Severe Storm, Flooding Threat Thursday

Thanks largely to warm, steamy air, there will be an elevated risk for flooding and flash flooding in the Tri-State Thursday and Thursday night.

First, most of the Tri-State is in a Flash Flood Watch from 4am Thursday through 4am Friday for the potential of heavy rain leading to flooding:

jul12-ffw

How much rain will it take to get a Flash Flood Warning? Here’s 1 hour flash flood guidance:

jul12-ffg1

Here’s 3 hour flash flood guidance:

jul12-ffg2

6, 12, and 24 flash flood guidance is not worth showing. The summary here is that it must rain quickly and heavily to get flash flooding. Thunderstorms will be needed to get flash flooding tomorrow. 1.5″ of rain per hour will likely trigger warnings.

There is also a slight risk for severe storms over most of the Tri-State tomorrow:

jul12-spc1

As I see it, there is a lot of instability to fuel storms, but other ingredients for severe storms are surprisingly absent. Here are my forecast severe weather impacts for Thursday:

jul12-impacts

Notice the most likely time for severe storms Thursday centers between 3pm and 8pm.

As of 3pm, it’s warm outside:

jul12-temps

It’s also disgustingly humid outside, with dewpoints well into the 70s:

jul12-3pmdewpoint

This means heat indices are over 90° for many:

jul12-feels

There are showers and storms developing over central Indiana at this time:

jul12-215pmclouds

Current thinking is as isolated showers and storms will brush into communities northwest of Cincinnati early this evening before the sky becomes mostly clear tonight:

jul12-evening

After isolated showers and storms in the morning, showers and storms will develop and increase in coverage Thursday afternoon:

jul12-thursday

Showers and storms will diminish Thursday evening. They will be isolated overnight Thursday night and scattered Friday. The weekend will be quiet and peaceful but also humid. More heat is coming next week:

jul12-temptrends

Be alert for heavy rain and strong to severe storms Thursday, especially during the afternoon and evening!

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Friday Afternoon Severe Weather & Forecast Update

Thanks to ample sunshine, more supportive temperature profiles in the atmosphere, and an increase in the amount of wind shear over the last few hours, the threat for severe storms remains elevated despite a weak round of storms northeast of Cincinnati now. Radar shows those storms and stronger clusters of storms east and northwest of Cincinnati at this hour:

jul7-3pmradar

Clusters of storms over central and northern Indiana are the ones to watch. Those will expand in coverage and move southeast this evening.

Through midnight, the Tri-State remains in an ENHANCED risk for severe storms:

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Damaging straight-line is still the main threat with large hail a close secondary threat. Tornadoes and flash flooding are the lowest of the severe threats at this time:

jul7-impactsafternoon

It’s warm outside. Temperatures are in the mid to upper 80s for most as of 3pm:

jul7-3pmtemps

 

It’s also steamy with dewpoints in the mid 70s:

jul7-3pmdewpoints

Showers and storms will develop late this afternoon and early this evening. Showers and storms will gradually end nearing midnight. Notice the large drop in temperatures due to showers and thunderstorms:

jul7-eveningafternoon

Cooler, less humid air is coming tomorrow. After areas of fog in the morning, a mix of sun and clouds is forecast during the afternoon:

jul7-saturdayafternoon

Enjoy the break from heat and humidity this weekend, because both are coming back next week!

jul7-temptrend

You should have multiple ways to get watch and warning information this afternoon and evening. Be alert!

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Today’s Severe Weather Threat Update

The Storm Prediction Center has placed the entire Tri-State in an ENHANCED risk for severe storms through this evening:

jul7-spc

The primary threats this afternoon and evening are damaging straight-line wind and large hail. Flash flooding and tornadoes are secondary threats. All of these threats are in play between 3pm and 8pm today:

jul7-impacts

There is already a Severe Thunderstorm WATCH in effect for parts of Ohio and Indiana just north of the Tri-State:

jul7-watch

Showers and storms have already developed over northeastern Indiana, and these clusters of showers and thunderstorms will expand in coverage and move southeast over the next several hours:

jul7-radar

Ahead of these showers and storms, there is plenty of sunshine:

jul7-clouds

Sunshine will boost instability levels available to storms this afternoon and evening. In addition to sunshine supporting storms, it’s also warm. Temperatures are already in the 70s and 80s, and these numbers are rising:

jul7-temps

It’s also steamy. Dewpoints are in the low to mid 70s:

jul7-dewpoint

The necessary ingredients for severe storms are already in place. Temperatures will rise through the 80s this afternoon with showers and storms developing:

jul7-afternoon

Temperatures will crash through the 80s and 70s this evening underneath the weight of showers and storms:

jul7-evening

Have more than one way to get watch and warning information this afternoon and evening!

