Colder Air moving in

Big changes are coming. On Monday we set a record high for the day with 87 degrees. Today, a cold front is pushing through that will bring about an end to the hot weather. Wednesday, should be significantly cooler that Monday.

After that, an upper level low will meander across us for the rest of the week. That will throw clouds and off & on showers at us right through Saturday morning. The good news is high pressure will dry us out for the weekend and really make it feel more like fall around here!

Fall Foliage Cont.

You may remember a few weeks ago, I blogged about the fall colors. Well, tonight on Channel 4 Action News at 6 pm, Stephen Cropper talked about the fall colors and why they happen. We’ll post that video here tomorrow for you to watch, so check back then.

And don’t forget about that great Web site, Fall In PA. Check it out here and learn more about the colors in our great state.

Today is the Fall Equilux

In the northern hemisphere, fall begins when the Sun moves southward across the Equator. Most textbooks describe the Equinox as the day in which day and night are equal. This is not true though. In Springtime, that day usually occurs BEFORE the Equinox…in Autumn that day falls AFTER it.

Truth is, the Equinox isn’t a day, it’s a point in time. At 5:51 am the Sun did make that trip across the Equator. That moment was the Autumnal Equinox. But on Sunday, there were still a few more minutes of daylight than night. We’ve been losing about two minutes of daylight each day since then.

Today’s Sunrise is 7:12 and the Sunset, yup you guessed it, 7:12. Today is the Autumnal Equilux in Pittsburgh! Equilux is the correct term for the day in which daylight and nighttime are equal.

Here is a very in-depth explaination of all of this stuff.

In essence, the party ends today. From here on out, the days will be shorter than nights til the Spring Equilux.

DI

Fall Colors

I was just talking with one our behind the scenes folks the other day about fall colors. She said one of her favorite drives in Pennsylvania is the one from Pittsburgh to State College and I agree. All those folks who travel from here to New England for the fall colors just don’t know what’s in their own back yard. But what makes a great color season as opposed to just an average one? It’s the weather (thus my writing about it in this blog).

The weather we see in September and October can directly affect fall foliage. Drier than normal weather in those months can speed up the fall color process and make for a shorter than normal season.

On the other side of the coin, a wetter than normal late season can cut down on the number of colors and also cause a shorter season with rain and wind bringing the leafs down early. The ideal weather is normal rainfall with lots of sunny days and the temps in the 60s-70s. Nights need to be cool and crisp without frost or freezing conditions. You can learn much more about what causes different colors by going to the US forestry website here.

As for that drive, just take 22 west to Altoona about the second weekend in October and you won’t be disappointed! While you are over there, stop in Hollidaysburg and have a frozen custard at the original Meadows. It’s awesome!

To learn more about the colors in our great state, check out this great website. Until next time…

The August Heat Wave

While Sunday was dreary and rainy… at least it was a break from the heat. The rain and cloud cover made for dramatically cooler temperatures. After FOUR consecutive days of 90 degree temperatures last week… highs in the 70′s came as a welcome change. Just look:

Wed, Aug 1st – 91
Thu, Aug 2nd – 91
Fri, Aug 3rd – 91
Sat, Aug 4th – 91
Sun, Aug 5th – 75

So until Sunday were we in a mini heat wave? Well, according to our big fat American Meteorological Society Dictionary in the weather center… a heat wave is “a period of abnormally and uncomfortably hot and usually humid weather.” It goes on to say that “In 1900 A.T. Burrows more rigidly defined a ‘hot wave’ as a spell of three or more days on each of which the maximum shade temperature reaches or exceeds 90F.”

So looks like we did it with 4 days in the 90′s, and we’re not done yet. This week promises to bring the return of heat and humidity and once again… temperatures near 90.

Enjoy August!

EK

July 2007: Climatology

With July in our rear-view it’s a perfect time to look back and see what type of month it turned out to be.

The climatology shows that July 2007 was cooler and drier than normal.

AVERAGE TEMPERATURE (found by putting together the daytime highs and lows): 70.5°

NORMAL AVERAGE TEMPERATURE: 72.6°

DEPARTURE FROM NORMAL: -2.1°

PRECIPITATION: 3.01″

NORMAL PRECIPITATION: 3.96″

DEPARTURE FROM NORMAL: -0.95″

August is already off to a hot start. The map below shows the forecasted high temperatures for today. There will be 90° readings in 41 states!

Red= Hot Dark Red=HOTTER! Purple=Just Move Away!

DI

Let’s Play a Game

Weather is a 24-hour deal. There is never time to “take a breather” for more than a brief moment. We’re here through weekends, holidays, vacations, and even when the news isn’t on.

