National Weather Service The Short-Range Ensemble Forecast: The Short-Range Ensemble Forecast: Applying Uncertainty and Applying Uncertainty and Probabilistic Forecasts of Winter Probabilistic Forecasts of Winter Storms Storms Matt Steinbugl, NOAA/NWS Des Moines Matt Steinbugl, NOAA/NWS Des Moines Rich Grumm, NOAA/NWS State College Rich Grumm, NOAA/NWS State College
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National Weather Service The Short-Range Ensemble Forecast: Applying Uncertainty and Probabilistic Forecasts of Winter Storms Matt Steinbugl, NOAA/NWS.
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National Weather Service
The Short-Range Ensemble Forecast: The Short-Range Ensemble Forecast: Applying Uncertainty and Probabilistic Applying Uncertainty and Probabilistic
Forecasts of Winter Storms Forecasts of Winter Storms
Matt Steinbugl, NOAA/NWS Des Matt Steinbugl, NOAA/NWS Des MoinesMoines
Rich Grumm, NOAA/NWS State Rich Grumm, NOAA/NWS State CollegeCollege
• ConveyConvey and and applyapply uncertainty to the uncertainty to the forecast processforecast process• RecognizeRecognize and and assignassign probabilities to probabilities to crucial winter weather forecast crucial winter weather forecast parametersparameters
This will allow forecasters:This will allow forecasters:• To To increase overall confidenceincrease overall confidence within within each individual forecast through a each individual forecast through a probabilistic approachprobabilistic approach• To To make better decisionsmake better decisions while allowing while allowing users better decision making capabilitiesusers better decision making capabilities
•Uncertainty in initial conditions Uncertainty in initial conditions and model calculations can alone and model calculations can alone lead significant outcome changes lead significant outcome changes (run-to-run)(run-to-run)
•Need to account for non-linear Need to account for non-linear processesprocesses
•Atmosphere is chaotic in natureAtmosphere is chaotic in nature
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Why Ensembles?Why Ensembles?
•Needed to deal with inherent forecast Needed to deal with inherent forecast uncertaintyuncertainty
•Recognize high uncertainty/high Recognize high uncertainty/high probability outcomes and relate these probability outcomes and relate these to each phase of the forecast processto each phase of the forecast process
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National Weather Service
What is the SREF?What is the SREF?
Multi-model based ensemble Multi-model based ensemble prediction system (EPS) with each prediction system (EPS) with each member having different dynamical member having different dynamical cores and physics packages.cores and physics packages.
21 individual members:21 individual members:
5 ETA (BMJ) + 5 ETA (KF) + 5 RSM 5 ETA (BMJ) + 5 ETA (KF) + 5 RSM ++6 WRF NMM/ARW (BMJ/KF) = 6 WRF NMM/ARW (BMJ/KF) = 21 21 membersmembers
-3 hourly output out to 87hrs-3 hourly output out to 87hrs-Produced at NCEP 03Z, 09Z, 15Z -Produced at NCEP 03Z, 09Z, 15Z and 21Z and 21Z
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Deterministic (GFS) vs. Deterministic (GFS) vs. Probabilistic (SREF)Probabilistic (SREF)
ModelModel Initial Initial ConditionCondition
s (ICs)s (ICs)
Model Model corescores
RemarksRemarks
GFSGFS 1 IC1 IC 1 model 1 model corecore
run-to-run-to-run run
(jumpine(jumpiness)ss)
SREFSREF Multiple Multiple ICsICs
Multiple Multiple corescores
More More consistenconsisten
cycyComparing deterministic models is a 50/50 Comparing deterministic models is a 50/50
proposition!!!proposition!!!
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SREF PerformanceSREF Performance
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Case Study DataCase Study Data
•Examine 3 significant winter Examine 3 significant winter weather events across the weather events across the Eastern United StatesEastern United States
•We need to extract the We need to extract the following from the data:following from the data:
-Amounts/timing of pcpn?-Amounts/timing of pcpn?-PYTPE?-PYTPE?-Temps for Snow vs. Ice?-Temps for Snow vs. Ice?-Pattern Recognition?-Pattern Recognition?-Atypical/typical event?-Atypical/typical event?
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Case Study #1 22-23 Dec 2004Case Study #1 22-23 Dec 2004
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SpaghettiSpaghetti//Probability charts - 0° Probability charts - 0° isothermisotherm
Mean Mean and and probabilprobabilityity
sprespreadad
22mm
850850mbmb
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Mixed/Conditional Probability Mixed/Conditional Probability charts PYTPEcharts PYTPE
Detroit, MI Plume DiagramDetroit, MI Plume Diagram
National Weather ServiceNOHRSNOHRSCC
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SummarySummary EPSs are an important means of:EPSs are an important means of:•Explicitly conveying and applying uncertainty Explicitly conveying and applying uncertainty through a probabilistic approachthrough a probabilistic approach
•Visualizing and quantifying uncertainty Visualizing and quantifying uncertainty within the forecast processwithin the forecast process
Using ensembles will allow forecasters to Using ensembles will allow forecasters to relate probabilities to each phase of the relate probabilities to each phase of the warning decision processwarning decision process
In turn, this will allow forecasters to make In turn, this will allow forecasters to make better decisions and users to have better better decisions and users to have better decision making capabilitiesdecision making capabilities
SREF Exploitation at NCEP’s Hydrometeorological Prediction Center SREF Exploitation at NCEP’s Hydrometeorological Prediction Center (HPC) (HPC) http://nws.met.psu.edu/severe/2005/23April2005.pdfhttp://nws.met.psu.edu/severe/2005/23April2005.pdf
Dealing with uncertainties in forecasts – M Steven Tracton Dealing with uncertainties in forecasts – M Steven Tracton NWS/NCEP/EMCNWS/NCEP/EMC