A Review of Issues Doswell C.A. III, 2001: Severe Convective Storms – An Overview. Severe Convective Storms, Meteor. Monogr., 28, no. 50, Amer. Meteor.

A Review of Issues Doswell C.A. III, 2001: Severe Convective Storms – An Overview. Severe Convective Storms, Meteor. Monogr., 28, no. 50, Amer. Meteor. Soc., 13-26

General Outline of this Review
Severe Convection Definitions & Distinctions Observations of Processes Leading to Severe Convection Prediction of Severe Convection Prospects and Unsolved Problems

Severe Convection Definitions & Distinctions: Issues
Definition of severe convection based upon threat to life and property Threshold setting philosophy based upon threat: 1” inch or larger diameter hail; thunderstorm straight-line wind gusts of 50 knots (57 mph) or greater; any tornado -Beyond these thresholds for “severe” forms of hail, wind and precip the probability of damage increases substantially, although set somewhat arbitrarily. -PROBLEM:The storm is classified as “severe” however, if only 1 or 2 isolated examples are found, whereas real hail and convective wind gusts occur in areas of various length/width/size. Doswell suggests that the severe reports based on a point instead of an area create a mismatch between a severe event and the report, leading to a lack of trust in our climatological records and reality. -PROBLEM: Heavy rain not officially considered severe weather SOLUTION? -Hales proposed a new set of thresholds that include the current system, but add a set definition of “significant” severe weather, which he determines has been more nearly constant than current “ marginally” severe events. PROBLEM: HOWEVER, Worldwide the climatological reports, records and definitions are even more erratic

Arbitrariness is always in issue when creating a threshold Thresholds do not take into account combinations of subthreshold elements that could yield a threat Thresholds are “mindless”: Example: Should the average hail size and wind gust be reported as “severe” instead of the single largest size reported?

Potentially damaging or life-threatening precipitation and lightning thresholds not defined for precipitation not officially defined because any thunderstorm can produce either Frequent cloud-to-ground lightning (clearly related to threat to individuals and structures) not clearly related to the meteorological ingredients leading to otherwise severe thunderstorms

Amendments to the definitions based upon threshold have been made Hales’ “Two Tier” System…conventional thresholds AND Second tier involving risk of EF2-EF5 tornadoes; 2” or larger diameter hail; thunderstorm wind gusts greater than 64 knots

Focus should be on potential negative or catastrophic impacts on society Thunderstorm forecasters should concentrate on the ingredients that distinguish between severe and non-severe forms of convection Arguing about where the thresholds should be set distracts forecasters from this mission.

Observations of Processes Leading to Severe Convection: Large Scale (Synoptic Scale)
To some extent biased by outmoded conceptual models Early conceptual models biased by trains of thought that focused on regional buoyancy Thus early conceptual models centered on the observational network that sampled regions that were subsynoptic or low end synoptic scale, including the radiosonde network TO OBSERVE Large scale severe convection: most important are atmospheric soundings : less important are satellite images and data, and aircraft observations - however the large gaps in worldwide network of observations leads to the main knowledge of synoptic-scale being dominated by studies in the N.Hem. Continents - most often analyzed are “outbreak” events, SUCH AS FIGURE 10 and there are relatively few per year.

Fig 10: composite chart depicting features at different levels, is “especially favorable” for severe weather. -polar and subtropical upper level jets -lower level jets - hatched: Sev. Conv. Storms most likely in next 6-12 hr - “I”: storms considered most likely at “I”, where PJ intersects LJ -However, most severe convective DAYS are not outbreaks -therefore the description of the typical synoptic scale situation is eluded here

Early conceptual models centered on either major severe thunderstorm outbreaks or high end events (e.g., the Wichita Falls F5 tornado) Early conceptual models were descriptive,based upon pattern recognition and, not surprisingly, were based upon studies of Great Plains’ prototypes. Such models thus could not account for the vast majority of severe weather events that are not high end, and not “synoptically-evident” Fig 10: composite chart depicting features at different levels, is “especially favorable” for severe weather. -polar and subtropical upper level jets -lower level jets - hatched: Sev. Conv. Storms most likely in next 6-12 hr - “I”: storms considered most likely at “I”, where PJ intersects LJ -However, most severe convective DAYS are not outbreaks -therefore the description of the typical synoptic scale situation is eluded here

