A Training Course on Quantitative Precipitation Estimation/Forecasting (QPE/QPF) Crowne Plaza Manila Galleria, Quezon City, Philippines 27-30 March 2012 Frequently used QPF techniques and developments Extrapolation, Climatology, Similarity Kuo-Chen Lu Central Weather Bureau, Chinese Taipei Training Course on QPE/QPF Manila 2012 1 contents Introduction Philosophy Synoptic forcing Frontal system Development of forecast guide Typhoon Climatology approach Rain gauge and Grid base Dynamic model approach Development of forecast guide Training Course on QPE/QPF Manila 2012 2 philosophy QPF : is the expected amount of melted precipitation accumulated over a specified time period over a specified area. Amount: Maximum value, or the mean value ? Time period : Hourly, Daily or, A Storm lifespan. Specified Area : A rain gauge, a river basin, A township, A high risk area. How they evaluate QPF ? What’s the reporter said on the newspaper ? They evaluated the QPF is based on the rain gauges. So the forecaster should forecast the value to meet the reporter need, that is based on the rain gauges. Besides, they show the maximum value first. What’s the type of QPF that the user need ? The type of the value should be in the range or in probability. Daily or hourly, the spatial resolution and the duration of request. Training Course on QPE/QPF Manila 2012 3 Forecasting QPF Must determine Where When How Much rainfall will occur area. Must understand the processes that determine the size, scale and intensity of an area of precipitation (synoptic, mesoscale, and even microscale meteorology) Must ..Possess Good Pattern Recognition Skills and understand what gives the pattern the potential to produce significant rainfall Must Possess a working Knowledge of Local Climatology Understand numerical models especially model biases and why they occur Training Course on QPE/QPF Manila 2012 4 Subjectively QPF Analyze situation looking at the synoptic and mesoscale environment. (use the current data and model output to assess situation Does the environment favor high rainfall rates. Use model guidance as a first guess but understand model limitations and biases. Based on model output, radar and satellite imagery and conventional upper air data, try to figure out where rainfall will be most intense for the longest period. This is where the heaviest rainfall will occur. Modify model guidance based on your understanding of the physics that determines how much rainfall will fall. Calibrate forecasts through verification. Verification is very important for manual and computer generated forecast. But how do you verify a forecast. Training Course on QPE/QPF Manila 2012 5 Philosophy Synoptic Checking Large Scale checking on a specific area, with regard to the itemized synoptic forcing. Dynamic guidance Numerical Model may perform well on synoptic forecast, but not on the convective scale, especially on the heavy rain fall. It is worth to evaluate the synoptic forcing by NWP. Decision Making A check list of synoptic forcing by the NWP might help us to expect when and where the heavy rain will occur. Training Course on QPE/QPF Manila 2012 6 Synoptic Checking of Frontal System 1. Surface front 2. Low level horizontal wind shear 3. Sub synoptic system 4. Moist Field 5. Low level Jet 6. Cold tongue 7. Pressure depression 8. Upper level diference 9. Instibility Composited chart 0000 UTC June 1, 2000 Training Course on QPE/QPF Manila 2012 7 Terrential Rainfall Check list Table for 12 48 hrs during the Mei-Yu Season Initial time Year______Mon.