Transcript Slide 1

Using Ensemble Probability Forecasts
and High Resolution Models
To Identify Severe Weather Threats
Josh Korotky
NOAA/NWS, Pittsburgh, PA
and
Richard H. Grumm
NOAA/NWS, State College, PA
Overview
› Review a vigorous and a marginal severe weather event
 Examine diagnostic fields from the NAM-WRF
 Examine single and combined probability forecasts from the SREF
› Examine threshold probabilities for:
 CAPE
 Storm-Relative Helicity (SRH)
 Mean shear (total shear divided by shear depth)
 The Energy Helicity Index (EHI)
 The Supercell Parameter
 The Significant Tornado Parameter
› Examine the combined probability of MUCAPE > 1000 J/kg, effective bulk shear
> 30/40 kts, and 3 hr. convective precipitation > .01 inch
Overview
› This study illustrates the value of using diagnostic information from higher
resolution models with probability information from SREF forecasts to better
understand the nature of a severe weather threat potential
› A forecast strategy is proposed:
 Use ensemble data for assessing the likelihood of a severe weather event
and the confidence level of NWP forecasts
• Uncertainty information is critical for forecast users
 Use climatological anomalies for evaluating the historical context of a model
forecast
• Important for users to appreciate possible impacts
 Use high resolution model data for determining the timing, evolution, mode,
and intensity of forecast convection, including important mesoscale
structures and relevant forcing mechanisms
• The devil is in the model details
SREF Configuration
› EMC runs a 21 member multi-model, multi-analysis system with
enhanced physics. The SREF is run four times daily at 03, 09, 15, and
21 UTC, with forecasts to 87 hours
› The current SREF configuration:
 10 NAM-Eta members
 5 Regional Spectral Model (RSM) members
 6 WRF members
› Why SREF?
 SREF designed to address both initial state and model uncertainties
Introduction – Case 1
› A deep cyclone and frontal system
brought severe weather to much of
the central Mississippi and lower Ohio
Valleys on 2 April 2006
› 871 severe weather reports
› 85 tornadoes
› 29 deaths
SPC Day One Outlook
04/02/06 UTC valid 0402/12 UTC – 0403/12 UTC
SPC SREF Forecasts
April 02/09 UTC valid April (02-03)/(21 – 00) UTC
› Single and combined probabilities - David Bright
› http://www.spc.noaa.gov/exper/sref/
04/02/09Z valid 0402/21 UTC
04/02/09Z valid 0403/00 UTC
Prob Effective Shear ≥ 40 kts, Mean Effective Shear ≥ 40 kts (yellow)
Prob Effective Shear ≥ 40 kts, Mean Effective Shear ≥ 40 kts (yellow)
Prob Conv Precip ≥ .01 in x Prob MUCAPE ≥ 1000 x Prob Eff Shr > 40 kts
Prob Conv Precip ≥ .01 in x Prob MUCAPE ≥ 1000 x Prob Eff Shr > 40 kts
04/02/09Z valid 0402/21 UTC
04/02/09Z valid 0403/00 UTC
Prob Supercell Composite ≥ 3, Mean Supercell Composite = 3 (yellow)
Prob Supercell Composite ≥ 3, Mean Supercell Composite = 3 (yellow)
Prob Sig Tor ≥ 3, Mean Sig Tor = 3 (yellow)
Prob Sig Tor ≥ 3, Mean Sig Tor = 3 (yellow)
SREF Departures from Climatology and Probability Forecasts
April 01/21Z valid April 02/00Z
› Climate anomaly: SREF forecasts assessed relative to seasonal climatology; Rich Grumm
› http://nws.met.psu.edu/ensembles/index.html
› http://eyewall.met.psu.edu/ensembles/
a.
SREF init: 21Z01APR2006 valid 00Z03APR2006
Mean MSLP and Anomaly (shaded)
SREF MSLP and PWAT Anomalies
valid 00Z 03APR2006
› Deepening surface cyclone
› Central pressure forecast > 2 SD below
climate normal over the upper
Mississippi Valley
b.
SREF init: 21Z01APR2006 valid 00Z03APR2006
Mean PWAT and Anomaly (shaded
› Moist air surging poleward
› PWAT anomalies forecast 2 to 3 SDs
above climate normal
› CAPE anomaly + 2-3 SD (not shown)
a.
SREF init: 21Z01APR2006 valid 00Z03APR2006
Mean CAPE
(shaded)
Mean CAPE
(shaded) andand
EHI EHI
Mean CAPE, SRH, EHI, Shear Forecasts
valid 00Z 03APR2006
› Mean CAPE 1200-2500 Jkg-1
› Mean EHI 1-3 from Illinois to lower
Mississippi Valley
b.