That’s why it’s great to be a part of the largest team in the ‘Burgh. We’re able to work together, so that no one has to pull more than his or her fair share of the load. Many people think that we create our forecasts individually. That is the farthest from the truth. It’s a collaborative effort. There is contribution from each of us in every 5-Day forecast.

Most times that contribution comes in the form of a forecast discussion. Each Weather Watch 4 met leaves one when their shift is over. It’s usually just a few paragraphs that tells the next guy/gal what happened and what’s coming our way.

I’m the guy who gets the baton from Erin Kienzle after she completes here marathon weekend shift. The first line in her discussion last Sunday read.

“It’s time to play…Let’s time the vorts!”

That line by itself told me what type of week this would be. Lemme let you in on the joke. First, what’s a vort?

FROM THE NWS DALLAS/FT. WORTH WEATHER GLOSSARY:
VORT MAX
Short for vorticity maximum. Vorticity is similar to the amount of shear (or spin) in the air. A vorticity maximum represents the point where vorticity is at its highest value. Short waves often are referred to as a vort max, but in theory, a short wave is what produces the vorticity maximum. When a vorticity maximum is moving it often causes the air to lift out ahead of them (which may result in precipitation) and sink behind them.

Got that? Didn’t think so. I like to spare viewers and call vorts “disturbances” on air. It’s basically when there is something going on in the atmosphere which will provide lift…a necessity for precipitation. Here is what one looks like. Look for the “X” north of Pittsburgh.

The end result was a very off/on rainy pattern. Scattered showers and thunderstorms developed each day. Y’know…the kind where it rains in some neighborhoods and not in others?

Funny thing about that is, we get calls and emails from viewers both saying “You got it right” and “Better luck next time.” I guess, since we forecast as a team, we all should take the praise and um…non-praise as a team too.
DI

NHC Director Reassigned Amid "Revolt"

Time for a follow up:

Not long ago we linked this blog to a Good Morning America story in which Bill Proenza, then director of the National Hurricane Center, stated that if an aging satellite wasn’t replaced then the ability of his forecasters to predict future storms could be affected. Turns out, many of his employees disagreed and now Proenza is out.

Click here to see the story.

Mr. Proenza was reassigned to unspecified other duties on Monday, and Deputy Director Ed Rappaport assumed the director’s duties on a temporary basis.

Speaking of tropical storms:

Things have been quiet for some time in the Atlantic. We started this season making history with our earliest named storm ever. (Andrea). June brought the weak Barry but nothing this month. Atlantic Satellite from this morning…not much there.

During July storms are most likely to develop in the southern Caribbean and move north. Here is a graphic from the National Hurricane Center climatology page.

It’s Not The Heat It’s The Humidity

Monday’s high temperature climbed to 90°.

It was the first time we were that warm this month, however, the sixth time this year. We saw five 90° days during the month of June. (Normal is 1.7).

Pittsburgh averages three 90° days during the month of July. Remember, that’s the average, but there can be great variance from year to year. The graphic below shows the number of 90° days which actually occurred during the past five months of July and August.

Let’s take a moment to rejoice that 2002 is over….Ahhhhh.

Back to Monday. Yes, it was hot but you may have noticed that it wasn’t very humid. We reached the high temperature at 3:30 pm. At that hour, the Relative Humidity was around 41%. Not high at all. When that humidity is factored in you get a Heat Index of 91°. That’s what it felt like in the shade. At that level extreme caution is advised as prolonged exposure can cuase sunstroke, muscle cramps, and/or heat exhaustion.

The surface map below shows the processes which were at work. With the Jet Stream well north of the US/Canada border and a strong Bermuda High to the southeast, the “door was open” for heat to creep up from the Southern US. The humidity…it’s on the way. Look for dewpoints to climb to near 70° today!

Why are there so many…

After work last night, I jetted to White Oak for my kids swim meet. When I’m in my work clothes, and at an event, folks inevitably want to know “what’s the weather?”. Last night, however, was a different story. After 10 minutes of a steady rain, a beautiful rainbow appeared. The question of the hour then was, “How does that happen?” Here’s the answer…

Sunlight make look like one color, but it’s actually ALL of the colors of the rainbow wrapped up into one bright little package. We can see these different colors separate by running the sunlight through a piece of glass called a prism. It looks like this.

As the light passes through the prism, the prism causes it to bend. This ‘angle of bending” is different for the different colors of light and the colors spread out. When you see a rainbow, each raindrop is acting like a little prism. As the sunlight enters the rain drop, it reflects of the inside, and bounces separated into the different colors.

In a double rainbow, there are actually TWO reflections occurring on the inside. The raindrops have to be a very specific size for this to happen.

That’s it, that’s how a rainbow works. Of course, the simplest answer is the one I was told as a kid… “that’s just god showing his paintbrush.” Until next time.