FXUS63 KFSD 260339
AFDFSD
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
939 PM CST FRI DEC 25 2009
.DISCUSSION...
LOW PRESSURE PRESENTLY LOCATED OVER NORTHWESTERN IOWA AND SAGGING
EVER SLOWLY TO THE SOUTHEAST. CONTINUE TO SEE BANDS OF SNOW ROTATE
AROUND THE FEATURE...THOUGH SNOW HAS DECREASED IN INTENSITY THROUGH
THE EVENING HOURS AS ATMOSPHERIC INSTABILITY AND FRONTOGENESIS
WEAKENS. QUITE A WARM CONVEYOR BELT WRAPPING AROUND THE SYSTEM...AND
SURFACE TEMPERATURES WARMED INTO THE LOWER AND MID 30S DURING THE
EVENING FROM SOUTHWESTERN MINNESOTA AND ALONG THE I29
CORRIDOR...THOUGH ARE NOW BEGINNING TO DROP AS COLDER AIR TO THE
SOUTHEAST WRAPS AROUND THE LOW. STILL EXPECT LIGHT SNOW TO CONTINUE
ACROSS THE CWA THROUGH THE NIGHT WITH A WEAKENING TROWAL REMAINING
OVER THE REGION. STRONG WINDS HAVE YET TO MATERIALIZE THIS EVENING
IN OUR EAST WHERE WARM AIR ADVECTION WAS OCCURRING...THOUGH EXPECT
THEM TO PICK UP THROUGH THE NIGHT AS THE LOW MOVES EAST AND CAA
ENSUES. ELECTED TO KEEP HEADLINES GOING AS THEY WERE...IN SPITE OF
THE LIGHTER WINDS IN THE EAST...IN CONSIDERATION OF THE AMOUNT OF
SNOW THAT HAS FALLEN AND THE EXPECTATION THAT THE WINDS WILL BEGIN
TO PICK UP LATER TONIGHT. EVEN SO...OVERNIGHT SHIFT MAY HAVE TO LOOK
AT THE POSSIBILITY OF SHORTENING OR DOWNGRADING HEADLINES FOR
SATURDAY IF CONDITIONS DO NOT LOOK TO MEET WARNING CRITERIA. UPDATE
OUT. /JM
&&
.PREV DISCUSSION...
CHRISTMAS STORM CONTINUES TO ROLL ALONG. BLIZZARD AND WINTER STORM
WARNINGS CONTINUE THROUGH NOON SATURDAY. RADAR RETURNS INDICATING
INSTABILITY AND SEEING SOME CONVECTIVE TYPE SNOWS FALLING OVER THE
AREA. COLD POCKET OF AIR WITH THE UPPER LEVEL LOW IS INCREASING MID
LEVEL LAPSE RATES...CONTRIBUTING TO CONVECTIVE POTENTIAL THIS
AFTERNOON. BAND OF CONVECTIVE LIKE SNOW WILL SHIFT WEST ACROSS MUCH
OF THE CWA THE REMAINDER OF THIS AFTERNOON. SNOW RATES IN EXCESS OF
ONCE INCH PER HOUR ARE POSSIBLE AT TIMES. ONCE THIS INSTABILITY IS
RELEASED...SNOWFALL RATES WILL DECREASE QUITE A BIT BY THIS EVENING.
TROUGH OF WARM AIR ALOFT WILL REMAIN IN PLACE TONIGHT INTO
TOMORROW...ALLOWING FOR LIGHT TO MODERATE SNOW TO CONTINUE.
WINDS WILL REMAIN A PROBLEM TONIGHT...ESPECIALLY THROUGH THE
MISSOURI AND JAMES VALLEYS WHERE 30 TO 40 MPH WILL BE THE RULE.
VISIBILITIES IN RURAL AREAS WILL REMAIN NEAR ZERO INTO SAT MORNING.
