As new model runs complete, the overall forecast remains unchanged. At this point, we are nowcasting the event. Satellite, radar, and surface observation trends are becoming much more important as tonight’s rain and snow event nears.

In my blog post yesterday, I discussed how rain would begin around dinner tonight, continue through the evening, transition to snow nearing and especially past midnight, and snow would end nearing sunrise Tuesday. Microcast shows widely scattered showers developing (especially north and northwest of Cincinnati late this afternoon) in the Tri-State:

Microcast has only rain in the Tri-State until late evening, when the transition from rain to snow will begin north and northwest of Cincinnati:

After midnight, all rain will transition to snow, and snow will gradually push south and southeast nearing sunrise Tuesday. By 6am, Microcast shows snow showers south of Cincinnati:

If this model – and all of the forecast models that push snow mainly south of Cincinnati by 6am – verifies, the first half of the morning commute tomorrow will be more problematic than the second half. By lunchtime Tuesday, the arctic front (and the snow along it) will be to our south, and temperatures will only be in the mid 30s.

Up to 1″ of snow is forecast in the Tri-State through Tuesday morning. With temperatures around freezing overnight, snow may struggle to stick in spots, and not all of it will be on the ground at once. When we say “snowfall accumulation tonight,” there are some important considerations included in that prediction:

The morning commute tomorrow will be tricky. If you’re going to work early tomorrow (especially 3:30 to 5am), be prepared for pockets of visibility-reducing snow and slick roads. After 5am, the coverage and intensity of snow will decrease from northwest to southeast, but slick spots on the roads will likely linger for at least a couple of hours after snow ends. Any snow that is able to accumulate early Tuesday morning will likely melt Tuesday afternoon, especially snow that is exposed to direct sunlight once clouds clear out Tuesday morning.

High temperatures will only be in the mid to upper 30s Wednesday and Thursday. Low temperatures will likely drop into the low to mid 20s early Wednesday and Thursday morning.

Now is the time to prepare for the snow and cold. While a major snow storm is not expected tomorrow, the first snow of the season (and really any snow event in the Tri-State) usually takes some off guard. Allow for extra time getting to work or school tomorrow morning!

There is already a lot of buzz about the cold front moving through the Tri-State tomorrow night and early Tuesday…specifically about the chance for snow that will come with it. This upcoming event is more than just a chance for snow.

The rest of tonight and early tomorrow will be as quiet as this weekend was. Microcast suggests high- and mid-level clouds will overspread the Tri-State nearing sunrise Monday. Here’s what Microcast shows for 6:30am Monday morning:

Temperatures will be in the low to mid 30s by early Monday morning. Other than thickening clouds and temperatures rising through the 30s, 40s, 50s, little change in the weather is expected from early tomorrow morning through tomorrow afternoon. Microcast only has thickening clouds at noon Monday…

…or at 5pm Monday (but notice showers nearing from the northwest):

After 5pm, showers will begin overspreading the Tri-State from northwest to southeast. Through 10pm Monday, only rain is expected in the Tri-State; after 10pm, rain will begin transitioning over to snow. Microcast has the rain/snow line (in pink) nearing the Ohio River by midnight Tuesday:

By 7am Tuesday, Microcast – and nearly all other forecast models – have snow showers and flurries pushing south of the Ohio River:

Temperatures will drop to around 30° by 7am Tuesday, so snow will struggle to accumulate at times for many. If temperatures were well into the 20s, snow would easily stick, and we would get a lot more than we are forecasting now. Given temperature profiles, the timing of the cold front behind the front, and the temperature of the ground, we are not expecting a lot of snow, but accumulations are still expected for many if not most in the Tri-State.

While this is not a specific forecast for a given point, Microcast matches our thinking closely for accumulation on cold, elevated, and grassy surfaces:

Again, this is a more accurate depiction of snowfall accumulation on grassy, cold, elevated surfaces. Little to no snow is expected on roads, especially if they are treated. Some roads, however, may still be slick, and patches of ice on roads can’t be ruled out (especially in low-lying areas where pavement temperatures may drop near 32°). Overall, 1/5″ to 1″ of snow is expected for our area tonight and early Tuesday morning on cold, elevated, grassy surfaces.

