Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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671
FXUS63 KFSD 021715
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1215 PM CDT MON MAY 2 2016

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 355 AM CDT MON MAY 2 2016

THE MAIN FEATURE TODAY IS AN UPPER SHORT WAVE MOVING SOUTHWARD...
ENTERING NORTH DAKOTA AT THIS TIME FROM SOUTH CENTRAL CANADA. THE
MODELS ARE IN GOOD AGREEMENT IN TRACKING THIS LOW DOWN INTO WESTERN
AND CENTRAL SOUTH DAKOTA AND NEBRASKA THROUGH THE DAY TODAY. THIS IS
EVIDENCED BY FOLLOWING THE MID AND UPPER LEVEL QG FORCING. MOISTURE
IS FAIRLY DEEP WITH THIS SYSTEM IN OUR FAR WESTERN FRINGE OF THE
FORECAST AREA...PRIMARILY AROUND THE CHAMBERLAIN AREA...WHERE HIGH
END SCATTERED POPS ARE WARRANTED. BUT HEADING EASTWARD INTO THE
MIDDLE JAMES RIVER VALLEY...THE MOISTURE PROFILE SHALLOWS OUT AS YOU
MOVE FURTHER AWAY FROM THE WAVE. THIS WARRANTS JUST LOW END
SCATTERED OR ISOLATED POPS. IN OUR WEST...THE TEMPERATURES ARE COLD
ENOUGH AT THE TOP OF THE CLOUD LAYER TO WARRANT A MENTION OF TSRA.

A SECOND FEATURE WHICH IS INTERESTING IS ALONG AND JUST EAST OF THE
I 29 CORRIDOR. THE VARIOUS MODELS SHOW ABOUT A 75MB THICK CU DECK
CENTERED NEAR 750MB IN THAT STRIPE...WITH THE MOISTURE MORE SHALLOW
IN OUR EXTREME EASTERN ZONES FROM WINDOM TO STORM LAKE. BELIEVE WITH
THE AMOUNT OF COLD AIR ALOFT AND REMAINING UPPER CYCLONIC FLOW...
THAT WE WILL CU UP THIS AFTERNOON FROM I 29 EASTWARD...AND THE
MOISTURE DEPTH COULD BE THICK ENOUGH TO SPARK SOME ISOLATED SHOWERS
ALONG AND JUST EAST OF I 29. THERE IS A SUBTLE UPPER LOW CIRCULATION
NOTED AT 500MB VERY CLOSE TO SIOUX FALLS AT 00Z TUE...MAXIMIZED
WHERE THE AIR ALOFT IS THE COLDEST. WITH THE MID AND UPPER FLOW
SLIGHTLY NORTHWEST AT SIOUX CITY...KEPT KSUX DRY FOR THIS
AFTERNOON...BUT OTHER AREAS ALONG AND JUST EAST OF I 29 COULD HAVE
ISOLATED SHOWERS FROM ABOUT 3PM TO 6PM. THE LATEST OPERATIONAL AND
EXPERIMENTAL HRRR SOLUTIONS SHOW THIS...AS WELL AS THE ARW AND NMM.

OTHERWISE OVERALL THOUGH...WITH LIGHT WINDS IT WILL BE A NICE DAY
TODAY...WITH HIGHS IN THE 60 TO 65 DEGREE RANGE. FOR TONIGHT...IT
SHOULD BE UNEVENTFUL AS OUR WESTERN WAVE DEPARTS LEAVING A RISK OF
SOME EARLY EVENING SHOWERS FOR THOSE LOCATIONS. THE HEATING DRIVEN
CUMULUS NEAR I 29 WILL DISSIPATE RAPIDLY. LOWS WILL BE A COUPLE OF
DEGREES EITHER SIDE OF 40.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 355 AM CDT MON MAY 2 2016

TUESDAY ANOTHER STEP IN THE WARMER DIRECTION WITH A HEALTHY WESTERLY
FLOW SETTING UP AHEAD OF SOUTHWARD DROPPING FRONTAL BOUNDARY.
BOUNDARY IS EXPECTED TO BE SCRAPING UP ALONG NORTHERN/NORTHEASTERN
CWA BORDER TOWARD EVENING...WHICH WILL GIVE A FULL DAY OF MIXING FOR
THE AREA. PLENTY OF SUNSHINE EARLY...BUT LOOK FOR A GREATER DEGREE
OF CLOUDINESS DEVELOPING DURING THE AFTERNOON. HIGHS SHOULD REACH
MIXED VALUES IN THE UPPER 60S TO LOWER 70S. A TAIL OF DIV Q WILL
BRUSH THROUGH SOUTHWEST MINNESOTA AND INTO NORTHWEST IOWA LATE
AFTERNOON INTO EARLY EVENING...AND DIURNAL HEATING AND WEAK FRONTAL
CONVERGENCE COULD BE ENOUGH TO ENTICE A FEW MORE WELL DEVELOPED
CUMULUS AND AN ISOLATED SHOWER THREAT LATE DAY.  HOWEVER...WITH
TEMPERATURES IN THE CLOUD LAYER STRUGGLING TO REACH -10C...LIKELY
NOT ENOUGH ICE PROCESS EVEN WITH 100-200 MLCAPE TO THREATEN ANY
LIGHTNING.

