02/03/08 to 02/04/08 FCST (Winter WX): IA/MN/WI/IL

January 6th, 2009
  • Another in a series of winter weather systems will bring a mixture of precipitation to the Upper-Midwest towards the end of the weekend. The first wave will bring light snow and freezing rain to the east-central Iowa area. This will be followed by a lull in the precipitation during the morning hours on Monday, and then cold rain will fall Monday afternoon, possibly accompanied with thunder and small hail south of I-80. Following are specific point forecasts for locations in east-central Iowa:

    Cedar Rapids:
    Snowfall will start at 5:30 PM Sunday afternoon and accumulate to 0.8 inches before changing over to light freezing rain at 10 PM. Freezing rain will accumulate to a few hundredths of an inch before it ends at 11 PM and shouldn’t cause more then minor travel problems. On Monday, rain will develop during the mid-day hours and continue until after Midnight Tuesday. Expect 0.25 inches of rainfall.

    Iowa City:
    Snowfall will start at 4:00 PM Sunday afternoon and accumulate to 1.2 inches before changing over to light freezing rain at 8 PM. Freezing rain will accumulate to a few hundredths of an inch before it ends at 11 PM and shouldn’t cause more then minor travel problems. On Monday, rain and a few thunderstorms will develop during the mid-day hours and continue until after Midnight Tuesday. Expect 0.25 inches of rainfall.

    Marengo:
    Snowfall will start at 3:45 PM Sunday afternoon and accumulate to 1.0 inches before changing over to light freezing rain at 7:30 PM. Freezing rain will accumulate to a few hundredths of an inch before it ends at 10 PM and shouldn’t cause more then minor travel problems. On Monday, rain and a few thunderstorms will develop during the mid-day hours and continue until after Midnight Tuesday. Expect 0.25 inches of rainfall.

    Paris/Coggon:
    Snowfall will start at 5:45 PM Sunday afternoon and accumulate to 0.6 inches before changing over to light freezing rain at 10:30 PM. Freezing rain will accumulate to a few hundredths of an inch before it ends at 11 PM and shouldn’t cause more then minor travel problems. On Monday, rain will develop during the mid-day hours and continue until after Midnight Tuesday. Expect 0.25 inches of rainfall.

    Synopsis:
    UA charts indicated a number of disturbances ejecting ahead of a broad WRN CONUS trough. The first S/WV brought a few inches of SN to ERN IA earlier today, and this system appears to have been associated with forcing in the left-exit region of a 130kt H3 max and isentopic lift along the 290K SFC and had little in the way of a SFC reflection. Looking upstream, WV imagery and the H5 chart indicated disturbances over CO and WA/NRN CA. MDLS have a good handle on these features. The SFC map was relatively featureless, with moderating temperatures over IA despite weak NWRLY flow and high pressure. A pressure rise bulls-eye was noted over IL.

    Discussion:
    This is a difficult FCST due to uncertainty of timing and type of winter precipitation and possibly convective precipitation on Monday. The effect of the CO S/WV arrives in the area Sunday afternoon, with precipitation starting as SN from SW to NE. Forcing will be strong but brief as the left-exit region of a 90kt H3 speed max with attendant QG-forcing and isentropic up glide translates through the area. FCST soundings indicate a transition to FZ RA by mid evening, by which time the strongest forcing and QPF will have moved E of the area. ULVL ridging and subsidence will follow and then the main trough will arrive Monday afternoon, bringing a prolonged period of rain with isolated thunderstorms. Moisture will be plentiful as a 50kt LLJ noses into the area during this period. Elevated instability will result from steepening mid-level lapse rates to 7C/km. Small hail will be possible in any vigorous updrafts Monday afternoon in an environment consisting of impressive LLVL helicity and deep-layer shear, especially S of I-80.

    - bill
    10:00 PM CST, 02/02/08


  • The models did incredibly poor with this one. An unforecasted and nearly stationary band of "convective snow" has developed along a line from near Sigourney to Iowa City (where I'm at) to Clinton. We're seeing very rapid snowfall rates along this 10 mile-wide band of enhanced snowfall. At the rate we're going, along with the 4" of new snow having already accumulated since 2 PM, 6-8" total isn't out of the question for Iowa City before the snow winds down during the early evening. I also wouldn't be surprised to see a flash or two of lightning.

    Update - 9 PM CST: precipitation has ended in eastern IA. Iowa City saw 6-8 inches and Cedar Rapids about 1 inch according to spotter reports, which continue to come in. In eastern IA, the winner so far is What Cheer (40 miles WSW of Iowa City), with 13 inches. Below is the KDVN accumulated liquid equivalent.

    http://weather.cod.edu/nexrad/local/DVN/DVN.PRETX.gif

    - bill


  • Looks like elevated thunderstorms/hailers are moving north into the snow band. Very interesting situation. Thundersnow is being reported all over southeast IA and western IL now. Some spotters are reporting visibilities down to less than a few hundred yards!


  • Wow what a snowburst as the warmer air olft over ran the colder air at the surface..we had about 5 inches this evening...quite a bit more then originally forecasted. Now with temps expected near 40 on Monday with rain we should have a good mess here.


  • You said it Bill. The models didn't have this one forecasted well at all. QPF was forecasted in the 0.10-0.20 range by all the 12z models in the area that got that convective snow. What an incredible dump of snow over a relatively short time. Up to a foot of snow fell in 5-6hrs.

    Here in Erie we only received 3.5".


  • Wow, some interesting weather this afternoon with this fast-moving little wave. Someone in Scotland County MO reported 2" of snow in 45 minutes a short while ago. Thundersnow is actually pretty common in northeast MO and southeast IA, moving into IL as we speak. Lightning data is really lighting up (no pun intended lol) over these areas.

    Looks like heavy freezing rain/sleet with thunder is also occuring further south in MO, and moving into central IL. Very interesting little wave.

    It's really interesting noting that temps down in OK are in the 70s. That's not all that far away.


  • According to the NWS in STL, some locations around Quincy, IL have gone from thundersnow to half-inch hail in a short time. This seems to be producing a similar combination of thundersnow, sleet, and hail to the storms around Denver night before last. I actually thought briefly of trying to chase this, but by the time I was aware of it I didn't think I could really get there in time.







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