The August Outlook
Six thunderstorms usually occur in August. They are most likely to occur on the hot afternoons between the 1st and the 11th. Total precipitation is near three inches in Yellow Springs, a little less than in July.
The days with the most precipitation are usually August 4th, 5th, 10th, 11th, 18th, 19th, 21st, and 28th. The driest days in my weather history: August 9th, 12th, 13th, 14th, and 22nd.
Nights grow longer in August, one hour and nine minutes longer by the end of the month. The first week loses two minutes in a day; by the last week, the loss is up to three minutes every 24 hours. Even though the days shorten, the percentage of possible sunshine per day increases to near 80 percent, the highest of the Ohio year.
The eighth month typically brings ten completely sunny days and up to two weeks of partly cloudy weather. The brightest August days, those with better than an 80 percent chance for sun, are the 1st, 2nd, 8th, 9th, 12th, 13th, 25th, and 26th. Totally cloudy days are rare; the 18th, the 23rd and the 28th are the only days on which the chances for overcast conditions reach 50 percent.
Normal average temperatures decline from the mid 70s to the lower 70s all across the region. Highs fall from their peak of 85 at the rate of about one degree every week, reaching 81 by the first of September. Average lows drop from 64 to 60.
The August days most likely to bring milder temperatures (highs below 80 degrees) occur in the second half of the month: the 20th, 23rd, 24th, 29th, and 30th. The hottest days, those most likely to bring 90s or above, generally come at the beginning of the month. Adding to the warmth, August’s wind speed is the lowest of the year, and humidity is the highest, an average of about 80 percent after sundown. Chances for oppressive heat gradually fall from 35 percent between the 1st and the 4th down to 15 percent by the end of the month.

Summercount
Front 11: August 4th: This weather system sometimes provides an early break from the Dog Days.

Front 12: August 10th: This front can be one of the most shocking of the year, bringing an end to the Dog Days five years in ten.

Front 13: August 17th: This is the first front of the summer which can bring chances for frost at higher elevations and along the Canadian border.

Front 14: August 29th: This front brings the chance of light frost as far south as the Ohio Valley.

WEEKLY WEATHER
WEEK 1
The Dog Days usually continue this week of the year throughout the country, the daily possibility of highs in the 80s and 90s remaining near July levels. August 3rd, 4th, and 5th are the last days of the summer on which there is a 40 percent chance of highs in the 90s, and chances for highs in the 80s are steady at around 50 percent. Cool days do occur 15 to 25 percent of the years, and afternoons only in the 60s are occasionally recorded between August 2nd and 11th. Morning lows are typically in the 60s, although one fourth of the nights carry temperatures into the middle 50s.

WEEK 2
Weather statistics continue relatively stable for this second week of the month: 50 percent of the afternoons are in the 80s, twenty-five percent in the 90s and another 25 percent in the 70s. Rainfall is typically light, with the 9th, 12th, 13th, and 14th carrying just a ten to 15 percent chance for a shower. At the arrival of the August 10th cold front, however, the 10th and 11th have a 40 percent chance for precipitation as well as the slight possibility of a high only in the 60s for the first time since July 13th. And within the next seven days, lows reach into the 40s fifteen times more often than they do during the first week of August.

WEEK 3
The weather in the third week of August brings highs in the 90s on 15 to 20 percent of the afternoons, milder 80s fifty-five percent of the time, and cool 70s the remaining 25 percent. The 19th of the month, however, breaks from the pattern many years, and it has the highest frequency of 90s (35 percent chance) of any other day in the week. Chances for rain increase from 25 percent at the beginning of the period to 30 percent by August 21st, then drop abruptly to just ten percent on the 22nd.

WEEK 4
This is the week when frost becomes likely in the northern states; snow even occurs at the upper elevations in the Rocky mountains and in Canada. Across the Plains, the Midwest, and the East, the third major high pressure system of the month brings chances for highs in the 70s a full 40 percent of the time on August 24th, the first time since July 6th that odds have been so good for milder weather. As that cool front moves east, the period between August 25th and August 27th usually brings a return of warmer temperatures in the 80s or 90s. The 26th, 27th, 28th, and 29th each carry a 30 percent chance of highs in the 90s, and the 25th and 26th are the last days of the year on which there is only a ten to 15 percent chance for mild weather in the 70s.

On the 28th, however, the final cool wave of August approaches, and even though chances for 90s remain strong, the likelihood for chilly highs only the 60s or 70s jumps to 30 percent. August 30th is typically the coldest day of the month, and it brings a 50 percent chance for a high just in the 70s, the first time chances for that have been so good since the last day of June.
Nights in the 40s or 50s continue to occur an average of 40 percent of the time, and the morning of the 29th brings the slight possibility (a five percent chance) of light frost to the 40th parallel for first time since the beginning of June.

Chances for rain are typically 35 percent per day now, with the exception of August 28th, on which date thunderstorms cross the region 65 percent of the years in my record. The 25th and 26th are usually the sunniest days this week.

