Severe Thunderstorm Warning 60, NWS Sioux Falls, SD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1030 AM CDT WED APR 21 2004

.DISCUSSION...
NOT MANY CHANGES ARE PLANNED TO THE GOING FORECAST. FORECAST TODAY
IS RATHER TRICKY. AT 15Z...HAD TWO AREAS OF STRATUS TO WORRY ABOUT.
ONE WAS SLIDING INTO THE HON AREA WITH SFC TROUGH. THE SECOND WAS
ACROSS SW MINNESOTA ASSOCIATED WITH DEPARTING UPPER LOW. BASED ON
MORNING SOUNDINGS FEEL THE AREA OF STATUS ACROSS THE WEST SHOULD MIX
OUT RATHER QUICKLY THIS AFTERNOON AND HAVE MINIMAL IMPACT ON TEMPS
WHILE CLOUDS SHOULD HOLD ON A BIT LONGER IN THE EAST. WILL RAISE
HIGHS A TAD IN AREAS THAT HAVE CLEARED OUT THIS MORNING...BUT EXPECT
SUNSHINE TO CAUSE A CU FIELD TO DEVELOP QUICKLY AS TEMPS ALOFT
RATHER CHILLY. FOR WX...CURRENT FORECAST LOOKS PRETTY GOOD BASED ON
LATEST MODELS. SHORTWAVE EXPECTED TO SLIDE ACROSS AREA THIS
AFTERNOON AND MAINLY JUST ADJUSTED THE TIMING A BIT. RADAR MOSAICS
SHOW SCATTERED COVERAGE ACROSS CENTRAL NEBRASKA SO POPS LOOK
REASONABLE...BUT WILL CUT BACK A BIT ON THE NORTHERN FRINGE.

&&

.PREV DISCUSSION...
ON THE LARGE SCALE...VIGOROUS UPR LVL SYSTEM MOVING EWRD THRU MN AND
PHASING IN WITH ENERGY LIFTING NWRD THRU IA. THIS DENOTES WHERE SPLIT
FLOW STARTS ACRS WRN NA...BETWEEN NRN STREAM THRU CANADA AND STG SRN
STREAM CNTRL PAC COAST TO SRN ROCKIES. REGION BETWEEN IS FAIRLY
CHILLY ALFT WITH TRAIN OF WAVES BACK INTO CNTRL PAC.  FEW SHRA ON
REGIONAL RADARS REALLY WINDING DOWN FOR MOST PART.  SEEMS HANDLING
SPLIT FLOW IS THE MODEL FORECAST CHALLENGE NEXT SEVERAL DAYS...AND
NOW BIG CHALLENGE IS TO WEED THROUGH THE MIXED SIGNALS TO COME UP
WITH VIABLE PCPN FCST. OVERALL...THINK ETA ON THE MORE PROPER COURSE
AS EVEN 5 WAVE GFS SHOWING A BACKING TO LARGE SCALE FEATURES A
BIT...INFERRING MORE EMPHASIS ON NRN STREAM TOWARD END OF WEEK.

WITH WRAPPING UP OF SYSTEM TO E EARLY THIS MORNING...LOW LVL
FRONTOGENETIC AXIS REMAINS CLOSE TO FAR ERN CWA...AND WL MAKE LAST
SECOND DECISION REGARDING LINGERING AM POPS FAR E.   NEXT VORT LOBE
SHEARING INTO SWRN SD WITH SCT PCPN ALREADY. BETWEEN WL FIND AREA OF
LESSER CLDS WHICH WL ALLOW SFC HEATING.  ATM DOES DESTABILIZE FAIRLY
WELL WITH ANY SFC HEATING TDA...AND RESULTS IN SFC BASED CAPE OF
3-500 J/KG. SUGGESTS ADDING AT LEAST ISOLD TSRA TO MIX. FOCUS WOULD
SEEM TO BE OVR SRN CWA AHEAD OF WK MID LVL SHEAR AXIS...BUT HARD
PRESSED NOT TO THINK EVEN SOME WITH COOLER AIR ALFT TO N AS LOW LVL
CONVERGENCE AXIS ROTATES TO S.  WL HAVE TO LINGER SOME FOG EARLY
MORNING IN JAMES VALLEY WHERE PARTIAL CLEARING AND WK GRADIENT AHEAD
OF SECONDARY TROUGH OVR SRN ND. TMPS FAIRLY CLOSE TO MIXING SEEM IN
ORDER,

TONIGHT...WL SEE LINGERING BAND OF SHRA IN VORT AXIS DIMINISH WITH
LOSS OF HTG AND SHEARING AWAY OF ENERGY. HOWEVER...AFTER DECREASING
CHC OF PCPN...WL SEE INCRS AGAIN AS LOBE OF SRN STREAM ENERGY LIFTS
INTO CONVERGENCE ZONE. BEST CHC BY FAR NR MO RVR...AND WL CONTINUE
GRADIENT TO DRY I 90 AND NORTH. IF NOT FOR CLDS...WOULD THINK THAT
IT COULD BE COOLER THAN FCST...AND ONLY TWEEKED N DOWN A TOUCH.

