THE DECEMBER OUTLOOK

Average high temperatures in the Lower Midwest fall from 44 on the first of the month down to 36 on the 31st. Typical lows move from 29 to 21. Most Decembers bring one or two days above 60, and four days in the 50s, those temperatures frequently recorded before the arrival of early winter (around December 8th). The remaining afternoons reach into the 40s an average of seven times, into the 30s thirteen times, finding the 20s three times, and stay in the teens or lower on three occasions.
A morning or two below zero is experienced three years in ten. The period most likely to produce such lows is December 18th through the 26th. The coldest December days, those with better than a 35 percent chance for temperatures in the 20s or below, are the 17th, 18th, 19th, 25th, and 26th. The warmest days, those with a 25 percent or better chance of producing highs in the 60s or 50s, are the 1st, 2nd, 3rd, 7th, 10th, 12th, and 29th.
Skies are completely cloudy on about 12 December days. They are partly cloudy on 15 days, completely cloudless on only four. The average amount of sunshine available this month is 37 percent, the lowest average of the Yellow Springs and Midwestern year.
The darkest December days, those with better than a 60 percent chance for totally overcast conditions, are the 2nd, 3rd, 5th, 6th, 7th, 8th, 11th, 15th, 18th, 19th, 21st, 23rd, 26th, 27th, 28th, 29th, and 31st. The sunniest days, those with more than a 60 percent chance for at least partly cloudy conditions, are the 9th, 14th, 22nd, and the 25th.
A typical December in the Lower Midwest (except along the Great Lakes) brings a little more than two and a half inches of precipitation - included in which are an average of five and a half inches of snow (one inch of snow equals approximately .05 of an inch of water).
The wettest days of the twelfth month, those with more than a 40 percent chance of precipitation, are the 6th, 8th, 10th, 15th, 17th, 19th, 20th, 21st, 22nd, 24th, 30th, and 31st. Rainy days usually outnumber snowy days by about two to one. The days with the least precipitation (just a 20 percent chance): the 1st, 4th, 11th, 16th, and 26th

Autumncount and Wintercount
The final front (the 18th front, ordinarily) of fall typically arrives around December 3rd. After that, the chances for chillier weather increase, and winter arrives on the 8th with the first of its 16 major cold fronts.

December 3: The warmest days of December often take place just before the arrival of this front. As the weather system approaches, rain or snow occurs about one year in two. Once the December 3rd cold wave comes through, however, dry weather is the rule for the next two days. Now average temperatures are falling at the rate of one degree every two days in most states, and lows almost always fall below freezing above the Mason-Dixon line. By the 6th, the wind shifts to the south and the skies darken in anticipation of the first major high of early winter.

December 8: This wave of high pressure is typically the first severe system of early winter, and a secondary front often reinforces the chill between the 11th and the 13th. Completely overcast skies dominate more than half the days, and precipitation should be expected as the cold waves approach. The days immediately following the front are typically sunny, and the 10th and 12th often bring warmer conditions. Severe weather with below-zero temperatures and highs only in the teens is still relatively rare below the northern tier of states, but the December 8th front initiates the sixteen-week period during which most snow falls within the borders of the United States.

December 15: The strongest cold wave so far in the season typically moves across the nation between the 15th and the 17th. Some of the coldest December days follow this front. One of the most bitter is the 19th, with a solid chance for highs only in the teens as far south as Cincinnati. The first significant bout of below-zero temperatures in weather history also occurs after this front, and double-digit below-zero temperatures enter the realm of possibility in over half the states. The strength of the December 15th high-pressure system is also associated with higher-than-average precipitation both before and after its arrival.

December 20: The December 20th high-pressure wave is the first of two “white-Christmas” fronts. It is often a relatively mild system, but it has about a 40 percent chance of producing snow in the East and Midwest. Travel is typically favored after the arrival of this front but before the general meteorological disturbances of the 24th.

December 25: The Christmas front is usually a potent one; it brings snow about half the time to the upper half of the nation, and its temperatures are brisk. With the cold comes sun, and the 25th and 26th are historically some of the brightest days of December. It is not unusual for the 27th to initiate a slight warming trend; as the New Year’s weather system approaches, however, the sky usually grows cloudy, making the 28th one of the year’s gloomiest days.

December 31: The New Year’s front often brings wind, sleet or snow. A 50 percent chance for precipitation begins on the 30th and continues through the 31st, but relatively mild weather accompanies the moisture. After this weather system moves to the east, however, the chill of middle winter grips the nation for the next six to twelve weeks.

