UPDATE 12:40 PM, 7/24: Storms may carry damaging wind risk on Tuesday
UPDATE 12:40 PM: The storm cluster that has weakened some but maintained some strong winds in western Ohio is sinking south-southeast and may affect far southwest Virginia west of I-77 this afternoon. Other storms will continue to develop farther south and east, some of which may become severe with locally damaging winds. END UPDATE
UPDATE 10:20 AM: Here is some good news for folks not wanting a derecho today: The current damaging-wind storm line in Indiana is expected to weaken over the next couple of hours hitting rain-cooled air in western Ohio. The bad news: There are other storms in West Virginia that may strengthen and affect parts of Southwest Virginia, some possibly as early as the next couple of hours (in fact, one such cluster is about to enter Craig and Giles counties now), and the storm line in Indiana may kick out an outflow boundary that helps develop strong to severe storms later when it runs into more unstable air than that in western Ohio. Short summary: A long-lived derecho system moving in from the Ohio Valley is NOT likely, but smaller storm clusters and possibly a re-developing squall line later may pose a high-wind risk to at least some parts of Southwest Virginia through the remainder of the day. END UPDATE
UPDATE 8:30 AM, 7/24: Radar this morning shows a series of storm clusters from West Virginia northwestward through the Ohio Valley into Minnesota, generally moving southeastward. The strong line in the Chicago area is perhaps the most eye-catching — that of course is where the June 29 derecho started. The Storm Prediction Center is closely monitoring this area to see if it develops into a more organized bow echo that could produce widespread damaging winds. As the day heats up, severe storms may be possible just about anywhere in the region, though locations west of I-77 have the greatest risk. END UPDATE
The battle lines between the central U.S. heat dome and cooler air out of Canada will shift southward over us on Tuesday. The result is likely to be that a disturbance will ride southeastward over the heat dome toward Southwest Virginia. With strong northwesterly winds aloft, it is possible that one more clusters of storms may develop in the Ohio Valley and move rapidly southeastward, building strength in afternoon heat and 
humidity. So there is a threat of severe storms, with damaging winds as the main threat. That is why we are in a slight risk of severe weather for Tuesday. The “d” word — derecho — has been mentioned by a few online weather outlets, and that word makes folks very nervous after June 29, rightfully so. A derecho is within the realm of possibility Tuesday — though probably not as widespread or powerful as June 29 — but the more likely outcome is a bow echo or squall line that produces some damaging winds but doesn’t meet the longevity requirements of a derecho (6 hours/240 miles of continuously damaging winds, according to different interpretations ) or multiple storm clusters capable of some damaging wind gusts over smaller areas. There may also be storms that develop in Southwest Virginia ahead of anything that might move at us from the northwest — such pop-up storms will have the potential to become severe with damaging winds themselves, and would somewhat reduce instability available for a storm cluster moving in later from the northwest. June 29 became so ballistic largely because of the historic heat (104 at Roanoke) that built up throughout the day remaining “capped” by warm air aloft until it could all be used at once to fuel the bow-echo that developed near Chicago and continued into the Atlantic. The heat is not expected to be nearly as intense (upper 80s-low 90s mostly) nor as bottled up as it was on June 29. That said, there will be plenty of fuel for severe storms, and it’ll basically be a matter of tracking on radar Tuesday how things develop. Damaging winds are possible in storms that develop Tuesday, along with large hail, torrential rain and frequent lightning. So be aware when out and about on Tuesday.
Somewhat cooler air moves in for Wednesday, before the front retreats and brings a surge of hotter air for Thursday, perhaps a brief taste of extreme heat well into the 90s. The overall long-range outlook still suggests most of the extreme heat to stay west of us, with storms developing in humid air most afternoons, occasionally stirred up a little more by passing cold fronts and/or disturbances from the northwest.
July 24, 2012 - 12:15 AM
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Thanks Kevin. After you hit the last one on the head (heard you on NPR the day of the 6/29 and the week after), I hope the Roanoke Times, and other weather outlets will give yours and others warnings out for all to see.
Your weather-prediction average has definitely instilled faith in me to keep up with your blogs and forecasts. However I find it a little disturbing that weather.com isn’t mentioning the potential for what may occur today. At least not yet anyway.
Thanks again for all you do.
NWS-Blacksburg is currently expecting locations west of I-77 to have the best chance of severe weather, but there is this caveat that does mention the “d” word:
IF THE MCS BECOMES MORE ORGANIZED THAN CURRENTLY EXPECTED…WE COULD BE DEALING WITH ANOTHER DERECHO AND A MORE WIDESPREAD DAMAGING WIND EVENT FOR AREAS EAST OF THE ALLEGHANYS AS WELL. AS SUCH…SPC IS HINTING AT A
POTENTIAL MODERATE RISK IF THIS BECOMES EVIDENT LATER IN THE DAY.
