Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 030858
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
358 AM CDT SUN MAY 3 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 358 AM CDT SUN MAY 3 2015

CONCERNS THIS TODAY AND TONIGHT DEAL WITH CONVECTION CHANCES THIS
AFTERNOON ALONG WITH POST FRONTAL FIRE DANGER. EARLY THIS
MORNING...LOW LVL JET CONTINUES TO VEER AND PUSH CONVECTION EASTWARD
AND AWAY FROM THE CWA INTO CENTRAL IOWA. THERE REMAINS AN OUTSIDE
CHANCE FOR A FEW SHOWERS TO POPUP OVER THE EASTERN ZONES...BUT
LOOKING LESS LIKELY.

THE MAIN STORY TODAY WILL BE FOCUSED ON A FRONTAL BOUNDARY DROPPING
SOUTHEAST THROUGH THE AREA THIS EVENING.  EARLY THIS MORNING...THE
FRONT WAS DRAPED ACROSS CENTRAL SOUTH DAKOTA...ALLOWING LOW TO MID
50 DEW POINTS TO POOL AHEAD OF IT. THIS FRONT WILL SLOWLY PRESS
SOUTHEAST STRETCHING FROM WORTHINGTON TO YANKTON BY 4PM.   MODELS
CONTINUE TO SHOW MODEST DESTABILIZATION THROUGH THE DAY...WITH
UPWARDS OF 1500-2000 J/KG MLCAPE VALUES DEVELOPING ALONG AND BEHIND
THE BOUNDARY BY LATE AFTERNOON.  THERE WILL LIKELY BE TWO MAIN
FORCING MECHANISMS THIS AFTERNOON...INCREASING FRONTAL CONVERGENCE
LATE THIS AFTERNOON ACROSS THE NORTHEASTERN HALF OF THE FRONT IN
MN...AND A SHORTWAVE ROTATING ACROSS NEBRASKA.  WHILE DIFFICULT TO
PICKUP IN WV IMAGERY...THIS SHORTWAVE WAS BEGINNING TO ENTER THE
WESTERN PLAINS EARLY THIS MORNING...EVIDENT BY VEERING NPN/VWP. THE
DIFFICULTY THUS FAR...IS ASSESSING THE STRENGTH OF THIS
SHORTWAVE...WHICH MODELS HAVE BEEN STRUGGLING WITH.

SOUNDINGS INDICATE A RELATIVELY CAPPED ENVIRONMENT...WHICH SHOULD
HOLD OFF SFC BASED CONVECTION UNTIL MID-LATE AFTERNOON...WHEN
CONVERGENCE ALONG THE BOUNDARY OVER CENTRAL MN SHOULD BE SUFFICIENT.
LATEST GUIDANCE SUGGESTS THIS BOUNDARY MAY SURGE A BIT FASTER OVER
NORTHERN AND CENTRAL MINNESOTA WITH RATHER HIGH PRESSURE RISES
ACROSS THE WESTERN DAKOTAS. THIS IN RETURN COULD LIMIT THE
CONVECTIVE POTENTIAL OVER OUR SW MN COUNTIES. HOWEVER...FURTHER
SOUTHWEST ALONG THE LINE...INTO FAR SE SD...NW IA...AND NE...INITIAL
ISOLATED CONVECTION MAY BE MORE POST FRONTAL AND ELEVATED IN
NATURE...DEVELOPING ALONG A SECONDARY 925:850 CONVERGENCE ZONE.
MORE SCATTERED SFC BASED CONVECTION COULD DEVELOP ONCE FORCING ALOFT
CATCHES UP TO THE SFC FRONT TOWARD 00Z. AT THIS POINT...FORCING
ASSOCIATED WITH THE SHORTWAVE MAY BE THE MORE DOMINATE FOCUS FOR
CONVECTION AS OPPOSED TO THE FRONT...WITH THE BEST CHANCES FOR
THUNDER ALONG A YANKTON TO SPENCER LINE.

AGAIN...INSTABILITY IS MODERATE...BUT SHEAR PROFILE SEEMS MARGINAL
FOR THE EVENT.  BEST SHEAR IS ACTUALLY IN THE POST FRONTAL
ENVIRONMENT. THAT SAID...WOULD ANTICIPATE FAIRLY SCATTERED
CONVECTION...WITH ISOLATED SVR STORMS.  RELATIVELY STEEP LAPSE
RATES...AND POCKET OF MID-LVL DRY AIR WOULD SUPPORT DAMAGING WIND
THREAT. CAPE PROFILE FAIRLY ELONGATED...BUT SKINNY IN NATURE. WITH
THE RELATIVELY LOW SHEAR ENVIRONMENT...LOOKING AT A MARGINAL HAIL
THREAT.  TORNADIC THREAT APPEARS LOW...GIVEN POOR 0-1KM SHEAR...AND
RATHER HIGH LCLS.

