Widespread Severe Weather Event Today, Millions Could Be Impacted.

Today's Weather Chatter will focus on the Severe Weather Event that is currently unfolding in the Central Great Lakes region. This target area will shift throughout the day to include a very large portion of the Ohio Valley up to the Northeast.

As we briefly spoke yesterday, there is the potential for a large area to experience destructive wind gusts in excess of 70 mph, enough to bring down trees, damage structures and cause power outages that could last for days. Major metropolitan areas, including Cleveland, Pittsburgh, Philadelphia, New York City, Albany and Hartford, are among those included in the enhanced risk zone for damaging winds through tonight. But it does not stop there. An even larger area will still be at risk for severe weather, stretching from the mid-Mississippi Valley near St. Louis and Paducah all the way east into the mid-Atlantic and north to New England. This is a very LARGE and POPULATED area that is going to be impacted.



In addition to the threat of powerful wind gusts, the setup appears ripe for a few storms to spawn tornadoes. This will especially be the case near the leading edge of a push of warm, humid air from northern Pennsylvania and southern New York into southern New England at night.

Last night the SPC upgraded a portion of the Slight Risk area to Moderate. This is due to, in part that an area of strong instability developed with MlCape readings rising in the 3000 J/KG range in the Warm Sector. Storms were developing near the Frontal Triple Point during the night. Here is a quick refresher for the definition of Triple Point.
There are three basic frontal types you will see drawn on surface maps and they are the warm front, cold front and occluded front. An occluded front is when a cold front overtakes a warm front. The warm front is generally found to the right of the low pressure center. It is where the warm sector is wrapping around the low pressure system. The cold front is typically on the left side wrapping colder air around the low pressure system. Since the cold front typically moves faster than the warm front, where the cold front lifts the warm front will result in an occluded front. The triple point is where the occluded front, cold front and warm front all intersect. This intersection point will have a great amount of lifting. If enough moisture is wrapping in from the warm sector than big rains and storms can fire along the triple point and along the fronts and wrap into the low pressure. There is a great amount of wind shear also near the triple point and fronts.

Severe weather will often fire up ahead of the cold front, along the warm front and near the triple point where shear is enhanced. Here is an example of a Triple Point.



Today's SPC Convective Outlook



DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0102 AM CDT THU JUL 26 2012

VALID 261200Z - 271200Z

...THERE IS A MDT RISK OF SVR TSTMS FROM A PORTION OF
IND...OH...PA...SRN NY INTO SRN NEW ENGLAND...

...THERE IS A SLGT RISK OF SVR TSTMS FROM A PORTION OF THE SRN
PLAINS...GREAT LAKES...OH VALLEY...NERN STATES AND MID ATLANTIC...

...SYNOPSIS...

SYNOPTIC UPPER TROUGH WILL UNDERGO GRADUAL AMPLIFICATION THURSDAY
OVER THE GREAT LAKES...OH VALLEY AND NERN STATES. EMBEDDED WITHIN
THE LARGE SCALE TROUGH IS A VORT MAX OVER SRN MANITOBA THAT WILL
DROP SWD THROUGH MN AND WI. ANOTHER IMPULSE OVER THE MID-UPPER MS
VALLEY WILL CONTINUE THROUGH THE OH VALLEY AND SRN PORTIONS OF THE
GREAT LAKES...REACHING THE NERN STATES THURSDAY NIGHT. FARTHER WEST
THE RIDGE WILL BUILD OVER THE NRN ROCKY MOUNTAIN REGION WHILE AN
UPPER TROUGH LINGERS OFF THE PACIFIC NW COAST.

AT THE SFC A COLD FRONT CURRENTLY EXTENDS FROM A SFC LOW IN LOWER MI
SWWD THROUGH THE MID MS VALLEY AND CNTRL PLAINS. THIS BOUNDARY WILL
ADVANCE SEWD WHILE WARM FRONT LIFTS NWD INTO SRN NEW ENGLAND.

