THE BIG PICTURE

The weather pattern on October 31 was more of a trick than a treat for me, as my high temperature forecast didn't turn out the way I planned.  I predicted the high temperature from 06Z October 31 to 06Z November 1, the time frame outlined by the rules of the WxChallenge, would be 60 degrees, but the actual high was 64 degrees.  Let's start by examining the big picture on this day.  The 24-hour forecast surface map below valid at 12Z October 31 shows a cold front was supposed to be near Green Bay, with an area of high pressure ready to move in behind it.  The lack of precipitation and tightly packed isobars over Wisconsin was a sign the front could be weak.


This is a 24-hour forecast surface map valid at 12Z October 31, 2008 which shows a cold front moving through Green Bay,
courtesy of the Hydrometeorological Prediction Center.

The upper-air pattern was fairly benign, too.  The image below is a 24-hour forecast map of 500-mb heights, wind and vorticity valid at 12Z October 31.  You can see a trough over Hudson Bay in Canada which housed the low pressure system that pushed a cold front through Green Bay.  The lack of a strong trough and associated vorticity near Wisconsin was another sign the front may be weak. Not realizing this is why my forecast busted.


Thisis a 24-hour forecast of 500-mb heights, wind and vorticity valid at 12Z October 31, 2008 which shows a trough east of Hudson Bay in Canada that helped push a
cold front through Green Bay, courtesy of the National Centers for Environmental Prediction.

I based my forecast on the fact that a cold front would be moving through Green Bay on the morning of October 31. One tool I used to make my high temperature forecast was these MOS tables from NOAA's Meteorological Development Lab.  It shows the high temperature on October 31 ranging from 57 degrees as predicted by the ETA to 60 degrees by the GFS.  Also, I looked at these forecasts from the SREF at Penn State's e-wall valid at 18Z and 21Z October 31. They showed the SREF mean having the temperature in the upper 50's.

After looking at this data, I decided to make a high temperature forecast of 60 degrees, but, as I said, the actual high temperature on October 31 rose to 64 degrees.  This became my biggest forecasting error in the first week of the WxChallenge for Green Bay.  In the next section, I'll tell you what I overlooked and what I learned from this busted forecast.


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