This came from the NWS in Des Moines. It’s very techinical, but really shows how big the second storm Tuesday into Wednesday could be.

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
347 AM CST SUN DEC 6 2009

…MAJOR WINTER STORM SET TO AFFECT IOWA ON TUESDAY AND WEDNESDAY…

.SHORT TERM /TODAY AND TONIGHT/…
MAIN ITEM OF INTEREST DURING THIS PART OF THE FCST PD IS THE
APPROACHING WINTER WX SYSTEM LATER TODAY. -SN IS EXPECTED TO BEGIN IN THE WESTERN CWA BETWEEN 18Z-00Z…AND SPREAD EASTWARD TO AFFECT THE ENTIRE CWA BY 00Z. ALTHOUGH SNOW AMOUNTS WILL BE RELATIVELY LOW
/1 TO 4 INCHES/…HAVE DECIDED TO ERR ON THE SIDE OF CAUTION AND ISSUE A WINTER WEATHER ADVISORY IN CONJUNCTION WITH THIS SYSTEM. MAIN REASONING IS THAT FOR MUCH OF THE CWA…THIS WILL BE THE FIRST WINTER WX SYSTEM WITH MEASURABLE SNOWFALL…ESPECIALLY FROM HWY 20 SOUTHWARD INCLUDING THE DES MOINES METRO AREA. THE SNOW IS EXPECTED TO BE ENOUGH TO CAUSE SOME TRAVEL ISSUES…DUE MAINLY TO SLICK ROADS. SYSTEM WILL WEAKEN AS IT MOVES EASTWARD ACROSS THE CWA. BLOWING AND DRIFTING SNOW IS NOT EXPECTED TO BE MUCH OF AN ISSUE.

.LONG TERM /MONDAY THROUGH SATURDAY/…
MONDAY MAY SEE SOME LINGERING FLURRIES IN FAR EASTERN AREAS EARLY IN THE DAY…HOWEVER FORCING WL DIE OFF QUICKLY AS SFC RIDGING BUILDS INTO THE MISSOURI RIVER VALLEY. HOWEVER…ATTENTION WILL BE TURNING TO A MAJOR SYSTEM THAT WILL AFFECT THE CENTRAL US ON TUESDAY AND WEDNESDAY. ALL MODELS SEEM TO BE LINING UP ON A FINAL SOLUTION WHICH TAKES A SFC LOW FROM EASTERN COLORADO THROUGH MISSOURI AND INTO INDIANA DURING THAT TIME. 00Z EURO IS PARTICULARLY OMINOUS WITH SFC LOW DEEPENING TO 976MB BY 12Z WEDNESDAY AND TO A LESSER EXTENT ON THE GEM AND GFS. AT THIS POINT…IT APPEARS TO BE A LONG DURATION SNOWFALL EVENT OF 24 TO 30 HOURS OVER PORTIONS OF THE CWA WITH NAM/GFS AND EURO ALL SPITTING OUT OVER 1 INCH OF QPF ACRS SOUTHERN IA. COBB OUTPUT ON SNOWFALL RANGED FROM OVER 15 INCHES IN THE SOUTH TO AROUND 8 INCHES IN THE NORTH. IN ANY CASE…IT APPEARS THAT MUCH OF THE STATE WILL SEE WARNING CRITERIA SNOWFALL. THE MORE WORRISOME ASPECT OF THIS STORM IS THE AFOREMENTIONED DEPTH OF THE LOW. SHOULD THE EURO BE CORRECT…WE WOULD SEE BLIZZARD CONDITIONS ACRS THE CWA LATE TUESDAY NIGHT THROUGH WEDNESDAY AFTERNOON. EURO 925MB WINDS AT 12Z ON WEDNESDAY WERE 50+KTS WITH SFC WINDS APPROACHING 35KTS. GIVEN THE AMOUNT OF SNOWFALL…THESE WINDS WOULD PRODUCE WHITEOUT CONDITIONS WITHOUT MUCH OF A PROBLEM. HOWEVER…EURO REMAINS THE STRONG OUTLIER WITH OTHER MODELS SOMEWHAT WEAKER…YET STILL QUITE STRONG IN OVERALL DEPTH. WILL HIT HWO VERY HARD AND ANTICIPATE THAT WATCHES WILL BE ISSUED LATER TODAY. THE EURO SOLUTION WOULD PRODUCE THE WORST CONDITIONS IN THE STATE SINCE THE MARCH 1ST BLIZZARD OF 2007 THAT AFFECTED MUCH OF WESTERN AND NORTHERN IOWA. AFTER SYSTEM PASSES…WL SEE COLD AIR ENTRENCHED ACRS THE STATE FOR MUCH OF THE REST OF THE WORK WEEK ALONG WITH RELATIVELY DRY CONDITIONS.