...OH VALLEY THROUGH NERN STATES...

CORRIDOR OF MODERATE TO STRONG WSWLY DEEP LAYER FLOW WILL PERSIST
WITHIN BASE OF AMPLIFYING UPPER TROUGH WITH 40-50 KT BETWEEN 850 AND
700 MB FROM THE OH VALLEY INTO THE NERN STATES. THE SWLY LLJ WILL
CONTRIBUTE TO NEWD DESTABILIZATION AS RICHER BOUNDARY LAYER MOISTURE
/UPPER 60S DEWPOINTS/ ADVECTS NEWD IN WAKE OF ADVANCING WARM FRONT.
A FEW STORMS WILL LIKELY BE ONGOING NORTH OF THE WARM FRONT OVER A
PORTION OF NY INTO NEW ENGLAND. OTHER MORE ORGANIZED STORMS WITH A
THREAT FOR DAMAGING WIND MAY BE IN PROGRESS OVER SWRN NY OR NRN PA.
THIS ACTIVITY MAY CONTINUE TO POSE A THREAT OF DAMAGING WIND AS
DIABATIC WARMING COMMENCES AND LOW LEVEL LAPSE RATES STEEPEN. OTHER
STORMS WILL LIKELY DEVELOP WITHIN LOW LEVEL CONFLUENT FLOW REGIME
AHEAD OF THE COLD FRONT AS THE CAP WEAKENS. STRONG INSTABILITY WITH
2000-3000 J/KG MLCAPE...STEEP LOW LEVEL LAPSE RATES AND 30-50 KT
DEEP LAYER FLOW WILL PROMOTE A THREAT OF WIDESPREAD WIND DAMAGE AS
STORMS EVOLVE INTO LINES AND CLUSTERS. A FEW STORMS MAY ALSO DEVELOP
SUPERCELL STRUCTURES WITH POTENTIAL FOR LARGE HAIL AND PERHAPS A
TORNADO OR TWO...ESPECIALLY OVER A PART OF THE NERN STATES WHERE
STRONGER EFFECTIVE SHEAR WILL EXIST NEAR AND JUST S OF THE WARM
FRONT.


...OK THROUGH MID MS VALLEY REGION...

OTHER STORMS WILL REDEVELOP AND INTENSIFY ALONG SWRN EXTENSION OF
FRONT AND PRE-FRONTAL OUTFLOW BOUNDARIES FROM THE MID MS VALLEY INTO
NRN PARTS OF THE SRN PLAINS. MOST OF THIS REGION WILL REMAIN SOUTH
OF THE STRONGER FLOW ALOFT ASSOCIATED WITH AMPLIFYING UPPER TROUGH.
HOWEVER...THE THERMODYNAMIC ENVIRONMENT WILL FAVOR A THREAT OF
ISOLATED DAMAGING WIND AND DOWNBURSTS WITH MULTICELL CONVECTION AS
LOW LEVEL LAPSE RATES STEEPEN ALONG THERMAL AXIS.

...UPPER GREAT LAKES AREA...

RESIDUAL MOISTURE IN POST FRONTAL REGIME WITH DEWPOINTS IN THE LOW
60S ALONG WITH DIABATIC WARMING WILL PROMOTE AN AXIS OF MODEST
/1000-1500 J/KG/ MLCAPE OVER THE UPPER GREAT LAKES. DEEP FORCING FOR
ASCENT IN ASSOCIATION WITH THE APPROACHING SHORTWAVE TROUGH WILL
PROMOTE THE DEVELOPMENT OF STORMS AS THE BOUNDARY LAYER
DESTABILIZES. STORMS WILL EXIST WITHIN A UNIDIRECTIONAL WLY FLOW
REGIME WITH 30-35 KT EFFECTIVE SHEAR. A FEW STORMS MAY BECOME
CAPABLE OF PRODUCING ISOLATED DAMAGING WIND AND HAIL THROUGH EARLY
EVENING.

