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!

May is the second busiest month of the year for severe weather warnings. After a record number of tornadoes last year, this year – especially this month – has been anything but stormy.

There have been no Severe Thunderstorm Warnings issued in the Tri-State so far this month. Compare that to the average of 23 warnings each May and the 76 warnings issued in the Tri-State in May 1996:

From January 1st to May 31st, an average of 44 Severe Thunderstorm Warnings are issued in southwestern Ohio, northern Kentucky, and southeastern Indiana. So far this year, only 10 Severe Thunderstorm Warnings have been issued in the Tri-State:

If no Severe Thunderstorm Warnings are issued for the rest of the month, the year-to-date number of Severe Thunderstorm Warnings will be at a record minimum (at least since the National Weather Service in Wilmington started issuing warnings for our area).

There have also been no Tornado Warnings issued in the Tri-State so far in May 2013; on average three Tornado Warnings are issued each May. Here’s the breakdown of how many Tornado Warnings have been issued each May since 1995:

In addition to no Tornado and Severe Thunderstorm Warnings, no Flash Flood Warnings have been issued in the Tri-State. On average, 7 Flash Flood Warnings are issued in the Tri-State every May. Here’s how many year warnings have been issued each year during the month of May since 1995:

Why have been there been so few Severe Thunderstorm, Tornado, and Flash Flood Warnings so far this year? You can’t place the blame on a single ingredient, but the lack of low-level moisture and cooler than average air for most of the spring are the biggest reasons.

Data from NOAA’s ESRL shows colder than average temperatures (blue, purple) over most of the Midwest, Mississippi Valley, and Plains since March 1st:

Warm air is a key ingredient for getting severe storms. While you need warm air near the ground to get strong storms, you also need cold air aloft. Data from NOAA’s ESRL shows that there has been plenty of that this season (in blue):

However, most of this cold air has been associated with upper-level lows and dips in the jet stream. Severe weather is not common when you have cold air aloft and little support at the surface.

NOAA’s ESRL data suggests there has also been a lack of instability this spring. One way to measure instability is by looking at a plot of Lifted Index:

Higher Lifted Index values mean less instability and lower Lifted Index values mean more instability. Notice relatively unstable air (blue, purple colors) over the Ohio and Tennessee Valley compared to our northwest. In the last couple of months, the best instability has been to our southwest, south, and east. As a result, the strongest storms in this country so far this spring have been focused there.

A quiet start to the peak severe weather season doesn’t necessarily mean that we’ll see a quiet end of severe weather season. Be prepared for what could be a busy summer of severe weather!

A cold front will push through the Tri-State over the next couple of hours, bringing showers and thunderstorms to some but not all. Overall, late week looks quiet and cool.

This morning’s run of Microcast does a nice job with cloud cover and rain chances through through tomorrow. Microcast keeps the the best chance for scattered showers and thunderstorms southeast of Cincinnati at 8pm tonight:

By midnight, we will likely still be mostly cloudy, but rain will be gone. Microcast has a good handle on this:

Clearing in earnest will begin just after midnight. By 7am, we’ll be clear, as Microcast shows:

If you love sunshine without the heat, tomorrow will be a nice day. Microcast shows a sunny to mostly sunny sky overhead for tomorrow’s afternoon rush at 5pm:

It will be cool tonight, tomorrow, and into the start of the weekend. This morning’s WRF model suggest we’ll bottom out in the upper 30s and lower 40s Friday morning:

I don’t think we’ll be quite that cold by 6am Friday. Most will drop into the low to mid 40s tomorrow morning,  10-15° below average.

This morning’s WRF model suggests we’ll reach to near 60° by lunchtime Friday:

High temperatures tomorrow will be in the mid 60s. This morning’s GFS model suggests we’ll be in the upper 60s (orange colors) by late Saturday afternoon:

We’ll likely reach into the upper 60s and lower 70s Sunday, and into the 80s nearing the middle part of next week. If your yard isn’t soggy, you’ll be able to mow tomorrow, Saturday, and most of Sunday:

Many saw frost in the Tri-State this morning thanks to a clear sky overhead, a calm wind, and a dry air mass in place. The warmest Tri-State locations only dropped into the lower 40s, but most hit the mid and upper 30s to begin Mother’s Day 2013:

Today’s official early morning low temperature of 37° at the Cincinnati/Northern Kentucky International Airport makes Mother’s Day 2013 the 6th coldest start to Mother’s Day on record (the first Mother’s Day was in 1908):

Tonight looks to be colder than this morning with slightly drier air over the Tri-State and winds lighter for a longer period of time.

