Transcript Kein Folientitel - European Storm Forecast Experiment

Gatzen, Groenemeijer: Forecasting tornadoes using
model- and sounding derived parameters
Introduction A:
Importance of sounding information doing convective forecasts
http://physics.uwstout.edu/wx/Notes/
Introduction B:
Sounding-derived parameters using parcel-theory
Introduction B:
Sounding-derived parameters using parcel-theory
CAPE
Introduction B:
Sounding-derived parameters using parcel-theory
CAPE
CIN
Introduction B:
Sounding-derived parameters using parcel-theory
CAPE
CIN
SBCAPE
Introduction B:
Sounding-derived parameters using parcel-theory
CAPE
CIN
SBCAPE
Introduction B:
Sounding-derived parameters using parcel-theory
CAPE
CIN
SBCAPE
MUCAPE
Introduction B:
Sounding-derived parameters using parcel-theory
CAPE
CIN
SBCAPE
MUCAPE
LCL
Introduction B:
Sounding-derived parameters using parcel-theory
CAPE
CIN
SBCAPE
MUCAPE
LCL
LFC
Introduction B:
Sounding-derived parameters using parcel-theory
Introduction B:
Sounding-derived parameters using parcel-theory
CAPE
CIN ~ 0 J/kg
SBCAPE
MUCAPE
Introduction B:
Sounding-derived parameters using parcel-theory
CAPE
CIN
SBCAPE
MUCAPE
LCL
Introduction B:
Sounding-derived parameters using parcel-theory
CAPE
CIN
SBCAPE
MUCAPE
LCL
LFC
Introduction C:
Sounding-derived parameters in horizontal forecast charts
Is it useful to use them on horizontal maps?
Introduction C:
Sounding-derived parameters in horizontal forecast charts
Is it useful to use them on horizontal maps?
• Horizontal cross sections provide barely enough information
for convective forecasts:
Introduction C:
Sounding-derived parameters in horizontal forecast charts
Is it useful to use them on horizontal maps?
• Horizontal cross sections provide barely enough information
for convective forecasts: Inversions, moist layers, shear profile
not well represented.
Introduction C:
Sounding-derived parameters in horizontal forecast charts
Is it useful to use them on horizontal maps?
• Horizontal cross sections provide barely enough information
for convective forecasts: Inversions, moist layers, shear profile
not well represented.
• Looking at forecast soundings or vertical cross sections
yields required information, but it takes time to find regions of
interest.
Introduction C:
Sounding-derived parameters in horizontal forecast charts
Is it useful to use them on horizontal maps?
• Horizontal cross sections provide barely enough information
for convective forecasts: Inversions, moist layers, shear profile
not well represented.
• Looking at forecast soundings or vertical cross sections
yields required information, but it takes time to find regions of
interest.
• Parameters highlight interesting regions as well as selective
variables and are helpful...
• ...to get a brief overview.
• ...to compare different numerical models.
Introduction C:
Sounding-derived parameters in horizontal forecast charts
Complex parameters using “significant” levels
• Total totals index (TOTL) = T850 + Td850 - 2 * T500 [°C]
• K index = T850 + Td850 - T500 - (T-Td)700 [°C]
• Sweat index = 12*Td850+20*(TOTL-49)+2*U850+5*U500+125*(0.2+sinf)
where f=(wind direction500-wind direction850), U=wind speed[kts], TOTL=0 if TOTL<49
Introduction C:
Sounding-derived parameters in horizontal forecast charts
Complex parameters using significant levels
• Total totals index (TOTL) = T850 + Td850 - 2 * T500 [°C]
• K index = T850 + Td850 - T500 - (T-Td)700 [°C]
• Sweat index = 12*Td850+20*(TOTL-49)+2*U850+5*U500+125*(0.2+sinf)
where f=(wind direction500-wind direction850), U=wind speed[kts], TOTL=0 if TOTL<49
We do not use them for tornado forecasting.
• Using them requires a guide of “magical” numbers - and not
physical understanding of the weather situation.
“One-slide introduction” of myself…
Pieter Groenemeijer
•
(almost) M.Sc. in Meteorology
Utrecht University
•
Oklahoma University (spring semester 2002)
•
2002 and 2004 European Severe Storms
Conferences (Prague, León)
•
ESWD (European Severe Weather Database)
•
“Sounding-derived parameters associated with
large hail and tornadoes in the Netherlands“
•
Co-initiator of ESTOFEX (with Johannes Dahl
and Christoph Gatzen), Oct, 2002.
