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Friday, July 02, 2004

Weather columnist Kevin Myatt: A treat in store for fans of rain and humidity

Kevin Myatt is The Roanoke Times' weather columnist.

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@roanoke.com

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After a brief hiatus, the summer of humidity has resumed.

We probably won't see all-day washouts nor will we see scorching heat this Fourth of July weekend, but instead, sticky days with afternoon rumbles of thunder and a few firecracker-drowning downpours here and there. We still have a weather pattern where no feature is really stepping forward to take control.

For days, a front that pushed through last weekend as a refreshing cool front has been stalled to our south. Moisture from the Gulf of Mexico has been building up on the south side of the front, producing lots and lots of rain and thunderstorms from Texas to Georgia.

Gradually, the winterlike weather pattern that allowed this front to move through has relaxed, and the stalled frontal boundary has been slowly working northward. With each day, the tropical moisture has been advancing farther north, and our days have been getting more and more humid.

Wednesday afternoon, the humidity bubbling in the intensifying cauldron of midsummer sunshine was enough to cook up some late afternoon and early evening showers and thunderstorms.

A well-timed downpour at the Roanoke Regional Airport in the closing hours of June on Wednesday raised it to the sixth-wettest June on record. The airport collected 0.84 inch in an evening thundershower, pushing the month's total to 6.48 inches. That is 0.17 inch more than last year's wet June - but well short of the record 10.32 inches in June 1995.

The best dynamics for producing heavy thunderstorms and widespread rainfall will be moving north of us with the jet stream the next several days. The deepest moisture, however, will remain to our south.

In the limbo between these two zones, we'll simmer in a thickening stew of humidity, cooked up by afternoon heat into showers and thunderstorms.

This is called "diurnal" precipitation, forming in the daytime heating and diminishing quickly with evening cooling. It's the kind of pattern where one side of town can have street flooding while the other side stays dry. Sometimes, it pours on one side of the street and sprinkles on the other. A sunny day can turn stormy in minutes.

It seems like there is little that can truly break this pattern for the next seven to 10 days or so. We may get a weak front or two through, bringing more organized thunderstorms before a brief respite from the humidity. But no real strong front to plow out the sticky air looks to be in the offing.

The kind of massive heat dome high-pressure area that can take charge of the pattern, baking one part of the country while steering weather systems around it to bring regular rains elsewhere, is just not forming yet. The tropics are also not yet yielding any signs of a system that could mature into our season's first hurricane.

So we are left with an anarchy of mediocre systems, temperatures that are not particularly hot or cool, and a weird intermingling of downpour and dryness each day whose sum total is neither drought nor deluge for anyone.

But the humidity in the air will be a constant. Spend any time outdoors, and you'll be soaked, whether it rains or not.

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