Now, lets look at the Craven's Significant Severe Parameter. This is created using a combination of the 100mb MLCAPE and 0-6km magnitude of the vector difference, or also known as the "deep layer shear" This model accounts for the compensation between instability and shear magnitude and gets the information from a database of about 60,000 soundings, the majority of significant severe events that includes 2+ inch hail, 65+ knot winds, and F2+ tornadoes occur which this product is excellent at detecting.



As you can see throughout the day the parameter fro severe weather increases greatly. The big white bulls-eye is indicating a 80 to 100 percent chance of severe weather throughout the Major Metropolitan Areas of the Northeast.

This event will be ever changing throughout the day. I will check in on the short range modeling and post any changes. This will be a great event to watch unfold and a good opportunity to learn how the Derencho events are created and unfold.

Thanks for the info E. Great blog!

Another great blog e!!! Thanks for putting together an easy to understand analysis.

Thank you Ladies

TROPICAL WAVES...

A 1012 MB LOW IS SW OF THE CAPE VERDE ISLANDS NEAR 13N29W MOVING
W NEAR 20 KT. LOW IS EMBEDDED WITHIN AN AREA OF DEEP LAYER
MOISTURE AS DEPICTED ON TOTAL PRECIPITABLE WATER IMAGERY.
ISOLATED SHOWERS ARE WITHIN 90 NM OF THE LOW OVER THE NE
SEMICIRCLE.

The tropical wave is looking impressive this morning.



[youtube][/youtube]

One might wounder how things are going to unfold today. Here is the "Best Guess" at the moment.

The storm over the Great Lakes will continue it's Easterly track towards the major metro areas in the Northeast.
The frontal boundary will become almost stationary later tonight. When this happens, ripples or waves of Low Pressure will develop and move across this boundary line.

Now, as the warm front approaches the New York area this morning from the West it will have a few storms that will come with it. This will move off to the Northeast. Now go back and do you remember the storm across the Great Lakes we have been talking about? this feature, which is an upper trough, will begin to deepen this afternoon as it moves to the East. The area where the warm front had already moved through will begin to rapidly destabilize with the MLCAPE Values increasing to over 3000 J/KG and the Bulk Shear will increase to 40 or 50 Kts. As lines and clusters of Storms develop, they will turn Severe. If these storms merge and can hold together, a Derecho Line could form. Either way, the Severe Storms will develop. At the moment, I see nothing that stands out that would cause this to be a bust.

Quite a few people in southern Ontario got an extra-early wakeup call from Mother Nature this morning. But a few night owls were still awake, like the storm chaser who captured this incredible lightning shot.




Photo: Spencer Sills, Parkhill, ON

A Differential Heating Boundary is what is setting up in the graphic below. Pennsylvania has a really good chance of seeing winds near or in excess of 80 to 90 Mph given the high cape values, low level lapse rates, and shear. If the storms get organized in the next several hours this will likely occur. Peeps in that area definitely need to watch this.



A Differential Heating Boundary is a small scale "cold-frontal" type boundary that results from unequal surface heating. To understand how this comes about, consider this example. This morning with varying cloud coverage between Pittsburgh and Philadelphia.. Pittsburgh remains under cloud cover all morning, and by noon has a temperature of 73 degrees, while Philadelphia has sunshine during the morning and a temperature at noon of 85 degrees. This temperature (and resulting pressure) difference can result in the development of a small scale line of convergence, similar to a front. This can be a triggering mechanism for thunderstorms during the warm season. This usually has the potential of creating some storms capable of creating significant downdrafts.

It's beginning.



Convection is building in the Ohio and Western Pennsylvania areas and should begin to pop in the next couple of hours. My guess is that the SPC will start to discuss this in a MD shortly.

Great explanation on the Differential Heating Boundary e!!!