Much of the snow that falls may melt on contact, so few if any areas will have their full storm total on the ground at any given time.

Like all snowfall events, specific amounts are subject to change as new forecast models complete tonight and tomorrow. Stay tuned for possible changes in the forecast.

What This Event Is

This event is likely going to be the first accumulating snow event for many in the Tri-State. Snow accumulations will be light, but the Tuesday morning commute – especially early – could be messy in spots given snow in the area and wet roads. Snow will not be powdery; it will be relatively wet, and much of it will not stick or at least not stick for long. Clouds will decrease quickly Tuesday morning and afternoon, and the sun will help to melt a lot of the snow that falls early Tuesday.

Here’s a timeline of temperatures and precipitation changes for Cincinnati in next 36 hours:

High temperatures Tuesday are only forecast to be in the mid to upper 30s, and we’ll be only 1-2° warmer Wednesday afternoon – even with lots of sunshine. Overnight lows will be in the low to mid 20s Wednesday and Thursday night.

This morning’s ECMWF model shows arctic air (in blue) cutting through the Great Lakes and Ohio Valley by 8am Tuesday:

…but has that same arctic air mass retreating back into Canada by late in the work week. Brighter colors (warmer temperatures) from the ECMWF model return nearing this coming weekend:

What This Event Isn’t

The cold front that comes into and through the Tri-State Monday night and Tuesday isn’t going to be a major storm. It will not be a major disruption, but it will be an inconvenience. This event isn’t going to close dozens of school districts, but parts of the morning commute Tuesday will be tricky…especially early. The odds of this event producing a “shoveling” amount of snow in your community is unlikely at this point.

Please allow for extra time on your drive to work or school Tuesday!

For the last few days, there has been a lot of focus on the federal government shutdown. National parks and non-essential government employees have felt the effects of this shutdown. Like it or not, many are speculating that the government shutdown could continue for at least a few days or even weeks.

With all of the focus on the consequences of the shutdown, I thought I would try to lighten the mood and see if there was a correlation between a government shutdown and how much cold and snow Cincinnati got in the winter that followed. Ian Livingston of the Washington Post’s Capital Weather Gang looked at a similar correlation (just for the Washington D.C. area), so I tip my hat to him for this idea.

In the modern era (since the mid 70s), Cincinnati winters that follow a federal government shutdown are usually colder, snowier, or both colder and snowier than average. For the sake of this discussion, “winter” is considered to be “meteorological winter,” or December, January, and February only.

Here are winter snowfall totals in Cincinnati following a federal government shutdown:

Only 3 out of the 12 winters shown above were warmer than average. Note that the second coldest and coldest winters on record (1976-1977 and 1977-1978, respectively) are listed. The average of all of the “shutdown winters” above is roughly 3.2° below average, although the brutal winters of 1976-1977 and 1977-1978 pull the average down significantly; without these two years included, the “shutdown winters” average is about 1.7° below the seasonal average.

What about snow? Here’s a list of snowfall totals in the winter following a federal government shutdown:

Only 7 out of the 12 “shutdown winters” above were snowier than average. The average of all of the “shutdown winters” above is roughly 3.7″ above average, although the brutal winters of 1976-1977 (5th snowiest all time) and 1977-1978 (snowiest all time) pull the average up significantly; without these two years included, the “shutdown winters” average is only 0.2″ above the seasonal average.

7 of the 12 “shutdown winters” were both colder and snowier than average.

Of course, this exercise is all for fun. A government shutdown does not mean we will get a certain type of winter. A winter forecast will be developed in the days and weeks to come; look for it later this year.

