Area Forecast Discussion
Issued by NWS Sioux Falls, SD

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KFSD 270917
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
417 AM CDT MON JUL 27 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 417 AM CDT MON JUL 27 2015

STATE OF THE REGION IN THE WEE HOURS OF THE MORNING REVEALS A COUPLE
AREAS OF CONVECTION ONGOING. THE FIRST IS ACROSS NORTH CENTRAL SOUTH
DAKOTA WITH A SOUTHWARD TAIL...ASSOCIATED WITH LEADING WEAK WAVE
LIFTING OVER RIDGE INTO NORTH DAKOTA...AND THE LEADING LOW LEVEL JET
INCREASE THROUGH CENTRAL SD. WILL BE A CLOSE CALL...BUT WILL LIKELY
FIND AN ISOLATED SHOWER/THUNDERSTORM BRUSH AREAS AROUND KHON IN THE
PREDAWN HOURS.  SECOND AREAS OF CONVECTION IS A BROAD MASS OF
THUNDERSTORMS ACROSS KANSAS AND EXTENDING NORTHWARD INTO NEBRASKA...
THE NORTHERN EXTENT OF WHICH REMAINS MORE ACTIVE AT TIMES TOWARD
NORTHEAST NEBRASKA. AS WAVE MOVES EASTWARD THROUGH THE CENTRAL
PLAINS...LIKELY TO SEE AT LEAST ISOLATED CONVECTION PUSHING THROUGH
THE LOWER MISSOURI VALLEY INTO NORTHWEST IOWA DURING THE EARLY TO
MID MORNING HOURS...ON THE LEADING GRADIENT OF STEEPENING MID LEVEL
LAPSE RATES. FAIRLY MODIFIED AIRMASS TO THE SOUTH WILL BE A STRUGGLE
TO DESTABILIZE GREATLY FOR A GOOD PORTION OF THE DAY...AND WILL ALSO
LIKELY BE BETWEEN WEAK SYSTEMS DURING THIS TIME...SO ELIMINATED A
GREAT DEAL OF THE LOWER POPS THROUGH THE MIDDLE PORTIONS OF THE DAY.
SOME OF THE LATEST HIGH RESOLUTION MODELS INDICATE THIS TREND OF
LESSER ACTIVITY AFTER DWINDLING OF MORNING ACTION...AND HARD TO
ARGUE WITH LACK OF BOUNDARIES AND DELAY TO DESTABILIZING. ANY
SIGNIFICANT SURFACE OR NEAR SURFACE BOUNDARY WILL REMAIN WELL WEST
AND SOUTH THROUGH THE AFTERNOON...BUT DISCONTINUITY SHOULD BE
WORKING NORTHWARD TROUGH NEBRASKA...AND LOW PROBABILITY TO IGNITE A
FEW STORMS FAR WEST AND MISSOURI VALLEY LATE DAY.

OVERALL...BEST DYNAMICAL FORCING LOOKS TO REMAIN WEST OF THE AREA
THROUGH THE DAY AND EVEN INTO EARLY EVENING...AND WILL LIKELY IGNITE
CONVECTION NEAR DEVELOPING DRYLINE/COLD FRONT IN THE HIGH PLAINS
LATE AFTERNOON. MODELS APPEAR TO BE A BIT OVERZEALOUS IN INSTABILITY
AND WEAKENING WHAT SHOULD BE A FORMIDABLE CAP OVER THE AREA THIS
AFTERNOON. GREATEST WEAKENING OF THE CAP WOULD OCCUR IN BETTER
HEATING AXIS IN THE FAR WESTERN CWA...WHERE INCREASING MOISTURE
TRANSPORT THROUGH THE DAY AND ADVECTION OF ELEVATED MIXED LAYER
WOULD PERHAPS BRING UP TO 2000 J/KG MLCAPE...STILL WEAKLY CAPPED BY
PEAK HEATING.  LOW LEVEL JET WILL INCREASE THROUGH THE DAY...AND BY
THE EVENING INCREASE SHOULD REACH 45 TO 55 KNOTS. BEST CONVERGENCE
FROM FEATURE WILL ALSO FAVOR AREAS NORTH OF THE CWA. DEEP SHEAR WILL
BECOME IMPRESSIVE...BUT STRONGEST VALUES LAGGING TO THE WEST. ENOUGH
FOR ORGANIZATION...LIKELY MORE TOWARD THE LINEAR SIDE BY THE TIME
ANYTHING PROGRESSES EASTWARD...BUT WOULD NOT COUNT OUT A SLIGHTLY
ELEVATED SUPERCELL ONCE LOW LEVEL JET REALLY KICKS IN BY LATE
EVENING.  OVERALL...SET UP IS ONE WHERE IF STORMS FORM...THEY DO
PRESENT A DECENT PROBABILITY OF SEVERE STORMS...WITH BEST SEVERE
CHANCES NORTH AND WEST IN THE CWA...AND MAINLY A HAIL/WIND THREAT
DURING THE LATTER EVENING AND OVERNIGHT.

