FXUS63 KFSD 100306
AFDFSD
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
907 PM CST WED DEC 9 2009
.DISCUSSION...
NOT MUCH IN THE WAY OF CHANGES TONIGHT. WIND CHILL ADVISORY WILL
REMAIN IN EFFECT UNTIL NOON ACROSS THE CWA. OVERALL TEMPERATURES IN
PRETTY GOOD SHAPE. SHAVED A FEW DEGREES OFF IN THE WEST WHERE
TEMPERATURES WERE CLOSE TO THE LOWS...BUT SHOULD SEE TEMPERATURES
REMAIN STEADY OR SLOWLY DROP THE REST OF THE NIGHT. TRICKIEST
TEMPERATURES INTO SW MN WHERE OBS ARE BEGINING TO SHOW MID LEVEL
WARM ADVECTION CLOUDS FORM. THESE SHOULD REMAIN IN PLACE MOST OF THE
NIGHT...HOLDING TEMPERATURES STEADY THE REST OF TOINGHT. ACTUALLY
HAVE SEEN TEMPERATURES WARM A FEW DEGREES IN THE LAST FEW HOURS.
REGARLESS...WIND CHILLS WILL STILL BE IN THE 20 TO 30 BELOW ZERO
RANGE TONIGHT. 97
&&
.AVIATION...
VFR CONDITIONS EXPECTED THROUGH THURSDAY.
&&
.PREV DISCUSSION...
FINALLY STARTING TO SEE THINGS QUIET DOWN...AND THE WIDESPREAD
BLOWING SNOW COMING TO AN END ON LATEST WEBCAM IMAGES...MORE
SPORADIC AND NOT AS LOW VISIBILITY. HOWEVER...TMPS REALLY HAVE
RECOVERED LITTLE DURING THE AFTN...AND THE COLD TMPS ALONG WITH
DIMINISHING WINDS WL PROVIDE THE GREATEST SHORT TERM CONCERN.
DECREASING GRADIENT WL ALLOW WINDS TO CONTINUE TO DECREASE HEADING
INTO THE EVENING. IN FACT...WK LOW LVL RIDGE BUILDS THRU JAMES VLY
LATER EVNG...AND INTO THE I29 CORRIDOR IN 06-09Z WINDOW. THERE
REMAINS A WLY GRADIENT OVERNIGHT...BUT IS THE CLASSIC SET WITH FRESH
SNOWFIELD TO HAVE WINDS DECOUPLE TOWARD A LIGHT WSW FOR A TIME.
SOME HIGH LVL CLOUDS ARE EXPECTED TO MOVE THROUGH...AND PERHAPS SOME
MID CLOUDS LATER IN THE NIGHT AS WK TROUGH/WARM FRONT PUSHES TOWARD
THE REGION. EVEN THOUGH WIND SPEEDS ARE LKLY TO DROP FOR QUITE A
WHILE...APPARENT TEMPS ARE LKLY TO REMAIN IN THE -20 TO -25F RANGE
ON THE AVERAGE...SO WL GO AHEAD AND MATCH UP WIND CHILL HIGHLIGHTS
TO THE AREA WITH SOMEWHAT STRONGER WINDS THRU THE ERN CWA.
/CHAPMAN
THERE IS NOT A LOT HAPPENING OVERALL IN THE THURSDAY THRU SATURDAY
PERIODS. THE UPPER FLOW BEGINS TO FLATTEN TO MORE OF A QUASI ZONAL
FLOW BY SATURDAY. BEFORE THAT...COLD UPPER LOW PRES IS SITUATED IN
CENTRAL AND ERN CANADA THURSDAY AND FRIDAY LATE THIS WEEK WHICH
SHIFTS SLOWLY EWD. THEREFORE ARCTIC AIR CONTS TO BE IN PLACE FOR
THURSDAY AND FRIDAY BEFORE MODIFYING SOME ON SATURDAY. FOR THE
DETAILS...CONTINUED THE TREND OF GOING WELL BLO GUIDANCE ON
THURSDAY...AT LEAST PERTAINING TO THE MAV. THE NAM AND GFS AT H925
SHOW A LOW LEVEL AIR MASS WHICH IS ABOUT 5 TO 8 DEG C WARMER THEN
THIS AFTERNOONS H925 TEMPS. SO WARMED OUR MAX TEMPS ON THURSDAY
ABOUT 8 TO 10 DEGS F WARMER THAN OUR CURRENT READINGS. STILL COLD.
FCST SNDGS HINT AT SOME STRATOCU DEVELOPMENT POSSIBLE IN THE NERN
SECTIONS OF OUR FA NEAR A VERY SUBTLE SFC TROF THUR AFTERNOON...AND
I ALMOST KEPT OUR MENTION OF SCT FLURRIES IN FOR SW MN. BUT THE
MOISTURE DOES INDEED LOOK SHALLOW SO DECIDED TO TAKE IT OUT.
