The EPS Forecast for Friday the 13th of April 2007

Outline

1. Summary of events of Friday

2. The “deterministic” forecasts (FPs)• The 120 and 72 hr GEM Global forecasts

3. The EPS forecasts• The 120 and 72 hr EPS forecasts: Sunday

and Tuesday night model runs

4. How do we utilize the EPS information?

5. Conclusions

1) Summary of Events on Friday the 13th April

CMC MSLP Analysis Thu. Eve.

CMC MSLP Analysis Fri. Morn.

CMC MSLP Analysis Fri. Eve.

CMC 500 hPa Analysis Thu. Eve.

CMC 500 hPa Analysis Fri. Morn.

CMC 500 hPa Analysis Fri. Eve.

URP Radar Taken Near Noon

URP Composite Taken Late Friday Morning

NB Storm Totals

NEW BRUNSWICK SNOW RAIN PK WND (CM) (MM) (KM/H)ST LEONARD AIRPORT 19 - -WOODSTOCK (COOLTAP) 14 - -FREDERICTON AIRPORT16.8 - -SAINT JOHN AIRPORT 8.5 4.2 70MONCTON AIRPORT 13.2 2.4 -MIRAMICHI 16.2 2.4 -BATHURST AIRPORT 4.6 - 50

NS Storm Totals

NOVA SCOTIA SNOW RAIN PEAK WIND (CM) (MM) (KM/H)HALIFAX AIRPORT 3.8 2.4 80YARMOUTH AIRPORT 6.2 3.8 45BACCARO POINT - - 104GREENWOOD AIRPORT 7.6 4.2 45MCNABS ISLAND - - 76BEAVER ISLAND - - 65SYDNEY AIRPORT 4.6 3.2 52INGONISH BEACH 11 3 -GRAND ETANG - - 158

The GEM Global and GFS 96 and 120 hr Forecasts for Thursday and Friday

Sunday night model run

GEM Global and GFS 96/120 hr Forecasts Showed “Clear Sailing”

• Following GEM Global Model output was from the Sunday evening run.

• Served as guidance for the long range forecast issued by the ASPC Monday morning.

The GEM Global 96 and 120 hr Forecasts for Thursday/Friday

MSLP Prog for Thursday evening

MSLP Prog for Friday evening

The GEM Global 120 hr Forecast for Thursday Friday

12hr QPF prog-Thursday evening

12 hr QPF Prog-Friday evening

The GFS 96 and 120 hr Forecasts for Thursday and Friday

Sunday night model run

GFS Run

Thursday Evening

Friday Evening

How Did Ad Hoc Ensemble Work?

• Most models run Sunday night overdid ridge over Maritimes and showed low skirting well south of NS

• Exception was UK Met which showed low passing just south of NS

2) The Deterministic Forecasts (FPs)

Sunday night model run

Forecast Called for Nice WeatherFPCN51 CWHX 090741

EXTENDED FORECASTS FOR WEDNESDAY THURSDAY AND FRIDAY FOR NOVA SCOTIA ISSUED BY ENVIRONMENT CANADA AT 5.00 AM ADT MONDAY 9 APRIL 2007.

THE NEXT SCHEDULED FORECAST WILL BE ISSUED AT 11.00 AM.

HALIFAX METRO AND HALIFAX COUNTY WEST HALIFAX COUNTY - EAST OF PORTERS LAKE LUNENBURG COUNTY QUEENS COUNTYSHELBURNE COUNTYYARMOUTH COUNTYDIGBY COUNTYGUYSBOROUGH COUNTY.

WEDNESDAY..SUNNY. LOW MINUS 5. HIGH PLUS 5. THURSDAY..SUNNY. LOW MINUS 3. HIGH 7. FRIDAY..SUNNY. LOW MINUS 4. HIGH 6. NORMALS FOR THE PERIOD..LOW ZERO. HIGH 8.

The GEM Global and GFS 72 hr Forecasts for Thursday and Friday

Tuesday night model run

Tue. night it became evident this storm was a threat to Maritimes

• Ad Hoc Ensemble members unanimous that low would affect both NS and NB with significant weather.

