1 December 2006 Severe Weather Event

An unseasonably mild air mass was in place over much of New York and New England for December. Temperatures were running a good 15-20 degrees above normal prior to the severe weather event. A backdoor cold front moved southward across the forecast area Friday morning between 05Z-12Z FRI. The shallow cold air made it far enough southward to roughly Hudson, NY. Temperatures on the north side of the boundary fell into the mid 30s to lower 40s...except over the Berkshires, where temps stayed in the 60s the entire time (Fig. 1). An 18Z KALY sounding was done (Fig. 2). It should be noted the depth of the cold/cooler air was less than 1500 ft deep. This boundary would lift north of ALY towards 23Z (Fig. 3), as an impressive line of convection was forecast to develop ahead of the strong cold front approaching from the west. The WRF model did the best job forecasting the backdoor surface cold frontal passage through ALY and hanging it up north of KPOU. The cold air had the most difficult time scouring out of the valleys prior to the severe convection.

Figure 1. MSLP and station plot. Note the extreme temperature and dew point gradient through PA, NY and New England associated with the front.

Figure 2. ALB sounding at 1800 UTC 1 December. Note the extreme low level inversion and conditional instability above 925 Mb and winds of 40-70 Kt between 850 Mb and 600 Mb.

Figure 3. MSLP and station plots at 2100 UTC 1 December. Note the continued extreme temperature and dew point gradient along the front through eastern NY and New England, and the low pressure centered near SYR.

An exceptionally strong mid level trough quickly moved N/NE from the TN and Ohio Valley during the late morning. The 500 mb jet streak was around an impressive 120 kts. Portions of the ALY forecast area would get into the left front quadrant of the jet streak...as the upper level trough and its incipient sfc low pressure system moved across western and northern NY in the late afternoon and early evening. The upper level trough strengthened and turned negative pushing the main cold front through the forecast area with multiple lines of severe convection ahead of the front (Fig. 4).

Figure 4. Infrared satellite picture and lightning overlay, 2200 UTC 1 December. Note the frequent lightning associated with the thunderstorms well north into the cold air, and the enhancement of the clouds, indicating deep convection.

At 1300 UTC..SPC upgraded the entire forecast area to a moderate risk (Fig. 5). It actually was the first one for the ALY forecast area, since the significant squall line of 6 June 2005. The last one before that event was 21-22 JUL 2003, which was ALYs last big tornadic event.

The mesoscale environment was very volatile. It was a classic high shear-low CAPE environment. 0-1 km bulk shear values of 50 kts were forecasted. The deep layer shear (0-6 km) was progged to be in excess of 75 knots. 0-3 km helicity values off model hodographs produced values well in excess of 500 m^2/s^2. A strong southerly 850 hPa low-level jet in excess of 60 kts advected in low-level theta-e rich air (Fig. 6). Surface dewpoints were in excess of 15C in the southern portion of the forecast area. DCAPE values in excess of 1000 J/kg were forecaseted by the GFS and WRF model runs at 12Z and 18Z. LCLs were low under 3kft. All signals of a possible widespread wind damage/isolated tornado threat.

Figure 5. Storm Prediction Center Severe Weather Outlook for day one showing a moderate risk for severe weather over much of the northeastern U.S., extremely rare, especially for December.

Figure 6. KENX Velocity Azimuth Display wind profile at 2200 UTC 1 December. Note the directional and speed shear present in the lowest few thousand feet and winds of 50-80 Kt between 4000 feet and 10000 feet.

A severe thunderstorm watch box was put up to the west of ALY forecast area around noon to 1 pm. Jeff Evans, SPC lead forecaster called ALY, PHL and OKX to coordinate a new severe thunderstorm watch box between 3-330 pm. Everyone agreed a watch was necessary and the possibility of isolated tornadoes was mentioned due to the dangerous low-level shear and 0-3 km hodographs. Jeff initially had Hamilton and Warren counties out of the WCL proposed. He listened to our suggestions to put them in. Adding these counties worked out well...as multiple Quasi Linear Convective Systems (QLCSs) approached eastern NY. The QLCSs coalesced into two main lines between 5-730 pm as they pushed through the forecast area (Figs. 7-11).

(Click on the next 3 images for enhanced movies)

Figure 7. Regional radar mosaic of base reflectivity at the 0.5 elevation angle with lightning overlay at 2100 UTC 1 December. Click on figure for movie showing blinking lightning.

Figure 8. KTYX base reflectivity at the 0.5 elevation angle with lightning overlay at 2130 UTC 1 December. Click on figure for movie showing alternate reflectivity and base velocity. Note the extreme winds indicated in the base velocity displays associated with the bowing segments.

A highly concentrated tornado watch box was proposed by Rich Thompson, SPC lead forecaster, at approximately 6 pm. The tornado threat was increasing based on tornado warnings issued and damage coming in possibly related to them in Luzerne and Pike counties. Ulster, Dutchess and Litchfield counties were put in the Tornado Watch box (a watch that would last less than 4 hours).