And these words from the Storm Prediction Center:
MULTICELL CLUSTERS AND SUPERCELLS ARE EXPECTED WITH A THREAT OF DAMAGING WINDS AND LARGE HAIL. IF STORMS CAN ORGANIZE PERPENDICULAR TO DEEP-LAYER FLOW THEN A MORE WIDESPREAD THREAT OF DAMAGING WINDS WILL EXIST. THIS THREAT WILL BE REASSESSED IN LATER OUTLOOKS.
My mantra for today…NO repeat of June 29…NO repeat of June 29.
What was odd though was what met me when I went outside this morning. To back track, what I found odd about the day of June 29 was the very warm, dry breeze prior to the derecho. When I walked out the door this morning rather than being met with the cooler, moist air I was met with a warm, dry breeze. I know that probably means nothing but I sure will be securing anything that might fly around!
Thanks for keeping us updated Kevin. I will keep checking in throughout the day!
It is more humid than June 29. The trade off there is that (1) it may trigger more storms earlier in the day, which would reduce the instability a larger storm complex could tap but (2) it provides a little more fuel for the daytime heating and atmospheric dynamics to work with.
Well, between here, my Twitter account, and Facebook…I’ll be keeping tapped in to the weather today for sure, watching to see if the complex gains strength, or if the storms ahead of it suck the life from it as it moves toward our area. Regardless, this is another day with plenty of advance notice out there for the people who aren’t completely oblivious to the world…so if we do experience another severe wind event, hopefully folks will be a bit better prepared than last time.
Another contrast to June 29 is that there’s more low level shear around today, which is probably why the SPC Day 1 outlook has most of Virginia under a small (2%) but discrete tornado risk.
Joe, if you ever have a day off, today might be a good time to cash in you raincheck. The big windy has already had many cancellations.
Kevin…can you give us a time frame? I’m seeing reports of VA being affected as early as noon/1:00.
Yea…I can feel that it is more humid but the breeze felt hot and dry.
Re Chris 9:02 comment: Also why there is a mention of supercells today by the SPC. Increases the hail threat.
SPC is expecting storms near Chicago to encounter rain cooled air and weaken as they move across Indiana. That is one advantage of having several storm clusters instead of just one. But it might kick out an outflow boundary that helps develop storms farther south later.
As for timing, the stuff developing in WVa west of Beckley could be here by noon. The multiple-cluster nature of today’s storms makes pinpointing specific times difficult. The earlier in the day we could get storms in, the less heating there will be, and the earlier the air aloft will be “turned over” with cool air brought to the surface, and therefore the less the severe threat would be.
Best-case scenario: Lots of storm clusters with sporadic wind reports, but primarily rainmakers for still-dry ground.
There are some 70-80 mph wind reports and power outages near Chicago. But right now, all that rain in western Ohio/eastern Kentucky may be our “derecho shield” today. Those storms are going to be moving into that rain-cooled air and weakening later today.
We had not had a night where it did not get below 70, in about 10 years………..until June 29, Derecho Day. This morning it happened again, 71. That better not mean…………
Accuweather says a Derecho is happening right now in Indiana and coming our way.
http://www.accuweather.com/en/weather-news/live-storms-with-fierce-winds-aim-for-chicago/68391
I’ll take the shield! I have noticed that NWS has upped our high temp for today to 90, and Thursday and Friday have went up a bit too. And we still have August to go!
Other John..yep, keeping people update on FB today myself. It’s the only way some people get any news!
SPC is NOT calling it a derecho yet. That said, it has produced wind damage over a fairly long area.
SPC also expects it to run into the rain-cooled air in Ohio and weaken.
My bigger concern for our area is not the storm line in Indiana, but stuff developing out ahead of it. The West Virginia cluster may be here before noon, and could strengthen into severe storms with gusty winds.
That is interesting Rick…accuweather’s report that is. Are they jumping the gun calling this a derecho?
Looks to me like some of that WV cluster is weakening a bit on radar.
Storm Prediction Center mesoscale discussion just issued stating storms in Indiana will WEAKEN hitting rain-cooled air in Ohio.
http://www.spc.noaa.gov/products/md/md1563.html
The main severe threat for us isn’t that line, it’s storms developing farther south and east, including current cluster in West Virginia.