I’ve blogged about this before because it continues to amaze me with each month that goes by. After a record number of Tri-State tornadoes in 2012, this year has been a very slow one for severe weather. In fact, 2013 will be the quietest year for severe weather in the Tri-State on record by most measures.

How do Severe Thunderstorm, Tornado, and Flash Flood Warnings so far this year compare to average??

The current Tri-State Severe Thunderstorm Warning count of 61 this year is tied (with 2005) for the fewest Severe Thunderstorm Warnings issued in a year (since the National Weather Service in Wilmington started issuing warnings for the Tri-State in 1995):

19 Flash Flood Warnings have been issued in the Tri-State so far this year. While our Flash Flood Warning count is likely to be below average this year, there have been several years since 1995 with fewer Flash Flood Warnings.

The statistic that continues to amaze me is the fact that no Tornado Warnings have been issued in the Tri-State so far this year. Since 1995, we have never gone an entire year without at least one Tornado Warning being issued in the Tri-State; in fact…since 1995, at least one Tornado Warning had been issued somewhere in the Tri-State prior to July 28th. For perspective, 24 Tornado Warnings were issued in the Tri-State through this date last year.

Here’s a comparison of Tri-State Tornado Warnings issued by year since 1995:

The only thing better to see than 0 Tornado Warnings in a year is 0 confirmed tornadoes in that same area. If we don’t see a confirmed tornado for the rest of the year, 2013 will be the first year since 1987 without one:

We need to thank our lucky stars for a boring severe weather season. After going through deadly tornadoes last year (including March 2, 2012 – the deadliest severe weather day in the Tri-State since official tornado records began in 1950), we needed a year to rebuild and regroup.

The last tornado in the Tri-State was on September 8, 2012…389 days ago. Let’s hope we make it another 389 days without a tornado.

Welcome to October! Today is the first day of the second month of meteorological fall. October, like many months in the Ohio Valley, is a month of change; the most drastic change is in the temperature. While each October is different, the average high temperature drops 11° and the average low temperature drops 10° from October 1 to October 31:

The gradual drop in temperatures – especially low temperatures – signals an increase in the likelihood of frosts and freezes. Historically (1870 to 2012), the majority of first fall frost and first fall freeze events occur in October:

In October, extreme cold is very rare in Cincinnati. The temperature has only dropped into the teens 3 times and below 30° 128 times in October since 1870. On the flip side, 90°+ heat is very rare in October. The temperature has hit 90° 6 times in October since 1870. In most years, the last 80°+ day of the year in Cincinnati is in October; the average last 80°+ day of the year is October 8th.

On average, October is the 4th driest month of the year in Cincinnati. September is the typically the driest month of the year, and the average monthly precipitation total increases from September to October and slightly from October to November:

Like it or not, snow becomes a possibility in October. The earliest flurries have fallen in Cincinnati during the fall was on October 12, 1917. The earliest autumn day with measurable snow in Cincinnati was on October 19, 1989. Here are the earliest fall dates where measurable snow fell in the Queen City:

What Does October 2013 Look Like?

The latest outlook from the Climate Prediction Center released Monday suggests the Ohio Valley, Great Lakes, and New England will likely be warmer than average in October:

Released Friday, the latest run of the ECMWF Weekly model suggests each week in October will be warmer than average despite a brief blast of Canadian air diving south late in the weekend and early next week. In fact, the latest ECMWF Weekly model suggests the week of October 16th will be abnormally warm over most of the country. The newest ECMWF Weekly model also suggests precipitation amounts will be near or below average in the Tri-State this month.

The possibility for frost in the Tri-State rises from mid-September through early October. Our first light frost (a low temperature around 38°) of the season usually occurs in early October but has occurred as early as mid-September.

Frost is more likely when the air temperature drops to or below 36°. The average date for the first fall morning in Cincinnati with a temperature of 36° or lower is in early to mid-September. A damaging frost, however, can happen as early as late September.

Here’s some perspective on fall frost dates in Cincinnati:

The “average” above uses temperatures data from 1981 to 2010, and the “long-term average” uses temperature data from 1871 to 2012.

