Nowcasting Thunderstorm Intensity from Satellite

Robert M Rabin

NOAA/National Severe Storms LaboratoryNorman, OK USA

Cooperative Institute for Meteorological Satellite StudiesUniversity of Wisconsin

Madison, WI USA

Outline● Purpose● The first pictures (1960's) TIROS

- Basic cloud structure, Environmental conditions ● GEO arrives (1970's) ATS and GOES

- Time rate of change, anvil expansion

- More structure, Enhanced-V● Multispectral (1990's) AVHRR and GOES

- Plumes, near storm environment● Outlook for the future

Purpose

● Review past discoveries in relation to radar.● Explore prospects for operational severe storm detection.

The First Pictures

TIROS-I

27 May 1960, 1719 LST

from: L. Whitney

JAM 1963:

Severe Storm Clouds

as seen from TIROS

From: L. F. Whitney, 1963, JAM, figure 3

●Clouds are “conspicuous and distinctive”

●Medium size, not linear

●Highly reflective, combined anvils

●Sharp edges, scalloped structure

●Much larger than area of radar echoes and sferics

●Contiguous clear areas, useful in determining severity?

Relationships between size of cirrus shields and severity

R.J. Boucher 1967, JAM

TIROS IV-VII

17 cases1962-1964

From: Fig. 2

From Fig. 3, Boucher 1967, JAM

●Diameter of cirrus shield is an index of storm severity:

- Rarely severe < 60 n mi

- Usually severe > 150 n mi

●Penetrative convection: not always severe weather

●Contiguous clear areas not common

●Results based on a limited sample of cases

Satellite imagery and severe weather warnings

James F.W. Purdom, 1971

Polar orbiting: NOAA-1

●Squall lines: characteristic appearance, narrowing to south

●Locations of jets: polar and subtropical

●Shear with height: thermal ridge and amount of veering

ATS-3 Visible imagery (1971): 11-minute updates on demand

●Early detection of squall lines as compared to radar

●Isolation of areas under threat for severe weather:

- Often southern portion of convective clusters

●Growth of anvil:

- Pause in expansion linked time of tornado occurrence

- McCann(1979) linked collapsing tops to downdraft

and tornado formation

Convective Initiation

Some uses of high-resolution GOES imagery in the mesoscale forecasting of

convection and its behavior

James F.W. Purdom, 1976 MWR

●Detection of mesoscale processes: - Important for storm initiation and maintenance- Effects of terrain (coast lines, rivers and lakes)

●Precise location of convective (outflow) boundaries

●Merging and intersecting of boundaries

●Given favorable conditions:

- New convection and intensification

Exploration of Infrared imagery

Detection of tropopause penetrations byintense convection with GOES enhanced

infrared imageryPeter Mills, Elford Astling, 1977, 10th SLS

●First observations of warm spots on anvil●Near tropopause penetrations

- confirmed by radar●Possible causes

- higher emissivity above updraft- stratospheric cirrus- rapid sinking

Anvil outflow patterns as indicators of tornadic thunderstorms

Charles E. Anderson, 1979

●Observed characteristics of cirrus plumesof severe storms (limited cases)

- Displaced to the right of the ambient wind- Anticyclonic rotation- Spiral bands- Similarity to hurricanes

On overshooting-collapsing thunderstorm tops

Donald W. McCann, 1979

●Previously observed by aircraft (Fujita, 73;Umenhofer, 75)

●Collapse does NOT cause tornado

●May be related to acceleration of gust front:

- Occlusion of mesolow

- Strong surface outflow (i.e. bow echo)

Thunderstorm intensity as determined from satellite data (SMS 2: IR 5-minute)Robert Adler and Douglas Fenn, JAM 1979

●Tornadoes during or after rapid expansion (7 of 8)

●Statistical relation to severe weather:- Severe storms: colder and more rapid growth

●Potential warning lead time: 30 minutes

●Divergence and vertical velocity:- Twice as large for severe storms

●Limitations: - Results from a single day- Existing anvil may obscure new storm growth- Storm top heights underestimated as compared to radar

Mesoscale convective complexesRobert Maddox, 1980 BAMS

●Identified unique class of convective system

●Defined from IR imagery

- Cold cloud tops (< -32 C)