I’m thinking the same thing Brandon is…looks like those WV storms aren’t packing much of a punch right now. Sun is gone and clouds have rolled in here. I’m still going to secure any loose objects that might fly away in strong gusts, and still going to be checking in here throughout the day.
Yea…ORD was active…came in at 5am…into a hornets nest…ATC takes their time with morning coffee…and neatly timed teleconferences…gladly it was through quickly..on the wx side…i dont see much early on…spcly east of PSK
Saw a report of 182,000 without power in Chicago area. SPC continued the severe watch on that line because of its momentum, think there could be some severe winds as far south/east as the Ohio River.
Well, Accuweather is sticking to their guns that is was/is a derecho…guess time will tell. From the link Rick posted earlier:
“A derecho moved 277 miles and has produced numerous reports of wind gusts over 58 mph through 9:30 a.m. CDT on Tuesday July 24, 2012. A derecho is defined as a wind damage swath extends more than 240 miles and includes wind gusts of at least 58 mph or greater along most of its length.”
It may have met the technical definition for derecho by now.
There is some chance the rain cooled air to the east may funnel this storm complex more to the west, where it can feed on more unstable air just to th west. This may be where some of the models are focusing on west of I-77. Rick and others further west be on notice.
I hope the storms can hold together well enough coming over the mountains to give us some rain. Looks like we may get a brief downpour or two in the next hour, probably with some gusty winds.
Now 89 with a dewpoint of 72 here in Roanoke.
Sticky.
Reporting Live from Teterboro NJ Airport. I’m here in NJ til 3PMish which is our planned departure time back to VA. Good news is I’m about to have a good lunch at Angelo’s and it’s only 50 minutes flight time back home. Bad news is we may hit some of this stuff as we get airborne. Just checked FAA ATC Command Center updates and it’s already a mess in the midwest especially Chicago & Indianapolis. Knew I should have stayed home in bed.
Back with update after lunch.
What is this storm looking like for the Dublin/Pulaski area?
Looks to me that what’s in SW Ohio now will move more towards Eastern Kentucky and far SW VA. Looking at the 500mb meso page on the SPC, it will bring that area of rain in south central Ohio more towards western VA and if it hits more unstable air (which is in place right now in western VA: CAPE 2500-4000J/KG per mesoanalysis page) it could become stronger, maybe severe, fairly quick unless this current rain and cloudiness moving in reduces the instability. Also noticing some other storms firing again in West Virginia. Looks to me this won’t be another June 29th repeat, but rather a more sporadic wind event. I could be wrong as I’m still an amateur, but just my best guess on what’s going on currently.
The Capital Weather Gang on the Washington Post’s website included this little note:
“Note: despite pronouncements from AccuWeather and The Weather Channel that this convective system is a derecho, it not yet clear it has met derecho criteria.”
This website from Storm Prediction Center suggests 75 mph as the threshhold …not 58 mph … though today’s storm system did have several 70-80 mph reports near Chicago.
http://www.spc.noaa.gov/misc/AbtDerechos/climatologypage.htm
The sky here in Rocky Mount is beginning to look ominous. I know looks can be deceiving, but the atmosphere definitely looks “juicy”.
I’m thinking the same thing, Ben.
Angela: Do you mean the overall storm event, or this morning’s storm cluster? The storms out of WVa have weakened and split and you are in the middle. The overall storm threat for the day is still developing and so it’s not possible to be too specific yet.
I’ve learned via Twitter this AM that the original paper defining “derecho” in 1987 (the term was first used in 1888, but then updated for the modern era) requires at least 3 damage reports/wind measurements of 75 mph separated by 64 nautical miles. Using that criteria, it’s doubtful this mornings system in IL/IN would qualify. Much arguing about it among meteorologists on Twitter.
Dr. Greg Forbes is calling it a derecho:
“A derecho is in progress near Cincinnati OH and heading southeast. It formed this morning in south WI. Damage to roofs of Muncie Mall in IN and an aeronautical museum there. Lots of trees and power lines down. 165,000 customers without power in Chicago.”
http://www.facebook.com/twcdrforbes
Lots of conflicting information out there this morning.
Kevin, do happen to know much about gravity waves and what they could possibly mean about severe weather?
http://www.aviationweather.gov/adds/data/satellite/20120724_1431_CLT_vis.jpg
I noticed some on the visible this morning and was curious to know if they were signs of very unstable air, or maybe a lift type mechanism in the atmosphere to cause the storms to lift.
