FXUS63 KFSD 111845
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1245 PM CST THU MAR 11 2010

.DISCUSSION...
HEAVIER PRECIP BAND HAS MOVED WEST OF I-29 AS OF 18Z...AND WILL
CONTINUE TO PUSH WEST AHEAD OF MID LEVEL DRY SLOT THROUGH THE
AFTERNOON. AS EXPECTED...HEAVIER INTENSITY PRECIP CHANGED TO ALL
SNOW...WITH ACCUMULATIONS ON THE ORDER OF 1/2 TO 1 INCH FROM REPORTS
AND APPEARANCE ON WEBCAMS AROUND THE AREA SO FAR. MAIN CONCERT
THROUGH THE AFTERNOON/TONIGHT IS WHETHER PRECIP WILL REMAIN SNOW IN
RIBBON OF COLDER AIR ALOFT INDICATED BY MOST MODELS THROUGH THE
JAMES VALLEY INTO EXTREME NORTHEAST NEBRASKA. WOULD THINK WITH ONLY
VERY SHALLOW NEAR SURFACE LAYER ABOVE FREEZING...MOST OF THE PRECIP
IN THIS AREA WILL BE SNOW...WITH POSSIBLE EXCEPTION OF LOWEST VALLEY
ELEVATIONS ALONG THE JAMES RIVER...THOUGH PRECIP TYPE DID BEGIN AS
SNOW IN BOTH KHON AND KMHE...SO EVEN VALLEY AREAS COULD SEE MAINLY
SNOW. BUMPED SNOW AMOUNTS IN THE WEST JUST A BIT FROM PREVIOUS
FORECAST WITH POTENTIAL FOR RAIN LIMITED...AND ALSO ADDED A FEW
COUNTIES WITHIN THAT RIBBON OF COLDER AIR ALOFT...FROM THE LOWER
JAMES RIVER INTO DIXON COUNTY NEBRASKA...TO EXISTING WINTER WEATHER
ADVISORY WITH LATE MORNING UPDATE.

CONCERN FOR THE REST OF THE NIGHT IS HOW FAR WEST THE DRY SLOT WILL
WRAP...AS THIS COULD END UP LIMITING SNOWFALL AMOUNTS IN EASTERN
PARTS OF THE ADVISORY. WILL TAKE A CLOSER LOOK AT THIS FOR THE
AFTERNOON FORECAST ISSUANCE.

&&

.AVIATION...
GENERAL IFR CIGS...AND IFR/MVFR VSBYS EXPECTED ACROSS THE AREA
THROUGH TODAY. TEMPERATURES APPEAR WARM ENOUGH THROUGH MOST OF THE
I-29 CORRIDOR EASTWARD THAT MAIN PRECIP TYPE WILL NOW REMAIN LIQUID
THROUGH THIS EVENING. GREATER POTENTIAL FOR SOME SNOW MIXING WITH
THE RAIN FROM KSUX AREA INTO NORTHWEST IOWA LATER TONIGHT...AS
COLDER AIR WRAPS IN SOUTH OF THE TIGHTLY WOUND UPPER LEVEL SYSTEM.
MOST LIKELY AREA TO SEE ALL SNOW IS JAMES VALLEY WESTWARD...WHERE
GREATER ACCUMULATIONS ARE LIKELY THROUGH THE AFTERNOON AND EVENING.
WINDS GUSTS TO 25-30 KTS WEST OF THE JAMES VALLEY AS WELL...WILL
CAUSE FURTHER REDUCED VSBYS IN SOME BLSN AS SNOW MOVES INTO THE AREA
AFTER 21Z.

