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weatherwiz

General Severe Weather Discussion 2018

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There is a reason we do May 1st as the countdown until severe weather season and that's b/c the season begins in May and looks like we're right on time this year as we are looking at the likelihood for showers and thunderstorms both tomorrow and Friday and the potential exists for some of the thunderstorms to become strong to severe. 

While the main cold front is still well west tomorrow, several pieces of shortwave energy will be moving through the fast westerly flow aloft during the afternoon tomorrow and a pre-frontal trough may be set up just to our west but the main driver for forcing tomorrow will be pieces of energy moving through the flow aloft. 

With temperatures well into the 80's to near 90 away from the coast and dewpoints climbing into the mid-60's combined with fairly steep mid-level lapse rates will yield the development of moderate instability tomorrow afternoon. While winds in the lowest couple km aren't particularly strong there is plenty of speed shear tomorrow afternoon with a LLJ exceeding 30-35 knots and MLJ exceeding 50 knots. 

As the impulses move overhead we'll likely see showers and thunderstorms develop, however, there is some uncertainty as to the aerial coverage of the storms. Given moderate instability and strong shear the potential will exist for thunderstorms to become strong to severe and pose a threat for strong to damaging wind gusts and perhaps some hail. Higher LCL's, modest low-level directional shear, and weak flow in the lowest few km should preclude any tornado potential.

Friday can be discussed after

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This is intriguing ... 

Morning hi res vis imagery shows that the mid and high level convective debris that clogged the ceilings around dawn is rapidly peeling away and exposing the surface to the sky.. 

Western zones (SNE) are full open to the sun, as is much of the southern tier of NYS west of ALB clear out to the longitudes of Syracuse.   This area is going to envelope all of SNE (S VT/S NH) if that has not already happened, over the next hour.  We are hesitated initially out of the box for temperature rises ...despite the rich potential for explosive recovery, but as this clearing evolves temps should work toward and exceed 80 F in short order - probably prior to noon.   The NAM and some other model-based products appeared overly pessimistic with sky coverage over the last three cycels for this day and we may be seeing that proven true here over the next couple of hours.. 

As it were, this should add to the convection concerns for SBCAPE ...however, what I am seeing looking around at area obs is a dearth of moisture.  DPs at most official sites are 47 to 52 ... Our source is WSW trajectory, and we need to get out almost PIT in western PA before we near 60..   

Having said that, I don't know what the convective temperature is... I also don't know if there may be a layer of better moisture transport available to cloud seeding above the arid boundary layer that's prevalent at this hour.  You can get differential theta-e too..  

SPC maintains the SLIGT - I haven't read their text products to determine precisely what their thinking is.  

Typically in this sort of pattern, the sky actually improves as the sun gains toward it's zenith.. I've seen large debris blobs of wet in NYS with milk sun end up just sunny here as the radar never gets the dead MCS east of the Berk's... the sun heats the troposphere and that ends it.   But we're opening these synoptically enforced sky trends without that factor, anyway.

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Okay... I see..  It seems they are picking up on the DP challenges ... if perhaps implicitly ..

 

"...Great Lakes adjacent Allegheny Plateau into New England... Peak boundary layer destabilization along and just south of the quasi-stationary surface frontal zone may be fairly modest (generally on the order of 500-1000 J/kg) today. However, a belt of 30-50 kt lower/mid tropospheric flow with a number of small-scale perturbations, well in advance of the main impulse emerging from the Great Basin, may enhance afternoon and evening thunderstorm development. Some of this may become capable of producing damaging wind gusts."

One up shot is that this type of growth is actually a bonanza for cloud videography/photo ops.  Clear air CB's with crispy edge ... low obscuring visibility air mass.  

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Usually westerly flow FTW. Pretty good winds aloft (50kts near 700). ML CAPES are not that impressive, but I still note guidance is bring some good storms right to the coast and even srn areas. So I was intrigued and looked to see why. Initially best instability is pike north where better srfc to 850 theta-e lies. However by late day it looks like a surge of higher theta-e down to 925 moves in. Also coincides with better MU CAPE draped near the Pike at 00z. So, this almost looks like storms forming at nose of good low level theta-e..almost like an elevated type deal, but not quite. Also seems  like H5 temps are slightly cooler E and N you go. So that will help. Warmer temps in srn NY state at that level. Note the HRRR has decent UH swaths near pike and north. UH Udraft Helicity, could mean a couple of these could be rather strong or even severe.

