Four days ago, a strong cold front plowed through Florida, dropping temperatures dramatically (Fig. 1). In almost as rapid a time frame, the mercury rebounded (Fig. 2 and Fig. 3). Well, it’s time for a replay of the wild roller coaster temperature pattern. Today’s temperature graph (like those displayed in Figures 1 to 3 in meteogram format) is going to look a lot like Figure 1. By Wednesday (Jan. 8), look for a repeat of Fig. 2. By later in the week, daily temperature traces will again resemble those shown in Figure 3
These up and down swings in temperature are linked to a series of strong high-pressure systems moving southeastward from Canada and being heralded by correspondingly strong cold fronts. Initially, winds from the north or north-northwest blow straight down the Florida peninsula (Fig. 4), limiting any oceanic warming.
However, usually within 12- to 24-hours, surface winds swing around to the northeast. This is due to the clockwise circulation of high-pressure systems and their movement from a position over the Tennessee River Valley or other locales to the northwest of Florida (Fig. 4) to positions closer to the Atlantic Coast (Fig. 5).
As the winds blow over warmer waters (and the Gulf Stream), heat and moisture are added to the atmosphere from below (Fig. 6). Temperature and dew point readings rise accordingly (Fig. 2).
Today’s weather pattern is forecast to be similar to the one that just affected southwest Florida. The day will start off tropically pleasant with temperatures in the 60’s, rising to the mid 70’s by noon. Then the cold front arrives with a striking wind shift from southwest to northwest. Winds will become gusty very quickly and temperature and dew point readings will start to tumble. By Tuesday morning, temperatures in the Naples, FL area will be some 40 degrees lower than midday Monday. In nearby Hendry and Glades counties, a freeze watch has been posted. Wind chill readings will also tumble to unusually low values for so far south. A day after cold frontal passage, high temperatures are some 20 degrees lower than those of the previous day.
Consider what happened as the cold front pushed through Dothan, AL early this morning. At 12:16 am. C.S.T, the temperature in Dothan was 61 degrees. Thirty-four minutes later, with a 13-degree drop, the temperature was 48 degrees. This morning, the mercury should drop to the upper 20’s in Dothan. During today, the high temperature might reach a degree or two above freezing. By Tuesday morning, Dothan will shiver in the upper teens.
Another way of looking at this wall of advancing cold air is to compare temperatures between two cities perpendicular to the axis of the cold front. Shortly before 3:00 a.m. C.S.T., this Monday morning, the temperature difference between Tallahassee, FL (67 degrees) and Dothan, AL (41 degrees) was 26 degrees across a distance of 91 miles.
Another reason that this cold front is so strong involves snow cover. Yesterday’s storm system added to the area covered by snow (Fig. 7). Parts of southeast Missouri have at least six inches of snow on the ground. Parts of southern and southeastern Tennessee have at least an inch on the ground. Typically, as cold air moves southward through the Plains and middle Mississippi River Valley, it warms a little as it passes over warmer ground. With snow cover, that warming doesn’t occur. Hence, the cold air arrives at southern latitudes colder than it normally would.
The good news is that, yet again, the cold blast will be limited in duration (Fig. 8). Tuesday morning will see the coldest readings so far this winter across southwest Florida. Daytime temperatures on Tuesday will struggle to reach the mid and upper 50’s. With north winds blowing at 10 to 15 miles per hour, it will feel even chillier.
Wednesday morning will be cold, too. However, with winds starting their transition to the northeast, it will actually be a few degrees warmer than Tuesday morning. Daytime readings will be dramatically warmer on Wednesday and return to the low 80’s by Thursday.
For the Midwestern snowbirds who are gracing our area, one has only to look to Minnesota where sub-zero readings and wind chills down to minus 50 and lower have dominated weather news all weekend.
© 2013 H. Michael Mogil