THE DAILY WEATHER HISTORY

August 1
Today is usually in the 80s, with a 15 percent chance for an afternoon in the 70s, and 20 percent for 90s. The sun shines on at least 85 percent of the days, and chance for rain is 25 percent. Cool lows in the 50s occur only 15 percent of the time.
August 2
Cool morning temperatures in the 50s occur today 25 percent of all the years, but afternoons in the 90s come 30 percent of the time, 80s sixty percent, and 70s just ten percent. The sun shines at least a little on nine out of ten August 2nds, but thundershowers pass through 35 percent of the time.
August 3
Highs in the 90s come 40 percent of the time on this date, 80s fifty-five percent, with 70s only five percent. Skies are clear to partly cloudy eight years in a decade, with rain passing through one year in three. Most night lows are in the 60s; just 20 percent reach into the 50s.
August 4
Continued hot and very humid most years. Highs climb to the 90s forty-five percent of the time; there’s a 45 percent chance for 80s too, only ten percent for 70s. The likelihood of rain increases to 60 percent, the highest since the 3rd of July, and the second highest of the summer. Clouds block the sun all day three years in a decade. There is just a ten percent chance for a cool low below 60.
August 5
Today’s highs are shared equally between the 80s and 90s, thirty-five percent chances for each, with a 30 percent possibility for an afternoon in the 70s. Rain falls four years out of ten. Totally cloudy skies are likely one year in four. Cool nights in the 50s occur about 30 percent of the time.
August 6
Thirty percent chance for a high in the 90s today, 35 percent for 80s, thirty-five percent for 70s. Rain is likely one year in three. A nighttime temperature in the 40s is possible now for the first time since the first week of July.
August 7
Highs in the 90s come 20 percent of the days, in the 80s sixty percent, in the 70s twenty percent. Rain falls one year out of five. Totally overcast conditions occur just 15 percent of the years. Cool lows in the 50s are recorded 15 percent of the years
August 8
Today’s highs are in the 90s thirty-five percent of all the years, in the 80s forty-five percent of the time, 70s the remainder of the years. The chance for rain is 20 percent. Sun dominates. Conditions may be unsettled, however, as a cool front typically crosses the Mississippi between today and the 11th. Chilly nights in the 40s come 15 percent of the years.
August 9
This is one of the sunniest of all the August days, with a 95 percent chance for clear to partly cloudy skies. Showers pass through 15 percent of the time. Hot temperatures in the 90s occur 25 percent of the afternoons, and 80s come on 50 percent, 70s on 20 percent. But, for the first time since June 29th, there is a five percent chance for an afternoon high only in the 60s.
August 10
Today is one of the most decisive days in the decline of late summer. The chances for 90-degree temperatures, which have remained fairly steady between 30 and 45 percent since the beginning of July, abruptly fall to between 15 and 20 percent. Completely cloudy conditions occur 30 percent of the years; chances for highs in the cool 70s are 25 percent, and chances for rain increase to 40 percent. Average temperatures have fallen just one degree since July 28th, the date on which the stability of middle summer began to deteriorate. Beginning today, averages drop a degree and a half per week until September 10th, when they decline one degree every three days into January.
August 11
There is a 50 percent chance for rain today, but the sun comes out seven years in ten. Most afternoons are in the 80s, but there is a 20 percent chance for 90s, fifteen percent for 70s, and ten percent for a high only in the 60s. Evenings cool into the 50s half of the years.
August 12
Today, the 13th and the 14th are usually sunny and dry, with a 15 percent chance of highs in the 90s, sixty percent chance for 80s, and 25 percent chance for 70s. Lows reach into the 50s half of the years, and into the 40s ten percent.
August 13
Temperatures are in the 90s twenty-five percent of the days, in the 80s forty-five percent, in the 70s twenty percent, and in the 60s ten percent. Lows fall into the 50s forty percent of the nights, and into the 40s fifteen percent. Rain comes only one day in a decade, and skies are clear to mostly sunny nine days out of ten.
August 14
Chances for highs in the 90s are 15 percent, for 80s fifty-five percent, for 70s thirty percent. Precipitation is uncommon: rain falls only one year in ten on this date, and the sun almost always shines. Chances for lows in the cool 50s are 40 percent.
August 15
The likelihood of highs in the 90s is relatively low - just 15 percent. Temperatures in the 80s are common; they occur 55 percent of the time, and mild 70s come 30 percent of the days. Cool nights in the 50s continue to be recorded four years in ten, and the chances for rain begin to rise, climbing from yesterday’s ten percent up to 25 percent. The likelihood of completely overcast conditions is also 25 percent.
August 16
This date brings a 30 percent chance for highs in the cool 70s, a 55 percent chance for 80s, and a 15 percent chance for 90s. Chances for a shower as well as for totally cloudy skies are 30 percent. Nights in the 40s come one year in ten, 50s three in ten.
August 17