I think a lot of the confusion is based on there being multiple definitions of “derecho” from equally credible sources, sometimes from the same source. Now that the term has entered the major media mainstream, it needs precise criteria recognized across the meteorological community.
Personally, I like the 75 mph wind requirement over some considerable distance, not just the 58 mph basic severe-level wind. A derecho should be something a notch or two higher than a squall line with damaging winds.
SPC thinking the storm cluster — weakened, but still holding together — diving more south than east … kinda like Ben was thinking at 11:26 a.m.
http://www.spc.noaa.gov/products/md/md1564.html
Finally got a break from NYC flights…hotyest area of wx is now in area of Ohio just north of Louisville…based on current vector..I put it just west of ROA around 6pm local…..2 hours to go on this shift..
Ben:
What you see over the Blue Ridge is a moutain wave. The mid level winds are interacting with the mountains as the air flows perpendicular to the ridges. To answer your question, yes it is a sign of unstable air. As far as a lifting mechanism, yes & no. For the most part, the mountains will change the air flow causing “mini waves” but sometimes the mountains can disrupt the flow which can also cause any moisture to be lifted up into stable air & evaporate. You will see the same view in the winter time during a NW flow during a lake effect snow event (snow showers over WV)
In this case, the clear skies east of the Blue Ridge is also bad news for eastern & central VA/NC if these storms stay together.
KM,
Your updates are welcomed reading. I don’t think we thank you enough for all you do.
Thanks again,
Mark
Glad Quagmire jumped in on the gravity waves question. I know there is ongoing study about their relationship to various kinds of weather.
Thank-you, Captain! I knew it had some type of relation to all of what you mentioned, but I wasn’t entirely sure. As you also mentioned, I’d be more worried if I was in central VA/NC about storms as destabilization is occurring more there than western parts of VA.
Newest MD has northern VA for a possibility of a watch with long track supercells that could move S/SSE through the afternoon and evening.
Here’s what Ben is talking about…
http://www.spc.noaa.gov/products/md/md1565.html
MESOSCALE DISCUSSION 1565
NWS STORM PREDICTION CENTER NORMAN OK
1048 AM CDT TUE JUL 24 2012
AREAS AFFECTED…ERN OH…WRN AND SRN PA…NRN VA…MD…ERN WV
CONCERNING…SEVERE POTENTIAL…WATCH LIKELY
VALID 241548Z – 241715Z
PROBABILITY OF WATCH ISSUANCE…80 PERCENT
SUMMARY…STORMS ARE EXPECTED TO INCREASE IN COVERAGE AND INTENSITY
AND A WATCH MAY BE NEEDED SOON.
DISCUSSION…DESTABILIZATION CONTINUES ACROSS THE REGION WITH
POCKETS OF HEATING AND MIXING. EARLY CELLS CROSSING FROM SWRN PA
INTO MD DID NOT PERSIST…BUT CIN WILL CONTINUE TO DECREASE…AND
DEEP LAYER SHEAR IS FAVORABLE FOR SUPERCELLS TO FORM WHICH COULD
TRACK FOR LONG DISTANCES ONCE DEVELOPED. THE CELL OVER FAR WRN MD
APPEARS TO BE BECOMING BETTER ORGANIZED WITH A HAIL THREAT.
OTHER CU OF INTEREST WERE ACROSS NERN OH NEAR THE COLD FRONT.
ADDITIONAL CELLS MAY FORM HERE AND TRACK SEWD WITH A HAIL AND WIND
THREAT.
..JEWELL/HART.. 07/24/2012
Severe T-Storm Watch just issued.
http://www.spc.noaa.gov/products/watch/ww0510.html
Thunderstorm in Blacksburg now, with some pretty good rain. The Severe Thunderstorm Watch went out about 10 minutes before it hit.
Looking at the radar, the right edge (NE side)just may clip the Roanoke Valley. Watching with RadarLab HD+ today it shows the line approaching at around 50mph with some cells around 60mph (these were more towards the middle). Already cleared the Ohio River and Charleston WV next…right around 3 hours (4:30pm) if it holds together to be in ROA Valley.
What’s the deal with the circular radar signatures around the Wilmington Ohio doppler? Looks almost like tropical rain bands around an eye.
POURING rain here in Radford right by the New River at the River Course…some thunder. Not much wind.
