If you’re concerned about the risk for severe storms Wednesday, Wednesday night, and very early Thursday, you should be. If you’re scared, you shouldn’t be. If you’re not prepared for the threat for severe storms, you should be.

As I mentioned in my blog post early Tuesday evening, the Storm Prediction Center has issued MODERATE risk for severe storms in the Tri-State from 8am Wednesday to 8am Thursday; the biggest concern for severe storms will be Wednesday evening and overnight.

What exactly is a “Moderate Risk?” Here are the differences on the Slight, Moderate, and High Risk outlooks issued by SPC:

March 2, 2012 was a High Risk day, and it – unfortunately – verified with numerous violent tornadoes and more than a dozen killed in our area. We are not in an SPC High Risk Wednesday or Wednesday night, but we are in an SPC Moderate Risk, suggesting the threat for strong and severe storms is significant.

When you take data from this morning’s NAM forecast model for Wednesday night and compare it to similar weather event and setups in the past (using St. Louis University’s CIPS Analog Guidance), the top 15 closest matches suggest an elevated risk for severe storms. Here are all of the SPC storm reports from those top 15 closest matches:

All of the blue dots are damaging wind reports. Blue dots far outweigh green dots (severe hail reports) and red dots (tornado reports), so history would suggest this pattern will give us more damaging wind reports over other forms of severe weather.

This is supported by this afternoon’s (18z) WRF model, which suggests winds 2,000-3,000 above Cincinnati at 2am Thursday morning will be in excess of 60mph:

This same run of the WRF shows storm relative helicity (a measure of how likely storms are to spin) values are elevated tomorrow night, but not abnormally high:

These numbers support a marginal tornado threat Wednesday night and early Thursday. With the winds just above the ground very strong out of the west tomorrow night and a strong surface wind out of the southwest, there is little directional shear (needed for tornadoes) but strong speed shear (supporting a damaging straight-line wind threat).

What will the system look like on radar? There is still a fair amount of uncertainty regarding this, but most models suggest a bowing line of thunderstorms will be pushing through the Ohio Valley Wednesday evening and early Thursday. Our in-house WRF-ARW model shows a line of showers and thunderstorms moving into our area around 2am Thursday:

…and moving into the heart of the Tri-State nearing 3am:

…and pushing south by 8am Thursday morning:

This is just one model’s thoughts on what will happen tomorrow night. I suspect this model is off on timing given that most storms tomorrow night will generally be moving northwest to southeast at 40-50mph. This model, however, supports a bowing line of storms pushing through over a line or clusters of supercells.

The elevated severe storm risk is being driven by strong southwesterly flow tomorrow, pumping warm moist air into the Ohio Valley. While the raw numbers from this morning’s Microcast run are off (especially for temperatures and dewpoints late in the day Wednesday) , the model clearly shows Wednesday and Wednesday evening will be warm and humid:

There is still a lot to be resolved about the severe weather threat in the next 48 hours. As with most severe weather events, the threat often changes hour-by-hour as the event draws closer. We don’t yet know exactly what shape these storms will take, and the timing of the peak severe weather threat hasn’t been pinned down yet. We do, however, know that damaging straight-line winds appear to be the main threat, and the secondary threats will be tornadoes, large hail, and flooding.

Are you prepared for the possibility of severe storms? Here are some things to consider:

– Is your NOAA Weather Radio working and programmed properly?
– Are there fresh batteries in your NOAA Weather Radio, and it is also plugged into a wall outlet?
– Do you have a flashlight with fresh batteries, hard-soled shoes, bottled water, and a first aid kit in your basement?
– Do you and your family know where to take cover if a warning is issued?
– If you’re going to be away from your home tomorrow night, do you know where to take cover if needed?
– Do you have more than two ways to get watch and warning information (NOAA Weather Radio, phone app, text messaging service, Twitter, Facebook)?

Please be prepared and weather aware for storms in the next 48 hours. Now is the time to plan; don’t wait until the storms hit!

While there will be clusters of showers and thunderstorms in and around the Tri-State this evening and also late tonight/early tomorrow, the main threat for severe storms in the Tri-State will come tomorrow night. While tornadoes and large hail will be possible with the strongest storms tomorrow and tomorrow night, damaging straight-line winds will be the main concern.

As a 6:13pm, satellite and radar data showed showers and thunderstorms taking aim on the Tri-State:

These clusters of showers and thunderstorms will be around through most of the evening.