Sounding-derived parameters associated with
large hail and tornadoes in the Netherlands
Pieter Groenemeijer (IMAU; ESTOFEX), Aarnout van Delden (IMAU)
F3 tornado near Deil, 25-06-1967. (A.C. Frenks)
Sounding-derived parameters associated with
large hail and tornadoes in the Netherlands
study done at Institute for Marine and
Atmospheric Research Utrecht
Main questions
• What sounding-derived parameters can be
used to forecast tornadoes?
• ………………….. large hail?
sub-question:
•
How do the results differ from studies from the United States?
Basic idea
1. Find soundings taken in the proximity of
severe weather events (here: tornadoes)
2. Find if they have special characteristics
(w.r.t. other soundings)
method: look at parameters
that represent something physical
and that have been studied before
Proximity soundings
What is a proximity sounding…?
Used definition:
• within 4 hours of the sounding
(before or after)
• within 100 km from a point that
is advected by the 0-3 km mean
wind from the sounding location
at the sounding time
Data sets
•
radiosonde observations
Dec 1975 – Aug 2003
(thanks to KNMI, DWD,
KMI)
•
severe weather reports
from Dutch voluntary
observers (VWK)
Sinds 1974
Vereniging voor Weerkunde en Klimatologie (VWK)
http:/www.vwkweb.nl
Data
soundings associated with:
hail (2.0 - 2.9 cm)
hail (>= 3.0 cm)
tornadoes F0
tornadoes F1
tornadoes F2
waterspouts
thunder (1990-2000 only)
all soundings
number
46
47
24
37
6
26
2045
67816
results…
Most-unstable CAPE (MUCAPE)
Number of events 
US studies: MUCAPE highly
variable with tornadoes.
Strong tornadoes may occur
with low CAPE when shear
is high
maximum
 75th perc.
median
 25th perc.
MUCAPE not very high with tornadoes…
Most-unstable CAPE released below 3 km A.G.L.
US studies: Davies (2004)
has found a relation between
tornado occurrence and high
CAPE below 3km (in his
study M.L.CAPE)...
MUCAPE<3km high with F0, not with F1+
(most-unstable) LFC height (m)
US studies: Davies (2004)
has found a relation between
low LFC and tornado
occurrence
LFC relatively low with tornadoes (esp. F0)…
LCL height (50 hPa mixed layer parcel)
US studies: Low LCL favors
significant tornadoes, e.g.
Craven et al. (2002)
LCL not sign. diff. between tornadic and thunder
Average soundings
LARGE HAIL
F0
F1+
note the distribution of parcel buoyancy with height
0-6 km A.G.L. bulk shear (m/s)
US studies: strong
tornadoes often occur with
supercells associated with
>20 m/s 0-6 km shear (e.g.
Doswell&Evans, 2003)
0-6 km bulk shear high with F2 tornadoes
0-1 km A.G.L. bulk shear (m/s)
US studies: strong 0-1 km
shear favours for sign.
tornadoes (e.g. Craven et
al., 2002).
0-1 km shear high with F1, esp. F2 tornadoes..
0-1 km A.G.L. storm-relative helicity (m2/s2)
US studies: high values
favor supercell tornadoes
(e.g. Rasmussen, 2003).
0-1 km shear high with F1, esp. F2 tornadoes..
Some conclusions
• F1 and esp. F2 tornadoes occur with higher-thanaverage 0-1 km shear (and SRH, but less clearly).
• F0 tornadoes (and waterspouts) occur with lowerthan-average 0-1 km shear values
• (MU)CAPE is not extreme with tornadoes and
thereby has limited value for tornado forecasting.
Some conclusions
• MUCAPE released below 3 km / low LFC heights
seem to be important for the formation of weaker
(and likely non-supercellular) tornadoes….
(but of course we rather want to forecast the stronger
tornadoes)
• LCL heights are probably not as much a limiting
factor for tornado development in the NL (and in
Germany?) than in much of the U.S.A.
i.e. LCL heights are practically always low enough
here for tornadoes
References
(ask me if you want to see this slide again)
Craven, J. P., H. E. Brooks, and J. A. Hart, 2002: Baseline
climatology of sounding derived parameters associated with deep,
moist convection. Preprints, 21st Conference on Severe Local
Storms, San Antonio, Texas, American Meteorological Society, 643–
646.
