Winter Storm Discussion (Dec 8-9)
ISSUED: 00z 12/08/09 VALID: 00z 12/10/09
A MAJOR WINTER STORM WILL TRACK ACROSS THE CENTRAL U.S. AND MIDWEST THROUGH WED. PROVIDING HEAVY SNOW AND BLIZZARD CONDITIONS...
DISCUSSION:
The calm before the storm...a significant winter storm is forecasted over the next 48 hrs. across the midsection of the country. Already, the disturbance that will cause major weather problems in the coming days is taking shape in the 4-corners region of the U.S. This disturbance will eject out of the western U.S. trough as cyclogenesis occurs off the eastern Rockies later tonight. This surface low-pressure system will continue to develop and become a mature and dynamic mid-latitude cyclone and track across the Central Plains into the Midwest along a tight baroclinic zone through 12z Wed. Gulf moisture will be feeding into this low pressure system causing a severe weather episode across the Deep South where instability and moisture will be key and on the cold-side of the storm a blizzard for portions of the Midwest. Expect isentropic lift and WAA to begin in earnest in the plains later tonight moving into our area in the morning. Initial precip will struggle with an initial dry atmosphere in place, but the column will quickly saturate during the morning and snow will begin northwest and southwest of Moline, IL and in all areas by afternoon. Precip should begin in snow in most areas. Northwest of a Burlington, IA-to-Moline, IL line should stay all snow during the entire event. QPF at or above an inch of liquid precipitation forecasted by models using a 10:1 snow ratio suggests many areas reaching 8-12" + in central and eastern Iowa extending toward southern Wisconsin. A mix of precip south of I-80 in Illinois will trim totals 4-8" in most areas with some light ice accumulation. This will be due to the warm conveyor belt allowing warm air to surge into the deepening surface cyclone. A messy mix of all forms of precipitation will be found in this area as the low-pressure nearly tracks overhead as most bufkit profiles from the NAM and GFS support this conclusion. Track of the system should be over central Illinois to just south of Chicago by 12z Wed. Deformation zone axis should be confined to central and eastern Iowa extending into southern Wisconsin. The low pressure deepens to near a whopping 980mb at this point and with a tight pressure gradient expect high winds sustained 20-30 mph with gusts near 50mph causing intense blowing and drifting snow and blizzard conditions in all areas that received snowfall. Cold air will filter into the area as well with strong CAA and a fresh snow pack in place support frigid temps in the singled digits with wind chills well below zero. A powerhouse of a storm no doubt!
Travis Carlson
TornadoVortex.net Storm Chaser/Photographer
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