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.

For those that like warmer air, temperatures will rise to around 50° Saturday afternoon. If you’re not a fan of cold air, you’re not going to like what’s coming next week. Computer forecast models are coming into consensus regarding an upcoming polar plunge.

The latest ECMWF model shows arctic air (in purple, maroon, and yellow) north of Cincinnati tomorrow morning:

After a brief warmup Saturday, the arctic airmass makes a run to the south. This morning’s ECMWF model has arctic air over much of the Ohio Valley, Great Lakes, and the interior Midwest by 8am Sunday morning:

High and low temperatures will likely be well below average through Monday, Tuesday, and Wednesday. By Thursday morning, the latest ECMWF model has a weak ridge of high pressure developing and an increase in warmth over the central United States:

For now, Tuesday looks to be the coldest day in the next seven. Early morning low temperatures are forecast to dip briefly into the single digits, and afternoon highs are forecast to be around 20°.

Does this kind of cold sound familiar? It shouldn’t! It’s been a couple of years since we saw a low temperature below 10° or a high temperature below 20° in Cincinnati:

Enjoy the warmth Saturday because it won’t last long!

We are halfway through January, and halfway through meteorological winter. Almost 8″ of snow has fallen since December 1st in Cincinnati, but the main concern will be ice tonight. The best chance for seeing ice outside of your home will be from 9pm to 3am; communities north and west of Cincinnati may see little or no ice, while many south and east of downtown will see a glaze of ice by Wednesday morning.

The latest model data disagree on the exact position and amounts of ice, sleet, freezing rain, and snow. PrecisionCast is not excited about our ice accumulation chances tonight:

Microcast is more excited (perhaps too excited) about the threat for ice accumulation tonight:

I think that Microcast is overdoing ice amounts, and PrecisionCast is under-doing them. If Microcast were to verify, an Ice Storm or Winter Storm Warning would be issued for several counties south and east of Cincinnati.

Realistically, most along and south of I-71 will get 0.05″ to 0.15″ of ice accumulation through mid-morning Wednesday. Little to no snow is expected with this event, including northwest of Cincinnati. Here’s our thinking on snow and ice in the Tri-State tonight and early tomorrow morning:

This forecast may change later tonight, but confidence is high that we will have a rain, snow, freezing rain, and sleet mix tonight and early tomorrow.

Use caution traveling tonight and early tomorrow, as roads may be partially covered with ice. Bridges and overpasses will freeze first!

The weekend is coming to an end, and so is a rather warm and soggy pattern. Cincinnati hit 66° before 3am this morning, and temperatures will crash into the 20s overnight in the wake of a strong cold front.

Compared to most of this weekend, the week ahead looks much colder, but still reasonably close to average (average low today: 23°, average high today: 38°).

There are a couple of cold punches to track in the next two weeks.

Arctic Air Coming Later This Week

The latest run of the GFS model (from this morning) is very aggressive arctic air later this week, bringing it into the Great Lakes and southeastern Canada by Thursday morning (as shown in purple, red, and yellow):

This morning’s GFS model was not this aggressive with the cold air compared to last night’s or yesterday morning’s run, so I am skeptical of how aggressive the newest run is with arctic air.

With that being said, there is support for this arctic blast from the GFS model runs that are used to create the main GFS model run; meteorologists call these “mini” model runs ensembles. Ensembles are a series of models with the initial conditions changed slightly; if model runs with different initial conditions all point towards a specific solution in time, the odds that a certain type of weather will happen increases. Ensemble forecasting is based off of the idea that computer models often don’t have time (or access to computing power) to ingest every little weather detail for the entire world. Computers often make approximations to save time; ensembles allow us to see how differences in initial conditions make a difference in the forecast. Taking an average or mean of all of the ensembles is a convenient way to see what the ensembles think – overall – in one simple graphic.

This morning’s GFS ensemble mean also has this arctic air over southeast Canada and the Great Lakes Thursday morning, but the core of arctic air (shown in light blue and purple) isn’t quite as strong and isn’t as far south:

The European model’s ensembles also have this cold punch to our north by Thursday morning, but is even less aggressive with the arctic air into the northern United States:

Clearly, there is some uncertainty on the positioning and strength of the cold air coming later this week. Despite some differences, there is fairly high confidence that this arctic air will put a stop to subtle warming trend forecast Monday through Wednesday.