- Size (> 100,000 km**2)

- Shape: circular (eccentricity > 0.7)

- Duration: > 6 hours

●Produce wide variety of severe weather

●Difficult to forecast

- Weak upper-level support

- Low-level warm advection

Observations of damaging hailstorms from geosynchronous satellite digital data

(GOES 30-minute data: 9 storms)

David W. Reynolds, 1980 MWR

●Cloud tops colder than tropopause

- Infer vigorous updrafts

●Expect better relation for hail

- Tornadoes: depend on boundary layer conditions●Large hail storms

- Long lasting (3-5 h)- Large, high cloud tops

●Onset of large hail- Rapid vertical growth- Cloud top becoming colder than tropopause

●Requires proper enhancement

The enhanced-V: a satellite observable severe storm signature

Donald W. McCann 1983, MWR

●Relatively large sample: 884●Interaction of winds and overshooting tops

- Strong upper level wind (20-60 m/s)●Many severe storms do not have enhanced-V

- POD is low ( .25 )- Cause of enhanced-V needs more research

●FAR similar to other methods (.31)

●Lead time of 30 minutes

●Requires proper enhancement

Detection of severe Midwest thunderstormsusing geosynchronous satellite data

SMS-2 and GOES-1: ~5 minute data

Robert Adler, Michael Markus, Douglas FennMWR 1985

●Combine parameters into single index ●Index correlated with severe weather and max reflectivity

- Parameters related to updraft intensity- Cloud top ascent rates- Expansion rates of isotherms

- Based on 4 dependent, 1 independent case

●V-shape with embedded warm spot

- Similar to McCann findings●Limitations

- Identification of cloud tops during certain stages- Resolution in IR (cloud tops too warm)- Ambiguity in height from cloud top temperature

Thunderstorm cloud top dynamics as inferred fromsatellite observations and a cloud top parcel model

Robert Adler, Robert Mach, 1986 JAS

●Used GOES stereoscopic observations (May 1979)

●Three classes of storms identified and simulated

- 1. concentric: monotonic temperature-height

Cold-warm couplet with coldest and highest point

- 2. collocated: isothermal

- 3. offset: inversion with mixing

●“Close in” warm point: subsidence undershooting

Upper-level structure of Oklahoma tornadic stormson 2 May 1979, I: Radar and satellite observations

Gerald Heymsfield, Roy Blackmer, Steven SchotzJAS, 1983

●Three severe storms investigated (single day)

●“V” pattern of low cloud top temperature

- Strong divergence●Close-in warm area:

- 10-20 km downwind- Moves with storm motion

- Forms at time of tropopause penetration- Subsidence mechanism proposed

●Distant warm area (not in all cases) - 50-75 km downwind- Moves with upper-level winds- No visible stratospheric cirrus

●Rapid growth stage

- Cold areas collocated with radar echo●After rapid growth

- Cold areas sometimes displaced from echo core

●IR temperature change

- Not always consistant with stereographic

height change

Satellite-observed characteristicsof Midwest severe thunderstorm anvils

Gerald Heymsfield, Roy Blackmer, MWR 1988

●Statistics from several cases (9)

●Thermal couplets

- Second distant warm point often observed

- Width of V: spacing of cold and distant warm

- T-diff (warm-cold): related to amount of overshoot

●Ingredients for “V”

- Strong shear near troposphere

- Intense updrafts and overshooting tops

●Various hypotheses

- Internal cloud dynamics

- Radiative transfer effects

- Flow over and around storm top: waves

- Combination of above

●Limitations

- IR pixel resolution

- Unknown temperature and ice crystal structure

- Complexity of multistorm structure

- 3-D models too simplified

Aircraft overflight measurements of Midwestsevere storms: Implications on

geosynchronous satellite interpretations

Gerald Heymsfield, Richard Fulton, James Spinhirne, MWR 1991

●Dimensions of overshooting tops- Size of single GOES pixel- 15 degs colder than GOES

●Thermal couplets: much more pronounced●Warm areas: not due to variation in optical depth●Above cloud wind and temperature perturbations

- Cold dome in temperature field

The AVHRR channel 3 cloud topreflectivity of convective storms

Martin Setvak, Charles Doswell, 1991 MWR

●Areas of enhanced reflectivity at 3.7 microns

- Convective cell: widespread or localized

- Plume-like: less common

●Association with hail (limited sample)

