Frost Advisories & Freeze Warnings Posted For Our Area! How Cold Will It Get?
The is the first time in our fall 2012 season that we have seen widespread freeze warnings in our area. The NWS has made a few adjustments to the counties, so I wanted to update you and talk about the setup.
Cold Weather Setup
Clear skies, light winds and low dewpoints define the coldest nights in our area. When you get all three of these conditions occurring at the same time, we ultimately have chilly readings. Looking at the setup, we would need to see dewpoints below 32 to allow temperatures to drop below the freezing mark tonight. Notice many are at 32 degrees and Evansville has a dewpoint in the 20s right now.
Next, we would need clear skies across our area and the regional satellite shows plenty of clear skies across the area.
Finally, we need light winds so let's look at the current winds in our area.
The winds are not light, so how are we going to go into MAX cooling mode? That would be a legit question to ask and when we look at the setup tonight, we see a high pressure sitting right on top of us by Thursday morning and that will insure light winds tonight.
My Thoughts On A Frost/Freeze
The data suggests we will go into MAX cooling mode very quickly after sunset. This setup allows for radiational cooling which simply means the earths heat will escape to space with no resistance. The NWS recognizes this and has place the eastern half of our area in a freeze warning and the western half in a frost advisory.
I like the placement of each advisory. In case you weren't sure the definition of a freeze warning, let me share the official definition from the NWS...
Freeze Warning - Widespread temperatures below freezing are expected during the growing season.
Note there is a difference between a freeze warning and a true hard freeze. A hard freeze occurs when temperatures go below freezing for at least 4 hours and traditionally defines the end of the growing season. For allergy sufferers, this is normally ends the worst part of the year for you.
As we look at the data tonight, you can see the NAM is the coldest. Since the NAM is one of the truly superior models when it comes to cold nights, I would weigh its solution best. The NAM has superior low level resolution and it can resolve max cooling events better. I want to show you the suite of models for the night, so keep in mind the name of the model / timestamp is in the top right part of each image.
It is simple, if you have any plants that are sensative to a freeze, then you must cover or bring them inside tonight. If you roll the dice and just hope, there is a high likelihood they will have freeze burn or the cold could kill the plants.
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