Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 210902
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
402 AM CDT TUE OCT 21 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 402 AM CDT TUE OCT 21 2014

CONTINUED DRY AIR AT ALL LEVELS WILL KEEP SKIES CLEAR TODAY.
INCREASING SOUTHERLY/SOUTHEASTERLY LOW LEVEL FLOW WILL STEADILY
BRING WINDS UP TO BREEZY/MARGINALLY WINDY WEST AND NORTH.
TEMPERATURES WILL REACH THE MID 60S EAST TO MID 70S WEST. THIS IS A
LITTLE WARMER THAN WE WERE GOING FOR A COUPLE DAYS AGO WHICH FITS
WITH THE SMALLER STABLE LAYER THE MODELS ARE DEPICTING.

THE BREEZY AND DRY CONDITIONS WILL LEAD TO VERY HIGH FIRE DANGER
OVER THE WESTERN PART OF THE FORECAST AREA...HIGH FIRE DANGER NEAR
THE INTERSTATE 29 CORRIDOR...AND MODERATE FIRE DANGER IN MOST OF
SOUTHWEST MINNESOTA AND NORTHWEST IOWA.

DO NOT PLAN TO MENTION FOG FOR EARLY THIS MORNING. THERE COULD BE
SOME VERY SHALLOW AND VERY PATCHY FOG IN THE NEAR CALM AREA IN
NORTHWEST IOWA AND PART OF SOUTHWEST MINNESOTA BUT NO GENERAL
VISIBILITY REDUCTION IS EXPECTED WITH THE AIR DRY JUST ABOVE THE
SURFACE.

STILL PRETTY CLEAR SKIES AT THE START OF TONIGHT WILL GIVE WAY TO
INCREASING LOW CLOUDS FROM THE WEST AND SOUTH...SLOWLY AT FIRST THEN
MORE RAPIDLY. MODELS ARE NOT QUITE SHOWING THE LOW LEVEL MOISTURE
FIELD BECOMING SOLID AND WILL GO WITH SKY COVER FORECAST
ACCORDINGLY.

MIDDLE LEVEL MOISTURE WILL BE SLOWER TO INCREASE AS THE AIR BECOMES
SURPRISINGLY UNSTABLE LATER TONIGHT. WHILE A LIFTING MECHANISM IS
QUESTIONABLE...FEEL VERY SPOTTY CONVECTION COULD EASILY FORM IN THE
INCREASING INSTABILITY GRADIENT. THIS COMES OUT TO A SLIGHT CHANCE
SPREADING EAST ACROSS SOUTH DAKOTA LATE TONIGHT...WILL GO WITH
THUNDER DUE TO THE PROJECTED INSTABILITY. THIS INSTABILITY ACTUALLY
STARTS TO GET INTO MN AND IA BEFORE THE END OF THE NIGHT BUT THE
MARGINAL MID LEVEL MOISTURE INCREASE IN THE INITIALLY DRY AIR SHOULD
BE MOSTLY TO THE WEST. ANY SHOWERS AND STORMS THAT DO DEVELOP WILL
BE VERY LIMITED BY THE DRY AIR IN RAINFALL REACHING THE SURFACE.

A DECENT BREEZE WILL KEEP UP THROUGH TONIGHT AND LOW TEMPERATURES
SHOULD BE IN THE 40S EAST TO THE 50S WEST.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 402 AM CDT TUE OCT 21 2014

STILL ON TRACK FOR BAND OF SHOWERS...AND POSSIBLY A FEW
THUNDERSTORMS...MOVING ACROSS THE REGION WEDNESDAY/WEDNESDAY NIGHT.
WILL CARRY SLIGHT CHANCE OF ELEVATED CONVECTION INTO EARLY WEDNESDAY
MORNING...BUT PRIMARY FOCUS ON MAIN WAVE/FRONTAL BOUNDARY MOVING
ACROSS THE AREA WEDNESDAY AFTERNOON/NIGHT. NAM STILL LAGGING A BIT
SLOWER THAN GLOBAL MODELS...BUT GENERALLY SEEING BETTER AGREEMENT IN
FRONTAL TIMING AMONG MODELS...TRENDING SLIGHTLY FASTER THAN PREVIOUS
FORECAST. HAVE A LITTLE UNCERTAINTY REGARDING COVERAGE OF PRECIP
LATE WEDNESDAY AFTERNOON/EVENING...AND THUS OPTED TO CAP POPS IN
HIGH LIKELY RANGE FOR NOW...BUT COULD SEE THESE BUMPED UP INTO
CATEGORICAL RANGE IF CONFIDENCE INCREASES IN MORE WIDESPREAD
COVERAGE. WEAK INSTABILITY STILL PRESENT IN AREAS NEAR/SOUTH OF I-90
AND AHEAD OF THE LOW LEVEL BOUNDARY...AND WILL HANG ONTO ISOLATED
THUNDER MENTION IN THESE AREAS. WITH SLIGHTLY FASTER TIMING OF LOW
LEVEL THERMAL RIDGE SHIFTING EAST...HAVE COOLED HIGHS WEST OF THE
JAMES A FEW DEGREES. HIGHS THERE LIKELY BY MIDDAY-EARLY AFTERNOON...
FOLLOWED BY STEADY/SLOWLY FALLING TEMPS THROUGH THE AFTERNOON AS LOW
LEVEL COOLING PUSHES IN.

