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2013 Mt. Holly CWA Convection Thread


SouthernNJ

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Still highlighted in the extended day 4+

post-810-137405998814.jpg

Shear should be decent, I just have concerns about a few things.

- mid level lapse rates. I believe they're modeled to be mehh AOA 6-6.5* too far out to really see exactly

- storms out running the best forcing as they approach the coastal plain. Seems to be a constant problem this year

- the river

- capping. Haven't checked sounding forecasts today, but in pretty sure there is a warm

Nose somewhere above.

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Shear should be decent, I just have concerns about a few things.

- mid level lapse rates. I believe they're modeled to be mehh AOA 6-6.5* too far out to really see exactly

- storms out running the best forcing as they approach the coastal plain. Seems to be a constant problem this year

- the river

- capping. Haven't checked sounding forecasts today, but in pretty sure there is a warm

Nose somewhere above.

 

Shear is debatable.  Looking at the just the GFS, some runs drop the belt of westerlies farther south (35 kts at 500 mb at Philly) while others do not (keeping us at more like 25 knots).  Given that there's essentially no turning, that right there is the difference between adequate and inadequate deep-layer shear.

 

MLLR actually look better than they do for most events around here.  Sure, I've seen steeper on the Plains, but for our area, 6.5 C/km is not bad.

 

The river has no effect on severe weather.

 

Not capped.  700 mb temps of ~10 C above 850 mb temps of ~18-20 C certainly does not suggest it, and it does not show up in any modeled soundings.  (Aside: A quick calculation shows that if we use 10C and 20C, that produces a LR of ~6.1 C/km in that layer, which happens to be the part of the column with the weakest LR, as judged by the PHL sounding at 18z Sat.)

 

 

Bigger worry, imo, is timing of the front itself.  It looks to get hung up over the Great Lakes Saturday morning, so we may need to hope for something pre-frontal.  But let's see about that.

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- storms out running the best forcing as they approach the coastal plain. Seems to be a constant problem this year

 

The amount on instability may end up compensating for that as one goes south and east. Plus a pre-frontal trough may help.

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Shear is debatable. Looking at the just the GFS, some runs drop the belt of westerlies farther south (35 kts at 500 mb at Philly) while others do not (keeping us at more like 25 knots). Given that there's essentially no turning, that right there is the difference between adequate and inadequate deep-layer shear.

MLLR actually look better than they do for most events around here. Sure, I've seen steeper on the Plains, but for our area, 6.5 C/km is not bad.

The river has no effect on severe weather.

Not capped. 700 mb temps of ~10 C above 850 mb temps of ~18-20 C certainly does not suggest it, and it does not show up in any modeled soundings. (Aside: A quick calculation shows that if we use 10C and 20C, that produces a LR of ~6.1 C/km in that layer, which happens to be the part of the column with the weakest LR, as judged by the PHL sounding at 18z Sat.)

Bigger worry, imo, is timing of the front itself. It looks to get hung up over the Great Lakes Saturday morning, so we may need to hope for something pre-frontal. But let's see about that.

I really wasnt serious about the river lol. C'mon now!!

Otherwise, great points. Might have have to worth about other convective debris rounding the ridge the previous day.

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So much for a Day 7 Risk

 

day2otlk_20130719_0600_prt.gif

 

Seems that, like always, timing of the FROPA sucks, and SPC isn't biting on any pre-frontal activity.  Look at the epic collapse on 0z NAM sim radar that happens between 18z and 0z on Saturday as the storms cross the mountains and outrun the front.

 

On to the next FROPA I guess.  (Next Friday holds some potential...maybe.)

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If the NAM is to be believed, it might be time to issue a rare summertime Weenie Suicide Watch.

 

4 km NAM is a bit more generous, as are the NMM and SPC WRF (all based off their 12z runs) but none of the three look particularly impressive either.

