An observation regarding Florida cold outbreaks

[MiamiensisWx]

I have noticed that the overnight lows in Tallahassee, FL (Leon County) often reflect the magnitude of a cold outbreak elsewhere in the state. For example, a colder low at the capital city (i.e. <14°F) can indicate lower temperatures further south on the peninsula such as the Miami-Fort Lauderdale area. For example, the <14°F reading in Tallahassee supports a low of <40°F in the south Florida metropolitan area. Usually, this scenario is associated with a classical long-lived cold outbreak in the state via a strong shortwave trough and Canadian 500 mb high. Some good examples include January 1977, the 1894-1895 series of freezes (known as the "Big Freeze"), and early 2003. Conversely, a warmer low at Tallahassee (i.e. 22°F or greater) indicates a shorter-lived outbreak or warmer temperatures across the state. Therefore, the low in Miami-Fort Lauderdale is greater than >40°F, often reaching >45-50°F in several cases. The 850-1000 mb (low-level) easterly flow returns faster via a stronger ridge in this latter scenario, thus shortening the cold period or raising overnight lows. The warmer scenario has been more common over the past few winters, especially in south Florida (east coast metro areas).

Regardless, it appears that there is a correlation between the overnight post-frontal lows in Tallahassee and the cold outbreak's magnitude across the peninsula.

Warmer Tallahassee low = short-lived outbreak/warmer across state
Colder Tallahassee low = long-lived outbreak/colder across state

This post is not backed by any expertise, but it is interesting. I would appreciate any input, especially via a professional meteorologist or forecaster from a NWS office in FL (i.e. Tony Cristaldi/AJC3 in Melbourne).

[AJC3]

I have noticed that the overnight lows in Tallahassee, FL (Leon County) often reflect the magnitude of a cold outbreak elsewhere in the state. For example, a colder low at the capital city (i.e. <14°F) can indicate lower temperatures further south on the peninsula such as the Miami-Fort Lauderdale area. For example, the <14°F reading in Tallahassee supports a low of <40°F in the south Florida metropolitan area. Usually, this scenario is associated with a classical long-lived cold outbreak in the state via a strong shortwave trough and Canadian 500 mb high. Some good examples include January 1977, the 1894-1895 series of freezes (known as the "Big Freeze"), and early 2003. Conversely, a warmer low at Tallahassee (i.e. 22°F or greater) indicates a shorter-lived outbreak or warmer temperatures across the state. Therefore, the low in Miami-Fort Lauderdale is greater than >40°F, often reaching >45-50°F in several cases. The 850-1000 mb (low-level) easterly flow returns faster via a stronger ridge in this latter scenario, thus shortening the cold period or raising overnight lows. The warmer scenario has been more common over the past few winters, especially in south Florida (east coast metro areas).

Regardless, it appears that there is a correlation between the overnight post-frontal lows in Tallahassee and the cold outbreak's magnitude across the peninsula.

Warmer Tallahassee low = short-lived outbreak/warmer across state
Colder Tallahassee low = long-lived outbreak/colder across state

This post is not backed by any expertise, but it is interesting. I would appreciate any input, especially via a professional meteorologist or forecaster from a NWS office in FL (i.e. Tony Cristaldi/AJC3 in Melbourne).

Interesting observation. It pretty well logically follows that the colder the air is upstream, the colder that locations farther south will generally get.

My cold wx forecasting 'modus operandi' is a combination of diagnostic and prognostic tools. Often times, the most significant cold outbreaks down here follow as sort of a one-two punch combination, (obviously this is not always the case) - punch one being the first night advection cooldown, while punch two is the second or "radiation" night. First, I like to look at what kind of temps and dew points I have upstream. Obviously upstream temps give you an idea of how cold the air is that is coming toward you, while dew points will give you an idea of how much potential air mass radiational cooling there is, particularly if it looks like conditions will turn out quite favorable for it to occur.

Next, I'll try to to get a good synoptic picture of the pattern aloft via both watervapor imagery and RAOB plots at 500-250MB.

