Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 070910
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
410 AM CDT THU MAY 7 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 410 AM CDT THU MAY 7 2015

NUMEROUS THUNDERSTORMS ACROSS SOUTHERN NEBRASKA CONTINUE TO
INTERCEPT LOW LVL FLOW NORTHWARD TONIGHT...WITH BROAD ELONGATED
STRATIFORM PRECIPITATION REGION FLOWING NORTHEASTWARD ACROSS THE
EASTERN ZONES OF THE FORECAST AREA. IN GENERAL...NEARLY ALL MODEL
GUIDANCE HAS DONE A POOR JOB RESOLVING THE AXIS OF HEAVIER
CONVECTION OVERNIGHT...WITH CONVECTIVE INFLUENCES DRIVING MUCH OF
THE HEAVIER PRECIP EAST AND SOUTH OF THE AREA. THAT SAID...WITH
STRONG DYNAMICS STILL OVERHEAD...AND 850MB TROUGH AXIS WEST OF THE
CWA...SCATTERED SHOWERS MAY STILL DEVELOP WEST OF THE PRIMARY
STRATIFORM REGION THROUGH DAYBREAK. OVERALL...PRECIP AMOUNTS HAVE
BEEN LOWERED.

THE GENERAL TRENDS TODAY SUGGEST THAT SCATTERED SHOWERS WILL LINGER
INTO THE MORNING HOURS AS SFC TROUGH WEST OF A LINE FROM HON TO YKN
BEGINS TO SLIDE EASTWARD. MESOSCALE MODELS HAVE SPED UP THE EASTWARD
PROGRESSION OF THIS FRONT TODAY...PUSHING THE BOUNDARY TOWARD THE I-
29 CORRIDOR BY LATE MORNING.  LOW-MID LVL COOLING SHOULD
SUFFICIENTLY INCREASE LAPSE RATES BY MID-DAY...WITH POTENTIAL MODEST
SFC DESTABILIZATION AHEAD OF THE BOUNDARY RESULTING IN 500 TO 1000
J/KG MLCAPE EAST OF THE I-29 CORRIDOR. ANY ADDITIONAL CONVECTIVE
INITIATION AHEAD OF THE BOUNDARY AND 850 FRONT SHOULD OCCUR BETWEEN
11AM-2PM WITH THIS ACTIVITY SLIDING EASTWARD BY LATE AFTERNOON.

OVERALL SEVERE THREAT LOOKS CONDITIONAL AND MARGINAL IN
NATURE...DEPENDING ON DESTABILIZATION AS EFFECTIVE SHEAR SOMEWHAT
MARGINAL. COULD SEE AN ISOLATED STRONGER STORM WITH QUARTER HAIL.
GIVEN MOIST NATURE OF THE SOUNDINGS...FEEL WIND THREAT WOULD BE LOW.
A NON-ZERO TORNADO RISK IS POSSIBLE AHEAD OF THE FRONTAL
BOUNDARY...PRIMARILY IN THE FAR SOUTHEASTERN CWA.  SOUNDINGS SUGGEST
STEEP SFC-0.5 KM LAPSE RATES...LOW LCLS...AND 0-1 SRH APPROACHING 75-
100 M2/S2. AGAIN...VERY CONDITIONAL ON DESTABILIZATION.

LATER IN THE AFTERNOON...MAY SEE ADDITIONAL SHOWER ACTIVITY ALONG
FRONTOGENETICAL BAND DROPPING SOUTHWARD THROUGH THE DAKOTAS.
SOUTHERN EDGE OF THIS BAND MAY SWEEP INTO THE NORTHERN HALF OF THE
CWA INTO THE EARLY EVENING HOURS. OTHERWISE...WE WILL SLOWLY DRY OUT
BY FRIDAY MORNING.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 410 AM CDT THU MAY 7 2015

