Northern FL Freeze: 22 December 2012

Hard freezes that extend deep into the FL Peninsula are a high-impact event because of the impact they can have on the citrus crop and the FL economy. The NWS WFO from Tallahassee has been using the analog impact guidance over the last few days. In fact, they mentioned it in the long-term section of their AFD 3 days before the upcoming event.


000

FXUS62 KTAE 190819
AFDTAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
319 AM EST Wed Dec 19 2012

.LONG TERM [Friday Night through next Wednesday]...
The extended period will begin (Friday Night) with a freeze likely areawide. This would be the first notable freeze in nearly a month, with the last event occurring on November 26th. Since that time it has been fairly warm, with the average temperatures at TLH averaging about 6.1 degrees above normal. CIPS analog guidance suggests an 80-90% probability of a freeze over our area, and MOS guidance is in good agreement with sub-32 degree temperatures. The center of the surface high pressure is not expected to build into the area until late Saturday, so there is likely to be some slight wind until the pressure gradient relaxes. Wind chills in the eastern half of the area could dip close to 20 degrees.


The analog guidance based on the 36-h NAM forecast (20121221/0000) shows that a pattern similar to the one forecast has a history of sub-freezing temperatures well into the Tallahassee forecast area and into the FL Peninsula.

But how far south will the subfreezing temperatures extend? Ranking the top 15 analogs by the 2-m temperature guidance to find the most similar historic surface temperatures to the forecast may shed some light on this.

When doing this, the top analog (22 November 2000) and the third analog (26 November 2008) both have sub-freezing temperatures that extend further south than what the impact guidance shown above suggests.

However, the second analog (when ranked by the 2-m temperatures) does not.

The reason for this is the relatively higher dewpoints on 6 January 2001 across the FL Peninsula when compared to the forecast.

Yet another quick example of how important it is to use the individual analogs with the impact guidance based on the top 15 analogs.