A case study of tropical extratropical interaction Yucheng

Outline – Ensemble forecasts from NCEP and ECMWF showing mean and spread of mean

On Oct 14, 12 Z two low pressure systems developed Yucheng Song and Zoltan

Forecasts made starting with different initial dates NCEP Ensemble initialized on Oct 10, 00

A map taken from the previous slide shows the forecasts on a 4. 5

Forecast loop – initial time Oct 10 00 Z The animation on the left

MSLP animation (12 Z forecast added to mimic analysis) The animation on the left

Global IR animation – an example of tropical – extratropical interaction Yucheng Song and

Comparison of initial conditions – NCEP vs ECMWF - Mean Sea Level Pressure on

Difference of Mean Sea Level Pressure on Oct 11 00 z, 2005 between NCEP

Expected forecast error reduction in verification region by ETKF method using 19 -member NCEP

Precipitation verification – heavy rainfall was produced by the first system near Gulf of

Global PQPF animation - NCEP Global Ensemble Animation shows how the first system near

The blob shows the center of forecast error reduction evolution with forecast lead time

Summary • Influence of organized tropical convection on extratropical circulation – Tropical system picked

Summary (continued) • ETKF targeting method with ensemble from – NCEP - identified area

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A case study of tropical extratropical interaction Yucheng Song and Zoltan Toth Environmental Modeling Center National Centers of Environmental Prediction National Weather Service NOAA Yucheng Song and Zoltan Toth @EMC. NCEP. NWS. NOAA

Outline – Ensemble forecasts from NCEP and ECMWF showing mean and spread of mean sea level pressure – The ECMWF ensemble forecast is initialized 12 hour earlier than NCEP – Global IR image animation showing how the tropical convection interact with extra-tropical system – Difference in NCEP and ECMWF analyses for the case – Expected forecast error reduction in the verification region by NCEP and ECMWF ensembles using ETKF method – Precipitation verification by observation and probability forecast from NCEP global ensemble forecast – Animation of expected forecast error reduction by NCEP ensemble – Summary and discussion Yucheng Song and Zoltan Toth @EMC. NCEP. NWS. NOAA

On Oct 14, 12 Z two low pressure systems developed Yucheng Song and Zoltan Toth @EMC. NCEP. NWS. NOAA

Forecasts made starting with different initial dates NCEP Ensemble initialized on Oct 10, 00 z was able to predict the low pressure system near Gulf of Alaska on a 4. 5 day lead time Yucheng Song and Zoltan Toth @EMC. NCEP. NWS. NOAA

A map taken from the previous slide shows the forecasts on a 4. 5 day lead for NCEP forecast, 5 day lead for ECMWF forecast Yucheng Song and Zoltan Toth @EMC. NCEP. NWS. NOAA

Forecast loop – initial time Oct 10 00 Z The animation on the left shows the forecast initialized on Oct 10, 00 Z for NCEP, Oct 9, 12 Z for ECMWF The NCEP ensemble spread shows tropical influence to the Gulf of Alaska low Yucheng Song and Zoltan Toth @EMC. NCEP. NWS. NOAA

MSLP animation (12 Z forecast added to mimic analysis) The animation on the left mimics how the two low pressure systems in North Pacific formed Yucheng Song and Zoltan Toth @EMC. NCEP. NWS. NOAA

Global IR animation – an example of tropical – extratropical interaction Yucheng Song and Zoltan Toth @EMC. NCEP. NWS. NOAA

Comparison of initial conditions – NCEP vs ECMWF - Mean Sea Level Pressure on Oct 10 00 z, 2005 Differences in NCEP and ECMWF analyses can be spotted at initial time Yucheng Song and Zoltan Toth @EMC. NCEP. NWS. NOAA

Difference of Mean Sea Level Pressure on Oct 11 00 z, 2005 between NCEP vs ECMWF analysis Differences in NCEP and ECMWF analyses can be spotted at 24 hours later – the region corresponds well with expected forecast error reduction in verification region spotted by ETKF using NCEP ensemble well –denoted by square boxes in the two figures Yucheng Song and Zoltan Toth @EMC. NCEP. NWS. NOAA

Expected forecast error reduction in verification region by ETKF method using 19 -member NCEP ensemble Expected forecast error reduction in verification region by ETKF method using 25 -member ECMWF ensemble Yucheng Song and Zoltan Toth @EMC. NCEP. NWS. NOAA

Precipitation verification – heavy rainfall was produced by the first system near Gulf of Alaska Yucheng Song and Zoltan Toth @EMC. NCEP. NWS. NOAA

Global PQPF animation - NCEP Global Ensemble Animation shows how the first system near Gulf of Alaska formed by NCEP global ensemble forecast Yucheng Song and Zoltan Toth @EMC. NCEP. NWS. NOAA

The blob shows the center of forecast error reduction evolution with forecast lead time Yucheng Song and Zoltan Toth @EMC. NCEP. NWS. NOAA

Summary • Influence of organized tropical convection on extratropical circulation – Tropical system picked up by westerly jet, wave evolves into strong low in Gulf of Alaska – Strong downstream propagation of energy leads to explosive development of second low in front of original wave • Ensemble forecast performance – NCEP ensemble captures • First wave from Oct 7 12 Z on • Second wave from Oct 8 12 Z on – NCEP ensemble mean gives accurate forecast from Oct 10 00 Z – ECMWF ensemble captures developments at shorter lead times Yucheng Song and Zoltan Toth @EMC. NCEP. NWS. NOAA

Summary (continued) • ETKF targeting method with ensemble from – NCEP - identified area of tropical convection as main source of initial value uncertainty – ECMWF - no clear signal • What limits predictability for the first and second waves to 7 & 6 days? Errors in – Initial conditions – Observations • Quality • Quantity – Model representation of tropical convective processes – Other model problems? Yucheng Song and Zoltan Toth @EMC. NCEP. NWS. NOAA