000
FXUS63 KFSD 280258
AFDFSD
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
957 PM CDT MON JUL 27 2009
.DISCUSSION...
SECONDARY COLD FRONT MOVING THRU THE AREA THIS EVENING AND EARLIER
EVENING HAD A FEW STORMS THRU SCNTRL SD THAT THREATENED TO CROSS
INTO SVR CRITERIA. HOWEVER...UPDRAFTS COULD NOT ORGANIZE AND BE
PERSISTENT ENOUGH TO PROPEL INTO SEVERE STATURE...TAKING ON
MULTICELLULAR CHARACTERISTICS...WITH A STRONG COLD POOL. WITH LOSS
OF DAYTIME DESTABILIZATION...STORMS DIMINISHED RAPIDLY THIS EVENING
AND ONLY A FEW SHRA REMAIN IN NERN NEBRASKA. STRONG WAVE WL PASS
JUST S OF THE AREA OVERNIGHT...BUT INFLUX OF DRIER LOW TO MID LVL
AIR SHUD KEEP PCPN OUT OF THE MIX AFTER LAST OF ISOLD SHRA END LATE
EVENING. DESPITE LOW LVL CAA...WKR GRADIENT/DECOUPLING SEEMS TO BE
WINNING THE BATTLE FOR WINDS THIS EVENING...AND A STEADY STATE 5-10
KTS SEEMS MORE LIKELY FOR REMAINDER OF NIGHT. WL CLEAN UP ZFP
WORDING...BUT TMPS LOOK LARGELY ON TRACK FOR END STATE OVERNIGHT
WITH NICELY LOWER DWPTS LOOMING TO N...AND THREAT FOR MORE CLDS ALG
MO RVR CORRIDOR. /CHAPMAN
&&
.AVIATION...
VFR CONDITIONS ARE EXPECTED ACROSS THE AREA THROUGH 06Z WED.
&&
.PREV DISCUSSION...
SECONDARY COLD FRONT DROPPING SOUTHWARD THROUGH NORTHERN SOUTH
DAKOTA THIS AFTERNOON...AND BEGINNING TO SEE SOME
SHOWER/THUNDERSTORM ACTIVITY DEVELOPING THROUGH THE CENTRAL PORTIONS
OF THE STATE IN AREA OF LOW LEVEL CONVERGENCE WITH STEEP LAPSE RATES
IN PLACE. THE CHALLENGE FOR EARLY TONIGHT WILL BE HOW MUCH
CONVECTION WILL DEVELOP AS THIS FRONT CONTINUES TO DROP TO THE
SOUTH...AS A SHORTWAVE TRACKS INTO NEBRASKA THROUGH THE EVENING
HOURS. THE NAM IS MUCH MORE ROBUST WITH BREAKING OUT CONVECTION IN
OUR SOUTH LATE THIS AFTERNOON AND EVENING...WITH THE GFS KEEPING IT
SOUTH OF US. LOOKING AT MOST RECENT RADAR TRENDS...WENT CLOSER TO
THE NAM WITH PRESENT CONVECTION OVER CENTRAL SOUTH DAKOTA SLIDING TO
THE SOUTHEAST ACROSS OUR SOUTHWESTERN CWA INTO THE EVENING
HOURS...WITH POSSIBLE DEVELOPMENT FARTHER EAST AS THE SHORTWAVE
PUSHES TO THE EAST. THE FRONT/FORCING SHOULD THEN PUSH TO THE SOUTH
OF OUR CWA BY 06Z...THEN DRYING OUT FOR THE REMAINDER OF THE NIGHT.
WINDS SHOULD DIE OFF LATER TONIGHT...AND WITH LESS CLOUDS OVER OUR
NORTH...EXPECTING TEMPS TO FALL BACK INTO THE MID 50S...WITH
READINGS CLOSER TO 60 IN OUR SOUTH.
TUES SHUD BE QUIET ACRS THE CWA WITH NW FLOW KEEPING CWA PLEASANTLY
COOL WITH HIGHS 5 TO 8 DEG BLO NORM WITH GENLY PARTLY TO MOSUNNY
CONDITIONS. TUES NITE SHUD ALSO BE COOL AS SFC HIGH SETTLES OVR MN
AND IA. WL AGAIN SEE LOW BLO NORM ACRS THE CWA.
MODELS DIVERGE FAIRLY SIG FOR WED INTO WED NITE WITH NEXT S/W. GFS
APPEARS TO BE THE MOST AGRESSIVE AND MUCH FASTER WHILE GEM AND EC
MUCH SLOWER. NAM NOT AS SLOW AS EC OR GEM. IF ONE BELIEVES
GFS...THEN BULK OF RAIN WUD FALL DURING THE DAY ON WED WHILE GEM AND
EC SOLUTION WUD HOLD OFF RAIN UNTIL WED NITE. THAT WUD HAVE A SIG
IMPACT ON TEMPS. IF GFS CORRECT THEN ENTIRE CWA PBLY WONT GET OUT
60S. BOTH THE EC AND GEM HAVE BEEN CONSISTENT WITH SLOWER AND WEAKER
SOLUTION AND WL TEND TO FOLLOW A BLEND OF NAM/EC FOR SFC FEATURES
AND TIMING OF PRECIP. SO WL GO WITH HIGHEST POPS W MAINLY ALONG AND
WEST OF JAMES VALLEY WED AND THEN ACRS E WED NITE. WITH THIS IN
MIND...WIL HOLD HIGH TEMPS DOWN IN THE 60S ACRS THE W ON WED WITH
LOWER TO MID 70S E. WITH MORE OF AN OPEN WAVE EXPECTED...QPF AMOUNTS
PBLY WL NOT BE AS HIGH AS NAM AND GFS...BUT CUD SEE A DECENT 0.25 TO
0.50 ACRS CWA WITH THIS FEATURE.
NW FLOW BEHIND THIS WAVE WILL KEEP CWA COOL ON THU WITH PLENTY OF SC
EXPECTED ACRS THE E. THIS WL KEEP HIGHS IN THE 70S ACRS CWA WITH
LOWER 70S AT BEST E.
BRIEF WARMUP ON FRI AHEAD OF NEXT S/W AND CDFNT. TEMPS SHUD BE CLOSE
TO NORM ACRS THE W...BUT STILL A FEW DEG BLO NORM E. WL KEEP SMALL
POPS WITH THIS S/W FRI NITE INTO SAT BUT MOISTURE AND INSTABIL WL BE
LIMITED...SO WL NOT GO ANY HIGHER THAN 30%. COOLER TEMPS CAN BE
EXPECTED AGAIN SAT AND SUN WITH HIGHS IN THE 70S TO LOWER 80S.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&
$$
