June 1, 2012 - Severe Thunderstorms/Tornadoes Event

[Ian]

Even though the setup may not be super favorable - 5% tornado risks are not all that uncommon. I would say that we generally get a 5% when there's a 30%. 10% is where the rarity comes in. Maybe you are jaded by your tornado trip - Still, it's not the percentages that matter - it's the end result!

Strong closed lows are problematic for tornadoes and that area needs more help than most. At this pt I'd expect a 5 somewhere whether it 'verifies' or not. Probably hatched wind.. Maybe hail.

[mappy]

Strong closed lows are problematic for tornadoes and that area needs more help than most. At this pt I'd expect a 5 somewhere whether it 'verifies' or not. Probably hatched wind.. Maybe hail.

Hatched wind and hail are okay with me

[wxmeddler]

I'm not sure that makes sense.

I don't know why I said that... I had a long night and its too early I guess. My main point was the column is really saturated and with PWATS approaching 2" your going to have a tough time sustaining the kind of updrafts that support supercells and tornadoes. Not impossible by any means but difficult. Welcome to the Mid-Atlantic.

[yoda]

I don't know why I said that... I had a long night and its too early I guess. My main point was the column is really saturated and with PWATS approaching 2" your going to have a tough time sustaining the kind of updrafts that support supercells and tornadoes. Not impossible by any means but difficult. Welcome to the Mid-Atlantic.

12z GFS at KIAD has PWATs at 1.5 to 1.7"

[chris87]

I don't know why I said that... I had a long night and its too early I guess. My main point was the column is really saturated and with PWATS approaching 2" your going to have a tough time sustaining the kind of updrafts that support supercells and tornadoes. Not impossible by any means but difficult. Welcome to the Mid-Atlantic.

it happens...there is a delicate balance between buoyancy and adequate shear in this case

[mappy]

12z GFS at KIAD has PWATs at 1.5 to 1.7"

Yup, NAM is the same range

[OSUmetstud]

I don't know why I said that... I had a long night and its too early I guess. My main point was the column is really saturated and with PWATS approaching 2" your going to have a tough time sustaining the kind of updrafts that support supercells and tornadoes. Not impossible by any means but difficult. Welcome to the Mid-Atlantic.

Updrafts actually get less contaminated in high moisture environments...the w max has a higher proportion to the CAPE. Lapse rates suffer since the environmental lapse rate will begin to approach moist adiabatic. Downdrafts suffer in high moisture environments, though..so it's tougher to organize squall lines/downbursts.

[wxmeddler]

12z GFS at KIAD has PWATs at 1.5 to 1.7"

9z SREF's also have 1.7ish

[weatherwiz]

Ouch...

I really don't like the look of the 12z NAM/GFS or the 3z SPC SREF. They have really seemed to cut back on instability tomorrow which isn't good. In these type of situations you always have to worry about cloud cover and there are times that models tend to overdo cloud cover which makes this even more difficult. It also appears that the NAM at least really weakens the mlvl lapse rates from the late morning to the afternoon. Past runs of the NAM had the mlvl lapse rates as high as 6.5 C/KM, now the NAM has them below 6 C/KM...this limits updraft strength and also vastly limits the max instability that could develop.

The NAM/GFS are also showing two ULJ maxes, one to the SE of the region and the other to the NW of the region, this could create and area of subsidence...this could do a few things 1) It could actually help with thinning out any cloud deck leading to more in the way of heating potential and 2) This could also prevent any activity from developing until stronger lift enters the area. Anyways though it doesn't appear that the region isn't in the RFQ of the ULJ anymore, perhaps extreme northern MD is but you'd have to go into PA to get this.

The NAM/GFS also have the strongest instability removed from the better shear.

As was mentioned hopefully there will be some sort of Cap in place in the morning hours to limit any crud from developing and hopefully allowing for more in the way of sunshine, with SE winds off the ocean though and lots of llvl moisture along with the warm front around there could be lots of clouds around...not to mention any cloud debris from convection to the west and southwest.

Given the look of the 12z models I highly doubt we see an upgrade to moderate at this time. Today's runs bring in lots more questions...not good good to see models take a step back at this time. 12z runs gave us more questions than answers really.

Regardless still looks good for some severe weather and the potential still would exist for an isolated tornado or two but we'd be going more towards a wind threat than tornado threat...hail may also not be that much of a threat if those lapse rates turn out to be that weak.

[yoda]

I see 30% SLGT for 1730 DAY 2 OTLK. They might remove the mod upgrade wording, but we will see.

[weatherwiz]

Skew-t soundings across the region are rather moist in the mid-levels which as Nick mentioned is a lapse rate killer. Cape profiles is also rather skinny...normalized Cape values are less than 0.1 (like to see 0.2 to 0.25 at least). Could have an issue with getting strong and mature enough updrafts to really tap into the really strong shear/directional shear aloft.

[yoda]

Day 2 1730 outu.. still SLGT risk... 30% probs basically in same place

[yoda]

..ERN U.S

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.

[anti1clint]

I apologize for my weather ignorance....But can some please explain to me what a "CAPE" is and how that affects the atmosphere pertaining to thunderstorms? Thanks a lot. I have learned so much from reading everyone's snippets of information. :-)

[North Balti Zen]

I apologize for my weather ignorance....But can some please explain to me what a "CAPE" is and how that affects the atmosphere pertaining to thunderstorms? Thanks a lot. I have learned so much from reading everyone's snippets of information. :-)

Try this:

http://www.weatheronline.co.uk/reports/wxfacts/CAPE---Convective-Available-Potential-Energy.htm

[Kmlwx]

Unless things start looking more significant again I could see this being a run of the mill slight risk day with 30% wind 15% hail and 2% torn.