How unusual is it to see a frost or freeze in May? It’s unusual, but it happens every couple of years. Since 1871, Cincinnati has dropped to or below 32° 24 times, 34° 53 times, 36° 108 times, and 38° 185 times during the month of May (out of a total of 4,242 possible days). The latest spring hard freeze (28° or colder) on record in Cincinnati was in early May, but areas of frost have showed up in Cincinnati as late as May 31st:

Frost can occur at different temperatures; usually, a temperature of 36° or lower with a light wind means frost is a concern.

Nearly all of the temperatures we show you on television are measured about 6 feet above the ground. Because cold air is more dense than warm air (and therefore sinks), the temperature at the ground is often 2-4° colder than 6 feet above the ground. This is big reason why we are encouraging everyone to cover their plants or bring them inside overnight!

It is unusual to drop into the 20s in Cincinnati during the month of May. Since 1871, there have only been 2 hard freezes in Cincinnati between May 1st and May 31st. Here are some additional facts about near freezing temperatures in May:

The weather pattern from early May 2011 is very similar to the pattern we are in now. Note this morning’s low matches the morning low from May 4th, 2011 and tonight’s forecast low temperature matches the low temperature on May 5th, 2011.

I strongly recommend you bring in your plants tonight!

An upper-level area of low pressure continues to spin over the Tennessee Valley at this hour, but it will slowly push east nearing mid-week. This upper-level low can clearly be seen as the swirl in 7:30pm water vapor satellite imagery (sampling moisture 15,000 to 30,000 feet above the ground):

Ahead of this upper-level low is a large plume of low-level moisture, giving most in the Tri-State soaking rain now. Here are some 24-hour rainfall totals (8pm Saturday to 8pm Sunday) in the Tri-State:

The daily rainfall record for Cincinnati today (May 5th) has been already been broken. 1.72″ of rain fell through 8pm today at the Cincinnati/Northern Kentucky International Airport; the old daily precipitation record for this date was 1.67″, set in 1882.

Note many in the far northeastern part of the Tri-State have seen little or no rain, while some southwest of downtown Cincinnati have picked up more than 2″ of rain in the last day.

This morning’s Microcast run does a nice job with the timing of precipitation through Monday night. Microcast suggests light, moderate, and even some pockets of heavy rain will be around at midnight Monday:

Microcast suggests the coverage and intensity of rain will drop some overnight, but there will still be clusters of rain in the Tri-State at 8am Monday:

As temperatures rise through the 50s Monday morning, the coverage of rain will increase. Microcast suggests (and so do I!) you should plan for showers in and around your neighborhood at lunchtime tomorrow:

Microcast still has rain in the Tri-State at 5pm tomorrow, but I don’t expect it to be as widespread in Cincinnati as it was this afternoon:

Rain will be more scattered Monday night and Tuesday as this upper-level low slowly pushes east.

So when will the rain be done for a while? This morning’s GFS model suggests this upper-level area of low pressure (yellow, orange, and red colors) will to our southeast by early Tuesday morning:

Energy rotating around that low pressure center (bright colors) will trigger scattered showers in our area Tuesday. By Thursday morning, the GFS model has this disturbance to our east:

All of the energy with that system will be focused to our east by then, so Wednesday and early Thursday look quiet. The GFS model, however, has more energy (yellow and orange colors) to our west by Friday morning, meaning chances for showers and thunderstorms will return late in the work week:

Wednesday looks to be our only break from this active pattern this week! Longer-range forecast guidance suggests early next week will be quiet but cool.

In the world of meteorology, we spend a lot of time focusing on what is going on near the ground. What goes on above the ground, however, can be just as important if not more important than what is going on near the ground. It is not uncommon for there to be differences in model data near the ground, but upper-level differences are less common. Large upper-level differences often mean big problems when getting a forecast together.

A prime example of how upper-level differences affect the forecast comes later this week and early next week. Meteorologists often look about 18,000 feet above the ground for disturbances and areas of low pressure; later this week, we find little consensus on where a developing area of low pressure will go in the week ahead.

