A Flash Flood Watch has been posted for much of southwestern Ohio and southeastern Indiana, thanks in part to saturated soil after last night’s heavy rain:

While the coverage of showers will be low through mid-evening, scattered showers and thunderstorms will develop late this evening and early in the overnight. There is a risk for strong storms tonight, but the main concern is flooding and flash flooding in the watch area.

The Storm Prediction Center only has communities northwest of Cincinnati in the marginal risk for severe storms through sunrise:

Even if storms aren’t strong or severe, they may produce heavy rain and frequent lightning.

While the Flash Flood Watch will expire at 6am, the threat for flooding and heavy rain returns Saturday afternoon and evening. The threat for strong and severe storms will also be higher Saturday, especially for areas east of Cincinnati:

The most likely time for storms – including strong to severe storms – Saturday is 2pm to 9pm. Damaging straight-line wind is the main threat:

The key takeaways here are to be aware for flooding and strong storms through Saturday night. The risk for both of these is highest northwest of Cincinnati tonight and along and east/south of I-75 and I-71 Saturday afternoon and evening. Never drive through flooded roads!

While the threat is small, you should be alert for strong and severe storms Thursday and Friday, especially during the afternoon. Even if storms aren’t strong, some cells may produce heavy rain and lightning.

Models are quite sloppy with the coverage and timing of showers and storms Thursday and Friday. Wednesday morning’s NAM model has precipitation developing in the Ohio Valley around 2pm Thursday afternoon:

The same model also has showers and storms developing in the Tri-State Friday afternoon:

Other models and guidance is not as aggressive with the coverage storms both Thursday and Friday. My forecast for Thursday calls for scattered showers and storms developing, especially during the afternoon and ending in the evening.

The Storm Prediction Center has placed areas west and north of Cincinnati in a marginal risk for severe storms Thursday:

The marginal risk is farther west in SPC’s severe weather outlook for Friday:

At this point, all severe weather threats for Thursday and Friday are low and mainly during the afternoon and early evening. Here’s are forecast severe impacts for Thursday:

And here is the breakdown of threat for Friday:

Be alert! This threat may change in the next 24 to 48 hours.

As I highlighted in my Sunday blog post, there is a significant threat for severe storms Wednesday, Wednesday night, and early Thursday. Damaging straight-line wind was the main concern per yesterday’s guidance, and it still is the main threat. The tornado threat, though, has come up, but it is still a secondary threat at this time.

Just after 3am on Monday, the Storm Prediction Center placed the Tri-State in a slight to ENHANCED risk for severe storms Wednesday and Wednesday night:

The highest potential for severe storms is focused northwest of Cincinnati.

This morning’s guidance has shifted the main area of severe weather farther north into the Great Lakes. Despite this shift, we are still in a significant threat for severe storms Wednesday and Wednesday night.

In yesterday’s blog, I discussed the derecho parameter. While I am not forecasting a derecho at this time, this parameter gives us an idea of how high the damaging straight-line wind threat is IF storms occur. Here’s what this morning’s NAM model thinks the derecho parameter will be at 2am Thursday morning:

Clearly, these are high values (anything over 5 is very significant, really) over the Great Lakes and Ohio Valley. Here’s what this morning’s GFS model thinks for the same time:

While values are not as high, they are still high.

While computer guidance suggests the complex of storms may stay focused to our north, the Weather Prediction Center suggests there will be warm front (the leading edge of warmer air bisecting the Tri-State) Wednesday night:

The air mass lifting in from the southwest will be warm, humid, and unstable, and the front will help provide shear (the change in the speed and direction of the wind). All of these elements combined elevate the threat for tornadoes and damaging-straight wind locally (despite a higher threat closer to Chicago).

The Significant Tornado Parameter tells us where there is a elevated risk for tornadoes IF storms can form. Number greater than 1 are usually supportive of at least the potential for tornadoes. Here’s what Monday morning’s NAM model has the significant tornado threat at for 8pm Wednesday night:

This is elevated. Let’s see what Monday morning’s GFS model has for the same time:

This is also elevated. Notice that this does not guarantee tornadoes, but it does show us the magnitude of the tornado threat.

It is also important to note that model guidance is NOT is not a forecast. A meteorologist must review other guidance to make a forecast, and here is what I have come up with for now regarding late Wednesday and early Thursday’s severe weather threat:

This forecast may change as model guidance changes and as we near the event. Know that the damaging straight-line wind threat and tornado threat are both in play for late Wednesday and Thursday. I’ll update this blog as needed.

In the Ohio Valley, it is rare to be put in a severe weather risk area by the Storm Prediction Center more than 3 days out. This week will feature one of those rare occasions.

The Storm Prediction has put the Tri-State in the 15% severe storm risk for Thursday. The 15 percent risk means SPC feels there is a 15% probability of a tornado, severe hail, or severe wind event occuring within 25 miles of a point:

This is – essentially – a “slight” risk for severe storms on Thursday. The 30% area would be the equivalent of an “enhanced” risk. “Marginal,” “moderate,” and “high” risk equivalents are not issued on forecast days 4 through 8.

The takeaway here is that the Storm Prediction Center feels there is a significant severe weather threat in the Great Lakes and Ohio Valley Wednesday.

Or will it be Thursday? Models disagree on the timing of this mid-week storm threat.

There is already a buzz on social media about a complex of storms racing through the Midwest and Ohio Valley Wednesday. Some are predicting a “derecho” (a long-lived complex of storms that causes wind damage over a large area), which predicting at this range is not worth our time and ridiculous. The definition of a derecho is loose. The SPC believes a derecho must go 250 miles and contain separated 75mph wind gusts. Others disagree that a derecho needs to fulfill this requirements.