Today is the last day that temperatures above 100 are likely to occur above the 40th Parallel for the rest of the summer (although the slight possibility remains through the first week of October). Almost three-fourths of the afternoons, however, are in the 80s, the remaining fourth in the 70s. The sun appears 70 percent of the time, and showers passing through four days in ten. Evening lows are in the 60s seventy-five percent of the nights, fall to the 50s fifteen percent, to the 40s ten percent.
August 18
Chances for highs in the 90s are 15 percent today; they are 60 percent for 80s, and 25 percent for 70s. Rain comes four times in a decade on this date; completely overcast conditions occur as frequently. Evenings cool to the 40s or 50s one night in five.
August 19
The 19th is often the warmest day in the third week of August, bringing highs in the 90s on 30 percent of all the years. Temperatures reach the 80s forty-five percent of the time, stay in the milder 70s the remaining 25 percent. Nighttime lows stagnate in the 60s eighty percent of the time, and chances for rain continue at yesterday’s 40 percent.
August 20
Today is typically warm and humid, partly to mostly sunny, with rain four years in ten. Distribution of high temperatures: 20 percent 90s, forty percent 80s, forty percent 70s. Early morning lows find 40 three years out of ten, reach into the 50s five years in ten. Odds for a day in the 90s are only half of what they were two weeks ago, and the likelihood of highs in the 70s is twice as great as it was at the end of July.
August 21
Showers come three years out of ten today, highs in the 90s ten percent of the time, 80s six years in a decade, 30 percent for a day in the 70s. Skies are clear to partly cloudy 70 percent of the time. Lows in 60s occur on 80 percent of the nights, cool 50s on the remaining 20 percent.
August 22
Today is typically drier than any day of August’s final third, and it often begins a five-day period in which rain is 20 percent less likely to fall than during the rest of the month. This is also the first day of a mid-August cool spell during which afternoons in the 90s occur just ten percent of the time. However, temperatures rise to the muggy 80s sixty-five percent of the afternoons, and are in the 70s twenty-five percent of the time. Lows in the 50s cool almost half the nights on this date.
August 23
There is a 15 percent chance for highs in the 90s today, a 50 percent chance of a high in the 80s, and a 35 percent chance for a high in the 70s. Rain comes three years in a decade. Five nights in ten go below 60 degrees, a percentage that signals a definitive break with Dog Day weather and another step towards winter.
August 24
Today brings chances for highs in the cool 70s forty percent of the time, the first time since July 6th that odds have been so good for milder weather. Temperatures warm to the 80s, however, 45 percent of the time, with 90s occurring 15 percent of the afternoons. Rain comes one year in three. Clouds cover the sky four years in ten. Nighttime lows fall below 60 forty percent of the time.
August 25
The period between August 25th and August 27th usually brings warmer temperatures. Chances for highs in the 90s double over yesterday’s chances. Warm 80s come 60 percent of the afternoons, with cooler 70s only occurring ten percent of the time. Showers pass through three years in ten, but the sun shines most of the day (this is historically one of the clearest days in August). Half the nights provide pleasant sleeping in the 50s.
August 26
There is only a 15 percent chance for highs to remain in the mild 70s today. Eighties are most common, occurring 55 percent of the afternoon. Nineties come frequently too — 30 percent of the time. Chances for precipitation continue at late August's typical 25 to 30 percent, and sun almost always dominates the clouds. Evenings are cool, below 60 half the time.
August 27
Highs in the 90s come 25 percent of the years, 80s fifty-five percent, 70s twenty percent. Chances for completely overcast conditions: 25 percent, for rain 35 percent. Nighttime lows are usually in the 60s, but cool 50s come two or three years in ten.
August 28
Today is another pivot day on the way to autumn as the chances for a high in the 60s rise to 15 percent. Seventy-degree highs take place 25 percent of the time; 80s occur 40 percent, 90s twenty percent. Lows dip below 60 on a third of all the nights. Rain falls (and the sun fails to shine) today 65 percent of the years, making this is one of the three wettest and grayest days of the summer months. And, for the first time since the beginning of June, the lightest of frosts becomes a slight possibility at average elevations along the 40th Parallel.
August 29
Nineties come 30 percent of the afternoons, and 80s occur 30 percent of the time, 70s thirty percent, 60s ten percent. Today is typically twice as sunny as yesterday, with all but 20 percent of the days bringing clear or partly cloudy skies. Rain falls three years in ten. A very light frost could appear on the roof one year in every 20.
August 30
Today is mild in the 70s fifty percent of the time; there is a 40 percent chance for 80s, ten percent for 90s. Rain, along with a totally or mostly cloudy day, comes one year out of three.
August 31
Forty percent of the early morning temperatures are in the 50s today. Highs climb to 90 ten percent of the afternoons, to the 80s fifty-five percent, and the 70s forty percent. The chance for rain continues to be about 35 percent. A totally cloudy day occurs this last day of the month four years in ten.