VERY WARM AND HUMID CONDITIONS TODAY WILL SEE THE HEAT INDEX NUDGE
100 DEGREES AT TIMES THIS AFTERNOON FOR SPOTTY LOCATIONS THROUGH THE
MISSOURI AND JAMES VALLEYS...BUT NEITHER WIDESPREAD ENOUGH OR
PERSISTENT ENOUGH TO WARRANT ISSUING A HEAT ADVISORY. NONETHELESS...
WORTHY OF CAUTION TO AVOID OVEREXERTION IN THE HOT CONDITIONS.

IMPRESSIVE UPPER WAVE MOVING OUT OF THE NORTHERN ROCKIES TONIGHT
WILL PUSH COLD FRONT EASTWARD. CONVECTION ALONG THIS BOUNDARY MAY
START TO LOSE COHESION WORKING EASTWARD INTO A WARMER LAYER ALOFT...
ESPECIALLY EROSIVE TOWARD THE SOUTH LATER IN THE NIGHT. BOUNDARY
SHOULD PUSH JUST EAST OF JAMES VALLEY BY 12Z. AHEAD OF THE FRONT...
REMAINING VERY WARM...BREEZY AND HUMID...WITH SHARP DRYING BEHIND.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 417 AM CDT MON JUL 27 2015

AN UNSEASONABLY STRONG WAVE MOVING THROUGH TUESDAY...COMING A LITTLE
FASTER THAN WAS SUGGESTED YESTERDAY. THIS DROPS THE THREAT OF VERY
HOT AND HUMID CONDITIONS AHEAD OF THE FRONT SINCE THE BOUNDARY
SHOULD BE OUT OF THE CWA BY ABOUT 18Z TO 21Z. AREAS FROM WINDOM TO
SPENCER IOWA TO IDA GROVE COULD SEE SOME UPPER 90 HEAT INDICES BUT
THAT HEAT WILL GET QUICKLY FLUSHED OUT IN THE EVENING WHEN THE
STRONG COOL/DRY FRONT SWINGS THROUGH. THE REMAINDER OF THE CWA WILL
SEE DEW POINTS TANK THROUGH THE DAY AND THE WESTERN CWA MAY EVEN SEE
SOME DEW POINTS INTO THE 30S. A FAIRLY GUSTY NORTHWEST WIND AND
TEMPERATURES IN THE 80S IS EXPECTED.

THE MODELS HINTING AT SOME COOLER AIR WRAPPING SOUTH INTO THE CWA
TUESDAY NIGHT WHICH WOULD KEEP THE WIND UP THROUGH THE NIGHT. BUT
DRY AND MILD WITH LOW IN THE UPPER 50S TO LOWER 60S.

WEDNESDAY WILL BE A DRY...MIXY AND WARM DAY WITH HIGHS TOPPING OUT
IN THE LOWER TO MIDDLE 80S.

IN THE OUTER PERIODS(THURSDAY THROUGH SUNDAY)...FAIRLY FAST WEST TO
NORTHWEST FLOW ALOFT THROUGH THE ENTIRE PERIOD. THIS PATTERN SHOULD
SUPPORT LESS HUMIDITY AND LOWER CHANCES FOR THUNDERSTORMS SO ONLY
SOME SPOTTY SLIGHT CHANCES AT THIS TIME. AT THIS TIME THE BEST
CHANCE APPEARS TO BE ON SATURDAY NIGHT AS A LITTLE JET ACCELERATION
DROPS SOUTH INTO THE GREAT LAKES REGION AND IS EXPECTED TO SWING A
WEAK BOUNDARY INTO THE AREA. OVERALL A DECENT STRETCH OF WEATHER
WITH HIGHS IN THE 80S AND LOWS IN THE 60S. SATURDAY COULD PROVE TO
BE A BIT WARMER IF THE BOUNDARY SNEAKS IN FROM THE NORTH AT JUST THE
RIGHT TIME TO ALLOW FOR SOME ENHANCED WARMING AHEAD OF THE FRONT.
IF THE TIMING IS RIGHT WOULD NOT BE SURPRISED TO SEE HIGHS SATURDAY
WELL IN THE 90S IN SOME LOCATIONS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1127 PM CDT SUN JUL 26 2015

GUIDANCE SUGGESTING THE POSSIBILITY OF MVFR TO IFR STRATUS
DEVELOPING ACROSS PORTIONS OF THE AREA AFTER 10Z TONIGHT...THOUGH
DID NOT INCLUDE IN TAFS WITH MODEL DIFFERENCES. WHILE ISOLATED
THUNDERSTORMS WILL BE POSSIBLE THROUGH THE TAF PERIOD...CONFIDENCE
IN PLACEMENT AND TIMING TOO LOW TO INCLUDE IN TAFS. SOMEWHAT
BETTER AGREEMENT BY MODELS ON THUNDERSTORMS DEVELOPING WEST OF
THE INTERSTATE 29 CORRIDOR AFTER 03Z MONDAY EVENING.

&&

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

$$

SHORT TERM...CHAPMAN
LONG TERM...08
AVIATION...JM



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.