• GFS, NAM-WRF, GEM GLOBAL all showed threat.

• Significant snowfalls appeared to be likely in some areas.

72 hr NWP Forecast for Friday Evening

The following charts were taken from the Tuesday night NWP runs which were used for the Wednesday morning forecast:

72 hr Forecast for Friday Evening

GFS

NAM - WRF

GLOBAL

NS Special Weather Statement Issued:

WOCN11 CWHX 110730

SPECIAL WEATHER STATEMENT FOR NOVA SCOTIA ISSUED BY ENVIRONMENT CANADA AT 4:30 AM ADT WEDNESDAY 11 APRIL 2007.

ANOTHER ROUND OF WINTERY WEATHER IS EXPECTED ON FRIDAY... A LOW PRESSURE SYSTEM IS EXPECTED TO DEVELOP OVER THE EASTERN SEABOARD OF THE UNITED STATES ON THURSDAY AND PASS SOUTH OF NOVA SCOTIA ON FRIDAY. CURRENT INDICATIONS SUGGEST THAT PERIODS OF SNOW OR SNOW MIXED WITH RAIN CAN BE EXPECTED ACROSS MOST OF NOVA SCOTIA ON FRIDAY. IF THE PRECIPIATION FALLS MAINLY AS SNOW THEN SIGNIFICANT ACCUMULATION CAN BE EXPECTED.

THE PUBLIC IS ADVISED TO MONITOR FUTURE FORECASTS AS WARNINGS MAY BE REQUIRED.

END/ASPC

NB Special Weather Statement Issued:

WOCN14 CWHX 110738

SPECIAL WEATHER STATEMENT FOR NEW BRUNSWICK ISSUED BY ENVIRONMENT CANADA AT 4:38 AM ADT WEDNESDAY 11 APRIL 2007.

ANOTHER ROUND OF WINTERY WEATHER IS EXPECTED ON FRIDAY... A LOW PRESSURE SYSTEM IS EXPECTED TO DEVELOP OVER THE EASTERN SEABOARD OF THE UNITED STATES ON THURSDAY AND PASS SOUTH OF NOVA SCOTIA ON FRIDAY. CURRENT INDICATIONS SUGGEST THAT PERIODS OF SNOW CAN BE EXPECTED ACROSS MOST OF NEW BRUNSWICK ON FRIDAY HOWEVER IT MAY BECOME MIXED WITH RAIN IN THE SOUTH. SIGNIFICANT ACCUMULATIONS OF SNOW MAY OCCUR PARTICULARY IN THE SOUTH AND EAST.

THE PUBLIC IS ADVISED TO MONITOR FUTURE FORECASTS AS WARNINGS MAY BE REQUIRED.

END/ASPC

Forecast for Fri. Issued Wed. AMFPCN51 CWHX 110741

EXTENDED FORECASTS FOR FRIDAY SATURDAY AND SUNDAY FOR NOVA SCOTIA ISSUED BY ENVIRONMENT CANADA AT 5.00 AM ADT WEDNESDAY 11 APRIL 2007.

THE NEXT SCHEDULED FORECAST WILL BE ISSUED AT 11.00 AM.

HALIFAX METRO AND HALIFAX COUNTY WEST HALIFAX COUNTY - EAST OF PORTERS LAKE LUNENBURG COUNTY QUEENS COUNTY GUYSBOROUGH COUNTY. FRIDAY..SNOW OR RAIN. LOW MINUS 2. HIGH PLUS 3. SATURDAY..CLOUDY WITH 60 PERCENT CHANCE OF FLURRIES. LOW MINUS 2. HIGH PLUS 4. SUNDAY..SUNNY. LOW MINUS 4. HIGH 10. NORMALS FOR THE PERIOD..LOW MINUS 1. HIGH 8.

3) The EPS Forecasts

How Well Did the EPS Do?

• Will start with the one based on the Sunday evening Global run (0z Mon)

• This was the run used to “Scribe” the first long range forecast for Friday. (which called for a sunny day)

How Well Did the EPS Do?

