The Storm Prediction Center has much of southeastern Iowa under the gun yet again with an elevated risk of severe weather. As the beating used drum has gone over the past few days, a stationary continues to be progged from Dubuque to Shenandoah with no signs of moving until tomorrow morning. As a matter of fact, this might jog back to the northwest for a brief period this evening (as opposed to the traditional southeastward motion). Low pressure centers sit in southwestern Michigan and western Oklahoma.
The overall severe weather risk today is a bit up in the air. Radar this morning shows scattered showers and thunderstorms over central Iowa with GOES-16 visible satellite showing quite a bit of cloud cover. Temperatures are just getting to 70° in southeast Iowa with dew points in the low 60’s. We haven’t seen a whole lot of instability yet as a result — without a lot of heating, moisture, and lapse rates, it will be tough for the atmosphere to destabilize. Current numbers around the noon hour show most areas under 500 j/kg of SBCAPE, relatively low numbers. This may be on the increase this afternoon as some clearing occurs, but in all likelihood, we won’t see a ripe, high-fuel environment by any stretch. Due to these effects, the SPC removed the “enhanced” risk of severe weather that was previously in place this morning.
Regardless, the potential for some scattered severe storms remains possible. The big clue for bigger storms is where the most clearing happens. While our thermodynamic environment isn’t that impressive, there is enough shear to support some updrafts leading to supercellular development. This is indicative for the potential for some large hail (perhaps up to half dollar size), damaging winds to 60 MPH, and an isolated tornado or two. The short-range HRRR shows development occurring right around 3:00 or 4:00 in southwestern Iowa in the form of discrete supercells. I cannot imagine that the threat will last long as any CAPE we do have will fall off past sunset, which is at 8:17 p.m. today. In a lot of ways, today will probably be a tamed version of yesterday — not discounting the threat by any means, however. Beyond sunset, things will probably become linear and push eastward with potential for gusty winds, heavy rain, and frequent lightning. For those north of Highway 20, widespread light-to-moderate rainfall will be the bigger story.
With all of the rainfall we’ve had in recent days and continued rainfall today, we have noted an enhanced risk of flooding over the area tonight. Latest flash flood guidance numbers puts us at around 1.5″ of rain in an hour to produce flash flooding, about 2″ in three, and 2.5″ in six. It would not surprise me by any stretch to see more flash flood warnings today than severe thunderstorm warnings. Those particularly prone to flooding issues, such as in low-lying and urban areas, should monitor this risk closely. Flood headlines remain in effect all along the Mississippi River from Harpers Ferry to Keokuk, as well as on the Little Sioux, Big Sioux, and West Fork Des Moines Rivers in northwest Iowa.
Fortunately, the extended outlook looks less active and dry, which should help farmers out with continued planting. Mostly sunny-to-sunny skies will be the story through the beginning of next week. Friday will see highs in the 70s, Saturday in the 70s and 80s, and Sunday and Monday in the 60s and 70s. The pro to all of this rainfall is that it should help the current drought situation ongoing in southeastern Iowa.
Stay tuned to the Iowa Weather Network for the latest information!