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The challenge to verify operational weather warnings. Tanja Weusthoff and Marco Arpagaus EMS, 14.09.2011. MeteoSwiss official warnings (24h acc. precip.) for 4th September 2011. 152 warning regions. Introduction. 5 level. 8 different hazards.

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the challenge to verify operational weather warnings

The challenge to verify operational weather warnings

Tanja Weusthoff and Marco Arpagaus

EMS, 14.09.2011

MeteoSwiss official warnings (24h acc. precip.) for 4th September 2011

introduction

152 warning regions

Introduction

5 level

8 different hazards

 currentproject: developmentof an applicationfor an automaticverificationofweatherwarnings

introduction1
Introduction

specifications:

  • develop an automaticverificationforoperational warnings, whichallows a certaintolerance (spaceand time)
  • usesynergies(e.g. with GIN, a commonplatformfor all naturalhazards in Switzerland: http://www.gin-info.ch/index.html)

motivation:

  • replacecurrentmanual(subjective) verification in ordertoreleaseresources
  • provethequalityofofficialwarnings
  • singleofficialvoice (SOV, sinceJanuary 2011)  distribution via mediaforlevel 4 and 5
challenges
Challenges
  • how to evaluate the usefulness of warnings without knowing the needs of individual users (and their cost/loss)
  • how to interprete „tolerant results“ and what should be communicated to the users

Precautions causes Costs

Having no protection results in Losses

challenges1
Challenges
  • representativityofobservations
  • accountforfeedbackofauthorities
  • smallstatistics (rare events)

e.g. station Magadino / Cadenazzo (203 m asl) is only wind station for two warn regions with complex terrain (308 and 309)

> 2000 m

< 800 m

basic concept
Basic Concept

event-oriented verification, warnings as binary events

tolerant in space, time and threshold

distinguish two types of warnings

SHORT: short-term events (e.g. thunderstorms)

AKKU: accumulated events (e.g. 24h precipitation accumulation)

event definition and evaluation is (in principle) the same within each group; differentiate between basic verification (strict) and detailed verification

verification per warning region, summary for specific regions or whole Switzerland

example akku

Example: AKKU

Rain  level 3-5

Snowfall (lowlands and mountains)  level 3-5

Snowmelt  level 3-5

Heat wave level 3

  • snowmelt cannot be verified due to a lack of observations;
  • for snow and rain use of radar data (spatial information) and psychrometer temperature
event definition
Event-Definition

WarnEvent (ts to te)

acc/3

ti

issue time

t2

te

ts

t1

ObsEvent

(t1 to t2)

t2 - ti > tv?

AKKU

  • each warning is an event; duration of warning at least as long as accumulation period duration
  • observation: consider hourly 24h, 48h and 72h sum; important is first threshold exceedance (t2)

Hit

 An eventisobservedduring a valid warningandthefirstthresholdexceedance (t2) occursat least accumulationPeriod/3 hours (i.e. 8h,16h,24h) after thebeginningofthe warn event (ts) and not laterthenthe end ofthe warn event (te).

Miss

 A thresholdexceedanceisobservedwithout an activewarningorthefirstthresholdexceedanceoccurs bevor accumulationPeriod/3 hoursafter thebeginningofthewarning (ts).

FalseAlarm

 A warninghasbeenissued, but nothresholdexceedancehasbeenobserved.

evaluation a basic verification
Evaluation A: Basic-verification

Present results as:

POD

FAR

FBI

(TS)

 derived from contingency table

AKKU

Missing-D-problem:

what is a „non-event“?

Evaluation B: detailed verification

  • in principle like Evaluation A (Hit, Miss, False Alarm)
  • introduce additional category
    • combination of Hit, Miss und False Alarm  see definitions on next slide
evaluation b detailed verification
Evaluation B: detailed verification

WarnEvent (ts to te)

ti

issue time

te

t2

ts

t1

ObsEvent

(t1 to t2)

t2 - te < tshift

AKKU

(2.)

(1.)

WarnEvent (ts to te)

acc/4

acc/3

ti

issue time

t2

te

ts

ObsEvent

(t1 to t2)

Specifications

Miss + Hit + False Alarm

 the first threshold exceedance (t2) occurs maximal tshift hours after the end of the warn event (te) or less than accumulatioPeriod/3 (8,16,24h) but more than accumulationPeriod/4 (6,12,18h) after the start of the warning (ts).

evaluation b detailed verification1
Evaluation B: detailed verification

Presentation of results:

„perfect“ hit

„useful“ combined categories including a hit

„bad“ false alarm, miss

AKKU

„good“

... adapted from DWD

tolerance
Tolerance

Allowtolerances in:

threshold:LowHit = 90% ofthreshold

time:variationoftime components (e.g. tshift)

space:ifpossible, takeintoaccountneighbouring warn regions

applytolerancestobasicanddetailedverification

SHORT: possibilitytorequest a minimumleadtimetvforthewarning (i.e. a hitisonlypossibleifthewarninghasbeenissuedat least tv (= t1 - ti) hoursbeforetheobservedevent, otherwiseitisclassifiedas a miss)

SHORT + AKKU

application flow diagram
Application  Flow Diagram

warn DataBase

 warn events

  • Java Application
  • AWV
  • deriveobsevents
  • perform event-basedverificationforeachsettingandeachregion

store warn and obs events on a monthly basis

obs DataBase

 hourly data

per warn region

store evaluation results for each event on a monthly basis

  • aggregateresultsandcalculatescoresforspecificperiod
  • present results
  • per region
  • single event
a qualitative example

Luzern

MeteoSwiss official warnings (24h acc. precip.)

for 4th September 2011

Observations (surface stations): 24 h acc.

precipitation analysis for 4th September 2011 (prel.)

Bern

A qualitative example…

Level 3 warning:

WarnIssue 04.09.2011 08:56

WarnStart 04.09.2011 12:00

WarnEnd 05.09.2011 12:00

24h acc. precip.

35 mm/24h

50 mm/24h

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