Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 261127
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
627 AM CDT SUN APR 26 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 418 AM CDT SUN APR 26 2015

PLEASANT SPRING DAY AHEAD WITH LIGHT EASTERLY FLOW DOMINATING
THROUGHOUT THE DAY.  AS PREVIOUS FORECASTER MENTIONED...EXPECT DEW
POINTS TO DROP THROUGHOUT THE DAY AS DRY AIR MIXES DOWN FROM
ALOFT...WITH LITTLE RECOVERY EXPECTED TONIGHT.  WITH DRY
ATMOSPHERE...HAVE CONTINUED TO SIDE WITH WARMER GUIDANCE VALUES.

FOR TONIGHT...SHOULD SEE GOOD RADIATIVE CONDITIONS WITH CLEAR SKIES
AND LIGHT WINDS.  HAVE ADDED THE MENTION OF PATCHY FROST ACROSS
NORTHWEST IOWA...WHERE LOWS ARE EXPECTED TO BE IN THE MID AND LOWER
30S.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 418 AM CDT SUN APR 26 2015

EARLY TO MIDDLE PART OF THE UPCOMING WEEK CONTINUES TO LOOK DRY AND
MORE MILD AS UPPER RIDGE BUILDS OUT OF THE SOUTHWEST CONUS INTO THE
NORTHERN PLAINS. ALL MODELS SHOW A WEAK WAVE AND ASSOCIATED SURFACE
BOUNDARY SLIDING AROUND THE EAST SIDE OF THE RIDGE MONDAY NIGHT INTO
EARLY TUESDAY...BUT MOISTURE IS QUESTIONABLE AND WILL MAINTAIN A DRY
FRONTAL PASSAGE FOR NOW. WILL ALSO ONCE AGAIN LEAN TOWARD DRIER BIAS
CORRECTED DEW POINTS...ESPECIALLY EAST WHERE RAINFALL EARLIER IN THE
WEEKEND WAS MUCH MORE SPARSE.

UPPER RIDGE DOMINATES THROUGH THURSDAY...AS SURFACE RIDGE SHIFTS
EAST AND ALLOWS SOUTHERLY FLOW TO INCREASE OVER THE REGION. GULF IS
STILL CUTOFF AT THIS POINT...RESULTING IN PERSISTENCE OF VERY DRY
LOWER ATMOSPHERE. FORECAST SOUNDINGS SHOW STRONG MIXING POTENTIAL
THURSDAY...WHICH SHOULD FURTHER REINFORCE THE DRY SURFACE AIR AND
HAVE ADJUSTED BLENDED MODEL CONSENSUS DOWNWARD. CURRENT ADJUSTMENTS
RESULT IN MINIMUM HUMIDITY VALUES AROUND 25-30 PERCENT. WITH SURFACE
WINDS GUSTING TO 25-30 MPH...SHOULD SEE VERY HIGH FIRE DANGER IN
PARTS OF THE AREA THURSDAY...THOUGH EVENTUAL FIRE DANGER MAY CHANGE
DEPENDING ON HOW MUCH RECENT RAINFALL ALLOWS FOR GREENUP OF FINER
FUELS.

GREATER UNCERTAINTY CREEPS BACK INTO THE FORECAST FOR NEXT FRIDAY
AND SATURDAY...AS A LITTLE STRONGER WAVE IS FORECAST TO TRACK INTO
THE NORTHERN PLAINS. TIMING OF THE FIRST WAVE AND ASSOCIATED SURFACE
FRONT DIFFERS AMONG THE MODELS...WITH ECMWF LAGGING THE GEM/GFS BY
ABOUT 6 HOURS. ECMWF ALSO A LITTLE MORE BULLISH WITH MOISTURE THAN
THE NORTH AMERICAN MODELS...BUT GIVEN THAT A WEAK SURFACE RIDGE IS
STILL HANGING UP FROM EAST TEXAS  INTO THE MID-MISSISSIPPI VALLEY BY
MIDDAY FRIDAY...DIFFICULT TO COMPLETELY BUY INTO STRENGTH OF ECMWF
MOISTURE RETURN. THUS HAVE TRIMMED MOST POPS GIVEN BY BLENDED MODEL
SOLUTION FOR THIS PERIOD...AND AGAIN MADE SOME MINOR DOWNWARD TWEAKS
IN SURFACE DEW POINTS...ALONG WITH MINOR UPWARD TWEAKS IN DAYTIME
TEMPERATURES.

MODELS DIVERGE EVEN MORE FOR SATURDAY...WITH ECMWF REDEVELOPING
WEAK MID LEVEL RIDGE WHILE THE GFS QUICKLY TRACKS ANOTHER
SHORTWAVE INTO THE NORTHERN PLAINS. SOME POTENTIAL FOR THE GULF TO
OPEN BY THIS TIME AS THE AFOREMENTIONED SOUTHERN SURFACE RIDGE
SHIFTS EAST. WEAK SURFACE BOUNDARY WHICH PASSES THROUGH FRIDAY
SHOULD BE SOMEWHERE IN THE CENTRAL PLAINS AT THIS RANGE
THOUGH...AND DEPENDING ON EVENTUAL LOCATION...MAY SLOW UP THE
NORTHWARD MOISTURE TRANSPORT INTO OUR AREA. THUS AGAIN AM FAVORING
A DRIER PERIOD FOR SATURDAY THAN MODEL BLEND...TRIMMING BACK BOTH
POPS AND DEW POINTS BY A SMALL DEGREE. MODEL DIFFERENCES FOR THIS
PERIOD ALSO APPARENT IN TEMPERATURE FORECAST...WITH WETTER GFS
REMAINING COOLER THAN THE DRIER ECMWF. GIVEN THE PREFERENCE FOR
DRIER FORECAST...WILL ALSO FAVOR WARMER TEMPERATURES AGAIN
REACHING MID TO UPPER 70S.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 625 AM CDT SUN APR 26 2015

LIGHT FOG ACROSS THE AREA IN THE 4-6 SM RANGE WILL QUICKLY BURN
OFF WITHIN AN HOUR OF SUNRISE. LIGHT EASTERLY FLOW WILL PREVAIL
THROUGH THE PERIOD WITH VFR CONDITIONS.

&&

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

$$

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



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