• The MSLP plots will be shown in different formats

• You may find one more helpful than the others

3.1) The 120 hr CMC EPS

Issued Sunday evening

CMC Pressure Centres Chart

Valid Friday Evening (00 UTC Saturday)

All of the MSLP EPS 120 hr Plots:

Valid Friday Evening (00 UTC Saturday)

Valid Friday Evening (00 UTC Saturday)

546 dam, 500 hPa 120 hr Spaghetti Plots:

Valid Friday Evening (00 UTC Saturday)

AEPRI Products:(Atlantic Environmental Prediction

Research Initiative)

120 hr forecast

Synoptic Charts

Valid Friday Evening (00 UTC Saturday)

AREPIPoE QPF Charts

Some QPF areas not included in the AEPRI products

3.2) The 72 hr CMC EPS

Issued Tuesday evening

CMC Pressure Centres Chart

Valid Friday Evening (00 UTC Saturday)

Sample of the MSLP EPS Plots:

Valid Friday Evening (00 UTC Saturday)

Spaghetti Plot

Valid Friday Evening (00 UTC Saturday)

AEPRI Product:

Issued Tuesday evening

QPF Charts

4) In retrospect how could we have incorporated this information into the long range forecast ?

• Type of forecast product we issue (PUBPRO)

• Type of forecast production software in use – one model/one forecast

Very difficult due to limitations in:

Complex Forecast• Two possibilities for sky conditions

– clear– cloudy

• Three possibilities for precipitation– None– Rain– Snow

• At least two possibilities for temperature– Sunny - mild– Cloud/Precipitation – cool/cold

• Two possibilities for winds– None – Windy

Complex Forecast

• Fortunately all of these different possibilities are not independent.

• Reduces the number of possible forecasts but from a deterministic point of view still too many

Different Forecast OutcomesDepending on low’s track

1)Sunny. High 11.

2)Cloudy. High 6.

3)Cloudy with snow. Windy. High 1.

4)Cloudy with snow and rain. Windy. High 3.

Difficulties Faced

• Not clear on the probability of each event

• Given probabilities, there would be no way to include each scenario into the forecast.

• Can you imagine how complex the forecast could get?

• Not only sky conditions and pcpn affected but also temperatures ( a high of 11 on a sunny April day but perhaps 1 with pcpn)

Something Easily Conveyed to Public

• Special Weather Statement• Advisory• Special Synopsis• Graphical Forecast• Verbal consultations

Can We use Mean for the Forecast?

• Eg. for Friday “cloudy with a chance of snow. Windy. High 2.” as mean might indicate

• Must use with caution though!!

Can We use Mean for the Forecast?

• The ensemble mean is generally not a good forecast:– It is likely to verify better than any individual member. – And even better than the deterministic model.– But this is partly because it is smoothed out – smaller

variance.– Provides wrong information in case of clustering or

multi-modal distributions.– Ensemble mean and median work better as forecasts

when the distribution is near normal.– Also most EPS are under-dispersive (the truth may lie

outside the range of solutions offered by the ensemble members).

How to Use These Products

• Keep it simple – limited application to forecasts anyways

• Pick a few simple charts that work best

• May not have time for much more

How to Use These Products

• Check spread– Spaghetti plots– Magnitude of Standard Deviation– Pressure centre plots– Individual MSLP Plots

• To assess skill of deterministic model

• Check modality

How to Use These Products

• If there is lower skill (but not too much spread) and model is showing one type of solution using mean may help

• Multimodal – all bets are off

• If one mode is high impact perhaps an SWS would be in order

Conclusions – We Saw 3 Cases

• EPS cannot be taken at face value like deterministic progs.

• Used to evaluate based on spread-skill relation– Like deterministic NWP some runs are good– Others not good

• EPS does not always include the correct solution• When it does it can be very good• Primary function is to provide a measure of

deterministic model skill/forecaster confidence• When deterministic model skill is low EPS may

provide guidance to a better forecast

The End