WEEKLY WEATHER

WEEK 1
All along the 40th parallel, average highs fall three degrees this week into the lower 40s, and typical lows decline to the middle 20s. The first December cold front usually arrives between the 1st and the 3rd, bringing a 40 percent chance for rain or snow on the 2nd and 3rd. The 4th and 5th are dry two years in three; the 6th, however, usually anticipates the second high-pressure system of the month, and it is wet half the days in my record. Afternoons reach the 60s five percent of the time. Odds are far better for chilly afternoons in the 30s and 40s and lows well below freezing. December 1st is usually the brightest day of the week, with a 60 percent chance for sun; on the other days of this period, odds are better than 50/50 for clouds.

WEEK 2
This week of the year brings the second major cold front of the month between the 8th and the 10th, and the third major high- pressure system between the 11th and the 13th. Completely overcast skies dominate 60 percent of the days, and precipitation should be expected as the cold waves approach. Afternoon highs are usually in the 20s or 30s (a 55 to 65 percent chance for temperatures so cold). The 10th and the 12th are the days this week with the best chance for warmth in the 40s or 50s (slightly better than a 30 percent chance for that). Severe weather with below-zero temperatures and highs only in the teens is rare; the 14th is the only day when such things might occur.

WEEK 3
The third week of December almost always brings in a strong cold wave between the 15th and the 17th, and if this front arrives on its earliest date, the 15th, expect another front on the 19th or 20th. The coldest December days, those with better than a 35 percent chance for highs in the 20s or below, all come at this time of the month: the 17th, 18th, 19th, 25th, and 26th. The most bitter day this week in weather history is the 19th, with a 30 percent chance for highs only in the teens. And more below-zero temperatures occur between the 18th and the 26th than on any other December mornings. Precipitation is common throughout the period, with every day this week bringing a 50 percent chance for rain or snow except December 16th, which is typically the driest and the sunniest day between the 15th and 25th.

WEEK 4
This time of the year is ordinarily dominated by two major cold waves. The first comes in on the 21st or 22nd, and the second arrives between the 23rd and the 26th. Christmas is typically the brightest day of the week, bringing a 70 percent chance for sun. The 28th is the darkest day, with a 70 percent chance for clouds. Snow falls half the time on Christmas Eve and on the two days before New Year's Day. The 26th is typically the coldest day of the week and has almost a 40 percent chance for highs just in the teens or 20s.

