Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 281133
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
633 AM CDT SAT MAR 28 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 418 AM CDT SAT MAR 28 2015

EARLIER LIGHT PRECIPITATION PRETTY MUCH OVER IN STRONG MID LEVEL
FRONTAL BAND ACROSS THE EASTERN CWA...AS SUPPORT FROM UPPER WAVE HAS
EXITED AND LARGER SCALE SUBSIDENCE TAKES OVER. AS EXPECTED...CLOUDS
WHICH HAD BEEN PULLING EASTWARD WITH FRONTAL PROGRESSION HAVE
SLOWED...AND NOW STARTING TO BACK A BIT WESTWARD THROUGH EASTERN
SOUTH DAKOTA WITH THE NEAR SURFACE EASTERLY COMPONENT...AND A
TEMPORARY NORTHERLY FEED ABOVE 900 HPA. WINDS WILL GRADUALLY WORK
BACK TOWARD SOUTHERLY THIS MORNING IN THE CLOUD BEARING LEVELS...AS
APPROACH OF WAVE THROUGH THE NORTHERN ROCKIES WILL START STRONG
PRESSURE FALLS IN THE WESTERN PLAINS. SHOULD SEE CLOUDS GRADUALLY
WORK ON DECREASING THROUGH THE LATTER MORNING AND EARLY AFTERNOON
FROM THE ADVECTIVE PUSH AS WELL AS EROSION OF THE FAIRLY THIN LAYER.
DIFFERENTIAL THERMAL ADVECTION WILL KEEP THINGS LARGELY ON THE
STABLE SIDE THROUGH THE DAY...WITH NEAR SURFACE SOUTH TO SOUTHEAST
WINDS NOT AMENABLE TO A GREAT WARMING POTENTIAL...WITH UPPER 40S TO
LOWER 50S EAST...TO SOME LOWER TO MID 60S FAR WEST CLOSER TO THE
SURFACE FRONT IN THE WESTERN PLAINS.

THE STRONG TROUGH CURRENTLY ACROSS THE PACIFIC NORTHWEST WILL MOVE
THROUGH THE WESTERN RIDGE AND START TO DIVE ACROSS THE DAKOTAS
TONIGHT...PUSHING A STRONG FRONTAL BOUNDARY THROUGH THE STATE
OVERNIGHT.  TWO OVERRIDING CONCERNS WITH SYSTEM ARE THE POTENTIAL
FOR STRONG WINDS...AND THE PRECIPITATION TIMING/CHANCES. ECMWF HAS
PICKED UP THE PACE FROM EARLIER RUNS AND NOW FALLEN INTO LINE WITH
NAM/GFS/CANADIAN TIMING OF THE SHORT WAVE...INCREASING CONFIDENCE
A BIT IN TIMING. FRONT SHOULD BE NEAR THE EASTERN BORDER BY 12Z
SUN...AND BEHIND SEE 925 HPA WINDS OF 40 TO 50 KNOTS...AND A
PRESSURE RISE OF 4-6 HPA/3H. MAIN PRESSURE RISE COUPLET DOES NOT
IMPACT AREA UNTIL SUNDAY...BUT LIKELY THAT WILL SEE A BRIEF BURST OF
STRONGER WINDS IMMEDIATELY BEHIND THE BOUNDARY...PERHAPS EVEN AIDED
A BIT BY DIABATIC IMPACTS OF HIGH BASED PRECIPITATION NEAR THE
BOUNDARY. AREAS FROM THE JAMES VALLEY AND WEST MAY SEE A BRIEF
PERIOD OF WIND GUSTS TO AROUND 45 MPH AFTER PASSAGE OF THE BOUNDARY.
WITH MOST OF THE WIND IMPACTS EXPECTED SUNDAY...HAVE NOT ISSUED A
WIND ADVISORY AT THIS TIME...BUT DOES APPEAR THAT ONE WILL BE
INEVITABLE GIVEN THE STRENGTH OF POST FRONTAL WINDS FROM LATER
TONIGHT INTO SUNDAY.

IN TERMS OF A PRECIP THREAT...PRESENCE OF STRONG ELEVATED MIXED
LAYER AHEAD OF STRONGER DYNAMIC FORCING TONIGHT...WITH SOME FORECAST
SOUNDINGS SHOWING A COUPLE HUNDRED J/KG ELEVATED CAPE.  REMAINS
FAIRLY DRY AT LOWER LEVELS... SO WHILE QPF IS LIKELY GOING TO BE ON
THE SCARCE SIDE...SUPPORT FOR AT LEAST A SCATTERED COVERAGE. COMPACT
SYSTEM HAS A HISTORY OF PRODUCING PLENTY OF LIGHTNING ACROSS THE
PACIFIC NORTHWEST TONIGHT...SO NO QUALMS ABOUT INTRODUCING AN
ISOLATED THUNDER THREAT GIVEN OVERALL DYNAMIC/THERMODYNAMIC STATE.
WITH SHARPNESS OF MID LEVEL TROUGH...LIFT WOULD TEND TO BE FOCUSED
AHEAD OF THE STRONGEST PV ADVECTION...WHICH SLIPS TOWARD THE FAR
NORTHWESTERN CWA TOWARD 06Z...AND PRETTY MUCH CLEARS THE CWA IN ALL
SOLUTIONS BY 12Z.