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Forecast & Severe Weather Update

As of 3:15pm, the Storm Prediction Center is considering the issuance of a Tornado or Severe Thunderstorm WATCH for parts of the Ohio Valley including the western Tri-State:

mcd0577

Temperatures are rising through the 60s and 70s as of 3pm, increasing the amount of instability and likelihood for strong and severe storms:

temps

Dewpoints have also been rising this afternoon, and this is an impressive rise since this morning when dewpoints were in the the 40s:

dewpoints

A 3pm radar snapshot shows showers and thunderstorms developing to the west of Cincinnati and Tri-State:

radar

Current thinking is that showers and storms will rapidly develop and increase in coverage late this afternoon and early this evening and continue in waves through the second half of the evening and overnight:

evening

The coverage of showers and storms will gradually drop late in the overnight, but flash flooding is the main concern from late evening through sunrise:

overnight

Showers and thunderstorms will be favored early Saturday, then partial clearing and rapid warmup comes during the afternoon:

saturday

I have increased the threat for tornadoes, flash flooding, and large hail slightly from my last update this morning:

impacts

The tornado threat is focused along and south of the Ohio River through early evening. The other threats are distributed around the entire Tri-State.

The Storm Prediction Center still has the entire Tri-State in a slight to enhanced risk for severe storms through sunrise Saturday:

impacts

The threat for severe storms Saturday and Saturday night will be focused northwest of Cincinnati:

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This is forecast the threat of strong storms very early Saturday and also late Saturday night/early Sunday.

If you’re tired of this warm and stormy pattern, longer-range guidance has us much cooler next week:

temptrend

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Let’s Talk About The Severe Threat Later Today

Are you aware that strong and severe storms are a possibility later today? You should! If not, let’s break down the threats and timing.

The Storm Prediction Center has placed the Tri-State in a slight to enhanced risk for strong to severe storms through sunrise on Saturday:

The risk is driven by the large hail threat, but the threat for damaging straight-line wind and flash flooding are still significant. The tornado threat is in play, but it is a secondary threat at this time. Here’s a breakdown of how I see severe threats for later today:

Notice that the threat for severe storms is focused after 5pm today and throughout the evening. Additional rounds of thunderstorms are likely after midnight, but the atmosphere will likely be worked over pretty hard by then. Even with this considered, you should be weather aware through the tonight, including through the overnight.

There is also a Flash Flood Watch in place for most of the Tri-State from 7pm Friday through 11am Saturday:

Temperatures are the in process of rising through the 50s and 60s as of 11am:

…and dewpoints are also rising:

These numbers are not supportive of severe storms, but dewpoints will be rising through the 50s and 60s this afternoon and evening. This will support an increasing threat for thunderstorms – including severe storms – as the day and evening progresses.

A visibile satellite snapshot shows why the threat for severe storms is highest over central Kentucky and southwest of the Tri-State…more sunshine:

The first wave of showers will float through the Tri-State this afternoon (especially between now and 3pm) and is already appearing on radar:

These showers and storms are moving northeast at 45mph.

Showers will develop this afternoon, but the threat for thunderstorms will wait until late this afternoon and evening. Notice temperatures will rise through the 60s and 70s this afternoon:

Showers and thunderstorms are likely from late afternoon through this evening in waves:

Some storms may be strong or severe through tonight. Also, note that the Tri-State is in a marginal risk for severe storms Saturday:

This is an evolving threat, so stay weather alert through the day, evening, and throughout the weekend!

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Let’s Talk About Wednesday’s Severe Threat

The Storm Prediction Center has placed the entire Tri-State in an ENHANCED risk for severe storms Wednesday and Wednesday night:

apr4-blog-spc

This is a significant threat for strong and severe storms, but – as I will highlight below – it is conditional on how warm and unstable the low-levels of the atmosphere get.

