An Unusually Snowy Week for Britain: Heavy Snowfalls Feb 1-2,

2009 and February 5-6, 2009

Stephen J. Flood HPC, Camp Springs, MD

The February 2009 SnowsHistorical Significance

• Heaviest snowfalls in 18 years for portions of SW London, the E Midlands, and SW England [1]

• Long stretch of unseasonably cold weather the first half

of February • Temperatures fall as low as -18.4C (-1F) in Aviemore, in

the Scottish highlands [2].

• Other localized significant snowfalls in the UK (not

included in this study) fell during this cold period on the 9th, 10th,and 12th of February [1], [2].

1Courtesy of Tim Hewson, ECMWF, and 2Wikipedia

Effects of this Stormy Period• 4500 UK Schools closed on 3 February

• Transportation links greatly disrupted on February 2nd , including air traffic.

• Many snow-related casualties, including 4 deaths.

• Many sporting events disrupted.

• More heavy snow Feb 5-6 across Srn England- a whopping 55cm overnight in upper level deformation (lift) zone in SW England near Okehampton.

• A rain/heavy wet snow mix from a third storm across Srn England on Feb 9th combined with high tides to produce river flooding. Some damage from heavy wet snow at higher elevations to power lines/trees.

(1Courtesy of Wikipedia)

Radar Picture 02/0015Z showing moderate to heavy Snowfall over SE England

Ekofisk (North Sea) Sounding Loop

Nottingham Sounding Loop • Strong Advection Patterns define heaviest snowfall

Larkhill Sounding Loop

Abbreviated Surface Obs at London Heathrow, EGLL Time (Z) Wind (kt) Wx T/Td

011420……… 06018 2/-6

011520……… 06017 1/-8

011620……… 07017 0/-8

011720……… 06012 -1/-6

011820……… 05010 -2/-6

011920……… 04009 -2/-5

012020……… 05008 -2/-3

012120……… 04009 -SHSN -2/-3

012220……… 04008 -3/-4

012320……… 03008 SN -3/-3

020020……… 04006 SN -2/-3

020220……… 03009 -SN -2/-2

020320……… 02008 -SN 2/-3

020420……… 04007 -SN -2/-2

020520……… 03009 SN -2/-3

020620……… 03008 SN -2/-3

020720……… 03008 SN -2/-2

020820……… 02007 SN -2/-2

020920……… 03007 -SN -2/-2

021020……… 03007 -1/-2

021120……… 03006 -SN 1/-2

021220……… 02007 -SN -1/-2

021320……….02006 -SN -1/-2

021420……….01005 SN 0/-1

021520……….36007 SN 0/-1

021620……….36006 -SN 0/-1

021720……….36006 -SN 0/0

021820……….36004 -SN 0/0

021920……….VR02 -SN 0/0

022020……….CALM 1/0

022120……….17003 -RA 1/0

022220……….17006 BR 0/0

Surface Highlights of Feb 1-6, 2009

• First Storm: February 1-2, 2009-affected much of England especially the London area

• Second Storm: February 5-6, 2009. SW England hard hit with localized very heavy snowfall

Surface 09020112Z

Surface 09020200Z

Surface 09020212Z

Surface 09020300Z

Surface 09020312Z

Surface 020500Z

Surface 020606Z

• A westward moving deep cold core brings an

initial heavy snowburst to England the evening of Feb 1 and early on the 2nd.

• After making a cyclonic loop passing SW of Britain, it is picked up by a system to its N and heads back ENE late on the 5th into the 6th through the English Channel.

Synoptic Evolution: 500mb

500MB02010009

500MB02011209

500MB02020009

500MB02021209

500MB02030009

500MB02031209

500MB02040009

500MB02041209

500MB02050009

No 500mb Maps beyond 2009020500Z: Incomplete Data Available

Synoptic Evolution: 850mb

The chain of events at 850 mb is of particular interest since climatologically, Great Britain has a hard time accessing the low level cold air needed to support sustained heavy snowfall.

850MB09020100Z

850MB09020112Z

850MB09020200Z

850MB09020212Z

850MB09020300Z

850MB09020312Z

850MB09020400Z132

850MB09020412Z

850MB09020500Z

850MB09020512Z126 126

123

850MB09020600Z

850MB09020612Z

Snow Depth Analysis (cm)

• The Analysis is an estimate of total snowfall Feb 1-6. 6cm was added to reported weekly snow depths to approximate settling and melting of the two main snowfall events: Feb 2 and Feb 5-6, 2009.

• An excellent discussion of snowfall measurement difficulties is found in Northeast Snowstorms: Overview, by Paul J Kocin and Louis Uccellini.

• Elevation was also taken into account in the analysis, with additional snowfall data from Wikipedia. Estimated snowfall totals (cm) are plotted in bold white. Contours (cm) are drawn in purple, with isohyets in smaller yellow labels.

Topography Map of Great Britain

Est. Snowfall Anal (cm) Feb 1-6, 2009

Summary

• In the UK, the low level cold air source for widespread heavy snowfall comes from the East, rather than the North as in snowfall events along the E Coast of the USA.

• “Lake effect” enhancement of snowfall as cold air destabilizes crossing the North Sea can be a major factor.

• For additional information see link to article by 4Richard Grumm in References on the same storm system from a numerical model point of view.

References• 1. Hewson, ECMWF Data Contact, 29 June 2009

• 2. Wikipedia, February 2009 Great Britain and Ireland Snowfall, pages 1-10.

• 3. Paul J Kocin and Louis Uccellini, Northeast Snowstorms: Overview, Climatology, Ch. 2, page 9.

• 4. Grumm, Richard. Western European Snow of 1-2 February 2009.

(http://nws.met.psu.edu/severe/2009/03Feb2009.pdf)