Difference between 24 hours cumulated precipitations predicted by ALADIN (between 6 and 30 hours forecast ranges) and observed over France on second semester 2000.
(more details : samuel.westrelin@ meteo.fr)
1. COMMENTS OF CONTINGENCY TABLE - SECOND SEMESTER 2000
Tables below are the cloud cover and precipitation contingency tables for ALADIN-FRANCE 36 hours forecast range. Classes have been defined by EWGLAM.
These classes correspond to :
RR < 0.1 mm in 6 hours : no precipitations, 0.1 £ RR < 0.2 : light, 2.0 £ RR < 10 mm : moderate and RR ³ 10 mm : heavy. Units for classes intervals of cloud cover are octas.
In these contingency tables, the blue (respectively red) color means that the model forecasted a class of smaller (bigger) rank than observed, so it underestimated (overestimated) the parameter.
Main features are similar to the previous semester.
CLOUD COVER
The percentage of correct forecasts is only 49%. High cloud covers are much less often forecasted than observed (22% against 46%) this being mostly due to an overestimation of mid cloud covers. When the model predicts mid cloud cover class, in 49% of cases it is actually high one which is observed.
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200007-200012 |
CLOUD COVER |
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MODEL : |
ALADIN |
|
00 H start | ||
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AREA : |
FRANX01 |
Forecast Range |
36 H | ||
|
182 days |
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Forecast |
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0 - 2 |
3 - 6 |
7 - 8 |
SUM | ||
0 - 2 |
12.3% |
5.4% |
0.4% |
18.0% | |
Obs. |
3 - 6 |
10.0% |
20.8% |
5.5% |
36.4% |
7 - 8 |
4.3% |
25.5% |
15.8% |
45.6% | |
SUM |
26.6% |
51.7% |
21.7% |
43760 | |
|
Correct : |
48.9% |
Rousseau : |
0.21 |
Heidke : |
0.23 |
PRECIPITATIONS
The percentage of correct forecasts is 69%. Globally there is a quite good agreement between the predictions of a class and the observations. A tendency to predict too often light precipitations when no precipitations have been observed appears (12% of cases). The "no rain" class is not often enough forecasted : 67 against 73%. Climatology of heavy and moderate rain is quite good.
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200007-200012 |
PRECIPITATIONS |
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MODEL : |
ALADIN |
|
00 H start |
|||
|
AREA : |
FRANX01 |
Forecast Range |
36 H |
|||
|
182 days |
||||||
Forecast |
||||||
NO rain |
LIGHT |
MODERATE |
HEAVY |
SUM | ||
NO rain |
58.6% |
11.8% |
2.6% |
0.3% |
73.3% | |
LIGHT |
6.3% |
6.1% |
2.9% |
0.2% |
15.6% | |
Obs. |
MODERATE |
1.9% |
3.5% |
3.6% |
0.6% |
9.6% |
HEAVY |
0.2% |
0.4% |
0.7% |
0.4% |
1.6% | |
SUM |
67.0% |
21.8% |
9.7% |
1.5% |
46737 | |
|
Correct : |
68.7% |
Rousseau : |
0.32 |
Heidke : |
0.33 | |
2. COMMENTS OF SCORES AGAINST SYNOP - SECOND SEMESTER 2000
The scores (bias and root mean square error) are calculated against SYNOP over the whole domain ALADIN-FRANCE. Scores are averaged over the second semester 2000.
We use about 200 synoptic stations over the domain.
MSLP
The RMS rises with forecast range from 0.6 to 2.3 hPa. The model underestimates this parameter from 18 hours range till 48 hours to reach -1. hPa.
CORRECTED TEMPERATURE
It is slightly overestimated on afternoon (forecast ranges 12 and 36 hours) and underestimated on evenings and nights, about 0.5°K.
WIND INTENSITY
Its RMS is quite stable with ranges. It is not biased on night but clearly underestimated on afternoon.
3. COMMENTS OF PRECIPITATIONS MAPS - SECOND SEMESTER 2000
In France during this semester, the cumulated precipitations are very strong. Many floods where observed over west of France. In this region, forecast underestimation appears in most of the cases when observed precipitations have been particularly high. On the picture, overestimation of forecasted precipitations is observed along Atlantic coasts like last semester. Over flat regions, cumulated precipitations are often too moderate.
Difference between 24 hours cumulated precipitations predicted by ALADIN (between 6 and 30 hours forecast ranges) and observed over France on second semester 2000.
Observed 24 hours cumulated precipitations (from 06 UTC to 30 UTC) over France on second semester 2000 .
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