TEMPS WILL PROBABLY STRAY QUITE A BIT FROM A TYPICAL DIURNAL FASHION
TONIGHT WITH WARMER AIR PUSH AHEAD OF THE BOUNDARY...AND THE STRONG
MIXING BEHIND. OVERALL...FAVORED A WARMER VIEW OF OVERNIGHT
LOWS...BUT WARY OF THREAT FOR CLEARING IN DRY SLOT BEHIND PRECIP
BAND TO COINCIDE WITH PRESSURE GRADIENT WEAKNESS JUST AHEAD OF FRONT.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 418 AM CDT SAT MAR 28 2015

LATTER HALF OF THE WEEKEND WILL FEATURE VERY WINDY AND MORE MILD
CONDITIONS...LEADING TO ELEVATED FIRE WEATHER CONCERNS. ANTICIPATE
PRECIP THREAT TO LARGELY BE OUT OF THE AREA BY DAYBREAK...THOUGH
COULD SEE A FEW LIGHT SHOWERS WRAPPING INTO FAR NORTHERN AREAS
THROUGH MID MORNING. WITH QUICK MOVEMENT OF SYSTEM...SHOULD SEE
ABUNDANT SUNSHINE BY MIDDAY. HIGHEST WINDS SHOULD ACTUALLY MOVE
ACROSS THE REGION DURING THE MORNING/EARLY AFTERNOON...WHEN COLD
ADVECTION/PRESSURE RISES/SURFACE GRADIENT ARE AT THEIR STRONGEST.
HOWEVER...DESPITE A SLACKENING GRADIENT THROUGH THE AFTERNOON...
DEEPENING MIXED LAYER CONTINUES TO TAP INTO STRONGER WINDS ALOFT...
AND SHOULD CONTINUE TO SEE GUSTS IN 25-40MPH RANGE EVEN WEST OF I-29
WELL INTO THE AFTERNOON. WILL ALSO HAVE DRIER HUMIDITY LEVELS IN
THESE AREAS DURING THE AFTERNOON...SO SEEMS REASONABLE TO EXPAND THE
FIRE WEATHER WATCH WESTWARD TO THE JAMES RIVER VALLEY SUNDAY
AFTERNOON.

WINDS ACROSS THE REGION SHOULD QUICKLY DIMINISH WITH LOSS OF HEATING
SUNDAY EVENING...AND MUCH CALMER DAY EXPECTED FOR MONDAY. SOUTHWEST
FLOW AND WARMING ALOFT WILL LEAD TO A VERY MILD DAY...WITH HIGHS IN
THE MID 60S TO MID 70S.

SIMILAR TEMPERATURES EXPECTED TUESDAY AND WEDNESDAY...THOUGH TIMING
OF COLD FRONT WEDNESDAY COULD IMPACT DEGREE OF WARMING. THIS COLD
FRONT EXPECTED TO TRIGGER SHOWERS...AND EVEN SOME THUNDERSTORMS OVER
THE EASTERN PORTIONS OF THE AREA MAINLY WEDNESDAY AFTERNOON. GFS
MOST AGGRESSIVE WITH SURFACE BASED INSTABILITY...SHOWING CAPES
NEAR 1000J/KG WITH A WEAK CAP EAST OF YKN-FSD-IVANHOE LINE IN THE
EARLY AFTERNOON. GEM/ECMWF NOT QUITE AS BULLISH WITH THE
INSTABILITY...BUT STILL ON THE ORDER 300-600J/KG...SO WILL
CONTINUE MENTION OF THUNDER AS THE COLD FRONT PUSHES THROUGH
WEDNESDAY. GUSTY SOUTHWEST WINDS AHEAD OF THE FRONT SWITCHING TO
THE WEST-NORTHWEST AFTER PASSAGE. NOT AS STRONG AS SUNDAY...BUT
ENOUGH FOR VERY HIGH FIRE DANGER OVER MOST OF THE FORECAST AREA.

MODEL AGREEMENT DIVERGES QUITE A BIT DURING THE LATTER PERIODS OF
THE FORECAST...WITH GEM/ECMWF TRACKING A STRONGER SOUTHERN STREAM
WAVE INTO THE REGION WHILE THE GFS MAINTAINS LESS ACTIVE NORTHWEST
FLOW. THIS LENDS LITTLE CONFIDENCE TO INCLUDE PRECIP CHANCES IN ANY
ONE PERIOD AT THIS RANGE...SO OPTED TO LEAN TOWARD DRY FORECAST FOR
THURSDAY/FRIDAY AT THIS TIME. SHOULD BE COOLER THAN THE FIRST HALF
OF THE WEEK IN EITHER CASE THOUGH...WITH MID 50S-MID 60S THURSDAY
AND UPPER 40S-50S ON FRIDAY.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 633 AM CDT SAT MAR 28 2015