______Day______Hr.______ Z NWP: WRF JMA Items of check list OBJ 12H r 24Hr 36Hr 48Hr remark 1. Surface front location within 20 N 28 N 118 E 124 E ( ) ( ) ( ) ( ) ( ) Taipei near 100Km or passed 200Km ( ) ( ) ( ) ( ) ( ) KuoHsung near 200Km ( ) ( ) ( ) ( ) ( ) 2. Horizontal wind shear 22 N 28 N 114 E 127 E 850/700hPa ( ) ( ) ( ) ( ) ( ) 3. Sub synoptic South of Taiwan or east of 114 E surface/850hPa Meso-low ( ) ( ) ( ) ( ) ( ) 700/500hPa Short wave trough ( ) ( ) ( ) ( ) ( ) 4. Moist fields 850hPa Td 15 ( ) ( ) ( ) ( ) ( ) 850hPa e axi cross Taiwan ( ) ( ) ( ) ( ) ( ) 700hPa T-Td 3 ( ) ( ) ( ) ( ) ( ) 5. Low level Jet 18 N 26 N 115 E 125 E surface 10 20kts southwestly wind 850hPa 25kts southwestly wind ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 700hPa 30kts southwestly wind ( ) ( ) ( ) ( ) ( ) 850hPa 10kts south southwestly within north of ( ) ( ) ( ) ( ) ( ) South China Sea 15 N 6. Thermal Fields 850hPa cold tongue/warm tongue arount the wind shear ( ) ( ) ( ) ( ) ( ) 700hPa cold tongue/warm tongue arount the wind shear ( ) ( ) ( ) ( ) ( ) 7. Pressure depression (around Taiwan) Surface pressure P 24hr -3hPa 850hPa H 24hr -15gpm ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) Sea level pressure 1005hPa ( ) ( ) ( ) ( ) ( ) Low pressure around Hai-Nan Low Pressure ( ) ( ) ( ) ( ) ( ) 1004hPa 8. Upper level wind difluence 300/200hPa angle of difluence 45 ( ) ( ) ( ) ( ) ( ) 9. Stability Total Index 40 ( ) ( ) ( ) ( ) ( ) K-Index 35 ( ) ( ) ( ) ( ) ( ) Summary Yes ( ) 22 Training Course on QPE/QPF Manila 2012 8 Terrential Rainfall Check list Table for 12 48 hrs during the Mei-Yu Season Initial time Year______Mon.______Day______Hr.______ Z NWP: WRF JMA Items of check list OBJ 12H r 24Hr 36Hr 48Hr remark 1. Surface front location within 20 N 28 N 118 E 124 E ( ) ( ) ( ) ( ) ( ) Taipei near 100Km or passed 200Km ( ) ( ) ( ) ( ) ( ) KuoHsung near 200Km ( ) ( ) ( ) ( ) ( ) 2. Horizontal wind shear 22 N 28 N 114 E 127 E 850/700hPa ( ) ( ) ( ) ( ) ( ) 3. Sub synoptic South of Taiwan or east of 114 E surface/850hPa Meso-low ( ) ( ) ( ) ( ) ( ) 700/500hPa Short wave trough ( ) ( ) ( ) ( ) ( ) 4. Moist fields 850hPa Td 15 ( ) ( ) ( ) ( ) ( ) 850hPa e axi cross Taiwan ( ) ( ) ( ) ( ) ( ) 700hPa T-Td 3 ( ) ( ) ( ) ( ) ( ) 5. Low level Jet 18 N 26 N 115 E 125 E surface 10 20kts southwestly wind 850hPa 25kts southwestly wind ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 700hPa 30kts southwestly wind ( ) ( ) ( ) ( ) ( ) 850hPa 10kts south southwestly within north of ( ) ( ) ( ) ( ) ( ) South China Sea 15 N Training Course on QPE/QPF Manila 2012 9 Items of check list OBJ 12H r 24Hr 36Hr 48Hr remark 6. Thermal Fields 850hPa cold tongue/warm tongue arount the wind shear ( ) ( ) ( ) ( ) ( ) 700hPa cold tongue/warm tongue arount the wind shear ( ) ( ) ( ) ( ) ( ) 