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TODAY: July 17th-18th - Storms/Severe/Flooding

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Just now, CoastalWx said:

Feel like this will be one of those nrn RI to SE MA gully washers. 

Yes, some severe warnings south of pike. I think training right along the pike.

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10 minutes ago, sbos_wx said:

I'd be surprised if we do not see a severe watch considering the slight designation. As long as the sun breaks out. Looks like it will.

I don't think we'll see a watch today...or we shouldn't anyways. These are not setups which are prone to producing severe weather...at least on a large enough scale. 

The degree of sun is also a small factor IMO in these setups...it's more of a factor to enhance likelihood of parcels being able to reach the LFC but it isn't a huge factor in severe weather potential. 

All instability today is low-level...that's why SBCAPE is quite high. This is due to rich llvl moisture and the warming sfc temperatures...this again will help with getting parcels to LFC. The bigger issue though is what happens above the LFC. Very poor mlvl lapse rates and moist tropospheric profile mean there is very poor instability aloft..."tall skinny CAPE"...this can be seen by meh MLCAPE. As parcels rise above the LFC they will do so but not very rapidly or aggressively...this limits updraft strength. 

Wind fields are not very strong, but just sufficient enough to yield some updraft organization and the orientation of the flow will organize updrafts into a linear fashion...and as you mentioned a training fashion. 

Given rather warm temperatures aloft and poor instability not only will lightning production not be prolific but the overall look favors extremely heavy downpours and flash flooding. With warming sfc temperatures you'll develop an inverted-V signature and this would locally promote the potential for a wet microburst. DCAPE values though didn't seem overly impressive on soundings and that is likely a reflection by the saturated look up to the EL. 

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3 minutes ago, weatherwiz said:

I don't think we'll see a watch today...or we shouldn't anyways. These are not setups which are prone to producing severe weather...at least on a large enough scale. 

The degree of sun is also a small factor IMO in these setups...it's more of a factor to enhance likelihood of parcels being able to reach the LFC but it isn't a huge factor in severe weather potential. 

All instability today is low-level...that's why SBCAPE is quite high. This is due to rich llvl moisture and the warming sfc temperatures...this again will help with getting parcels to LFC. The bigger issue though is what happens above the LFC. Very poor mlvl lapse rates and moist tropospheric profile mean there is very poor instability aloft..."tall skinny CAPE"...this can be seen by meh MLCAPE. As parcels rise above the LFC they will do so but not very rapidly or aggressively...this limits updraft strength. 

Wind fields are not very strong, but just sufficient enough to yield some updraft organization and the orientation of the flow will organize updrafts into a linear fashion...and as you mentioned a training fashion. 

Given rather warm temperatures aloft and poor instability not only will lightning production not be prolific but the overall look favors extremely heavy downpours and flash flooding. With warming sfc temperatures you'll develop an inverted-V signature and this would locally promote the potential for a wet microburst. DCAPE values though didn't seem overly impressive on soundings and that is likely a reflection by the saturated look up to the EL. 

Haha, yes- you nail it. I'm with you on every point you typed. 

I don't have stats to back it up, but just feels like SPC is more prone to throwing out watches when we are in slight area.

One thing I will say- there is some solid MLCAPE on some of the mesos. Seems restricted to Eastern areas.

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3 minutes ago, Cyclone-68 said:

Feels more like a Florida severe weather day than say a Great Plains severe day assuming anything happens  

It's a no doubter. Clouds are breaking. If I fart too loud, CU will form. #downpours

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15 minutes ago, sbos_wx said:

Haha, yes- you nail it. I'm with you on every point you typed. 

I don't have stats to back it up, but just feels like SPC is more prone to throwing out watches when we are in slight area.

One thing I will say- there is some solid MLCAPE on some of the mesos. Seems restricted to Eastern areas.

Well it's not just the SPC...they'll collaborate with local offices when it comes to the issuance of watches. 

There may be a small area where shear/instability are maximized and could have a localized concentration of severe but don't think it will be too widespread. 

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A ton of bubbling TCU over NY State heading east. We'll see storms fire ahead of that and then eventually that line over NY (wherever it ends up) will be potential for sig flooding.

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Just now, dendrite said:

MMK up to 95/71

We rarely clear out like this, for this long, in a tropical airmass. Seems like it's always 30 minutes then a downpour. Timing today is quite good.

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1 hour ago, sbos_wx said:

It's like Florida out there

Similar but different! I'm in Delray Beach and it's 92F with a nice sea breeze; probably no breeze up there.

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1 minute ago, Modfan said:

Similar but different! I'm in Delray Beach and it's 92F with a nice sea breeze; probably no breeze up there.

Definitely better in Southie, gusting into the 20s on the water. Here at the office in Dorchester, it's pretty insufferable outside... Enjoy that breeze! And the Pool! And the beach! I can't wait until I can live down there lol.

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4 minutes ago, sbos_wx said:

PVD, 86/75... #Swamp

WST 87/79
PVD 85/77 now

Was just 82/77 at UUU. Dew of 77 at HVN.

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Last two runs of HRRR don't see to have a great handle on what is going on right now. 

3k NAM looks like it has more of a clue, comparatively. 

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Mesoscale Discussion 1500
   NWS Storm Prediction Center Norman OK
   1203 PM CDT Wed Jul 17 2019

   Areas affected...portions of the Mid-Atlantic and Northeast

   Concerning...Severe potential...Watch possible 

   Valid 171703Z - 171930Z

   Probability of Watch Issuance...60 percent

   SUMMARY...Storm coverage will increase in the coming hours and
   storms will move east-northeast across the Mid-Atlantic and
   Northeast along and east of the Appalachians. Damaging wind is the
   main severe threat with these storms, and a severe thunderstorm
   watch issuance is possible.

   DISCUSSION...An upper-level shortwave trough is currently moving
   over the Great Lakes and into the Mid-Atlantic and Northeast per
   satellite imagery. Forcing for ascent is spreading downstream of
   this trough helping to initiate storms across the Appalachians.
   Ahead of the cloud cover, surface temperatures have already warmed
   into the 80s F with dewpoints mostly in the 70s resulting in MLCAPE
   of 500-2000 J/kg. Storms will develop as areas reach their
   convective temperatures and along a weak pre-frontal trough that is
   focusing surface convergence south-southwest across the region with
   building Cu already on visible satellite imagery. 

   Flow through the vertical layer is marginal, but effective bulk
   shear of 25-35 knots is expected this afternoon/evening that will
   result in isolated supercells. Overall, the storm mode will be mixed
   given the strong upper-level forcing, forecast 2000-3000 J/kg of
   MLCAPE, and marginal shear. Upscale growth is possible with these
   storms and any QLCS or supercell could pose a damaging wind threat.

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124 PM EDT Wed Jul 17 2019

...FLASH FLOOD WATCH IN EFFECT UNTIL 11 PM EDT THIS EVENING...

The National Weather Service in Boston/Norton has issued a

* Flash Flood Watch for portions of northern Connecticut,
  Massachusetts, and Rhode Island.

* Until 11 PM EDT this evening.

* Numerous showers and thunderstorms are expected to develop
  during the mid to late afternoon hours and continue into the
  evening. The stronger thunderstorms will be capable of producing
  torrential rainfall with localized rainfall amounts exceeding 2
  inches in just an hour. This will result in the potential for
  localized flash flooding, particularly if this were to occur in
  an urban center.

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