A COUPLE PATCHES OF MVFR CEILINGS WILL LINGER EARLY THIS MORNING
AROUND THE KHON AREA...OTHERWISE EXPECT VFR CONDITIONS TO CONTINUE
THROUGH 12Z SUN. WINDS ARE THE PRIMARY CONCERN FOR THE PERIOD...
WITH SOUTH WINDS FEATURING OCCASIONAL GUSTS TO 25 TO 35 KNOTS
DURING THE AFTERNOON AND EVENING. EVEN WITH WINDS REMAINING GUSTY
THIS EVENING...THERE WILL BE ENOUGH OF A LOW LEVEL JET AT 50 TO 55
KNOTS TO PRODUCE LOW LEVEL WIND SHEAR FOR SEVERAL HOURS AT EACH
LOCATION. EVENTUALLY...THE APPROACH OF THE FRONTAL BOUNDARY WILL
RELAX WINDS A BIT...BUT AFTER PASSAGE ARE LIKELY TO FIND
NORTHWESTERLY WIND GUSTS TO 30 TO 40 KNOTS LATE NIGHT.

&&

.FIRE WEATHER...
ISSUED AT 418 AM CDT SAT MAR 28 2015

INCREASING SOUTH WINDS AND WARMING TEMPERATURES WILL LEAD TO A VERY
HIGH FIRE DANGER ALONG AND WEST OF THE JAMES RIVER VALLEY THIS
AFTERNOON. A STOUT COLD FRONT WILL PUSH INTO WESTERN PORTIONS OF THE
REGION EARLY SUNDAY MORNING...PRECEDED BY SOME LIGHT RAIN SHOWERS
SATURDAY NIGHT. PRECIPITATION AMOUNTS GENERALLY LESS THAN 0.10 INCH
WITH THIS RAINFALL...WHICH SHOULD PUSH EAST OF THE AREA BY MID
MORNING SUNDAY.

THE COLD FRONT AND LIGHT RAINFALL WILL BE FOLLOWED BY VERY STRONG
WINDS...ENTERING THE LOWER BRULE AND MIDDLE JAMES VALLEY BEFORE
DAWN...THEN SPREADING OVER THE REMAINDER OF THE REGION BY NOON. WIND
GUSTS OF 45-50 MPH ARE POSSIBLE WITH THE INITIAL POST-FRONTAL SURGE
OF WINDS SUNDAY MORNING. DESPITE THE EXPECTED LIGHT RAINFALL...THESE
WINDS AND INCREASING SUNSHINE SHOULD DRY OUT FINE FUELS BY SUNDAY
AFTERNOON. WIND SPEEDS ARE EXPECTED TO DIMINISH SLIGHTLY DURING THE
AFTERNOON...THOUGH STILL ANTICIPATE SPEEDS OF 25-35 MPH ALONG AND
EAST OF THE JAMES RIVER VALLEY THROUGH LATE AFTERNOON. HUMIDITY
LEVELS WILL DROP TO AROUND 25 PERCENT IN THE JAMES RIVER VALLEY...
WITH HIGHER READINGS AROUND 35 PERCENT ACROSS SOUTHWEST MINNESOTA.
CONDITIONS CERTAINLY FAR FROM IDEAL...AND POTENTIAL FOR EXTREME FIRE
BEHAVIOR DEPENDENT ON ABILITY TO RECOVER FROM OVERNIGHT RAINFALL.
THUS STICKING WITH JUST A FIRE WEATHER WATCH FOR NOW...BUT DID OPT
TO EXPAND INTO SOUTHEAST SOUTH DAKOTA AND NORTHWEST IOWA WE EXPECT
LESS OVERNIGHT RAINFALL AND LOWER AFTERNOON HUMIDITY LEVELS IN THESE
AREAS.

COULD AGAIN SEE VERY HIGH FIRE DANGER WEDNESDAY AFTERNOON...WITH
STRONG WESTERLY WINDS DEVELOPING IN POST-FRONTAL ENVIRONMENT.
CURRENT TIMING OF THE COLD FRONT WOULD FOCUS THIS THREAT IN
SOUTHEAST SOUTH DAKOTA AND SOUTHWEST MINNESOTA...THOUGH NORTHWEST
IOWA COULD ALSO SEE A FEW HOURS OF VERY HIGH FIRE DANGER WITH GUSTY
SOUTHWEST WINDS AHEAD OF THE FRONT IN THE EARLY AFTERNOON.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...FIRE WEATHER WATCH FROM SUNDAY AFTERNOON THROUGH SUNDAY EVENING
     FOR SDZ256>258.

MN...FIRE WEATHER WATCH FROM SUNDAY AFTERNOON THROUGH SUNDAY EVENING
     FOR MNZ900.

IA...FIRE WEATHER WATCH FROM SUNDAY AFTERNOON THROUGH SUNDAY EVENING
     FOR IAZ300-301.

NE...FIRE WEATHER WATCH FROM SUNDAY AFTERNOON THROUGH SUNDAY EVENING
     FOR NEZ249.

&&

$$

SHORT TERM...CHAPMAN
LONG TERM...JH
AVIATION...CHAPMAN
FIRE WEATHER...JH



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