This morning’s Microcast model run has more showers and thunderstorms moving in late tonight and early tomorrow:

Stronger storms can’t be ruled out both this evening and late tonight, but a much higher threat for severe storms will develop late tomorrow afternoon and tomorrow evening. Microcast isn’t too excited about the coverage of showers and thunderstorms at 5pm Wednesday:

…but tomorrow night is a different story. Precisioncast has a strong area of low pressure coming through the Ohio Valley Wednesday night and early Thursday:

The window for severe storms tomorrow night is fairly large right now. If you buy Precisioncast, strong and severe storms may not arrive until after midnight. Do you like Precisioncast’s thinking, or do you like what the WRF model thinks the radar will look like at midnight Thursday?

One version of the WRF model’s forecast radar for midnight Thursday is on the left; another version of the WRF is on the right. The difference in the strength and the timing of the showers and thunderstorms is significant, and we aren’t that far away from this event!

In summary, the Storm Prediction Center keeps the risk for severe storms well off to our northwest tonight:

Most of the Tri-State will be under a MODERATE risk for severe storms from 8am Wednesday to 8am Thursday (the main severe weather threat will be Wednesday night and very early Thursday):

Remember: damaging straight-line winds will be the main severe weather threat Wednesday and Wednesday night. Large hail, tornadoes, and localized flooding will be secondary severe weather concerns.

Are you prepared? Stay tuned for updates!

June is usually our busiest month for severe storms in the Tri-State. Spring – so far – has been very calm; only 13 Severe Thunderstorm Warnings have been issued in the Tri-State so far in 2013. On average, 26 Severe Thunderstorm Warnings are issued in southeastern Indiana, northern Kentucky, and southwestern Ohio each June. Model data suggests the next few weeks could be rather stormy.

Before diving into the data, the idea from this blog post came from me noticing a Twitter conversation between Ryan Wichman at WTOL in Toledo and Seth Binau at NWS Wilmington…and Ronald posting about this potentially stormy pattern on my Facebook page. Some of the topics mentioned below came from them.

Why do the next few weeks look so stormy? The best argument for this can be seen in the upper-level pattern. Models suggest an area of high pressure will be setting up over the Plains this week (and likely in the weeks to follow), forcing disturbances to ride up and over this ridge of high pressure and dome of heat. Here’s what this morning’s GFS thinks the upper-level flow will look like Friday morning:

The “bubble” over the southern Plains is the area of high pressure. The warm (red and purple) colors show where the core of heat will be; in this case, red and purple colors support daytime highs in the 90s and 100s if little or no rain is forecast.

This morning’s ECMWF model has a similar upper-level pattern for Friday morning:

It’s important to note that upper-level winds tend to flow parallel to the lines on the map. In essence, here is path upper-level disturbances will take later this week per the GFS and ECMWF model, respectively:

This pattern won’t change much into next week per this morning’s GFS Ensemble model:

…or this morning’s ECMWF Ensemble model:

One way to assess the potential for severe weather is to compare the upper-level pattern to other days with a similar upper-level pattern in the past…and see what happened. This technique is called analog forecasting. What do the analogs suggest will happen? If you look at the GFS model’s output for Wednesday, the top 15 analogs (similar patterns) suggest a threat for severe storms. Here are all of the Storm Prediction Center storm reports for those top 15 analogs (wind reports are in blue, hail reports are in green):

When last night’s GFS model data for Wednesday is fed into St. Louis University CIPS analog database, storm reports from those analogs suggest severe storms are a possibility Wednesday, especially damaging straight-line winds:

This storm pattern is likely not going to break down without a fight. The latest run of ECMWF Weekly model has the best chance for 3/4″+ of rain from June 18-24 in the Ohio Valley and Great Lakes:

…and the best chance from June 25 to July 1st in the Ohio Valley and southeastern United States:

When you look at all of the data, there is fairly high confidence for a stormy pattern in the second half of June. The specifics on timing and strength of each disturbance will be tricky to pin down until we get close to each event. Our first chance for seeing strong and severe storms in this pattern comes Wednesday and into Thursday.

Are you prepared for some bouts of storms?

