Forecasting Storm Duration Neil I Fox David Jankowski

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Forecasting Storm Duration Neil I. Fox David Jankowski, Elizabeth Hatter and Liz Heiberg Dept.

Forecasting Storm Duration Neil I. Fox David Jankowski, Elizabeth Hatter and Liz Heiberg Dept. Soil, Environmental and Atmospheric Science University of Missouri - Columbia

Considering rear edge propagation velocity in flash flood forecasting Why worry about your rear

Considering rear edge propagation velocity in flash flood forecasting Why worry about your rear u How your rear moves compared to your middle u Using knowledge of your rear to forecast rainfall totals u Stop the rear jokes u

Why worry about your rear? Current nowcasting tools (e. g. SCIT tracks) concentrate on

Why worry about your rear? Current nowcasting tools (e. g. SCIT tracks) concentrate on arrival time u Excellent for Severe Weather warning u Flash flood forecasting: Interested in total duration of precipitation u Event management / Emergency services like to know end time u

This study looked at u The use of three measures of storm velocity as

This study looked at u The use of three measures of storm velocity as indicators of flash flood potential • 1/vc • 1/vr • (vc-vr)/vcvr u The last of these is defined as the ‘Storm Duration Factor’

Storm duration factor (SDF) Duration (D) over a point at distance x : Rainfall

Storm duration factor (SDF) Duration (D) over a point at distance x : Rainfall accumulation (Ra) at x assuming steady-state rainfall rate R:

Data Initially data was taken from a number of cases where (flash) flooding occurred

Data Initially data was taken from a number of cases where (flash) flooding occurred u A range of storm types, locations and situations u Not all storm cells observed caused flooding u Then more data for more cases u

Analysis Centroid velocities found using the NSSL algorithms (SCIT) u Rear edge velocities found

Analysis Centroid velocities found using the NSSL algorithms (SCIT) u Rear edge velocities found by locating position from tracing centroid vector backward until Z falls below threshold u

Analysis u The three measures were plotted against rainfall accumulations • for the subsequent

Analysis u The three measures were plotted against rainfall accumulations • for the subsequent 60 minutes • 0 km and 25 km ahead of storm center location • Greater distances saw very little rain (storms don’t move that fast or dissipate within the distance)

Comparison of vc & vr

Comparison of vc & vr

1/vc & precip accumulation

1/vc & precip accumulation

1/vr & precip accumulation

1/vr & precip accumulation

SDF & precip accumulation

SDF & precip accumulation

Results All correlation coefficients are horrible u If you squint you can kind of

Results All correlation coefficients are horrible u If you squint you can kind of see what you want to see u More work required!! u

Next u This could be because • We don’t consider development/dissipation • We don’t

Next u This could be because • We don’t consider development/dissipation • We don’t consider size of storm • We don’t look at sensible distances or have good rainfall data

Accounting for storm size Tried a “pure” measure Unsuccessful – so try measure based

Accounting for storm size Tried a “pure” measure Unsuccessful – so try measure based on velocity and storm size

Test u Rainfall accumulation versus duration based on • centroid velocity (x+Δx/vc) • rear

Test u Rainfall accumulation versus duration based on • centroid velocity (x+Δx/vc) • rear edge velocity (x+Δx/vr) • Both (reduces to the others for x = 0)

Rainfall total vs vc/Δx

Rainfall total vs vc/Δx

Rainfall total vs vr/Δx

Rainfall total vs vr/Δx

Problems u Radar rainfall accumulations • use gauge u Rear edge velocity determination •

Problems u Radar rainfall accumulations • use gauge u Rear edge velocity determination • automate – make robust u Mixture of storm types • stratify

Thanks u Parts of this work have been funded by the COMET Partners Program

Thanks u Parts of this work have been funded by the COMET Partners Program and The University of Missouri Research Council

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