The April 28, 2011 Severe Weather and Flash Flood Event

Mike Evans / NWS Binghamton, NY

Outline

Large-scale pattern / meso-analysisRadar dataHigh resolution model outputSummary

500 mb heights and vorticity

Surface plot – 09z

Equivalent potential temperature, omega and wind speed cross section – 12z

SPC surface and 700 mb frontogenesis – 09z

SREF CAPE and 850 hPa wind

SPC analysis 0-1 km shear and significant tornado parameter

SPC Guidance

Reflectivity and storm relative motion 0522 – 0540 UTC

Reflectivity and storm relative motion 0654 – 0830 UTC

Reflectivity and storm relative motion 0945 UTC

13

T-9 T-8 T-7 T-6 T-5 T-4 T-3 T-2 T-1 T-00

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Verified Median NROT (Supercell tornadoes; Tim Humphrey)

.5 NROT

.9 NROT1.4 NROT1.9 NROT

NR

OT

14

T-5 T-4 T-3 T-2 T-1 T-00

0.2

0.4

0.6

0.8

1

1.2

Verified Median NROT (QLCS tornadoes; Tim Humphrey)

.5 NROT

.9 NROT1.4 NROT1.9 NROT

NR

OT

Normalized rotation – Erin tornado (QLCS)

Normalized rotation – Danby tornado(QLCS – broken S)

Normalized rotation – Pharsalia tornado (mini-supercell)

Normalized rotation – McDonough tornado (mini-supercell; range folding)

Normalized rotation – Columbus tornado (mini-supercell; RFD spin-up)

Normalized rotation – Herrick tornado(QLCS)

Severe reports

BGM CWA tornado climatology

High resolution model 1 km AGL reflectivity – valid 09z

High resolution model 1 km AGL reflectivity – valid 12z

HRRR 1 km AGL reflectivity valid 08z

SummaryTornadoes and flash floods affected central

New York and northeast Pennsylvania during the early morning on the 28th.

This was only the 2nd time since the late 1990s that a tornado was reported in our area between midnight and 9 am.

Tornadoes occurred with a variety of convective storm structures and a variety of rotational evolution patterns.

Summary continued00z hi resolution model runs forecast a

variety of structures; mostly broken lines of convection, composed of small line segments and some individual cells.

The 00z HRRR model was too weak with the line (especially over NY), but subsequent runs trended toward a better forecast.

All of the 00z models were too far west (too slow) with the convection from 06z through 12z.