Arctic Air Coming Next Week

As mentioned above, this morning’s GFS model is very aggressive with pushing arctic air south later this week…and also next week. The GFS suggests this piece of arctic air will be diving south sometime between Monday and Wednesday of next week. Here’s where this morning’s GFS model run puts it (shown in purple, red, and yellow) by Wednesday morning:

Again, this is a long range forecast and the GFS has just recently gotten aggressive with cold air. For a second opinion, here’s what the GFS ensemble mean suggests for arctic air (shown in light blue and purple) next Wednesday morning:

The GFS ensemble mean is farther west and not as cold as the GFS. The European ensemble mean is colder than the GFS in Canada but does not have the arctic air as far south:

Just like with the forecast later this week, there is a lot to get worked out regarding next week’s potential arctic blast.

For now, I’m thinking we’ll have have highs in the mid to upper 30s Thursday and in the 30s Monday through Wednesday next week. We will likely be on the fringe of both these arctic air masses. This arctic air is here to remind us that winter is not over!

The potential for heavy rain this weekend has been forecast for days, and – unfortunately – the time to deal with it has come. It will not rain all weekend, but when it rains, it will likely pour.

Rain will not fall in the Tri-State until at least 11am. Showers and scattered thunderstorms will likely overspread the Tri-State this afternoon. Microcast has moderate to heavy rain around Cincinnati at 4pm:

Most higher resolution model data suggests there will be at least a couple of hours tonight with little or no rain in our area, but the threat for heavy rain will rise again late tonight and early tomorrow. Microcast has heavy rain in the Tri-State by 7am Sunday morning:

Rain will be heavy at times Sunday morning and afternoon, but thunderstorms are not forecast thanks to falling temperatures, falling dewpoints, and little to no instability. Microcast still has heavy rain in the Ohio Valley late Sunday afternoon:

Models disagree on where exactly the heaviest axis of heavy rain will be through Monday morning. PrecisionCast has the 2-3″ swath of rain (in yellow) in the far northwestern part of the Tri-State and central Indiana:

Microcast has the axis of heavy rain through Monday morning farther to the southeast and closer to downtown Cincinnati:

Other computer models give Cincinnati about 0.7″ to 1.3″ of inch through Monday morning:

If you live in Cincinnati, the odds of getting 1″+ of rain through Monday morning are good. The odds of getting 2-3″ of rain are much higher northwest of Cincinnati.

The ground is soaked thanks to recent rain and almost 8″ of snow (and more northwest of Cincinnati) in the last month and a half. Flooding concerns will be focused northwest of Cincinnati this weekend, and I would not be surprised to see the Flood Watch (now in effect for Fayette and Union County from 7pm tonight through 1pm Sunday) expanded 1-2 counties farther southeast.

The last time Cincinnati saw a 60°+ high temperature in January was January 31, 2012. The last time before that was all the way back in 2008 (61° on January 8th). We don’t always get to see temperatures in the 60s in January. We average about two 60°+ days each January in Cincinnati, but we once went 5 years straight without hitting 60° in January (1976, 1977, 1978, 1979, and 1980) .

What are the historical odds of getting a 60°+ high temperature any given day in January? Here’s the breakdown:

After crunching the numbers, I was a little surprised the odds were this high. In January, getting a high in the 60s usually requires strong southwesterly flow, no snow on the ground, and an abundance of sunshine.

For perspective, the historical odds of hitting 65°+ any given January day is roughly 1.8%. The historical odds of hitting 70°+ any given January day is roughly 0.2%.

You have to hit 60° at least 6 times in January to make it on the “Most Number Of 60°+ January Days In Cincinnati” list:

The odds of us hitting 60° Friday and Saturday are good, especially with moisture surging up from the south and allowing lows temperature to only fall into the upper 40s to mid 50s.

If you love warm weather, enjoy the spike in warmth late week because high temperatures will be near average in the mid to upper 30s Monday, Tuesday, and Wednesday.