Historical Perspective On The Last Week In Cincinnati

There have been three significant winter storms in the Tri-State during the last 7 days. It is rare to have frequent rounds of heavy snow in Cincinnati. In fact, the last week ranks as the 18th snowiest week on record in Cincinnati. If you omit the overlapping streaks, Cincinnati just had it’s 6th snowiest week since 1893:


February is typically the snowiest month of the year in Cincinnati (with 6.53″ of snowfall on average); January is a close second with an average of 6.51″ of snowfall. Despite being the snowiest month of the year, it is rare to see more than 10″ of snowfall in a week during February; the last 7 days were among the snowiest during February back to 1893 :


This abnormally snowy stretch has pushed us to 5th place on the snowiest Februarys on record in Cincinnati:


…and the month is not over. The amount of snowfall recorded at the Cincinnati/Northern Kentucky International Airport in the last 7 days is 92% of the amount of snow that typically falls in all of meteorological winter (December, January, and February combined):


It’s worth noting that more snow has fallen in the first 21 days of February 2015 (18.6″) than falls during meteorological winter on average (18.1″). The snowfall total for meteorological winter 2014-2015 through February 21st is 19.9″.

The seasonal snowfall total through February 21st is now up to 25.0″. On average, 22.5″ of snowfall is recorded in Cincinnati from one summer to the next. All snow that accumulates for the rest of the winter and spring just adds to the surplus.

This winter has been “bottom heavy.” More than double the amount of snow that fell between last summer and February 14th has fallen in the last week:


“Bottom heavy” describes not just snowfall accumulation this winter, but it also describes cold. If February had ended at midnight on Sunday, February 2015 would be the 8th snowiest February on record:


If meteorological winter 2014-2015 had ended at midnight February 21st, it would rank as the 19th coldest back to 1870-1871. There is still plenty of time for our ranking to change, but it doesn’t look like the ranking going to slide down. Saturday morning’s American long-range (GFS) model has arctic air plunging into the Great Lakes and Ohio Valley to start off the work week:


It has another shot of arctic air coming late in the work week:


Saturday morning’s European long-range (ECMWF) model is similar to the GFS, bringing an arctic airmass into the Ohio Valley and Great Lakes Monday morning:


…and another area of arctic air to the Ohio Valley before next weekend begins:


The first blast of arctic air will likely bring temperatures of -5° to 5° to the Tri-State early Monday and Tuesday morning. The second blast will bring temperatures back into this range Thursday and Friday morning.

Winter is far from over. At least a few more waves of very cold air and snowy will swing into and through the Ohio Valley during the next 2 months. Temperatures will moderate some in March, but cold will win out for the next several weeks.

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Historical Odds Of A White Christmas In Cincinnati

Snow is common during December in Cincinnati, but the odds of getting snow on the ground Christmas morning is lower than you might think.

A “White Christmas” is a Christmas Day where the snow depth at 7am is 1″ or higher. This snowfall amount is rounded to the nearest inch in official weather records. For example, a 7am snow depth of 0.5″ would be recorded as 1″ officially, and a snow depth at 7am of 0.4″ would be recorded as a “trace” officially. With this rounding considered, a 7am snow depth of 0.5″ or more on Christmas Day would mean a “White Christmas.”

7am snow depth records for Cincinnati have been taken since 1916 with one year (1947) missing. Based on weather records, it is hard to say if December 25, 1947 was a White Christmas. The official high temperature that day was 31°, and the low temperature that day was 14°. 0.03″ of precipitation was recorded at the Cincinnati/Northern Kentucky International Airport that day, but the 7am snow depth and the snowfall total for that day are missing. It is highly likely that the precipitation that fell that day was snow or nearly all snow. A 10-to-1 snow-to-liquid ratio would mean 0.3″ of snow fell that day. The snow-to-liquid ratio that day, however, is unknown.

At the time, official records were taken at the International Airport. However, weather records taken at the National Weather Bureau office in downtown Cincinnati suggest 1947 may have had a White Christmas:


At 7:30pm on December 25th, 1947, 0.5″ of snow was reported on the ground in downtown Cincinnati. 0.8″ fell that day, but it is unclear whether the 0.5″ of snow on the ground at 7:30pm that day was also on the ground at 7am Christmas Day. Regardless of what happened at the Weather Bureau office, it is not part of the official weather record for Cincinnati.