FASTER TIMING ALSO MEANS PRECIP SHOULD BE EAST OF THE FORECAST AREA
BY DAYBREAK THURSDAY...WITH A GOOD CHANCE OF CLEARING BY MID-LATE
AFTERNOON FOR PARTIAL SOLAR ECLIPSE. SUNSHINE AND GOOD MIXING SHOULD
ALLOW FOR HIGHS IN THE MID 60S-LOWER 70S.

DRY AND MILD CONDITIONS CONTINUE FRIDAY THROUGH THE WEEKEND AS MID
LEVEL RIDGE BUILDS INTO THE REGION. FRIDAY CURRENTLY LOOKS TO BE THE
WARMEST DAY OF THE LONGER RANGE...WITH GOOD MIXING IN WESTERLY FLOW
HELPING LIFT HIGHS INTO THE 70S FOR MOST AREAS. 21/00Z ECMWF DRAGS
AN UPPER WAVE AND ASSOCIATED BACKDOOR COOL FRONT A BIT FARTHER SOUTH
INTO MN THAN GFS/GEM ON FRIDAY NIGHT...BUT THIS SHOULD HAVE LITTLE
EFFECT ON OUR WEATHER OTHER THAN POSSIBLY HOLDING TEMPERATURES A FEW
DEGREES COOLER ACROSS OUR NORTHEAST ON SATURDAY. FOR NOW WILL FOLLOW
GREATER CONSENSUS AND KEEP HIGHS IN THE MID 60S IN SOUTHWEST MN...
WITH LOWER 70S IN SOUTH CENTRAL SD.

GREATER DISCREPANCY IN LOW LEVEL TEMPS FOR SUNDAY DUE TO MODEL
DIFFERENCES IN TIMING FRONTAL BOUNDARY THROUGH THE REGION. ECMWF
SLOWER AND WARMER...WHILE GFS/GEM FASTER IN BRINGING SOME COOLER AIR
INTO WESTERN PARTS OF THE FORECAST AREA. GIVEN LOW CONFIDENCE...HAVE
NOT STRAYED TOO FAR FROM GIVEN CONSENSUS...THOUGH DID BUMP EASTERN
AREAS UP A BIT AS WE SHOULD SEE GOOD MIXING IN THERMAL RIDGE AHEAD
OF THE FRONT BY EARLY AFTERNOON EVEN IF THE FASTER MODEL TIMING PANS
OUT. THIS FRONT AND ASSOCIATED UPPER WAVE WILL BRING NEXT CHANCE OF
PRECIP TO THE REGION SUNDAY NIGHT/MONDAY TIME FRAME...ALTHOUGH WITH
UNCERTAINTY IN TIMING/STRENGTH...WILL KEEP POPS ON THE LOW SIDE FOR
NOW. INFLUX OF COOLER AIR BEHIND THE FRONT WILL HOLD HIGHS IN THE
50S ON MONDAY...MUCH CLOSER TO LATE OCTOBER NORMALS THAN WE HAVE
SEEN RECENTLY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1106 PM CDT MON OCT 20 2014

VFR WILL PREVAIL THROUGH TUESDAY AND TUESDAY EVENING WITH A COUPLE
OF CONCERNS. FIRST OF ALL...SOUTHERLY WINDS WILL LIKELY BE GUSTING
TO 25 KNOTS OR A LITTLE STRONG ALONG AND WEST OF THE JAMES RIVER
VALLEY TUESDAY AFTERNOON. CATEGORY WISE...KSUX IS ALREADY
EXHIBITING A VERY SMALL SURFACE DEW POINT DEPRESSION. THEREFORE
WOULD NOT BE SURPRISED IF SHALLOW FOG DEVELOPS FOR THAT TAF SITE.
DID NOT WANT TO INCLUDE TOO MUCH OF THIS POSSIBILITY YET...AND
ONLY MENTIONED A TEMPO MVFR AS A HEADS UP THAT SHALLOW RIVER FOG
COULD DEVELOP. MUCH LATER...THE NAM CONTINUES TO SHOW SOME SHALLOW
MOISTURE STREAMING UP LATE TUESDAY EVENING JUST BEFORE THE END OF
THE TAF PERIOD. IT APPEARS TO BE BASED BELOW THE BOUNDARY LAYER
AND WILL LIKELY NOT TRANSLATE INTO CLOUDS.

&&

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

$$

SHORT TERM...
LONG TERM...JH
AVIATION...MJ


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