Status:Ongoing analysis Material from: Ervin, Linus
Discussed in the following Daily reports:
http://intra.ecmwf.int/daily/d/dreport/2015/01/26/sc/
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1. Impact
On 27 January 2015 a blizzard hit the northern part of the U.S east coast. The worst affected areas were in a band from Long Island towards Boston and further north. The storm was expected to also hit New Jersey and New York City and strong actions were taken before the event (closing motorways etc.). However, this part only got a little snow and NWS was criticised. The model that gave the strongest indication for severe snow over NYC was ECMWF.
2. Description of the event
The plot below shows NEXRAD 24 hourly precipitation product which is valid for 00-00 yesterday and the NWS snow total map from snow fall reports (produced from a lot of observations in the order of a hundred). The nexrad is in mm and the snow is in inch. The maximum precip was 20-35 mm in the east of the area, around 7-10 mm in NYC. The snow however was up to over 30 inches (around 36 inches as the highest observation) and about 5-10 in NYC. Most of the precip was between 00z-00z, at least in the southern part of the affected areas anyway, so the nexrad map is more or less relevant estimation. The few observations we have in the GTS (for the whole 36 hour period) are in line with this nexrad map.
The below below shows our NEXRAD verification product with the last HRES forecsast included.
3. Predictability
3.1 Data assimilation
The plot below shows the MSLP increment for 27 Jan 18z.
3.2 HRES
HRES 24-hour total precip. 27 Jan
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3.3 ENS
Cyclone feature plots for 27 Jan 12z max snowfall
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EFI snowfall 27 Jan
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The plot below shows the CDF for 24-hour snowfall for NYC for 27 January.
The plot below shows the CDF for 24-hour snowfall for Boston for 27 January.
3.4 Monthly forecasts
The plots below show monthly forecasts for 2-metre temperature anomalies valid for the week 26 Jan - 2 Feb.
2-metre temperature anomalies
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3.5 Comparison with other centres
The plots below show comparison between ECMWF, UKMO and NCEP HRES for MSLP and precipitation. It is quite clear that the last few runs, apart from the last (27.00) UKMO and also NCEP were better, especially the MetOffice model. The UKMO (and with a little bit less clarity NCEP) MSLP fields are very similar to the analysis and also very consistent. However, the EC-HRES had the eastward shift already discussed yesterday. The earlier runs (2412 2500 and 2512) have the same feature, UKMO and NCEP had the cyclone more to the east.
The 2300 2312 and 2400 runs are a mixed bag, with I think UKMO being the best. We had a good forecast only from the 2400 run, while the metoffice model was quite good already 24 hours before and also better 12 hours earlier. However, their 2400 run was worse.
4. Experience from general performance/other cases
201402 - Snowstorm - US east-coast
201401 - Snowstorm - North-eastern U.S.