000
FXUS63 KFSD 220348
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1048 PM CDT TUE MAY 21 2013

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 302 PM CDT TUE MAY 21 2013

UPPER LOW THAT IS DOMINATING THE WEATHER IN THE SHORT TERM IS
CURRENTLY LOCATED OVER NORTHEAST SOUTH DAKOTA PER LATEST WATER VAPOR
IMAGERY. THIS LOW HAS ALREADY FULLY OCCLUDED AND WILL SLOWLY DRIFT
SOUTHEAST ACROSS NORTHERN IOWA THROUGH WEDNESDAY. LIGHT BUT
PERSISTENT SWATH OF RAIN TODAY LOOKS TO BE FORCED BY FGEN ON THE
NORTH SIDE OF TROWAL FEATURE...AND ALSO WITH FGEN ALONG LEADING EDGE
OF COLDER AIR AT H85. THIS FGEN IN THE NAM SHOWS WEAKENS THIS
AFTERNOON WHICH VERIFIES WELL WITH THE AFTERNOON TRENDS OF ECHOES
WEAKENING ON THE MOSAIC REGIONAL RADAR. FGEN FORCING DOES STRENGTHEN
A BIT THIS EVENING ACROSS EAST CENTRAL SOUTH DAKOTA AND INTO PARTS
OF SOUTHWEST MN...SO EXPECT SOME REDEVELOPMENT ACROSS THOSE AREAS
AND WILL GO LIKELY COVERAGE FOR POPS. COLDER AIR IN THE LOW LEVELS
/MAINLY H85 AND BELOW PER FORECAST SOUNDINGS/ WILL ADVECT INTO THE
REGION FROM THE NORTHWEST TONIGHT AND WEDNESDAY. UPSTREAM AIR IS
STILL MOIST HOWEVER SO CLOUDY CONDITIONS WITH LOW CEILINGS ARE
EXPECTED TO PERSIST DESPITE A NORTHWEST WIND. LATE IN THE DAY
WEDNESDAY...SOME SUN MAY BEGIN TO FILTER IN FROM THE W/NW ALONG WITH
SOME WARMER H85 TEMPS ACROSS CENTRAL SD AND HAVE INCREASED HIGH
TEMPS A BIT THERE. NEVERTHELESS...ANOTHER COOL CLOUDY DAY /WITH SCT
SHOWERS MAINLY EAST ACROSS SOUTHWEST MN/ IS EXPECTED FOR TOMORROW.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 302 PM CDT TUE MAY 21 2013

WEDNESDAY NIGHT INTO THURSDAY WILL SEE A RIDGE OF HIGH PRESSURE MOVE
EAST AND SOUTHEAST...SETTING UP JUST EAST OF THE AREA BY THURSDAY
AFTERNOON. THIS SHOULD SET UP A NICE DAY WITH COOL MORNING LOWS IN
THE 40S AND HIGHS IN THE UPPER 60S TO LOWER 70S.

FRIDAY LOOKING WINDY WITH A STRONG SOUTHERLY GRADIENT EXPECTED TO
DEVELOP. THE 925MB WINDS EXPECTED TO BE IN THE 20 TO 30 KNOT RANGE
WHICH SHOULD MIX TO THE SURFACE. CLOUDS WILL BE ON THE INCREASE
THROUGH THE DAY AND WITH INCREASED LAPSE RATES MAINLY WEST OF
INTERSTATE 29 BUT LOW LEVEL INSTABILITY LACKING MAYBE SOME ACCAS
DEVELOPMENT THROUGH THE DAY BUT AT THIS TIME NOT LEANING TOWARDS ANY
WIDE COVERAGE OF ACTIVITY.

THE MAIN FEATURE SATURDAY THROUGH TUESDAY SHOULD BE AN UPPER LEVEL
RIDGE WHICH WILL GRADUALLY BREAK DOWN BY MONDAY NIGHT AS WEST COAST
TROUGH WORKS INTO THE ROCKIES. THE GFS AND GEM ARE A BIT SHARPER
WITH THIS RIDGE THAN THE ECMWF WHICH SUPPORTS WARMER CONDITIONS WITH
850MB TEMPERATURES ABOUT 5 TO 8 DEGREES HIGHER. THE GFS ENSEMBLE
DOES HINT THAT THIS MIGHT BE A BIT OVERDONE BUT IS STILL RUNNING
ABOUT 3-5 DEGREES WARMER THAN THE ECMWF. THE ECMWF ENSEMBLE
SPAGHETTI PLOT DOES INDICATE THAT THE MAJORITY OF THE 850MB
TEMPERATURE MEMBERS ARE WARMER THAN NORMAL DURING THIS TIME FRAME AS
WELL SO AT LEAST THE 0Z ECMWF MAY BE RUNNING A BIT ON THE COOL SIDE.
THUNDERSTORM CHANCES SHOULD EXIST THROUGH MOST OF THE TIME FRAME
WITH SOME DECENT INSTABILITY SUGGESTED THROUGH THE PERIOD. WILL
CONTINUE THE MID RANGE POPS FOR THIS POTENTIAL WITH NO REAL WAY AT
THIS TIME TO PINPOINT ANY PARTICULAR. THE MAIN FOCUS OF INTEREST
WITH THE THUNDERSTORM CHANCES WILL BE THE POTENTIAL FOR A WARM FRONT
TO WORK INTO THE AREA AND STALL OUT WITH CAP BREAKING BECOMING THE
MAIN CHALLENGE THROUGH THE PERIOD. ALSO OF NOTE UPPER LEVEL FLOW
PRETTY WEAK SO THE LOW LEVEL FLOW WILL DICTATE MOTION WHICH IN THIS
CASE WOULD BE MORE OF A SOUTH OR SOUTHEAST DIRECTION...KEEPING MUCH
OF THE ACTIVITY IN FAR SOUTHERN CWA OR JUST SOUTH. THE 0Z ECMWF IS
MUCH MORE STABLE DURING THIS TIME WHILE THE GEM IS MORE IN LINE WITH
THE GFS SO CONFIDENCE FAIRLY LOW WITH MODEL DISAGREEMENT.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 1046 PM CDT TUE MAY 21 2013

ONCE AGAIN...MVFR CONDITIONS WILL LIKELY DOMINATE THE WEATHER
FOR THE REST OF TONIGHT AND WEDNESDAY ALONG AND NORTH OF I
90...WITH MVFR TO LOWER END VFR SOUTH OF I 90. ONE CHALLENGE IN
THIS FORECAST IS THAT THERE WILL PROBABLY BE PATCHES OF DRIZZLE
MOVING THROUGH THE AREA TONIGHT AND WEDNESDAY. DRIZZLE WILL LIKELY
LOWER THE CONDITIONS INTO THE IFR CATEGORY FOR BRIEF PERIODS OF
TIME. HOWEVER...DUE TO THE INTERMITTENT AND SPOTTY NATURE OF THE
DRIZZLE...IT IS EXTREMELY DIFFICULT TO PREDICT THESE EPISODES MUCH
AHEAD OF TIME. THEREFORE SHORT TERM AMENDMENTS TO THE TAFS COULD
OCCUR TO ACCOUNT FOR THESE CONDITIONS.


&&

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

$$

SHORT TERM...
LONG TERM...08
AVIATION...