Heat And Storms: Let's Update Things This Wet Tuesday

Almost all of those orange, red and burgundy shades on today's
National Weather Service map represent heat warnings, advisories
and watches. 

Excessive heat warnings and watches have expanded over a huge section of the United States today, covering an area from the central Plains to the Ohio Valley and on to parts of the East Coast.

More heat warnings and advisories will go up in the coming days in the eastern half of the country as the hot spell takes hold.  I'll update Vermont impacts a bit further down.

This is a particularly humid one. The air is tropical. Many areas subjected to this heat wave have had lots and lots of rain in recent months. So that will add moisture to the air.

The high humidity, then, will be the danger part of this heat wave. There will probably be only a few afternoon record high temperatures during this, as there have been more intense heat waves.

But the incredible humidity will not allow temperatures to fall much at night. Forecasters expect a lot of new records for warmest overnight lows.  This is a dangerous type of heat wave. Drier heat waves create hotter afternoon temperatures, but readings quickly cool at night.

Humid ones like this spell keep nighttime temperatures up. That gives people without air conditioning no break.  It wears people down, especially those with underlying health problems.

By the way, heat waves are not the kind of disasters you see on television. They are not telegenic. But heat is usually the Number One killer of all types of bad weather in the United States. Heat in most years is deadlier than floods, tornadoes, hurricanes, blizzards and lightning.

A supercell thunderstorm this morning near Beresford, SD.
Photo by Joe Zweifel, via Twitter

As expected, the heat contributes to pockets of severe thunderstorms if there are any disturbances or weather boundaries around to act as triggers.

On particularly nasty batch of thunderstorms went across South Dakota and on into Iowa early this morning.

I'm sure my relatives in Yankton, South Dakota were around 6 a.m. local time today by a storm that had warnings of winds that could gust to 80 mph. A tornado warning was in effect for a time just northeast of Yankton.

A wind gust of 89 mph was reported in Parkston, South Dakota, west of Sioux Falls, early this morning.

There will continue to be pockets of locally severe storms around the edges of this heat wave. Today, the risk zones are in the northern and central Plains, western Great Lakes, southern New England, the NYC metro area and parts of Pennsylvania and New Jersey.

There will be pockets of severe weather here and there on the northern fringes of the heat wave through Saturday.

The humid air also raises the risk of flash floods. You can get an incredible amount of rain in a short period of time.  I don't think there will be widespread areas of flooding, like we just had with Tropical Storm Barry, but some individual towns will get nailed.

VERMONT IMPACTS

The humidity is here, and so is the rain, as the last of Barry's remnants sweep by. As of 9 a.m. this morning the first batch of rain was already beginning to taper off in western areas of Vermont, but more is on the way.

It won't rain all day, but there will be a constant threat of showers and some afternoon thunderstorms. With this juicy air, some of the storms will produce torrential downpours.

Rainfall totals will be uneven as a result. Some areas might only get less than a half an inch of rain today or even less, while others who get bullseyed by downpours clock in with up to two inches.

This might be enough to cause a few local water problems. The National Weather Service office in South Burlington says there won't be any widespread flooding, but a few small streams and creeks could get a little wild. If a downpour hits a more urban area, we run the risk of some street flooding. (You know the drill: If the road is flooded, don't drive through it!)

A very weak cold front will actually give us some slight relief from the humidity late tonight and much of Thursday, which will be a rather quiet day.

Then Friday comes. So does the heat. I won't be at all surprised if we go under a heat advisory on Friday. The heat index by then could go up to 95 degrees or a little higher.

Such extreme heat and humidity mean thunderstorms can develop explosively. But there won't be much in the way of triggers to set them off on Friday. A cap of warm air will largely prevent clouds from billowing upward, so that will make it hard for storms to form

It's possible that clouds could break through the cap in a few spots in the late afternoon and evening, so a few strong storms could fire up toward the end of the day. Most spots won't get a storm, but the few places that do could get strong gusty winds and heavy downpours.

Saturday looks downright ugly.  First of all, we will have (hopefully!) survived a very hot, humid Friday night. Then the temperature will once again get up to 90 or so Saturday afternoon, with heat indexes well into the 90s.

A cold front will be approaching from the northwest on Saturday meaning we have a good shot of some strong or severe thunderstorms in the afternoon and evening We'll have to keep an eye on that, because it could get nasty.

The good news is that cold front is the start of a weather pattern change that will gradually drop temperatures to comfortable levels during the first half of next week.