464
FXUS63 KFSD 100255
AFDFSD
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
855 PM CST MON NOV 9 2009
DISCUSSION
A CPL LTL ADJUSTMNTS TO ERYR FCST. CLEARING IS NOT AS SHARP AS FCST
WITH A TRAILING AREA OF MID AND HI LVL MOISTURE WHICH CAN BE SEEN ON
SATLT AND NEW NAM/NAM12. THESE MID AND HI CLDS SHUD NOT BE SOLID AO
VERY THICK...BUT SOME MAY LINGER MUCH OF THE NGT BEFORE BETTER
CLRNG LATE. EVE TEMP DROP HAS BEEN PRETTY FAST XCP SERN CRNR OF FCST
AREA...AND DESPITE A FEW MORE CLDS THAN WE HAD BEFORE...WRN END OF
LINGERING HI PRES AND DELAY ON DVLPG LO LVL SRLY BREEZE REACHNG THE
SFC SHUD CONT TO ALLOW DECENT COOLING CONDS...SO LOWS MAY BE 2-3
DEGS LWR MANY AREAS THAN ERYR FCST.
AVIATION
VFR CONDITIONS SHUD CONT THRU 11/06Z. SOME PATCHY LINGERING MOISTURE
AND CLDS TNGT IS AT MID AND HI LVLS AND LO LVLS REMAIN DRY. SLWLY
INCRG SRLY GRADIENT WILL ALLOW FOR WNDS TO INCRS STEADILY TUE...WITH
SFC GUSTS ARND 25 KTS WRN EDGE OF FCST AREA 18Z-11/00Z.
PREV DISCUSSION
LIGHT WINDS IN SURFACE RIDGE AXIS...CLEARING OF SOUTHERN CIRRUS
SHIELD AND DRY LOW LEVEL AIR SHOULD ALLOW FOR QUICK DROP IN TEMPS
THIS EVENING. WILL LIKELY SEE STRONG ELEVATION SIGNATURE TO TEMPS
AGAIN BY DAYBREAK...WITH MAV GUIDANCE SEEMINGLY HAVING BEST HANDLE
ON THIS IDEA WITH VALLEY LOCATIONS DIPPING INTO THE UPPER 20S WHILE
HIGHER ELEVATIONS REMAIN IN THE LOWER TO MID 30S. /JH
TUESDAY SHUD BE SUNNIEST DAY OF WEEK FOR MOST...WITH SOME CI MOVING
INTO THE WRN HALF OF THE AREA DURING THE AFTN. SFC RIDGE LINGERS
SOMEWHAT THRU E...BUT A STRONGLY INCREASING GRADIENT THRU W WL
PROVIDE SOME BREEZY CONDITIONS...AND SOME GRADUAL INCREASE IN
MOISTURE. TMPS PROBABLY NOT MORE THAN A STONES THROW FROM TDA...
WITH INCREASING STABILITY THRU W STIFLING MIXING SOMEWHAT AND
CAPPING OFF FULL WARMING POTENTIAL.
TUE NIGHT...GRADIENT INCREASES THRU THE AREA...AND CONCERN SURFACES
ON DEVELOPMENT OF LOW CLOUDS...PERSISTENT ENOUGH TO AFFECT
TEMPERATURES THRU THE REMAINDER OF THE SHORT TERM. WHILE THE CROSS
SECTIONS/TIME SECTIONS LOOK QUITE SIMILAR TO FCST EVENT FROM LAST
FRIDAY MORNING...THERE ARE TWO DISTINCT DIFFERENCES WHICH LEND
INCREASED CONFIDENCE IN STRATUS DEVELOPMENT. FIRST...THERE ARE
ALREADY SOME LOWER CLOUDS THRU PARTS OF THE SRN PLAINS. SECOND...
THE PERSISTENCE IN LLJ FROM LTR TUE INTO THU WL LKLY ALLOW A MORE
EFFECTIVE TRANSPORT OF MOISTURE. FIRST LOWER CLDS LKLY TO SPREAD UP
FROM WRN KS/SWRN NEBRASKA INTO WRN CWA TUE NIGHT...THEN WL HAVE TO
WATCH A BIT FARTHER EWRD THRU NEBRASKA LTR TUE NIGHT AND WED TO
ADVECT NWRD INTO NERN NEBRASKA/SERN SD. BACKED OFF SOMEWHAT ON DZ
THREAT TIMING...WHICH LOOK TO ACCOMPANY INCREASE IN SHEAR AND SOME
TENDENCY FOR DRYING ALFT/WK LIFT WHICH COMES IN WED NIGHT INTO THU
AM. COULD END UP WITH SOME SMALL MEASURABLE AMOUNTS THRU SW MN.
