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
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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