THE SHORTWAVE WILL MOVE QUICKLY EASTWARD IN THE EVENING...WITH
CONVECTION PUSHING THE ELEVATED MOISTURE LAYER SOUTH OF THE CWA.
DEPENDING ON THE CLEARING...LOOKING AT LOWS IN THE 40S.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 358 AM CDT SUN MAY 3 2015

WHILE STRONGER RIDGING WILL ATTEMPT TO BECOME REESTABLISHED ACROSS
THE NORTHERN PLAINS ON MONDAY...WILL HAVE TO DEAL WITH LIFT
ASSOCIATED WITH EXITING UPPER JET ENTRANCE REGION PULLING ACROSS THE
AREA MONDAY INTO MONDAY EVENING. THE MORNING HOURS WILL SEE MAIN
BOUNDARY AT LOWER LEVELS CONTINUING THE PUSH TO AREAS BETWEEN I-80
AND I-70...WITH FAIRLY STRONG PUSH OF LOWER LEVEL DRY AIR THROUGH
MUCH OF THE CWA. MID LEVEL MOISTURE SHOULD STALL ACROSS THE AREA...
BUT NO MORE THAN A MINIMAL THREAT OF A MID BASED SHOWER ALONG THE
EXTREME SOUTHERN BORDER THROUGH THE MORNING. INSTABILITY DISPLACED
WELL SOUTHWARD TO PRECLUDE ANY THUNDER MENTION...BUT THIS SHOULD
START TO CHANGE DURING THE AFTERNOON AS STRONGER UPPER FORCING WILL
COMBINE WITH INCREASE IN ISENTROPIC LIFT TO BULGE PRECIPITATION BACK
NORTHWARD THROUGH THE MISSOURI RIVER CORRIDOR ALONG WITH WEAK
ELEVATED INSTABILITY FOR AN ISOLATED THUNDER MENTION.

GOING THROUGH MONDAY NIGHT AND TUESDAY...LARGER SCALE BROAD
ISENTROPIC LIFT WILL SPREAD GRADUALLY NORTHWARD TO THE NORTH OF
STRONG SURFACE WARM FRONT LIFTING GRADUALLY NORTH OF I-80. MOST
SOLUTIONS DO SUGGEST THAT MAY SEE A MIDDAY MINIMA IN QG SUPPORT FOR
PRECIP WITH RIDGING STRENGTHENING ALOFT TO EAST...AND AHEAD OF NEXT
LOBE EJECTING FROM SOUTHERN ROCKIES CLOSED LOW PUSHING TOWARD
WESTERN CWA. HOWEVER...WITH PERSISTENT ISENTROPIC LIFT...EXPECT AT
LEAST A SCATTERING OF SHOWERS TO BE PRESENT. INSTABILITY IS JUST TO
THE WEAK SIDE OF NEUTRAL...SO THUNDER WILL BE FAR FROM PREDOMINANT
IN COVERAGE...AND HAVE GENERALLY KEPT A CATEGORY OR TWO BELOW ANY
PRECIP MENTION.

ON TUESDAY NIGHT...COULD ACTUALLY SEE A DECREASE IN COVERAGE OF
PRECIP CYCLING NORTHWARD THROUGH THE EASTERN CWA...WITH MAIN
ISENTROPIC BAND LIFTING NORTH OF THE CWA...AND LULL AHEAD OF
MOISTURE CONVEYOR LOBE WHICH WILL WRAP RAPIDLY NORTH AND EASTWARD
TOWARD THE MISSOURI VALLEY BY LATE NIGHT. THE MAIN DYNAMIC FORCING
WILL SWING NORTHEASTWARD LATER WEDNESDAY AND WEDNESDAY NIGHT AS
UPPER LOW LIFTS FROM COLORADO THROUGH THE DAKOTAS...AND SHOULD FOCUS
PERIOD OF MOST SIGNIFICANT RAINFALL ACROSS THE AREA. INSTABILITY
JUST A BIT STRONGER...BUT DEEP LAYER SHEAR IS QUITE MINIMAL...SO
PROSPECT OF SEVERE STORMS MINIMAL WITH WAVE OUT OF PHASE WITH
DIURNAL CYCLE AS WELL.  THURSDAY WILL SEE THE LOW LEVEL BOUNDARY
PUSHING EASTWARD ACROSS THE CWA AS UPPER LOW LIFTS NORTH OF THE
REGION. DEPENDING ON TIMING OF BOUNDARY...DEGREE OF POTENTIAL
WARMING AHEAD...MAY SEE SEVERE PARAMETERS FALL OUT A BIT STRONGER
NEAR FRONTAL ZONE.  MUCH OF THE TUESDAY TO THURSDAY PERIOD WILL HAVE
QUITE A BIT OF CLOUDINESS AND MOISTURE...WITH LOWER DIURNAL RANGE.
STILL SHOULD SEE TEMPS AT OR ABOVE NORMAL WITH UPPER 60S TO MID 70S
COMMON FOR HIGHS...AND 50S TO AROUND 60 FOR LOWS.

