LOUISVILLE, Ky. — We’ve reached mid-May and the spring has finally decided to take hold. Thunderstorms are forecast for Sunday and Monday. It’s a challenging forecast because of a cut-off low. As the saying goes in our world, “cut-off low, weatherman’s woe.”
- Temperatures warm into the middle 80s Sunday
- Showers and thunderstorms again likely Sunday afternoon and evening, continuing overnight
- A very difficult forecast
- Cooler and cloudier weather seems likely next week.
Weather setup: Saturday afternoon saw a mostly cloudy day, but still warm. Temperatures managed the lower 80s across the area and a few thunderstorms fired up in the afternoon, like Friday. This is because of a stationary front draped along the Ohio River. This has helped set the stage for persistent popcorn thunderstorms that bring brief heavy rain and gusty winds before moving on their way and diminishing.
That stationary front will lift north as a warm front starting tonight. It’s attached to our main storm system which could be found in the Plains Saturday afternoon. Our forecast is especially challenging because this area of low pressure is “cut off” from the main atmospheric flow. These are called cut-off lows and are extremely difficult to forecast because they tend to just meander about in no real hurry to go anywhere.
The first half of Sunday should stay largely dry. A few showers are possible, but otherwise we’ll stay mostly cloudy as the warm front lifts north and pulls warm and humid air into the Ohio Valley. Temperatures should manage the middle 80s in our neck of the woods and dewpoints in the middle and upper 60s…so it’s going to feel a bit stuffy.
The atmosphere should become unstable enough by mid-afternoon to see more spotty popcorn thunderstorms develop. This will be ahead of the main storm and cold front very slowly moving east. Models have continually slowed down this cold front which means a few things. First, a slower cold front means a slower arrival of the main rain event, currently scheduled for Sunday night. Second, a slower front means temperatures Monday could be warmer than currently forecast. Key word there is “could.” Third, a slower front may also mean heavier rain.
A line of thunderstorm should be firmly established to our west early Sunday night. This is when things get a little trickier. Current thinking is that the cold front and line of thunderstorms will enter our western counties early Monday morning with thunderstorms moving across Louisville and the I-65 corridor late morning and early afternoon.
After the front passes cooler air will settle in. Highs Monday should only manage the low 70s, but if the front continues to slow down then we might creep into the middle 70s for high temperatures. Most rain should be done Monday evening, but showers will linger through the evening.
Severe weather threat: While a few strong-to-severe thunderstorms are possible, the risk of severe weather is low. We’re currently at threat level 1 of 5 for severe weather Sunday into Monday. Primary threats are downpours, gusty winds, and perhaps some hail.
How much rain? This is again a bit tricky given the movement of the front. Amounts will likely vary quite a bit because of the spotty nature of the initial storms Sunday afternoon. Possible lingering showers through Tuesday could also add to totals. Models may be a bit aggressive, but rain amounts exceeding 1” are possible by Tuesday evening.
Long term: The cut-off low is going to do what it does best…meander. A chance for showers hangs around Tuesday through Thursday. Though widespread rain isn’t likely, sporadic showers are certainly possible. Cooler air should settle in much of next week with temps dipping into the upper 60s Tuesday and Wednesday before we begin to warm back into the 70s to close the work week with 80s again possible by the weekend.