Pattern-based recognition led to inaccurate or under assessment of the potential for severe weather and led to unacceptable POD This was especially true in other areas of the country and the world -Doswell instead proposes an ingredients based approach to understanding weather events rather than defining by the characteristic pattern, such as this chart. (BECAUSE the ingredients for an event may be uncharacteristic in pattern, but the event may still happen)

Although synoptic scale pattern-based recognition is still a part of severe storms forecasting, it has been replaced by more thoughtful approaches Ingredients-based approach Conditional instability (meaning LFC exists not at ground Low level moisture (meaning deep moisture leading to wet adiabatic ascent) Some source for parcel lifting to LFC -Doswell instead proposes an ingredients based approach to understanding weather events rather than defining by the characteristic pattern, such as this chart. (BECAUSE the ingredients for an event may be uncharacteristic in pattern, but the event may still happen)

Ingredients-based approaches have been amended to include estimates of wind shear profiles to distinguish between the various “modalities” of convection This augmented approach allows forecasters to estimate whether convection is liable to be “common” or “severe” and the mode with which thunderstorms will take (single cell, multicell and supercell) -Doswell instead proposes an ingredients based approach to understanding weather events rather than defining by the characteristic pattern, such as this chart. (BECAUSE the ingredients for an event may be uncharacteristic in pattern, but the event may still happen)

Observations of Processes Leading to Severe Convection: Mesoscale
Radiosonde network inadequate to account for convective storms developing at the mesoscale Processes acting at the mesoscale (local destabilization; locally developing wind circulations impacting shear profiles; sources for parcel lift) can only be estimated by an observational network at the same or smaller scale. Satellite images – qualitative Radar is marginally useful b/c “line of sight” limitations - also mostly qualitative, except Doppler Radar can attain wind info in “clean air” mode - Important aspect: Convective outflow as outflows from nearby convection interact and merge to form large areas Processes: free internal instabilites – such as “symmetric”, ie oil in frying pan when heated from below, if you saw movement, symmetric, homogeneous, hexagons, ie : forced “external” – topography variations : fronts – normal to the boundary in mesoscale respects - dynamics of non-traditional boundaries of fronts (drylines etc) relatively poorly known : gravity waves – generally common, but rarely do size make them of obvious importance to DMC

Some Issues assessed at mesoscale Convective initiation Areas of low end mesoscale destabilization (differential heating/cooling; regional or less moisture advection etc.) Areas of regional destabiliztion (layer lifting associated with synoptic-scale upper tropospheric divergence and mid tropospheric lift; regional orographic lifing; frontal lifting etc.) Sources of parcel lift (outflow boundaries, turbulence, gravity waves, local topography etc.) Satellite images – qualitative Radar is marginally useful b/c “line of sight” limitations - also mostly qualitative, except Doppler Radar can attain wind info in “clean air” mode - Important aspect: Convective outflow as outflows from nearby convection interact and merge to form large areas Processes: free internal instabilites – such as “symmetric”, ie oil in frying pan when heated from below, if you saw movement, symmetric, homogeneous, hexagons, ie : forced “external” – topography variations : fronts – normal to the boundary in mesoscale respects - dynamics of non-traditional boundaries of fronts (drylines etc) relatively poorly known : gravity waves – generally common, but rarely do size make them of obvious importance to DMC

Some Issues assessed at mesoscale Convective mode Areas of wind shear augmentation and weakening (outflow boundaries/seabreeze/mountain valley circulations) Areas of local effects augmenting directional shear (outflow boundaries, local topography etc.) Satellite images – qualitative Radar is marginally useful b/c “line of sight” limitations - also mostly qualitative, except Doppler Radar can attain wind info in “clean air” mode - Important aspect: Convective outflow as outflows from nearby convection interact and merge to form large areas Processes: free internal instabilites – such as “symmetric”, ie oil in frying pan when heated from below, if you saw movement, symmetric, homogeneous, hexagons, ie : forced “external” – topography variations : fronts – normal to the boundary in mesoscale respects - dynamics of non-traditional boundaries of fronts (drylines etc) relatively poorly known : gravity waves – generally common, but rarely do size make them of obvious importance to DMC