If you throw out Christmas Day 1947, there have been 16 White Christmases in Cincinnati since 1916:


16 White Christmases in 96 years worth of records shows there is, historically, a 17% chance of a White Christmas in the Queen City:


If you say 1947 was a White Christmas, there is, historically, a 18% chance of a White Christmas in Cincinnati:


The math gets even more complicated if you include Christmas Day of 1992, which is the only year since 1916 where there was no snow on the ground at 7am but 1″ or more fell on that day after 7am. You could make an argument that 1992 had a White Christmas; if you believe it counts, the historical odds go up to 19%.

These historical odds are long-term. In the last 10 years, there have been 2 White Christmases in Cincinnati:


The long-term average and the last 10 years suggest that a White Christmas happens in Cincinnati about once every 5 years. Back to 1916, the highest 7am snow depth recorded in Cincinnati on Christmas Day was in 2004 (9″).

Historically, the odds of a White Christmas Eve are about the same, but the years with a White Christmas and White Christmas Eve don’t always match up. Here is the list of years with 1″ or more of snow on the ground on Christmas Eve in Cincinnati:


Weather records for Cincinnati are messy, but history suggests there is a 15 to 20% chance of a White Christmas any given year in the Queen City. We will know more about the likelihood of a White Christmas this year in the hours and days to come.

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Cold Air, Snow Chances Coming To The Tri-State Soon

October and November are transition months in the Tri-State. The first frost and freeze of the season almost always occur in at some point in these two months. The first flakes of the season often fall in October or November. We’ve already had our first frost, freeze, and flakes. The next item on the list is the first accumulating snow of the season; the opportunity for accumulating snow comes this weekend.

To get snow, we need cold; we will have plenty of that later this week. Despite what you may have heard, the “polar vortex” is not coming behind Tuesday’s front. The polar vortex is an upper-level feature; it lives in the stratosphere (the layer of the atmosphere above the one we live in) and occasionally dips down into the upper troposphere (the layer of the atmosphere we live in and where weather occurs). Sunday morning’s European (ECMWF) Ensemble model mean places the polar vortex (labeled as “PV”) near the North Pole, well away from Cincinnati (the purple dot):


While this drop in temperatures later this week is being called everything under the stars, the reality is that the jet stream is just headed south. When you’re north of the jet stream, it’s relatively cold; when you’re south of the jet stream, it’s relatively warm. The jet stream is a fast moving current of air 35,000-45,000 feet above the ground that is trying to restore a balance in the atmosphere by bringing cold air south and warm air north.

I believe we’ll reach into the upper 50s and lower 60s both Monday and Tuesday afternoon with winds sustained out of the southwest. Tuesday and Tuesday night will be the transition period in the week ahead. A cold front moving through the Ohio Valley will push temperatures from the 60s Tuesday afternoon into the 30s by Wednesday morning. Some models give us scattered rain showers Tuesday, while others give us a well-defined line of rain. At this point, I believe most will see light rain Tuesday and Tuesday evening, but there is some uncertainty on the coverage of rain.

The cold air pouring into the Ohio Valley, Mississippi Valley, and Great Lakes later this week will not warm much as it nears us thanks to a fresh snowpack being put down ahead of it from the Dakotas to the Upper Peninsula of Michigan:


Areas in the white and blue shades will see anywhere from a few inches to a couple of feet of snow of the ground by Wednesday afternoon. Without this snowpack, high and low temperatures in Cincinnati later this week would be warmer.

Highs are forecast to be in the mid to upper 30s Thursday, Friday, and Saturday. While this is abnormally cold for mid-November, it is not unprecedented. Here are the lowest high temperatures recorded in Cincinnati on November 12 (Wednesday) since 1870:


The record lowest high temperature for November 13 (Thursday) is 29°, and I don’t foresee that getting broken or tied:


Since 1870, high temperatures have only hit the low 30s a couple of years in Cincinnati on November 14th (Friday):


It appears unlikely that a new minimum high temperature record will be set on November 15th (Friday):


While it will be very cold, all of these graphs suggest record-breaking cold is unlikely later this week.

After some flurries Thursday, our attention returns to a system developing late in the upcoming weekend. At long range, it is not uncommon for models to disagree on the timing and strength of systems; this upcoming event is no exception.

