A new diary has been published. Click here.
The Storm Prediction Center doubled-down on yesterday's forecast of a moderate risk for severe weather today by expanding the moderate risk zone to include parts of the I-95 corridor. Thunderstorms will rapidly begin firing up over the Ohio Valley this afternoon, and the storms will spread east, engulfing most of the risk area by 2-5PM EDT.
Here's the threat zone today. The red MDT is a moderate risk for severe storms. The yellow SLGT is a slight risk for severe storms. The green TSTM (thunderstorm) means that there is a general risk for non-severe thunderstorms.
Here's the damaging wind outlook today. The percentage means there's xx% risk of damaging winds (60+ MPH) within 25 miles of any point within the shaded area. The black hatching means that there's a risk of significant winds over hurricane force (75+ MPH). 15% warrants concern, so a black-hatched 45% is the reason why today's weather is so concerning.
Here's the tornado outlook for today. The percentage means there's xx% risk of tornadoes within 25 miles of any point within the shaded area. 2% is concerning, so the band of 5% is where there's an enhanced possibility of tornadoes today.
Here's the hail outlook. Same with the previous two...the percentage means there's a xx% risk of hail within 25 miles of any point within the shaded area.
Jump the fold.
Here's the latest Public Severe Weather Outlook from the SPC:
PUBLIC SEVERE WEATHER OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1138 AM CDT THU JUL 26 2012
...SEVERE THUNDERSTORMS INCLUDING WIDESPREAD DAMAGING WINDS EXPECTED OVER PARTS OF THE OHIO VALLEY TO INTERIOR SOUTHERN NEW ENGLAND THIS AFTERNOON INTO EARLY THIS EVENING...
THE NWS STORM PREDICTION CENTER IN NORMAN OK IS FORECASTING THE DEVELOPMENT OF WIDESPREAD DAMAGING WINDS OVER PARTS OF THE OHIO VALLEY TO INTERIOR SOUTHERN NEW ENGLAND THIS AFTERNOON INTO EARLY THIS EVENING.
THE AREAS MOST LIKELY TO EXPERIENCE THIS ACTIVITY INCLUDE
CONNECTICUT
NORTHERN DELAWARE
SOUTHEASTERN INDIANA
A SMALL PART OF NORTHERN KENTUCKY
SOUTHWESTERN MASSACHUSETTS
NORTHERN MARYLAND
NORTHERN...CENTRAL...AND WESTERN NEW JERSEY
SOUTHEASTERN NEW YORK
CENTRAL AND SOUTHERN OHIO
MUCH OF PENNSYLVANIA
NORTHERN WEST VIRGINIA
ELSEWHERE...SEVERE STORMS ARE ALSO POSSIBLE FROM OKLAHOMA TO THE MID ATLANTIC REGION...AND ACROSS WISCONSIN.
SURFACE LOW PRESSURE WILL TRACK EAST-NORTHEASTWARD FROM THE LOWER GREAT LAKES REGION INTO THE NORTHEAST...WHILE A COLD FRONT TRAILS SOUTHWESTWARD FROM THE LOW TO THE SOUTHERN PLAINS. HOT AND HUMID CONDITIONS AHEAD OF THE FRONT WILL ALLOW NUMEROUS CLUSTERS AND BANDS OF THUNDERSTORMS TO ERUPT BY MID AFTERNOON FROM INTERIOR SOUTHERN NEW ENGLAND SOUTHWESTWARD TO THE OHIO VALLEY AND FARTHER SOUTHWEST INTO THE SOUTHERN PLAINS. STORMS ARE EXPECTED TO PERSIST INTO THE EVENING HOURS.
IN ASSOCIATION WITH AN UPPER-LEVEL STORM SYSTEM...THE STRONGEST WINDS ALOFT WILL BE FOUND FROM INDIANA AND OHIO ACROSS PENNSYLVANIA...SOUTHERN NEW YORK...AND INTO SOUTHWESTERN MASSACHUSETTS AND CONNECTICUT. A MODERATE RISK AREA COVERS THESE REGIONS...WHERE WIDESPREAD DAMAGING WINDS ARE EXPECTED. A THREAT FOR SIGNIFICANTLY SEVERE WINDS WILL ALSO EXIST. ADDITIONALLY...ONE OR TWO TORNADOES WILL BE POSSIBLE THIS AFTERNOON AND EVENING ACROSS PARTS OF SOUTHERN NEW YORK AND NORTHERN PENNSYLVANIA INTO SOUTHWESTERN MASSACHUSETTS...CONNECTICUT...AND NORTHERN NEW JERSEY.
