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General Thunderstorm Discussion: Late June


Quincy

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It's funny because the mid level clouds tell you forcing is there...but then it inhibits heating. My gut says storms will fire in ern NY state, but I wonder how organized it will be.

 

You can see some surface based stuff west and northeast of KBGM. 

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It seems to work much better than the operational RAP. Sometimes the mesoanalysis site gets a little crazy eliminating CIN and boosting CAPE.

 

This is good to know, thanks!  The RAP in general loves to do that and really loves to crank instability.  It was supposed to be better than the RUC but I don't really see it.  The only time the RUC/RAP ever really come in handy is when you have strong cooling aloft, especially after dark and it would continue to indicate an unstable airmass or even destabilize it further, which happened quite often in 2008.

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The problem certainly isn't instability.  SBcape values across CT are up to 2000 J/KG, MLcapes 1500 J/KG, MUcapes 2000 J/KG, LI values of -4C to -6C, Ncape values though only around 0.1 so Cape profiles are certainly skinny.  The better forcing from the RFQ of the ULJ is still to the north and west of SNE as is the better forcing/height falls associated with the s/w

 

One issue is this may be a much later show and by that time instability will be weakening.  With that said, I still think we see widespread storms but severe will be isolated.  

 

Extreme.

 

The problem is the skinny CAPE profiles. These are much more supportive of heavy rain. The low levels lapse rates aren't nearly as high as yesterday or the day before, so precip loading won't generate as much wind as those days either. Even with the late arrival of the shortwave, steep low level lapse rates (or high DCAPE) could make up for it with this early diurnal stuff.

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Extreme.

 

The problem is the skinny CAPE profiles. These are much more supportive of heavy rain. The low levels lapse rates aren't nearly as high as yesterday or the day before, so precip loading won't generate as much wind as those days either. Even with the late arrival of the shortwave, steep low level lapse rates (or high DCAPE) could make up for it with this early diurnal stuff.

 

Yeah the skinny cape profiles certainly suggest heavy rain as the main threat, especially with PWATS approaching 1.5'' and greater.  

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Here comes the damage.
mcd1249.gif

MESOSCALE DISCUSSION 1249
NWS STORM PREDICTION CENTER NORMAN OK
0202 PM CDT WED JUN 26 2013
 
AREAS AFFECTED...A LARGE PART OF MA...PARTS OF NRN/ERN CT...RI
 
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
 
VALID 261902Z - 262130Z
 
PROBABILITY OF WATCH ISSUANCE...40 PERCENT
 
SUMMARY...THE AREA IS BEING MONITORED FOR INCREASING SVR POTENTIAL AND THE POSSIBLE ISSUANCE OF A SVR THUNDERSTORM WATCH THIS AFTERNOON.
 
DISCUSSION...ACROSS THE MCD AREA...A POCKET OF PARTLY CLOUDY TO MOSTLY SUNNY SKIES LIES BETWEEN HIGHER-DENSITY/OPAQUE MULTI-LAYERED CLOUDS STREAMING ACROSS CNTRL/NRN NEW ENGLAND...AND AN EWD-EXTENDING PLUME OF SIMILAR CLOUDS MOVING ESEWD ACROSS SERN NY AND SRN CT INTO THE ADJACENT WRN ATLANTIC. SFC DIABATIC HEATING ACROSS THIS POCKET OF ENHANCED ISOLATION AMIDST MIDDLE 60S SFC DEWPOINTS IS CONTRIBUTING TO AROUND 1000-1500 J/KG OF MLCAPE PER MODIFIED 12Z RAOBS AND FORECAST SOUNDINGS. FURTHER DESTABILIZATION WILL BE CONTRIBUTED BY /1/ CONTINUED STEEPENING OF LOW-LEVEL LAPSE RATES THROUGH THE AFTERNOON...AND /2/ INCREASING LARGE-SCALE UPWARD MOTION PRECEDING A MID-LEVEL SHORTWAVE TROUGH APPROACHING FROM THE GREAT LAKES REGION. THUNDERSTORMS WILL LIKELY INCREASE IN NUMBER/INTENSITY THROUGH THE AFTERNOON AMIDST THE MODERATE INSTABILITY AS LOW-LEVEL ASCENT ALONG THE FRINGES OF THE MULTI-LAYERED CLOUDS/DIFFERENTIAL HEATING ZONES IS AUGMENTED BY INLAND-MOVING SEA BREEZE CIRCULATIONS.
 
BOX VWP DATA INDICATE AROUND 30 KT OF FLOW IN THE 3-5-KM-AGL LAYER...AND SOME INCREASE IN MID-LEVEL FLOW MAY OCCUR AS THE HEIGHT GRADIENT TIGHTENS IN ASSOCIATION WITH THE APPROACH OF THE SHORTWAVE TROUGH. CORRESPONDING MODERATE DEEP SHEAR MAY SUPPORT ORGANIZED STORM STRUCTURES INCLUDING MULTICELLS AND PERHAPS MARGINAL SUPERCELL STRUCTURES...WITH THE POTENTIAL FOR DMGG WINDS AND SVR HAIL. HOWEVER...MID-LEVEL LAPSE RATES ARE NOT PARTICULARLY STEEP...AND THE STRONGEST DEEP-LAYER FORCING FOR ASCENT COULD REMAIN DISPLACED TO THE W OF THE AREA THROUGH PEAK HEATING. THESE FACTORS BREED UNCERTAINTY REGARDING THE ANTICIPATED CONVECTIVE INTENSITY...THOUGH THE AREA WILL BE MONITORED FOR THE POSSIBLE ISSUANCE OF A SVR THUNDERSTORM WATCH THROUGH THE AFTERNOON.
 
..COHEN/KERR.. 06/26/2013
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