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August 2012 Severe Thunderstorm/Convection Discussion


earthlight

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The models are indicating the potential for a closed low severe potential later in the week into next weekend.

We have seen interesting outcomes in the past with these summer closed lows from severe to flooding.

From the SPC discussion:

FOR DAY 5/FRIDAY...IT APPEARS A MORE CERTAIN SEVERE POTENTIAL IS

EXPECTED TO MATERIALIZE ACROSS THE MID-ATLANTIC REGION/DELMARVA

VICINITY AND PERHAPS THE CAROLINAS. CURRENT GUIDANCE SUGGESTS THAT

AMPLE FORCING FOR ASCENT/VERTICAL SHEAR ATTENDANT TO THE UPPER

TROUGH WILL OVERSPREAD A RELATIVELY MOIST AND WEAK TO MODERATELY

UNSTABLE PRE-COLD FRONTAL WARM SECTOR. A 30 PERCENT EQUIVALENT

SEVERE RISK AREA HAS BEEN INTRODUCED FOR THIS SCENARIO ON DAY

5/FRIDAY.

INTO DAY 6/SATURDAY...SEVERE POTENTIAL COULD LINGER ALONG/AHEAD OF

THE COLD FRONT...INCLUDING AREAS FROM NEW ENGLAND TO THE

NEAR-COASTAL ATLANTIC SEABOARD AND CAROLINAS/SOUTHEAST STATES.

INCREASED UNCERTAINTY REGARDING THE TIMING OF THE UPPER TROUGH/COLD

FRONT INTO DAY 6/SATURDAY PRECLUDES A SEVERE RISK AREA AT THIS TIME.

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The models are indicating the potential for a closed low severe potential later in the week into next weekend.

We have seen interesting outcomes in the past with these summer closed lows from severe to flooding

From the SPC discussion:

FOR DAY 5/FRIDAY...IT APPEARS A MORE CERTAIN SEVERE POTENTIAL IS

EXPECTED TO MATERIALIZE ACROSS THE MID-ATLANTIC REGION/DELMARVA

VICINITY AND PERHAPS THE CAROLINAS. CURRENT GUIDANCE SUGGESTS THAT

AMPLE FORCING FOR ASCENT/VERTICAL SHEAR ATTENDANT TO THE UPPER

TROUGH WILL OVERSPREAD A RELATIVELY MOIST AND WEAK TO MODERATELY

UNSTABLE PRE-COLD FRONTAL WARM SECTOR. A 30 PERCENT EQUIVALENT

SEVERE RISK AREA HAS BEEN INTRODUCED FOR THIS SCENARIO ON DAY

5/FRIDAY.

INTO DAY 6/SATURDAY...SEVERE POTENTIAL COULD LINGER ALONG/AHEAD OF

THE COLD FRONT...INCLUDING AREAS FROM NEW ENGLAND TO THE

NEAR-COASTAL ATLANTIC SEABOARD AND CAROLINAS/SOUTHEAST STATES.

INCREASED UNCERTAINTY REGARDING THE TIMING OF THE UPPER TROUGH/COLD

FRONT INTO DAY 6/SATURDAY PRECLUDES A SEVERE RISK AREA AT THIS TIME.

This looks to be a potential widespread severe weather event through parts of the Eastern US but the tropical moisture could throw a wrench into the set up. That being said, some of the models now have an anomalous surface low tracking to our northwest. Check out the GFS solution. It almost looks like there's a warm front extension from the surface low too.

f114.gif

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This looks to be a potential widespread severe weather event through parts of the Eastern US but the tropical moisture could throw a wrench into the set up. That being said, some of the models now have an anomalous surface low tracking to our northwest. Check out the GFS solution. It almost looks like there's a warm front extension from the surface low too.

f114.gif

It does look like the chance of a warm front followed by a cold front here. The models seem to honing in on

the closed low potential. We usually get some type of interesting weather with these summer closed low set ups.

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Got 0.58'' of rain yesterday in Bridgewater. I was up in Teaneck where they got very little but down back in Bridgewater it sounds like the first line of storms that came through yesterday evening was pretty intense. A decent-sized tree branch (about 1.5-2'' in diameter) actually fell on our roof.

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the euro shows the WAR slowing the weekend system down and pushing the threat to saturday

I like that. As currently progged on the GFS, the best height falls are after 00z, Saturday. 500mb winds are faster on Saturday, as well. Maybe an overnight threat on Friday with the warm front?

But I do think we can do well on both days. If the threat gets pushed to Saturday, then perhaps clearing and reaching our convective temperatures would be an issue.

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The best directional shear also appears to be at the lower levels, which is good for tornadoes. The GFS shows a SE wind barb of 15 knots just offshore on 00z, Saturday, but at the same location, 20 knot SW winds at 850mb.

Not that I anticipate a huge tornado threat, of course, but if we can get the triple point to be just to our NW, we would be in a good spot.

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Ahem:

post-187-0-87188100-1344339069_thumb.gif

...MID MS AND OH VALLEYS THROUGH THE NERN STATES...

