Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 241752
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1252 PM CDT FRI APR 24 2015

.UPDATE...
ISSUED AT 1252 PM CDT FRI APR 24 2015

IMPACT OF WAVE LIFTING ACROSS NORTHWEST IOWA AT MIDDAY HAS BEEN
TWOFOLD...FIRST TO GENERATE AS EXPECTED SCATTERED SHOWERS AND A
FEW THUNDERSTORMS MAINLY NORTHWEST IOWA INTO SOUTHWEST
MINNESOTA...AND SECOND TO BRING A GREATER DEAL OF CLEARING TO THE
WESTERN/SOUTHERN CWA.

SOME ALTERATIONS MADE TO THE CONVECTIVE TRENDS THROUGH THE DAY.
WITH SUBSIDENCE FOR THE TIME BEING SETTLING ACROSS THE CWA... HAVE
DROPPED MOST OF THE LOWER POPS IN REGION BEHIND WAVE...WHILE
INCREASING CERTAINTY A BIT AHEAD. CONCERN THEN BECOMES WITH THE
LATTER AFTERNOON...WHERE THE DESTABILIZATION FROM THE ADDED
HEATING WILL ERODE WEAK CAPPING. AT LEAST MODEST CONVERGENCE
ALONG BOUNDARY LIKELY TO POOL ENOUGH MOISTURE TO RESULT IN A
500-1200 J/KG MIXED LAYER INSTABILITY...BUT DEEPER LAYER SHEAR IS
FAIRLY WEAK DUE TO THE LACK OF ANY MID LEVEL WINDS. PERHAPS COULD
SCARE UP A PULSE MULTICELL MARGINAL SEVERE HAILER ACROSS AREAS
NEAR/WEST OF THE JAMES RIVER LATE AFTERNOON INTO EARLY
EVENING...BUT OVERALL ANY SEVERE THREAT IS MINIMAL.

TOUGH PART OF TEMPERATURE FORECAST FOR LOWER MISSOURI VALLEY IS
HOW WARM IT COULD GET PRIOR TO RETURN OF STRATUS FROM THE SOUTH
AROUND MID AFTERNOON. PUSHED READINGS UP QUITE A BIT...FROM 4 TO 7
DEGREES...BUT MAY NOT BE ENOUGH IF CAN REACH POTENTIAL INDICATED
IN RAP MODEL...WHICH IS MUCH MORE IN TUNE WITH CURRENT TRENDS.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 415 AM CDT FRI APR 24 2015

NOT EXACTLY A CLEAR CUT FORECAST WITH REGARD TO PRECIPITATION
CHANCES OVER THE NEXT 24 HOURS. SEEING JUST SPOTTY ELEVATED SHOWERS
IN OUR FAR SOUTHEAST THUS FAR THIS MORNING...WITH LOW LEVEL JET
FOCUSING MORE CONSOLIDATED PRECIPITATION WELL NORTH OF OUR AREA.
MORE CONCENTRATED LOW LEVEL MOISTURE INCREASE EXPECTED OVER THE
WESTERN CWA THROUGH THE EARLY MORNING...THOUGH THUS FAR THIS HAS
BEEN SLOWER TO DEVELOP THAN EXPECTED. NEVERTHELESS...BEGINNING TO
SEE SPOTTY ELEVATED ECHOES DEVELOP THROUGH EASTERN NEBRASKA AND HIGH
RES MODELS IN FAIR AGREEMENT DEVELOPING ISOLATED SHOWERS FROM NEAR
THE JAMES VALLEY TO WEST OF I-29 THIS MORNING. OVERALL THOUGH...
BETTER POTENTIAL FOR SHOWERS THROUGH THE DAY APPEARS TO BE IN OUR
FAR SOUTHEAST WHERE DEEP ISENTROPIC LIFT PERSISTS THROUGH MUCH OF
THE DAY. DEPTH OF MOISTURE A BIT OF A CONCERN AND HAVE TRIMMED BACK
RAINFALL AMOUNTS A BIT FROM PREVIOUS FORECAST FOR TODAY...WITH
AROUND A TENTH OF AN INCH OR A LITTLE MORE ALONG/SOUTHEAST OF
HIGHWAY 60 CORRIDOR...AND LESS THAN A TENTH ELSEWHERE IN THE CWA.

AS FOR TEMPERATURES...HOLDING A FEW DEGREES COOLER THAN THURSDAY IN
THE EAST DUE TO THICKER CLOUD COVER AND PRECIP CHANCES...BUT A SHADE
WARMER WEST WHERE 925MB TEMPERATURES ARE FORECAST TO CLIMB A DEGREE
OR TWO HIGHER THAN THURSDAY IN THERMAL RIDGE JUST AHEAD OF THE
SURFACE BOUNDARY. WITH THE WARMER TEMPERATURES AND BETTER LOW LEVEL
MOISTURE WEST...BEGIN TO SEE BETTER SURFACE BASED INSTABILITY AND
LEADING TO POSSIBLE ISOLATED TO SCATTERED THUNDERSTORM DEVELOPMENT
IN OUR FAR WEST BY LATE AFTERNOON. GFS/NAM SHOWING SBCAPE VALUES
REACHING 1000-1500 J/KG...BUT RAP CONSIDERABLY LOWER DUE TO WARMER
MID-UPPER LEVEL TEMPERATURES. IF GFS/NAM PROFILES PAN OUT...CANNOT
ARGUE WITH SPC MARGINAL THREAT FOR HAIL IN OUR SOUTHWEST CWA LATE
THIS AFTERNOON/EVENING.