Sunday morning’s GFS (American) and ECMWF (European) models disagree on the coverage of precipitation when the disturbance is moving out of the Rockies and into the Plains. The GFS model keeps much of the Plains dry, while the ECMWF has precipitation falling from Iowa to the Gulf Coast (Cincinnati is the purple dot):


Any errors in the forecast model at this time will likely degrade the quality of the forecast beyond this time. As an example: Sunday morning’s GFS and ECMWF models disagree on if precipitation will be falling in Cincinnati at 1pm Sunday:


The forecast gets even more complex into next Monday. Sunday morning’s GFS models says precipitation will be to our east, while the ECMWF model still has precipitation in the area:


Clearly, there is uncertainty in the strength, timing, and positioning of this system. If precipitation falls on Sunday or Monday, models are in agreement that this preicpitation will likely be snow given temperatures in the 30s near the ground and in the teens and 20s just a few thousand feet above the ground. Confidence in the overall forecast will rise and specifics will be resolved with time.

Here is a summary of forecast uncertainties in the week ahead:


While nearly all of the uncertainty in the week ahead deals with the area of low pressure a few days from now, there is a high confidence that the following will happen between now and next Monday:



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Cold Coming Next Week, But Not Worth Overhyping

Like every blast of cold air in recent winters, there is already a big social media buzz about temperatures next week. Yes, it will be cold, but what comes next week is not unprecedented for early to mid-November.

In the longer range, I like to use ensemble forecast models to gauge the strength and positioning of cold. Ensemble forecast models are models made up of smaller models with the initial conditions changed slightly. All of these smaller models are run and may or may not produce slightly different results. A low spread in the solutions of an ensemble forecast model suggests a higher confidence that a certain weather event or pattern will happen; a high spread suggests a lower confidence forecast. In addition to looking at one ensemble model, a meteorologist can use other ensemble models and compare them to measure the confidence of a forecast. Ensemble models are often more reliable than other forecast models – especially a few days to a couple of weeks into the future – because outlier members of the ensemble models are easy to spot and can be discounted if needed.

What does the average (mean) of these ensemble models say will happen by Sunday morning?


This morning’s GFS (American) ensemble mean suggests temperatures roughly 5,000′ above the ground will be in the low 30s (-1°C) at 7am on Sunday morning, while the ECMWF (European) and CMC (Canadian) ensemble mean suggests temperatures a few thousand feet above the ground will be in the low to mid 20s (-3° to -6°C). Forecasting temperatures just above the ground are often easier to forecast than close to the ground due to uneven heating of the ground and terrain. Clearly, there is a large spread on what the temperature 5,000′ above the ground will be at 7am Sunday; this suggests there is limited confidence in the temperature forecast this weekend. Current thinking is that surface temperatures will be in the upper 20s and lower 30s early Sunday morning, but this forecast may change depending on the trend of models.

Before we go forward, know that errors in the each of the models will be compounded with time. A large bust on a temperature forecast from a model this weekend will likely mean a large (or even larger) bust on the temperature forecast for next week.

What does the mean of the ensemble models say will happen by next Thursday morning?


There is reasonably good consensus with Wednesday morning’s ensemble model runs that temperatures 5,000′ over Cincinnati will be around -9°C (16° F). Accounting for the fact that temperatures are usually colder aloft than at the ground, cloud cover, and the rate of temperature changes near the ground, these maps support low temperatures in the 20s. Temperatures aloft rise a couple of degrees during the day Thursday, but there is some uncertainty in the cloud cover and precipitation coverage (if any at all). All things considered, highs will likely be in the 30s and/or 40s Thursday.

Since 1870, the high temperature in Cincinnati hasn’t hit 40° 12 years on November 12th, 11 years on November 13th, and 19 years on November 14th. In other words, the historical odds of not making it to 40° on any one of these days is 8 to 13%.

As a mentioned above, there are uncertainties in cloud cover and precipitation timing next week. Look at the differences in the upper-level flow for the second half of next week. The GFS Ensemble has a ridge in the western United States and a trough in the eastern United States, but the positioning of the trough looks to be too far east and likely moving through the U.S. too quickly:


The ECMWF Ensemble has the trough and the ridge both farther west by 7am Friday, but likely doesn’t have the ridge strong enough in the western United States (which I’ll explain why below):


I think the CMC (Canadian) Ensemble has the right idea: a strong ridge in the western United States, a strong trough in the Pacific Ocean, and a strong trough in the eastern United States:


Why do I the think the ECMWF Ensemble ridge in the western United States is too weak? Because tropical activity in the Pacific suggests strong ridges and troughs near and over North America.

