FXUS63 KFSD 230235
AFDFSD
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
835 PM CST TUE DEC 22 2009
.DISCUSSION...
UPDATED FORECAST TONIGHT TO DROP MENTION OF LIGHT SNOW TONIGHT. LOW
LEVEL EASTERLY FLOW IS EXPECTED TO RESULT INCREASING AMOUNTS OF LOW
LEVEL MOISTURE...WHICH MAY RESULT IN SOME LIGHT FREEZING DRIZZLE
MAINLY ALONG AND EAST OF INTERSTATE 29. REPORTS FROM AROUND THE AREA
ONLY INDICATE PATCHY AREAS OF DRIZZLE THIS EVENING ACROSS NORTHWEST
IOWA AND SOUTHWEST MINNESOTA. EXPECT FREEZING DRIZZLE MAY BECOME A
LITTLE MORE WIDESPREAD AFTER MIDNIGHT AS LOW LEVEL LIFT INCREASES.
AT THIS TIME...WILL REFRAIN FROM ISSUING ANY ADVISORY TO AVOID
HEADLINE CONFUSION ON UPCOMING STORM. OTHER CONCERN TONIGHT WILL BE
FOG WITH INCREASING LOW LEVEL MOISTURE. EXPECT VISIBILITIES TO HANG
IN THE ONE TO 3 MI RANGE FOR MUCH OF THE NIGHT...BUT WILL WATCH
CLOSELY. TEMPERATURES TONIGHT SHOULD REMAIN STEADY OR RISE A DEGREE
OR TWO AS WINDS REMAIN STEADY OR INCREASE EVER SO SLIGHTLY. UPDATE
POSTED. /BT
&&
.AVIATION...
EXPECT MAINLY IFR CONDITIONS TO CONTINUE THROUGH THE NIGHT FOR BOTH
CEILINGS AND VISIBILITIES FOR FOG. DO NOT BELIEVE THAT THE FZDZ
THREAT WILL BE VERY WIDESPREAD AND SHOULD BE CONFINED TO AREAS
MAINLY EAST OF I29. BY WEDNESDAY AFTERNOON SNOW WILL SPREAD NORTH
FROM NEBRASKA INTO THE TRI STATE AREA AFTER ABOUT 20Z. AFTER THIS
TIME VISIBILITIES COULD BECOME LIFR AT TIMES DURING THE NIGHT.
&&
.PREV DISCUSSION...
WITH LOW LVL MOISTURE LOCKED IN AND EXPECTED TO GET A LTL DEEPR...
CONTG FOG SHUD HANG IN TNGT WITH VSBYS PRBLY LWRG A LTL. QSTN IS
WILL FOG BCM DNSE. WITH LO LVL FLOW TENDING TO INCRS SLWLY AND
EVENTUALLY BCM A LTL MORE NERLY...HAVE OPTED NOT TO MENTN DNS FOG
FOR NOW. INDEED IT IS ENTIRELY PSBL THAT VSBYS WILL BEGIN TO INCRS A
LTL LATE TNGT...OR AT LEAST HANG STEADY.
AGN WITH THE LO LVL MOISTURE AND SFC UNSTBL LYR GETTING A LTL
DEEPER...THE THREAT OF FREEZING DRZL SHUD INCREASE TNGT. SO FAR WE
HAVE HAD VERY LTL...WITH A COUPLE REPORTS ERYR OF SOME ICING JUST
FROM FOG MOISTR DEPOSITS. AT THIS TIME WILL NOT GO WITH ADVSY FOR
THIS SINCE ITS SIGNIFIGANCE IS IN QSTN...SOME ICY AREAS PSBL JUST
FOR THE REASON MENTND ABV. IN ANY EVENT WE WILL NOT HAVE A REPEAT OF
LAST NGTS FZRA/PL/SN EVENT.
LATER TNGT DEEPER ST CUD START TO PRODUCE SOME VERY LGT SNOW...TO
THE EXTENT OF GETTING A COATING OF LGT SNOW/SNOW GRAINS. IT IS THAT
BASIS FOR KEEPING SOME POPS LATE TNGT...THO WITH MAIN SYS NOT
ARRIVING LATE TNGT WILL KEEP/CUT POPS TO AT MOST THE 30 RANGE EVEN
ALG THE MO RVR.
TEMPS OF COURSE WILL NOT SHOW MUCH DROP...HOLDING MOSTLY IN THE
20S...DIPPING JUST BLO 20 SOME AREAS IN THE N WHERE IT IS NOT FAR
ABV THAT NOW. E/ENE WINDS SHUD HOLD PRETTY STEADY...BUT THERE MAY BE
A SLGT INCREASE AND TENDENCY TO GO A TAD MORE NERLY LATER ON.