Davies, J. M., 2002: On low-level thermodynamic parameters
associated with tornadic and nontornadic supercells. Preprints, 21st
Conf. on severe local storms, Kananaskis Park, Alberta, Canada,
Amer. Meteor. Soc., 558–592.
Davies, J. M., 2004: Estimations of CIN and LFC Associated with
Tornadic and Nontornadic Supercells. Wea. Forecasting, 19, 714–
726.
Doswell, C. A. III, and J. S. Evans, 2003: Proximity sounding
analysis for derechos and supercells: An assessment of similarities
and differences. Atmos. Res., 67-68, 117–133.
Rasmussen, E. N., 2003: Refined supercell and tornado forecast
parameters. Wea. Forecasting, 18, 530–535.
back to Christoph….
Using parameters:
A scenario for a weather pattern associated with “critical” values
In collaboration with Lars Lowinski (Meteos Munich) a
scenario was designed that is characterized by “critical”
values of mentioned parameters.
This scenario is based upon the synoptic situation of four
tornado outbreaks over Central Europe:
• Aug. 1st, 1925 (NL, five tornadoes, one F4)
• June 1st, 1927 (northwestern GER, four F3/F4 tornadoes)
• June 24th, 1967 (northern F, F4/F5 tornadoes)
• June 25th, 1967 (NL, four F3/F4 tornadoes)
Using parameters:
A scenario for a weather pattern associated with “critical” values
500 hPa level
568 • High geopotential over
southern Europe due to
well-mixed airmass
originating from Atlas
mountains
560
552
T
576
H
592
584
• Strong upper SW-erly
jet streak coupled with
negatively tilted shortwave trough
Using parameters:
A scenario for a weather pattern associated with “critical” values
Surface chart
1015
• Frontal boundary with
embedded frontal waves
from Iberian Peninsula to
northern Germany
1020
1010
H
H
L1005
1010
L
1015
• Easterly surface winds
over Germany south of
Scandinavian surface
high pressure system
Using parameters:
A scenario for a weather pattern associated with “critical” values
moist maritime airmass
north of the warm front
19
16
rich low-level moisture
underneath an inversion
north of convergence line
27
22
31
14
well-mixed airmass south
of convergence line
Using parameters:
A scenario for a weather pattern associated with “critical” values
Warm sector north of the
convergence zone:
19
16
• CAPE
• winds veer strongly with
height
27
22
• strong low-level wind
shear
31
14
• maybe low LFC heights
• quasigeostrophic
forcing due to WAA and
DCVA
Using parameters:
A scenario for a weather pattern associated with “critical” values
Would this scenario
be associated with a
tornado outbreak?
1015
1020
1010
H
H
L1005
1010
L
Using parameters:
A scenario for a weather pattern associated with “critical” values
Would this scenario
be associated with a
tornado outbreak?
1015
1020
1010
We don’t know.
H
H
Tornadogenesis is
not well understood.
L1005
1010
L
Probably, this scenario is
associated with an
enhanced chance for
tornadoes.
Using parameters:
23th June, 2004
Estofex
Christian Schöps
23 June, 2004: 500 hPa height, wind speed
23 June, 2004: 850 hPa height, theta-e
23 June, 2004: MUCAPE, deep layer wind shear
23 June, 2004: MUCAPE, low level wind shear
23 June, 2004: LCL height
23 June, 2004: LFC height
Soundings from north-central
Germany. Proximity soundings were
not available. Soundings indicate...
• rather weak CAPE
• winds veer strongly with height
• strong low level wind shear
• rather low LFC heights
Note: Models did indicate
SW-erly surface winds
Conclusions
• Sounding information is essential for convective forecasts.
Conclusions
• Sounding information is essential for convective forecasts.
• Parameters derived from model soundings give a good
overview when plotted on maps.
Conclusions
• Sounding information is essential for convective forecasts.
• Parameters derived from model soundings give a good
overview when plotted on maps.
• They make it easy to compare different models or model
runs.
Conclusions
• Sounding information is essential for convective forecasts.
• Parameters derived from model soundings give a good
overview when plotted on maps.
• They make it easy to compare different models or model
runs.
• Parameters without physical meaning are not used by
Estofex. Learning “magical numbers” associated with complex
variables won’t increase our knowledge about tornado
forecasting.