424
FXUS63 KFSD 161552
AFDFSD
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1052 AM CDT FRI MAY 16 2008
DISCUSSION
NO CHANGES ANTICIPATED FOR THE FIRST 12 HOURS OF THE FORECAST.
OUTSIDE CHANCE FOR AN ISOLATED SHOWER OR THUNDERSTORM LATE AFTERNOON
AND EARLY EVENING SEEMS REASONABLE. DID INCREASE RISE IN
TEMPERATURES A LITTLE THIS MORNING...BUT HIGHS LOOK IN LINE.
08
AVIATION
VFR CONDITIONS WILL DOMINATE AT TAF SITES THROUGH THE DAY...ALTHOUGH
THERE WILL BE AN OUTSIDE CHANCE OF A STRAY SHOWER OR ISOLATED
THUNDERSTORM AROUND KHON AND KFSD AFTER 21Z. TIGHTENING PRESSURE
GRADIENT ACROSS THE REGION WILL RESULT IN INCREASING WEST/NORTHWEST
WINDS OVER THE AREA DURING THE AFTERNOON...WITH GUSTS AROUND 25 KTS.
PREV DISCUSSION
WEAK FRONT NOW IN WESTERN ND WILL DROP SOUTHEAST ACROSS THE CWA THIS
AFTERNOON/EVENING. MODELS CONTINUE TO SHOW SOME WEAKLY UNSTABLE AIR
NEAR THE BOUNDARY AS IT MOVES INTO THE AREA...SO HAVE ADDED A SMALL
POP FOR ISOLATED SHOWERS ACROSS THE NORTHWEST HALF OF THE FA FOR THE
LATE AFTERNOON...AND FARTHER SOUTHEAST INTO PARTS OF NORTHWEST IOWA
FOR THE EVENING. WITH WEAKLY NEGATIVE LIFTED INDICES AND 100-300J/KG
CAPE INDICATED BY BOTH NAM AND GFS...WILL INCLUDE SLIGHT CHANCE OF
THUNDER...ALTHOUGH FREEZING LEVEL ABOUT 3KFT HIGHER THAN YESTERDAY
AND COLD POOL WILL HAVE SHIFTED WELL TO THE SOUTHEAST OF THE AREA BY
THIS AFTERNOON...SO NO THREAT OF HAIL EXPECTED. DECENT MIXING SHOULD
BE SEEN AHEAD OF THE BOUNDARY WITH DEEP WESTERLY FLOW ALLOWING FOR
WIND GUSTS OF 30-35MPH IN THE AFTERNOON. HIGHS IN THE UPPER 70S TO
AROUND 80 EXPECTED MOST AREAS.
LOOKS LIKE A PLEASANT WEEKEND SHAPING UP...THOUGH STILL ON THE WINDY
SIDE SATURDAY. NORTHWEST-SOUTHEAST TEMPERATURE GRADIENT IN THE LOWER
LEVELS WITH TROUGH OVER THE GREAT LAKES AND UPPER RIDGING ACROSS THE
ROCKIES/WESTERN CONUS. ANY WAVES ROTATING AROUND THE WEST SIDE OF
THE UPPER TROUGH WILL REMAIN FAR ENOUGH EAST AS TO NOT INFLUENCE
OUR WEATHER...EXCEPT TO KEEP NORTHEAST HALF OF THE FA COOLER THAN
WESTERN AREAS THROUGH THE WEEKEND. STILL EXPECTING 70S MOST AREAS
THOUGH...STICKING RIGHT AROUND OR JUST A SHADE ABOVE NORMAL IN THE
EAST AND 5-10 DEGREES ABOVE NORMAL WEST OF THE JAMES RIVER.
UPPER TROUGH SHIFTS SLOWLY EAST INTO NEW ENGLAND/APPALACHIANS SUNDAY
NIGHT...ALLOWING FOR PUSH OF WARM ADVECTION ACROSS OUR FA. LOW LEVEL
MOISTURE A QUESTION...BUT LOOKS TO BE ENOUGH SUPPORT FOR AT LEAST A
FAIR AMOUNT OF MID CLOUDS...AND HAVE ADDED A SLIGHT CHANCE FOR LATE
NIGHT SHOWERS IN OUR EAST. EVEN POTENTIAL FOR ELEVATED INSTABILITY
VERY LIMITED AT THIS TIME WITH INITIAL WARMING IN THE MID LEVELS...
SO HAVE LEFT OUT ANY MENTION OF THUNDER AT THIS TIME.
00Z RUNS OF BOTH GFS AND ECMWF FLATTEN THE RIDGING WITH A WAVE
DROPPING INTO NORTHERN MINNESOTA ON MONDAY...WHICH IS DAMPENING THE
WARMING POTENTIAL FOR MONDAY WHICH EARLIER RUNS HAD INDICATED. 00Z
RUNS STILL SHOWING 22-25C AT 925MB ACROSS SOUTH SOUTHWEST FA...BUT
THIS A FAR CRY FROM THE 30C WHICH PREVIOUS FORECASTER INDICATED WAS
SEEN ON EARLIER RUNS. HAVE SHAVED A FEW DEGREES FROM PREVIOUS HIGH
FOR MONDAY AS A RESULT...AND MAY STILL BE A LITTLE TOO WARM IF 00Z
RUNS VERIFY. BUT DID NOT WANT TO MAKE WHOLESALE CHANGE BASED ON JUST
THIS MODEL RUN...GIVEN LACK OF RUN TO RUN CONSISTENCY SEEN IN RECENT
DAYS.
GFS MUCH STRONGER WITH AFOREMENTIONED WAVE...AND AS A RESULT BECOMES
QUITE A BIT COOLER THAN ECMWF BY TUESDAY AFTERNOON. DID COOL EASTERN
AREAS A LITTLE TO ACCOUNT FOR THE WAVE...BUT NOT AS MUCH AS 00Z GFS
LOW LEVEL TEMPERATURES WOULD INDICATE.
SIGNIFICANT PATTERN SHIFT FOR LATTER HALF OF THE WEEK...AND MODELS
NOT HANDLING TRANSITION/EVOLUTION OF WESTERN CONUS TROUGH VERY WELL.
00Z GFS DOES APPEAR TO BE TRENDING TOWARD A LESS PROGRESSIVE PUSH TO
THE TROUGH THROUGH THE NORTHERN PLAINS THAN DID THE 18Z RUN...THOUGH
STILL NOT LAGGING THE TROUGH BACK ACROSS THE ROCKIES NEARLY AS MUCH
AS THE SOMEWHAT MORE CONSISTENT ECMWF. NO CHANGES FROM WEDNESDAY ON
AT THIS POINT.
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
JH/JM
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