Quite the progressive weather pattern is in store for south Florida and much of the southeast U.S. The first of two cold fronts has moved past south Florida and this will be the beginning of what should be an extended period of cooler and drier than normal conditions for the area. Below is a breakdown of what's to come for today and tomorrow.
------------------------------TODAY -----------------------------------
The first real change in our weather is already underway. A shortwave trough at the mid-levels is located over the Appalachians, driving a cold front southward across the Deep South. If not for the strong upper-level forcing, the front may have stalled to our north and the cooler air would not have made it. But that has not happened, and our Friday morning greeted us with comfortable conditions. Figure 1 (http://weather.cod.edu/forecast/) below shows the 500 hPa (~18,000 feet/~5500 metres above sea level) wind speeds.
Morning temperatures were anywhere from the upper 50s to lower 60s (15-17 C) area-wide, but dew point temperatures have dropped down to the mid 40s (7-8 C), making the air much more comfortable than in days past. Cooler and drier air will continue to filter in from the northwest, and most of Broward and Palm Beach may even get some peeks of sun later this afternoon. However, moisture will remain in place around the area and, should the front stall sooner rather than later, rain may be possible for portions of Miami-Dade. Highs for Friday are only expected to range between 67-70 F (19-21 C) due to the cloud cover and significant cold air advection. Either way, it should be more than pleasant conditions to end the work week.
--------------------------------SATURDAY--------------------------------
For Saturday, the first cold front is expected to stall out over the Florida Keys as a quick return to mostly zonal (West-East) flow with the departing shortwave prevents any advances. At the same time, a newly approaching and stronger shortwave trough will coincide with the strong subtropical jet stream. This will push the second cold front through south Florida with more ease by Saturday night. Wind speeds aloft will be approaching 130-150 knots (~150-175 mph) and, as the shortwave encounters the subtropical jet, surface cyclogenesis is expected to take place. Coupled with increasing moisture from the stalled first front, the end result is an increased chance for some convection. Thus, a high probability for rain is expected, especially Saturday night as the front nears. Figures 2A (top) and 2B (bottom) show the 250 hPa (~34,000 feet/~10400 metres) and 500 hPa wind speeds, respectively (below).
For forecast purposes, south Florida is looking at highs in the mid 70s if not tempered by extensive cloud cover throughout the day. Northeasterly winds during the day will give way to backing (counterclockwise) wind flow by the evening returning the flow to a northwesterly origin and hence, a reintroduction of cooler and drier air. Once the pre-frontal action moves through and clears the region, a gradual drop in humidity and temperatures is expected. Morning lows for Sunday are expected to be in the upper 40s to mid 50s with somewhat clearing skies.
A follow up post (Part II) will be coming soon detailing what to expect for Sunday night and the start of the following work week. Just waiting for the new model runs to come through for accuracy purposes.