June 29: Flash Flood Watch - Severe Wx Possible

[CanisLupusArctos]

The National Weather Service in Gray Maine (http://www.nws.noaa.gov/er/gyx) issued a Flash Flood Watch for this afternoon and evening for central and northern New Hampshire. This is for anticipated thunderstorms with heavy rain that could drop 1 to 3 inches of rain in addition to the 1"+ we had in the last 24 hours.

Forecasters at Gray ME and also at the Storm Prediction Center in Norman OK (http://www.spc.noaa.gov) are monitoring for the possibility of a severe weather outbreak today. Right now the cloud cover is preventing the heating necessary for the storms to form. If the cloud cover breaks and allows sun to warm the low-level air, it will rise into the much cooler air aloft and form thunderstorms. Some of the storms would be capable of producing large destructive hail, damaging straight-line winds, and conditions are right for isolated tornadoes today.

It all depends on whether or not the sky clears to allow the sun to heat things up near the ground.

SPC has outlined much of New England south and west of the Maine border in a slight risk for severe weather today and stated they may need to upgrade to moderate if the sky clears soon enough. Remember, theirs is a sensitive scale on which "slight" is worthy of attention, "moderate" is a dangerous situation, and "high" is only seen a handful of times each year, usually on the Plains.

In any case, plenty of non-severe thunderstorms (lacking damaging hail or damaging wind) are expected to develop and bring heavy downpours to many communities late this afternoon and evening.

[Island Girl]

When will this start at vthe southern part of the lake?

[CanisLupusArctos]

The watch is in effect from 4 pm through late tonight. Other than that, it's hard to tell because we're dealing with summer thunderstorms rather than wintertime's giant blobs of precip that can take up several states.

They won't even hit every town, although many will get one. Those places that do get one will have a chance of flash-flooding... when you go from bare ground to a foot of water within a matter of minutes.

The general area of thunderstorms is moving from west to east. Radar shows some moderate showers over Vermont that are not growing. The main activity is a line of severe thunderstorms from southern Ontario to eastern Ohio... and those are moving east, growing with time.

If we don't get enough sun/heat before they get here, they will weaken as they approach our area but we would likely still get their rainfall and some thunder.

SPC and NWS-Gray are still nervously watching to see how much sun & heat we get this afternoon. All the other ingredients for severe thunderstorms are already in place here. There is currently a severe thunderstorm watch for far western NY state and only the minute-by-minute conditions will determine whether or not it needs to be extended eastward, and if so, how far.

In the meantime a flash flood watch implies the potential for sudden, localized floods. It is different from a general (area-wide) flood watch, which is issued for heavy rainstorms of greater coverage and longer duration.

[CanisLupusArctos]

While a severe thunderstorm watch has not been issued, there is one in effect just to our west and south, and the storms are already developing in our area outside the defined watch area.

A severe thunderstorm warning has just been issued for the Concord area including Loudon.

Some of the storms in southern NH are moving from SW to NE at 45-55 mph (storm forward speed, not wind speed) and have already produced widespread damage across Worcester County MA.

Warning text from the NWS follows. Warnings are also in effect for other parts of southern NH.

SEVERE THUNDERSTORM WARNING
NHC013-292145-
/O.NEW.KGYX.SV.W.0090.080629T2101Z-080629T2145Z/

BULLETIN - EAS ACTIVATION REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE GRAY ME
501 PM EDT SUN JUN 29 2008

THE NATIONAL WEATHER SERVICE IN GRAY MAINE HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
CENTRAL MERRIMACK COUNTY IN CENTRAL NEW HAMPSHIRE...

* UNTIL 545 PM EDT

* AT 459 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
SEVERE THUNDERSTORM CAPABLE OF PRODUCING NICKEL SIZE HAIL...AND
DAMAGING WINDS IN EXCESS OF 60 MPH. THIS STORM WAS LOCATED NEAR
HOPKINTON AND HENNIKER...AND MOVING EAST AT 24 MPH.

* SOME LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO
HOPKINTON...CONCORD...CANTERBURY AND LOUDON.

THIS STORM HAS A HISTORY OF PRODUCING DESTRUCTIVE WINDS AND LARGE
HAIL. SEEK SHELTER NOW INSIDE A STURDY STRUCTURE AND STAY AWAY FROM
WINDOWS!

[gtxrider]

Looks like it is now raining in Loudon and from what I see on the Weirs Cam rain coming down there as well!

HEED THE WARNINGS!

[CanisLupusArctos]

Race fans and other weekenders... (if you know someone who is on the road, call them on cell phone to pass this along)...

Check your routes if you are heading south.
These storms have created numerous reports of trees across roads in Worcester Co. Massachusetts and also in southwestern NH from the Keene area to the Nashua area.

One report relayed to the NWS Taunton MA states flooding at intersection of Rts. 3 and 495 with 6 cars out of service as a result.

Lowell MA... numerous trees and wires down

Dracut MA... trees and wires across intersection

Once again, if you know someone who is on the road and headed south, forward this info to them.

Remember the motto.... "Turn around Don't Drown." Do not drive into areas where water covers the road... As 6 drivers at the intersection of 495/3 just learned.

[nj2nh]

Just as we were leaving to head back to NJ, we had the mother of all rainstorms over Alton Bay. My goodness, I had never seen it rain like that and there were some doozies just this week. The drops were so large that I thought it was hail, but when it didn't "bounce," I knew it wasn't.

Fortunately, it only lasted about 10 minutes, but it was a wicked one. Funny thing, though. I spoke with someone who lives in Alton not long after. It hadn't rained at his place at all!

nj2nh