THE OLD SQUEEZE PLAY...
We've had a couple days to dry out and cool off. A welcome change that was really needed at my house where nearly 6 inches of rain fell last Friday. The quiet weather was with us again on Monday but there was a noticeable uptick in the temperatures and humidity, especially by late afternoon. The trend becomes even more noticeable Tuesday as a developing cold front funnels heat and moisture into the central Midwest (the old squeeze play). Highs on the HRRR reach 90-95 from north to south. Fortunately dew points are confined to the mid to upper 60s keeping heat index's under 100. A decent SW breeze of 15-25 will also help. Still, it's going to be a very toasty day.
With the warm air will come instability but EML (an elevated mixed layer of warm air aloft) will create a significant cap. That appears to be the death knell for any thunderstorms when the cold front passes Tuesday night. In other words, there won't be enough lift or vertical velocity to bust the cap. Despite the surface air mass being ripe for thunderstorms, we won't have the right environment to sustain updrafts. It's like shaking a can of pop. You know when you release the tab it's going to explode, it's highly unstable. However, you avoid popping that top and nothing happens. The energy eventually fades away and the can stabilizes. Unless something drastically changes, I look for a dry frontal passage. SPC keeps the main thunderstorm threat north as well.
Wednesday high pressure behind the cool front brings brisk northwest winds and lower humidity levels. Temperatures will also be cooler but full sunshine and good mixing means a warm day with highs in the mid to upper 80s. Thursday looks similar but just a bit warmer and more humid. Highs of 85 to 90 seem on track.
RING AROUND THE ROSIE (make that heat dome)
As has been the case much of the month, the heat ridge that has baked the Plains is set to make some eastward expansion into the Midwest. We don't get the full blast but we are going to be close enough to get into a very warm and sultry pattern. Not only that, our weather should turn active as we sit on the northern periphery of the heat dome.
That's the spot known as the ring of fire, the breeding ground for thunderstorm complexes.
While it's easy to recognize the pattern and it's heavy rain producing potential, its far more difficult to ascertain exactly where the storm complexes will form. Usually, the "ring" vacillates some as energy ripples along it which can alter its position daily. Additionally, EML capping can be a factor as well as mesoscale processes from outflow boundaries due to earlier rounds of convection. Debris clouds can also alter the environment. These are known challenges forecasters are going to have to deal with going forward.
At least for now, guidance is suggesting a multi-day period where ridge riding storm complexes are likely to be found on a daily basis in some part of my area. Severe weather can occur from time to time but the biggest concern comes from the heavy rain potential. As you can see, by Saturday water vapor is shown exceeding two inches over the northern half of my area.
Almost every time I see 2 inch plus PWATS somebody in my area ends up with a 1-3 inch rain, sometimes more. That's in just one MCS. That could happen in the north, central, south, or some combination of all three. Only select bands approximately 50 miles wide tend to see such amounts. That said, most places have a good shot of picking up 1-2 inches over a 4-5 day period. I think that's the type of potential on the table starting this weekend and perhaps lasting into Tuesday of next week.
Another concern this weekend is heat, especially over my southern counties. The EURO is now coming in hot with highs near 100 in parts of the south Saturday. Here's what it shows.
Saturday highs EURO
The GFS in its latest run looks similar to the EURO. Here's what it suggests for highs.
After that the latest trend is for cooler temperatures Sunday as a cold front sinks southward during the day. Both the GFS and EURO have shown agreement on this Monday night. However, just 6 hours earlier the GFS was not in the cool camp Sunday or beyond showing highs at Ft. Madison reaching highs of 100 for 8 consecutive days July 22nd-July 29th.
Now the GFS shows this in Ft Madison. That's a radical change in one 6 hour run of the model. Nothing worse as a forecaster than to see flip flops like that.
So what's the verdict? I'm still a bit skeptical but think there is merit to the cooler look. Models have been struggling mightily with the strength and position of the ridge and its associated heat for at least a couple of weeks. One day they are on, the next off. Most of the time they have overestimated the heat due to the tenacity of a sympathetic trough in the northeast which holds it at bay. I see hints of that surfacing again so my confidence is low regarding long term temperatures after a steamy day Saturday. I would say moderate confidence when it comes to rains Friday through the middle of next week. Now we play the waiting game when it comes to finding out the truth.
Thanks for visiting the site and as always, roll weather...TS
