Abstract:The author of the present paper made a special assessment on the contribution of Prof. Tao Shiyan to the study of heavy rainfall in China in 1998. Titled “East Asian Monsoon and Torrential Rain in China“, the assessment was published in the volume of the Collected Papers to coincide with Prof. Tao's 80th birthday. Although he passed away in 2012, Prof. Tao's scientific wisdom and concepts continue to enlighten his successors. His valuable heritage in the study of heavy rainfall in China has exerted a profound influence on research and operational development for past and present generations and will continue to influence future research on this topic.
The present paper further evaluates Prof. Tao's contributions to the study of heavy rainfall in China in the context of recent research achievements in this area, with a particular focus on dynamic and thermal conditions as well as related mechanisms. The paper is structured with the following six sections: (1) seasonal abrupt change and its effect on the onset of the Meiyu season in China, (2) multiple-scale interaction in the occurrence of heavy rainfall, (3) the impact of the warm and moist monsoon conveyor on excessively heavy rainfall in northern China, (4) the role of the upper-level jet in heavy rainfall, (5) physical conditions for the occurrence of heavy rainfall and severe convective storms, and (6) the effect of topography on heavy rainfall.

Abstract:In memory of the excellent contributions made by academician Tao Shiyan to the study on East Asian winter monsoon (EAWM), the characteristics and internal dynamical causes of winter surface air temperature in China and the EAWM occurring near the late 1990s are analyzed in this paper by using observational data in China and reanalysis data of the NCEP/NCAR and ERA-40/ERA-Interim. The analyzed results show a significant jump of interdecadal variability of winter surface-air temperature in China and the EAWM occurrence in the late 1990s. With the strengthening of the EAWM, this variability of winter surface air-temperature in China has undergone a change from a "similar pattern in the whole China" to a "south-north oscillation pattern" (i.e., cold in the north but warm in the south) since 1999. Because the winter surface-air temperature in northern China shifted into a colder state during 1999-2012, wintertime disasters of low temperature, snowstorms, and blizzards have frequently occurred in this region. In addition, the dominant period of the interannual variability of winter surface-air temperature and the EAWM turned into 2-8 years from previous 3-4 years. Moreover, the results show that this interdecadal jump of the EAWM is attributed to the strengthening of the Siberian high and the Aleutian low. The internal dynamical causes and physical mechanism of this interdecadal variability of the EAWM are discussed further from the dynamical theories of Arctic Oscillation (AO) and quasi-stationary planetary wave activity. Since the late 1990s, the propagation of quasi-stationary planetary waves into the stratosphere over high latitudes of the Northern Hemisphere along the polar wave-guide was enhanced, while the propagation into the upper troposphere over the subtropics along the low-latitude wave-guide weakened, which caused the strengthening of the convergence of Eliassen-Palm (E-P) fluxes of quasi-stationary planetary waves in the troposphere and stratosphere over high latitudes and strengthening of the divergence of E-P fluxes in the middle and upper troposphere over the subtropics of the Northern Hemisphere. This led to the weakening of wintertime zonal-mean zonal flow from the troposphere to the stratosphere over high latitudes of the Northern Hemisphere and the polar front jet and strengthening of the wintertime subtropical jet during 1999-2012, which caused the weakening of the wintertime AO and strengthening of the EAWM.

Abstract:During the winter storm, freezing rain is one of the most difficult to forecast among the various types of precipitation. The freezing rain over Guizhou and Hunan provinces is formed because of the interaction between the mid-higher latitude and the lower-latitude weather systems. The most important weather systems are the high-level subtropical jet stream front, the lower-level Yunnan-Guizhou quasi-stationary front, and the southwesterly jet. To accurately analyze the occurrence of freezing rain under these complex weather systems, we have proposed a new set of diagnostic method, which is a combination of the "dynamical factor" and the "three-step judge method." Meanwhile, we have applied the method to forecast freezing rain in Guizhou Province, China, where freezing rain occurs most frequently. We first used the dynamical factor vertical integral baroclinic vorticity parameter (q_Bsum) to find the possible weak rainfall region owing to atmospheric baroclinity, and then used single-station radiosonde data to employ the following three-step judge method. Finally, we determined the regions where freezing rain may occur in the future.