WINDS SHOULD STAY UP BEHIND THE BOUNDARY WHILE SHIFTING TO THE
NORTH...ANY MAYBE A TOUCH STRONGER THAN ADVERTISED BY GUIDANCE AS 20
TO 30 KNOTS IN WITHIN 1 KFT OF SURFACE DURING POST FRONTAL COLD
ADVECTION PERIOD...SO ADDED A TERRAIN ENHANCED 3-5 KNOTS BEHIND THE
FRONTAL BOUNDARY THROUGH THE NIGHT. BLENDED IN TYPICALLY BETTER
CONSRAW MODEL DATA...AND EVEN THIS KEPT READINGS A BIT HIGHER TO
MATCH EXPECTED BREEZIER AREAS.

WEDNESDAY THROUGH FRIDAY SETTLE IN FOR A PLEASANT AND DRY PERIOD AS
OMEGA BLOCK BECOMES ESTABLISHED OVER THE MID CONUS. SLIGHT COOLING
WEDNESDAY AS SURFACE RIDGE BUILDS INTO THE HEART OF THE AREA BY
EVENING...AND STILL OPEN FOR SOME BREEZIER NORTHERLY WINDS THROUGH
THE DAY IN PARTS OF SW MN AND NW IA.  RIDGE LINGERS EAST OF I 29
ACROSS MAINLY NW IA WEDNESDAY NIGHT...AND AGAIN FAVORING SOME OF THE
COLDER GUIDANCE SOLUTIONS ALONG AND EAST OF I 29. MORE SUN...
SOUTHERLY FLOW AND WARMING OFF SURFACE TEMPS SHOULD AGAIN BOOST
READINGS INTO THE 70S DURING THE AFTERNOON.  FRIDAY...AS UPPER RIDGE
CONTINUES TO NUDGE EASTWARD OVER THE AREA...EVEN SLIGHTLY WARMER
TEMPS WITH A FEW 80 DEGREES READINGS POPPING UP...BUT ALSO LIKELY
DEALING WITH A FEW MORE CLOUDS.

THE OVERALL SITUATION BECOMES MUCH MORE MUDDLED BY THE WEEKEND...
WITH OMEGA BLOCK WEAKENING/BREAKDOWN SUBTLY DIFFERENT BETWEEN
VARIOUS SOLUTIONS. MAIN DIFFERENCE LOOKS TO BE HOW STRONG HUDSON BAY
LOW MAINTAINS...AND WHAT KICK WAVE SLIDING TOWARD THE GREAT LAKES
GIVES TO EASTERN UPPER WAVE PORTION OF OMEGA BLOCK. IMPACT FOR OUR
AREA IS HOW AGGRESSIVELY A LOWER TO MID LEVEL FRONTAL BOUNDARY
PROGRESSES INTO THE AREA BY SATURDAY AND SATURDAY NIGHT.
ECMWF/CANADIAN STRONGEST WITH WAVE FLATTENING RIDGE AND FASTEST AND
FURTHEST SOUTHWARD WITH FRONTAL PROGRESSION...WHILE GFS A BIT MORE
LEISURELY IN PUSHING BOUNDARY SOUTHWARD. QUITE A BIT OF VARIATION ON
EVENTUAL PRECIPITATION THREAT BETWEEN SOLUTIONS...WITH GFS
PARTICULARLY WET THROUGHOUT THE WEEKEND...AND ECMWF QUICKLY SENDING
FOCUS MORE TOWARD I 80. ENOUGH UNCERTAINTY TO KEEP FROM ANY STRONG
CONSENSUS AROUND THE REGION...AND AS A RESULT HAVE ONLY TRENDED FROM
FAIRLY BLANKETED UNIFORM POPS TO SHOW A BIT OF A LESSER CHANCE NORTH
VS. SOUTH BY SATURDAY NIGHT AND SUNDAY. WESTERN UPPER LOW BEGINS A
WOBBLE NORTHEAST TOWARD THE REGION BY SUNDAY NIGHT AND MONDAY... AND
LIKELY TO SEE ANOTHER BETTER CHANCE FOR RAIN/THUNDER DEVELOP JUST
BEYOND THE FORECAST PERIOD. TEMPS NORTH OF THE BOUNDARY WITH MORE
PREVALENT CLOUDS AND EASTERLY FLOW SHOULD BRING BACK SEASONABLE 60S
ON SUNDAY.

WILL CERTAINLY HAVE TO KEEP ONE EYE ON FRONTAL PROGRESSION ON
SATURDAY. GIVEN LIKELIHOOD OF DECENT INSTABILITY NEAR THE BOUNDARY
AND POTENTIAL FOR CONSIDERABLE LOCALIZED SHEAR...MAINLY LOWER IN THE
WIND PROFILE...COULD POTENTIALLY SEE A COUPLE STRONGER STORMS IN THE
AREA OF THE BOUNDARY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1213 PM CDT MON MAY 2 2016

VFR CONDITIONS EXPECTED THROUGH THE PERIOD. SCATTERED
SHOWERS/ISOLATE THUNDERSTORMS ARE EXPECTED AFTER 20Z ACROSS
CENTRAL SOUTH DAKOTA. COULD SEE A MARGINAL WIND THREAT AS FAR EAST
AS THE JAMES RIVER VALLEY. ELSEWHERE...LIGHT WESTERLY WINDS SHOULD
PREVAIL.

&&

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

$$

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



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