The next 24 hours will be fairly quiet in the Ohio Valley, but a threat for storms continues in the Ohio Valley Tuesday night and early Wednesday. Severe weather is not a guarantee, but the threat for severe weather has increased since yesterday.

This morning’s WRF model suggests clusters of thunderstorms will be northwest of the Tri-State for mid-afternoon Tuesday:

Also note the line of showers and thunderstorms organizing in the Mississippi Valley tomorrow afternoon. This morning’s WRF model has that line of showers and thunderstorms (and perhaps some individual cells ahead of the line) moving into the western half of the Tri-State by 4am Wednesday:

The WRF model has this line of showers and thunderstorms moving east of Cincinnati by 10am Wednesday:

As I mentioned in yesterday’s blog post, damaging winds will be the main severe weather threat early Wednesday morning. One indication of this is the strength of the wind 5,000 feet above the ground; this morning’s NAM model shows 60-80 knot (70-95mph) winds 5,000 feet above the Tri-State at 7am Wednesday:

This morning’s GFS model has winds about as strong at 1am Wednesday in the Ohio Valley:

If these winds can be transferred down to the ground, storms may produce damage.

When it comes to wind shear, the speed shear (the change in wind speeds going away from the ground) is impressive but the directional shear (often needed for tornadoes and defined as the change in the wind direction going away from the ground) is not as impressive. For this reason, the latest SREF model from the Storm Prediction Center has the best tornado support along the Mississippi River at 1am Wednesday (Cincinnati is the blue dot):

Summary

Damaging straight-line winds will be the main concern with any strong storms in the area early Wednesday morning. Storms will likely arrive in the Tri-State in a weakening mode, but storms may still be strong or even severe. Large hail and heavy rain are secondary threats with the strongest storms, and the tornado threat is the lowest threat. Be prepared for heavy rain and gusty winds during Wednesday morning’s commute.

Last last week, there were indications from computer forecast models that there would be some instability available for thunderstorms  in the Ohio Valley Tuesday night and Wednesday. Based on upper-level support alone, the support for heavy rain Tuesday night and Wednesday has been in the forecast since last Friday. The thunderstorm threat will need to be monitored closely nearing mid-week.

For now, the severe weather threat in the Tri-State is not a major concern, but strong or severe storms can’t be ruled out. The main reason why severe weather will be favored outside of the Tri-State will be the time of day. The latest round of model data suggests the cold front – the surface feature supporting the chance for thunderstorms early Wednesday in the heart of the Ohio Valley – will be moving through during the early morning commute Wednesday, as NOAA’s Hydrometeorological Prediction Center shows in their latest forecast surface analysis:

If this cold front was moving through during the afternoon (when instability and the temperature would be higher), the risk for severe weather would be noticeably higher. Since the cold front (and it’s associated thunderstorms) will be moving through late at night, instability will be lower, which tends to support a lower severe weather threat.

This morning, the Storm Prediction Center felt the best severe weather threat Tuesday morning through Wednesday morning was west of the Tri-State, where greater instability and low-level moisture would be focused:

This is a rather large “slight risk” area from the Storm Prediction Center. While not likely, they may be looking to issue a moderate risk in the Ark-La-Tex, where shear and dewpoints will be elevated and the tornado/large hail threat will be higher. The Storm Prediction Center, though, is likely going to wait until more model runs complete before making adjustments and/or issuing a moderate risk. SPC has placed much of the Mid-Atlantic and Carolinas under an enhanced risk for severe storms Wednesday morning and afternoon (highlighted in red):

The Tri-State has not been placed the Tri-State under a slight or enhanced risk for severe weather yet, but that may change.

One thing I’ll be watching as new models come in is the strength of winds aloft, especially 5,000 feet or so above the ground. Without going into great detail, strong winds 5,000 feet or so above the ground often serves as a signal that damaging straight-line winds are possible in an otherwise favorable thunderstorm environment. In other words, these strong winds aloft don’t always mean an area will see damaging winds, but it is a concern when thunderstorms are forecast.

So what do the winds look like 5,000 above the ground Tuesday night and Wednesday? This morning’s NAM forecast model suggest winds will be roughly 50-60 knots (60-70mph) overhead at 7am Wednesday morning (Indiana, Ohio, and Kentucky are on the right half of the screen):

These are fast winds! This morning’s GFS model also suggests winds will be 50-60 knots (60-70mph) 5,000 above the ground at 7am Wednesday morning:

In heavy rain, most – if not all – of these winds tend to be mixed down to the ground, and we can get blasted with strong or severe winds. In this particular setup, this is not a guarantee, but it is something to watch. 

With storms gradually weakening to our west late Tuesday as instability drops, our severe weather threat is conditional. This morning’s high-resolution WRF model has numerous showers and thunderstorms to our west by 4pm Tuesday:

The latest high-resolution WRF model has showers and thunderstorms congealing into a line by 1am Wednesday:

While the high-resolution WRF model doesn’t go out through the morning commute Wednesday, a slightly lower resolution WRF model does…and here’s what it thinks the radar will look like by 7am Wednesday:

With this “future radar” product painting yellow and red colors in our area, heavy rain is a concern, but this also highlights the potential for a solid line of strong or severe thunderstorms to sweep through the Tri-State.