Then I look at the various model forecasts at both the lower levels (SLP and surface/925MB/850MB temp and wind progs) to get an idea of the potential strength/severity/duration of the cold outbreak), and aloft (500 through H250 MB) to get a general idea as to the trajectory of the cold air mass - some plow southward then eastward, some plow straight southeastward, others drop more southward. It is dependent on the orientation, placement and movement of the mid-upper trough, since this is what will "drive" the cold air mass. Also, looking aloft at H250 windspeed/RH/divergence charts will give you and idea as to the potential for jetstreak CI, which can throw a wrench into the 'second night' forecasts.

During a La Nina, I've noticed that the resiliency of the southeast CONUS/western ATLC ridge greatly modulates these cold outbreaks. It generally doesn't allow for full (or nearly full) latitude eastern CONUS troughs to penetrate quite as much or stick around particularly long. This limits the extent of NW flow aloft - the coldest air masses tend to turn or move bodily eastward pretty quickly, which is the death knell for cold outbreaks (especially on the east side of the state) as winds will flop around to onshore.

Don't know if the majority of this rambling diatribe speaks much to your initial observation. I'm sure if you did a rigorous analysis you'd find a significant correlation between TLH min temps AOB ~20F (give or take) and peninsular freezes, though I'm not sure what the exact cutoff temps would be. If you go any farther with this, let me know if I can help you out with data, etc.

[MiamiensisWx]

Tony,

This is the exact response I was expecting. It really contributes to the discussion, although I do know the basics regarding the tools that you utilize, the effects of CAA/WAA (some aspects), proper digestion of model data and MOS at all atmospheric levels, etc. - basically, I'm just searching for hard data, although I am not an expert or meteorologist. I still need to study many basics of meteorology. This post was entirely an opinion-based inquiry regarding my observations, but your entire response and "on-site" overview of the basics is appreciated. Obviously, the effort (at least the project I might consider) would require some math and sleuthing, so I would greatly appreciate any data that you can find. I think more research is needed for the 500 mb setup, low-level dynamics, and history of cold outbreaks (especially historical events in the 1800s-early 1900s) in the Sunshine State. The correlation between TLH lows and the magnitude or duration of cold outbreaks and freezes elsewhere on the peninsula would be very intriguing, but it has been unfortunately ignored for many years.

I have heard that the most significant cold outbreaks in Florida have usually followed the "one/two" punch: the second frontal passage usually ushers the best radiational cooling, while the original (first) passage is 1) stationary (second front via s/w does the "dirty work") or 2) the "first night advection cooldown." Additionally, I have noticed that the type of upstream low/generation and pattern progression often affects the magnitude of cold air intrusion into the Southeast and Florida peninsula. I have noticed that pre-frontal convective initiation over the eastern Gulf of Mexico often is a precursor to a 1) short-lived outbreak, 2) warmer temperatures than expected by the NWS offices, or 3) no measurable outbreak takes place. Do you think this observation is correct? A situation like ex-Olga (western FL) can throw a monkey wrench into those forecasts that anticipate a large scale cold air invasion in FL, especially because the upstream progression often unfolds differently than expected. The smallest variables often influence big forecast busts.

Anyway, my second question asks, "Do you think pre-frontal convective initiation over the eastern Gulf of Mexico often is a precursor to a 1) short-lived outbreak, 2) warmer temperatures than expected by the NWS offices, or 3) no measurable outbreak takes place?"

Thanks for your time. I really appreciate your work at the Melbourne office.

Finally, here is my final question. What are your expectations for this cold event (Tue-Thur) across the Florida peninsula, including my locale in the south Florida metropolitan area? Please feel free to offer a brief synoptic analysis.

Thank you!

[MiamiensisWx]

Bump. Do you have any thoughts regarding this event or my question?

[AJC3]

Tony,

Additionally, I have noticed that the type of upstream low/generation and pattern progression often affects the magnitude of cold air intrusion into the Southeast and Florida peninsula. I have noticed that pre-frontal convective initiation over the eastern Gulf of Mexico often is a precursor to a 1) short-lived outbreak, 2) warmer temperatures than expected by the NWS offices, or 3) no measurable outbreak takes place. Do you think this observation is correct? A situation like ex-Olga (western FL) can throw a monkey wrench into those forecasts that anticipate a large scale cold air invasion in FL, especially because the upstream progression often unfolds differently than expected. The smallest variables often influence big forecast busts.

