Saturday June 11th MCS/Derecho Discussion

[Rtd208]

Still some uncertainty how this will play out but both the SPC and Mt.Holly NWS office are highlighting the potential, Upton not hitting the potential to hard (yet).

 

SPC:

http://www.spc.noaa.gov/products/outlook/day3otlk.html

 

Mt.Holly:

For Saturday and Sunday...While the details during this time frame
are still less certain, the overall setup involves a strengthening
surface low that tracks to our north later Saturday. This will allow
a warm front to advance into our area Saturday as downstream warm
air advection is maintained along with some increase in the low and
mid level wind fields. The model guidance shows a pronounced 850 mb
thermal gradient moving across the area along with a rapid increase
in the PW values Saturday. This should allow for building
instability with the warm front and enough forcing should help
initiate convection. The forecast challenge is the timing, coverage
and intensity of the convection.

This setup appears to be conducive for the development of a
convective cluster or MCS upstream, which then rolls east-southeast
near the advancing 850 mb warm front. The forecast soundings suggest
strengthening flow which would lead to fast storm motions and the
potential for strong to locally damaging winds. At least some
guidance is stronger with suggesting the flow veers with height. The
convective intensity will be determined by the amount of instability
present along with forcing and the strength of the wind fields (i.e.
deep layer shear). There still remains the potential for locally
damaging wind gusts Saturday and Saturday night with a couple of
episodes of convection, however the track of any organized
convection remains a bit uncertain at this time. A strong cold front
is then forecast to be settling south of our area on Sunday with
much drier air arriving from the northwest.

 

[NJwx85]

Not much in the way of instability which is further West over PA and not much in the way of jet support which is more towards New England. There could be a nice line of convection but I don't think it's a MCS or anything terribly organized. 

[NJwx85]

The GFS is so far North with the upper level energy on Saturday that we're dry and cool. High temps in the low 70's and sunny skies. More like September weather than almost mid June.

[forkyfork]

The GFS is so far North with the upper level energy on Saturday that we're dry and cool. High temps in the low 70's and sunny skies. More like September weather than almost mid June.

wrong, it shows temps near 80 and dewpoints in the 70's

[NJwx85]

wrong, it shows temps near 80 and dewpoints in the 70's

Huh? I'll give you the dew points. Upper 60's to lower 70's. The heat stays to our Southwest.

 

 

[Dsnowx53]

Almost all of NJ is 75F+ at 5pm, with most of the state 80F+:

 

[NJwx85]

Almost all of NJ is 75F+ at 5pm, with most of the state 80F+:

 

 

Since when does this sub-forum care about the temps in Central and Southern NJ? Most of NNJ, Long Island and Upstate NY are in the lower to possibly mid 70's. 

[Dsnowx53]

Since when does this sub-forum care about the temps in Central and Southern NJ? Most of NNJ, Long Island and Upstate NY are in the lower to possibly mid 70's. 

 

 

Mid to upper 70s for most of Northern NJ, and also the 12z GFS MOS shows a high of 78F for NYC, and 81 for EWR on Saturday. 

 

http://www.nws.noaa.gov/mdl/forecast/text/avnmav.txt

[NJwx85]

The Euro gets around 1250 J/KG of SBCAPE into Western sections by 03z but the LLJ max is displaced towards Philly. Looks like this is becoming more of an isolated event. The only model right now showing something really significant is the NAM.

[dmillz25]

Isn't this convection based again?

[NJwx85]

Isn't this convection based again?

Yes. MCS complexes and thunderstorms are convection. Derecho's are typically a result of a long tracking MCS system. On extremely rare occasions, MCS can form out in the Plains and track all the way to the coast, as happened in June of 2012. I rode out the storm in a RV is rural southern NJ and it was the scariest three hours of my life.

 

 

[dmillz25]

Ill take the Labor day Derecho please. Scary and probably awesome at the same time

[NJwx85]

[Jason WX]

The hole in N jersey must be an error

[NJwx85]

The hole in N jersey must be an error

Look at the SBCAPE

[Allsnow]

Lol yanks is back

[Morris]

The SPC has expanded the slight risk for severe weather on Saturday to cover the entire area: https://t.co/7cd0oBYNhY

[Rtd208]

 

...LOWER GREAT LAKES REGION INTO NORTHEAST...
CONSIDERABLE UNCERTAINTY STILL EXISTS CONCERNING SEVERE WEATHER
POTENTIAL. THE MAIN UPPER IMPULSE AND ASSOCIATED COLD FRONT APPEAR
LIKELY TO REMAIN WELL NORTH OF THE LOWER GREAT LAKES REGION THROUGH
MUCH OF THE DAY. HOWEVER...A MORE SUBTLE IMPULSE MAY PROGRESS
SOUTHEAST OF THE LOWER GREAT LAKES...THROUGH NORTHERN MID ATLANTIC
AND SOUTHERN NEW ENGLAND COASTAL AREAS...DURING THE DAY. THIS MAY
BE ACCOMPANIED BY EARLY DAY CLOUD COVER AND PRECIPITATION THAT COULD
LIMIT DESTABILIZATION.

