Snowfall during anticyclonic, non-frontal, and foggy conditions is surprising. Because it is often not forecast, it can present a hazard to transport and modify the surface albedo. In this report, we present some observations of snowfall during conditions of freezing fog in the UK during the winter of 2008/09

Harrison, R. Giles

Wood, Curtis Ron

English

arXiv

Abstract: Snowfall during anticyclonic, non-frontal, and foggy conditions is surprising. Because it is often not forecast, it can present a hazard to transport and modify the surface albedo. In this report, we present some observations of snowfall during conditions of freezing fog in the UK during the winter of 2008/09

Curtis R. Wood

R. Giles Harrison

CiteSeerX

1 Some reports of snowfall from fog during the UK winter of 2008/09

Central Archive at the University of Reading

9 February 2009  http://arxiv.org/abs/0902.1326  1  Some reports of snowfall from fog during the UK winter of 2008/09 Curtis R. Wood* and R. Giles Harrison Department of Meteorology, University of Reading, UK  Abstract: Snowfall during anticyclonic, non-frontal, and foggy conditions is surprising. Because it is often not forecast, it can present a hazard to transport and modify the surface albedo. In this report, we present some observations of snowfall during conditions of freezing fog in the UK during the winter of 2008/09. Keywords: Snow fog, anthropogenic snowfall event, freezing fog.  Introduction Snow falling from freezing fog† during non-frontal conditions has been reported elsewhere (e.g. Parungo and Weickmann 1978, Koenig 1981, Van den Berg 2008). In those cases, it appears that anthropogenically-produced particles were present and contributed to the snow production, hence these events are usefully labelled Anthropogenic Snowfall Events (ASEs). Two further such snowfalls that occurred during non-frontal freezing fog conditions in the UK during the winter of 2008/09 are reported here. Event 1: 31 December 2008 Freezing fog was the sole weather reported at most synoptic stations across the UK and central Europe (radiosonde ascents showed a typical fog depth of 300–400 m) on 31 December 2008. Despite the absence of frontal activity (Figure 1) and cloud (Figure 2) over the UK, there were reports of snow at Hereford, Dudley, Gloucester, Watlington, Tadley, Eccles, and mentioned on the UK’s BBC television weather forecast.                                                  * c.r.wood @ reading.ac.uk † We propose that since snow grains falling from freezing fog are drizzle-like, we term the precipitation as swizzle (a contraction of the words ‘snow’ and ‘drizzle’). Some reports of snowfall from fog during the UK winter of 2008/09  2     Figure 1: Synoptic analyses at 06 hours UTC, on 31 December 2008 (left) and 10 January 2009 (right). (With permission from the Met Office.)   Figure 2: Cloud radar profiles for 31 December 2008 and 10 January 2009 at Chilbolton, Hampshire. In both cases no cloud was observed until after 12:00, and that was thin cirrus cloud above ~ 7 km. (With permission from CloudNet; www.cloud-net.org)  Wood and Harrison 2009 (http://arxiv.org/abs/0902.1326) 3 In Hereford, an opportunity presented itself to drive a car through and around Hereford to make observations of lying and falling snow, take photographs and record air temperature. The map (Figure 3) shows that most snow was observed within a kilometre of the city centre, and that towards the west there was snow observed several kilometres away in Breinton villages. The edges of the snow area were ascertained in all compass directions. Photos of falling and lying snow were taken at many of the locations (Figure 4), and the route and timings are listed in the Appendix.  Figure 3: Central Hereford (map constructed using Google Maps), 31 December 2008 from 13:20–17:00. Blue pins are where falling snow was observed, purple pins are where lying snow was observed, and red pins are where there was no evidence of snow at all.   Figure 4: Photographs around Hereford on 31 December 2008 at times 13:34, 13:50 14:10, 14:25, 16:00, and 16:30 (the locations can be inferred from the Appendix). Note the falling snow in photograph (a). Some reports of snowfall from fog during the UK winter of 2008/09  4 In Gloucester, the maximum temperature was –1.2°C and the minimum was –5.9°C (Severn Tales Weather Station, Figure 5). Snow was seen falling at about 08:30 for 10 minutes in the Brooklands Park area of Longlevens (Bennett 2009), as marked on Figure 6.  Figure 5: Gloucester (map constructed using Google Maps) on 31 December 2008. Blue pins are where snow was reported, the red pin is where there was no evidence of snow at all, and the yellow pin is SevernTales Weather Station.   