The Governor of New York is warning residents.



http://www.nyalert.gov/Public/News/AllHazPRView.aspx?notID=3674081&refer=HOME&source=RSS&messageID=AghxO4T6A

Inverted V Sounding in PIT Sounding this morning. Definite classic profile of a damaging wind event in Pittsburgh.

Strong-Extreme Instability with 40-50 knots of shear will give way to severe storms this afternoon across OH Valley/Northeast

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 524
NWS STORM PREDICTION CENTER NORMAN OK
120 PM EDT THU JUL 26 2012

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

EASTERN INDIANA
NORTHEAST KENTUCKY
WESTERN MARYLAND
SOUTHWEST NEW YORK
OHIO
WESTERN AND CENTRAL PENNSYLVANIA
NORTHERN AND CENTRAL WEST VIRGINIA
LAKE ERIE

EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 120 PM UNTIL
1000 PM EDT.

HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 80
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 105
STATUTE MILES NORTH AND SOUTH OF A LINE FROM 40 MILES WEST OF
DAYTON OHIO TO 20 MILES EAST OF WILLIAMSPORT PENNSYLVANIA. FOR A
COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE
UPDATE (WOUS64 KWNS WOU4).

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...SEVERAL CLUSTERS OF INTENSE AND FAST-MOVING
THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS AFTERNOON ACROSS MUCH OF
THE UPPER OH VALLEY...SPREADING EASTWARD INTO PARTS OF NY/PA. HIGH
CAPE VALUES COUPLED WITH FAST FLOW ALOFT WILL PROMOTE THE RISK OF
RATHER WIDESPREAD POTENTIAL FOR DAMAGING WINDS AND SOME HAIL. AN
ISOLATED TORNADO OR TWO IS ALSO POSSIBLE ALONG A RETREATING WARM
FRONT OVER PARTS OF PA/NY LATER THIS AFTERNOON.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 70
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 550. MEAN STORM
MOTION VECTOR 27040.

Great work, e; appreciate the constant updates.

Current MD's

...A TORNADO WARNING REMAINS IN EFFECT UNTIL 215 PM EDT FOR VENANGO
AND MERCER COUNTIES FOR THIS CELL...

Right on cue.

This line of storms will eventually have the capacity of producing Winds IN EXCESS OF 70 MPH GUSTS POSSIBLY NEAR 90 MPH GUSTS. Serious situation.

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 525
NWS STORM PREDICTION CENTER NORMAN OK
210 PM EDT THU JUL 26 2012

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

WESTERN CONNECTICUT
WESTERN MASSACHUSETTS
CENTRAL AND EASTERN NEW YORK
NORTHEAST PENNSYLVANIA
SOUTHERN VERMONT

EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 210 PM UNTIL
900 PM EDT.

TORNADOES...HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 80 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 65 STATUTE
MILES NORTH AND SOUTH OF A LINE FROM 15 MILES SOUTH SOUTHWEST OF
ELMIRA NEW YORK TO 20 MILES NORTHEAST OF PITTSFIELD
MASSACHUSETTS. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU5).

REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND 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.

OTHER WATCH INFORMATION...CONTINUE...WW 524...

DISCUSSION...INTENSE THUNDERSTORMS ARE EXPECTED TO DEVELOP ACROSS
THE WATCH AREA THIS AFTERNOON. ONE CLUSTER OF ONGOING STORMS OVER
WESTERN NY/PA WILL MOVE RAPIDLY EASTWARD WITH A THREAT OF DAMAGING
WINDS AND HAIL. OTHER MORE DISCRETE STORMS MAY FORM ON/NORTH OF
RETREATING WARM FRONT. THESE STORMS WILL POTENTIALLY BECOME
SUPERCELLULAR WITH A RISK OF LARGE HAIL...DAMAGING WINDS...AND
ISOLATED TORNADOES.

