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Fig4.2-10: The plot shows the difference in 500hPa ensemble mean height initialised DT 00UTC 26 October 00UTC 2024 (black) and DT 00UTC 28 October 00UTC.  At 2024 (red).  In the 26 October forecast run, VT T+168h 192 01 Nov the forecast has a trough over Scandinavia while .  In the 28 October forecast run, VT 28 October, VT T+120h 144h 01 Nov the forecast has something like a ridge, shown weak ridge.  This is highlighted by a large area of negative (purple) difference.  The error can be traced back to north-eastern U.S.A and eastern Canada at DT 00UTC 26 October, T+48h where compared with 26 DT 00UTC 28 October, T+0).  In this case it is difficult to identify severe weather in the model or in reality, or any significant analysis increments over that part of U.S.A.

The jump between the forecasts has a major impact on the forecast surface weather in Scandinavia.  The forecast of DT 00UTC 26 October develops an intense low over Finland on Friday at T+192 VT Fri 1 Nov bringing strong winds and cold air with a cold snap over southern Scandinavia.  The forecast of DT00UTC 28 October develops a broader low and more zonal winds over southern Scandinavia with more neutral conditions.

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Fig4.2-11: Comparison between the 26 October forecast the forecast from DT 00UTC 26 October 2024 (black) and the corresponding analyses (red).  The forecast from DT 00UTC 26 October forecast 2024 (black) failed to capture the weak ridge over Scandinavia shown by a large negative (purple) difference from the analysis.  The forecast of DT 00UTC 26 October forecast  was 2024 was effectively a bust.

Incorrect analysis increments

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