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http://intra.ecmwf.int/daily/d/dreport/2015/01/26/sc/
http://intra.ecmwf.int/daily/d/dreport/2015/01/27/sc/
http://intra.ecmwf.int/daily/d/dreport/2015/01/28/sc/
http://intra.ecmwf.int/daily/d/dreport/2015/01/29/sc/
http://intra.ecmwf.int/daily/d/dreport/2015/01/30/sc/
http://intra.ecmwf.int/daily/d/dreport/2015/02/04/sc/
Picture
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.
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.
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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 26 Jan 18z.
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The plots below show the z1000 increments for 26 Jan 18z for LWDA (left) and ELDA (right). In this cycle the DA moved the large-scale (within the cyclone developed) further east.
Observation statistics for 26 Jan 00z are available...
for radiosonde mid-troposphere temperatures are shown in the plot below. To stations (72215 and 72230) show large positive observation departures (model too cold), both in respect to first guess and analysis.
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
Gallery includeLabel hres_tp sort comment title HRES 24-hour total precip. 27 Jan
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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