Figure 9. KBGM base reflectivity at the 0.5 elevation angle with lightning overlay at 2145 UTC 1 December. Click on figure for movie of alternating reflectivity and base velocity. Note the extreme winds indicated in the base velocity displays associated with the bowing segments.

Figure 10. KENX base reflectivity at the 0.5 elevation angle at 2327 UTC 1 December. Note the lines of thunderstorms with bowing segments over the region.

Figure 11. KENX echo tops with lightning overlay at 2200 UTC 1 December. Note the frequent lightning throughout the area of thunderstorms, and the echo tops between 30000 feet and 40000 feet, which is very deep convection for early December.

Many more SVRs were issued with lots of wind damage from bowing segments in the strongly forced convective line(s). The initial line weakened a bit over the eastern Capital District possibly due to the slightly cooler/more stable air in the boundary layer. However...the line refired heading into western New England and the mid Hudson Valley. Three Tors were issued. One was in the mountainous terrain of Ulster County...where beam blockage occurs. Modest rotation existed with a weak mesocyclone detected. The circulation strengthened passing into western Dutchess county with several scans of a meso detected with a TVS (Fig. 12). At one point the cell exhibited 29 kts of rotation gate to gate with a VR-shear value of 0.033 s-1 on the 0.5 elevation angle of VCP-12. From past research this was on the low or marginal end for a tornado warning and very justifiable. A tornado warning was issued based on this. The last tornado warning was issued in Litchfield County after an SVR was issued. OKX and ENX radars showed modest mid-level rotation with the radar beams up at 5-6 kft. It was a tough call on this one.

a) b)

Figure 12. KENX Storm Relative Velocity (SRM) at the 0.5 elevation angle with TVS and legacy mesocyclone overlay at a) 2323 UTC 1 December and b) 2327 UTC 1 December. Note the TVS and mesocyclone indicated in addition to the rotation in the SRM display.

***What was observed***

Map of 061201_rpts's severe weather reports

 

 

 

New York

Location or County

Date

Time

Type

Mag

Dth

Inj

PrD

CrD

1 Hinsdale

12/01/2006

01:06 PM

Thunderstorm Wind

N/A

0

0

25K

0K

2 Hornell

12/01/2006

02:05 PM

Thunderstorm Wind

N/A

0

0

1K

0K

3 Wallace

12/01/2006

02:15 PM

Thunderstorm Wind

N/A

0

0

5K

0K

4 Johnson City

12/01/2006

02:56 PM

Thunderstorm Wind

N/A

0

0

0K

0K

5 NYZ009 - 018 - 036>037 - 044>046 - 056>057

12/01/2006

03:00 PM

High Wind

59 kts.

0

0

70K

0K

6 Port Byron

12/01/2006

03:00 PM

Thunderstorm Wind

N/A

0

0

10K

0K

7 Whitney Pt

12/01/2006

03:38 PM

Thunderstorm Wind

N/A

0

0

1K

0K

8 Lisle

12/01/2006

03:45 PM

Thunderstorm Wind

N/A

0

0

2K

0K

9 Marathon

12/01/2006

03:47 PM

Thunderstorm Wind

N/A

0

0

2K

0K

10 Groton

12/01/2006

03:50 PM

Thunderstorm Wind

N/A

0

0

1K

0K

11 Greene

12/01/2006

04:00 PM

Thunderstorm Wind

N/A

0

0

1K

0K

12 Smyrna

12/01/2006

04:05 PM

Thunderstorm Wind

N/A

0

0

1K

0K

13 Watson

12/01/2006

04:15 PM

Thunderstorm Wind

N/A

0

0

10K

0K

14 Camden

12/01/2006

04:18 PM

Thunderstorm Wind

N/A

0

0

3K

0K

15 NYZ053>054 - 063 - 084

12/01/2006

04:24 PM

High Wind

50 kts.

0

0

0K

0K

16 NYZ001>008 - 010>014 - 019>021 - 085

12/01/2006

04:29 PM

High Wind

58 kts.

0

0

360K

0K

17 Ohio

12/01/2006

04:51 PM

Thunderstorm Wind

N/A

0

0

0K

0K

18 Beaver River

12/01/2006

04:52 PM

Thunderstorm Wind

N/A

0

0

0K

0K

19 Clinton

12/01/2006

04:55 PM

Thunderstorm Wind

N/A

0

0

1K

0K

20 Summit

12/01/2006

05:00 PM

Thunderstorm Wind

N/A

0

0

0K

0K

21 Johnstown

12/01/2006

05:05 PM

Thunderstorm Wind

N/A

0

0

0K

0K

22 Glen

12/01/2006

05:09 PM

Thunderstorm Wind

N/A

0

0

0K

0K

23 Page Hill

12/01/2006

05:13 PM

Thunderstorm Wind

N/A

0

0

0K

0K

24 Halcottsville

12/01/2006

05:24 PM

Hail

0.88 in.