&&

.PREV DISCUSSION...
A REAL MESS OF A FCST FOR THE NEXT 24 TO 36 HRS ACRS THE CWA. MAIN
PBLM WILL BE TODAY AND TONIGHT WITH PRECIP TYPES. WARM ENUF E OF I29
THAT PRETTY SURE PRECIP WL BE IN THE FORM OF RAIN...PSBLY MXED WITH
A LTL SNOW EARLY THIS AM. HWVR...ALONG AND W OF I29 IS A DIFFERENT
STORY. GFS/NAM CONT TO INDICATE THAT LAYER WL REMAIN COLD ENUF FOR
SNOW CHANGING TO RAIN E OF THE JAMES VALLEY BY AFTN. RUC ON THE
OTHER HAND SHOWING THE LAYER WL BE WARM ENUF FOR RAIN XCP SNOW JAMES
VALLEY WWD. CONSIDERING THIS IS STILL MARCH...CONVECTIVE PRECIP WITH
THE MARGINAL SOUNDINGS WUD GO OVER TO SNOW. LARGE AREA OF PRECIP
MOVG NWWD THRU IA AND WITH LAYER SO CLOSE TO SNOW...ANY HEAVIER
BANDS OF CONVECTIVE PRECIP CUD COOL THE LAYER ENUF TO PRODUCE BANDS
OF MOD SNOW. THIS IS IMPLIED WITH THE FAIRLY IMPRESSIVE H85 FNTLGEN
THAT WRAPS WWD ACRS CWA TODAY WEAKENING A BIT AS IT MOVES INTO JAMES
VALLEY AND REMAINS WEAK OVR THE JAMES VALLEY THRU TONIGHT. SO WL
NEED TO MENTION AROUND 2 INCHES OF SNOW ALONG THE I29 CORRIDOR WITH
2 TO 5 INCHES TO THE WEST. WITH WINDS ALSO EXPECTED TO BE STRONGER
ACRS WRN CWA...WL ISSUE A WINTER WX ADVY JAMES VALLEY WWD FROM 8Z
TODAY THRU 12Z FRI. CUD BE AN INTERSTING DAY AND WL NEED TO WATCH
TRENDS FOR RAIN CHAGNING TO SNOW ACRS ERN NEB THIS MORN. MAY NEED TO
ISSUE ADVY ALONG I29 CORRIDOR THIS MORN IF SNOW BECOMES HEAVIER.

UPPER LOW WILL CONT TO ROTATE ACRS IA/MO AND IL THE NEXT FEW DAYS
WHICH WILL WRAP BANDS OF PRECIP WWD ACRS CWA INTO SAT. THE MAIN
SURGE OF HEAVIER PRECIP WL BE TODAY AND PBLY WL NOT BE AS WDSPRD E
OF I29 TONIGHT WITH MORE WDSPRD PRECIP FURTHER W IN AREA OF WEAK
TROWAL. SO WL DROP POPS TO CHC TONIGHT E OF I29 AND KEEP HIGH POPS
GOING W.

FRI IS ALSO INTERSTING AS SOUNDINGS AGAIN CLOSE TO R/S ACRS CWA AND
IF HEAVIER PRECIP DOES WRAP AROUND...CUD AGAIN SEE CHANGEOVER TO
SNOW. IF THIS DOES OCCUR...THE BEST CHC FOR ACCUM SNOW ON FRI CUD BE
ALONG THE I29 CORRIDOR DURING THE MORN.

DIRURNAL RANGE IN TEMPS WL NOT BE MORE THAN 5 DEG ACRS CWA THRU FRI
WITH CLOUD COVER AND PRECIP. WL TREND FOR COOLER HIGH TEMPS THRU
WEEKEND AS NOT MUCH SUN EXPECTED. WL KEEP POPS GOING ALL THE WAY
THRU SAT...AND CAN NOT RULE OUT A FEW SPRINKLES E ON SUN. ALL AND
ALL A RATHER DREARY NEXT SEVERAL DAYS WITH WINTER NOT GIVING UP
ESPEC ALONG AND W OF I29.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
MN...NONE.
NE...WINTER WEATHER ADVISORY FROM NOON TODAY TO 6 AM CST FRIDAY FOR
NEZ013.
SD...WINTER WEATHER ADVISORY FROM NOON TODAY TO 6 AM CST FRIDAY FOR
SDZ038-050-052-053-057>059-063>065-068-069.

&&

$$



Back to Main Forecast Discussion Page