Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 300848
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
348 AM CDT SAT APR 30 2016

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 347 AM CDT SAT APR 30 2016

UPPER LOW MOVES FROM NORTHEAST KS TO SOUTH CENTRAL NEB TODAY...
BEFORE FILLING AND MORPHING INTO AN UPPER TROUGH TONIGHT ACROSS
WISCONSIN AND IOWA. THE SURFACE LOW WILL REMAIN AHEAD OF THE UPPER
LOW WITH THIS SYSTEM...AND WILL ALSO WEAKEN TONIGHT AS IT MOVES INTO
THE MID MS VALLEY. EAST TO WEST ORIENTATED THETAE RIDGE AXIS MOVES
NORTHWARD WITH THIS SYSTEM TODAY AND THE PRECIPITATION FOLLOWS SUIT.
THE THETAE RIDGE AXIS IS MAXIMIZED IN THE 310-320K LAYER...OR
APPROXIMATELY 700-500MB AND MOVES SQUARELY INTO THIS FORECAST AREA.
IN THE LOWER LEVELS...THE POSITIVE 850MB THETAE ADVECTION IS STILL
PRETTY STRONG THIS MORNING FROM I 90 SOUTHWARD...AND LOW LEVEL
FRONTOGENESIS MAXIMIZED IN THE 900-850MB LAYER ALSO RESIDES FROM I
90 SOUTHWARD. IT STILL APPEARS BECAUSE OF THE LIMITING STREAMLINES...
THAT THE RAINFALL WILL HIT A BRICK WALL OF DRIER AIR BETWEEN I 90
AND HIGHWAY 14. IN FACT...LEFT OUR AREA FROM HURON SD TO MARSHALL MN
DRY...WITH A VERY SHARP POP GRADIENT INCREASING HEADING SOUTHWARD
TOWARD I 90. AN INCH OR MORE OF RAIN IS VERY LIKELY ALONG AND SOUTH
OF A LINE FROM NORTHERN GREGORY COUNTY...EASTWARD TO SPENCER IOWA
TODAY AND TONIGHT...WITH AMOUNTS OBVIOUSLY DECREASING HEADING
NORTHWARD FROM THERE TO VIRTUALLY NOTHING ALONG HIGHWAY 14. TONIGHT
AS THE LOW FILLS AND MOVES EASTWARD...THE AFOREMENTIONED DRY AIR TO
THE NORTH WILL GRADUALLY MOVE SOUTHWARD DECREASING THE INTENSITY OF
THE RAINFALL...AND ALSO PUSHING IT TO OUR SOUTHERN ZONES AFTER
MIDNIGHT.

HIGHS TODAY WILL BE CHILLY AND WITH WINDY CONDITIONS OF 20 TO 35
MPH...IT WILL CERTAINLY BE A NASTY DAY WHEN IT IS RAINING. THE RAW
MODEL VALUES STILL LOOK GOOD UNDER THE RAIN COOLED AIR WITH 40S
PREVAILING FOR HIGH TEMPERATURES...NOT MUCH WARMER THEN THEY ARE
NOW. HURON SD TO MARSHALL MN SHOULD SEE 50 TO 55. TONIGHT...THERE
SHOULD BE ENOUGH GRADIENT LEFTOVER TO KEEP MINIMUM TEMPERATURES FROM
TANKING TOO BAD ACROSS OUR NORTHERN AND WESTERN AREAS WHERE SKIES
WILL BECOMING MOSTLY CLEAR. HAVE UPPER 30S ACROSS OUR NORTH AND
WEST...WITH READINGS STILL IN THE 40S ELSEWHERE NOTING LITTLE IN THE
WAY OF DIURNAL TEMPERATURE CHANGE.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 347 AM CDT SAT APR 30 2016

WHILE SUPPORT FOR LINGERING PRECIPITATION WILL WANE FAIRLY QUICKLY
ON SUNDAY MORNING...SOUTHWARD SINKING OF THE WEAKENING DEFORMATION
BAND NORTH OF UPPER LOW WILL KEEP A FEW LIGHT SHOWERS GOING ACROSS
AREAS SOUTH OF A YANKTON TO SPENCER IOWA LINE EARLY IN THE DAY.
AFTER THIS...LARGER SCALE SUBSIDENCE AND PERSISTENT NORTH TO
NORTHEAST FLOW WILL KEEP DRYING TREND GOING. HOWEVER...CLOSER
INSPECTION OF THERMODYNAMIC ENVIRONMENT IN MOST MODELS SUGGEST THAT
THE LINGERING LOWER LEVEL MOISTURE AND SOME DIURNAL SUPPORT WILL
GENERATE A VERY SMALL AMOUNT OF SURFACE BASED INSTABILITY SOUTH OF
PERHAPS A KMWM-KFSD-KYKN LINE. THERE IS A DEPTH OF WEAK CYCLONIC
CURVATURE AS WELL. HOWEVER...WITH IDEA THAT LINGERING CLOUDINESS
WILL IMPACT THE POTENTIAL TO WARM ENOUGH TO FULLY DESTABILIZE...WILL
GO ONLY WITH SOME INCREASE IN SKY COVERAGE...BUT WOULD NOT BE
TOTALLY SURPRISED TO FIND A COUPLE OF SPRINKLES DURING THE AFTERNOON.
HIGHS WILL MODERATE A BIT WITH INCREASED SUNSHINE OVER TODAY...
MAINLY UPPER 50S TO LOWER 60S.