Abstract:Both the Yangtze River and the Huaihe River lie in mid-latitudes in East Asia, and so the large-scale circulation and climatic background of weather events in the Yangtze River valley and the Huaihe River valley are similar. However, there are different interannual variations between anomalous rainfall events in the Yangtze River valley and in the Huaihe River valley in summer. This study focuses on differences in circulation in middle to high latitudes in Asia and middle to low latitudes in the southern hemisphere, and the associated mechanisms. Both physical and statistical methods were used in this study. We looked at the differences in Asian circulation for anomalous rainfall events in the Yangtze River basin and the Huaihe River valley in summer. East Asian subtropical westerly winds at 200 hPa strengthened (weakened) and a longitudinal (zonal) pattern with anomalous geopotential height at 500 hPa occurred in middle to high latitudes over East Asia. Meanwhile, the locations of both the Australian anticyclone and the Mascarene anticyclone shifted further east (west), respectively, than normal, the cross-equatorial flow strengthened in the areas 150°E to 180° and weakened in the areas 50°E to 60°E (weakened in the areas 150°E to 180° and strengthened in the areas 50°E to 60°E), and anomalous rainfall in summer occurred in the Yangtze River valley (the Huaihe River valley). Thus, the intensity of East Asian subtropical westerly winds as well as the locations of both the Australian anticyclone and the Mascarene anticyclone played an important role in the occurrence of anomalous rainfall events in the Yangtze River valley and the Huaihe River valley in summer.

Abstract:The ERA-Interim reanalysis dataset is used to investigate the climatological characteristics of the South Asia High (SAH) formation and related possible mechanisms. In addition, we examine the influence of ENSO events on the interannual variability of SAH formation. The results indicate that the climate-mean SAH is generated in the upper troposphere over the southeastern Indo-China Peninsula on the 24th pentad. The process is attributed to enhanced convection over the southern Philippines and the Indo-China Peninsula in late spring. Convection over the southern Philippines is intensified to produce a negative vorticity source to the north, which is transported to the South China Sea (SCS) by the tropical upper easterly to induce a close anticyclone in the upper troposphere, representing the preliminary generation of SAH. Furthermore, convection over the Indo-China Peninsula facilitates the development of SAH, moving its center to the upper troposphere over the peninsula. The meridional position of convection near the Philippines determines the formation location of SAH, whereas the enhancement and northward migration of SAH is controlled by the strength of convection over the Indo-China Peninsula in late spring and early summer. Therefore, the warm and cold phases of ENSO events could influence the pattern and position of SAH during its formation process via regulation of the convection over the two regions. After the occurrence of warm ENSO events, tropical convection is intensified to the east of Kalimantan, resulting in SAH establishment in the upper troposphere over northern Sumatra and the Gulf of Thailand. Meanwhile, the convection over the Indo-China Peninsula is too weak to support the northward movement of SAH. Conversely, cold ENSO events contribute to reinforced convection over the mid Philippines, stimulating SAH over the central Indo-China Peninsula. Subsequently the rapid flourishing of convection over the Indo-China Peninsula cases SAH to expand westward and shift significantly northward. Thus, the warm and cold phases of ENSO events have significant effects on the formation location of SAH.