SREF init: 21Z01APR2006 valid 00Z03APR2006
Mean SR-Helicity
SRH
(shaded)
and 1.5 km Shear ≥ .006 s-1
(shaded);1.5 km Shear (103) & vectors
› Mean SRH 300-400+ m2s-2 along and north
of a strong warm front
› Mean SRH 200-300+ m2s-2 along and east of
the cold front
› Mean 1.5 km mean shear .009-.010+ s-1
(~30 kt) across the Mississippi Valley
a.
Prob CAPE ≥ 2000 m2s2 (shaded)
SREF NARR 21Z01APR2006 valid 00Z03APR2006
Mean
CAPE
≥ 1200
J/kg
Prob CAPE
> 2000
Jkg-1; Mean
CAPE
≥ 1200 Jkg-1
SREF CAPE Threshold Probabilities
valid 00Z 03APR2006
› CAPE forecast to exceed 2000 J/kg from
southern IL (>30%) to TX (> 90%)
b.
SREF 09Z01APR2006 valid 00Z03APR2006
-1
Probability
CAPE≥> 1000
Prob
CAPE
1000JkgJ/kg
› CAPE forecast to exceed 1000 J/kg (70% 90%) across much of the Mississippi Valley
a.
SREF NARR 21Z01APR2006 valid 00Z02APR2006
-1
ProbProbability
1.5 km1.5km
shear
≥ .006
shear
> .006 s
s-1 (shaded);
mean shear ≥ .006 s-1
SREF Shear and SRH Threshold Probabilities
valid 00Z 03APR2006
› Mean shear will likely exceed .006 s-1
(> 90%) across entire outlook region
…ranging from .012 - .018 s-1
b.
SREF 09Z01APR2006 valid 00Z03APR2006
Probability
> 200
Prob
SRHSRH
≥ 200
mm22ss22
› SRH will likely exceed 200 m2s2 (50% 70+%) along and east of cold front
SREF Summary
› SREF departures from climatology indicate an anomalously deep cyclone with
atypical moisture and instability in the warm sector
› SREF forecasts indicate a high likelihood of severe weather… including a
potential for supercells with significant tornadoes… across much of the lower
and central Mississippi Valley on 2 April 2006
› Additional SREF products (not shown) indicated considerable agreement
among the ensemble members
› Users need to know that forecast confidence is high for a high impact event
NCEP Operational NAM-WRF Graphics
› 00 UTC and 1200 UTC:
 http://www.emc.ncep.noaa.gov/mmb/mmbpll/nampll12_fullcyc_2mbtop/index.html
› 0600 UTC and 1800 UTC:
 http://www.emc.ncep.noaa.gov/mmb/mmbpll/opsnam_offtime/index.html
NAM-WRF and SREF
SREF Probability of the 2m Dew Point > 60o F valid 0403/00 UTC
› SREF: Greater than 90% probability of
the surface dew point > 600 F across
central and southern Mississippi Valley
NAM-WRF Dew point valid 0403/00 UTC
› NAM-WRF illustrates distribution and
magnitude of warm sector dew points
NAM-WRF Best CAPE
› CAPE forecast 2000-3000J/kg along and ahead of the cold front
› NAM-WRF illustrates distribution and magnitude of warm sector instability
NAM-WRF Forcing and Vertical Wind Shear (not shown)
› NAM-WRF highlighted important forcing mechanisms in a forecast of
significant low-level frontogenesis and strong moisture flux
convergence along the frontal features
› NAM WRF substantiated the SREF probabilities of a highly sheared
environment and added details to magnitude and distribution of shear
NAM-WRF Instant and Convective Precipitation
Instant Pcp Rate - 36 H Forecast valid 0403/00 UTC
Conv Pcp Rate - 36 H Forecast valid 0403/00 UTC
› NAM-WRF instant and convective precipitation shows
convective potential along banded frontal structures and grid
scale precipitation northwest of the surface cyclone
a.
Mosaic of radar base reflectivity
valid 0001 UTC 3 April 2006
NAM-WRF Simulated Radar
Reflectivity
› Although it is not valid to make direct
comparisons between actual and
simulated radar at 12 km resolution…
simulated radar can reveal important
details about the mode of convection
and evolution of a severe storm
environment
b.
› Indicates banded frontal and pre-frontal
structures with a potential for cellular
elements…which correspond rather well
with the actual radar, even though the
actual radar shows much greater
reflectivities in the convection
NAM-WRF 24 hr forecast of simulated refl
at 1 km AGL – valid 04/03/0000 UTC
Mosaic of radar base reflectivity
valid 0001 UTC 3 April 2006
Mosaic of radar base reflectivity
valid 0001 UTC 3 April 2006
NAM-WRF 24 hr forecast of simulated refl
at 1 km AGL – valid 04/03/0000 UTC
WRF-NMM4 24 hr forecast of simulated refl
at 1 km AGL – valid 04/03/0000 UTC
a.
b.
