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:

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.

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.