Summary

There is still uncertainty about the strength and timing thunderstorms Tuesday night and early Wednesday. The time of day tends to favor weaker storms, but strong winds above the ground suggest gusty or damaging winds are possible with any strong storm that is able to form.

Models suggest better support for severe storms (higher dewpoints, great shear, better instability, and stronger lift) will be closer to the Mississippi River. There are also indications from the newest computer model runs that we will get “cut off” from Gulf moisture that will fuel thunderstorms.

Storms will likely be in a weakening mode as they arrive in the Tri-State late Tuesday night and Wednesday. At this time, isolated strong storms appear more likely than a widespread severe weather event.

Stay tuned for updates! I hope to have a new blog entry up tomorrow…

The area of low pressure that gave the Tri-State a quick shot of snow is heading east in a hurry; high pressure over the Mississippi Valley is already moving in from the west. The clearing line along the Indiana/Illinois border now will be moving into the Tri-State early this evening. By late evening, the sky overhead will be clear to partly cloudy. Tonight’s hour-by-hour forecast shows temperatures falling into the upper teens late:

High pressure will settle into the Ohio Valley Saturday. With high pressure nearby, ample sunshine is forecast tomorrow morning, and a partly cloudy sky is forecast Saturday afternoon:

High pressure will push east Saturday night and early Sunday, allowing low pressure to move in from the west. Mid- and high-level clouds will increase Saturday night, and only filtered sun is expected Sunday. Sunday’s hour-by-hour forecast shows a mix of freezing rain, sleet, snow, and rain developing in the Tri-State Sunday afternoon:

Temperatures will be above freezing most if not all of Sunday night, so the mix of precipitation types will likely transition to all rain by early Monday morning. Only rain is forecast Monday afternoon through Wednesday. While there are large model discrepancies in next week’s forecast, the latest GFS forecast model shows some limited instability (shown in purple) in the Tri-State Wednesday afternoon:

For this reason, a mention of thunderstorms will be put into the forecast Wednesday.

Cold air is likely to return late next week. Little to no snow accumulation is expected Thursday as a cold front sweeps through the Ohio Valley.

Two different areas of low pressure and a large upper-level disturbance approaching the Ohio and Tennessee Valley tonight will produce snow in the Tri-State tomorrow. This is not going to be a big winter storm, but accumulation will be widespread.

The National Weather Service has posted a Winter Weather Advisory for the Tri-State. This advisory will be in effect from 6am to 5pm Friday:

The heaviest snow will likely fall between 9am and 3pm.

This morning’s Microcast model run has a good handle on the timing of snow Friday. At 8am Friday, light snow will be moving in from the west:

By noon Friday, Microcast suggests snow will be widespread:

By late Friday afternoon, Microcast shows snow exiting the Tri-State:

By early Friday evening, most in the Tri-State will get 1-2″ of snow accumulation; some will see 2-2.5″ of accumulation. Overall, Microcast has a good handle on amounts, but amounts for specific towns on this map are approximate:

As new model data comes in, we will adjust totals through the night and early tomorrow. Please be careful traveling tomorrow!

The flurries and snow showers passing through the Ohio Valley today will end tonight, and clouds will gradually dissipate this evening and overnight.

With high pressure nearby tomorrow, our attention turns to a late week system that looks to bring us accumulating snow. Temperatures will be around 20° early Friday and around 30° by late Friday afternoon; this is certainly cold enough to support snow and set concerns for freezing rain, sleet, and rain aside…at least for now.

When it comes to forecasting an amount of snow, meteorologists often see what liquid amounts computer models are suggesting and then convert that liquid amount to a snow amount based on temperatures. Here is what the latest forecast models think for liquid amounts Friday morning through Friday night:

Notice one model has no precipitation for our area Friday. We are ignoring this model for now. Because temperatures will in the 20s Friday, snow to liquid ratios will be roughly 15:1 to 20:1; in other words, temperatures Friday suggest forecast liquid amounts need to be multiplied by 15 or 20 to get snow amounts. When the calculations are made, here’s approximately how much snow this morning’s models are suggesting for Friday:

Remember, these are computer model suggestions, not a forecast. Given the good consensus among models (with the exception of the model that gives us nothing and is being thrown out for now), we are fair game for a couple of inches of snow Friday.

Specifics on snow amounts in the Tri-State will likely have to wait until tomorrow. Stay tuned!

Have you ever heard of “cooling stack enhanced snow?” Odds are you probably haven’t, but it was the reason behind light snow bands in the Tri-State this morning.

When “lake effect snow” or “lake enhanced snow” falls in the Ohio Valley, cold air is passing over a relatively warm lake, such as Lake Michigan. In the Tri-State, bodies of water are very small, and lake effect snow bands rarely form downwind of these bodies of water.