FOR TONIGHT...UPPER TROUGH SWINGING OUT OF THE CENTRAL ROCKIES
SHOULD BRING INCREASING THREAT OF RAIN TO OUR SOUTHEAST AS IT
STRENGTHENS AND SLIDES EAST THROUGH THE CENTRAL PLAINS. QUESTION IS
HOW FAR NORTH THE PRECIP SHIELD WILL EXPAND BEFORE THE WAVE PULLS
EAST LATE TONIGHT. FOR NOW HAVE EXPANDED LIKELY POPS A BIT FARTHER
NORTH...TO NEAR A VERMILLION-WORTHINGTON LINE...WITH MORE WIDESPREAD
ACTIVITY SOUTH OF SIOUX CITY-SPENCER. PRECIP AMOUNTS AGAIN EXPECTED
TO REMAIN ON THE LIGHTER SIDE...AROUND A TENTH OR TWO OVER NORTHWEST
IOWA AND MUCH LESS FOR MOST OF SOUTHEAST SOUTH DAKOTA AND SOUTHWEST
MINNESOTA.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 415 AM CDT FRI APR 24 2015

ON SATURDAY MORNING...IT IS UNCLEAR HOW FAR TO EXTEND POPS FROM
NORTHWEST IOWA BACK TO THE WEST. MOST MODELS SUGGEST POPS ACROSS
NORTHWEST IOWA...BUT SOLUTIONS VARY TO THE WEST AS LIMITED DYNAMICS
AND RELATIVELY SHALLOW MOISTURE LIMIT PRECIPITATION POTENTIAL. WITH
EASTERLY FLOW CONTINUING THROUGH THE DAY...KEPT TEMPERATURES BELOW
NORMAL IN THE EAST WITH WARMER HIGHS ACROSS SOUTH CENTRAL SOUTH
DAKOTA.

MODELS SHOW SWATH OF DRIER AIR WORKING INTO THE REGION ON SUNDAY
FROM THE EAST.  WITH RELATIVELY DRY AIR...WENT AHEAD AND LOWERED DEW
POINTS AND SKY COVER AND RAISED TEMPERATURES.  THIS ONCE AGAIN WILL
CREATE ELEVATED FIRE WEATHER CONCERNS THOUGH WITH WINDS ALOFT ONLY
IN THE 15-20 KNOTS RANGE...AM NOT EXPECTING WINDS TO GET STRONG
ENOUGH FOR RED FLAG.

MONDAY LOOKS TO BE A RELATIVELY PLEASANT DAY ACROSS THE AREA WITH
WEAK WINDS AHEAD OF A FRONT MOVING THROUGH MONDAY EVENING. LEFT SOME
SLIGHT CHANCE POPS ACROSS THE NORTH WITH THE FRONTAL PASSAGE.
CONSIDERED REMOVING POPS ALL TOGETHER AS MOISTURE REMAINS QUITE
LIMITED.

LOOKS TO BE YET ANOTHER DRY WEEK ACROSS THE REGION. UPPER LEVEL JET
BUCKLES TO THE NORTH LEADING TO A WARMING TREND.  WINDS APPEAR TO
INCREASE LATE IN THE WEEK...POTENTIALLY CREATING ADDITIONAL FIRE
WEATHER CONCERNS LATE NEXT WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1252 PM CDT FRI APR 24 2015

HAVE BROKEN OUT INTO LARGELY VFR CONDITIONS ACROSS THE AREA WITH
EXCEPTION OF AREAS OF MVFR CEILINGS AHEAD OF UPPER WAVE LIFTING
ACROSS NORTHWEST IOWA. MVFR STRATUS WILL ATTEMPT TO SPREAD BACK
NORTHWARD THROUGH EASTERN NEBRASKA TOWARD KSUX BY MID TO LATE
AFTERNOON...FIGHTING MIXING ALL THE WAY. OTHER CONCERN WILL BE
WITH POTENTIAL CONVECTIVE DEVELOPMENT VERY LATE AFTERNOON AND
EARLY EVENING NEAR SURFACE CONVERGENCE TOWARD SOUTH CENTRAL SD AND
THE LOWER TO MID JAMES VALLEY. CONVECTION WOULD LIKELY HAVE BRIEF
IFR VISIBILITY AND MVFR CEILINGS. WHILE ACKNOWLEDGE THERE IS A
SMALL THREAT AT KFSD AND KSUX...WOULD SEEM A BIT LOW PROBABILITY
AND MORE DIFFICULT TO TIME AND THUS HAVE LEFT OUT ON THIS 18Z
ISSUANCE.  MORE WIDESPREAD MVFR TO IFR CEILINGS WILL DEVELOP
DURING THE EVENING AND OVERNIGHT...LINGERING THROUGH SATURDAY
MORNING AS MOIST EASTERLY FLOW INTENSIFIES.

&&

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

$$

UPDATE...CHAPMAN
SHORT TERM...JH
LONG TERM...
AVIATION...CHAPMAN



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