WEAK LOW LEVEL RIDGING ON SUNDAY NIGHT...AND PERHAPS THE INITIATION
OF SOME WESTERLIES NEAR SURFACE AS RIDGE SINKS SOUTH OF THE AREA.
WILL HEDGE TEMPS DOWN A BIT...ESPECIALLY LOWER ELEVATIONS IN SE
SD...WITH MID 30S TO LOWER 40S EXPECTED.

MONDAY SHOULD FEATURE MORE SUNSHINE...BUT ECMWF HAS COMPLICATED A
BIT WITH SOLUTIONS A BIT JUMPY OVER THE LAST FEW RUNS DEALING WITH
EARLY TO MID WEEK. LATEST HICCUP IS BRINGING A MORE STURDY UPPER LOW
SOUTHWARD ACROSS THE AREA MONDAY AFTERNOON AND MONDAY NIGHT ALONG
WITH THREAT FOR SHOWERS. HAVE NOT BOUGHT INTO THAT SOLUTION...YET...
AS THERE IS AT LEAST A SINGLE MEMBER OF THE GFS ENSEMBLE IN SUPPORT.
REGARDLESS...SHOULD AGAIN AT LEAST GET A FEW HEATING STRATOCUMULUS
AND SOME HIGH LEVEL CLOUDS SPREADING IN FROM THE NORTH DURING THE
MIDDAY AND AFTERNOON. ANOTHER STEP IN THE RIGHT DIRECTION...WITH
HIGHS LOWER TO MID 60S...ALTHOUGH RAW MIXING OF GFS LEADING THE WAY
WITH SEVERAL MORE DEGREES ON TOP OF THAT. EVEN WARMER ON TUESDAY AS
BETTER WESTERLY FLOW AND WARMER AIRMASS...LIKELY AT LEAST LOWER TO
MID 70S...WITH GFS AGAIN SUGGESTING EVEN A BIT WARMER.

SOLUTIONS CONVERGING ON TROUGH DIGGING INTO THE GREAT LAKES NOW
PUSHING A BACK DOOR FRONTAL ZONE THROUGH THE REGION TUESDAY NIGHT
AND EARLY WED. NOT OUT OF THE QUESTION THAT TAIL OF MID LEVEL
FRONTOGENESIS MAY YET YIELD A FEW LIGHT SHOWERS ACROSS SW MN AND NW
IA LATER TUE NIGHT OR EARLY WED...BUT STRONGER DYNAMICS CERTAINLY
LOOK TO REMAIN WELL EAST OF AREA. OVERALL...GFS IS A BIT STRONGER ON
THE COOLING FOR WEDNESDAY AND ESPECIALLY THURSDAY...AND HAVE SIDED A
SHADE COOLER THAN INITIAL BLEND GIVEN THE RECENT SUPPORT ADDED BY
MOIST GROUND.

NO QUESTION THAT LONG TERM TRENDS IN MODEL SOLUTIONS ARE TO SET UP
AN OMEGA BLOCK PATTERN OVER THE CONUS...WITH RIDGE OVER THE MID
CONTINENT AND LARGE CLOSED LOWS ON EITHER SIDE. FOR THE MOST PART...
SHOULD SET UP A PERIOD OF VERY PLEASANT WEATHER THROUGH THE END OF
THE WEEK. COULD PERHAPS SEE PATTERN SHIFT ENOUGH TO GET A SHOWER OR
THUNDER THREAT IN BY THE WEEKEND...BUT DRY WEATHER EXPECTED IN THE
MEANTIME.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1047 PM CDT FRI APR 29 2016

MVFR STRATUS GENERALLY SOUTH OF I90 WILL VERY SLOWLY LIFT BACK
NORTHWARD OVERNIGHT THROUGH SATURDAY MORNING...HOWEVER THERE IS
SOME INDICATION THAT THE US HIGHWAY 14 CORRIDOR MAY REMAIN VFR FOR
THE BULK OF THE TAF PERIOD. BAND OF RAIN WILL ALSO LIFT SLOWLY
NORTHWARD...REACHING THE I90 CORRIDOR MID TO LATE MORNING
SATURDAY...AND WILL FURTHER LOWER CEILINGS AND REDUCE VISIBILITY.
RAIN WILL BE MODERATE TO HEAVY AT TIMES ESPECIALLY THROUGH THE
MISSOURI VALLEY. RAIN WILL PERSIST ACROSS THE REGION THROUGH THE
END OF THE TAF PERIOD. AGAIN...THE HIGHWAY 14 CORRIDOR MAY SEE
VERY LITTLE TO NONE OF THIS ACTIVITY.


&&

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

$$

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



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