While we did not have “lake effect snow” or “lake enhanced snow,” many saw “cooling stack enhanced snow.” Cooling towers at Tri-State power plants often release warm, moisture-laden air into the atmosphere. Because their is a large temperature difference between this air and the air surrounding it, the air from the cooling stack cools and condenses rapidly, forming a cloud. Excess moisture falls from the cloud as light snow.

This process happened early this morning downwind of the Miami Fort Power Station in northern Boone County near the Cincinnati/Northern Kentucky International Airport:

At 8:30 this morning, you could see bands of snow on our live radar over northern Kentucky and downwind of the Miami Fort Station:

You could also see a narrow band of light snow on radar east-southeast of the Zimmer Power Plan in Moscow at 8:30 this morning:

We don’t know how warm the air was coming out of the cooling stack this morning, confidence is high that the temperature difference between this air and the air surrounding it was large. Early morning lows were reached around the time these bands were forming and producing light snow, and it was cold:

As promised over the last several days, arctic air is on the move. The core of this arctic air will remain over the Great Lakes and southern Canada through mid-week, but it will still be very cold over the Ohio Valley Monday, Tuesday, and Wednesday.

As of 8pm Sunday night, temperatures are mostly in the 20s and 30s:

Most locations in the Ohio Valley are 10-25° colder than they were 24 hours ago:

Northwesterly flow has dominated for most of the day in and around Cincinnati, allowing the arctic air centered over southern Canada to be transported into the United States. As of 8pm Sunday night, most major cities in Canada are below zero:

It will be very cold Monday, and it will also be quite windy (especially during the afternoon); winds will likely be out of the west between 5 and 15mph Monday morning and between 15 and 25mph Monday afternoon. As a result, wind chills will be in the teens and single digits even though temperatures will be in the low to mid 20s all day:

The core of arctic air will dive farther south Monday night and Tuesday. Winds will be slightly weaker compared to Monday afternoon, but wind chills will still be between -10° and 10° from 7am to 7pm Tuesday:

Thanks to flow out of the east and southeast (instead of the northwest) and arctic air lifting north, Wednesday won’t be as cold. Winds will also relax some Wednesday thanks to high pressure moving in from the west. Temperatures are forecast to be in the teens and 20s Wednesday, and wind chills will be in the single digits and teens:

The National Weather Service Forecast Office in Wilmington may issue a Wind Chill Advisory for parts of the Tri-State Tuesday morning. A Wind Chill Advisory is issued when winds are expected to be at least 10mph and the wind chill is forecast to drop between -10° and -24°. The minimum wind chill Monday night or Tuesday morning should be around -10° in Cincinnati; -10° to -15° wind chills are possible north of Cincinnati.

Need to get prepared for the cold? Here are some cold safety tips from the Centers for Disease Control: http://www.bt.cdc.gov/disasters/winter/guide.asp

Today marks the 36th anniversary of the coldest low temperature on record in Cincinnati. The Cincinnati/Northern Kentucky International Airport dropped to -25° on January 18, 1977; the high temperature that afternoon was only 0°.

It was brutally cold in the Tri-State that morning, but a map of early morning lows for January 18, 1977 reveals that some spots got colder than others:

Data from NOAA’s Earth Systems Research Laboratory shows arctic air (in purple) surging not just into the Ohio Valley that day, but all the way down to Florida and the Gulf of Mexico:

While you may not remember the date, you may remember the Ohio River being frozen. Video from the WKRC-TV archives shows many walking across the Ohio River that day:

Many unsuccessfully tried to drive their cars across the river while the river was frozen. You may also remember seeing the Cincinnati buildings perspiring in the arctic air:

Cincinnati has only dropped under -20° four times since the coldest day on record…once each in January 1984 and 1985 and twice in January 1994. This anniversary is a reminder that arctic air can – and often does – push south this time of the year. While it won’t be as cold as January 18, 1977, next week looks to be the coldest stretch so far this season.

A well-advertised blast of arctic air will be coming soon to the Ohio Valley. We will be on the outer edge of this arctic air mass; the core of cold air will remain over the Great Lakes and southern Canada.

As I mentioned in yesterday’s blog post, the last day with a high temperature below 20° in Cincinnati was on February 4, 2009; the last day with a low temperature below 10° was on February 10, 2011. Cincinnati has only dropped below 10° 74 days in the last 10 winters.

Cincinnati doesn’t always drop below 10° in the winter. Here are the coldest low temperatures we’ve reached during the winter season for the last several years:

I’m thinking we drop down to 9° by early Tuesday morning in Cincinnati, which will be the coldest temperature of the 2012-2013 winter season so far.

While temperatures will rise and fall some early next week, both high and low temperatures will likely be well below average. The latest GFS model suggests temperatures 5,000 feet above the ground will be 15-20° below average Monday night:

The latest SREF model also suggests temperatures 5,000 feet above the ground will be 15-20° below average Monday night:

Confidence is rising that this below average temperature stretch will end by late next week with a ridge of high pressure and warmth moving in from the west.