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 526
NWS STORM PREDICTION CENTER NORMAN OK
150 PM CDT THU JUL 26 2012

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

SOUTHERN ILLINOIS
SOUTHERN INDIANA
WESTERN AND CENTRAL KENTUCKY
SOUTHERN MISSOURI

EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 150 PM UNTIL
900 PM CDT.

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 75
STATUTE MILES NORTH AND SOUTH OF A LINE FROM 35 MILES NORTH
NORTHWEST OF WEST PLAINS MISSOURI TO 55 MILES NORTHEAST OF
LOUISVILLE KENTUCKY. FOR A COMPLETE DEPICTION OF THE WATCH SEE
THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU6).

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.

OTHER WATCH INFORMATION...CONTINUE...WW 524...WW 525...

DISCUSSION...SCATTERED THUNDERSTORMS ARE EXPECTED TO RAPIDLY
INTENSIFY ACROSS THE WATCH AREA DURING THE NEXT FEW
HOURS...SPREADING EAST-SOUTHEASTWARD THROUGH THE EARLY EVENING.
STRONG INSTABILITY COUPLED WITH SUFFICIENTLY STRONG WESTERLY FLOW
ALOFT WILL PROMOTE A RISK OF LOCALLY DAMAGING WINDS IN THE STRONGER
STORMS.

Here is the 3-Dimensional Cross Section of the potent and severe thunderstorm/tornado warned storms in Western Pennsylvania.

good blog and I love that last picture...layers of shelf clouds around
a thunderstorm with cyclonic vorticity...too cool

The NAM did great with this event... The big pic is the NAM from this morning. The little pic is the live radar for the time of that NAM run. Amazingly good job.

Tornado captured near Horsehead, NY. This is the same one that reportedly hit Elmira, NY

Big ass bow. Can't imagine what the winds are in that mess.

found a live stream from an all news channel out of NYC..

http://abclocal.go.com/wabc/livenow?id=7241659

Now that's a bow. You will see winds in the 90 MPH range with that one. WOW

Nice tornado pic....man e, you are doing a fantastic job posting all of these updates.....on top of all of the info you are providing in the chat room!!!

Sure hope that bow eases back a little bit...or it is going to be bad!!!

Looks like another bow is developing just to the West of NYC. The one to the North of the city is still amazing.

Based on latest instability data, this squall line/derecho event should continue into the big cities from New York City to Boston through evening. Shown here is CAPE, or convective available potential energy. Note the uncapped (in white) and unstable air streaming northeast ahead of the convective line. Should arrive in the next 1-2 hours

Current SPC loop

Wall Cloud ahead of approaching storm in Hazleton, Luzerne County. A tornado warning was issued for this area.



WOW, Near Elmira.



Auto Repair Shop blown over in Freeland



NYC

Those are all very impressive pics, but gotta say, the Elmira one was fascinating!!!

The most recent pass on the tropical wave just west of Africa....



The spin is very evident...



But it has SAL wrapped around it...

Wow San the African Blob has still got some good spin to it. Something to watch for sure over the next several days.

As midnight nears on the East Coast, the forecast of severe storms across the East today panned out quite well. The majority of reports remained to be wind but a few hints of hail were also added in the mix. One tornado report was reported in New York. As the next few days progress certain wind reports may be surveyed and changed into tornado reports.

Although, radar indicates storms slowly weakening across the Mid-Atlantic, storms are still threatening over the Tennessee Valley. More reports certainly aren't out of the question by morning.

Here are a few more pics of today's event.

Storm moving in over Long Island Sound, Crab Meadow Beach in Northport.



Absolutely Gorgeous Super-cell



Shelf cloud in Pt. Pleasant, WV.



This was taken in Marion, IL.



Menacing sky over Tioga, PA.



And I will close out with this beautiful Sunset in Gulf Shores, AL.



Peace.

Beautiful pics e.....I imagine today's pics won't be as nice to look at.......will show some damage from NY and PA.....