1083 replies to this topic

[irishbri74]

just to add what TOM TIMMER is adding (which is a great post tom). here's the sounding for baltimore hr 54:



look at the bottome right. look at the turning of the winds. Here's the associated HODO:



Thats pretty solid for the region. I know it's baltimores, but this is what the wind profiles/hodo's would look like just along the warm front.

[Boch23]

Awesome stuff guys, very informative. To Bri's point i feel like 20 miles isn't that much. And if nothing else gives me something to watch to get through the day thursday and friday.

[wederwarrior]

Great usage of helicity tombo. Good discussion

I don't think a shift of 20-30 miles is out of the question. We shall see what transpires.

[stormspotterlive]

Great post tombo and bri! I do think with the strong shear in place storms with the front will be moving east at a rather fast pace vs the slower pace we saw on Tuesday. The warm front like every other warm front will probably come down to nowcasting or last minute as we have seen earlier in the year. Any event interested to see how the spc responds to newer model data which is continuing to make things more interesting.

[MGorse]

It does appear that the Friday system is looking more and more interesting, but I am not quite sold on a decent severe thunderstorm threat for our area. Despite rather impressive wind fields overspreading the area, the timing is what may be against us. It looks like the best ascent and wind fields arrive after 00z Saturday and the gist of the guidance has what instabilty develops lowering during the night. I see the new 00z NAM has a 925 mb jet of 40-50 knots moving across most of the area after 00z Saturday. The southeasterly low-level inflow may also allow lower clouds to arrive sooner, cutting off the surface based CAPE. This could be an event where a convective line develops to the west and then it turns into not having much lightning with it as it becomes more low-topped with an eastward extent. This could be maintained through the night despite lowering instability due to decent height falls and a strengthening wind field.

[irishbri74]

It does appear that the Friday system is looking more and more interesting, but I am not quite sold on a decent severe thunderstorm threat for our area. Despite rather impressive wind fields overspreading the area, the timing is what may be against us. It looks like the best ascent and wind fields arrive after 00z Saturday and the gist of the guidance has what instabilty develops lowering during the night. I see the new 00z NAM has a 925 mb jet of 40-50 knots moving across most of the area after 00z Saturday. The southeasterly low-level inflow may also allow lower clouds to arrive sooner, cutting off the surface based CAPE. This could be an event where a convective line develops to the west and then it turns into not having much lightning with it as it becomes more low-topped with an eastward extent. This could be maintained through the night despite lowering instability due to decent height falls and a strengthening wind field.

Kinda like the other night! Killjoy :-)

[NeffsvilleWx]

Excellent post tombo, learned quite a bit. Thanks!

[Thunder Road]

I'm sorry but this has been bothering me.

LI is not a direct measure of "lift" in the atmosphere. It's just a crude approximation of instability (T(Parcel) - T(Environment) at 500 mb) and generally inferior to CAPE. It's better to look for significantly negative VV's (Vertical Velocities) specifically at 700 mb to isolate what the source of "lift" is.

I'm sure most of us know this already, but for those who are learning, here's another lesson.

[Thunder Road]

As for the threat overall, I'm still conditionally optimistic. I can recall more warm front busts that busted south than busted north. I think Maryland is game but I'm not so sure we are up here (although this could change).

That said, those are good dynamics for a Plains set-up (well one in June anyway), let alone an EC one, with a 50-knot LLJ at 925 mb and 850 mb and good veering with height. Remember that backed surface flow is going to mean we get a wind off the ocean. Even with the ridiculously warm SSTs we have up here, that it still a potentially-stabilizing marine layer. Again this is another reason why central MD might make out better than SE PA.

[SmokeEater]

Day 2 slight just issued, main threats widespread damaging wind and a possible tornado threat from VA to PA/NJ if discrete cells form ahead of the line, and sufficient destabilization happens in the area of the warm front. Also Moderate Risk may be needed in subsequent outlooks.

[phlwx]

As for the threat overall, I'm still conditionally optimistic. I can recall more warm front busts that busted south than busted north. I think Maryland is game but I'm not so sure we are up here (although this could change).

That said, those are good dynamics for a Plains set-up (well one in June anyway), let alone an EC one, with a 50-knot LLJ at 925 mb and 850 mb and good veering with height. Remember that backed surface flow is going to mean we get a wind off the ocean. Even with the ridiculously warm SSTs we have up here, that it still a potentially-stabilizing marine layer. Again this is another reason why central MD might make out better than SE PA.