Summary – Case 1
› SREF graphics indicated the likelihood of a severe weather event with a high
potential for supercells and tornadoes across the mid Mississippi Valley on 2
April 2006. EPS forecasts also indicated substantial agreement between the 21
SREF members… increasing confidence in the forecast
› Climate anomalies indicated the event would be associated with an
uncharacteristically deep surface cyclone and an anomalously moist warm
sector
› High resolution model data helped fill in the details of the mode, evolution, and
intensity of forecast convection, and highlighted important mesoscale
structures, including relevant forcing mechanisms
Overview – Case 2
› A marginal severe weather event occurred across parts of the Ohio Valley and
Pennsylvania on 4 October 2006
October 04, 2006 Ohio Valley Severe Weather
› A frontal system moved southward across the Ohio Valley and PA during the
late afternoon/evening of 10/04/06
› Significant heating/destabilization were questionable because morning
convection was expected across OH and PA
› 35 to 45 kt mid-level flow was expected across the region ahead of front
› SPC highlighted locally-damaging winds and some hail… with storms
organized linearly along/ahead of the front
SPC SREF
Oct 04/09Z Valid Oct (04-05)/21Z – 00Z
10/04/09Z valid 10/04/21Z
Prob Conv Precip ≥ .01 in x Prob MUCAPE ≥ 1000 x Prob
Eff Shr > 40
Mean MUCAPE (shaded/contour), Eff shear vectors, 3km SRH (green)
Prob Conv Precip ≥ .01 in x Prob MUCAPE ≥ 1000 x Prob
Eff Shr > 30
Craven Brooks Mean Sig Svr and Standard Deviation
10/04/09Z valid 10/04/21Z
Prob Supercell Composite > 1 and Mean Supercell Comp = 1
Prob Craven Brooks Sig Svr > 20000 and Mean Sig Svr = 20000
10/04/09Z valid 10/04/21Z
Mean Precipitable Water Forecast
and Normalized Climate Anomaly
Mean MSLP Forecast
and Normalized Climate Anomaly
› PWAT 2-3+ SD above climate norm….MSLP 1-2 SD above climate norm
10/04/09Z valid 10/04/21Z
CAPE (shaded) and EHI
› Mean CAPE < 1200 J/kg (PA); > 1200J/kg OH and IN
› Mean EHI ≤ 1 IN/OH
SRH (shaded), 5km Shr > .003 s-1
10/04/09Z valid 10/04/21Z
› Mean SRH < 150 m2/s2 PA; 150-200+
m2/s2 along/south of front
› Mean deep (5 km) Shear ≤ .003 s-1 (30 kt)
along front
1.5km Shr > .003 s-1
› Mean low-level (1.5 km) Shear ≤ .006 s-1
(18kt) along front
Prob CAPE > 1200 J/kg
10/04/09Z valid 10/04/21Z
› Prob CAPE > 1200 J/kg 30% PA to 70+% OH
› Mean EHI < 1
Prob EHI > 1
› Prob EHI > 1 20-30%
SREF Summary
› SREF single and combined probabilities illustrate an environment marginally
favoring severe weather from organized convection across the parts of the
Ohio Valley and Pennsylvania on 10/04/06
› Isolated supercells are possible but not probable. Tornadoes are unlikely
› Main threat: damaging winds
AWIPS NAM-WRF
Oct 04/12Z Valid Oct (04-05)/21Z
10/04/12Z valid 10/04/21Z
Front
CAPE 1500-2000
Supercell composite
EHI 3+, 0-3km Shear >.007s-1
Pre-frontal mconv
Front
10/04/12Z valid 10/04/21Z
Significant Severe 30000+
SRH 150-200+
10/04/12Z valid 10/04/21Z
850 mb
850 - 500mb
Frontal Omega
500 mb
700 - 500mb
Frontal Omega
250 mb
500 - 300mb
Frontal Omega
200 mb – 300 mb
Divergence
10/04/12Z valid 10/04/21Z
850 mb
500 mb
250 mb
NCEP Operational NAM-WRF Graphics
10/04/09Z valid 10/04/21Z (L) and 10/05/00Z (R)
NAM-WRF Summary
› NAM-WRF depicts more unstable environment with greater shear than SREF
› It appears high resolution model provides valuable additional information
…especially when a marginal severe event is expected
Simulated Radar Reflectivity, Real-time Satellite and Radar
10/04/09Z valid 10/04/21Z (L) and 22Z (C and R)