Updated D1 Severe Weather Outlook for Tuesday, July 7, 2009...

Updated and final D1 SWO will be as follows. Slight Risk has been locally extended in MA/CT/NY and now includes parts of NH/NJ. Slight Risk includes the following counties...

Connecticut: Fairfield, Hartford, Litchfield, Middlesex, New Haven, New London, Tolland, Windham.

Massachusetts: Berkshire, Bristol, Franklin, Hampden, Hampshire, Middlesex, Norfolk, Worcester.

New Hampshire: Cheshire.

New Jersey: Bergen, Essex, Hudson, Hunterdon, Mercer, Middlesex, Monmouth, Morris, Passaic, Somerset, Sussex, Union, Warren.

New York: Albany, Bronx, Chenango, Columbia, Delaware, Dutchess, Fulton, Greene, Hamilton, Herkimer, Kings, Madison, Montgomery, Nassau, New York, Oneida, Orange, Otsego, Putnam, Queens, Renssalaer, Richmond, Rockland, Saratoga, Schenectady, Schoharie, Suffolk, Sullivan, Ulster, Warren, Washington, West Chester.

Rhode Island: Bristol, Kent, Newport, Providence, Washington.

Vermont: Bennington, Windham.

Discussion...

Quick update too adjust Overnight D1 SWO to accommodate recent trends. This includes locally extending Slight Risk area on western/eastern periphery as well as to include the northern half of NJ. First batch of convection that moved thru south central NY/N East PA earlier this morning has organized now pushed into E NY/W MA/S VT/W CT, and will continue moving west into favorable environment across remainder of CT into RI and parts of MA.

Meanwhile, back to the west, storms have reformed to the lee of Lake Ontario across N Central NY. Some of these storms will likely be severe as they tap into pool of modest instability that was relatively untouched by previous convection this morning to the south. These storms will move southeast into E NY this Afternoon and Evening.

Elsewhere into PA, feeling storms will be more isolated, although a few could be severe, especially along and east of I-81 and along and north of I-80. Post-game wrap-up later this Evening.

..EGAN..

Overnight Severe Weather Outlook for Tuesday, July 7, 2009...

Overnight D1 SWO July 7, 2009 will feature a Slight Risk for severe storms over parts of E and SE NY/W CT/W MA/SW VT. Slight Risk includes the following counties…

Connecticut: Fairfield, Hartford, Litchfield, New Haven.

Massachusetts: Berkshire, Franklin, Hampden, Hampshire.

New York: Albany, Columbia, Dutchess, Fulton, Greene, Montgomery, Orange, Putnam, Renssalaer, Rockland, Saratoga, Schenectady, Schoharie, Ulster, Washington, West Chester.

Vermont: Bennington, Windham.

Discussion...As of 1:42AM 7/7/09

SWO for Today is one of below normal confidence than usual heading into D1. Of biggest concern will be the amount of instability that is realized from Late Morning into the Evening hours in what otherwise is an environment of decent negative lift and sufficient shear to support organized thunderstorm activity, some of which could become severe. Again, this will depend on the amount of CAPE that is realized as to whether or not this potential is maximized to its fullest extent.

As of now, degree of destabilization is modeled around 750-1500 J/KG. Should the upward part of this range be realized or exceeded, potential will be in place for an area of favorable for large hail/damaging winds, and perhaps a tornado or two given ample bulk shear values aoa 40 kts and supportive low level helicity values across much of the Slight Risk area. ATTM, best window of opportunity for severe appears to be Late Morning into mid-Afternoon, which makes the amount of instability even more important.

Given unusually high uncertainty surrounding the forecast, outlook will almost certainly need to be fine tuned and adjusted accordingly later this morning once 12z NAM/RUC analysis is complete.

..EGAN..

Afternoon Update on Severe Weather Outlook for Today, July 6, 2009...

Discussion... As of 12:56PM 7/6/09
Latest visible imagery shows well-defined ULL sitting in the vicinity of the Ontario/Quebec border with attendant cold front sitting just to the north of the US border. Recent trends showing CU field now popping up across the Lake Ontario Plain of Upstate NY spanning primarily along and north of I-90 from the Niagara Frontier to the Genesee Valley.

Latest Surface Analysis yields a pool of around 1000 J/KG in place along the I-81 corridor from Messena NY to Syracuse NY out ahead of this developing CU Field. A few storms have also fired to the north into far N New York/Vermont, and see no reason for this development not to occur further south into N Central/E NY as the Afternoon wears on. Hence, will continue D1 SWO as is thru this Afternoon/Evening. Hail will be the lead threat with perhaps an isolated damaging wind gust in the strongest cells.

Previous Discussion below...

..EGAN..

Discussion...
Low Pressure situated well north of the border in the Canadian province of Quebec and it’s attendant cold front will be the triggering mechanism for showers/storms later Today, primarily across Upstate NY/New England.

For all intent and purpose, Mesoscale Forecaster Chris Broyles has a pretty good looking D2 Outlook structure based on 00z runs, and wouldn’t think much change is needed for the rollover into D1.

Strongest deep layer/bulk shear looks to remain dislocated from axis of best destabilization, south of I-90 and north of I-90, respectively. With CAPE of generally 1000-1500 J/KG and Negative Lift around -3 to -5, potential is once again low, but not non-zero for some of the expected storms to reach short-lived severe status. Also, with freezing levels once again unseasonably low and less than 10000ft., added potential is there for a few hailers. Most favorable area looks to reside across N Central NY east into N New England. Debated whether to highlight a 5% wind threat with hail being the lead threat, but for now, will do so with the outside potential for an isolated wind damage report. Late Morning update can re-evaluate and locally fine-tune if conditions should warrant.