I agree completely. I would also add Lancaster, Harrisburg, and York are in a prime spot as well...they typically do well in these types of setups and I think they probably get hammered pretty hard tomorrow around dinner time.

I'm not sold at all on Philly or NJ...I think the timing stinks for us and I think the wind trajectory is a bit too off the water to get us instability in the city and east. That said, could be a gusty round of thunder locally.

[tombo82685]

I agree completely. I would also add Lancaster, Harrisburg, and York are in a prime spot as well...they typically do well in these types of setups and I think they probably get hammered pretty hard tomorrow around dinner time.

I'm not sold at all on Philly or NJ...I think the timing stinks for us and I think the wind trajectory is a bit too off the water to get us instability in the city and east. That said, could be a gusty round of thunder locally.

yea the lower susq valley looks game on. This could be another event where we get a weakening line of storms coming in. You can see it on the models esp the nam. If this event had better timing, it could of been one of the better setups we have seen in a while. Will also depend how far north that wf gets to. The nam continues to slow the progresion of the front which isnt good for svr weather, crosses it around midnight..

[Voyager]

Allentown/Tamaqua too far north?

[Rainshadow]

I got a quick flutter in my heart.


Then I remembered yesterday.

lol from the discussion...: "perhaps even a tornado threat". i'm stocking up on glue to sniff so i'm ready for friday.

To be fair about the other day, the spc discussion about tornadoes was focusing on the NY Hudson Valley eastward.

Its been pretty well stated about the potential with this event overall and the probable limitations in our area for tomorrow.

[NeffsvilleWx]

I would also add Lancaster, Harrisburg, and York are in a prime spot as well

yea the lower susq valley looks game on.

Hazardous Weather Outlook

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE STATE COLLEGE PA
241 AM EDT THU MAY 31 2012

PAZ035-036-056-057-059-063>066-010645-
FULTON-FRANKLIN-PERRY-DAUPHIN-LEBANON-CUMBERLAND-ADAMS-YORK-
LANCASTER-
241 AM EDT THU MAY 31 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL PENNSYLVANIA.

.DAY ONE...TODAY AND TONIGHT.

HAZARDOUS WEATHER IS NOT EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY.

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FRIDAY AFTERNOON
AND EVENING. STORMS WILL LIKELY CONTAIN HEAVY DOWNPOURS WITH
INTENSE RAINFALL RATES...POSSIBLY RESULTING IN LOCALIZED FLOODING.

DAMAGING WINDS AND LARGE HAIL WILL BE THE PRIMARY SEVERE THUNDERSTORM
HAZARDS. HOWEVER...THERE WILL BE AN ELEVATED CONDITIONAL THREAT
FOR ISOLATED TORNADOES.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS LIKELY ON FRIDAY AFTERNOON AND EVENING.

[chubbs]

From 1AM SPC outlook


SOME SUPERCELLS...INCLUDING A TORNADO
THREAT...COULD OCCUR MAINLY ACROSS VA/DELMARVA REGION INTO SOUTHERN
PA/NJ PROVIDED 1/ SUFFICIENT DESTABILIZATION OCCURS NEAR THE WARM
FRONT AND 2/ SEMI-DISCRETE DEVELOPMENT OCCURS AHEAD OF THE COLD
FRONT WHERE A LINEAR MODE SHOULD BE MORE DOMINANT. SOMEWHAT HIGHER
PROBABILITIES/PERHAPS EVEN A CATEGORICAL MODERATE RISK MIGHT BE
WARRANTED IN SUBSEQUENT CONVECTIVE OUTLOOKS.

[SmokeEater]

Hazardous Weather Outlook

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE STATE COLLEGE PA
241 AM EDT THU MAY 31 2012

PAZ035-036-056-057-059-063>066-010645-
FULTON-FRANKLIN-PERRY-DAUPHIN-LEBANON-CUMBERLAND-ADAMS-YORK-
LANCASTER-
241 AM EDT THU MAY 31 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL PENNSYLVANIA.

.DAY ONE...TODAY AND TONIGHT.

HAZARDOUS WEATHER IS NOT EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY.

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FRIDAY AFTERNOON
AND EVENING. STORMS WILL LIKELY CONTAIN HEAVY DOWNPOURS WITH
INTENSE RAINFALL RATES...POSSIBLY RESULTING IN LOCALIZED FLOODING.

DAMAGING WINDS AND LARGE HAIL WILL BE THE PRIMARY SEVERE THUNDERSTORM
HAZARDS. HOWEVER...THERE WILL BE AN ELEVATED CONDITIONAL THREAT
FOR ISOLATED TORNADOES.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS LIKELY ON FRIDAY AFTERNOON AND EVENING.

