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:

spc2

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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Near Record Warmth Fuels Severe Threat Tonight

Temperatures will soar into the mid 70s this afternoon with more sun than clouds. Today’s record high temperature is 72°, set in 1930. The all-time record high temperature in Cincinnati for February is 76°, set on February 10, 1932.

As of 11am, temperatures are already in the upper 60s and lower 70s:

feb24-blog-11amtemps

For February standards, the dewpoint is very high at 55° as of 11am:

feb24-blog-11amdewpoints2

For perspective, the average February dewpoint in Cincinnati is 24°, and the record highest dewpoint in Cincinnati.

As of 11:30am, the entire Tri-State is in an ENHANCED risk for severe thunderstorms through tonight:

feb24-blog-spc

This threat will be maximized this evening. More sun than clouds will lead to temperatures rising into the 70s as instability grows:

feb24-blog-1015amclouds

Plan for a mix of sun and clouds this afternoon before isolated showers and storms begin developing between 4pm and 6pm. Wind speeds will increase this afternoon (sustained between 15 and 25mph by 5pm):

feb24-blog-afternoon

Rain and storms will increase in coverage and intensity this evening as a cold front nears:

feb24-blog-evening

Rain and storms will push east of the Tri-State between 12am and 3am. Notice temperatures will fall through the 60s and 50s this evening and then through the 50s, 40s, and into the 30s late tonight:

feb24-blog-overnight

Over the last few days, I’ve been posting a impact graphic for Friday’s severe threat. Now that it’s Friday, I’ll break the threats down by period, starting with late this afternoon:

feb24-blog-impacts1

This is a minimal severe weather impact, but this evening’s severe threat will be much higher with damaging straight-line wind being the main concern (and tornado and large hail being secondary threats):

feb24-blog-impacts2

The threat for severe storms will end and be focused east of Cincinnati in the early overnight:

feb24-blog-impacts3

Since 1995 (when the National Weather Service in Wilmington opened), the record for the greatest number of warnings in the Tri-State during a single February is 12 (set in 2002). There are an average of 3 Severe Thunderstorm Warnings issued in the Tri-State each February.

So what might the radar look like? Guidance is still messy, so I encourage you to follow the overall trend in these graphics. Here is what high-resolution guidance suggests the radar might look like at 4pm today:

feb24-blog-4pmradar

Basically, storms are starting to develop along/north/west of I-71, but the coverage is limited. The main event comes this evening. Let’s fast forward to 7pm:

feb24-blog-7pmradar

Storms are increasing in intensity and coverage. Other guidance suggests two lines of storms forming near and west of the Tri-State. Let’s go to 10pm:

feb24-blog-10pmradar

Lines of showers and storms are sweeping into and through the Tri-State late in the evening. Some storms may be strong or severe at this time. Let’s fast forward to 1am Saturday:

feb24-blog-1amsaturday

Rain and storms are moving through southwestern Ohio and northern Kentucky. Strong and severe storms are still a possibility at this time, but the overall threat is diminishing.

Have a way to get watch and warning information today and tonight. Do not think because the sun sets tonight that the threat for severe weather is dropping. 

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Friday’s Severe Threat Has Increased

Before sunrise this morning, the Storm Prediction Center pushed much of the Tri-State into an enhanced risk for severe storms Friday:

spc

This is an upgrade to the risk from yesterday when the enhanced risk only came into Fayette, Union, and Franklin County of southeastern Indiana. The risk is lower in the southeastern Tri-State.

A line of rain and storms will likely sweep into and through the Tri-State Friday night with discrete, individual cells (potential troublemakers favoring areas along/west/north of I-71 and along/west of I-75).

Much of this bump up in the risk is driven by the tornado threat. SPC’s Short Range Ensemble Forecast “Tornado Ingredients” composite (a mush-mash of tornado parameters with varying weights) has highlighted the Tri-State at 11pm Friday:

feb23-blog-spcingr

Note that 11pm Friday is not the specific time severe weather is expected in the Tri-State; there is a window, and this time is near the center of that window.

I talked about the SHERB parameter earlier this week in a blog post earlier this week in a blog post; as a review, it has skill in highlighting severe weather areas where there is limited instability and high wind shear (a similar environment to what we have Friday). SHERB values of 1+ signal and elevated threat for severe storms in this mode. Here’s what this morning’s NAM model has for SHERB at 7pm Friday:

feb23-blog-sherbnam

Those values are higher and positioned more to the east than runs earlier this week. Does this morning’s NAM model agree?

feb23-blog-sherbgfs

It does, and these values are not extreme, but high. This suggests confidence is rising in strong or severe storms late Friday.

I could show you additional parameters and signals, but ultimately, you need to know the threats and timing. My latest thinking is below:

impacts

The damaging straight-line wind threat, large hail, and tornado threat have increased since yesterday, but this threat may lower or increase again later today or Friday. Stay alert!

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Friday Severe Threat Update

Early Wednesday morning, the Tri-State was placed in a slight to enhanced risk for severe storms for Friday. This should not be a surprise if you saw my blog post from yesterday. The enhanced risk is northwest of Cincinnati, and the rest of the Tri-State is in the slight risk:

feb22-spc

The enhanced risk is the higher risk, and the slight risk is the lower risk.

There will be a main line of rain and storms sweeping through Friday night, but there is also a concern – especially northwest of Cincinnati – for discrete, individual cells or “troublemakers” ahead of the main line late Friday afternoon and early Friday evening. These cells can sometimes be supercellular, but not always. In this case, guidance supports tornadic thunderstorms and supercells over northern and central Indiana, but the threat is more nebulous and conditional in southeastern Indiana.

Temperatures will likely be in the mid 50s early Friday morning:

feb22-temps1

…and the dewpoint will likely be within a couple of degrees of the temperature. Warm, humid air supports the storm threat. Wednesday morning’s NAM model future radar product suggests there will be stray showers – especially northwest of Cincinnati – early Friday morning:

feb22-blog-7amradar

Temperatures will rise into the low and mid 70s Friday afternoon. This kind of warmth fuels storms, especially in February:

feb22-temps2

Tuesday morning’s NAM model suggests a line of showers and storms will develop to the west of the Tri-State early Friday afternoon:

feb22-blog-1pmradar

This line is likely to intensify during the afternoon as it pushes east:

feb22-blog-4pmradar

Let’s stop here, and introduce the supercell parameter. What’s that? It’s an index that shows the support for supercell storms and tornadoes. Higher values of the supercell parameter suggest a higher threat for tornadoes, and the NAM model has these high values in northwestern Indiana at 4pm Friday:

feb22-blog-namsp

…and a lower, but still significant threat here. The GFS model is not as impressed at 5pm Friday:

feb22-blog-gfssp

…but it, too, has us in a relatively low threat. Here’s what the NAM model thinks the radar will look like at 7pm Friday:

feb22-blog-7pmradar

The highest radar echoes are still over Indiana, but the line is marching east. This line will gradually weaken as it moves east, but strong and severe storms are still a possibility Friday evening. My overall thinking on the severe threat late Friday is here:

feb22-impacts

Damaging straight-line, large hail, tornadoes, and flooding are late Friday’s severe weather threats, in that order. Stay alert and be prepared!

 

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