Regardless, let’s investigate this severe threat using the derecho parameter, which suggests where derechoes may grow or evolve IF storms are able to occur. The higher the derecho parameter, the better the support for them. Here’s what Sunday morning’s NAM model suggests the derecho parameter will be at 2pm Wednesday:

Clearly, there is a significant risk for storms with damaging wind to our west Wednesday afternoon if you believe this model. Let’s compare it to Sunday’s morning’s GFS model:

The GFS is not as impressed with the threat compared to the NAM, especially for Indiana. It is a model model with a different engine, but it is still showing a significant risk for storms with damaging straight-line wind. The GFS model actually holds the better threat off until Thursday:

The NAM model produces a future radar product. Here’s what Sunday’s morning’s NAM model suggests the radar might look like Wednesday morning:

…and here’s what it suggests the radar will look like 12 hours later:

Even history suggests we need to watch for a damaging straight-line wind threat. The Storm Prediction Center’s database suggests the historical odds of seeing severe weather on June 22 is focused over the Tri-State, central Plains, and Carolinas:

When severe weather occurs in the Ohio Valley on June 22nd, it is very likely to be a damaging straight-line wind report versus a tornado or large hail report:

It is apparently that we need to monitor the damaging straight-line wind threat later this week, although tornadoes and large hail are possible with any storms that sweeps through the Ohio Valley. Our confidence, however, is muted when we see discrepancies in model guidance. The last two runs of the European forecast model (ECMWF) suggest the damaging straight-line wind threat will peak late Wednesday night or early Thursday. It is the “middle of the pack” right now.

Stay tuned. Wednesday and Thursday are days to be prepared for strong and severe storms.

Morning showers and storms have stabilized the low-levels of the atmosphere and have prevented temperatures from rising significantly. As of 11am, most in the Tri-State are in the 70s:

Sunshine is, however, returning to the Tri-State per the 10:45am visible satellite image:

Note a boundary (in the form of clouds) from southern Indiana back close to Dayton. The Ohio Valley radar image as of 11:15am shows showers and storms moving east and southeast of Cincinnati:

While the boundary now from southern Indiana into west-central Ohio is moving southeast and will trigger isolated to scattered storms early this afternoon, the main axis of instability is in northwestern Indiana and is dropping southeast. This secondary front will be the one that triggers storms later this afternoon and early this evening.

The Storm Prediction Center has the entire Tri-State in a slight risk for severe storms through this evening:

This is mainly for the potential of damaging straight-line wind. Secondary threats include large hail and localized flooding, especially with dewpoints in the upper 60s and lower 70s as of 11am. Here’s a breakdown of severe weather threats through this evening:

The most likely time for severe weather today centers between 3pm and 9pm, especially between 5pm and 8pm.

Clusters of rain and storms will develop to our northwest later today, gradually coalescing into a line as it moves southeast. The afternoon forecast calls for showers and storms to redevelop this afternoon. Highs today will be in the mid to upper 80s, and it will be steamy:

Showers and storms will diminish and end this evening. Strong and severe storms will be favored early:

Be alert, friends!

If you were watching Ohio Valley radar yesterday afternoon, you might have noticed radar returns in southern Indiana. Were these showers and storms bubbling up due to temperatures rising through the 70s? Did I bust a forecast?

Despite what you may think, the same device that suggests I blew the forecast also suggests I got it right. Modern radar is a power thing when used to it’s fullest potential.

First, is it realistic to have radar returns in this area? A visible satellite snapshot of the Ohio Valley shows cumulus clouds in southern Indiana at 5:15pm yesterday afternoon:

We need clouds to have showers and storms, so the returns on radar could be precipitation. Notice there are no towering clouds in the area though (unlike in northern Ohio were showers and storms were in progress with higher instability); satellite imagery leads us to believe there was just a sea of shallow cumulus clouds yesterday afternoon in southern Indiana.

Here are the radar returns as viewed by the National Weather Service Doppler radar in Indianapolis late yesterday afternoon. The reflectivity (commonly shown on television or apps) is on the left, and correlation coefficient (showing the relationship between the height and width of objects like raindrops, hail, or debris sampled by radar) at the right. Blue values of correlation coefficient here suggest these returns are particles of different shapes and sizes and likely not raindrops, hailstones, or something related to meteorology:

Radar cross sections show these returns did not extend well into the atmosphere. Here’s the reflectivity cross section from NWS’ Indianapolis’ radar at 5pm ET yesterday:

These returns are relatively close to the ground (below 10,000′). Here’s the correlation coefficient cross section at the same time:

Blue values here suggest these radar returns are likely not raindrops or hailstones. So what could it be?

The radar returns become apparent around 4:40pm in the afternoon. See the green dot in the reflectivity at the left with blue (low) correlation values in the same area at the right:

This is surprisingly close to Camp Atterbury in Indiana. The military is known for dropping chaff to scramble radar and serve as a countermeasure. Low (blue) correlation coefficient values on radar are common with smoke plumes and military chaff. The meteorological environment did not support showers and storms, so military chaff is the most likely bet.

Need some additional evidence? Fast forward to this morning. Here’s the visible satellite snapshot as of 8:45am Wednesday:

Notice no clouds in the sky. There were still no clouds over southern Indiana as of 10:30am ET.

Yet there is something on radar in the same area near Camp Atterbury as of 10:20am ET:

Reflectivity values are high and correlation coefficient values are low in the image attached. It looks like chaff is the culprit here. Remember, we need clouds to have showers and storms, and there were no clouds in the sky when these returns were on radar.

Radar is a powerful tool if you review the data thoroughly. Even as a meteorologist, it’s easy to fall into the trap of seeing radar returns and assuming showers and storms are developing. Radar can sample dirt, bugs, plumes from wildfires, tornado debris and precipitation. Things aren’t always as they seem!