..EGAN..

Overnight Severe Weather Outlook for Monday July 6, 2009...

SWO Product for D1 complete.

Discussion...
Low Pressure situated well north of the border in the Canadian province of Quebec and it’s attendant cold front will be the triggering mechanism for showers/storms later Today, primarily across Upstate NY/New England.

For all intent and purpose, Mesoscale Forecaster Chris Broyles has a pretty good looking D2 Outlook structure based on 00z runs, and wouldn’t think much change is needed for the rollover into D1.

Strongest deep layer/bulk shear looks to remain dislocated from axis of best destabilization, south of I-90 and north of I-90, respectively. With CAPE of generally 1000-1500 J/KG and Negative Lift around -3 to -5, potential is once again low, but not non-zero for some of the expected storms to reach short-lived severe status. Also, with freezing levels once again unseasonably low and less than 10000ft., added potential is there for a few hailers. Most favorable area looks to reside across N Central NY east into N New England. Debated whether to highlight a 5% wind threat with hail being the lead threat, but for now, will do so with the outside potential for an isolated wind damage report. Late Morning update can re-evaluate and locally fine-tune if conditions should warrant.

..EGAN..

Severe Weather Outlook Verification for July 3, 2009...

Discussion...

With the thunderstorm action dying off, time for the traditional post-game wrap-up that comes with each one of our forecasts. 4 separate severe cells were the culprit for Today’s 6 severe weather reports. Of the 6 reports, 4 were for severe hail/2 for damaging wind. All reports were located in the New England states.

As for the forecast, it was pretty much straight-forward. Not much could have gone wrong given the overall synoptic setup. Could have probably tightened up the probability corridor a bit more than was forecasted (E.G. removed Vermont/Immediate Tri-State). However, the furthest east that any severe storms reached was far western Maine, which pretty much fell in line with what was forecasted on my part. Overall, results pretty much speak for themselves.

Here is the brief breakdown…

* No Slight Risk was issued
* No Tornado Probability was issued

Isolated Severe Probability captured 6/6 severe weather reports…
5% Severe Wind Probability: Captured 2/2 damaging wind reports.
5% Severe Hail Probability: Captured 4/4 severe hail reports.

..EGAN..

Afternoon Severe Weather Outlook for July 3, 2009...

Discussion...as of 12:43PM 7/3/09

No changes needed to current SWO product already on the street as this looks like an excellent forecast. Latest RUC evaluation yields a similar scenario for this Afternoon compared to the 00z NAM/GFS in terms of severe potential. MLCAPE values continue to come in at or below 1500 J/KG almost everywhere. The best axis of destabilization looks to occur from Western ME southwest into NJ. Within this axis of destabilization, low level bulk shear values are still progged below 30kts, and Negative LI's from -3 to -5. All in all, most storms should remain below severe limits, with an outside chance that a few reach short-lived severe status. If this should happen... best chance will be from far Western ME southwest to NJ.

Previous Discussion below...

..EGAN..

Discussion...as of 12:51AM 7/3/09

Updated D1 SWO product is now on the street. As has been the case the past few days, yet another shortwave will rotate in tonight across NY/PA and into New England during the day on Friday. Based on latest radar, general Thunder line for D1 will start in place south of I-80 as showers, with perhaps an embedded rumble of thunder move thru PA/NY during the Overnight. This shortwave will be the focal point for producing yet another round of showers/storms over much of the Northeast on Friday.

0z NAM keeps MLCAPE generally under 1250 J/KG over the entire area, and coupled with weak lift/shear, storms will have a very hard time undergoing strong vertical development. Even the usual more robust GFS downplays the severe threat today as well. Based on latest NAM/GFS, debated whether to even include a severe threat today given the overall lack of favorable ingredients for severe convection.

As is, I can probably see a few (likely less than 5, most certainly less than 10) locally damaging wind gusts/marginally severe hail reports today with the strongest of cells, especially given added lift from the rather mountainous terrain of New England. Therefore, will carry a low 5% severe wind/hail probability to account for this. With very low helicity/destabilization expected, tornado threat will be less than 2%.

..EGAN..

Day 1 Severe Weather Outlook for July 3, 2009...

Discussion...

Updated D1 SWO product is now on the street. As has been the case the past few days, yet another shortwave will rotate in tonight across NY/PA and into New England during the day on Friday. Based on latest radar, general Thunder line for D1 will start in place south of I-80 as showers, with perhaps an embedded rumble of thunder move thru PA/NY during the Overnight. This shortwave will be the focal point for producing yet another round of showers/storms over much of the Northeast on Friday.

0z NAM keeps MLCAPE generally under 1250 J/KG over the entire area, and coupled with weak lift/shear, storms will have a very hard time undergoing strong vertical development. Even the usual more robust GFS downplays the severe threat today as well. Based on latest NAM/GFS, debated whether to even include a severe threat today given the overall lack of favorable ingredients for severe convection.

As is, I can probably see a few (likely less than 5, most certainly less than 10) locally damaging wind gusts/marginally severe hail reports today with the strongest of cells, especially given added lift from the rather mountainous terrain of New England. Therefore, will carry a low 5% severe wind/hail probability to account for this. With very low helicity/destabilization expected, tornado threat will be less than 2%.

..EGAN..