0

0

0K

0K

25 Duanesburg

12/01/2006

05:25 PM

Thunderstorm Wind

N/A

0

0

0K

0K

26 Roscoe

12/01/2006

05:30 PM

Hail

0.75 in.

0

0

0K

0K

27 Margaretville

12/01/2006

05:35 PM

Hail

0.75 in.

0

0

0K

0K

28 Saratoga Spgs Co Arp

12/01/2006

05:35 PM

Thunderstorm Wind

N/A

0

0

0K

0K

29 Barryville

12/01/2006

05:40 PM

Thunderstorm Wind

N/A

0

0

2K

0K

30 Monticello

12/01/2006

05:44 PM

Thunderstorm Wind

N/A

0

0

3K

0K

31 Loch Sheldrake

12/01/2006

05:45 PM

Thunderstorm Wind

N/A

0

0

1K

0K

32 Schroon Lake

12/01/2006

05:45 PM

Thunderstorm Wind

N/A

0

0

10K

0K

33 Port Jervis

12/01/2006

05:47 PM

Thunderstorm Wind

N/A

0

0

0K

0K

34 Glenmont

12/01/2006

05:49 PM

Thunderstorm Wind

N/A

0

0

0K

0K

35 NYZ077>078

12/01/2006

05:53 PM

High Wind

50 kts.

0

0

0K

0K

36 Rock Hill

12/01/2006

05:55 PM

Thunderstorm Wind

N/A

0

0

2K

0K

37 West Coxsackie

12/01/2006

06:01 PM

Thunderstorm Wind

N/A

0

0

0K

0K

38 Wurtsboro

12/01/2006

06:05 PM

Thunderstorm Wind

N/A

0

0

2K

0K

39 Whitefield

12/01/2006

06:06 PM

Thunderstorm Wind

N/A

0

0

0K

0K

40 Petersburg

12/01/2006

06:20 PM

Thunderstorm Wind

N/A

0

0

0K

0K

41 Rhinebeck

12/01/2006

06:26 PM

Thunderstorm Wind

N/A

0

0

0K

0K

42 Greendale

12/01/2006

06:27 PM

Thunderstorm Wind

N/A

0

0

0K

0K

43 Copake

12/01/2006

06:38 PM

Thunderstorm Wind

N/A

0

0

0K

0K

44 Monroe

12/01/2006

06:45 PM

Thunderstorm Wind

N/A

0

0

0K

0K

45 Salt Pt

12/01/2006

07:00 PM

Thunderstorm Wind

N/A

0

0

0K

0K

46 Poughkeepsie

12/01/2006

07:15 PM

Thunderstorm Wind

N/A

0

0

0K

0K

47 Ossining

12/01/2006

07:30 PM

Thunderstorm Wind

N/A

0

0

0K

0K

48 NYZ010 - 019 - 085

12/01/2006

11:00 AM

Seiche

N/A

0

0

40K

0K

49 NYZ026>027

12/01/2006

11:00 AM

Winter Weather

N/A

0

0

100K

0K

50 (jhw)jamestown Arpt

12/01/2006

11:28 AM

Thunderstorm Wind

N/A

0

0

10K

0K

51 Camden

12/02/2006

12:05 AM

Thunderstorm Wind

N/A

0

0

0K

0K

 

Vermont

Location or County

Date

Time

Type

Mag

Dth

Inj

PrD

CrD

1 VTZ013

12/01/2006

06:00 PM

High Wind

50 kts.

0

0

0K

0K

2 Shaftsbury

12/01/2006

06:12 PM

Thunderstorm Wind

N/A

0

0

0K

0K

TOTALS:

0

0

0

0

Top of Page


 

1 West Dover

12/01/2006

07:00 PM

Thunderstorm Wind

N/A

0

0

0K

0K

TOTALS:

0

0

0

0

Massachusetts

Location or County

Date

Time

Type

Mag

Dth

Inj

PrD

CrD

1 North Adams

12/01/2006

06:36 PM

Thunderstorm Wind

N/A

0

0

0K

0K

2 Lenox

12/01/2006

06:57 PM

Thunderstorm Wind

N/A

0

0

0K

0K

3 Lanesborough

12/01/2006

07:06 PM

Thunderstorm Wind

N/A

0

0

0K

0K

TOTALS:

0

0

0

0

Connecticut

Location or County

Date

Time

Type

Mag

Dth

Inj

PrD

CrD

1 Norfolk

12/01/2006

07:12 PM

Thunderstorm Wind

N/A

0

0

0K

0K

2 Winsted

12/01/2006

07:25 PM

Thunderstorm Wind

N/A

0

0

0K

0K

TOTALS:

0

0

0

0