Paper # 7.11 CAPTURING OF STORMS AND EXTREME EVENTS FROM MODIFIED SURFACE WEATHER CHARTS

1. Paper # 7.11CAPTURING OF STORMS AND EXTREME EVENTS FROM MODIFIED SURFACE WEATHER CHARTS By ATA HUSSAIN Meteorologist Pakistan Meteorological Department WMO-WWRP International Symposium on Nowcasting and Very Short Range Forecasting Toulouse, France, 5-9 September 2005

2. INTRODUCTION • Severe storms like thunderstorms and extreme events like heavy rain or hail and high winds occur on small scale and often for short duration. Although the occurrence of a storm especially severe storm is mostly of localized in nature, the impact of such weather phenomenon is much serious and hazardous one for diversified aspects of human life and property. The small scale and short duration of such weather events make them difficult to observe with conventional observing systems and even predict with numerical computer models. • This study is aimed at discussing some techniques and methodologies which may lead to incremental improvements in the prediction of storms & extreme events and that can be employed in the meteorological services of the world, the examples of storms, high impact weather systems and the proposed techniques are, however, given with reference to Pakistan.

3. INTRODUCTION Precipitation is one of those weather phenomena which are not uniformly distributed in space and time. The following table shows amounts of rainfall at various locations in the twin cities of Islamabad & Rawalpindi on 23rd of July, 2001 which speaks of how much the weather phenomenon was localized in nature. The event was responsible for huge urban storm flooding in the twin cities and adjoining areas which caused about 200 human casualties, leaving behind more than 1500 houses abolished and 2500 partially destroyed. No such event has ever occurred in the recorded history of Islamabad.

4. INTRODUCTION Some regions in Northern Pakistan (among Argentina, central Africa, Florida & northern India) experience some of the most intense lightning (Thunderstorms (TS) activity) on the planet due to the local orography and regional airflow patterns. In Pakistan, the areas of higher lightning or TS activity lie above 30º N. There is no region beyond 30º North or South in the world having such a higher TS activity. Units expressed are flashes/kilometer square/year Source: NASA GHCC Lightning Team

5. On the average, possibly, every 2nd or 3rd day and every 3rd or 4th day could be a TS day over Northern Pakistan during monsoon (July-September) and pre monsoon (April-June) seasons respectively. (Mir, et al (2005))

6. In some eastern, northwestern and central parts of Pakistan (especially the areas having geographical proximity to the Thal & Cholistan deserts), dust storms (DS) frequency is quite high with the highest frequency being 16 DS days/year at Shorkot (a town at about 400 km to the south of Islamabad) (Hussain,(2005)).

7. Plot of daily precipitation (1961-2003)over Islamabad. It is evident that precipitation related extreme eventsare on the increase over Islamabad.

8. PREDICTION OF HIGH IMPACTWEATHER: a Challenging Task • Prediction of storms and extreme conditions is generally considered a challenging task. Severe storms are mostly of short duration, yet their impacts are not brief. • In this study some techniques are discussed which can be deployed at meteorological / weather forecasting offices in order to have micro analysis of prevailing weather characteristics which may lead to incremental improvements in the prediction methods of high impact weather systems. The techniques involve the methods, most of which are not new but need to be modified and refined. • The modifications and refinements seem to be very useful especially for those countries and regions where most of the work (involving plotting of data, analysis of weather charts and etc.) is done manually.