Kevin…time for an update…
JUST ISSUED SEVERE THUNDERSTORM WATCH 510 until 8:00 PM for VA
http://www.spc.noaa.gov/products/watch/ww0510.html
URGENT – IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 510
NWS STORM PREDICTION CENTER NORMAN OK
110 PM EDT TUE JUL 24 2012
THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF
DISTRICT OF COLUMBIA
DELAWARE
MARYLAND
NORTHERN NORTH CAROLINA
SOUTHERN PENNSYLVANIA
MUCH OF VIRGINIA
EASTERN WEST VIRGINIA
COASTAL WATERS
EFFECTIVE THIS TUESDAY AFTERNOON AND EVENING FROM 110 PM UNTIL
800 PM EDT.
HAIL TO 2 INCHES IN DIAMETER…THUNDERSTORM WIND GUSTS TO 75
MPH…AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.
THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 85
STATUTE MILES NORTH AND SOUTH OF A LINE FROM 45 MILES SOUTH
SOUTHWEST OF BLUEFIELD WEST VIRGINIA TO 45 MILES EAST NORTHEAST
OF BALTIMORE MARYLAND. FOR A COMPLETE DEPICTION OF THE WATCH SEE
THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU0).
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 508…WW 509…
DISCUSSION…SCATTERED THUNDERSTORMS WILL DEVELOP THIS AFTERNOON
OVER THE MOUNTAINS OF WESTERN VA AND SOUTHERN PA…SPREADING ACROSS
THE WATCH AREA THROUGH THE AFTERNOON AND EARLY EVENING. HOT/MOIST
SURFACE CONDITIONS COUPLED WITH STRONG LOW/MID LEVEL WESTERLY WINDS
WILL PROMOTE THE RISK OF SCATTERED SEVERE STORMS CAPABLE OF DAMAGING
WINDS AND HAIL.
AVIATION…A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 65
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM
MOTION VECTOR 30035.
…HART
I will post something new soon.
http://www.spc.noaa.gov/products/md/md1569.html
MESOSCALE DISCUSSION 1569
NWS STORM PREDICTION CENTER NORMAN OK
1242 PM CDT TUE JUL 24 2012
AREAS AFFECTED…SRN MD INTO SERN VA AND NERN NC
CONCERNING…SEVERE THUNDERSTORM WATCH 510…
VALID 241742Z – 241945Z
THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 510
CONTINUES.
SUMMARY…ADDITIONAL STORMS MAY FORM WITHIN THE LOW PRESSURE
TROUGH…WITH DAMAGING WINDS AND HAIL LIKELY.
DISCUSSION…TEMPERATURES HAVE RISEN INTO THE MID 90S F OVER VA AND
SRN MD…WHILE DEWPOINTS REMAIN IN THE LOWER 70S F. VISIBLE IMAGERY
RECENTLY INDICATES THAT STABLE WAVE CLOUDS WERE MIXING
OUT…SUGGESTING THAT CAPPING IS BEING REMOVED. FURTHER HEATING IS
LIKELY…WITH WILL ENHANCE SFC CONVERGENCE ALONG THE TROUGH AXIS.
MOST MODEL SUGGEST A SEPARATE AREA OF DEVELOPMENT WILL TAKE PLACE IN
THIS AREA BETWEEN 18-20Z. GIVEN VERY LARGE INSTABILITY AND AMPLE W
TO NWLY FLOW ALOFT…EXPLOSIVE DEVELOPMENT WOULD OCCUR WITH STORMS
QUICKLY BECOMING SEVERE WITH LARGE HAIL…THEN MERGING INTO SEWD
MOVING CLUSTERS PRODUCING DAMAGING WIND…WITH SOME SIGNIFICANT
GUSTS POSSIBLE.
IF TCU BEGIN TO FORM IN THESE AREAS AS PREDICTED BY SEVERAL HIGH
RESOLUTION MODELS…THE WATCH MAY NEED TO BE EXTENDED TO INCLUDE THE
REST OF SERN VA AND FAR NERN NC.
..JEWELL.. 07/24/2012
Not much in the way of rain here. Hubby said it was raining hard in C’Burg. It’s just windy here, but the temps are down at least. Wondering if Paul is correct and the Roanoke area just gets clipped by the bow echo that is moving over Charleston right now. If I recall correctly did we not just get clipped in the NRV by the June 29 event? I know we were on target for the middle of the bow on that one. Just curious, but wondering if I should be prepared for any strong wind at all outside of the T-storms that are moving through now?
Here’s great link that has all the tools us weather geeks need from the Storm Prediction Center. The SPC Mesoscale Analysis.
http://www.spc.noaa.gov/exper/mesoanalysis/new/viewsector.php?sector=17
Of note…CAPE (Convective Air Potential Energy) is over 4000 J/kg east of the Blue Ridge. A CAPE reading over 1500 is considered high.
Off to work…