A morning with temperatures to or below 32°  – as known as a “freeze” – first occurs in late October, on average. A freeze often signals the end of the growing season for most plants. The first “hard freeze” (low temperature of 28° or below) of the fall in Cincinnati typically occurs in early November. With the exception of hardiest and herbaceous crops, any plants that are able to survive a freeze will likely be killed in a “hard freeze.”

Here’s some perspective on fall freeze dates in Cincinnati:

If left outside, your plants will likely have a couple of weeks left before getting their first taste of fall frost. The latest ECMWF Weekly model run suggests late September will be near or warmer than average. I suspect our first frosts of the year will come in early to mid-October this year…right on schedule.

After a record number of tornadoes in 2012, there have been no tornadoes and no Tornado Warnings in the Tri-State so far this year. Since the National Weather Service in Wilmington began issuing warnings for the Tri-State in 1995, at least one Tornado Warning has been issued somewhere in the Tri-State in the first seven months of the year…until 2013.

Here’s how 2013’s warning count so far compares to yearly averages and records:

Severe storms, however, don’t just occur in the spring and summer; storms can – and often do – develop each fall and even winter. In fact, some of the strongest and deadliest storms in the Ohio Valley have occurred October and November.

In just the Tri-State alone, the average number of Severe Thunderstorm Warnings issued increases slightly from September to October and again from October to November:

May, June, and July are the most common months for seeing severe storms in the Tri-State.

Tornado Warnings are more rare than Severe Thunderstorm Warnings. On average, April and May are the most common months for Tornado Warnings to be issued, but there is a subtle spike in the average number of Tornado Warnings issued in October and November:

While the likelihood for Severe Thunderstorm and Tornado Warnings goes up some late in the year, few Flash Flood Warnings are issued after October 1st in the Tri-State:

In fact, only 5 Flash Flood Warnings have been issued in the Tri-State since 1995 during October, November, and December.

The threat for tornadoes seems to trump all other severe weather threats and tends to be the one that gets people most concerned. Statistically, April, May, and June are our biggest months for tornadoes. April’s number is partially inflated by the 12 confirmed tornadoes of April 3, 1974. While the monthly tornado count drops from August to September, it increases again through the fall:

Why does the chance for severe storms and tornadoes gradually increase in the fall? The main reason is that the polar jet stream is pushing south and is almost always stronger in the fall than it is over Canada during the summer. Certain parts of the jet stream are focal points for rapidly rising air, and these focal points are usually where severe weather occurs in the fall (if other key conditions are present).

Don’t let the cooling trend fool you; autumn can be a nasty time of year, especially when warm, moist air surges north and the polar jet stream surges south.

After summer-like heat and humidity earlier this week, cooler, less humid air has returned to the Tri-State. The Weather Authority is forecasting low temperatures in Cincinnati early Saturday and Sunday morning to be in the mid to upper 40s. Communities north, northeast, and northwest of Cincinnati will likely drop into the lower 40s early Saturday and Sunday morning.

The record low temperature in Cincinnati for Saturday morning is 37°, set in 1964. The record low temperature in Cincinnati for Sunday morning is 41°, also set in 1964. How uncommon are lows in the 30s and 40s in September? Here’s a Cincinnati September low temperature distribution graph (for all September days since 1871):

In the last roughly 4,200 September nights in Cincinnati, we’ve only dropped into the 30s 66 times and into the 40s 712 times. When you focus on just the last several years, we typically drop into the 30s or 40s a couple of times each September:

In September 1918, Cincinnati dropped into the 30s and 40s a record 17 times. Note that these are low temperatures for the entire month of September; September low temperatures in the 30s and 40s are usually saved for the second half of the month. When you look at just the records for the first half of September, dropping into the 30s or 40s more than twice in the same month is rare:

In 1969 and 1975, Cincinnati dropped into the 30s and 40s 5 times in the first 15 days of September; these are records for the most number of days with a low temperature below 50° in the first half of September.