First, let’s address how we get there. We’re around 60° as of noon:

apr4-blog-11amtemps

Clouds will win out over sun today, but at least some cracks in the clouds will allow the temperature to rise. Here’s a cloud snapshot as of 11:15am:

apr4-blog-1015amclouds

Temperatures will rise into the low and mid 60s this afternoon under a mostly cloudy sky:

apr4-blog-afternoon

Partial clearing is forecast this evening with temperatures falling through the 60s and 50s:

apr4-blog-evening

Clouds will increase and thicken Wednesday. From mid-morning through mid-afternoon, scattered showers and stray, non-severe storms will develop. The coverage and intensity of storms will increase between mid afternoon and early evening. The environment these storms will be in is important. For this, we’ll use the NAM model from Tuesday morning, which has a higher resolution than most models and has a decent handle on the overall setup.  It shows an intensifying upper-level disturbance around 18,000 above the ground at 4pm Wednesday:

apr4-blog-vort

This will provide lift in the atmosphere and help to generate storms. The Significant Tornado Parameter (the higher the number, the more likely tornadoes are if other conditions are supportive) shows the tornado threat focused over Indiana at 4pm Wednesday, but that threat will diminish (but still be more than high enough to watch) and move east from 4pm Wednesday through late evening:

apr4-blog-sigtor

The SHERB parameter (an index of severe thunderstorm in low-instability/high-shear environments; see more in this blog post) shows a significant threat for strong to severe storms in the Ohio Valley late Wednesday afternoon and Wednesday evening. Values in the red usually gather my attention:

apr4-blog-sherb

If thunderstorms form Wednesday, how likely are they to rotate? A good indicator of this is storm relative helicity. In simple terms, a tightly-thrown spiral on a football tossed straight up into the sky has good helicity. Here is what the NAM model thinks for helicity at 4pm Wednesday:

apr4-blog-srh

That bubble of 200 (m2/s2) is enough to get my attention and support a tornado threat.

There is, however and as discussed above, uncertainty on how much instability we get. Dewpoints are forecast to rise into the upper 50s Wednesday afternoon, but the instability forecast is messy. Weak instability means a lower severe threat.

Here’s my overall thinking on Wednesday’s severe weather threat as of Tuesday afternoon:

apr4-blog-impacts

The window for severe storms is 4pm to 11pm Wednesday, but the highest threat centers between 5pm and 8pm Wednesday.

Remember, this is not a final forecast. Conditions and guidance may change in the next 36 hours.

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Let’s Talk About Tonight’s and Wednesday’s Severe Weather Threat

Temperatures have been slow to rise today thanks to soaking rain. As of 11am, temperatures are in the upper 40s and lower 50s:

feb28-blog-11amtemps

Dewpoints are in the upper 40s and rising. These numbers will rise through the 50s and to near 60° this afternoon and evening:

feb28-blog-11amdewpoint

As of 11am, clusters of rain and storms have been marching east through the Tri-State this morning:

feb28-blog-11amradar

Showers and thunderstorms will decrease in coverage and intensity this afternoon as temperatures rise through the 50s and 60s:

feb28-blog-afternoon

Few if any showers will be floating through the Tri-State late this afternoon and this evening, allowing instability to build and increasing the likelihood for strong and severe storms as a cold front nears from the west:

feb28-blog-evening

Wind speeds will increase this evening as low pressure to the west deepens.

Based on the latest guidance and recent trends, there are two windows of opportunities for severe storms through Wednesday. The first comes between 11pm and 3am tonight. This is the main driver behind the Storm Prediction Center’s enhanced to MODERATE risk for severe storms through sunrise:

feb28-blog-spc1

Between 11pm and 3am, the main severe weather threats are damaging straight-line wind and large hail. Tornadoes are a secondary threat at this time. Storms that come through will likely sweep through as clusters, not a distinct line:

feb28-blog-impacts1

A secondary wave of strong and severe storms will come between 6am and 10am. With this wave, the main severe weather threats are tornadoes and damaging straight-line. Large hail is a secondary threat at this time:

feb28-blog-impacts2

This early morning threat is fueling the Storm Prediction Center’s slight to enhanced risk on Wednesday:

feb28-blog-spc2

In addition, there is a Flash Flood Watch for most of the Tri-State through 4pm Wednesday:

feb28-blog-watch

1-2″ of rain will fall tonight and early Wednesday.

Be alert. Have a way to get warnings!

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