MAJOR WINTER STORM WILL BEGIN TO TAKE SHAPE WED AND REALLY GET GOING
WED NITE AND CONT INTO FRI. UPPER LOW WL START TO LIFT NEWD WED AND
WED NITE AND PHASE IN WITH DIGGING WAVE FM THE NW. THIS SHUD GET THE
STORM CRANKED UP AS WE HEAD INTO WE NITE AND CONT INTO FRI AS UPPER
LOW MEANDERS ACRS THE CNTRL PLAINS THRU THU BEFORE MOVING EWD ON
FRI. THIS SHUD PRODUCE A WIEDPREAD AREA OF HEAVY PRECIP ACRS THE CWA
WED NITE INTO THU NITE WITH THE BULK OF PRECIP BEING IN THE FORM OF
SNOW. ALL MODELS DO SHOW WARMER AIR ALOFT PUSHING INTO NW IA WED
NITE INTO EARLY THU MORN AND THIS WL LIKELY CREATE A ZR PROBLEM ACRS
NW IA MAINLY IN THE SLB AREA WHERE UP TO A THIRD OF AN INCH OF
FREEZING RAIN WL BE PSBL WED INTO EARLY THU MORN. DUE TO THE LONG
DURATION OF THIS STORM...WDSPRD 12 TO 16 INCH SNOWFALL CAN BE
EXPECTED WITH 10 TO 12 ACRS PARTS OF NW IA WHERE INIT FREEZING RAIN
WL OCCUR FOR A TIME. WUD NOT BE SUPRISED TO SEE 20 INCHES OF SNOW IN
SOME LOCATIONS...BUT PINPOINTING EXACT LOCATION NEARLY IMPOSSIBLE.
NONETHELESS ONE IF THE BIGGEST STORMS IN YEARS AND IF FSD HITS 13.4
INCHES OVER A 2 DAY PD IT WL BE THE MOST SINCE 1998 AND EVEN MORE
IMPRESSIVE IS IF FSD HITS 14 INCHES WITH THIS STORM OVER 2 DAYS...IT
WILL BE THE MOST IN A 2 DAY STORM SINCE 1968.
THE NEXT PBLM WILL BE THE WIND. INIT THE WINDS WL NOT BE TOO STRONG
THRU THU MOR WITH GENLY NELY WINDS OF 15 TO 25 MPH. HOWEVER AS NRN
STREAM PHASES WITH THIS UPPER LOW...STRONG WINDS OF 30 TO 40 MPH WL
DEVELOP FM WEST TO EAST THU AFTN INTO FRI MORN AND WILL CREATE NEAR
WHITEOUT CONDITIONS. LATER SHIFTS WL NEED TO DETERMINE IF WS WARN WL
NEED TO BE UPGRADED TO BLIZZARD WARN. HWVR...STRONGEST WNDS MAY NOT
OCCUR UNTIL BULK OF THE HEAVIEST SNOW BEGINS TO SHIFT EWD. LOOKS
LIKE THE AXIS OF THE HEAVIEST SNOW WL OCCUR CLOSER TO H85 FNTLGEN.
HWVR...SINCE THIS AREA WL BE FAIRLY LARGE...EVERYONE WL SEE THE
HEAVY SNOW.
WS STORM WARNINGS HAVE ALREADY BEEN ISSUED AND WL DELAY START ACRS S
UNTIL 21Z WED WITH NRN WARN STARTING AT 00Z.
WITH SUCH A LARGE STORM EXPECTED...DID NOT MESS TO MUCH WITH
EXTENDED. AFTER FRI...SHUD BE COLD WITH GENLY DRY WEATHER. WL REMAIN
WNDY FRI WITH A GRADUAL DECREASE IN WNDS THIS WEEKEND.
&&
AVIATION...
IFR CIGS AND VSBYS IN STRATUS AND FOG SHUD RULE TNGT...WITH A FEW
AREAS JUST BARELY INTO MVFR ZONE ERY TNGT. AREAS OF LIFR IN FOG CUD
DVLP DURG THE NGT...THO CUD SEE A HALT TO THIS TREND OR EVEN A LTL
IMPROVEMENT LATE TNGT...NORMALLY AN UNLIKELY TIME...AS LO LVL FLOW
BCMS SLGTLY MORE NERLY. STILL...THE GNRL IFR REGIME WITH A FEW
POCKETS OF MVFR REDVLPG SHUD RULE IN THE 23/12Z-18Z TIME FRAME WITH
PCPN FROM APPCHG MAJOR SYS PSBLY ARRIVING SRN EDGE OF FCST AREA AT
THE END OF THAT TIME SPAN. LO LVL ICG WILL BE A FACTOR AS WELL THRU
PD.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
IA...WINTER STORM WARNING FROM 3 PM WEDNESDAY TO 6 PM CST FRIDAY FOR
IAZ001>003-012>014-020>022-031-032.
MN...WINTER STORM WARNING FROM 3 PM WEDNESDAY TO 6 PM CST FRIDAY FOR
MNZ089-090-098.
WINTER STORM WARNING FROM 6 PM WEDNESDAY TO 6 PM CST FRIDAY FOR
MNZ071-072-080-081-097.
NE...WINTER STORM WARNING FROM 3 PM WEDNESDAY TO 6 PM CST FRIDAY FOR
NEZ013-014.
SD...WINTER STORM WARNING FROM 3 PM WEDNESDAY TO 6 PM CST FRIDAY FOR
SDZ050-057>071.
WINTER STORM WARNING FROM 6 PM WEDNESDAY TO 6 PM CST FRIDAY FOR
SDZ038>040-052>056.
&&
$$
