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A Composite Analysis of Northeast Severe Weather Events wit A Composite Analysis of Northeast Severe Weather Events wit

A Composite Analysis of Northeast Severe Weather Events wit - PowerPoint Presentation

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A Composite Analysis of Northeast Severe Weather Events wit - PPT Presentation

Matthew Vaughan Brian Tang and Lance Bosart Department of Atmospheric and Environmental Sciences University at AlbanySUNY Albany NY 12222 Northeast Regional Operational Workshop XVI Nanoscale ID: 465554

hpa slight utc 500 slight hpa 500 utc event strong risk events flow severe report weak northeast lapse composites

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Slide1

A Composite Analysis of Northeast Severe Weather Events with Varying Spatial Impacts

Matthew Vaughan, Brian Tang, and Lance BosartDepartment of Atmospheric and Environmental SciencesUniversity at Albany/SUNYAlbany, NY 12222Northeast Regional Operational Workshop XVINanoscale College South AuditoriumAlbany, NYWednesday 4 November 2015

Supported by the NOAA Collaborative Science,

Technology and Applied Research Program (NA13NWS4680004)Slide2

Severe weather in the Northeast a topic of recent research

Hurlbut and Cohen (2014) conducted a proxy sounding study on events of varying severitySignificant discriminators:850–500-hPa and 700–500-hPa lapse ratesDowndraft CAPE (DCAPE)Mixed-layer CINMotivationHurlbut and Cohen (2014)Slide3

Hitchens and Brooks (2012) verified SPC day-1 slight risk convective outlooks over CONUS

Found increased forecast performance with timeMotivationBlack line represents slight risk performanceGray line represents moderate risk performance Source: Hitchens and Brooks(2014)Slide4

Launched a CSTAR-supported Master’s thesis studying high-impact severe weather in environments with poor predictive

skillAdditional research opportunity from these two studies?Magnitude of severe event and slight risk occurrenceMotivationSlide5

MethodologySlide6

Methodology

Create Northeast domainPlot SPC convective outlook contours over the domainAnalyze storm report area and slight risk occurrence from 1980–2013 Similar method used in Hitchens and Brooks (2012)Slide7

Northeast Domain

Courtesy of amaps.com Slide8

Northeast Domain

HereCourtesy of amaps.com Slide9

Algorithm Example

40 km

Slight Risk

Issued: 0600 UTC

Valid: 1200–1200 UTC Slide10

Algorithm Example

40 km

Sev

ere

reportSlide11

Algorithm

Example

40 km

40 km

Sev

ere

report

Area of influenceSlide12

Northeast Severe Report TrendSlide13

Northeast Severe Report Trend

55th percentile linear regression45

th

percentile linear regressionSlide14

Northeast Severe Report TrendSlide15

Northeast Severe Report Trend

Underperform (Weak) SlightOverperform (Strong) SlightSlide16

Types of Slight Risk Events

Weak Slight Events (N= 585)Slight risk presentSevere report coverage below 45th percentileStrong Slight Events (N= 585)Slight risk presentSevere report coverage above 55th percentileSlide17

Monthly

VariabilitySlide18

Monthly

VariabilitySlide19

Event-Centered CompositesSlide20

Event-Centered Composites

0.5° NCEP Climate Forecast System Reanalysis (CFSR)Morning (1200 UTC) data for mid-level flow and spatial compositesAfternoon (1800 UTC) data for convective parameter analysisComposited April–September events to focus on warm seasonAll events centered at point of maximum report densityUsed Hurlbut and Cohen (2014) results to guide analysisSlide21

Most-Unstable CAPE

850–500-hPa Lapse RateArithmetic mean and 95% confidence interval shown. Additional median significance tests support results.Event-Centered Composites1800 UTCSlide22

Downdraft CAPE

Lowest 150-hPa Mean RHArithmetic mean and 95% confidence interval shown. Additional median significance tests support results.Event-Centered Composites1800 UTCSlide23

Let’s Digest this a little…Slide24

Majority of slight risk events occur under westerly flow at 500 hPa

Do the previous statistics hold for each flow regime?Event-Centered Composites

Mid-level (500 hPa) Flow DistributionSlide25

Threat Score for Strong Slight Events

Event-Centered CompositesArithmetic mean and 95% confidence interval shown.

Mid-level (500 hPa) Flow DistributionSlide26

Threat Score for Strong Slight Events

Event-Centered CompositesArithmetic mean and 95% confidence interval shown.

Mid-level (500 hPa) Flow DistributionSlide27

Most-Unstable CAPE

850–500-hPa Lapse RateArithmetic mean and 95% confidence interval shown. Additional median significance tests support results.Northwesterly Flow Regime1800 UTCSlide28

Downdraft CAPE

Lowest 150-hPa Mean RHArithmetic mean and 95% confidence interval shown. Additional median significance tests support results.Northwesterly Flow Regime1800 UTCSlide29

Downdraft CAPE

Lowest 150-hPa Mean RHArithmetic mean and 95% confidence interval shown. Additional median significance tests support results.Northwesterly Flow RegimeDoh!

Doooohhhh

!

1800 UTCSlide30

What does this actually look like?Slide31

250-hPa geopotential height

(dam, black contours), 250-hPa winds (knots, shaded every 20 knots starting at 50 knots, and barbed). Red dot signifies event center.Weak Slight vs. Strong Slight1200 UTC 250 hPa

Weak Slight

Strong SlightSlide32

500-hPa geopotential height

(dam, black contours), 500-hPa winds (knots, barbed), 700–500-hPa lapse rate (K km−1, shaded every 0.5 K km−1). Red dot signifies event center.Weak Slight vs. Strong Slight1200 UTC 500 hPa

Weak Slight

Strong SlightSlide33

Weak Slight vs. Strong Slight

1200 UTC MUCAPE & Shear

Weak Slight

Strong Slight

850

–500-hPa lapse rate (K/km, black

contours every .5 K from 6 K/km)

, 1000–500-hPa shear (knots, barbed), M

ost-Unstable

CAPE(J/kg,

shaded every 250 J/kg). Red dot signifies event center.Slide34

Composite Difference

1200 UTC MUCAPE (SS−WS)MUCAPE difference (J/kg, fill), t-test statistical significance (Stipple, starting at 95%). Red dot signifies event center.Slide35

Composite Difference

1200 UTC 850–500-hPa lapse rate (SS−WS)850–500-hPa lapse rate difference (K km−1, fill), t-test statistical significance (Stipple, starting at 95%). Red dot signifies event center.Slide36

Composite Difference

500-hPa height difference (dam, fill), t-test statistical significance (Stipple, starting at 95%). Red dot signifies event center.1200 UTC 500-hPa heights (SS−WS)Slide37

NE slight risk events

Peak in July. More events in Spring than FallMost common under westerly and southwesterly 500-hPa flow conditionsNE strong slight days and weak slight daysResults support findings of Hurlbut and Cohen (2014)MUCAPE, DCAPE, 850–500-hPa lapse rate, and lowest 150 hPa layer-averaged RH are found to be helpful discriminatorsNorthwesterly (strong and weak) slight risk daysSubtle differences includeFaster flow aloft in strong cases, enhanced advectionStronger upstream mid-level ridge, higher lapse rates, and higher MUCAPE in strong caseComposite Summary and Key PointsSlide38

FIN

Matthew VaughanEmail: mvaughan@albany.eduSlide39

Average Slight Risk Size