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Average First Frost

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Matthew92

From Mobile NWS discussion (forecast area includes as far east as Okaloosa Country)

Area Forecast Discussion...CORRECTED
National Weather Service Mobile AL
1225 PM CST Mon Nov 30 2020

Deep layer dry air will overspread the region tonight into
Tuesday. Lingering clouds over our northeast zones should decrease
into the early-mid evening hours, with generally clear skies
otherwise anticipated tonight into Tuesday. Surface high pressure
also gradually builds eastward across the Gulf Coast states late
tonight into Tuesday. Northwesterly winds should gradually
decrease tonight. Clear skies, dry air, and cold advection will be
supportive of the first widespread freeze of this season and the
Freeze Warning continues for all zones tonight. Lows are still
forecast to range from 25-30 across locations especially along and
north of Interstate 10, and in the lower 30s along the immediate
coast. The only places that may stay above freezing are along the
barrier islands, where winds remain elevated. Highs Tuesday remain
well below normal in the lower to mid 50s. /21
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JJPalmer

Has a ‘Winter 2020-2021’ thread been established? Feel like a full thread dedicated to documenting cold plunges / microclimates could be useful instead of searching for one-off events. 

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chinandega81
9 hours ago, JJPalmer said:

Euro vs GFS vs NAM for 7AM Wednesday morning. 

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Which one of those models is the most reliable? Please don't say the coldest one...

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JLM

None of these models this year have been reliable. With the lack of air travel, less data is being put into each model run.

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JLM
5 hours ago, Matthew92 said:

From Mobile NWS discussion (forecast area includes as far east as Okaloosa Country)


Area Forecast Discussion...CORRECTED
National Weather Service Mobile AL
1225 PM CST Mon Nov 30 2020

Deep layer dry air will overspread the region tonight into
Tuesday. Lingering clouds over our northeast zones should decrease
into the early-mid evening hours, with generally clear skies
otherwise anticipated tonight into Tuesday. Surface high pressure
also gradually builds eastward across the Gulf Coast states late
tonight into Tuesday. Northwesterly winds should gradually
decrease tonight. Clear skies, dry air, and cold advection will be
supportive of the first widespread freeze of this season and the
Freeze Warning continues for all zones tonight. Lows are still
forecast to range from 25-30 across locations especially along and
north of Interstate 10, and in the lower 30s along the immediate
coast. The only places that may stay above freezing are along the
barrier islands, where winds remain elevated. Highs Tuesday remain
well below normal in the lower to mid 50s. /21

That discussion covers everywhere from the Okaloosa/Walton line to parts of Mississippi. I sometimes get confused, which is worse, and advective or radiative freeze? I would assume radiative?

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kinzyjr
12 minutes ago, JLM said:

That discussion covers everywhere from the Okaloosa/Walton line to parts of Mississippi. I sometimes get confused, which is worse, and advective or radiative freeze? I would assume radiative?

It depends to some degree on the particular plant's tolerance to frost, but in my case, I would go with the advective freeze. 

The worst effect of a radiational freeze for most tropical plants is frost.  This is mostly mitigated by overhead canopy.  The air is also very stratified during a radiational freeze.  You may measure 28F at 6 feet, but if you put another weather station at the top of a telephone pole it might be at or near 40F.  This is one reason why you see large, tall palms survive radiational freezes.  @sonoranfans has written about this quite a bit.

Advective freezes are a completely different bird.  They typically don't leave frost due to the air movement of the winds blowing, but the damage is relatively asymmetric with the actual air temperature.  The advective freeze in 2018 caused some of my sea grapes to drop leaves at 28F.  I've had lower temperatures during radiational events before and not had a single leaf turn brown.  The air is well mixed, so you won't have the temperature difference between 6 feet and 30 feet that makes the weather a little more bearable for large palms.  Then there is the wind chill.  What really matters is the temperature of the bud.  If it lives, the palm lives.  During 2018, I had very breezy conditions all night.  15-20MPH sustained winds with gusts in the 30MPH range.  That will cool off the bud a lot faster than a very still night at 26F.  A good defense against an advective freeze is to shield your plants from the north and west winds (on the east coast), either with dense shrubs/bamboo or putting them tight against a brick wall. 

You'll notice on the Remarkable Palms of Tampa Bay thread that a lot of our "shouldn't grow here" stuff in Lakeland is relatively close to a concrete wall that faces south or east in the city's interior.  Done 100% on purpose to mitigate freeze events.

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JLM

Sounds like i might want to wrapand plug in the christmas lights on my queens anyway. Wind chills 20-30 could be deadly.

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Jeff985

I took some screenshots at around 5:30 am. Looks like I bottomed out at around 39. Tonight’s forecast low is 60. Proximity to water definitely made a difference, as did the UHI. Most of them are Texas, but I grabbed a few of Florida. I believe this is supposed to be worse for Florida tomorrow so I’ll do it again then. 

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JLM

@JJPalmer i would say the GFS is probably a good bet.

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