Prediction of Severe Convection ~Current accuracy levels
Progress The “Infrastructure” put into place progressively since the 1950s (observations, tools and models related to forecasting severe thunderstorms) has Increased prediction accuracy Better public awareness and communication has contributed to more support for development of infrastructure and decreasing damage and injuries. Advances in forecasting severe storms and tornadoes - decreasing fatalities - increase in reported tornadoes NOW FIG 12!! - prediction accuracy increased by a factor of 2 Doswell suggests (1990) - there also has been the advancement of public awareness and communication Frustration - non-tornadic events receive relatively little attn - flash floods: consideration of must combine the areas’ hydrology and meteorology - hail formation and convective wind events: difficult to mitigate due to short range forecasts

Heidke unadjusted skill score for reporting tornado and severe t-storm watches is contrasted with his skill score for reporting severe events that has been adjusted for the inflation of severe weather reports nearly all of increase in reported events are “weak” F0/F1 on Fujita scale, events that account for only 2% of fatalities anyway…. # of “violent” events reported per yr – that account for most tornado casualities - has not changed that much with time

Prediction of Severe Convection ~Current accuracy levels
Progress Lagging Not as much attention to non tornadic events Flash floods/heavy convection not offic-ally “severe” Hail formation is difficult to predict and not much can be done to mitigate potential effects forecasts Advances in forecasting severe storms and tornadoes - decreasing fatalities - increase in reported tornadoes NOW FIG 12!! - prediction accuracy increased by a factor of 2 Doswell suggests (1990) - there also has been the advancement of public awareness and communication Frustration - non-tornadic events receive relatively little attn - flash floods: consideration of must combine the areas’ hydrology and meteorology - hail formation and convective wind events: difficult to mitigate due to short range forecasts

Prediction of Severe Convection Global Issues
Awareness of risks of DMC outside of U.S. is poor In many countries, situation is as it was in the United States Great Plains in the 1930s and 1940s (no systematic reporting of events or underreporting) and California through the 1980s. Systematic should be made to have complete data bases Systemic reporting leads to a better appreciation of the threats associated with DMC storms Database provides a history of factual info about threat to inform citizens, otherwise ignorance can be perpetuated Potential for disaster if events are possible and unplanned for (system designed to mitigate the effects of severe convection THROUGH FORECASTING Basic forecasting and climatological record (for hazard planning, public awareness and research possibilities) Scientific forecasting approaches (should be based not only in statistical but also in physically-based concepts in order to develop forecasting methods…Doswell further states that statistical or checklist approaches have difficulty adapting to new research concepts, and hard to it’s hard to predict probability of accuracy if events are not “TYPICAL”) AWARENESS and once aware, how to react to reduce damaging effects

Official responses are often muted because of the preconceived notion that sever DMC is rare or absent sufficient planning must be undertaken for possible severe events in areas where threat is rare Attempts to increase public awareness, and to outline appropriate reactions to severe events (Netherlands) Systemic reporting leads to a better appreciation of the threats associated with DMC storms Database provides a history of factual info about threat to inform citizens, otherwise ignorance can be perpetuated Potential for disaster if events are possible and unplanned for (system designed to mitigate the effects of severe convection THROUGH FORECASTING Basic forecasting and climatological record (for hazard planning, public awareness and research possibilities) Scientific forecasting approaches (should be based not only in statistical but also in physically-based concepts in order to develop forecasting methods…Doswell further states that statistical or checklist approaches have difficulty adapting to new research concepts, and hard to it’s hard to predict probability of accuracy if events are not “TYPICAL”) AWARENESS and once aware, how to react to reduce damaging effects

