May-like Heat should end next Wed.

Early May-like heat and humidity will last until next Wednesday. Scattered shower chances on Friday will increase on Saturday, but much depends on where you live. Decent afternoon shower chances should persist Sunday and Monday, but a significant cold front should barrel through next Wednesday featuring a line of thunderstorms.

The reason for the the heat, humidity, and lack of rain can be found on the current surface map (Does it bother you that I rarely show this?). The Bermuda High is pumping hot humid air in from the southeast, while an almost stationary front lies west-to-east just north of the Ohio Valley. It’s still winter north of the front where Chicago is 39, but jumps up to 67 in Louisville. Because the upper air pattern is also west-to-east, we stay warm.

The Foreca graphic looks fine with this temperature trace that looks like it came out of an electronics lab. The only comment on temperatures: Highs will be about 4-5 degrees cooler within a mile of the Lake and Sound.

There could be a piddly shower or two around on Thursday, but scattered showers (40-70% chance) become the rule on Friday. The biggest chances and the largest amounts should be in inland areas 20 miles or more north of the Lake and Sound. Saturday’s showers will be more organized as a broken line will approach from the NW courtesy of a dying front. Again, biggest chances and largest amounts to the NW. Sunday and Monday still feature a decent shower chance. Adding up the rain for the next week, amounts could range from a few tenths to a half-inch in areas from New Orleans to Slidell to Biloxi. Areas inland might see an inch.

The pattern changes by next Wednesday as shown by this ECMWF upper air forecast. A sharp, full-latitude trough cuts through the middle of the country. This will create a strong cold front just to its east with a line of storms. The good news is that sharp troughs like this move rapidly through, so the cold behind the front will blow in and blow out quickly.

Given this feature, the ECMWF is forecasting the following temperatures starting Thursday March 12. None of the modeling has shown that the March 12 cold snap will get colder than the low 40s at some inland locations. Average high in mid March is about 74, so this forecasts a return to normal after the two days of cool air. Also note the drop in temperatures at or about the 19th from another front. It’s too early to say much about this, except that even though upper 30s are possible in late March, it’s tough for the winds to die down to get frost.