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Highest Confidence Forecasts. Model agreement NGM=WRF=AVN Run-to-run changes (dMod/dt) very small Models trending toward agreement Example: OLD run: WRF=AVN but *not* NGM NEW run: NGM trends toward WRF & AVN Models have current weather “in hand”

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highest confidence forecasts
Highest Confidence Forecasts
  • Model agreement
    • NGM=WRF=AVN
  • Run-to-run changes (dMod/dt) very small
  • Models trending toward agreement
    • Example:
      • OLD run: WRF=AVN but *not* NGM
      • NEW run: NGM trends toward WRF & AVN
  • Models have current weather “in hand”
  • Parameterized processes not significant part of feature
lowest confidence forecasts
Lowest Confidence Forecasts
  • Large model disagreement
    • NGM, WRF, AVN all have different solutions
  • Run-to-run changes (dMod/dt) large
  • Don’t have current weather “in hand”
  • Parameterized processes significant part of feature
when models disagree
When models disagree …..
  • In a 12-36 hr. fcst, lean toward model/s that has “best” handle on current weather!
  • Lean toward a model whose run-to-run change is small, especially if other models are trending toward it
  • Lean away from a model if it is showing its bias!
  • Take consensus!
when models disagree1
When models disagree …..

AVN

Rainfall forecast:

Cape Canaveral, FL

Postpone a launch?

ETA

NGM

when models disagree2
When models disagree …..

AVN

15Z RADAR

ETA

Which model do you go with?

NGM

KJAX 141756Z 33008KT 1 1/2SM -RA BR OVC010 15/15 A3013 60086

model trend single model
MODEL TREND: Single Model

Is the Trend a useful forecast technique?

model trend single model1
MODEL TREND: Single Model

Is the Trend a useful forecast technique?

model trend single model2
MODEL TREND: Single Model

Is trend any help at all in this case?

model trend single model3
MODEL TREND: Single Model
  • LAGGED AVERAGE FORECAST
  • Average of each forecast valid at same time
  • “Poor man’s” Ensemble
model trend
MODEL TREND

Trending toward New York City?

model trend1
MODEL TREND

Trend can cause problems…look for at least 3 consecutive runs of the trend

interpreting model trends what s legitimate
Interpreting Model Trends: What’s Legitimate ??
  • Least significant if associated with “parameterized” situation
  • 3-model run trend stronger signal than 2-model trend
  • Hierarchy of model run-to-run trends
    • 24 ->12 hours most significant
    • 60-> 48 hours least significant
model confidence utilizing trend agreement6
MODEL CONFIDENCE: Utilizing Trend & Agreement

What’s a forecaster to do? Suggestions???

ensemble forecasts
ENSEMBLE FORECASTS
  • What are ENSEMBLE FORECASTS?
    • Model’s initial conditions are perturbed
    • Variety of solutions occur
ensemble forecasts1
ENSEMBLE FORECASTS

THESE ARE THE MEMBERS OF THE ENSEMBLE

- Negative and Positive tweaks

ONE MODEL … MANY TWEAKS

ensemble forecasts2
ENSEMBLE FORECASTS

EACH MEMBER IS RUN OUT IN TIME

- Provides “unique” solution

ensemble forecasts3
ENSEMBLE FORECASTS

ENSEMBLE MEAN IS “most likely” SOLUTION averaged over ALL cases

ensemble forecasts4
ENSEMBLE FORECASTS

HOW CONFIDENT ARE WE IN THE ENSEMBLE MEAN?

ensemble forecasts5
ENSEMBLE FORECASTS

IS THE ENSEMBLE MEAN more likely than the CLUSTERS?

ensemble forecasts6
ENSEMBLE FORECASTS

MEM 1

ENSEMBLE

MEAN

MEM 2

Which solution is LEAST likely?

ensemble forecasts another approach
ENSEMBLE FORECASTS: Another Approach

THESE ARE DIFFERENT MODELS

- ETA, AVN, NGM, MM5, EUR, MRF, UKM, CMC

MANY MODELS … MANY DIFFERENT “PHYSICS” & IC

ensemble forecasts7
ENSEMBLE FORECASTS

MULTI-MODEL

CONSENSUS

What’s the better approach?

ensemble forecasts8
ENSEMBLE FORECASTS

Many “perturbations”, Many People

Many “perturbations”, One YOU

What’s the better approach?

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