7. Pressure depression (around Taiwan) Surface pressure P 24 hr -3hPa 850hPa H 24 hr -15gpm ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) Sea level pressure 1005hPa ( ) ( ) ( ) ( ) ( ) Low pressure around Hai-Nan Low Pressure ( ) ( ) ( ) ( ) ( ) 1004hPa 8. Upper level wind difluence 300/200hPa angle of difluence 45 ( ) ( ) ( ) ( ) ( ) 9. Stability Total Index 40 ( ) ( ) ( ) ( ) ( ) K-Index 35 ( ) ( ) ( ) ( ) ( ) Summary Yes ( ) 22 Heavy raainfall (50mm < PQF <130mm a day) resuilts Terrential Rainfall Training(QPF Course >= on 130mm QPE/QPF a day)Manila 2012 10 EX: Surface Fronts 20°N～28°N，118°E～124°E ( x ) Taipei near 100Km or passed 200Km ( x ) KuoHsung near 200Km ( - ) Training Course on QPE/QPF Manila 2012 11 EX: Low level Jet（18°N～26°N，115°E～125°E） surface 10～20kts southwestly wind 850hPa ＞25kts southwestly wind 700hPa ＞30kts southwestly wind Training Course on QPE/QPF Manila 2012 12 Composited chart 0000 UTC June 14, 1997 QPE 15 items selected Training Course on QPE/QPF Manila 2012 13 Composited chart 0000 UTC May 18, 1998 QPE 9 items selected Training Course on QPE/QPF Manila 2012 14 Composited chart 0000 UTC May 19, 1999 QPE 11 items selected Training Course on QPE/QPF Manila 2012 15 Composited chart 0000 UTC June 12, 2000 QPE 15 items selected Training Course on QPE/QPF Manila 2012 16 Distribution of the number of items for the synoptic forecing 15.0% 14.3% 13.9% 12.0% percentage 9.0% 8.3% 7.8% 7.8% 7.4% 6.5% 百分比 6.0% 5.7% 5.7% 5.7% Rare events 4.3% 3.9% 3.0% 2.6% 2.6% 1.7% 1.3% 0.4% 0.0% 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Number項目數 of items Training Course on QPE/QPF Manila 2012 17 Distribution of the number of items for the frequency of heavy rainfall 100% 2500 90% Blue 大雨發生頻率bar : freq. of 80% heavy發生總雨量 rain 2000 everystations for fall rain total is the line black 70% frequency heavy rain rain heavy 60% 1500 50% 1000 40% 總雨量值 發生大雨頻率 30% 20% 500 10% 0% 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Number勾選因子數目 of items Training Course on QPE/QPF Manila 2012 18 the correlation among the synoptic items Pressure Upper Synopic Level Sub Moist Low Thermo Average Front Depressio level Instability items Shear System Fields Level Jet Fields of items n difluence Average 17% 8% 6% 23% 14% 7% 4% 4% 17% 5.7 Rain 16% 8% 7% 22% 15% 6% 3% 4% 19% 4.1 Heavy 19% 7% 6% 24% 12% 8% 5% 4% 15% 8.6 rain Terrenti 20% 6% 6% 23% 13% 6% 6% 5% 15% 10.6 al Rain Correlat ion 0.55 0.35 0.26 0.60 0.31 0.29 0.25 0.35 0.31 0.65 Coef. Training Course on QPE/QPF Manila 2012 19 Verificaion of the number of synoptic items (forecast v.s. Analyis ) 21 21 18 12 hrs 18 24 hrs 十 二 二 15 十 15 小 四 時 12 小 12 預 時 測 9 預 9 項 測 目 6 項 6 數 目 3 數 3 0 0 3 6 9 12 15 18 21 0 0 3 6 9 12 15 18 21 客觀分析項目數 客觀分析項目數 21 36 hrs 21 F o r e c a s18 t 18 48hrs 三 四 十 十 15 15 六 八 小 小 12 12 時 時 預 預 9 9 測 測 項 項 6 6 目 目 數 數 3 3 0 0 0 3 6 9 12 15 18 21 0 3 6 9 12 15 18 21 客觀分析項目數 客觀分析項目數 a n a lTraining ys i sCourse on QPE/QPF Manila 2012 20 Verificaion for differenct valied time Training Course on QPE/QPF Manila 2012 21 Summary of Frontal System There are good relation between the rain event and Synoptic forcing, if the forcing can be quantitatively define.