Validation of the NCEP CFS forecasts

1
Validation of the NCEP CFS forecasts

• Suranjana Saha
• Environmental Modeling Center
• NCEP/NWS/NOAA/DOC

2
Chosen Topics

• Validation of Extremes, especially in 500 hPa
  geopotential, temperature and precipitation
• QBO validation
• SST validation by ocean basins

3
About extremes

• What is an extreme?
• Large departure from normal, for example in
  temperature and/or precipitation, we have heat
  waves, cold spells, droughts, floods, etc.
• Given how important the effect of extremes is on
  society (life, property and the economy), did the
  CFS predict these events ?

4
About extremes

• We evaluate skill in CFS predictions only on
  occasions when an extreme occurred in
  observations.
• Using monthly mean data, we define an
• extreme value of anomaly of variable gt
  2 or 1.5 times local standard deviation.

5
EXTREME EVENTS IN PNA and NAO In 500 hPa
Geopotential (Reanalysis 2 used for validation)
6
(No Transcript)
7
(No Transcript)
8
(No Transcript)
9
(No Transcript)
10
(No Transcript)
11
(No Transcript)
12
(No Transcript)
13
(No Transcript)
14

• Conclusions (for PNA and NAO)
• Modest capability to predict extreme values in
  PNA and NAO.
• PNA extremes mainly related to ENSO (Feb 1983,
  Jan 1989)
• NAO extremes appear equally predictable (Nov
  1993, Feb 1986). Causes less clear
• Skill for extremes, in terms of anomaly
  correlation, is an amplified version of skill in
  general.

15
EXTREME EVENTS IN TEMPERATURE (Reanalysis-2 used
for validation)
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
(No Transcript)
27
Conclusions (for Temperature) 1. US
Modest skill mainly in late spring 2. Europe No
skill 3. India Modest skill mainly in
winter 4. Africa Modest skill mainly Northern
winter 5. South America Moderate skill
throughout the year.
28
EXTREME EVENTS IN PRECIPITATION (Xie-Arkin Precip
used for validation)
29
(No Transcript)
30
(No Transcript)
31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
(No Transcript)
35
(No Transcript)
36
(No Transcript)
37
(No Transcript)
38
(No Transcript)
39
(No Transcript)
40
(No Transcript)
41

• Conclusions (for Precipitation)
• US Modest skill mainly in winter
• Europe No skill at all
• India Modest skill mainly Feb-May
• Africa Modest skill mainly Aug-Jan
• South America Modest skill throughout the year
  only for lead-1.
• (Keep in mind there are complications when
  precipitation is skewed, or standard deviation is
  small (like deserts).

42
QBO MONTHLY MEAN ZONAL MEAN ZONAL WIND ANOMALY
AT THE EQUATOR (Reanalysis-2 used for validation)
43
(No Transcript)
44
(No Transcript)
45
(No Transcript)
46
(No Transcript)
47

• Conclusions (for QBO)
• Baseline experiment regarding the QBO.
• (No skill was expected)
• The phenomenon disappears slowly in CFS, but is
  clearly identifiable in forecasts out to 6
  months. This is better than anybody expected.
• CFS has 64 levels in the vertical, of which 20
  are above 100 hPa. The top of the model is at 0.2
  hPa. It is possible that high density of levels
  near 50 hPa has been helpful in sustaining zonal
  winds.

48
VALIDATION OF SST FOR DIFFERENT OCEAN
BASINS (NCEP GODAS used for validation)
49
(No Transcript)
50
(No Transcript)
51
(No Transcript)
52
(No Transcript)
53
(No Transcript)
54
(No Transcript)
55
(No Transcript)
56

• Conclusions (for SST)
• Spring Barrier clearly evident in prediction of
  SST in Nino 3.4 and Northern Pacific Regions
• Moderate skill is present in the Indian Ocean
  only during spring.
• Skill highest during September for both Southern
  Atlantic and Pacific Oceans.
• Moderate skill is present in the equatorial
  Atlantic Ocean including the hurricane season
  (ASO)
• Least skill present in the Northern Atlantic
  Ocean, mainly during the winter.