THE BIG PICTURE
My low temperature forecast for November 12 became a
forecasting bust. I predicted a low temperature of 47 degrees,
while the actual low was 51 degrees. The forecasting period for
the WxChallenge on this day was 06Z November 12 to 06Z November 13. The
forecast surface map below valid at 00Z November 13 shows a cold front
was supposed to move through Quillayute earlier in the day; therefore, I
thought the low temperature would occur at the end of the period,
06Z November 13. However, this series of METARS shows the temperature didn't start to fall until after the 06Z deadline.
This is a 48-hour surface forecast valid at 00Z November 13, 2008 which shows a cold front east of Quillayute,
courtesy of the Hydrometeorological Prediction Center.
The reason the temperature didn't fall until later that night was
because the front didn't move as quickly as I thought it would. Below, you can see on the 24-hour forecast image of
700-mb heights and relative humidity valid at 12Z November 12 that the
winds were predicted to blow nearly parallel to the cold front, the ribbon of
high relative humidity, over the Pacific Ocean. Therefore, this
slowed the progression of the front and kept the temperature higher in Quillayute on the evening of November 12.
This is an 24-forecast image of 700-mb heights, relative
humidity and omega valid at 12Z November 12, 2008 that shows winds
blowing nearly parallel to the cold front
which helped slow it down, courtesy of the National Centers for Environmental Prediction.
One important tool I used for predicting the low temperature at 06Z November 13 was these MOS tables from NOAA's Meteorological Development Lab.
They show the temperature at this time would be 48 degrees as
predicted by the GFS and NGM to 45 degrees by the ETA. Also, I
looked at this image of dew points from the SREF at the Storm Prediction Center.
It shows the dew point would be in the mid 40's. With light
rain still expected as indicated by the MOS tables, I thought the
temperature would be near these dew point levels.
After examining the above data, I made a low temperature forecast
of 47 degrees, four degrees too low. Now, I'll tell you some
valuable lessons I learned as a result of this forecast.
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