SOME OF THE LARGER CITIES WITHIN THE MODERATE RISK AREA THAT WILL HAVE THE POTENTIAL TO BE IMPACTED BY THE SEVERE THUNDERSTORMS WITH WIDESPREAD DAMAGING WINDS INCLUDE CINCINNATI AND COLUMBUS IN OHIO...PHILADELPHIA AND PITTSBURGH IN PENNSYLVANIA...AS WELL AS NEW YORK CITY.
STATE AND LOCAL EMERGENCY MANAGERS ARE MONITORING THIS DEVELOPING SITUATION. THOSE IN THE THREATENED AREA ARE URGED TO REVIEW SEVERE mWEATHER SAFETY RULES AND TO LISTEN TO RADIO...TELEVISION...AND NOAA WEATHER RADIO FOR POSSIBLE WATCHES...WARNINGS...AND STATEMENTS LATER TODAY.
..COHEN.. 07/26/2012
Dewpoints are in the 70s across the Mid-Atlantic and Ohio Valley, with surface temperatures quickly climbing up into the mid- to upper-90s. This mix of high moisture and high heat creates a very unstable airmass, which we can measure by using CAPE, or Convective Available Potential Energy. CAPE is like atmospheric fuel thunderstorms use to feed their updrafts -- the higher the CAPE, the stronger the updrafts, and the stronger the storm is.
The opposite of CAPE is CIN -- convective inhibition. If you've ever heard of a "cap" or a "capping inversion," that's what CIN is. It acts like an atmospheric lid that prevents updrafts, and subsequently thunderstorms, from developing. The latest SPC mesoanalysis shows zero CIN and CAPE of 3000-4000+ j/kg over the Ohio Valley, so that's likely where the thunderstorms are going to initiate and thrive.
One of the composite indicies available on the SPC's website is called the "derecho composite." This index takes into account those atmospheric conditions that allow derechos to develop and thrive (like wind shear, downdraft processes, and CAPE). A significant number is in the low single digits (something like 2 or 3, I think), and the composite is up in the double digits (10 and 12) in the moderate risk area where thunderstorms are expected to develop.
The line(s) of thunderstorms will begin to move east through the evening and approach the rest of the slight and moderate risk zone. Where the thunderstorms develop, and how they develop (individual or lines) will dictate who gets hit and who gets nothing.
(Update 127PM EDT) Large severe t'storm watch issued for the counties highlighted in blue. Hail 2.00" in diameter (larger than golf balls), 80+ MPH winds, very heavy rain, and frequent lightning are possible.
(Update 214PM EDT) Tornado watch in effect for the counties highlighted in red. Tornadoes, 2.00" hail, and thunderstorm winds of 80+ MPH are possible within the watch area.
I will try to keep a liveblog going here on DKos when things get going and start threatening major cities. In the meantime, you can "like" me on Facebook and follow me on Twitter for more frequent updates.
Keep a very close watch on the weather today if you live anywhere from Indiana to Rhode Island.
Severe weather safety tips from Ready.gov
National Weather Service Main Page
National Weather Service -- Indianapolis, IN
National Weather Service -- Wilmington, OH
National Weather Service -- Cleveland OH
National Weather Service -- Pittsburgh PA
National Weather Service -- State College PA
National Weather Service -- Baltimore/Washington DC
National Weather Service -- New York City
National Weather Service -- Albany NY
National Weather Service -- Boston MA
National Weather Service -- Burlington VT
National Weather Service -- Portland ME
Storm Prediction Center Main Page
Storm Prediction Center -- Current Severe Weather Watches
Storm Prediction Center -- Convective (Severe Weather) Outlooks
Storm Prediction Center -- Mesoscale Discussions
Storm Prediction Center -- Storm Reports
Storm Prediction Center -- Mesoscale Analysis Pages
Wunderground's Detailed Radar (click the + nearest to you to see your local radar)
NOAA Weather Models
TwisterData.com's excellent GFS/NAM/RAP model website.
iMapWeather Radio App for iPhone/iPod Touch (costs $9.99 but well worth it)
10:47 AM PT: Tornado warning for Venango and Mercer Counties in NW Pennsylvania. Very nasty rotation on radar approaching Franklin and vicinity.
11:03 AM PT: The NWS in State College, PA is issuing severe thunderstorm warnings 100 miles ahead of the storms.
12:10 PM PT: The State College, PA radar failed around 200PM EDT. We're now blind in Central PA. As my friend over at TerpWeather just said, the storms just got much more dangerous now that we can't see the winds inside of them.