FARTHER E...CURRENT WIND SPEED OF GENERALLY 10 TO 20 MPH ARE
OCCURRING OVER MUCH OF NW IA AND SW MN THIS AFTERNOON. WINDS ARE
EXPECTED TO AGAIN INCREASE INCREASE TONIGHT AS ARCTIC MAKES AN EWRD
PUSH. ONE INTERESTING NOTE...ALSO SEEING COLD AIR WRAPPING ALL THE
WAY AROUND THE LOW PRESSURE CENTER...WITH COLD AIR ADVECTING W INTO
NW IA FROM ERN IA.
WRAPAROUND SNOWSTORM WEAKENS FROM SATURDAY THROUGH SATURDAY NIGHT AS
SYSTEM FILLS...AND CAN BASICALLY CALL IT PERIODS OF LIGHT SNOW WITH
AREAS OF BLOWING SNOW SAT...BECOMING SCATTERED AREAS AS THE SYSTEM
PULLS EAST SAT NGT. 1 TO 3 INCHES ADDITIONAL SNOWFALL EXPCD...MAINLY
IN THE NWRN CWA WHERE BEST WRAPAROUND BAND LINGERS THRU SAT MRNG.
LEFTOVER CLOUDINESS AND NLY WIND FLOW SHOULD KEEP TEMPS FROM
DROPPING TOO MUCH SAT NGT. SUBSIDENCE SHOULD BREAK UP CLOUDS AND
WINDS DCRS BY SUN NGT PERMITTING TEMPS TO DROP BLO GUID WITH FRESH
SNOW COVER...ESP WITH WEAKER GRADIENT IN THE WRN CWA. THEN SNOW
COVER ALBEDO WILL LIKELY KEEP TEMPS BELOW GUID FOR REST OF
FCST...ESP WITH EXPCD RESURGENCE OF COLDER AIR FROM NORTH BY THURS.
SOME WARMING PSBL NEAR MISSOURI VALLEY FRI AS WMFNT APPROACHES. DID
ADD SLGT CHC -SN MAINLY SERN CWA FOR TUE NGT INTO WED WITH WEAK
SHORT WAVE...BUT SURE DOES NOT LOOK LIKE MUCH. /RYRHOLM
&&
.AVIATION...
WEATHER CONDITIONS TONIGHT WILL BE HAZARDOUS AS A WINTER STORM
CONTINUES ACROSS THE AREA. WIDESPREAD LIFR TO IFR CONDS WL OCCUR
WITH SN AND BLSN. NW WINDS WL BE STRONG...AVERAGING 25 TO 45 MPH
ALONG AND W OF I 29. SOMEWHAT LIGHTER WINDS WILL BE FOUND IN SW MN
AND NW IA...BUT PERIODS OF SNOW WILL GREATLY REDUCE VISIBILITIES IN
THOSE AREAS. IN THE BLIZZARD WARNING AREA WHICH BASICALLY
ENCOMPASSES THE I 29 CORRIDOR AND POINTS WWD...VLIFR VIS WL OCCUR AT
TIMES. PILOTS NEED TO STAY ABREAST OF AIRPORT CLOSURES IN THIS AREA.
AT THIS TIME...FSD AIRPORT IS EXPECTED TO BE CLOSED UNTIL 10 AM SAT.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
IA...BLIZZARD WARNING UNTIL NOON CST SATURDAY FOR IAZ001-012-020-031.
WINTER STORM WARNING UNTIL NOON CST SATURDAY FOR IAZ002-003-013-
014-021-022-032.
MN...WINTER STORM WARNING UNTIL NOON CST SATURDAY FOR MNZ071-072-080-
081-089-090-097-098.
NE...BLIZZARD WARNING UNTIL NOON CST SATURDAY FOR NEZ013-014.
SD...BLIZZARD WARNING UNTIL NOON CST SATURDAY FOR SDZ038>040-050-
052>071.
&&
$$