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mcd1447.gif


MESOSCALE DISCUSSION 1447

NWS STORM PREDICTION CENTER NORMAN OK

1236 PM CDT SAT JUL 20 2013

AREAS AFFECTED...ERN PA...NJ...SERN NY...CT...RI...MA...SRN VT...SRN

NH...SRN ME

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 201736Z - 201830Z

PROBABILITY OF WATCH ISSUANCE...80 PERCENT

SUMMARY...THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS AFTERNOON

ACROSS MUCH OF THE URBAN CORRIDOR...AND ADJACENT AREAS OF THE

NORTHERN MID ATLANTIC REGION AND NEW ENGLAND...POSSIBLY AS EARLY AS

THE 18-20Z TIME FRAME. A FEW OF THESE ARE EXPECTED TO BECOME

SEVERE...PARTICULARLY WITH THE RISK FOR POTENTIALLY DAMAGING WIND

GUSTS...AND A WATCH LIKELY WILL BE ISSUED WITHIN THE NEXT HOUR OR

SO.

DISCUSSION...SURFACE HEATING IS MAXIMIZING WITHIN THE LEE SURFACE

TROUGH ALONG THE URBAN CORRIDOR...FROM WASHINGTON D.C. AND BALTIMORE

NORTHEASTWARD THROUGH PHILADELPHIA...NEW YORK AND BOSTON...WHERE

TEMPERATURES ARE NOW IN THE 90S. THIS IS CONTRIBUTING TO LARGE

MIXED LAYER CAPE IN THE PRESENCE OF HIGH PRECIPITABLE WATER CONTENT

NEAR 2 INCHES...WHICH INCLUDES SURFACE DEW POINTS IN THE LOWER 70S.

CONVERGENCE WITHIN THE SURFACE TROUGH CURRENTLY APPEARS WEAK...BUT

ISOLATED STORM DEVELOPMENT ALONG IT DOES NOT APPEAR OUT OF THE

QUESTION DURING THE NEXT FEW HOURS...AS SEASONABLY STRONG CYCLONIC

FLOW GRADUALLY OVERSPREADS THE REGION. A MORE PROMINENT FOCUS FOR

STORM DEVELOPMENT MAY BE AN INITIAL CONVECTIVELY GENERATED BOUNDARY

TO THE NORTH AND WEST...NOW EXTENDING FROM PORTIONS OF SOUTHEASTERN

MAINE THROUGH SOUTHERN NEW HAMPSHIRE AND VERMONT...INTO AREAS

NEAR/EAST AND SOUTH OF THE CATSKILLS AND POCONOS...AS IT CONTINUES A

SLOW SOUTHEASTWARD PROGRESSION.

GIVEN THE THERMODYNAMIC PROFILES...SHEAR BENEATH 30-40+ KT WEST

SOUTHWESTERLY 500 MB FLOW WILL BE SUPPORTIVE OF ORGANIZED SEVERE

STORM DEVELOPMENT...PERHAPS INCLUDING ISOLATED SUPERCELLS. THE RISK

FOR DAMAGING WIND GUSTS APPEAR THE MOST PROMINENT THREAT IN MOST

AREAS.

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Kind of surprised we're not even in a 5% Hail.  I know deep-layer shear is lacking (only ~30 kts 0-6 km north, less closer to the city) and that because of that we won't have sustained hailers, but with such big CAPEs you'd think even pulse storms could briefly be hailers.

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Kind of surprised we're not even in a 5% Hail. I know deep-layer shear is lacking (only ~30 kts 0-6 km north, less closer to the city) and that because of that we won't have sustained hailers, but with such big CAPEs you'd think even pulse storms could briefly be hailers.

Check out. West of Hazelton

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Soooo....not that I have nothing better to do in this stifling heat, as long as I don't have to break a sweat I might as well be watching for these forecasted storms.  Thought we'd be seeing more activity up to the north and west by now.  Cold front is bisecting PA east to west, with cooler temps from State College north and west.  Guess I better find something else to do!

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