An investigation of slow-moving East Coast Winter Storms during the past 55

years

Jase BernhardtNortheast Regional Climate Center

Cornell University

Why study slow-moving ECWS?

• East Coast Winter Storms (ECWS) wreak havoc on the people and infrastructure of the eastern seaboard.

• Oft overlooked is storm surge and coastal flooding that results, especially when these storms last over multiple tidal cycles.

• Examples: February 23, 2003 storm (Fast) and December 7, 2003 storm (Slow).

Fast vs. Slow Storms (Tidal cycles)• The top image shows the faster ECWS while the lower image is the slower ECWS.

• There are substantial differences between the two types of storms.

• Tide gauge information is from the NOAA Center for Operational Oceanographic Products and Services

Methodology

• Exclusively used storms found in the Hirsch (2001) study- as well as an update which tracked storms through early 2006.

• Potential storms were identified in the dashed box, but all storms had to fall within the solid box during at least two six-hourly periods.

• Three other criteria also had to be met: Closed circulation criterion

Movement criterion

Wind speed criterion

Methodology

• Utilized data from the Hirsch study and update along with an automated program to develop speed for each storm at all six-hourly points.

• Speed determined by movement between 2.5 X 2.5 degree points each period.

• Calculated the average, minimum, and maximum speed for each storm.

• Also extended these calculations to monthly, seasonal, and yearly averages.

Initial Results

• Initial results followed what would be climatologically expected.

950 960 970 980 990 1000 1010 10200

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Average Speed Vs Minimum Central Pressure Attained

Initial Results

• Monthly average storm speed also showed a clear, predictable trend, as early and latter portions of the season see weaker storms.Month Average SpeedOctober 24.68November 29.31December 33.48January 34.27February 33.43March 33.12April 26.52AVG 31.05

• Middle months sustained higher average speeds despite more storms.

• Will come back to this table soon as results are looked at in more detail.

Initial Results

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 20050

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Average Speed vs. Year

ENSO + ECWS

• Previous studies including Hirsch and my own work have concluded that El Niño years have more East Coast Winter Storms.

• No such connection exists for storm speed and ENSO, however.

• During El Niño years more southern storms form, but there is little correlation between latitude of origin and storm speed.

Origin + ECWS

• Longitude of origin did seem to show a connection to storm speed.

• Of the 13 months with the western most origins, 12 featured faster than normal storms.

• All 13 of these months (including March 1993) also featured south of average origins.

Upper Air Pattern + ECWS

• A distinctive upper air pattern accompanied fast and slow storm months, specifically heights at 500 mb and zonal wind at 300 mb.

• These patterns held up when looking at multiple fast/slow months as well.

• Significant deviations from climatological norms were also present during these months.

Upper Air Pattern + ECWS

• 500 mb height pattern for slow (left) and fast (right) storm months.

Upper Air Pattern + ECWS

• 300 mb zonal wind pattern for slow and fast storm months.

Upper Air Pattern + ECWS

• 300 mb zonal wind anomalies.

Upper Air Pattern + ECWS

• 500 mb heights anomalies.

NAO + ECWS

Month Average Speed NAO IndexOctober 24.68 9.58November 29.31 10.41December 33.48 13.11January 34.27 14.28February 33.43 13.09March 33.12 10.91April 26.52 7.93AVG 31.05 11.33

• Going back to month vs. speed, the monthly speed trend matches up with the monthly NAO trend.

Pressure (Azores High) – Pressure (Icelandic Low)

NAO Data: Dr. Sultan Hameed, Stony Brook

NAO + ECWS

• Unlike ENSO, NAO has a significant correlation with ECWS storm speed.

• 17 of the top 20 fastest storm speed months were NAO positive.

• Meanwhile, 9 of the top 10 most negative NAO months had below average storm speed.

• NAO positive months also often shared the upper air pattern signature with fast months.

• This was not as common for NAO negative and slow months, however.

Case Study- Late February 2010 Storm

• All of the elements for an extremely slow moving ECWS came together for the final storm of the 2009/2010 season.

• Very negative NAO the entire season.• The Upper Level wind pattern matched that of

slow-moving storm months.• Result-robust snowfall amounts for much of

the Northeast!

NAO

• The entire 2009/2010 season saw negative NAO coupled with El Niño conditions.

• The subtropical jet was active, while a blocking high persisted.

• This led to many storms, which generally moved slowly.

• The NAO Index for February 2010 was -1.98.

500 mb heights pattern, Feb 25-28

• 500 mb trough pushed well to the south of the Northeast.• Upper level low over Northeast = weak steering.

300 mb zonal wind pattern, Feb 25-28

• Bull's-eye of weak/NEGATIVE winds over the Northeast and New England.• Hence, the surface low moved slowly and then retrograded once inland.

Results

• The surface low tracked up the east coast February 25, and stalled out near New York City on the 26th.

• Then, the system, moved inland and retrograded on February 27th.

• The low occluded and weakened over New York State on February 28th.

• Snowfall amounts were considerable over a large swath of this region.

NESIS Report

Upcoming Work

• Delve further into the statistical “grunt work.”• Look at the upper air pattern and storm speed

connection in more detail.• Ascertain how much stock can be placed in

the longitude of origin vs. speed connection.• Apply to weather forecasting issues.

Questions ?