Anyway, my second question asks, "Do you think pre-frontal convective initiation over the eastern Gulf of Mexico often is a precursor to a 1) short-lived outbreak, 2) warmer temperatures than expected by the NWS offices, or 3) no measurable outbreak takes place?"

Thanks for your time. I really appreciate your work at the Melbourne office.

Finally, here is my final question. What are your expectations for this cold event (Tue-Thur) across the Florida peninsula, including my locale in the south Florida metropolitan area? Please feel free to offer a brief synoptic analysis.

Thank you!

Firstly, thanks for the kind words.

From a synoptic perspective, the scenario you describe - central and eastern GOMEX low/SQLN formation - is usually a result of a short wave moving either southeastward through the northern stream, or moving eastward through the southern stream. When it's a northern stream feature, it usually amplifies along or west of 90W. My experience is that this pattern leads to arctic outbreaks into the southern plains/ARKLATEX/MS valley. While these outbreaks can and do spread eastward, they are usually slower to evolve, less dramatic, and can modify somewhat before reaching Florida. I look for short wave energy that will amplify farther eastward (along/east of 90W) as a precursor to large scale arctic outbreaks over the eastern CONUS and peninsular Florida. This type of pattern usually occurs too far east to provide the right dynamics for GOMEX low/SQLN formation.

For this event, I think the Jan 24, 2003 freeze is a very good analog to use. The synoptic pattern which occurred then is quite similar to what is forecast to occur over the next 2 days. THU morning will yield temperatures well below freezing across the entirety of the peninsula away from the east coast. I have to admit I am not all that familiar with the south Florida urban/suburban area layout, but I would venture a guess at near to just above freezing for the PBI metro area...and M-U30s farther south. Outlying areas of PBC will likely see M-U20s...probably 30-32F for the burbs out to west of FLL-MIA...maybe even a few U20s in spots.

Over the past couple days, I have gone on 'unofficial' record at the office as saying there will be at least one report of some flakes of light snow falling near the coast in our CWA.

[MiamiensisWx]

The local geography affects the Crestview-Tallahassee-Cross City region. The band of sandy soils supports good radiational cooling, thus producing colder overnight lows, especially during calm conditions. The same case can be said for Ocala, FL. It is situated near Ocala National Forest, thus the forested region fosters a microclimate ("cold spot") like the aforementioned areas.

Well, it's time to test this theory. Currently, the projected overnight low for TLH is 26°F. If I'm correct, it would support a "muted" outbreak further south, with warmer lows than originally expected for the east coast metro areas of south FL.

[AJC3]

The local geography affects the Crestview-Tallahassee-Cross City region. The band of sandy soils supports good radiational cooling, thus producing colder overnight lows, especially during calm conditions. The same case can be said for Ocala, FL. It is situated near Ocala National Forest, thus the forested region fosters a microclimate ("cold spot") like the aforementioned areas.

Well, it's time to test this theory. Currently, the projected overnight low for TLH is 26°F. If I'm correct, it would support a "muted" outbreak further south, with warmer lows than originally expected for the east coast metro areas of south FL.

I'm a little confused. THU morning's low in TLH (according to their CCF, which is automatically generated from their grids) is 19F...and 24F for FRI morning. Are you referring to their previous forecasts for early this morning (25F) which wound up being quite a bit colder than what actually occurred (33F)?

[MiamiensisWx]

The local geography affects the Crestview-Tallahassee-Cross City region. The band of sandy soils supports good radiational cooling, thus producing colder overnight lows, especially during calm conditions. The same case can be said for Ocala, FL. It is situated near Ocala National Forest, thus the forested region fosters a microclimate ("cold spot") like the aforementioned areas.

Well, it's time to test this theory. Currently, the projected overnight low for TLH is 26°F. If I'm correct, it would support a "muted" outbreak further south, with warmer lows than originally expected for the east coast metro areas of south FL.

I'm a little confused. THU morning's low in TLH (according to their CCF, which is automatically generated from their grids) is 19F...and 24F for FRI morning. Are you referring to their previous forecasts for early this morning (25F) which wound up being quite a bit colder than what actually occurred (33F)?

Oh, yes... I was referring to their previous forecasts. I didn't notice the updated data.