BUT LATE THURSDAY NIGHT IS A DIFFERENT STORY...IN THAT THE VARIOUS
MODELS POINT AT A WEAK MID LEVEL S/W NEAR 700MB MOVG SEWD DOWN THE
BACKSIDE OF THE LARGE CANADIAN UPPER LOW. AFTER WHAT SHOULD BE SOME
TEMPORARY CLEARING THURSDAY EVENING...RELATIVELY DEEP MOISTURE MAY
RETURN TO THOSE SAME NRN AREAS IN OUR FA...WHICH MAY SPAWN A FEW
FLURRIES ALONG AND NE OF A DE SMET SD TO WORTHINGTON MN LINE.
CONCERNING TEMPS...MINS THURSDAY NIGHT ARE A TOUGH CHALLENGE...AND
DECIDED TO KEEP OUR LOWS WL BLO GUIDANCE VALUES. BUT THE WINDS DO
REMAIN OUT OF THE SW AM AND WORRIED ABOUT CLOUD COVER COMING DOWN FM
THE NW...AT LEAST ACROSS THE NRN HALF OF OUR FA. ATTM...ALTERED OUR
MINS LITTLE...TANKING SOME OF THE LOWER LOCATIONS...UNTIL WE GET A
BETTER BEAD ON ANY LATE NIGHT CLOUDS OR NOT.
FRIDAY THROUGH SATURDAY LOOK PRETTY QUIET FOR NOW IN A FAIRLY STEADY
WAA REGIME. FRIDAYS HIGHS MAY BE ABOUT THE SAME AS THURSDAYS AS WE
ARE DEALING WITH A WARMER LOW LEVEL AIR MASS...BUT ABSOLUTELY NO
MIXING POTENTIAL AS THE SFC FLOW RETURNS FM THE S OVER A LOT OF DEEP
SNOW COVER. FRIDAY NIGHT...A DECENT SLY BREEZE SHOULD HELP TO KEEP
OUR MINS ABOVE ZERO FOR A CHANGE. ON SATURDAY...WARMED OUR MAX TEMPS
UP A CATEGORY OR TWO AS THE AIR MASS CONTS TO MODIFY. IN ADDITION...
THE MODELS AT THIS POINT ARE SHOWING NO ARCTIC FRONT COMING DOWN AT
ALL. YESTERDAY...SOME OF THE MODELS WERE SHOWING ANOTHER INTRUSION
COMING DOWN. /MJF
THE EXTENDED SAT NIGHT THRU WED HAS ITS WARTS. THE UPPER FLOW
REMAINS RATHER WLY THRU MONDAY. THEN SWITCHES TO MORE OF A NW FLOW
ALOFT TUE AND WED AS ANOTHER COLD UPPER VORTEX MEANDERS IN CENTRAL
AND ERN CANADA...WITH SOME WRN CONUS REGION. THE BIGGEST THING TO
WORRY ABOUT PCPN WISE CONTS TO BE SUN AND SUN NIGHT. BOTH THE ECWMF
AND GFS ARE BEGINNING TO SHOW A LOW LEVEL WRMFNT GENNING UP IN OUR
FA ON SUNDAY...THEN PULLING TO THE EAST SUNDAY NIGHT AS LOW PRES
ORGANIZES INTO A SFC CDFNT. MID LEVEL ENERGY IS ABUNDANT MOVG ACROSS
THE SRN STREAM WHICH MAY PHASE IN WITH THE WRMFNT ON SUNDAY.
THEREFORE KEPT OUR LOW POPS GOING ON SUNDAY...AND EVEN MENTIONED
SOME -FZDZ IN MUCH OF OUR EAST WHERE H85 TEMPS ARE POSITIVE. THE H85
BAROCLINIC ZONE IS QUITE STRONG ON SUNDAY...AND MOISTURE IS
BEGINNING TO DEEPEN UP...SO THIS SYSTEM WL NEED TO BE WATCHED. OUR
LOW POPS ON SUNDAY NIGHT ALSO REMAIN WITH COLD FRONTAL LIGHT SNOW
POSSIBLE. RIGHT NOW...MONDAY THRU WED LOOK DRY. IT LOOKS LIKE
ANOTHER ARCTIC INTRUSION DRAINS DOWN ON TUE BUT RIGHT NOW...THE GEM
AND ECMWF KEEP THE COLDEST TEMPS NORTH OF OUR AREA. ADMITTEDLY
THOUGH...I AM WORRIED I AM NOT COLD ENOUGH TUE AND WED MORNING
BECAUSE OF THIS CHILLY AIR MASS. /MJF
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
IA...WIND CHILL ADVISORY UNTIL NOON CST THURSDAY FOR IAZ001>003-
012>014-020>022-031-032.
MN...WIND CHILL ADVISORY UNTIL NOON CST THURSDAY FOR MNZ071-072-080-
081-089-090-097-098.
NE...WIND CHILL ADVISORY UNTIL NOON CST THURSDAY FOR NEZ013-014.
SD...WIND CHILL ADVISORY UNTIL NOON CST THURSDAY FOR SDZ038>040-050-
052>071.
&&
$$
