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In today's Weather Journal column, I noted that summer 2009 (June 1 to August 31) had, somewhat surprisingly, finished slightly above normal in temperature. Well, that's still true, but the margin is much smaller than I had written. Roanoke's summer average temperature of 74.5 degree was only two-tenths of a degree above the summer normal average of 74.3 degrees. I misfigured the average for the summer normal temperature.

The overall gist is the same -- warmer nights in June and August were enough to offset the seventh coolest July on record, producing what was essentially a normal summer in temperatures. But the takeaway lesson here is: Always double-check your math!

With temperatures projected to push the mid 90s as early as Sunday, let's take a quick look back at our cool July before we move on.

First, here's a map of the United States from the National Climatic Data Center depicting July temperatures based on statewide averages. The darkest blue shade from Pennsylvania west to Iowa -- most of Big Ten country, plus West Virginia -- depict the coldest July on record in those six states, dating back to 1895. All the states in the next lighter shade of blue, including Virginia, had July temperatures among the 12 coldest on record, or "much below normal."

In Roanoke and Blacksburg, this is how July stacked up (some data problems at the National Weather Service led me to listing some different rankings earlier, but those have been squared away now and this is what stands for July).

* Tied for 7th coolest overall average temperature in Roanoke, dating to 1912, with an average of 73.3 degrees, equalling that of July 2000. (Top 10 list here)

* Fifth coolest average high temperature in Roanoke of 82.6 degrees. (Top 10 list here)

* Fourth coolest overall average temperature in Blacksburg, dating to 1952, of 68.4 degrees. (Top 10 list here)

* Third coolest average high temperature in Blacksburg of 78.2 degrees.  (Top 10 list here)

The National Weather Service in Blacksburg also notes that having only one day at or above 90 degrees in July at Roanoke was the first time there had been so few 90-degree days since 1950. (Click here for a weather service summary about that and other facts about the cool July).

So that's the way it was in July.

July 2009 is truly astounding when you consider the temperature extremes in different parts of the country.

Across the northern and eastern parts ... record or near-record chill (dating almost to the Civil War in some cases), in places like Madison, Wisc., the Chicago area, Michigan,  Nebraska and New York City.

Meanwhile, across the southern and western tier ... record or near-record heat at Portland, Las Vegas, Phoenix, the San Antonio-Austin area, and far South Texas.

As I've written before, the two extremes are linked. As hot air stagnated under strong high pressure parked over the western U.S., the clockwise circulation around that same big high continuously funneled down cool air into the northern and eastern states.

Another cold front pulled down by that northwest flow will move into our region on Sunday, triggering some showers and thunderstorms. But it probably won't bust through with a big push of cool air, so warm, humid, showery weather will likely be common in Southwest Virginia this coming week.

Due to some weather data issues and other problems, I've scrapped what was on this blog entry altogether and recapped July on a later entry that can be found by clicking here.

If you wonder where the summer heat is ... try somewhere you wouldn't expect, Seattle, which shattered its all time record high temperature by 3 degrees on Wednesday hitting 103. Meanwhile, it's still a strangely cold summer around the Great Lakes.  The two are related, as the jet stream is pushing far north into Canada above strong high pressure in the West, then diving southward bringing cool air into the East.

Here in Southwest Virginia, Thursday should be about normal, with highs in Roanoke in the mid to upper 80s after morning lows in the upper 60s. There could be scattered afternoon thunderstorms as daytime heating bubbles moisture upward.

"This is the first day of summer," somebody told me in the Roanoke Times office a little while ago. With a high of 91 ... only the fifth day at or above 90 this entire year to date ... and a dew point in the 60s (some 70s dew points in the New River Valley), it did indeed feel like a real July day.

Don't get used to it. A new cold front moving through will cut the legs out from under July heat once again, with temperatures likely at least 5 degrees cooler on Friday. Saturday will be about as pleasant as you can expect for the historical peak of summer heat, with highs in the mid 70s to low 80s and lows in the mid 50s to low 60s. Every day for about the next week (at least) is likely to be below normal for afternoon highs (normal this time of year is 88 at Roanoke, 83 at Blacksburg).

Even with today's heat, July is averaging only 73.3 degrees in Roanoke through the first 16 days. If the month ended today, it would be tied for sixth coolest (with 2000) among all Julys dating back to 1912. The record coolest July averaged 71.7 degrees in 1947. The expected upcoming weather pattern, featuring a deeply dipping jet stream over the East, and a few rainy days along the way holding highs in the lower half of the 70s could put that record in play.

Roanoke set a record low for May 19 on Tuesday, dropping to 37, eclipsing the previous record of 39 set in 1994. The temperature is about to make a huge rebound upward. Though Wednesday will start out cool, with temperatures in the 40s, the afternoon will heat quickly into the 70s, maybe scraping 80 here and there. Highs above 80 are likely Thursday through Saturday.

Using the National Weather Service-Blacksburg data set, Blacksburg set another record high of 85 today, topping the 84 for April 26 set in 1990. (See my last blog entry and comments for the issues concerning the conflicting data sets.) Roanoke's high of 89 today fell 4 degrese short of the 93 set in 1915.

There appears to be two more days of this summer preview left, with highs in the mid 80s to low 90s possible Monday and Tuesday under strong high pressure.  By Wednesday, a cold front begins to make headway into the hot air mass, additional moisture returns. Highs closer to normal in the 70s are expected those days. By late in the week, a cold front will finally push through the heat dome, and more normal temperatures will return to the area.

Roanoke's official high this afternoon was 91 degrees, making this the first 90-degree day in the Star City since April 16, 2002. Lynchburg and Danville also each hit 91 degrees. None of the three sites set records, however, which are in the mid 90s.

The automated weather station at Martinsville was reporting temperatures as high as 97 degrees this afternoon.

The National Weather Service is reporting that Blacksburg has set a record high of 86, topping the previous record for April 25 of 84 set in 1960. This report is somewhat different than the Southeast Regional Climate Center, which lists 88 in 1957 as the record for the date in Blacksburg. I'll see if I can get a clarification on that.

The heat was enough to kick up a few showers and thunderstorms, as moisture in the middle layers and cooler air aloft combined with the surface heating. Sunday is likely to be very similar, both in terms of heat and scattered short-lived afternoon showers and storms.

We're about to shift out of the mode of posting photos of late April snow (some links posted in the comments of my last entry) to watching how high the mercury can climb. Thursday will be a nice spring day in the upper 60s to mid 70s, but the next four or five days after that are likely to be in the 80s. As high pressure builds in at the surface and aloft, we'll get a setup similar to a summer heat dome going, with stable air aloft inhibiting clouds and precipitation, and bright sunny skies each day to push the temperature up. Various forecasts are currently peaking Roanoke in the mid to upper 80s on Saturday, but I think there's even some chance we could scrape 90. Even if we do, it won't be setting any records. Record high for April 25 is 95 set in 1925, it's 93 for April 26 set in 1915, and it's 95 for April 27 set in 1957. Roanoke's earliest 90-degree day was March 19, set in 1945.

Blacksburg's records for those three dates are 88, 86, and 90, respectively, all set in 1957, so those probably will stand, too. (Blacksburg's records go back to 1952, Roanoke's to 1912).  That must have been a torrid late April in 1957 ... all of Blacksburg's record highs between April 25 and May 1 date to 1957.