9. DEVELOPMENT OF HIGH RESOLUTION MODIFIED SURFACE WEATHER CHARTS A surface analysis chart is like a weather snapshot showing weather features at a specified time. The conventional surface weather charts used for synoptic analysis are too small in scale to capture a localized severe storm or extreme event. Some meteorological stations appeared to be too close on the maps (because of the small size map) that it seems to be impossible to plot the synoptic data of many a meteorological station. So it seems quite logical that making prediction of small scale severe weather systems from surface charts requires micro analysis. The need can be fulfilled by plotting the maximum data on modified large scale (high resolution) charts to be used for detailed analysis. These charts should preferably contain only the large size country map on it (and some adjoining areas of neighboring states). Continued…

10. DEVELOPMENT OF HIGH RESOLUTION MODIFIED SURFACE WEATHER CHARTS • In addition, topography, orography, water reservoirs like lakes, dams & etc. (in addition to rivers), land cover and land use information of the country or region (or area of interest) should also be reflected on these charts (with light color shading in the background) while printing. This can be very useful for the forecasters during the process of micro analysis of these charts. • More than one chart can also be developed for various regions of the country (especially in case a country is having very large area), giving special attention to those regions where the frequency of formation of storms and occurrence of extreme events is maximum. • These modified surface weather charts can be used in addition to the conventional synoptic charts already employed in the meteorological service of a country.

11. Domain of conventional Synoptic Surface weather chart used in Pakistan.

12. Domain of proposed modified Surface weather chart for Pakistan (To be used for capturing storms and extreme events).

13. Satellite image showing topography, orography & land cover of South Asia. This information (in addition to rivers & lakes) if reflected on modified surface weather charts with light colors in the back ground while printing can be very helpful for the weather forecasters during micro analysis of these charts.

14. More than one chart can also be developed for various regions of a country. (especially in case a country is having very large area or having dense network of Met. observatories). The figure shows theDomain of proposed modified Surface weather chart for Punjab (a province of Pakistan).

15. EXPANDING THE NETWORK OF REAL TIME DATA GENERATING POINTS In order to make the proposed high resolution charts more effective, it is desirable to increase the real time data generating points (i.e. surface meteorological (met.) observatories) so that maximum surface data is available for plotting and analysis. Many countries of the world do have their networks of Aeromet and Agromet observatories. In most of the cases, these observatories do not issue 3-hourly synoptic messages (i.e. these observatories do not work as synoptic observatories although they do record hourly met. observations). These observatories can be re-designated as Agromet-cum-Surface or Aeromet-cum-Surface observatories as the case may be. So these observatories can also issue 3-hourly synoptic messages ( and even hourly messages if so needed) along with their routine agrometeorological work. This will not require any extra financing. What only will require for the meteorological authority is to provide the observatory staff with the suitable correction tables and code books for making synoptic observations and issuing the synoptic messages accordingly. It will take only 10-15 minutes for the on-duty official in generating and transmitting the surface weather conditions after every three hour.

16. SPEEDY TRANSMISSION OF DATA TO THE FORECASTING OFFICES • Synoptic data of a meteorological station can only be useful for a weather analyst sitting at a forecasting office, if it becomes available for plotting on the weather charts well in time. • In developing countries, the ways of data communication may not be very fast. If so then this may involve some extra expenditure in adopting the faster mode of data transmission. But this extra burden can be minimized by using the faster mode only in the months or season/seasons during which frequency of formation of severe storms and occurrence of extreme events is maximum (which can be confirmed from the past data).

17. SURE PLOTTING OF ALL THE AVAILABLE SURFACE DATA ON MODIFIED SURFACE CHARTS • After the receipt of data from all the meteorological stations of a country, it is desirable to assure that all the data must be plotted on the modified charts to make the subsequent micro analysis of the charts more accurate. In the mean time, if the data of some meteorological stations from the neighboring states/regions (close to the country border) are received, then these may also be plotted so that the analysis may become symmetrical and the orientation of the weather systems (if present) may appear close to the reality.