PRE-FRONTAL WARM SECTOR WILL CONTINUE TO MOISTEN AS LOW-MID 60S

DEWPOINTS ADVECT THROUGH THE OH VALLEY AND NERN STATES. ONLY MODEST

MID LEVEL LAPSE RATES ARE EXPECTED...BUT DIABATIC WARMING OF THE

BOUNDARY LAYER WILL CONTRIBUTE TO MODERATE INSTABILITY DURING THE

DAY. STORMS WILL LIKELY INCREASE IN COVERAGE ALONG AND SOUTH OF THE

FRONT AS THE BOUNDARY LAYER DESTABILIZES. THOUGH STRONGEST WINDS

ALOFT WILL REMAIN POST FRONTAL...THE MID-UPPER FLOW WILL GRADUALLY

INCREASE AS THE UPPER TROUGH AMPLIFIES. PRIMARY STORM MODE WILL BE

MULTICELLULAR FROM THE OH VALLEY INTO THE NERN STATES WITH A THREAT

OF ISOLATED DAMAGING WIND. STRONGER VERTICAL SHEAR WILL SPREAD SEWD

THROUGH THE MID MS VALLEY IN ASSOCIATION WITH SEWD ADVANCING

SHORTWAVE TROUGH. POTENTIAL WILL EXIST FOR ORGANIZED STORMS IN THIS

REGION INCLUDING A FEW SUPERCELLS...BUT STORMS WILL LIKELY

EVENTUALLY EVOLVE INTO AN MCS DURING THE EVENING. DAMAGING WIND AND

LARGE HAIL WILL BE THE MAIN THREATS.

post-187-0-81689300-1344339044_thumb.gif

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0342 AM CDT TUE AUG 07 2012

VALID 101200Z - 151200Z

...DISCUSSION...

DAY 4/FRIDAY...MODEL CONSENSUS IS THAT HIGH AMPLITUDE POSITIVE TILT

TROUGH WILL HAVE EVOLVED FROM THE GREAT LAKES INTO THE OH AND TN

VALLEYS WITH RESULTANT MODERATE FLOW ALOFT ACROSS THE APPALACHIANS

AND MID ATLANTIC. A MOIST WARM SECTOR WILL SUPPORT MODERATE CAPE AS

DIABATIC WARMING COMMENCES. STORMS MAY BE ONGOING WITHIN ZONE OF

FORCING ACROSS THE OH AND TN VALLEYS...AND ADDITIONAL STORMS SHOULD

DEVELOP AND INTENSIFY ALONG AND EAST OF THE APPALACHIANS WITH

POTENTIAL FOR MAINLY DAMAGING WIND GUSTS.

DAY 5/SATURDAY...SOME SEVERE THREAT MAY LINGER FROM ERN CAROLINAS

INTO THE COASTAL MID ATLANTIC AND NERN STATES...MAINLY THE FIRST

HALF OF DAY. UNCERTAINTIES REGARDING EFFECTS OF ONGOING CONVECTION

PRECLUDES INTRODUCTION OF A DAY 5 RISK AREA AT THIS TIME.

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What's the storm threat looking like for Fri and sat?? Haven't seen anyone discussing it lately!!

Im not a severe guy but we are in a slight risk area from spc. I think the biggest threat is heavy rain and flash flooding. A few storms could throw down a nice microburst but wide spread winds and tornadoes look unlikely to me.

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The NAM also is showing winds east of south at 850mb. That is really bad for directional shear purposes, and also allows for a deeper marine layer intrusion. This would seem to favor heavy rain more than anything.

Considering we know that the mid-level shear is going to suck, we really need some good low-level shear to compensate. Low level shear is more important for tornadoes, anyway.

Also, with the potentially deep marine layer intrusion, weak capping, not great instability, and then SSW flow from 700mb and above (as opposed to a WNW flow at 500mb), that would also seem to favor lots of moisture for heavy rain. But not much in the way of severe weather.

The GFS looked a lot better than the NAM in all aspects, IMO, so we'll see. The 18z GFS definitely did show low level veering, so we'll see what 00z shows.

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The thing is, though, the synoptic pattern in general looks really good. Plus we'll actually have a bit of height falls. It's hard to ignore the general look of the pattern.

Plus, the GFS and NAM both are showing a strong LLJ...winds of around 30 knots at 925mb, which is great for low-level shear. I still would like to have those winds be turned a bit more to the west, but it's hard to pick and choose everything at our location.

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I'm sorry but I dont see a severe threat worth tracking over the next few days. Flooding rain/vivid lightning/iso downbursts, yes, but other than that, not much to speak of other than typical pulsers.

Also, the forecaster that has been barking on these outlooks at SPC, DIAL, he is one of their worst forecasters.

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You know it's really bearish for the prospects of an upcoming severe weather "event" when neither earthlight, Superstorm93, HM, CoastalWx, SmokeEater, TheTrials or Isotherm posts in this severe thread that only expanded by less than 10 posts since yesterday, especially when we are 24 hours from the "event." :D

And we almost never see severe events when PWATS are forecast to be over 2". As soon as I see those values forecast, I immediately stick a fork in most of the severe threat since most of the storms will be watered-down and dull.

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Severe Thunderstorm Warning now for E PA:

AT 121 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A

SEVERE THUNDERSTORM CAPABLE OF PRODUCING QUARTER SIZE HAIL...AND

DAMAGING WINDS IN EXCESS OF 60 MPH. THIS STORM WAS LOCATED NEAR

GREEN LANE...OR 17 MILES SOUTH OF ALLENTOWN...AND MOVING EAST AT 15

MPH.

* THE SEVERE THUNDERSTORM WILL BE NEAR...

GERYVILLE AROUND 130 PM EDT...

SOUDERTON AROUND 155 PM EDT...

QUAKERTOWN AROUND 200 PM EDT...

PERKASIE AROUND 205 PM EDT...

DUBLIN AROUND 225 PM EDT...

BEDMINSTER AROUND 230 PM EDT...

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