Hail and high water

O.K. Here, apparently, are our choices du jour on the weather menu: severe drought & blowing dust OR raging cumulonimbus clouds spitting hail the size of lemons and racquetballs. That’s a tough one. Whatever happened to gentle, steady, soaking, all-day rains? Granted, summer rains tend to be “convective”, showery, hit-or-miss, but no, you’re not imagining it: when it does rain the drops are coming down faster & harder. Extreme rain events have spiked in recent decades, more flash flooding, more wild downpours. One recent study showed a 34% increase in “extreme precipitation events” in Minnesota since 1947. Nationwide National Weather Service statistics show a 20% increase in flash flooding since 1900. What’s up? Lot’s of theories, but the most probable explanation: higher dew points, more water in the air, more fuel for thunderstorms to tap.

Some days dew points are higher in Iowa and southern Minnesota than along the Gulf Coast, which is odd, considering the Gulf is our biggest source of moisture. A number of leading scientists point a finger at corn. Yes, corn. Improved farming techniques have packed more corn rows into an acre, which results in more “evapo-transpiration.” Simply put, corn “sweats” at night, it releases water into the air. The more corn, the more water leaking into the lower atmosphere, the higher the dew points and relative humidity. It’s just one of many examples where we may be (unwittingly) nudging Mother Nature in a certain direction. Don’t get me wrong. I like corn. I consider myself very pro-corn. I won’t stop eating corn on the cob anytime soon, but I do find it fascinating that there may be some unintended consequences, the mere thought that improved farming techniques MIGHT be increasing the frequency and intensity of heavy rain events.

File: Wall Cloud. If you see a cloud formation like this, with OBVIOUS rotation, thunder, lightning, large hail – time to run for the hills or better yet, the nearest basement. This is what a tornado-forming thunderstorm looks like. The larger the hail, the stronger the updraft, the higher the probability of a tornado, which is really a process, not an “object”, the manifestation of an especially severe updraft.

Pack the thunder-wear today, should be a wild one, conditions ripe for strong to (isolated) severe storms as early as late morning/midday. There’s a slight risk of severe storms statewide, the greatest potential for large hail, straight-line winds and even a few isolated tornadoes coming south and east of St. Cloud and the Twin Cities. (See SPC prediction below).

SPC Prediction for today, showing a 30% probability of hail/damaging winds within 25 miles of the red-outlined area, covering most of southeastern Minnesota. Stay alert and check in often – I do expect severe watches and warnings nearby today as powerful storms rumble in from the Dakotas.

WRF/NMM Outlook for 1 pm today. The models have consistently predicted very heavy/severe storms pushing into Minnesota today. The timing is tricky, but St. Cloud may see heavy weather by late morning, reaching the Twin Cities by early/mid afternoon.

A quarter to a half inch of rain may fall today, a few lingering showers and storms possible from the Twin Cities on south and east Friday as cooler air approaches from the north/west. Behind this unusually vigorous cool front, a cleansing outbreak of low humidity, fresh winds and bright, Canadian-fed sunshine just in time for what appears to be a memorable weekend. Saturday may be a little on the cool side for the lake, temperatures holding in the low and mid 70s up north. Sunday should offer up less wind, temperatures moderating to near 80 over central and southern counties, a bit more pool-friendly.

No sizzling heat in sight, no more 90s looking out 7-10 days. Just a thundery Thursday, an unsettled Friday, and a Saturday that will look and feel more like early September than early July. Badly needed moisture on a work day, comfortable sunshine on the weekend? Maybe we finally have that timing thing down…

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