THE DAILY WEATHER HISTORY

December 1
This is the December day most likely to bring temperatures above 50 degrees (there’s a 45 percent chance of that).  Highs are in the 40s fifteen percent of the time, in the 30s twenty percent, in the 20s twenty percent.  The sun shines seven years out of ten.  Rain falls an average of one year in five.  Snow comes once in a decade.  Early winter, a pivotal time of decisive cold, is likely to arrive within the next few days, no later than the 8th. 
December 2
Although today and tomorrow can see 70 degrees five percent of the time, high temperatures are rarely in the 60s, reach the 50s twenty-five percent of the days, are in the 40s twenty percent, in the 30s thirty percent, are in the 20s fifteen percent, and in the teens five percent.  Strong north wind helps nighttime lows drop below freezing 80 percent of the nights.  Precipitation: one day in three, with the odds even for rain or snow in most areas of average elevation along the 40th Parallel. 
December 3
Chances for highs in the 70s are five percent, for 60s ten percent, for 50s fifteen percent, for 40s ten percent, for 30s fifty percent, for 20s ten percent.  Skies are cloudy almost two-thirds of the time; rain falls one year in three, snow less than once in a decade.  This morning is the first since March 9th that carries a five percent chance for the temperature to drop to zero or below.
December 4
Highs remain in the teens five percent of the days, are in the 30s six years in ten, warm into the 40s twenty percent of the time, into the 50 ten percent, and into the 60s five percent.  Precipitation is relatively infrequent, rain or snow only falling 25 percent of the years.  Clouds, however, are more common than sun; overcast conditions occur 55 percent of the time. 
December 5
Today's high temperature distribution is as follows: 25 percent chance for 50s, forty percent for 40s, thirty percent for 30s, and 15 percent for 20s or teens.  Skies are overcast half the time; chances for precipitation: 35 percent.  Until 1994, December 5th was the latest date for he first snow in central Ohio.  The record was broken that December, the latest date moved to December 10th. 
December 6
There is a five percent chance for highs in the 60s or 70s, twenty percent for 50s, thirty-five for 40s, twenty percent for 30s, fifteen percent for 20s, and five percent for teens.  Chances for rain today are 35 percent, for snow 15 percent, and totally overcast conditions occur six years in a decade.  This is the last day for the chance of a high above 70 until January 21st.  And from today until March 1st, record low temperatures in most of the lower Midwest remain below zero.
December 7
Today's high temperatures are in the 50s thirty percent of the years, in the 40s another 30 percent, in the 30s twenty-five percent, 15 percent in the 20s or teens. The sky is completely overcast half of the time, and chances for rain are 30 percent, for snow five to ten percent.  The 16-week snow period begins for many states along the 40th Parallel within the next seven days.
December 8
Early winter normally begins no later than this date, with the first of the season's 16 major cold fronts.  By today, the possibility of snow is now 30 percent greater than it was at the end of November, and frozen precipitation falls more frequently today and on the 10th, than on any other days in the first two weeks of December. 
The temperature distribution for the 8th: five percent of the highs are in the 60s, five percent in the 50s, thirty percent in the 40s, forty percent in the 30s, twenty percent in the 30s.  The sun shines on four to five days out of ten. Freezing nighttime temperatures occur 85 percent of the nights, giving this date more dark cold than any other day so far since the end of summer.
December 9
    Today is one of the coldest and sunniest days of the first part of December, with highs remaining in the 20s more often than on any day so far this season (25 percent of the time).  The absence of clouds does allow highs to warm into the 50s twenty percent of all the years; 40s happen 25 percent of the time, 30s thirty percent.  Precipitation: 35 percent of the years, with odds 50/50 for snow or rain.
December 10
Today's average high temperature distribution: 50s thirty percent of the time, 40s just five percent, 30s forty-five percent, 20s twenty percent.  Chances for precipitation are a little higher than yesterday's chances: 40 percent today, odds even for snow or rain.  Clouds dominate the days more than half the time.
December 11
More than half the years, highs remain in the 30s; sometimes, they even fall to the 20s (five percent of the time).  But a rare afternoon above 60 was recorded back in 1978, and 65 is the record high.  Other benign possibilities: 15 percent chance for mild 50s and 15 percent for 40s.  Skies are overcast 50 percent of the years, but snow falls only one year out of five, and rain only one in ten.
December 12
Highs in the 50s occur 25 percent of the time.  Forties come 20 percent, 30s thirty percent, twenties 25 percent.  A morning below zero comes once every decade.  Clouds cover the sky half the years.  Chances for precipitation: 30 percent, with rain four times as common as snow.
December 13
Five percent of December 13ths are in the 50s, twenty-five percent in the 40s, fifty percent in the 30s, twenty percent in the teens.  Precipitation, frequently in the form of snow, occurs 30 percent of the time.  Skies are clear to partly cloudy 55 percent of the days.  Lows drop below freezing all but 20 percent of the nights.
December 14
Today’s high temperature distribution: five percent chance for 60s, five percent for 50s, thirty percent for 40s, forty percent for 30s, ten percent for 20s, and ten percent for teens.  Double-digit below-zero morning temperatures enter Midwestern record books, but even single-digit below-zero dawns are rare, coming only five percent of the years.  On this date, rain falls 20 percent of the days, snow just five percent.
December 15
Highs in the 60s come five percent of the afternoons; 50s occur on ten percent, 40s on 35 percent, 30s on 40 percent, 20s on five percent, teens on five percent.  Skies are cloudy half the time, and there is a ten-percent chance of a morning below zero.  Snow falls one day in four, rain one in five. 
December 16
Today’s temperature distribution: five percent chance for 60s, fifteen for 50s, thirty-five percent for 40s, twenty percent for 30s, and twenty percent for 20s.  And for the first time this winter, there is a five to ten percent chance for a high only in the single digits.  Morning temperatures fall below freezing all but 30 percent of the time, and below-zero temperatures occur one day in 20.  Rain comes about 15 percent of the days, snow another 15 percent.  The 16th is one of December’s brighter days, the sun appearing a full 70 percent of the time. 