Historically, May is the second most common month for Severe Thunderstorm Warnings to be issued in The Tri-State. On average, more Tornado Warnings are issued in May than any other month, and May is the second most likely month for a Flash Flood Warning to be issued. This May, however, has been abnormally quiet for warnings. Only 2 Severe Thunderstorm Warnings were issued during the month of May in northern Kentucky, southwestern Ohio and southeastern Indiana; no Tornado or Flash Flood Warnings were issued. Here’s a summary of local warnings in May compared to average:

Only 13 Severe Thunderstorm Warnings have been issued so far this year; this is a record minimum count from January 1st through June 4th and since the National Weather Service in Wilmington began issuing warnings for the Tri-State. On average, 46 Severe Thunderstorm Warnings are issued in the first 154 days of the year.

No Tornado Warnings have been issued so far this year. For comparison, 22 Tornado Warnings had been issued through this point last year, and 32 were issued through this date in 2011. There have only three years since 1995 (2013, 2002, and 2000) where a Tornado Warning had not been issued in the Tri-State through June 4th.

Only one Flash Flood Warning has been issued so far this year in the Tri-State. 15 Flash Flood Warnings are issued through this date each year, on average.

Here’s a summary of year-to-date warning counts compared to average:

Why are warning counts so low this year? Is it the temperature? May 2013 was warmer than average (46th warmest in the last 143 years). Typically, above average temperatures in May correlate to an above average number of thunderstorm-related warnings. Spring 2013, overall, was cooler than average (51st coldest in last 143 years); cooler than average springs tend to have fewer warnings.

While temperatures play a part, I think the two main reasons we haven’t seen a lot of severe weather comes the lack of low-level moisture and – more importantly – from the positioning of the jet stream. From March 1st through May 31st (meteorological spring), the jet stream was mainly focused to our south:

Foci for severe weather based on the positioning of the jet stream are circled in black. Note these foci are outside of our area.

For the whole year thus far, the jet stream has been positioned more southwest-to-northeast:

Foci for severe storms and rapid development of low pressure are circled in black. Note we are downstream of one of these foci. The jet stream was frequently dipping south into the Plains this winter; this is the main reason we are downstream of one of these foci and a reason why we had a lot of snow late in the winter. The jet stream’s positioning changed quite a bit from winter to spring. Note average position of the jet stream in just May:

…and note the favored areas for severe storms (the Plains and Mid-South, where severe storms have been frequent). After all these areas have been through, we have a lot to be thankful for this year!

Strong storms are possible not just through early evening in the Ohio Valley, but also nearing midnight as a cold front nears. The latest severe weather outlook from the Storm Prediction Center has much of southwestern Ohio and northern Kentucky in an elevated risk for severe thunderstorms through tonight:

The latest round of model data is messy with the handling of showers and thunderstorms tonight and very early Sunday morning. Visible satellite shows why models are struggling:

As of 3:45pm, you can see breaks in the clouds over central Kentucky, eastern Kentucky, and southwestern Ohio. Meanwhile, much of central Indiana and western Kentucky was cloudy, and there was more clearing ahead of the cold front pushing through Illinois. The setting sun will mean decreasing instability, further complicating the forecast.

Instability has been limited all day thanks to showers moving through early this morning and clouds slow to thin out this afternoon. While there is some wind shear (winds changing direction and speed going away from the ground) and some support for spinning thunderstorms in our area, instability is relatively weak, so the coverage of storms is rather low. As a result, the threat for severe weather is muted.

While there are some significant disagreements on the timing of showers and thunderstorms tonight, this morning’s Microcast model run matches my thinking fairly closely. Here’s what it thinks for shower and thunderstorm coverage at 8pm:

While the placement of showers and thunderstorms is likely off, the model suggests rain and thunderstorms will be scattered at that time. Some strong storms, especially south and east of Cincinnati, will likely linger through early evening.

By midnight, Microcast has showers and thunderstorms along the cold front (now to our west) moving into the Tri-State:

Brighter colors on Microcast here suggest some pockets of heavy rain, gusty winds, and lightning with the stronger cells in the line that forms. By 8am Sunday, showers and thunderstorms will be to our east, and we’ll enjoy a blend of sun and clouds:

In summary, the chance for showers and thunderstorms will be ramping up through the evening as the cold front nears. Damaging straight-line winds, heavy rain, large hail, and lightning will be possible with any strong storms that are able to form. Despite this being a short-term forecast, there is still a considerable amount of uncertainty about the timing, placement, and intensity of thunderstorms through the evening and overnight. Please be alert to the threat for strong and severe storms through Sunday morning!