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48 minutes ago, CoastalWx said:

Usually westerly flow FTW. Pretty good winds aloft (50kts near 700). ML CAPES are not that impressive, but I still note guidance is bring some good storms right to the coast and even srn areas. So I was intrigued and looked to see why. Initially best instability is pike north where better srfc to 850 theta-e lies. However by late day it looks like a surge of higher theta-e down to 925 moves in. Also coincides with better MU CAPE draped near the Pike at 00z. So, this almost looks like storms forming at nose of good low level theta-e..almost like an elevated type deal, but not quite. Also seems  like H5 temps are slightly cooler E and N you go. So that will help. Warmer temps in srn NY state at that level. Note the HRRR has decent UH swaths near pike and north. UH Udraft Helicity, could mean a couple of these could be rather strong or even severe.

That's precisely what I mentioned/wondering awhile ago ..if there may be theta-e off the deck - interesting... 

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15 minutes ago, Typhoon Tip said:

That's precisely what I mentioned/wondering awhile ago ..if there may be theta-e off the deck - interesting... 

Check out weather.cod and it has nice 925 and 850 theta e progs for NAM. Shows it nicely 

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1 hour ago, CoastalWx said:

Usually westerly flow FTW. Pretty good winds aloft (50kts near 700). ML CAPES are not that impressive, but I still note guidance is bring some good storms right to the coast and even srn areas. So I was intrigued and looked to see why. Initially best instability is pike north where better srfc to 850 theta-e lies. However by late day it looks like a surge of higher theta-e down to 925 moves in. Also coincides with better MU CAPE draped near the Pike at 00z. So, this almost looks like storms forming at nose of good low level theta-e..almost like an elevated type deal, but not quite. Also seems  like H5 temps are slightly cooler E and N you go. So that will help. Warmer temps in srn NY state at that level. Note the HRRR has decent UH swaths near pike and north. UH Udraft Helicity, could mean a couple of these could be rather strong or even severe.

Yeah I found it intriguing the past few days how the models increased instability towards the evening...something you don't usually see happen around here and especially this time of year. Initially I was thinking maybe a plume of steep lapse rates was moving in but yeah...that's a pretty decent plume of theta-e air which moves in later on. 

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56 minutes ago, CoastalWx said:

Check out weather.cod and it has nice 925 and 850 theta e progs for NAM. Shows it nicely 

This could presage a micro-burst potential if we get evap ...but I don't know/am not aware of any studies that especially outline the sigma level correlations for mixing ?  

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1 hour ago, Typhoon Tip said:

This could presage a micro-burst potential if we get evap ...but I don't know/am not aware of any studies that especially outline the sigma level correlations for mixing ?  

you just gave WWiz a microburst in his Wranglers

  • Haha 4

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1630 OTLK for Wiz from SPC:

 ...OH/NY/PA into southern New England...
   No changes have been made to the SLGT risk area in this region. 
   Strong daytime heating is occurring along a corridor from northeast
   OH, across southern NY/northern PA, into southern New England.  A
   cluster of thunderstorms over OH will track eastward along this
   axis, with a few strong storms possible.  Forecast soundings suggest
   that wind fields will be quite strong, but that CAPE and other
   thermodynamic parameters will be limited.  This should suppress the
   hail/tornado risk.  Nevertheless, the strongest cells may be capable
   of gusty/damaging winds.

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seems to be playing out now...  Broken line of forgettable showers is cutting through the area.. 

it'll take the edge of the heat and make for some pleasant evening b-q's -

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Had a nice pounding rainstorm in Methuen about an hour ago. Dropped the temp from 90 quickly down to 75. Suns back out now and temp slowly climbing back up to around 78. Round two later on? 

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looks like meager cape in mid levels screwed us. I’ll take the rain though. We’ll see if the stuff along the juice axis in srn NY survives. 

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2 minutes ago, CoastalWx said:

looks like meager cape in mid levels screwed us. I’ll take the rain though. We’ll see if the stuff along the juice axis in srn NY survives. 

It's interesting to watch the change in the models from 48 hours ago to now. The steep mid level lapse rates are clearly not here lol. Decent coverage of downpours though back this way with nice mid level moisture. 

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Just now, CT Rain said:

It's interesting to watch the change in the models from 48 hours ago to now. The steep mid level lapse rates are clearly not here lol. Decent coverage of downpours though back this way with nice mid level moisture. 

Yeah we had some heavy stuff move through and not one bolt. Probably means lapse rates blow aloft. Thought it would be better. Hopefully that stuff in NY can produce.

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1 minute ago, CoastalWx said:

Yeah we had some heavy stuff move through and not one bolt. Probably means lapse rates blow aloft. Thought it would be better. Hopefully that stuff in NY can produce.

That stuff in NY is struggling. 

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