December 17
The 17th brings a warm afternoon above 50 degrees five percent of the years.  It offers 40s on 35 percent of the years, 30s on 25 percent, 20s on 25 percent, teens on five percent, and single digits on five percent.  The sun shows through more than half the days, but chances for rain or snow are 50 to 60 percent.  Eighty-five percent of all the nights dip below 32 degrees.  One dawn in 20 falls below zero.
December 18
There is a 15 percent chance for highs in the 50s today, 30 percent for 40s, fifteen percent for 30s, twenty-five percent for 20s, fifteen percent for deep cold in the teens or colder.  Below-zero mornings occur ten to 15 percent of the time, making this the day most likely to have such conditions so far this winter.  The sun appears on only 30 percent of December 18ths.  Rain falls 20 percent of the time, snow 25 percent.
December 19
December 19th brings completely overcast conditions two years out of three, and this date has a 50 percent chance for precipitation, with the odds weighted a bit more towards rain than snow.  Today’s distribution of high temperatures: teens or 20s come 30 percent of the time; 30s come 30 percent and 40s another 30 percent, 50s only ten percent.  Below-zero mornings occur 15 percent of the time. 
December 20
There is a 50 percent chance for clear or partly clear
conditions today, but rain comes 25 percent of the time, snow 20 percent.  This morning and the morning of the 26th are the most likely (about 20 percent likely) to record below-zero temperatures in all December.  High temperatures are in the teens 20 percent of the time, in the 20s ten percent, in the 30s twenty percent, in the 40s thirty percent, and two out of every ten December 20ths provide a thaw in the 50s or 60s.
December 21
Skies are overcast five years in ten.  Snow falls one year in five, rain one year in four.  Highs in 60s occur five percent of the time, 50s twenty percent, 40s five percent.  Chilly days in the 30s come 55 percent of the time, and there is a five percent chance each for highs only in the 20s, teens, and single- digits.  Lows drop below freezing three fourths of the nights, but below-zero temperatures come only once or twice in a decade on this date.
December 22
Highs are above 50 ten percent of the time today, and they reach into the 40s forty percent of the time.  Thirties occur 30 percent of the afternoons; ten percent of the time, highs are only in the 20s; on ten percent of the days they do not get above ten degrees.  Below-zero temperatures come only five percent of the mornings, but 65 percent of the days bring lows below 32 degrees.  Chances for rain or snow remain steady at 45 percent. 
December 23
Highs in the 50s are more likely today than on most December days, such warmth occurring 20 percent of the years.  Many afternoons, however, are chilly.  There is a 25 percent chance for 40s, forty percent chance for 30s, fifteen percent chance for highs only in the teens.  Chances for precipitation are 35 percent, a drop from yesterday's 50 percent.  Completely overcast conditions darken the landscape five years in ten on this date.
December 24
Christmas Eve brings precipitation 50 percent of all the years, but a white Christmas comes more like 35 percent of the time (since sometimes that precipitation arrives in the form of rain).  Although 20 percent of the days are mild in the 50s or 60s, the 24th is one of the few days on which a below-zero high has been recorded (in the bitter winter of 1983).  Forty-five percent of the time temperatures warm to the 30s or 40s, with 20s occurring 20 percent of the afternoons, and teens on ten percent.  Odds for sun are 50/50. 
December 25
Christmas day is generally cold and partly sunny, snow remaining on the ground three to four years in ten above the Border States.  The arrival of the fifth high-pressure system of the month often brings flurries.  Chances for highs in the 60s are only five percent.  Forties come another five percent of the time, 30s forty percent, 20s or below 50 percent.  One Christmas per quarter century remains below zero.  The sun appears 60 percent of all the years.
December 26
    The 26th brings highs in the 40s thirty percent of the time, highs in the 30s on 30 percent of the afternoons, 20s on another 30 percent, and teens on the remaining ten percent.  Skies are completely cloudy two years out of three on this date.  Snow falls a third of the time, but rain is rare.  Chances for a morning below zero are 20 percent, 95 percent for a morning below freezing.
December 27
A slight warming trend begins today four years in ten, and it sometimes continues until the 1st of January.  Highs reach the 50s or 60s twenty percent of the time, and below-zero lows are rare.  Colder weather is certainly not unusual for this date, however.  Fifteen percent of the days are in the 40s, forty percent are in the 30s, and another 25 percent in the 20s or teens.  Clouds continue to dominate the sky, and snow or sleet comes 35 percent of the days.
December 28
Chances for highs in the 60s are 15 percent; mild 40s occur 30 percent of the days, and afternoons in the 30s come on 45 percent, leaving very little room for severe weather.  The sky is almost always cloudy on the 28th, and there is just a 30 percent chance for even partly sunny conditions.  Rain is more frequent than snow, coming 20 percent of the time; flurries occur just five to ten percent of the time.
December 29
    There is a ten percent chance for a high in the 60s today, 15 percent for 50s, fifteen percent for 40s, forty percent for 30s, fifteen percent for 20s, five percent for teens.  The sun appears on a little less than half the days, and precipitation occurs one day in three.
December 30
Highs in the 60s come five percent of the time, 50s come another five percent, 40s thirty percent, 30s forty percent, 20s ten percent, teens five percent, single digits five percent.  Today is partly sunny two years out of three, but rain or snow occurs half of all the days in my record.  Lows fall below freezing 55 percent of the nights, and below-zero temperatures occur one night in 20.
December 31
New Year's Eve is usually cloudier than the 30th, bringing overcast conditions seven days in ten.  There is a 35 percent chance for rain, ten percent for snow.  Today's highs are in the 50s twenty percent of the time, in the 40s twenty-five percent, in the 30s forty-five percent, in the 20s ten percent.  Below-zero temperatures on this date are infrequent.