Spring Flood Outlook & Active Weather Pattern Ahead

Thank you for stopping by the Weather Watch 12 blog.  The next two weeks will likely bring the Midwest several rounds of precipitation as a very active weather pattern takes hold.  With at least two ‘wetter’ systems on deck, the concerns for flooding in the Midwest are growing.

In this blog we’ll look at the current flood threat, and then use the LRC(Lezak’s Recurring Cycle) to pinpoint when some of the wetter storm systems will occur over the Midwest from now through April.

Let’s start with the Spring Flood Outlook.  This was released 2 weeks ago by the Hydrologic Information Center.  With record snows over parts of the upper Midwest this winter, it should come as no surprise that the highest threat for flooding is located over parts of Minnesota and the eastern Dakotas, and then along the Mississippi River south to St. Louis.

Here is why the National Weather Service is concerned about flooding in our part of the country.

Heavy late summer and autumn precipitation(twice the normal amount since October in parts of North Dakota and Minnesota) have left soils saturated and streams running high before the winter freeze-up.  NWS models show this year’s snowpack contains a water content ranked among the highest of the last 60 years.  The combination put a large portion of the North Central United States at risk of moderate to major flooding this spring, extending from northeastern Montana through western Wisconsin and along the Mississippi River south to St. Louis.

Since this map was published, the flood threat has also increased over parts of the eastern Midwest and Ohio Valley.

Now let’s use a weather pattern theory called the LRC, or Lezak’s Recurring Cycle to project forward and pinpoint when wet parts of the pattern will return from now through April over the Midwest.  If you are new to the blog or need a quick refresher, here are the basics of the LRC.

• A unique weather pattern sets up every year between October 1^st and November 10^th
• The weather pattern cycles, repeats, and continues through winter, spring and into summer. Identifying the cycle length helps tremendously when making long range weather predictions.
• Long term long-wave troughs and ridges become established and also repeat at regular times within the cycle. These dominant repeating features are a clue to where storm systems will reach peak strength, and where they will be their weakest.
• The LRC is a winter-long pattern! There is a pattern! It isn’t just one long-wave trough, storm system, or ridge. It is a sequence of troughs and ridges that are cycling across the Northern Hemisphere.

The cycle duration with this year’s pattern is roughly 46-52 days, but most events have consistently repeated around 50 days.  So the forecast made below will use roughly a 50 day cycle to project forward.

Let’s start with the rest of March, and again keep in mind this is for the Midwest!

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Rest of March 2011

March 8-9

A storm system will bring rain and snow to the Midwest.  This will be one of two potentially ‘wet’ storms that could produce 0.50″ or more of precipitation over a large part of the region.  Where colder air is in place, some 6″+ snow totals may occur.  This storm lines up most closely with a storm roughly 100 days ago, or 2 cyles.  That storm moved through around November 29-30.

March 11-12

This part of the pattern will drop a ‘clipper’ type system through the upper Midwest heading into the upcoming weekend.  This storm rolled through back on December 3-4, producing 6.1″ of snow in Minneapolis, and 3.6″ in Milwaukee.  It has repeated in each cycle, but I am referencing early December because I feel the jet stream position is most closely lined up with March.

Below is where the swath of precipitation(mostly snow) lined up in early December.

Here is the where the 18Z GFS computer model is forecasting the swath coming up late this Friday into Saturday.  Pretty amazing, even more is the precipitation on both maps over Maine!

This could be rain or snow, but parts of the upper Midwest will likely see several inchs of snow to start the weekend.

March 19-22

This is hands down the part of the pattern that has produced a major storm, or as I like to say a ‘signature’ storm each time through the cycle.  Keep in mind the cycle starts in the Fall.  The ‘signature’ storm has occurred on the following dates.

• October 26 (Record low pressure readings, very strong winds, severe weather)
• December 10-12 (Blizzards warnings, heavy snow and rain)
• January 31-February 2 (Record setting blizzard hits Milwaukee & Chicago)

This storm will once again repeat and likely produce precipitation totals of 0.50″ to 1.50″.  Areas that see snow could be well over 6″, and I also expect a severe weather component in the warm sector of the storm.  I expect this storm system to impact a large part of the Midwest with rain or snow!

To clarify, this storm has sent a little piece of energy ahead of the main low on a couple of occasions, this may impact western/southwest areas of the Midwest first, then the main piece of energy would follow, likely closer to the 21-22 timeframe.  Some areas east like Chicago, Detroit, and Milwaukee could see effects into the 23rd.  But the key dates to watch are most likely right around the 22nd.

Here is the March forecast specific to southeast Wisconsin that was posted in the blog back on February 27.

March Forecast

We have been talking about this ‘signature’ storm in the blog since January!

March 28-30

Another strong clipper type system will push precipitation through in a narrower band.  I expect total precipitation to stay below a 0.50″ for most locations.

For March, I expect snow totals above average in Milwaukee and Minneapolis.  And think that Minneapolis could be 5″-10″+ above average for the month!

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April Midwest Outlook

April 4-10

During this period I expect a major warm-up with temperatures during the day jumping at least 10 degrees above average for a 2-4 day window.  This warm-up can be traced back to the second week of November, the final days of 2010, and shortly after Valentine’s Day.  I believe this part of the pattern could bring the first 70s to the upper Midwest.

Here is what the 500mb(middle of the atmosphere) map looked like back on December 30.  There was a southwest flow aloft bringing in warmer air.  This southwest flow returned in February, and should again in early April.

Like most big Spring warm-ups, they can come crashing down.  A ‘wetter’ storm should arrive in the Midwest between April 8-11.

April 12-19

Likely quieter period with chances of ‘lighter’ precipitation.

April 20-May 20

The active part of the pattern will once again return.  This roughly 30 day stretch may produce some wild weather across the nation’s mid-section with the bigger storms returning, and warmer air trying to move north.  The result, is a chance of some large severe weather outbreaks.  How far north they push into the Midwest is a question that will be answered within a day or two of each storm system.

I would keep a close eye on April 21-23, April 26-28, and May 6-12.

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Those are the dates that need to be watched closely for ‘wetter’ storms.  Mother Nature can throw curveballs in at anytime, but using the LRC certainly increases our batting average when making long range forecasts.  We will continue to update the flood potential for the Midwest in the coming weeks, but right now it looks like the threat will increase over the next 2-3 weeks.

Please leave any thoughts or questions in the comments section of the blog!

Jeremy Nelson