10:30am UPDATE: Walking A Very Fine Line

watchA still complicated forecast remains just that, with a thin separation between rain and snow over the next 36 hours spelling the difference between small amounts of snow and a heavy snow event.  Current thinking by the National Weather Service indicates much of the precipitation that falls early on Saturday will be in the form of rain.  This will greatly reduce the expected snow totals over Iowa. 

The reason for this is a more northerly track now expected for the storm system.  Eventually, precipitation will changeover to snow and the winds will increase, creating the threat of blizzard conditions.  With that in mind the National Weather Service has issued a Blizzard Watch for portions of northern Iowa.  You can see those counties in the map to the right highlighted in green.  Areas shaded in blue remain under a Winter Storm Watch.  Areas of Minnesota and Wisconsin shaded in pink are under a Winter Storm Warning.

sref_b2m_030sTake a look at the graphic to the left.  This is from the 9Z SREF computer model.   This is the forecast model’s projected temperatures as of 9am Saturday. You can see much of eastern Iowa is expected to be above freezing even tomorrow morning.  Sometime before noon we expect that to change, but by then most of the moisture will have fallen.  You can also see how quickly temperatures will crash on the back side of this storm system.  Don’t be too alarmed by the negative numbers.  Remember that’s the temperature below FREEZING, not zero.

This remains a very fluid situation.  In the days leading up to this Saturday storm it seems the forecast has changed dramatically about every 12 to 24 hours.  I still feel there will be a period of rough travel for many in the state during the day and night on Saturday.  Temperatures are also expected to crash behind this storm system, with lows falling well below zero.

So here’s the predictions for this storm.  If the temperature forecasts are correct and it takes this storm longer to begin producing snow, 1-4” is possible in areas under the Winter Storm Watch.  The highest totals should fall the closer you are to the Minnesota border.  Areas to the south of Highway 20 should see a trace to 2” of snow at most.  But again, there is a very fine line between rain and snow with this system and a quicker changeover to snow will alter the forecast rather quickly.

One other thing to keep in mind, wind gusts in excess of 40mph will be out of the north on Saturday, this will cause blowing and drifting of snow as well as reduced visibilities regardless of how much snow falls. 

We’ll post another update later this afternoon whether there’s a change in the forecast or not.  And we’ll continue to monitor the track of this storm over the next 12 hours and post additional updates when and if needed.  At this time we still plan to conduct a live chat session Saturday as the storm moves through.

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