THE END OF THE LONGER RANGE FOR THURSDAY THROUGH SATURDAY CONTINUES
TO ADVERTISE SOME SIGNIFICANT DIFFERENCES IN DETAILS...WHILE A
LARGER SCALE AGREEMENT OF WESTERN TROUGHING TO EASTERN PLAINS
RIDGING REMAINS IN PLAY. ECMWF/CANADIAN SUGGEST A BIT MORE SOUTHWARD
AND QUICKER PUSH TO BAROCLINIC ZONE BY THURSDAY NIGHT AND FRIDAY
RESULTING IN A DRIER PERIOD PERHAPS LASTING INTO SATURDAY...AND
WOULD NOT BE SURPRISED TO HAVE THINGS SHAKE OUT IN THAT MANNER.
ANOTHER FAIRLY STRONG LOBE WILL BE MOVING IN JUST BEYOND THE END OF
THE FORECAST PERIOD...AND MAY HAVE SOMEWHAT SLIGHTLY BETTER SHEAR
AND INSTABILITY AT HAND.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1103 PM CDT SAT MAY 2 2015

MAIN FOCUS ARE WINDS AND CONVECTION THROUGH 06Z MONDAY. ISOLATED
ISOLATED THUNDERSTORMS MAY MOVE ALONG HIGHWAY 14 OVERNIGHT
ALTHOUGH THE BETTER CHANCE WILL BE FARTHER NORTH. WITH A LOW
PROBABILITY DID NOT INCLUDE THUNDERSTORMS IN THE KHON TAF. THEN A
COLD FRONT WILL MOVE SOUTHEAST REACHING KHON AROUND 12Z...KFSD
AROUND 17Z AND KSUX AROUND 23Z. AT THIS TIME...APPEARS CONVECTION
WILL DEVELOP BY 20Z BETWEEN KFSD AND KSUX AND THEN MOVE SOUTHEAST
TOWARD KSUX AROUND 00Z. DID NOT INCLUDE A CHANCE OF CONVECTION FOR
KFSD BUT DID INCLUDE A TEMPO GROUP FOR KSUX AROUND 00Z. AS FOR
WINDS...THERE WILL BE LLWS IN KSUX AFTER 06Z WITH THE 40 KT LOW
LEVEL JET. OTHERWISE...SOUTH WINDS WILL GRADUALLY VEER SW AND THEN
TO NW AS THE FRONT MOVES THROUGH. WINDS WILL GUST OVER 20 KTS AT
KHON AND KFSD AFTER THE FRONTAL PASSAGE IN THE AFTERNOON.


&&

.FIRE WEATHER...
ISSUED AT 358 AM CDT SUN MAY 3 2015

HIGH TO VERY HIGH FIRE DANGER EXPECTED TODAY...PRIMARILY ALONG
AND WEST OF A MARSHALL TO YANKTON LINE. THE DRIVING FORCE BEHIND
TODAYS HIGH FIRE DANGER WILL BE STRONG POST FRONTAL WINDS UP TO 20
KNOTS AT TIMES. THE AIR IMMEDIATELY BEHIND THE INCOMING FRONTAL
BOUNDARY WILL NOT BE ALL THAT DRY...SO RH VALUES WILL ONLY FALL TO
AROUND 25 TO 30 PERCENT. THUS...NOT ANTICIPATING RED FLAG WARNING
CONDITIONS BUT ANY BURNING SHOULD BE DONE WITH CAUTION.

&&

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

$$

SHORT TERM...DUX
LONG TERM...CHAPMAN
AVIATION...SCHUMACHER
FIRE WEATHER...DUX



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