Good chance I'll be out your way come Friday afternoon.

[NeffsvilleWx]

Good chance I'll be out your way come Friday afternoon.

if things look like they're coming together i might just have to try to take a day off.

[NeffsvilleWx]

Dr Forbes posted his initial TORCON forecast for Friday:

Friday, June 1

AL south - 2
DC - 4
DE - 4
FL panhandle - 2
GA east-central, south - 2
MD east - 4
MD central - 2 to 3
NC central, east - 2
NJ north - 2
NJ south - 3
PA southeast - 4
SC central, east - 2
VA north - 4
VA south-central, east - 2 to 3
Other areas - 1 or less

a 4 or higher in PA does not happen often at all

[Quakertown needs snow]

Guess I'm the one who is hoping for no tornado's in the area, especially populated areas.

[snowlurker]

Guess I'm the one who is hoping for no tornado's in the area, especially populated areas.

Count me in as rooting against them. I could go for a light show and heavy rain, but no twisters.

[mapgirl]

Just wanted to drop in from the MA and thank Tombo for that informative post. Good luck to you guys north of me!

[tombo82685]

It does appear that the Friday system is looking more and more interesting, but I am not quite sold on a decent severe thunderstorm threat for our area. Despite rather impressive wind fields overspreading the area, the timing is what may be against us. It looks like the best ascent and wind fields arrive after 00z Saturday and the gist of the guidance has what instabilty develops lowering during the night. I see the new 00z NAM has a 925 mb jet of 40-50 knots moving across most of the area after 00z Saturday. The southeasterly low-level inflow may also allow lower clouds to arrive sooner, cutting off the surface based CAPE. This could be an event where a convective line develops to the west and then it turns into not having much lightning with it as it becomes more low-topped with an eastward extent. This could be maintained through the night despite lowering instability due to decent height falls and a strengthening wind field.

music to lee's ears

[NeffsvilleWx]

Guess I'm the one who is hoping for no tornado's in the area, especially populated areas.

No one wants to see tornado's in population centers.

I'd love to see one in the middle of some farmland though. Plenty of that in my neck of the woods.

[greg ralls]

Even if you're obsessed with tornadoes, that doesn't mean you want to see one skipping through the Main Line or something. Anyone remember the PDS Tornado Watch for our area from around 10 years ago or so? I think it was a Saturday. Nothing happened, thankfully, but that's still the only time I remember truly thinking I might get to see a strong tornado. I remember typing in my zip code on the NWS site and there was a picture of a tornado for that day's weather, and the text said something like "Destructive tornadoes possible."

[Boch23]

No one wants to see tornado's in population centers.

I'd love to see one in the middle of some farmland though. Plenty of that in my neck of the woods.

I would have to believe this is the thought of most people on the board when they talk about wanting torandoes.

[stormspotterlive]

Even if you're obsessed with tornadoes, that doesn't mean you want to see one skipping through the Main Line or something. Anyone remember the PDS Tornado Watch for our area from around 10 years ago or so? I think it was a Saturday. Nothing happened, thankfully, but that's still the only time I remember truly thinking I might get to see a strong tornado. I remember typing in my zip code on the NWS site and there was a picture of a tornado for that day's weather, and the text said something like "Destructive tornadoes possible."

I believe I recall hearing about the PDS watch on the news that day of course this is back when warning were by a whole county not by a storm and its path like now a days.

[tombo82685]

not as impressed with this setup as i was yesterday. Models continue to back off on the instability for the region. I cab\n definitely see some svr weather esp west of the region, which will weaken some coming east. Timing of the front looks later also than yesterday,

[NeffsvilleWx]

Eric Horst's latest special weather disco:

Noon Thursday, May 31:
Textbook set up for severe storms tomorrow...from central PA southward through most of VA. Some tornadoes are possible.
Developing....

He's usually pretty conservative.

[stormspotterlive]

Looks to me despite the lack of Instability wind will be a threat for the area with storms due to high shear. Wild card will be how strong the storms are as they come into our area. And as stated in the NWS AFD if the storms can manage to pass the warm front where we are continuing to find very decent shear in place for storms to work with on the models it would support at least a marginal damaging wind threat . Obviously if the warm front ends up more north there would be a greater tornado Hail and wind threat could set up in the area.