HOWEVER...IN THE WAKE OF THIS FEATURE...BOUNDARY LAYER MOISTENING
MAY MAKE STEADY PROGRESS EAST OF THE LOWER GREAT LAKES...TOWARD NEW
ENGLAND. AND AN AREA OF ENHANCED LOW-LEVEL WARM ADVECTION COULD
SUPPORT RENEWED CONVECTIVE DEVELOPMENT IN THE PRESENCE OF A
DESTABILIZING BOUNDARY LAYER. THIS SEEMS MOST PROBABLE EAST OF LAKE
ONTARIO INTO PARTS OF THE MOHAWK VALLEY...BEFORE DEVELOPING
SOUTHEASTWARD LATE SATURDAY AFTERNOON AND EVENING. IN THE PRESENCE
OF SHEARED 30-50 KT LOWER/MID TROPOSPHERIC FLOW...ORGANIZED
CONVECTION IS POSSIBLE. THIS MAY INCLUDE BOTH SUPERCELLS AND AN
EVOLVING CONVECTIVE SYSTEM ACCOMPANIED BY AT LEAST THE RISK FOR
SEVERE WIND GUSTS AND HAIL.

[NJwx85]

Models are quite unstable around 00z Sunday. Both the RGEM and NAM bring a MCS through parts of New England. These typically end up further Southeast than modeled so we'll have to see if that comes to fruition here. 

 

Convection initiates over Michigan, so this could be quite the event if all comes to fruition. We'll have the benefit of max heating and a strengthening LLJ. Dew points should be near 70.

[NJwx85]

Does anybody know why models are showing diminished CAPE over E PA and NNJ with greater CAPE to the Southwest and Northeast?

[NJwx85]

Just kind of an odd setup. I guess the drop in instability is because the front comes through here to early.

 

 

 

Just a few hours later that's quite the line dropping South through PA

 

[NJwx85]

[NJwx85]

New Day 2

 

 

...LOWER GREAT LAKES REGION INTO NORTHEAST...
CONSIDERABLE UNCERTAINTY STILL EXISTS CONCERNING SEVERE WEATHER
POTENTIAL AND HAVE MADE NO CHANGES TO THE PREVIOUS OUTLOOK. THE
MAIN UPPER IMPULSE AND ASSOCIATED COLD FRONT APPEAR LIKELY TO REMAIN
WELL NORTH OF THE LOWER GREAT LAKES REGION THROUGH MUCH OF THE DAY.
HOWEVER...IT APPEARS INCREASINGLY PROBABLE A MORE SUBTLE IMPULSE MAY
PROGRESS SOUTHEAST THROUGH THE LOWER GREAT LAKES AND INTO THE NRN
MID ATLANTIC/SRN NEW ENGLAND COASTAL AREAS DURING THE DAY. THIS MAY
BE ACCOMPANIED BY EARLY-DAY CLOUD COVER AND PRECIPITATION THAT COULD
LIMIT DESTABILIZATION.

HOWEVER...IN THE WAKE OF THIS FEATURE...BOUNDARY-LAYER MOISTENING
MAY MAKE STEADY PROGRESS EAST OF THE LOWER GREAT LAKES...TOWARD NEW
ENGLAND. AND AN AREA OF ENHANCED LOW-LEVEL WARM ADVECTION COULD
SUPPORT RENEWED CONVECTIVE DEVELOPMENT IN THE PRESENCE OF A
DESTABILIZING BOUNDARY LAYER. THIS SEEMS MOST PROBABLE EAST OF LAKE
ONTARIO INTO PARTS OF THE MOHAWK VALLEY...BEFORE DEVELOPING
SOUTHEASTWARD LATE SATURDAY AFTERNOON AND EVENING. IN THE PRESENCE
OF SHEARED 30-50 KT LOWER/MID TROPOSPHERIC FLOW...ORGANIZED
CONVECTION IS POSSIBLE. THIS MAY INCLUDE BOTH SUPERCELLS AND AN
EVOLVING CONVECTIVE SYSTEM ACCOMPANIED BY AT LEAST THE RISK FOR
SEVERE WIND GUSTS AND HAIL.