Meet the leftovers of Typoon Nuri in the Pacific Ocean (satellite shot as of 9:30pm ET Wednesday). Nuri is the mass of clouds (bright colors) the upper-right hand part of this image:


Note southeastern Asia on the left side of this image. Nuri will be a troublemaker. The GFS ensemble suggests Nuri is headed northeast:


It is forecast to bomb out over the northern Pacific Ocean later this week. The surface low of “once Nuri” will die out next week, but the upper-level low of this system will likely spin over southern Alaska or in the northern Pacific Ocean, as the ECMWF model shows by next Wednesday (pointed out with the arrow, Cincinnati is the red dot):


This area of low pressure positioned where it is supports a ridge of high pressure just to the east of it, and a trough to the east of the ridge. This is very similar to what the CMC Ensemble above shows. The exact track and fate of this Pacific low can impact how cold we get next week.

For now, know that next week will be cold, but highs in the 30s and 40s are not uncommon in mid-November. Remember, we had a high of only 42° in Cincinnati this past Saturday.

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The First Snowfall Of The Season In Cincinnati

A trace of snowfall was recorded at the Cincinnati/Northern Kentucky International Airport on Saturday. A trace of snowfall in the records means snowflakes fell from the sky, but less than 0.1″ of snowfall accumulated (if any at all).

The first snowflakes of the fall and/or winter in Cincinnati usually fall in late October or November. On the first day that snowflakes fell during the fall and/or winter in Cincinnati, only 21 of the last 100 years reported snowfall accumulation (0.1″ or more) on that day; in other words, the first snowflakes of the season usually don’t stick because the ground is too warm.

Here are the average, earliest, and latest snowfall dates with measurable snowfall and any snow in the Queen City…


Note measurable snowfall records go back to 1893, but I have limited the “any snow” (at least a trace) record back to 1915. It is also worth noting that official snowfall records for Cincinnati have been kept in three different places since 1893:

-1893-1915: Downtown Cincinnati at the National Weather Service/Bureau office
-1915-1947: Abbe Observatory in Clifton
-1947-Present: Cincinnati/Northern Kentucky International Airport

The averages and the range of dates can be helpful, but there are more than two ways to measure the first snowfall of the season. Statistically, the most common ways to measure the “center” of a set of data are involve taking the mean, median, and mode. Simply put, the “mean” is the average, the “median” is the “center” value in the chronological list, and the “mode” is the most common value occurring in the list. For example, here are the mean, median, and mode dates for the date when the first snowflakes fall during the fall/winter in Cincinnati:


Historically, the first measurable snowfall of the season comes 2 to 3 weeks after the first snowflakes of the season fall from the clouds:


The first day of the fall or winter where 1″ or more of snowfall accumulation occurs in Cincinnati is in usually not far behind the first day of the season with measurable snowfall; sometimes, they are on the same day. Here are the mean, median, and mode for the first day of the fall and/or winter in the Queen City where 1″+ of snowfall accumulates:


The first day of 1″+ of snowfall accumulation in Cincinnati has come as early in the fall as October 19 (1989, 5″) and as late as March 5 (2012, 1.5″, two dates after the deadliest tornado outbreak on the Tri-State on record).

Seeing accumulating snowfall earlier than average in the fall does not necessarily mean a snowier than average winter is on the way.

Overall, I believe this upcoming winter will be snowier and colder than average in Cincinnati. Compared to last winter, I believe winter 2014-2015 will be colder but not as snowy as the winter of 2013-2014.

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Everything You Need To Know About Fall Frost In Cincinnati

Low and high temperatures have been above average the last few days in the Queen City, but the latest computer guidance suggests cool, Canadian air will arrive by next weekend. While there is no imminent threat for frost with this next shipment of cool air, the likelihood of frost will rapidly increase over the next month.

When forecasting frost, a meteorologist often looks for a very light or calm wind, a mostly clear to clear sky, and temperatures dropping into into or below the upper 30s early in the morning. Frost can form with air temperatures dropping into the mid and upper 30s; temperatures to or below 32° are not needed for frost. Why? The answer to this has to do with how temperatures are measured.