THU/THU NIGHT WL FIND PERSISTENT RAIN CHC TO S...BUT WL BE BATTLING
DRIER NELY TRAJECTORY. WL BE FAIRLY DECENT NRN BNDRY TO PCPN...BUT
HARD TO DEFINE WITH LOCATION JUMPING RUN TO RUN. WL TRIM BACK AND
ALLOW A GRADUAL ADVANCE NWRD DURG DAY AS DIV Q AXIS ELONGATES OUT TO
S. VERY FRONTOGENETIC BNDRY ALSO FAVORS PCPN S.  AGAIN...WL SEE SOME
WK INSTABILITY...BUT SHUD ONLY BE NR MO RVR IN AFTN. ISOLD NON SVR
TSRA AT BEST.

NRN STREAM WAVE SET TO APPROACH ON THU NIGHT/ERLY FRI...WITH MAIN
ENERGY STALLING IN SRN STREAM. HOWEVER...SRN JET IMPULSE DOES ROUND
THE CORNER AND LIFT INTO IA OVERNIGHT. ELONGATED LIFT MIGHT ENTICE
PCPN TO FARTHEST NWRD POINT OVERNIGHT. CDFNT WL SINK SWRD BEHIND NRN
STREAM WAVE ON FRIDAY AND WL KEEP LINGERING PCPN ACRS SE UP TO MID
LVL CONFLUENCE...THEN END N TO S BY EVNG. FRI NIGHT...WL KEEP DRY
FOR NOW...BUT MAY HAVE TO ADD IN LINGERING CHC OF PCPN INTO FAR S IF
MID LVL BNDRY HANGS MORE TO N.

EXTENDED RANGE...AGREE WITH ERLY METION OF SHRA ON SAT...BUT WL
HEDGE A BIT FARTHER TO THE NW WITH POTENTIAL PHASING OF STREAMS
SUGGESTED IN SEVERAL MDLS. WL LOWER TMPS A BIT TOO FOR MORE
CLDS/PCPN. REST UNCHANGED.

&&

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

&&

JRM

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1052 AM CDT WED APR 21 2004

SDZ038>040-050-052>071-MNZ071-072-080-081-089-090-097-098-
IAZ001>003-012>014-020>022-031-032-NEZ013-014-221200-
AURORA-BEADLE-BON HOMME-BROOKINGS-BRULE-BUENA VISTA IA-
CHARLES MIX-CHEROKEE IA-CLAY-CLAY IA-COTTONWOOD MN-DAKOTA NE-
DAVISON-DICKINSON IA-DIXON NE-DOUGLAS-GREGORY-HANSON-HUTCHINSON-
IDA IA-JACKSON MN-JERAULD-KINGSBURY-LAKE-LINCOLN-LINCOLN MN-
LYON IA-LYON MN-MCCOOK-MINER-MINNEHAHA-MOODY-MURRAY MN-NOBLES MN-
OBRIEN IA-OSCEOLA IA-PIPESTONE MN-PLYMOUTH IA-ROCK MN-SANBORN-
SIOUX IA-TURNER-UNION-WOODBURY IA-YANKTON-

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST SOUTH DAKOTA...
SOUTHWEST MINNESOTA...NORTHWEST IOWA...AND NORTHEAST NEBRASKA.

.DAY ONE...TODAY AND TONIGHT

THUNDERSTORMS...
A FEW THUNDERSTORMS WILL DEVELOP THIS AFTERNOON. WHILE THESE
STORMS ARE NOT EXPECTED TO BECOME SEVERE...COLD TEMPERATURES
ABOVE THE SURFACE MAY ALLOW THE STRONGER STORMS TO PRODUCE PEA
SIZE HAIL.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY AND TONIGHT.

&&

FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE AT
WWW.CRH.NOAA.GOV/FSD. THIS INCLUDES THE GRAPHICAL HAZARDOUS
WEATHER OUTLOOK.

JRM