SHOULD BE A FAIRLY QUIET PERIOD FOR FRIDAY AND SATURDAY...WHILE DEEP
TROUGH RELOADS ENERGY IN THE WEST...AND RIDGING ALOFT WITH STABLE
LOW LEVEL NORTH TO NORTHEAST FLOW.  TEMPS WILL BE GENERALLY NEAR TO
BELOW NORMAL ON FRIDAY IN THE 60S...AND MOST PLACES A FEW DEGREES
WARMER ON SATURDAY...BUT NEARLY MATCHED TO FRIDAY IN THE WEST WHERE
MORE CLOUDS WILL PREVAIL ALONG WITH A VERY SMALL CHANCE FOR THE
LEADING SHOWERS TO ROAM IN LATE DAY. SKIES WILL FEATURE A VARIETY OF
CLOUDS AND SUN...DEPENDING ON TIMING OF WEAK WAVES IN SOUTHWEST
FLOW...AND HOW QUICKLY THE ANY AREAS OF STRATOCUMULUS FADE ON FRIDAY.

WILL BEGIN TO SEE A TRANSITION TOWARD MORE ACTIVE WEATHER ON
SATURDAY NIGHT...AS DEEP CLOSED LOW STARTS TO PULL OUT OF THE
SOUTHERN ROCKIES INTO THE CENTRAL HIGH PLAINS. SAME CHALLENGING
SCENARIO DEALING WITH A FAIRLY DECENT ADVERTISEMENT OF A LOBE OF
ENERGY WRAPPING NORTHEASTWARD...ALONG WITH A FAIRLY DISTINCT MID
LEVEL DRY SLOT TAKING AIM ON THE EASTERN TWO THIRDS OF THE CWA BY
EARLY SUNDAY. AT THIS TIME...LOW LEVEL BOUNDARY WILL LIKELY BE
SOMEWHERE NEAR I-80...WITH STRONG LOW LEVEL JET OUT AHEAD OF FAIRLY
STACKED LOW NEAR NORTHWEST KANSAS. ALL WOULD SUGGEST A FAIRLY
COHERENT BAND OF SHOWERS AND THUNDERSTORMS WRAPPING NORTHWARD DURING
SATURDAY NIGHT...BUT HAVE SEEN THIS SCENARIO PLAY OUT WITH LESS
COVERAGE THAN EXPECTED A COUPLE TIMES RECENTLY. DEGREE OF ELEVATED
INSTABILITY AND LOCATION OF NOSE OF LOW LEVEL JET AND ELEVATED MIXED
LAYER WOULD AT LEAST BRING A MINIMAL RISK OF ELEVATED HAILERS INTO
THE LOWER MISSOURI VALLEY LATER AT NIGHT.

MOST CRITICAL PERIOD OF THE FORECAST WOULD BE SUNDAY INTO SUNDAY
EVENING. MODELS ARE REMARKABLY SIMILAR IN UPPER PATTERN /CANADIAN
GLOBAL JUST A TOUCH QUICKER/ PACING MID LEVEL CLOSED LOW BY EVENING
TOWARD SOUTH CENTRAL SD...TILTING TOWARD SURFACE LOW IN NORTHEASTERN
NEBRASKA. DURING THE DAY...WARM FRONT WILL BULGE NORTHWARD REACHING
THE FAR SOUTHERN CWA LATE DAY. SHOULD SEE CONVECTION LIKELY WINDING
DOWN AND MAIN PRECIPITATION SHIELD BACKING TOWARD MID LEVEL
BAROCLINIC ZONE IN CENTRAL SD AND MODE TO A MORE SCATTERED OR LESS
COVERAGE DURING THE DAY AS THE DRY SLOT AND CAPPING BECOMES MORE AND
MORE ESTABLISHED ACROSS THE FRONTAL ZONE. HAVE DROPPED POPS BACK FOR
LATTER DAY...AND THIS COULD HAPPEN EVEN A BIT SOONER IN THE DAY
ESPECIALLY IN THE SOUTH. GRADUALLY...SURFACE BOUNDARY WILL LIKELY
CREEP TOWARD THE FAR SOUTHERN CWA BY LATE DAY...AND BAROCLINICITY
WILL BE QUITE IMPRESSIVE NORTH OF THIS FRONT WITH CLOUDS AND COOL
EASTERLY LOW LEVEL FLOW...WHICH AGAIN COULD BE QUITE STRONG.
AFTERNOON TEMPERATURES SHOULD FEATURE 20 DEGREES OR GREATER
DIFFERENCE ACROSS THE CWA.