[SouthernNJ]

With the topic of tornadoes being discussed lately, it should be
pointed out that today is the 14th anniversary of possibly the
strongest tornado to impact the Mt. Holly CWA since it became
an office. The Lyons F3 struck at 9:10 PM on May 31, 1998 and
did severe damage to the borough, among other areas along its
8.3 mile path. A tornado warning was issued 23 minutes before
the tornado touched down, and 33 minutes before it hit Lyons.
As a result, there were no fatalities and just seven injuries.

[Boch23]

Fully prepared for a redux of tuesday night. 30% expanded more north and west and 15% to the north and east reduced to about slightly north of philly on the latest outlook. Anytime I'm on the edge of slight risk I just expect nothing imby.

[LMolineuxLM1]

Need I say gas station island effect maybe again? Murphys law. Next weeks cold pool pop-ups to the rescue for filming?

[NeffsvilleWx]

Latest from SPC:

AN AREA OF STRONG HEIGHT FALLS...ON THE ORDER OF 60-90M...WILL
OVERSPREAD THE OH VALLEY DURING THE DAY FRIDAY AS SLIGHTLY NEGATIVE
TILTED UPPER TROUGH AXIS PROGRESSES TO A POSITION FROM LOWER
MI...ARCING SEWD TO SC BY 02/00Z. AN EXPANSIVE AREA OF LARGE SCALE
ASCENT IS EXPECTED TO OVERSPREAD THE REGION AHEAD OF THIS UPPER
DIFFLUENT TROUGH AND SHOULD PROVE SUPPORTIVE OF WIDESPREAD
CONVECTION ALONG ADVANCING COLD FRONT AS IT SURGES EWD.

THUNDERSTORMS SHOULD BE ONGOING EARLY IN THE PERIOD ALONG THE COLD
FRONT FROM OH...SWD INTO NRN GA. WHILE STRONG SHEAR WILL COINCIDE
WITH THIS ACTIVITY IN ALL LIKELIHOOD BROKEN LINEAR TSTM SEGMENTS
SHOULD BE MOSTLY NON-SEVERE...OR PERHAPS MARGINALLY SEVERE AT
DAYBREAK. MAIN LIMITING FACTOR FOR SEVERE EARLY IN THE PERIOD WILL
BE DUE TO MEAGER INSTABILITY. HOWEVER...BOUNDARY LAYER HEATING
SHOULD AID IN AIR MASS DESTABILIZATION BY 18Z AND SUFFICIENT
BUOYANCY WILL DEVELOP FOR ROBUST UPDRAFTS WITHIN AN ENVIRONMENT MORE
THAN SUFFICIENTLY SHEARED FOR ORGANIZATION. IN FACT...FORECAST
SOUNDINGS SUGGEST ROTATING UPDRAFTS/SUPERCELL STRUCTURES ARE
POSSIBLE. GIVEN THE AFOREMENTIONED LARGE SCALE SUPPORT...IT APPEARS
A STRONGLY FORCED SQUALL LINE SHOULD BE NOTED WITH ADVANCING COLD
FRONT AND GRADUAL INTENSIFICATION IS EXPECTED AS AIR MASS
DESTABILIZES...PRIMARILY EAST OF THE APPALACHIANS AND WITH TIME
ACROSS PORTIONS OF PA. DAMAGING WINDS MAY BE COMMON WITH THE SQUALL
LINE...ESPECIALLY IF MUCAPE CAN EXCEED 1500 J/KG AS NAM SUGGESTS.
AT THIS TIME WILL MAINTAIN 30% SEVERE PROBS TO ACCOUNT FOR THE
EXPECTED STRONG WINDS WITH THE FRONTAL CONVECTION AND FOR ISOLATED
TORNADOES THAT COULD BE NOTED IF PRE-FRONTAL DISCRETE SUPERCELLS
DEVELOP. HOWEVER...THERE IS SOME CONCERN THAT A MORE WIDESPREAD
EVENT MAY EVOLVE IF LOW LEVEL LAPSE RATES/INSTABILITY RESPOND PRIOR
TO FRONTAL PASSAGE AND SEVERE PROBS MAY BE INCREASED TO ACCOUNT FOR
THIS SCENARIO IN LATER OUTLOOKS.

[stormspotterlive]

For what it's worth the 12z NMM and ARW just in has storms going right to the coast tomorrow. With wind and heavy rain being the main threat here if it were to verified.

http://www.meteo.psu..._12z/rloop.html

Additionally the 12z euro looks to be coming in stronger for just west of the metro area. Also looks a bit more like an occluded front with how close the warm front and cold front are together. Correct me if I am wrong though.