[NJwx85]

The Euro looks pretty good. Decent shear profiles and around 1250 J/KG of SBCAPE.

[Stormlover74]

New Day 2

 

 

2 days ago the threat was supposed to be south Jersey to VA

[NJwx85]

2 days ago the threat was supposed to be south Jersey to VA

I think I figured out what the issue is with the instability. They expect the earlier MCS activity to limit instability further Northeast over SNE.

 

Then in the afternoon, a surge of warmer moist air will be pushing East but it's unclear as to how far Northeast it will make it. So the threat up in New England is for earlier in the day and the threat to our Southwest is for the evening. We're somewhere in the middle, and there may be some surprises or there may be nothing at all. 

[Brian5671]

I think I figured out what the issue is with the instability. They expect the earlier MCS activity to limit instability further Northeast over SNE.

 

Then in the afternoon, a surge of warmer moist air will be pushing East but it's unclear as to how far Northeast it will make it. So the threat up in New England is for earlier in the day and the threat to our Southwest is for the evening. We're somewhere in the middle, and there may be some surprises or there may be nothing at all. 

good post.  I'd say you are right on the possible surprise.  Half the time on these setups, the activity ends up where it was supposed to be dry.  I think back to Memorial Day about 4-5 years ago we got a big MCS that morning that was completely unforecasted

[NJwx85]

good post.  I'd say you are right on the possible surprise.  Half the time on these setups, the activity ends up where it was supposed to be dry.  I think back to Memorial Day about 4-5 years ago we got a big MCS that morning that was completely unforecasted

Historically MCS systems dive Southeastward and end up further South than modeled. The Euro has the main focus over Central New England so it's conceivable that the main threat area might be closer to SNE than NYC. 

 

The new NAM (18z) is quite unstable late tomorrow, especially west of NYC, which actually pushes further East after 00z, It would make you believe that the main threat here would be very late in the day.

[NJwx85]

That's a really nice looking Supercell in Amish Country

 

[Rtd208]

Mt.Holly:

 

.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...

A warm front will lift northeastward through the area on Saturday
morning. An brief/isolated shower is possible with the fropa but not
much more is expected owing to a lack of upper support (the upper
ridge is still overhead). An impressive surge of warm and moist air
is forecast to occur in wake of the warm fropa. Both the NAM and GFS
show dewpoints surging 20-30 degrees (from the 40s/50s to 60/70s in
just over 12 hours.

Models are in rather good agreement with the track and timing of a
mid-level shortwave trough that passes through the Hudson Valley and
our northern zones near the I-80 corridor during the early
afternoon. Lift ahead of this disturbance will likely support a
round of precip mainly across northeast PA and northern NJ during
the midday. Instability will increase quickly from west to east as a
result of the post-warm frontal temperature/dewpoint surge in the
boundary layer. Mixed-layer CAPE profiles are forecast to increase
to near 1000 J/kg by midday across E PA, which would be supportive
of thunderstorms with the midday round of convection but it may be
too early in the day to maintain more robust updrafts that are
supportive of severe storms.

The aforementioned mid-level shortwave will complicate the forecast.
Debris clouds from this system may temporarily limit heating across
a portion of the area but the extent of the affect on
destabilization and ultimately our severe thunderstorm potential for
later in the day is still uncertain. The D2 outlook from SPC still
places eastern PA and NJ in a slight risk for thunderstorms but they
have also mentioned the uncertainty in the convective potential.
Storm coverage may be more scattered in nature during the mid to
late afternoon with the mid-level shortwave exiting the area. The
main threat with any storms will be locally damaging winds and large
hail.

The forecast soundings/hodographs from the 12Z NAM indicate a
potentially favorable tornadic environment across the area Saturday
afternoon if discrete/supercells develop and become right movers
(take more of a southerly turn in the storm motion). However, the
convective mode will depend on the orientation of the boundary
relative the northwesterly deep-layer shear vector, which is still
uncertain with a complex setup comprised of multiple boundaries to
focus convection. Initially, the SE to NW oriented warm front will
be oriented mainly parallel to the shear vector. Multiple modes of
convection (discrete, multi-cell and perhaps quasi-linear) are
possible later in the afternoon as storms become focused along a
more S to N oriented pre-frontal surface trough.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...

Saturday night: A cluster of showers and thunderstorms will likely
be ongoing and moving southeastward through the evening hours. These
showers and storms should end by late evening. Environmental factors
similar to the late afternoon will be in place, so some strong to
severe thunderstorms are possible within the main cluster. A muggy
night with lows in the upper 60`s and low 70`s is likely with the
main cold front still north of the region.