●Not often associated with “V”

●Possible cause

- Very small ice crystals- Generated from vigorous updrafts

Passive microwave structure of severe tornadic storms on 16 November 1987

Gerald Heymsfield, Richard Fulton, 1994 MWR

●Maximum polarization difference at 86 Ghz

- Correlates with internal warm region

- Convective core:

Symmetrical or tumbling ice particles

Small polarization difference

- Warm region:

Oriented ice crystals

Large polarization difference

●Microphysical variations

- Partially explain IR structure

Multispectral high-resolution satellite observations of plumes on top of convective

storms

Vincenzo Levizzani, Martin Setvak, 1996 JAS

●Enhanced reflectivity

- Small ice crystals

- Limited growth time: strong updraft (BWER)

- Vertical lifting/gravitational settling

●Vertical separation between plume and anvil

●Different from Fujita's (1982) stratospheric cirrus

●Link between plume source position and warm spot

Satellite observations of convective storm tops in the 1.6, 3.7 and 3.9 spectral bands

Martin Setvak, Robert Rabin, Charles Doswell, Vincenzo Levizzani, 2003 Atmos. Res.

●Study used GOES and Doppler radar

●Areas of high cloud top reflectivity

- Time scales: minutes to hours

- Size: pixels to entire anvils

- Linked to mesocyclone formation

- Move downwind once formed

- Not always associated with mesocyclones

●Mechanisms remain unknown

Moisture plumes above thunderstorm anvils and their contributions to cross-tropopause

transport of water vapor in midlatitudesPao Wang, 2003, JGR

●Storm simulated using 3-D, non-hydrostatic model

●Water vapor source: shell of overshooting dome

●Gravity waves

●Waves break when instability becomes large

●Water vapor injected into stratosphere

●Carried downwind in shape of a chimney plume

●Transport of water vapor to stratosphere: 3 tons/sec

Nowcasting storm initiation and growthusing GOES-8 and WSR-88D dataRita Roberts, Steven Rutledge, 2003 WF

●Based on observed cloud growth rates

- Eastern CO (4 days),

- Washington DC and New Mexico (2 days)

●Onset of storm development

- Surface convergence features

gust fronts, rolls, terrain, intersecting features

- Cloud tops reaching sub-freezing altitudes

- Rapid cooling of cloud tops

●Intensity related to rate of cooling

●Increased lead time

- 15 minutes prior to 10 dBZ echoes aloft

- 30 minutes prior to 30 dBZ echoes aloft

●NCAR automated nowcasting system

NCAR auto-nowcast systemCindy Mueller et al, 2003, WF

●Provides short-term (0-1 hr) nowcasts of storm location

●Identify boundary layer convergence lines

●Fuzzy logic to combine predictor fields

- Radar, satellite, mesonet, profilers, models

●Improves over extrapolation and persistence

- Tested at 3 locations (3 years)

- Plans to include in NWS AWIPS

Validation and use of GOES sounder information

Tim Schmit, et al., 2002 WF

●Thermodynamic stability parameters

- CAPE, CIN, PW

- Hourly updates for time trends

- Horizontal resolution (10 km)

- Only available in clear areas

●Subjective use in forecast offices

●Limited use in NWP

Storm trackerA Web-based tool for monitoring MCS

Robert Rabin, Tom Whittaker 2004

●Identify and track MCS

- Cold cloud tops

- Radar reflectivity

- Adjustable thresholds●Time trends of MCS characteristics

- Size

- Cloud top temperature stats

- Radar reflectivity stats

- Lightning

- Storm environment from RUC,...●Real-time and archived data on-line●Data access from NOMADS/THREDDS catalog

Data Flow

GOES

Radar

RUC model analysis

THREDDS

LightningTrackingAlgorithm Web Server

●Example session:

Summary

●40 year history of satellite research

●Hot research topic through 1980's

●Limits to Operational use of early ideas

- Advent of Doppler radar network

- Resolution limitations

- Limited early access

●Greatest impact: qualitative use of imagery

The Future?

●MSG (now)

●AWIPS

●GOES-R (2013)

●Space-borne Radars?