Figure 6: Photographs around the Longlevens area of Gloucester of the 31 December 2008 event of snowfall from fog. (With permission from Dave Bennett [a–d] and the Gloucester Citizen [e–f].) Wood and Harrison 2009 (http://arxiv.org/abs/0902.1326) 5 Event 2: 10 January 2009 Conditions were of freezing fog across southern UK (again in the absence of cloud (Figure 2) and frontal activity (Figure 1)), and temperatures until noon varied between –5.5 and –2.6°C at the University of Reading’s Atmospheric Observatory (www.met.rdg.ac.uk/~fsdata/obshome.html). Following a general email around the Meteorology Department, responses were compiled to reveal the extent of falling and lying snow in and around Reading (Figure 7). There was sufficient snow to require car windscreens to be cleared and to remain lying all day. Almost all observers volunteered that they thought the snow was very slight, consisting of small flakes and ‘like desiccated coconut’. A photograph was taken of the snow deposits on some garden furniture (Figure 8). Snowfall times varied slightly between observers, but most reports were at the times of 06:00, 09:00–10:00, and 11:00–12:00.  Figure 7: Reading (map constructed using Google Maps) on 10 January 2009. Dark blue pins are lying snow, light blue pins are falling snow, purple pins are very light falling snow, and red pins are where there was no evidence of snow at all.   Figure 8: Snow grains about 5 mm long, on garden furniture in Woodley (east of Reading town centre) at 09:00 on 10 January 2009. (With permission from Mike Blackburn.) Some reports of snowfall from fog during the UK winter of 2008/09  6 Closing remark These observations presented evidence for snowfall from freezing fog during non-frontal, anticyclonic conditions. There are growing numbers of reports of these events in the UK. Acknowledgements Thanks to Annette Osprey for help with the observations in Hereford; Dave Bennett, Karen Aplin, and Chris Witts for observations in Gloucester; numerous members of the University of Reading’s Meteorology Department for observation around Reading (including Mike Blackburn for the photograph); UK Met Office for synoptic analyses; and CloudNet for the cloud radar images.  References Bennett, D.  2009. In Snow and frost make for a magical new year: Gloucester Citizen, 2 January 2009. Koenig LR. 1981. Anomalous snowfall caused by natural-draft cooling towers. Atmospheric Environment 15: 1117–1128. Parungo AA, Weickmann HK. 1978. Snowfall induced by a power plan plume. Geophysical Research Letters 5: 515–517 Van den Berg W. 2008. Fog turning into snow. Weather 63: 248.   Appendix Below is the route taken to make the observations in Hereford, 31 December 2008. Times in hours UTC. 13:20 A49 North   No evidence of snow, -1.5°C outside city 13:30 Homer Road   No evidence of snow 13:34 Whitecross Common   Falling and settled snow 13:35 Chave Court Place   Falling and lying snow 13:37 The Vines   Falling and lying snow 13:38 Grandstand Road   Very light falling snow 13:39 Yazor Road   No snow 13:40 Sherrington Drive   No snow 13:41 Baggallay Street   Snow stopped falling 13:42 Plough Lane   Falling snow, 1°C Wood and Harrison 2009 (http://arxiv.org/abs/0902.1326) 7 13:43 Friar Street   Lightly falling snow, 1.5°C 13:44 Edgar Street   Heavier snow falling 13:45 Penhaligon Way   Very slight falling snow 13:49 Newtown Road   Very very slight falling snow 13:50 PC World   No falling snow, snow on some cars and posts 14:10 Widemarsh Street   Lying snow; no falling snow to start, then light falling snow 14:12 Blackfriars Street   Light falling snow, lying snow, 2.5°C 14:20 Blueschool Street   No falling snow, snow on ground 14:25 Cantilupe Street   Intermittent light snowfall, lying snow 14:30 Bartonsham Road   Lying snow 14:31 Outfall works road   No snow, 3.5°C 14:32 Hampton Park Road   No snow 14:35 Station approach   Lying snow 14:36 Rockfield Road   No snow, 4.5°C 14:38 Aylestone Hill   No snow 14:39 Venn's Lane   No snow 14:41 Old School Lane   No snow 14:42 Roman Road / Old Sch   No snow 14:44 Starting Gate   No snow 14:45 Roman Road / Kempton   No snow 14:46 Canon Pyon Road / Roman   No snow 14:48 Bakers Lane   No snow 14:49 Three Elms Road   No snow 14:50 Wordsworth Road   Lying snow, 0.5°C 14:51 Barrie Road   Lying snow 14:53 Emlyn Avenue   Lying snow 14:55 Westfaling Street   Lying snow 15:00 Breinton Road   Lying snow, 0.5°C 15:05 Upper Breinton   Lying snow 15:10 Breinton   No snow 15:15 Swainshill South   No snow 15:17 Swainshill   No snow 15:22 Bramley Court   No snow 15:23 Cotswold Drive   Lying snow (very patchy) 15:35 Barton Road   Lying snow 15:37 ASDA   Lying snow 15:39 Ross Road / Holme Lacy   Lying snow 15:40 Ross Road / Bullingham   Lying snow 15:42 Ross Road   Lying snow 15:44 Rotherwas Relief Road Roundabout   No snow 16:00 Coningsby Street   Lying snow 16:30 High Town   Lying snow 17:00 School   Playground covered in snow  

In Snow and frost make for a magical new year:

Snowfall induced by a power plan plume.

Some reports of snowfall from fog during the UK winter of 2008/09

Some reports of snowfall from fog during the UK winter of 2008/09

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