TRIED TO TIGHTEN UP THE DIURNAL RANGE TO TMPS SOMEWHAT...TO 10
DEGREE RANGE OR LESS THRU HEART OF CWA. HOWEVER...WITH DRIER AIR
ALFT AND MORE OF A SW FLOW INTO WRN CWA ON THU...COULD EASILY BREAK
OUT TO SOME NICE MILD TEMPERATURES FROM THE JAMES VALLEY WWRD ON THU
AFTN...WITH ONLY DENSER CI THREAT TEMPERING WHAT COULD MIX TO NEAR
70.
FOR THE EXTENDED RANGE /THU NIGHT THRU MON/ SEEMS TO BE LITTLE
CONTINUITY BETWEEN MODELS OR RUNS TO GET GOOD SOLID FEEL FOR AT THIS
TIME...TYPICAL OF SPLIT FLOW. ANOTHER KNEE BUCKLING CURVEBALL TOSSED
BY 12Z GFS AFTER 18Z/00Z/06Z OPERATIONAL AND ENSEMBLE SETS KEEPING
MORE DISTICNT FLOW SEPARATION WHICH ONCE AGAIN DEVELOPS A MAJOR
CLOSED LOW ACROSS THE PLAINS SUN INTO MONDAY...AND WOULD CERTAINLY
BRING A SIGNIFICANT WINTER SYSTEM TO THE IMMEDIATE AREA. ECMWF AND
CANADIAN ALSO SUGGESTING THAT A DEGREE OF PHASING COULD OCCUR
SOMEWHERE THRU THE CNTRL CONUS...WITH ECMWF SHIFTING FROM E ON 00Z
SET ACRS WI TO W ON 12Z SET THRU WRN PLAINS WITH CLOSED SYSTEM.
LATEST CANADIAN HAS BACKED OFF SOME ON EARLIER CLOSED SLN FOR LTR
SUN AND MON MOVING JUST SE OF THE AREA...FAVORING NRN STREAM AGAIN.
ALL SPEAKS VOLUMES FOR LOW CONFIDENCE...ESPLY WITH OPERATIONAL SLNS
NEARLY ALONE WITHIN ENSEMBLE SETS ON DEGREE OF FLOW PHASING. AN
ACCEPTABLE FIRST STEP WOULD BE TO AT LEAST PUT A SMALL POP IN FOR
SUN/SUN NIGHT...WITH TYPE KEPT AS RAIN FOR THE MOMENT SUPPORTING
THEORY THAT SRN STREAM SYSTEMS MOST OFTEN LIFT OUT A BIT MORE TO THE
W AND N THAN PROGGED AT LONG RANGES. THIS POP IS ALMOST MORE OF A
MEASURE OF THE LIKELIHOOD OF ANY CLOSED LOW SLN AT THIS TIME. IF
THIS SYSTEM STARTS TO SHOW ITS SPOTS...WL CERTAINLY NEED TO TIGHTEN
UP THE THERMAL RANGES.
AT THE LEAD IN OF THE EXTENDED...WL BE DEALING WITH NRN STREAM WAVE
PUSHING THRU PLAINS. BNDRY IS HIGHLY FRONTOGENETICAL...AND EXPECT
CHC OF PRECIPITATION TO OCCUR ALG BNDRY TO BE FAIRLY HIGH...BUT A
BIT DIFFICULT TO TIME WITH CONTINUED SHIFTING OF FORCING 12-18H
BETWEEN VARIOUS RUNS. THIS WOULD KEEP POPS MORE IN THE LOW TO MID
CHC RANGE IN ANY PARTICULAR PERIOD...WITH A GRADUAL NW TO SE DRIFT
ALONG WITH MID LVL BNDRY. BEST CHC THRU NRN CWA LTR THU NIGHT INTO
FRIDAY...HEART OF CWA FRIDAY...THEN DOWN THRU NW IA BY FRI EVENING.
SAT WOULD LKLY BE MORE LIKELY QUIET PERIOD...AND LOWERED TMPS A BIT
AS COOL SFC RIDGE NOSES SWRD INTO REGION. /CHAPMAN
FSD WATCHES/WARNINGS/ADVISORIES
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
WILLIAMS
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