Sunny spots and thunder this Memorial Day weekend

There are a few special forecasts each year meteorologists want to nail.

The 4th of July. Wedding day for special friends. Graduation parties. Memorial Day weekend?

The common weather wisdom is that Memorial Day weekend is going to be a washout in Minnesota. Climatologically speaking, we're now entering the wettest 12 weeks of the year in Minnesota. Average rainfall is about an inch each week from now through August.

The sweet spot for setting off your NOAA Weather Radio in the Twin Cities?

From Memorial Day weekend through the 4th of July. Historically that's when the Twin Cities NWS issues the most frequent severe weather warnings. The days surrounding June 17th are historically the peak of severe season in Minnesota. A good week for a meteorologist to plan a vacation?

So it's practically a given that showers and thunderstorms will be in the forecast this Memorial Day weekend. Looking at the maps, this weekend actually may end up better than average. There will be some sunny warm dry hours/days in the forecast.

Timing thunderstorms: High degree of difficulty

The real challenge this time of year is timing the micro-scale features that can trigger the next T-Storm wave. Forecast models still can't always grab hold of small features and provide precise storm timing. There's an element of convective chaos to summer thunderstorm forecasting. That's pretty cool, and also frustrating to forecasters. But then again, if we could nail each thunderstorm down to the minute all summer long, where would the mystery be?

The weather maps heading into Memorial Day weekend lays out the forecast challenge ahead. A broad area of low pressure spinning northeast from Kansas spawns occasional waves of scattered T-Storms.

Closer scrutiny of the forecast models reveals a few times with more likely sunny, dry periods. Thursday evening. Friday afternoon and evening? Most of Sunday. Parts of Memorial Day. The next T-Storm wave appears most likely to arrive before Friday morning's rush hour, then again Saturday.

Here's the European model's take on the upcoming forecast. Pick your sunny spots.

Thundery Friday morning commute?

NOAA's NAM 4 km model paints two primary thunderstorm waves in the next 48 hours. One sweeps into southern Minnesota after midnight, and arrives in the Twin Cities between about 3 am and 6 am into Friday morning's rush hour. A wet and thundery commute looks likely Friday morning. The second wave arrives Saturday.

As usual in convective storms, rainfall totals will vary locally. Another inch give or take is probably a good starting point for mush of eastern and southern Minnesota, with less up north. That's been a common theme this spring.

Again, NOAA's NAM 4 km model.

Rainfall in the past 3 days has been spotty. Some have picked up soaking rains of 2" to 3"+. Other spots less than an inch so far. Check your backyard on the map via the Twin Cities NWS.

Still dry up north

No doubt about it. northern Minnesota has missed the heaviest most widespread rains this month. Northern Minnesota  and a chunk of western Minnesota have been added to the abnormally dry, or what I like to call the "pre-drought" zone on this week's U.S. Drought Monitor. In fact a full 40% of Minnesota is now painted in yellow, compared to just 9% last week.

Cool start to June?

A few of the models suggest a cooler Canadian push the first week of June. The upper air map for next Wednesday features a low pressure system southwest of Hudson Bay with cooler northwest flow oozing into Minnesota.

NOAA's Climate Prediction Center picks up on the trend.

NOAA's GFS 16-day product cranks out highs in the 60s and 70s into early June.

No heat? No AC? Still no mosquitoes? I can live with that.

Moore, Oklahoma: Tornado epicenter of the world?

Is there a 'tornado bull's eye' within tornado alley? If so Moore, Oklahoma is it.

Here's a fascinating piece from FiveThirtyEight.

On the evening of May 3, 1999, a massive tornado tore through the Oklahoma City area. Known today as the Bridge Creek-Moore Tornado, it’s infamous for its size (a mile wide) and strength (wind speeds reached 300 miles per hour, on par with a Tokyo bullet train). It moved, as tornadoes so often do, from the southwest to the northeast, touching down in the rural plains before churning its way through the suburb of Moore and up to Midwest City, just east of downtown — which was where it pulverized my dad’s truck.

My dad, Howard Koerth, moved to Oklahoma in 1994 to teach art at Rose State Community College in Midwest City. He was there May 3, right in the tornado’s path. Instead of going to the storm shelter, he opened the back door of his building and watched the fat funnel tear apart an auto dealership. The tornado was gray, tinted with red from the layers of clay-filled topsoil it had peeled off the Earth. If you watch video of it today, you see it surrounded by a haze of confetti. When the camera zooms in, the ticker tape turns out to be, instead, a blizzard of two-by-fours, siding, whole trucks. Sixteen years later, Dad has yet to exorcise that image from his mind and he’s still asking me about the Bridge Creek-Moore tornado. Or, rather, he asks me about its sister storms — tornadoes that, to him, seem to follow the same path, flattening the same places over and over. Especially Moore. Always Moore.

He called me in 2003, when a slightly less powerful tornado — and, by “less powerful,” I mean one classified as “devastating” (an EF4) rather than “incredible” (an EF5) — hit Moore. He called me in 2010, when another EF4 struck the town. He called me in 2013, when Moore was hit — improbably — by a second EF5. He always asks the same question: “What is going on here?” One town. Sixteen years. Four big, powerful tornadoes. It’s a hell of a coincidence. Can it really be just the work of random chance?1