Three steps in disaster mitigation related to severe DMC Basic forecast verification and climatology Scientific forecasting approaches Event mitigation plans Systemic reporting leads to a better appreciation of the threats associated with DMC storms Database provides a history of factual info about threat to inform citizens, otherwise ignorance can be perpetuated Potential for disaster if events are possible and unplanned for (system designed to mitigate the effects of severe convection THROUGH FORECASTING Basic forecasting and climatological record (for hazard planning, public awareness and research possibilities) Scientific forecasting approaches (should be based not only in statistical but also in physically-based concepts in order to develop forecasting methods…Doswell further states that statistical or checklist approaches have difficulty adapting to new research concepts, and hard to it’s hard to predict probability of accuracy if events are not “TYPICAL”) AWARENESS and once aware, how to react to reduce damaging effects

Prospects and Unsolved Problems
Forecasting Improvements in observing systems (ie radar) and related forecasting systems Difficulties/ less progress Tornadic vs nontornadic supercell differentiation Forecasting nonsupercell tornado situations System to forecast and mitigate flash flood damage Forecasting: <note after difficulties> Doswell promotes the probabalistic appoach to improve forecasting skill and the forecasts’ value

Weather Modification possibilities Public appeal Lack of many severe convective weather processes New Observations Doppler RADARs are likely only a beginning Dual polarization observations possible and now being implemented Satellite remote sensor improvements Economic Issues Weather Modification possibilities – while largely appealing to the public due to apparent “cure”, current lack of understanding of severe weather processes make efforts to alter the weather potentially dangerous!!! - Doswell has little hope for the future benefits of modification of sev. conv. Storms New and improved radars – can positively impact hail detection and rainfall estimates Doswell admits that there are also problems – economic difficulties and push for cheaper alternatives that have reduced spatial density, frequency of sounding observations

“The difference between a major outbreak of severe convective weather and no convection at all might be associated with a very small difference in, for example, the initial convective inhibition…” Relates to the sensitive dependence of nonlinear* systems to initial conditions A great deal of this “nonlinearity” relates to the fact that these mesoscale systems interact with the synoptic scale environment, altering it, and vice versa. *Nonlinear system…a system that depends upon other factors that are themselves changing and which can be altered by the system itself. Officially, a nonlinear system is one whose performance cannot be described by equations of the first degree Mesoscale events comprise the majority of events that people worldwide are affected by, “sensible” weather Chaotic systems – sensitive dependence on initial conditions “almost certainly” (says Doswell) at work in DMC situations….which makes forecasting and understanding of processes difficult….more and better observations are needed Unobservables – Distribution of water substances in clouds -impossible to infer cloud water distribution by RADAR, aircraft obs in clouds is difficult, and no way to validate those inferred measurements - other unobserved variables are also potentially important to cloud dynamics -currently no methods are being proposed, at the time of Doswells writing, to provide routine microphysical observations - any new progress beyond existing systems will require resources

“The difference between a major outbreak of severe convective weather and no convection at all might be associated with a very small difference in, for example, the initial convective inhibition…” In DMC, it is possible that the observational network will ever be good enough to enable correct assessment of convective initiation Theory and modeling will never make up for lack of adequate observations Mesoscale events comprise the majority of events that people worldwide are affected by, “sensible” weather Chaotic systems – sensitive dependence on initial conditions “almost certainly” (says Doswell) at work in DMC situations….which makes forecasting and understanding of processes difficult….more and better observations are needed Unobservables – Distribution of water substances in clouds -impossible to infer cloud water distribution by RADAR, aircraft obs in clouds is difficult, and no way to validate those inferred measurements - other unobserved variables are also potentially important to cloud dynamics -currently no methods are being proposed, at the time of Doswells writing, to provide routine microphysical observations - any new progress beyond existing systems will require resources

A Review of Issues Doswell C.A. III, 2001: Severe Convective Storms – An Overview. Severe Convective Storms, Meteor. Monogr., 28, no. 50, Amer. Meteor.

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A Review of Issues Doswell C.A. III, 2001: Severe Convective Storms – An Overview. Severe Convective Storms, Meteor. Monogr., 28, no. 50, Amer. Meteor.

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Presentation on theme: "A Review of Issues Doswell C.A. III, 2001: Severe Convective Storms – An Overview. Severe Convective Storms, Meteor. Monogr., 28, no. 50, Amer. Meteor."— Presentation transcript:

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