"But seeing they could not See; hearing they could not Hear"
“The views expressed herein are those of the author and do not necessarily represent those of the National Weather Service or affiliate/related organizations. Please consult .gov sites for official information”

"From its chamber comes the whirlwind, and cold from the scattering winds." - Job 37:9.

"The wind blows to the south and turns to the north; round and round it goes, ever returning on its course".

Thursday, December 2, 2010

Drainage Flow and Florida Cold Snaps

Image shows morning dewpoint temperatures are down to a chilly and cold purple color, which is defined by the scale on the left side of the image.

RECAP: A cold front swept down the state yesterday producing little in rainfall over the Peninsula, although the spectacle created by its leading edge was somewhat impressive to view as sunrise approached coexistingly. Almost equally inspiring was the sharp clearing line that ensued around noon time. It's all water under the bridge now though as a mid-upper level trough will persist over the eastern 1/3 of the nation for the next 7-10 days.

TODAY: Dry and cool! See image above which shows the dew point temperatures. I like this depiction because it really points out those areas that are most prone to getting the coldest during the winter, which began climatically speaking yesterday. Note the cold spots around Punta Gorda and along the West Coast, all of the Panhandle, and north side of Lake Okeechobee. The warmest area is from Cape Canaveral south along A1A to Miami. Even Kendal in extreme South Florida often gets colder than Cocoa Beach. Pretty bizarre. Which leads to a topic in particular:

DRAINAGE (FLOW): You will see this term referred to in many a discussion during the winter...although it can be applied to as a temperature marker at almost any given time of the year; but it is during the winter that drainage flow has the greatest and most notable impact, undoubtedly to the citrus crop.

Drainage flow of cold air occurs on evenings under pristinely clear skies and dead calm winds. Cold air flows down the 'spine' of the state over the cooler land mass (than the surrounding waters) the whole way to Kendal. The immediate coastline such as along A1A corridor and all of the Florida Keys doesn't really feel the direct impact due to the intracoastal and/or the Atlantic Ocean waters. Clear skies allow any heat generated during the day to dissipate back into the atmosphere (whereas cloud cover at night acts as a blanket), and calm winds prevents mixing, or allows the atmosphere to "mix out"..think of it as that the molecules are all excited and rubbing up against each other creating 'heat' when it is windy.

Thus, when little to no wind and clear skies combine, and likely the affects of gravity and the Coriolis Force (perhaps) permitted to act without opposing outside influence "drainage flow" takes center stage. Net affect is the penetration of cooler/colder down the landmass to the most southern extent away from any bodies of water. Thus, Kendal's low temperatures often undercutting those locations much further north but closer to the Atlantic. The drier the overall air mass is the lower the dewpoint goes, and the lower the ambient air temperature can go as well. Thus, it is during the winter time when dew point temperatures fall the lowest, combined with drainage flow conditions, that sends even the Snow Birds on migration to the equator (in the most extreme, rare case situations).

QUIZ: Do you think Drainage Flow was the main reason the temperature was so cold toward Kendal and Punta Gorda this morning? If not, why?

THIS AFTERNOON: NNW-NW winds to continue as the cold air advection continues. Clear sky with a high struggling to reach the mid-60s. Temperatures begin to fall again 1 hour before sunset, during which will probably be quite a nice looking one. Might try for some photos tonight, but more likely Friday night.

FRIDAY: Another chilly start to the day with lows in the panhandle once again in the mid-upper 20s in some locales and gradually warming to the low 40s the further south one gets. The extreme east coast from the Air Force Station to Miami will again be the warmest in the state, not disguarding the Keys of course which are surrounded by modifying ocean water temperatures (cheaters!). High again unlikely to reach 70F.

SATURDAY-MONDAY: Only a slight warm up. Fall, and for that matter, early winter is here to stay. No rain with sunny days and lighter winds with each progressive day after today.

TUESDAY: Incoming re-enforcements of cold air! What? But we never got warm! So it is. A broad, deep trough of mid-upper level low pressure will presist over the east 1/3 to 1/4 of the country (mainly east of the Mississippi) for the next 7-10 days. As such, storm systems will continue to carve a path along and around the base of the trough, at which Florida is the recipient base. However, by the time these 'shortwave' systems reach Florida they are of a very weak moisture profile nature and yield neigh but some clouds as they pass over. Cold air on newly refreshed NW winds harbors in continued surges of cold Canadian air.
So far, Wednesday looks to be the peak of the cold spell, or maybe more appropriately, the bottom.

WEDNESDAY AND BEYOND: Oh yes, the great 'beyond'. What evil lurks in the mind of Old Man Winter? No need to prepare the chains and snow plows down here just yet, and perhaps the tanning oil will be needed as a stocking stuffer as we head toward Christmas if that's an indication of my hopeful ambitions concerning the unforeseeable future. For now though, it could actually warm a spell just in time for Christmas. No big storms / rainmakers are on the horizon, so the next topic of concern beyond possible freeze conditions next week (one of many to come) will be spreading drought conditions by the time late February rolls around and resultant Fire Weather.

Oh, almost forgot. The answer to the quiz is 'no'. We had too much wind state wide for "drainage flow" by definition to be the main reason it was so cold down there this morning. Now, in a day or two, the answer will be 'yes' as winds subside and we will see some pretty sharp temperature gradient boundaries become established by the numbers therefrom.

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