVE MOSTLY CLEAR SKIES OVERNIGHT WITH LIGHT WINDS.

AS FOR TEMPS...NW WINDS OF 10 TO 20 MPH WILL PROVIDE GOOD MIXING AS
NOTED ABOVE. EXPECT BL TO DEEPEN BETWEEN 1.5 AND 2 KM WHICH SUPPORTS
HIGHS IN THE UPPER 70S TO LOWER 80S. LOWS OVERNIGHT SHOULD REALLY
DROP AS WINDS GO LIGHT AND AIR MASS IS FAIRLY DRY WITH 50S EXPECTED
IN MOST PLACES.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 303 AM CDT TUE JUL 8 2014

DRY WEATHER...MILD TEMPERATURES...AND PLEASANTLY LIGHT WINDS
WEDNESDAY WILL GIVE WAY TO A WARM ADVECTION PATTERN SLOWLY
STRENGTHENING AND A SLOWLY INCREASING THREAT OF STORMS WEDNESDAY
NIGHT AND THURSDAY. THE THREAT OF STORMS IS EXPECTED TO PEAK
THURSDAY NIGHT WITH UPPER SUPPORT FOR AIDING DECENT LIFT FROM A WELL
DEFINED SHORT WAVE. SOME DECENT STORMS SEEM LIKELY THOUGH WIND
FIELDS DO NOT LOOK THAT THRILLING...AND SPC 5 PERCENT AREA FOR DAY
THREE SEEMS GOOD. THIS SHOULD PASS FRIDAY AND LEAVE A DRY 12 TO 18
HOURS BEFORE ANOTHER SHORT WAVE ARRIVES AND STARTS THE PROCESS OF
PUTTING A CLAMP ON UPPER RIDGING INTO THE AREA. THIS IS THE RIDGING
WHICH THE GFS SEVERAL DAYS AGO WAS SURGING INTO A MONSTER UPPER
RIDGE OVER THE AREA FOR A COUPLE DAYS OF ITS SOLUTIONS. AS IT
IS...THE WARMING SHOULD PEAK MODESTLY FRIDAY WITH THE MOSTLY DRY
WEATHER THAT DAY...AND HIGH TEMPERATURES IN THE 80S. THE RIDGE
DAMPING PROCESS WILL NOT BE INSTANT...WITH SHORT WAVES POSSIBLY
BRINGING A FEW STORMS OVER THE WEEKEND AS THE UPPER FLOW BEGINS TO
TURN BACK TO NORTHWESTERLY. BY MONDAY...SURFACE RIDGING AND DRY
WEATHER SHOULD TAKE OVER ON THE BACK SIDE OF A STRONG EASTERN
CANADIAN/UPPER GREAT LAKES UPPER LOW.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1109 PM CDT MON JUL 7 2014

VFR WILL PREVAIL THROUGH TUESDAY. NORTHWESTERLY WINDS WILL LIKELY
OCCASIONALLY GUST TO AROUND 25 KNOTS IN THE LATE MORNING AND
AFTERNOON HOURS ON TUESDAY.


&&

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

$$

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






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