Status:Ongoing analysis Material from: Fernando, David L., Linus
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1. Impact
A major storm was responsible for the floods in California on 17-19 February (strong winds were reported as well). This was not the first event of the season and California has been battered by anomalous wet weather. The week before more than 150K people were forced to abandon their homes due to a problem with a crack in Lake Oroville's dam as a result of excessive water. The anomalous wet season came after several years of drought conditions in California.
2. Description of the event
The extreme event was associated with a change of the weather pattern. The sequence of MSLP & 200hPa winds maps below are valid between 14 to 19 February shows the high pressure system, located NE Pacific, retreating (& weakening) westwards allowing the jet and disturbances to move towards the West Coast. A rapid cyclogenesis is taking place steered by the upper level jet as it moves SE towards the Baja California.
Daily totals of "observed" rainfall are available at the NWS (NOAA) web site. The word is in quotes because the maps were generated from the rain gauge "against long term climatologic precipitation (PRISM data), and derived amounts are interpolated between gauge locations" in mountain areas, which seems to be this case. The 3 maps show the rain pattern sliding down the coast of California.
The totals (24h) reported by the rain gauges for the 18@12 in south of California are displayed below (inch). They seem to be consistent with the totals generated for the gridded map.
3. Predictability
3.1 Data assimilation
3.2 HRES
3.3 ENS
The EFI signal of abnormal rainfall over the region 7 days before the event (and SOT values indicating an extreme scenario). As we get close to the event the EFI become higher.
3.4 Monthly forecasts
3.5 Comparison with other centres
4. Experience from general performance/other cases