The piece of equipment used to measure weather conditions at most airports in this country – called an Automated Surface Observing System or ASOS – measures the temperature 2 meters above the ground.Here is a picture of an ASOS and where the temperature sensor is located:


Because relatively cold air sinks and warm air rises, temperatures below this sensor are always colder than temperatures at the sensor. For example, the sensor may measure at air temperature of 36°, but the temperature at the ground may be 32° or lower. Patchy frost can form at the ground when the temperature at the sensor drops to 38°.

The first frost of the fall in Cincinnati almost always occurs in October; while the exact temperature where frost occurs can vary, using a temperature of 36° or 38° yields roughly the same dates on average:


The first frost has occurred as early as mid September and as late as late November.

Frost does not necessarily mean the end of the growing season, but frost can easily kill plants – especially if they are sensitive to cold. A freeze or hard freeze signals the end of the growing season for all seasonal vegetation. On average, the first freeze or hard freeze of the fall in Cincinnati occurs in late October or early November:


Note that a freeze has occurred as early as late September, and a hard freeze has occurred as early as early October.

The averages and the range of dates can be helpful, but there are more than two ways to measure first fall frost dates. Statistically, the most common ways to measure the “center” of a set of data are involve taking the mean, median, and mode. Simply put, the “mean” is the average, the “median” is the “center” value in the chronological list, and the “mode” is the most common value occurring in the list. For example, if we assume the first fall frost occurs when the temperature (measured 2 meters above the ground) drops to 38°, here are the mean, median, and mode dates for the first fall frost in Cincinnati:


If we assume the first fall frost occurs when the temperature drops to 36°, here are the mean, median, and mode dates for the first fall frost in Cincinnati:


These averages are based on data from 1871 to 2013. What is the mean, median, and mode date for our first freeze?


The mean, median, and mode dates for the first hard freeze in Cincinnati are:


Historically and statistically, if you assume the first fall frost occurs when the temperature drops to 38°, there’s a 75% chance we get our first frost by October 15th. The date slides about one week later if you use 36° as a temperature:


At this point, the cold blast coming in the wake of Friday’s cold front does not look to bring widespread frost to the Tri-State. Longer-range computer guidance suggests temperatures will warm back near or above average by the middle part of next week. Beyond the first full week of October, guidance suggests waves of cold air will gradually push southeast from southern Canada. While the first of these series of cold blasts may not bring frost, reinforcing shots of cold, Canadian air in October suggests our first fall frost will come very close the historical average date.

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What Happened To Tuesday Night’s Forecast?

As you probably noticed, the chance for showers and storms in the Tri-State Tuesday night was overdone. Even on-air at 5pm Tuesday, I mentioned a threat for severe weather – especially west of Cincinnati – and scattered showers and storms. I played the threat down on-air tonight, but the radar tonight suggested I didn’t play it down enough.

At 2pm Tuesday, the Storm Prediction Center had the western half of the Tri-State and most of Indiana under a slight risk for severe storms:


As a broadcast meteorologist, you need to present this threat, even if you don’t fully agree with the Storm Prediction Center. I’ll agree with the Storm Prediction Center that there was adequate low-level moisture, warmth, and instability available for thunderstorms to form and become strong or severe.

The missing piece – or at least the piece that was most in question – was the upper-level support. Tuesday morning’s NAM model showed the upper-level disturbance (yellow/orange/red) approaching Cincinnati (the black dot) at 8pm Tuesday:


Ahead of a disturbance like this, lift in the atmosphere increases, and the chance for storms – including severe storms – increases. Tuesday morning’s GFS model showed a disturbance of similar strength approaching the Tri-State at 8pm Tuesday:


Two models showing a disturbance moving through the Ohio Valley raises confidence about the coverage and intensity of showers and storms. The GFS model was farther south with the disturbance, and the NAM model had the disturbance more spread out.

It is hard to verify exactly where these disturbances were Tuesday evening (given they are 18,000 feet above the ground), but the 9pm run of the RAP model (which updates every hour) is our best hope for verification. Here’s where it placed upper-level disturbances at 10pm Tuesday night:


Clearly, the RAP has the strongest disturbance northwest of Cincinnati and has it more compact than the NAM model. Showers and storms developed well to the northwest of Cincinnati on the nose of the upper-level disturbance Tuesday afternoon, and outflow from the early evening storms supported new storm development through late evening (as 11pm Tuesday radar shows):


Models clearly missed the mark, and as a result, the forecast could have been better. Just like in the winter where the exact track has a big impact on snowfall totals, the track of this disturbance had a big impact on the placement and strength of showers and storms.


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