[Eskimo Joe]

The new SWODY2 is really well written by SPC and takes in account mitigating circumstances (ie: cloud cover) as well as the possibility that ample sunshine will allow for a robust event across NOVA, DC, E WV, MD, S-Central PA.

http://www.spc.noaa.gov/products/outlook/day2otlk.html

[mappy]

Unless things start looking more significant again I could see this being a run of the mill slight risk day with 30% wind 15% hail and 2% torn.

with how boring things have been lately - i'll take it

[Kmlwx]

with how boring things have been lately - i'll take it

But I didn't say it woudl even verify that much

[mappy]

But I didn't say it woudl even verify that much

you will enjoy whatever we get

[Kmlwx]

you will enjoy whatever we get

Sadly you are correct - Even if it's 12 raindrops

[weatherwiz]

I apologize for my weather ignorance....But can some please explain to me what a "CAPE" is and how that affects the atmosphere pertaining to thunderstorms? Thanks a lot. I have learned so much from reading everyone's snippets of information. :-)

Cape is Convective Available Potential Energy. It virtually is a measure of how unstable the atmosphere is...it's a measure of how much energy a parcel of air would have if you lifted it from a level of the atmosphere you choose. There are several different measurements of cape, you have surface-based Cape (SBcape), mixed-layer Cape (MLcape), most-unstable Cape (MUcape), normalized-Cape (Ncape), and downdraft Cape (Dcape).

SBcape is measured when you take a parcel of air from the surface and lift it to the Level of Free Convection (LFC).

MLcape is when you take a parcel of air in the lowest 100mb of the atmosphere and lift it to the LFC.

MUcape is virtually a measure of the most unstable parcel of air in the lowest 300mb I believe lifted to it's LFC.

Ncape values virtually measure how "fat" the Cape profile is...skinny cape profiles suggest a lot of water loading while fat cape profiles are more indicative of much more strong instability.

Dcape values measure the downdraft potential I believe.

The larger the Cape values the more unstable the atmosphere is said to be. It is an extremely important ingredient for t'storms and for severe weather. Cape is the energy that t'storms feed off of so higher Cape values = stronger upward acceleration of air parcels = much more robust updrafts and larger storm tops.

Virtually for cape values you'd like to see a minimum of 1000 J/KG for SBcape, MLcape, and MUcape, Ncape values you'd like to see greater than 0.2 to 0.25. Anything less suggests skinny cape. Dcape values once you get above 800-1000 J/KG that's considered really decent.

Once you see Cape values get above 2500 J/KG that's indicative of a highly unstable atmosphere and provided you have sufficient lift explosive thunderstorms are possible.

If you want to determine if there is alot of Cape in place or if the Cape profile is skinny by looking at a skew-t all you do is this...

Cape, however, is not the only measure of atmospheric (in)stability. You also have the lifted index (LI) which is another very useful tool. For the LI value anything below 0 is considered unstable, however once you get below -4 to -5 the atmosphere is considered to be very unstable.

[weatherwiz]

For people more familiar with the mid-Atlantic. in similar situations or setups to this how does the area do for cloud cover? Do models tend to overdo cloud cover?

I know in SNE models can often times overdo cloud cover, especially if winds in the BL and below are more from the SW...SW winds will usually tend to help mix the clouds out much faster and allow for more in the way of sunshine.

I'm going to assume though SE winds down there (like here) aren't very good b/c it draws in more llvl moisture off the water. While you want SE winds for increased helicity unless you have a capping inversion (EML) aloft SE winds just draw in llvl clouds.

[ChrisM]

Are you still heading down tomorrow Paul?

[weatherwiz]

Are you still heading down tomorrow Paul?

Not entirely sure right now but b/c of the distance to travel I think we may just go ahead and do it. We will probably leave around 6 AM.

Since I'm going to the skywarn meeting tonight in Chicopee (leaving around 4:30) I won't be able to look at 18z models so we'll just look at stuff when we get back tonight and make the decision then.

[WinterWxLuvr]

I haven't been following along with this. Is this threat this big? I mean, 6 pages and counting? Is it more of a threat east of the Blue Ridge, etc.

[mappy]

Both ARW and NMM slow the front down, the line doesn't get here until 00z or later

[mappy]

I haven't been following along with this. Is this threat this big? I mean, 6 pages and counting? Is it more of a threat east of the Blue Ridge, etc.

SPC issued a 30% on their Day 3 for us... just keeping an eye on it to see what happens.

[ChrisM]

Not entirely sure right now but b/c of the distance to travel I think we may just go ahead and do it. We will probably leave around 6 AM.

Since I'm going to the skywarn meeting tonight in Chicopee (leaving around 4:30) I won't be able to look at 18z models so we'll just look at stuff when we get back tonight and make the decision then.

You will win oty if you drive from ct to va for this, but Lmk what you decide, I have nothing to do tomorrow

[weatherwiz]

You will win oty if you drive from ct to va for this, but Lmk what you decide, I have nothing to do tomorrow

I think we're just going to go ahead and go (well this depends on whether or not I get my pay check today). We'll probably go to southern PA/MD border...would like to go right around where the warm front sets up. I'll send you a message on fb and we can discuss this.