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Writer's pictureMetro Weather Watch

A stormy day gives us a break from the heat, A pattern change possible by June? (5/26)

Updated: Sep 19, 2019

Good evening Metro Weather Watch followers!  I hope you all managed to take shelter from the strong storms we had earlier this afternoon, that is, if you managed to get one!  I will begin tonight’s blog by covering what transpired earlier this afternoon, then I’ll go into what we are expecting for the next week or so ahead.  We might be looking at some changes to the overall pattern going forward, some of which could involve additional storm chances.  We’ll go ahead and break down this possible change in just a bit!

A cluster of strong storm cells developed across Central Kentucky, Southern Illinois and Southern Indiana around Noon today, probably initially triggered by an old outflow boundary stretching across the region, likely a remnant from last night’s storms well to the North of us.  A few of the storms farthest to the West prompted severe thunderstorm warnings, with radar indicated threats of up to quarter hail and 60 MPH wind gusts.  They produced heavy rainfall and gusty winds as they passed through Evansville, with a whopping 0.97″ of much needed rain clocked in at the Evansville airport!  Fortunately, the only storm reports received as of this writing are from Louisville, where two trees were reported downed by winds from one of the stronger cells in the Eastern edge of the Metro Weather Watch outlook area.  We also have a report of at least one house fire near Henderson that might have been sparked by a cloud-to-ground lightning strike!  You can see from the RadarScope image below that we had quite a few storm cells scattered across the area at around 1 PM this afternoon.  We also have a decent picture shown below from near a CSX train yard (taken by Wayne Morrow) showing the shelf cloud on the leading edge of the strongest storm cells as they approached the Evansville area.  Will we see any more storms in the week ahead?  We just might!

Strong Storms Across the Region Early Sunday Afternoon (Image Credit: RadarScope Radar Viewer)

View from the CSX Train Yard of the Storm and Shelf Cloud as they Moved into Evansville (Image Credit: Wayne Morrow Twitter)


As we look at the next few days ahead, I can already tell you that we will not be losing the heat and humidity just yet.  I know everyone is waiting for a nicer day without the sticky 60-70°F dew points, but we will have to wait for a while longer before we see this air mass change much.  The ridge that is keeping our maritime tropical air streaming in from the Gulf of Mexico isn’t going anywhere just yet, so humid and warm daytime air in the 80s to close to 90°F will continue through at least Wednesday of this week.  The US rainfall map below is the average quantified precipitation forecast (QPF) from the 12z GFS ensemble members up through Thursday, with the “Ring of Fire” ridge clearly visible as the gaping hole in the coverage centered on the Southeast US.  Notice most of the members show less than 0.5″ of new rainfall in this period, indicating that the overall threat for heavy rain and storms will be low for next few days.  Isolated to scattered storms are still possible for portions of the Ohio Valley each day, especially north of the Ohio River itself.  However, we won’t likely see another widespread rainfall event for a little while – though we could see that change not too much farther in the future as we will see in a moment.

Average Rainfall Output from the 12z GEFS Through Midday Thursday (Image Source: College of Dupage NEXLAB)

I want to finally discuss how our dominant synoptic pattern could be changing in the extended outlook into June, and why it matters to the Ohio Valley.  The images below show the most recent ECMWF model’s output for 500mb heights at 12z Wednesday and then 12z Saturday.  Let’s go ahead and break down at a few things that change for this scenario.  First of all, the location for the highest heights (Around 588 decameters) that mark the strongest ridging move from Florida to near the center of the Gulf of Mexico.  In addition, the whole ridge becomes more flattened out, showing much more zonal or west-east flow beginning to start up to the North across the Central and Eastern US.  Lastly, we can see that the long wave trough in the west still remains, but it begins to become much weaker and fills in with warmer air.  So what’s this all mean for our weather?

Latest ECMWF Showing Change in Ridge Location and Shape from (1) Wednesday to (2) Saturday (Images Source: Tropical Tidbits)


In short, all of these changes would open up the possibility for more widespread rain and thunderstorm activity by the end of the week, seeing as the bigger storm systems would no longer be getting blocked from reaching us by the ridging currently in place!  Severe weather wouldn’t be out of the question with some of these storms, especially if we can manage to get a more pronounced shortwave trough to make it into the Lower Midwest.  This possible pattern shift also means we could finally get a chance for cooler, drier air to reach us as early as Thursday or Friday, finally giving us a more proper relief from the hot and humid air!  Note that there is still some uncertainty with how the ridge will behave, and the models could be trying to change the pattern too quickly.  We will have to wait and see whether we do finally see this pesky dome of hot air retrograde Southwest, or whether we will be stuck with this unpleasant air for a bit longer than what the consensus shows so far.

I hope everyone has a safe, pleasant Memorial Day, and we will hope to see this potential relief from the heat coming up in a few days!

-Meteorologist Alan Shriver

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