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SNE Convective/Thunder thread


free_man

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I don't know...the euro and ensembles are a little too far south for my liking, but maybe they'll creep north.

I do kind of wonder though how far south that front will sag...there really isn't a strong mechanism to drive it too far south and even heights in the lower levels of the atmosphere don't really fall much. I don't think it gets any further south than northern MA. Plus too in a way you want that front as far south as possible without being on the wrong wide of it b/c there will be some great jet dynamics right along that front and given how heights looks to rise somewhat we'll need that extra support to get more in the way of storms or severe potential.

Monday/Tuesday timeframe looks rather interesting.

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I do kind of wonder though how far south that front will sag...there really isn't a strong mechanism to drive it too far south and even heights in the lower levels of the atmosphere don't really fall much. I don't think it gets any further south than northern MA. Plus too in a way you want that front as far south as possible without being on the wrong wide of it b/c there will be some great jet dynamics right along that front and given how heights looks to rise somewhat we'll need that extra support to get more in the way of storms or severe potential.

Monday/Tuesday timeframe looks rather interesting.

As usual, we'll never know until the day before.

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As has been mentioned with several other posts within this thread the upcoming pattern appears quite favorable for multiple convective chances and the upcoming pattern also favors potential for setups which could produce more intense than average convective events across the Northeast. Of course potential isn't everything and a million other things have to fall in place, however, you do have to start off somewhere and no better way to start than with a favorable pattern. Let's get the kick off started with Saturday's convective potential.

On Saturday a piece of s/w energy moving along the US/Canadian border across New York State/VT/NH will allow for a weak backdoor cold front to sag southward through northern/central New England. South of this boundary the airmass is expected to be very warm and humid with temperatures ranging from the upper 70's across the higher elevation areas to lower to near mid 80's across the valley areas, especially if there is a great deal of sunshine. Dewpoints are expected to be in the lower to mid 60's. The combination of very warm surface temperatures along with high dewpoints will yield to a marginally unstable airmass.

While shear in the lower levels of the troposphere is expected to remain rather weak, which is usually the case with backdoor cold fronts, shear in the mid and upper levels of the troposphere will actually be quite strong thanks in large part to the region being on the crest of a fairly strong mid and upper level ridging. Computer models are forecasting a very strong upper-level jet streak of around 120 knots just north of the US/Canadian border across a chunk of southeastern Canada with upper level jet speeds ranging from 90-100 knots across northern New York and northern New England to 50-60 knots across southern New England. This should yield to a great deal of upper level convergence. The mid-level jet is expected to range anywhere from 30-40 knots south of the frontal boundary leading to vertical shear values of around 25-35 knots. Despite the lack of stronger low-level shear there will be some modest directional shear in place given how the flow in the lower troposphere will be more from the S to SW while as you rise to the mid and upper levels of the troposphere winds will veer more to the W/NW. This could yield to some elevated helicity values.

While the combination of forecasted instability/shear appear to be sufficient enough to warrant the development of showers/t'storms as well as the threat for a few strong to possible severe storms there are several other factors, however, to consider here which could work to mitigate the potential.

1) Lack of lowering heights. At this time computer models show very little fall of heights aloft, in fact, if anything heights may somewhat rise. With rising pressure this could really inhibit upward motion and make it a challenge for widespread convection to develop.

2) Timing of front. While we still are several days away and timing of fronts usually doesn't become nailed down until a few days out at this time it appears the front could work into the area early afternoon. If this scenario would to occur this would limit the amount of heating/destabilization that would take place and greatly reduce the threat for strong/severe storms.

3) Backdoor cold fronts also aren't really known for producing much in the way of thunderstorms, especially strong to severe storms. While it certainly isn't impossible you need ample instability along with great mid/upper level support. Very steep lapse rates certainly will help as well along with the development of any meso-low along the boundary. One of the best examples of a backdoor cold front producing severe weather occurred on June 20th, 1995. That setup featured a day with very warm temperatures, high dewpoints, very steep lapse rates, great mid/upper level support along with the development of a meso-low right along the boundary.

Being several days away there is still plenty of time to further fine tune the details and watch the trends within the computer models.

Good write-up, Paul. In case the front does get hung up, let's hope for some good action.

I don't know...the euro and ensembles are a little too far south for my liking, but maybe they'll creep north.

BOX AFD is hedging toward the cooler/dryer EC, FTSL (for the "severe" loss).

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HPC has been tossing the seemingly too cool and south Euro the last 2 days.

BOX is embracing it.

OVERVIEW...

WEAK MID LEVEL SHORTWAVE WILL LIFT ACROSS NEW ENG DURING THE END OF

THE WEEK WHICH WILL LEAD TO CHC SHOWERS/TSTMS. AS THE DISTURBANCE

EXITS...MID LEVEL RIDGE BUILDS NWD INTO THE GT LAKES THIS WEEKEND

WITH SNE ON THE EDGE OF THE POLAR JET. WARMER TEMPS ARE LIKELY BY

SATURDAY...BUT THE PROXIMITY OF THE POLAR JET WILL MAKE US

SUSCEPTIBLE TO A FRONTAL PASSAGE LATER IN THE WEEKEND AND SOME OF

THE GUIDANCE SUGGESTS THE BOUNDARY MAY EVENTUALLY STALL JUST S OF

NEW ENGLAND INTO EARLY NEXT WEEK WHICH WOULD RESULT IN A

CONTINUATION OF UNSETTLED WEATHER. HOWEVER...FORECAST CONFIDENCE IS

LOW FROM SUNDAY INTO EARLY NEXT WEEK AS MODELS ARE NOT IN AGREEMENT

ON WHERE THIS BOUNDARY SETS UP/MOVES AND POPS/TEMP FORECAST WILL BE

LARGELY DEPENDENT ON THE EXACT LOCATION OF THIS BOUNDARY. WE

TRENDED THE FORECAST TOWARD THE ECMWF WHICH IS ON THE COOLER AND

MORE UNSETTLED SIDE OF THE GUIDANCE.

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I just hope the front isn't too far south for next week. It would be great to be in the warm sector, but even having the front drape SNE would allow MCS type stuff. I'd like to see one of those s/w's dip south from Canada. That would introduce more mid level continental air from a good source region (better lapse rates).

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I just hope the front isn't too far south for next week. It would be great to be in the warm sector, but even having the front drape SNE would allow MCS type stuff. I'd like to see one of those s/w's dip south from Canada. That would introduce more mid level continental air from a good source region (better lapse rates).

Euro is too far south .(see SE ridge)

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I think Tuesday is the best day out of any for severe. Seems like overnight storms possible than cold fropa storms late day. The H5 pattern is not all that different from some of our good events in the northeast. As usual, we wait to see how it can be mucked up, but looks interesting.

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