18. MICRO ANALYSIS OF MODIFIED SURFACE WEATHER CHARTS • Like the picture in the Chinese proverb that is worth more than ten thousand words, a surface chart provides a wealth of information. In meteorology, the term weather analysis usually refers to the sequence of operations involved with the organization of the plotted information on the weather maps. This logical portrayal of the data leads to interpretation of the spatial distribution of various weather elements. Typically, a major part of the analysis phase involves drawing of isopleths (e.g. isobars, isallobars, isotherms and etc.). Map analysis increases the visual communication value of the chart. On surface weather charts isobars, their packing and pattern are of great importance. The packing of the isobars reveals how rapidly the pressure varies with distance in the horizontal direction. A tighter packing indicates a much more rapid horizontal variation of air pressure. • The surface analysis may include one or more color coded lines to identify a front (especially for mid latitude regions). ). A front is defined as the transition zone between air masses having dissimilar thermal and moisture properties. Usually, these transition zones are only 50 to 100 km wide, a sufficiently small horizontal distance to permit their representation as lines on a conventional surface analysis chart. But these zones can be represented and highlighted well on the proposed modified surface weather charts. Continued…

19. MICRO ANALYSIS OF MODIFIED SURFACE WEATHER CHARTS • Micro analysis of the modified charts refers to the weather analysis but with some more depth and with special focus on the following (giving due weightage to the smaller factors and fractions of forces which might be ignored during the analysis of synoptic scale weather systems on conventional weather charts). • (i) Pressure gradient and pressure gradient force • (ii) Pressure tendencies (3-hour, 24-hour pressure changes) • (iii) Temperature gradient • (iv) Moisture content of the air • (v) Localized convection • (vi) Fronts & frontal wedging • (vii) Wind convergence & Vorticity (Vorticity from the weather charts can be estimated by using some appropriate mathematical relation, one of such relation is shown below: ζ = (-∂V/ ∂n) + (V/ Rs) Where ζ is relative velocity, (-∂V/ ∂n) is Shear vorticity & (V/ Rs) is Curvature vorticity. • (viii) Topography & orography: Information about regional topography, orography and etc. This may be the mechanism of uplifting of air (in addition to convection) in certain areas. • (ix)Additional Information: Cropping season, land area under irrigation, land cover and land use information of various regions of the country should also be kept in mind by the forecaster.

20. LINKING OF SURFACE WEATHER FEATURES WITH CONVENTIONAL SYNOPTIC & UPPER AIR CHARTS AND RADAR & SATELLITE IMAGES After the analysis of modified surface weather chart, this chart required to be studied link with conventional synoptic & upper air charts, satellite and radar images. The amplitude (north-south height) and breadth (west-east) of troughs and ridges and vorticity information on a 500 Mb chart indicate the characteristics of the surface highs and lows beneath them. A radar or satellite image overlay on the surface analysis permits more additional information about regions of precipitation, its extent and intensity. On the basis of micro analysis, reasonable very short range weather forecast can be made.

21. DERIVING THE RESULTS AND COMMUNICATING TO THE CONCERNED AGENCIES • Finally deriving the results and communicating to the concerned agency/agencies in case any scientific clue about the occurrence of a storm or any high impact weather phenomenon is to be found. • Depending upon the prevailing weather conditions and the need to have snapshot of surface weather features after short intervals, modified surface weather charts can also be analyzed by using and plotting hourly surface data.

22. PROCESSING TIME • In the regions where the data on the weather charts is plotted manually, it takes one minute to plot data of three stations on a surface weather chart. If for a country, data of about one hundred met. stations are to be plotted, it will take the plotter 30 to 40 minutes to plot the data of these stations and a few met. stations of the neighboring countries on to the modified surface weather chart. Plotting of data of some adjoining met. stations of neighboring states/regions on the chart is important in the sense that it shall help in making the orientation and shapes of the weather systems closer to the reality while drawing isopleths. Analysis of the chart and preparation of the forecast product may take another half an hour. So it will take 1 to 1.5 hours for the whole process. However, the processing time shall further decrease in case if some part or whole of the process is computerized.

23. CONCLUSION • As micro scale phenomena need to be addressed and understood at micro level. The development and adaptation of proposed high resolution modified surface weather charts (in addition to the conventional synoptic charts) in the meteorological services of the world may lead to have better and improved prediction of high impact weather systems and small scale weather events and thus shall also enhance the capabilities of forecasters in the issuance of very short range forecasts and weather warnings.

24. THANK YOU for the patience