Status:Ongoing analysis Material from: Ervin, Linus, Mohamed
Discussed in the following Daily reports:
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http://intra.ecmwf.int/daily/d/dreport/2015/02/04/sc/
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 snow storm on 27 January was caused by a cyclone that rapidly formed after 26 Jan 12z outside U.S east coast. The cyclone formed on the eastern side of an upper-level trough. The trough had moved eastward and a part of it originated from a trough that almost reached the tropics 2 days before west of Mexico.
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The below below shows our NEXRAD verification product with the last HRES forecast included (27 Jan 00z).
3. Predictability
3.1 Data assimilation
The plot below shows the MSLP increment for 26 Jan 18z.
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The plots below show the time-series of the two stations. Both stations show similar departures on 26 January, although the magnitude of the departures are not extreme.
3.2 HRES
The plots below show the 24-hour precipitation from HRES valid 27 January. Before 24 January it was little trace of the system, although there was precipitation further out on the Atlantic. All forecast but the last had too much precipitation over New York city (marked with an hourglass symbol).
Gallery includeLabel hres_tp sort comment title HRES 24-hour total precip. 27 Jan
3.3 ENS
The two series of plot below show the cyclone feature plots for valid 27 Jan 12z. The spread decreased significantly around 24 January.
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The plots below show the position of the cyclone in each ensemble member at 27 Jan 12z (symbols). The line starts 12 hours before and ends 12 hours later. Grey lines are for ensemble members, green for HRES (currently missing in the right plot), and analysis (red). The plots are from 27 Jan 00z (left), 26 Jan 12z (middle) and 26 Jan 00z (right). The westward shift is apparent in the two earlier forecasts.
3.4 Monthly forecasts
The plots below show monthly forecasts for 2-metre temperature anomalies valid for the week 26 Jan - 2 Feb.
Gallery includeLabel mnth_2t sort comment title 2-metre temperature anomalies
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.
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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.
5. Good and bad aspects of the forecasts for the event
- Strong signal first appeared 24 Jan 00z, 3 days before the event
- Precipitation too far west in the short-range forecasts
- Too slow movement of the cyclone - or a secondary low forming in the forecast?
6. Additional material
- News item on the external web