There is not much to talk about this week. The warm weather pattern will continue for the rest of the month and into early March, and we won't see much rain over the next week, either.
The only exception to the warmth is coming tomorrow. It's Friday, and there will be another cold front moving into South Carolina (lately, Friday has been Cold Front Day). It will pass through this afternoon and tonight and become stationary tomorrow over Georgia. The air arriving behind the front won't be frigid and will only send our high temperatures back to near normal. It's a big change from the record warmth of yesterday, though.
It will feel 'chilly' tomorrow because it will not only be much cooler but also stay cloudy and damp. Most of the rain from the front will come tonight as an upper-level disturbance moves through, causing some intermittent light rain and drizzle to linger through tomorrow evening.
The front will retreat northward Saturday night and Sunday, so warmer air will return and most of the state will reach the 70s again on Sunday. After that, we will stay warm until the end of next week. A weak cold front will move through on Tuesday, bringing little or no rainfall and only a slight temperature change.
Later next week, a more substantial cold front will move through this part of the country. As this front moves through, we'll see a better chance for rain, maybe a soaking, and perhaps some thunderstorms. The timing is uncertain because the situation is complex, involving two separate storm systems. So, Thursday and Friday may be unsettled and wet, with the best chance for rain on Friday (of course). Next weekend is likely to be dry and cooler.
You might wonder why it's been so warm and why it will stay warm a while longer. We find the answer by looking at the upper-air pattern. The eastern part of the nation has persistently been under an upper-level ridge. A ridge is the opposite of a trough, a northward buckling of the upper-air winds. Below is what that looks like on a weather chart.
Forecast 500-millibar heights (contours) and anomaly (shaded) averaged over 24 hours between 0000 UTC February 26 and 0000 UTC February 27 from the ECMWF Deterministic model. An upper-level ridge is over the eastern part of the U. S.,
while an upper trough covers the western states.
Upper-level ridges tend to promote warm and tranquil weather because they cause storm systems to be deflected to their west and north. In the example above, the upper ridge is centered over western Cuba and extends northwestward toward the middle Mississippi Valley. Storms will track around the northern part of the upper ridge (air flows almost perfectly parallel to the contours on upper-level charts). A cold front trailing a storm might penetrate well to the south under the ridge, but it usually won't have a lot of punch in terms of rain and temperature change, like the situation we see this weekend.
This upper ridge has been persistent and will remain persistent, which is why it's been warm lately and will stay warm for at least another week. South Carolinians are thinking about getting a head start with their gardens. I advise caution with this. First, there is climatology to consider. The average date of our last freeze is in mid-to-late March; however, there is also a lot of variability in those dates. Our last freeze dates have occurred in February and even January in the Lowcountry, but they can be as late as April and even early May. In recent years, the last freeze has been in late March or April, as often as not.
This chart, compiled by Assistant State Climatologist Melissa Griffin, shows the recent last freeze dates and the average, earliest, and latest freeze dates on record for select locations in South Carolina.
The latest frost is usually later than the latest freeze. So, tender plants may be vulnerable even later than these dates above.
Along with the risks from climatology, some long-range computer model forecasts and other long-range indicators like the Madden-Julian Oscillation (it's not just for tropical cyclone forecasting) hint that a colder weather pattern may descend on the eastern part of the country starting around the middle of March.
The bottom line is that early planters need to understand the risks and use caution. I recommend not planting anything you can't protect from a late-season frost or freeze.