This morning’s GFS model run suggests this developing area of low pressure will be centered over southeast Arkansas Sunday afternoon (Cincinnati is labeled with a dot, and the area of low pressure is in green to our south):

Last night’s GFS model run, however, says that same area of low pressure will be over the Mississippi Valley Sunday afternoon:

Upper-level low uncertainties continue into early next week. This morning’s GFS model suggests this upper-level low will be to our east by next Tuesday evening:

Last night’s GFS model also has this model to our east by next Tuesday evening, but it is much weaker (which could affect rain chances):

Which run of the GFS should a meteorologist believe? Maybe this morning’s ECMWF model will help us decide; it puts the area of low pressure over Iowa Sunday afternoon:

This morning’s ECMWF model has that same upper-level low nearing Toronto by Tuesday evening:

Clearly, there are some large discrepancies regarding where this upper-level wave is headed. For now, we are forecasting little to no rain in the Ohio Valley Tuesday, Wednesday, and Thursday and an increasing chance for rain late Friday through the weekend. At this point, it looks like the best chance for rain and thunderstorms will be Monday, but that is highly uncertain given the forecast path (or lack thereof) of low pressure 18,000 feet above the ground.

Stay tuned for a changing forecast in the week ahead!

Only scattered showers are forecast through mid-evening, but the threat for rain will build later tonight. The threat for thunderstorms is barely there; most will just see rain – heavy at times – after midnight.

Clouds will stay thick through the night. The most recent satellite and radar data snapshot shows scattered showers in our area now, and plenty of rain along a cold front to our west.

This morning’s Microcast run does a nice job with the timing and intensity of rain tonight and tomorrow. Microcast suggests widely scattered showers will be around at 8pm tonight:

By midnight, Microcast keeps the best chance for rain west of Cincinnati:

Microcast (and other models all) suggest there will be plenty of rain around overnight and early tomorrow morning; be prepared for a wet morning commute:

Notice there will be some pockets of moderate to heavy rain early Wednesday morning. Ponding of water on the roads is the main concern for this event. The risk of severe thunderstorms and flooding is low at this point. By 5pm Wednesday, the widespread rain will be long gone and clouds will break some, as Microcast shows:

How much rain will we get? There are some disagreements amongst the latest round of model data on how much rain will accumulating, but most models – including Microcast – suggests most will see 1/4″ to 3/4″ of rain through tomorrow afternoon. Some may see 3/4″ to 1 1/4″ of rain:

Colder air will sweep in behind this cold front. Light winds and temperatures in the mid 30s Thursday morning and Friday morning suggests there may be some areas of frost before the sun comes up.

Today is “Day 1” of a rather active period of weather. While every day this week will not be a washout, there are significant chances for rain each day this week. April is known for showers and thunderstorms, and this week will be no exception.

Satellite and radar imagery reveals thick clouds over the Ohio Valley and showers northwest of Cincinnati as of 4:25pm:

While some in Fayette and Union County may see a quick, passing showers through 8pm, nearly all of the Tri-State will be dry this evening and most of the overnight. By late tonight and early tomorrow, the cold front to our west (the lifting mechanism that helped to produce showers today in the Ohio Valley) will be nearing the Tri-State, allowing for showers and isolated thunderstorms to develop in the Cincinnati early tomorrow morning.

Tuesday will be mostly cloudy with rain and scattered thunderstorms. Given dewpoints in the 60s and temperatures gradually rising through the 60s and 70s tomorrow, strong and severe storms are possible. The Storm Prediction Center has placed most of the Tri-State under a SLIGHT risk for severe storms tomorrow:

Based on the latest model data, large hail and damaging straight-line winds will be the main severe weather threats Tuesday. The tornado threat – for now – is low.

Rain and thunderstorms will be more scattered Wednesday, but ample low-level moisture will support a threat for heavy rain with the strongest showers and thunderstorms. This morning’s WRF models suggests dewpoints will be in the low to mid 60s (yellow and orange colors) Wednesday afternoon:

This morning’s WRF model suggests showers and thunderstorms will affect most of the Ohio Valley, Mississippi Valley, and the Great Lakes by late Wednesday afternoon (largely in part to this surge of low-level moisture):

Thursday will be very similar to Wednesday. This morning’s WRF models suggests dewpoints will be in the low to mid 60s (yellow and orange) Thursday afternoon:

As a result of this low-level moisture, the same WRF model suggest showers and thunderstorms will be widespread to our north and west at 8am Thursday morning; the coverage and intensity of showers and storms will continue building into the afternoon and evening:

In addition to a stalled out front in the area, ample low-level moisture, and warm air in the region, a large upper-level disturbance will approach us Wednesday, Thursday, and early Friday. This morning’s GFS model suggest this disturbance will take on a “bowling ball” shape by Friday morning:

This “bowling ball” shape – especially this time of the year – is usually a catalyst for severe storms if other conditions are present.

The primary focus for strong and severe storms this week will be Thursday night and Friday ahead of this disturbance and with a strong cold front coming through. It is too early to discuss specifics on severe weather threats and timing.