Bill Schintler
EF4
A fast moving winter storm will bring as much as four inches of snow starting Wednesday morning. Snowfall will taper down to flurries by late afternoon however winds will increase out of the northwest with gusts in excess of 30 mph, resulting in blowing and drifting of the snow. Travel conditions will be treacherous during the evening commute. Looking ahead, a clipper system will bring some minor accumulations on Saturday. Below are specific area forecasts for eastern IA locations:
Cedar Rapids (Eastern IA Airport):
Snow will start at 8:00 AM with a total accumulation of 3.8 inches.
Iowa City:
Snow will start at 9:00 AM with a total accumulation of 3.2 inches.
Northern Linn Co. (Paris and Coggon):
Snow will start at 7:30 AM with a total accumulation of 4.3 inches.
Marengo:
Snow will start at 8:00 AM with a total accumulation of 3.9 inches.
Discussion:
This is a complicated FCST due to subtleties in the phasing of two branches of the jet as well as the possibility of banding of the snowfall. Currently, the Upper Midwest is in a split stream flow with the northern wave overspreading the southern Hudson Bay while an upstream wave is amplifying over the Pacific NW and into the northern Rockies. At the SFC, a CF of Arctic origin will dive SE and sweep through all of ERN IA by 12Z. Post-frontal snowfall will develop in a zone of strong SFC-H7 frontogenetical forcing beneath an increasingly amplified H5 L/WV. Large scale assent will be enhanced beneath the right entrance region of a 130kt H3 streak. An H85 wave will develop over NRN OK and travel NE along the front during the day. This degree of lifting suggests banded structures and possibly even some convective snow, with locally enhanced higher rates. The storm motion will be progressive; however, there exist the possibility for a few hours of 1-2 inch/hour of snowfall rates within banded structures. I’ve gone with a snow to water ratio of 12:1, with the possibility for higher ratios verifying. The latest models (WRF, GFS, SREF) are advertising increased dendritic growth and higher snowfall amounts with the post-frontal precipitation.
The other feature of this system will be gusty northwest winds as the SFC-H85 gradients tighten. Temperatures will fall during the day Wednesday as strong CAA overspreads the area.
- bill
3:32 PM CST, 12/02/08
Cedar Rapids (Eastern IA Airport):
Snow will start at 8:00 AM with a total accumulation of 3.8 inches.
Iowa City:
Snow will start at 9:00 AM with a total accumulation of 3.2 inches.
Northern Linn Co. (Paris and Coggon):
Snow will start at 7:30 AM with a total accumulation of 4.3 inches.
Marengo:
Snow will start at 8:00 AM with a total accumulation of 3.9 inches.
Discussion:
This is a complicated FCST due to subtleties in the phasing of two branches of the jet as well as the possibility of banding of the snowfall. Currently, the Upper Midwest is in a split stream flow with the northern wave overspreading the southern Hudson Bay while an upstream wave is amplifying over the Pacific NW and into the northern Rockies. At the SFC, a CF of Arctic origin will dive SE and sweep through all of ERN IA by 12Z. Post-frontal snowfall will develop in a zone of strong SFC-H7 frontogenetical forcing beneath an increasingly amplified H5 L/WV. Large scale assent will be enhanced beneath the right entrance region of a 130kt H3 streak. An H85 wave will develop over NRN OK and travel NE along the front during the day. This degree of lifting suggests banded structures and possibly even some convective snow, with locally enhanced higher rates. The storm motion will be progressive; however, there exist the possibility for a few hours of 1-2 inch/hour of snowfall rates within banded structures. I’ve gone with a snow to water ratio of 12:1, with the possibility for higher ratios verifying. The latest models (WRF, GFS, SREF) are advertising increased dendritic growth and higher snowfall amounts with the post-frontal precipitation.
The other feature of this system will be gusty northwest winds as the SFC-H85 gradients tighten. Temperatures will fall during the day Wednesday as strong CAA overspreads the area.
- bill
3:32 PM CST, 12/02/08
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