IT WILL BE THE LOCATION OF THE WARM FRONT AND STRONG GRADIENT WHICH
END UP DEFINING WHAT COULD BE A FAIRLY SIGNIFICANT SEVERE WEATHER
THREAT FOR LATER AFTERNOON AND EVENING. SHEAR PARAMETERS ARE QUITE
IMPRESSIVE...MORE THAN 40 KNOTS DEEP LAYER SHEAR...AND HODOGRAPHS
NEAR THE BOUNDARY SHOWING AN ESPECIALLY STRONG 0-3KM COMPONENT. WITH
THE QUICK INCREASE IN LOWER LEVEL STABILITY NORTH OF THE BOUNDARY...
THIS SHOULD LIMIT THE MOST EXTREME MODES FAIRLY QUICKLY HEADING
NORTH OF THE BOUNDARY. ALL SEVERE MODES /HAIL-WIND-TORNADO/ IN PLAY
FOR THE SOUTHERN TWO TIERS OF THE CWA...QUICKLY WEENING OUT THE
TORNADO AND WIND THREAT NORTH OF A VERMILLION TO SPENCER LINE...
THEN GRADUALLY THE HAIL. SNAPSHOT OF THE POTENTIAL AIRMASS IN THE
WARM SECTOR WOULD SUGGEST THREAT FOR SOME VERY LARGE HAIL WITH ANY
SUPERCELLULAR DEVELOPMENT. BEING THE WEEKEND AND WITH POTENTIAL
MOTHERS DAY PLANS...IT WOULD BE A VERY GOOD IDEA TO KEEP ESPECIALLY
WEATHER AWARE AS WE GET CLOSER TO THE WEEKEND.

WRAPPED UP SYSTEM SHOULD KEEP A BAND OF DEFORMATION PRECIP ON THE
BACK SIDE OF THE UPPER LOW TRACK INTO MONDAY AND FINALLY DISSIPATING
ON MONDAY NIGHT. DOWNRIGHT CHILLY AND WINDY ON MONDAY...AND SHOULD
SEE SOME AREAS STRUGGLE TO HIT 50 DEGREES. TEMPS ACTUALLY ARE
GETTING FAIRLY CLOSE TO WHERE ONE MIGHT HAVE TO WORRY ABOUT A LITTLE
WET SNOWFALL ESPECIALLY IF ANY PRECIP LINGERS INTO MONDAY NIGHT...
BUT SOLUTIONS THAT COLD ARE A BIT TO THE EXTREME SIDE OF ENVELOPE.
ON TUESDAY AND WEDNESDAY...LITTLE TO NO ORGANIZED PRECIPITATION IS
IN STORE WITH SOME MODERATION ON TUESDAY...AND A BIT MORE ON
WEDNESDAY. ALMOST PULLED OUT THE MINIMAL CHANCE OF RAINFALL ON
WEDNESDAY WITH LITTLE MODEL CONSISTENCY IN PLAY...BUT MAINTAINED
SLIGHT CHANCES WITH SUPPORT OF ECMWF AND MORE DYNAMIC FORCING FOR
LIFT.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1103 PM CDT WED MAY 6 2015

PERIODS OF RAIN SHOWERS WILL LIFT ACROSS THE REGION THROUGH THE
OVERNIGHT HOURS. EXPECT PRECIPITATION TO EXIT THE EASTERN FORECAST
AREA. TOWARDS DAYBREAK...WITH A BREAK IN THE SHOWER ACTIVITY
THROUGH THE MORNING HOURS. EXPECT ADDITIONAL SHOWER ACTIVITY
MAINLY NORTH OF I90 AND INTO NORTHWEST IOWA AFTER 18Z. EXPECT MVFR
AND IFR CEILINGS AND VISIBILITY IN THUNDERSTORMS...WITH SOME
PREVAILING MVFR CEILINGS POSSIBLE TONIGHT INTO THURSDAY
MORNING...BUT CEILINGS SHOULD LIFT LATE MORNING.

&&

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

$$

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


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