With the wind sustained near 5 mph overnight and temperatures in the 40s, frost is not a possibility this weekend. Here’s some perspective on when our first fall frost is (using a low temperature of 38°):

Frost is rare in mid-September, but it has happened. The temperature dropped to 37° on September 14th, 1964 in Cincinnati. Our first fall frost is more likely in late September or early October.

Does an overnight low in the 30s or 40s in early or mid-September tell us anything about fall or winter temperatures? Let’s look at the years mentioned above where we dropped into the 30s and 40s and see how the fall and winter that followed turned out:

Notice there is no correlation between fall or winter temperatures and temperatures in the 30s and 40s in the first half of September. In other words, the cold blast we’re getting this week or the cold blast we had earlier this month doesn’t say much about what the rest of the fall or winter will look like.

Stay warm this weekend! We’ll have highs in the 80s and lows in the 60s again by Thursday and Friday.

There is no doubt that the heat we have seen recently and will see again Wednesday afternoon is significant, especially in mid-September. High temperatures were in the 90s for nearly everyone in the Tri-State on Tuesday:

With temperatures in the 90s and dewpoints in the 70s, maximum heat indices from local, reliable weather stations were in the 100-105° range Tuesday afternoon.

Is it rare to see 90°+ heat in September in Cincinnati? We average 2 90°+ days each September in Cincinnati, but it’s mainly feast or famine for 90°+ heat in September in the last several years:

On average (1871-2012), our last 90°+ day of the year in Cincinnati is September 9th. The 30-year-average for the last 90°+ day of the year is August 29th. The window for the last day making it to 90° is quite large, however:

While September 1st is the first day of meteorological fall, astronomical fall begins on September 22nd, so high temperatures in the 80s and 90s are still common in September. We missed out on a lot of heat this summer (especially compared to summers like 2012, 2011, and 2007), but we are making some ground late in the season. We are likely going to fall short of our yearly average number of 90°+ days (21 days) in 2013:

In the same week that we get summer heat, however, we’ll also get a true taste of fall. Low temperatures will likely be the 40s and 50s early Friday, Saturday, Sunday, Monday, and Tuesday morning. Here’s how forecast low temperatures match up against record low temperatures Friday through Sunday:

High and low temperatures will gladly return to near or above average into early next week. At this time, I don’t see any large temperature swings coming for the mid or latter part of next week.

While the Tri-State has dealt with several rounds of nasty storms this year, numbers show that relatively few Flash Flood and Severe Thunderstorm Warnings have been issued in the Tri-State so far in 2013. No tornado warnings have been issued in the Tri-State since the year began. Prior to 2013, the latest first Tornado Warning of the year was on July 27th, 2002. Here’s how the number of warnings so far this year match up with averages through this date:

Through the end of May, the number of Tri-State Severe Thunderstorm Warnings was at a record year-to-date minimum. The year-to-date count of 59 warnings so far this year is the 2nd fewest number of warnings issued through this date (since the National Weather Service in Wilmington first started issuing warnings for our area in 1995); only 2002 had fewer warnings through September 3rd:

This also feels like an unusually quiet severe weather season compared to 2011 and 2012.

The number of Flash Flood Warnings issued so far this year has also been below average, but we saw fewer warning through this point in 1999, 2004, 2005, and 2007:

Lower radar resolution and poorer rainfall estimation algorithms are partially to blame for the higher warning count in the late 1990s and early 2000s.

The story of the year – at least to me – seems to be the lack of tornadoes and number of Tornado Warnings. While there have been several years since 195o with no confirmed tornadoes in the Tri-State, we never made it to early September without a Tornado Warning being issued somewhere in the Tri-State from 1995 to 2012. We have, however, done just that in 2013:

Only Tornado Warnings have been issued in September since 1995. Tornado Warnings are even more rare in October, November, and December. Severe weather is unlikely in the next 7 days, so the window for getting Tornado Warnings is quickly closing.