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Old 05-27-2008, 11:44 AM   #1
CanisLupusArctos
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Default Severe Weather Threat - Tues May 27

NOAA's Storm Prediction Center in Norman OK has issued a Severe Thunderstorm Watch for the southern portion of the Lakes Region, along with southern New England and the mid-Atlantic states for this afternoon. Warning text follows my post.

This is our first severe weather threat of the year, in what has been a record year (so far) for severe weather nationwide. As I stated in another weather thread and also in comments on the Winnipesaukee WeatherCenter website, we are in a weather pattern that continues to throw cold air down from Canada. When it interacts with the early summer weather, it lifts it. This action creates strong updrafts, turbulence aloft, and condensation as the cold and warm mix. Put it all together and you've got what we call "Good dynamics" for severe thunderstorms, which sometimes give birth to tornadoes (but not always.) The only reason we have not been getting the severe weather that has been making headlines across the nation this month has been the fact that summertime air has been late reaching us... we are "the tailpipe of the nation" and weather usually gets to us last.

Well... here we are: The warm air has finally reached us, and yet another cold front is on its way, scheduled to cross the area tonight and turn tomorrow's weather back towards autumn.

This is a good time to review some definitions.

A SEVERE thunderstorm is one that has wind and/or hail that is capable of producing damage. Every severe thunderstorm has the capability to produce a tornado. Sometimes they produce other phenomena that are confused with tornadoes, such as microbursts. That's when the rain column gets so intense it literally drags air down from the cloud and when that air hits the ground it has the same effect as a stomping foot. Severe thunderstorms are also known for causing damage with basic everyday straight winds, usually along the "gust front" at the leading edge of the storm.

A Severe Thunderstorm Watch is issued by the Storm Prediction Center in Oklahoma, and may include several states as a general area where the storms will be most likely. Not everyone in the watch area gets them, and a few storms sometimes stray outside the watch area. A tornado is possible but not likely.

A Tornado Watch is the same thing, except the SPC sees a good likelihood that some of the severe thunderstorms will produce tornadoes. Once again, the storms are very localized, so it's impossible to determine which neighborhoods will get them and which ones won't. A watch means you could be one of them, so don't be caught off-guard. Monitor the weather via media and/or by watching the sky, and be ready.

A watch may be upgraded to a warning by the local National Weather Service office (ours is in Gray, Maine.) Warnings are issued for specific counties or sections of counties and their text usually explains where the storm is and what track it's taking. A warning means you should take action to protect yourself if you are in the warning area. Normally you will have a few minutes at best.

A note on lightning... when you hear thunder, you are within striking distance. The most dangerous part of the storm is up to 20 miles in front of it, but many high school sports leagues forbid the restarting of any lightning-delayed game until thunder has been absent for 20-30 minutes.

...Today's watch text...


URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 378
NWS STORM PREDICTION CENTER NORMAN OK
1225 PM EDT TUE MAY 27 2008

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

MUCH OF CONNECTICUT
MUCH OF MASSACHUSETTS
PARTS OF SOUTHERN MAINE
PARTS OF SOUTHERN NEW HAMPSHIRE
NORTHERN NEW JERSEY
PARTS OF SOUTHEASTERN NEW YORK
PARTS OF NORTHEASTERN PENNSYLVANIA
PARTS OF RHODE ISLAND
COASTAL WATERS

EFFECTIVE THIS TUESDAY AFTERNOON AND EVENING FROM 1225 PM UNTIL
800 PM EDT.

HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 70
STATUTE MILES NORTH AND SOUTH OF A LINE FROM 40 MILES EAST OF
PORTSMOUTH NEW HAMPSHIRE TO 25 MILES SOUTH SOUTHWEST OF
WILKESBARRE PENNSYLVANIA. FOR A COMPLETE DEPICTION OF THE WATCH
SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU8).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

DISCUSSION...THUNDERSTORMS WILL INCREASE IN NUMBER AND INTENSITY
AHEAD OF STRONG COLD FRONT NOW ACROSS NRN NEW ENGLAND WSWWD INTO
NWRN PA. WITH MLCAPES TO 1000 J/KG AND 40-50 KT OF UNIDIRECTIONAL
FLOW...DAMAGING WINDS WILL BE PRIMARY THREAT WITH FAST MOVING LINES
SEGMENTS.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 400. MEAN STORM
MOTION VECTOR 28035.


...HALES
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Old 05-27-2008, 12:00 PM   #2
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Default Severe Weather -- Building as I write this...

Hi Canis,

As I write this at my office window in Manchester, the c. nimbus clouds are building rapidly. My office faces west and my seat is at the window -- this is great for watching storms as I have a 180 degree sweeping view from the south to west to north.

It is quite dark toward Amherst/Nashua and a big CN is building over Goffstown. It is mesmerizing! I don't see much toward Concord yet....

GB
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Old 05-27-2008, 12:11 PM   #3
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Default

Yup!! I can see the Goffstown cell on the radar loop. It literally just popped from out of nowhere in the last frame.

That's currently the northernmost cell in a new and rapidly developing line that's just entering Massachusetts now from the NW corner of the state. Looks like this nasty little line is going to "do" Massachusetts over the next 3 hours or so. Wouldn't be surprised at all if some of these storms create headlines on tonight's local newscasts.

In the time it took me to write this (3 minutes?) the radar loop has just updated to show the line has suddenly grown and now extends from around Portsmouth all the way to northwestern New Jersey. These things are popping out of nowhere. It's gonna be an interesting afternoon....

Enjoy that view of the storms!
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Old 05-27-2008, 02:37 PM   #4
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Default Stand Down...

Severe Thunderstorm Watch has been cancelled for the Lakes Region and most of southern New Hampshire. It remains in effect for Massachusetts and southern New England.

The line of storms whose development was witnessed by gravy boat (see above) ended up being the primary line. It moved across southeastern New Hampshire and southern New England and now the line of storms reaches from around Gloucester MA to near NYC and westward in to Pennsylvania.

Colder air is now filtering into Northern New England which is stabilizing the atmosphere.

Tonight will be unseasonably cold. Currently there are frost advisories in effect for much of Vermont and upstate New York. I wouldn't be surprised to see the same issued for parts of this area later today. The immediate shores of ol' Winni (and other lakes) won't get below freezing thanks to a water temperature in the low 50s. I think the water will be back into the 40s again by morning.
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