Abstract:Even if a numerical weather prediction model is capable of predicting an extreme weather event, several questions remain such as the confidence level of the predicted event and the reliability of the information related to details such as timing, location, and magnitude. In this paper, a method known as Ensemble Anomaly Forecasting, which combines ensemble forecasts with climatology, is introduced and demonstrated by using a case of extremely heavy rain occurring in Beijing on July 21, 2012. The results show that these two questions can be effectively addressed through this method and ensemble forecasts by providing more reliable and consistent information than that provided by a single forecast. Therefore, we strongly recommend that forecasters apply this method in their daily operations to improve their prediction capability of rare high-impact weather events.
The following three aspects are discussed in detail in this study. (1) By comparing a forecast with climatology, the potential rarity of the predicted variable can then be quantitatively measured in terms of standardized anomaly (SA), which normally indicates an extreme event when the departure of a forecast from its climatology mean exceeds three standard deviations. By combining further with ensemble forecasts, the confidence of such an anomaly forecast can also be estimated on the basis of the SA of individual ensemble members, which provides critical information that enables a forecaster to make a more reliable forecast of a potentially rare weather event. A combination of the anomaly and confidence then defines a "societal impact matrix," which can be used to quantitatively measure a forecast's potential impact on society. (2) Because the synoptic scale pattern associated with this heavy rain event in Beijing is quite classical for extreme flooding events, it was a highly predictable event from the large-scale pattern perspective. For example, the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) model quite successfully predicted a rainfall event of approximately 115 mm over Beijing with a lead time of approximately six days (0600, July 16). However, the detailed information such as rainfall location and intensity were highly variable or uncertain in subsequent GFS forecasts, thus resulting in low predictability. Such shifting of the model solutions from one cycle to another significantly limits the usefulness of a forecast because it is difficult to follow. In contrast, and as demonstrated by this study, ensemble-based—particularly multi-model ensemble-based—ensemble mean and probabilistic forecasts can mitigate some of the issues associated with model shifting by providing more consistent information to greatly increase forecast utility. Additionally, ensemble-based forecasts may extend the practical predictability length. For example, the predictability length of rainfall exceeding 100 mm over or near Beijing can be extended for approximately two days by using THORPEX Interactive Grand Global Ensemble (TIGGE) based probabilistic forecasts as compared to that by a single GFS forecast. (3) If observation or analysis is used instead of forecasts in the calculation of SA, SA can also help to determine the possible causes responsible for an extreme event. In this case, the spatial distribution of the SA reveals that the immediate short-range synoptic cause of the extreme rainfall is the merging of a cold front from the northwest and strong ridge extending from a tropical system in the southeast, which formed a favorable moisture, convergence, and vertical lifting environment for the development and maintenance of meso-and small-scale convective systems. The time evolution of the SAs further reveals that the medium-range background cause is the flow's meridional development to form and maintain a large-amplitude low-high alternating wave train in high latitudes, particularly the development of a blocking system to the northeast of Beijing and a deepening trough to the west, resulting in a strong cold front that enhanced the north-south exchange including the northward advancement of a tropical system.

Abstract:The empirical orthogonal function (EOF) is applied to the 3-h interval black body temperature (TBB) from three geostationary satellites in the active periods of Meiyu during 1998-2008. The first seven independent leading modes (EOF1 to EOF7) of the Meiyu frontal cloud are extracted, and the variances explained by these modes are 7.78%, 5.83%, 5.20%, 4.27%, 4.19%, 3.62%, and 3.36%. These seven independent leading modes reflect cloud anomalies during the main rainy seasons. In contrast to the climatological Meiyu front cloud system (MFCS), the most similar cloud images for each leading mode show significant position shifts and shape changes, indicating the evolution of fracture, weakening, dissipation, and rebuilding of the MFCS.
Circulation configuration for the climatological MFCS is the three-resistance highs type. In addition, two typical circulation types are noted for the seven leading modes of the MFCS. The first type is the resistant high, in which the middle and high latitudes are occupied by a blocking high. This characteristic is evident in the positive EOF2, EOF5, EOF6, and EOF7 as well as the negative EOF4 and EOF6. In the second type, one trough and two highs or one high and two troughs occur in the middle and high latitudes of 500 hPa. This circulation type is often companied by positive EOF1 and EOF4, as well as negative EOF1, EOF2, EOF3, EOF5, and EOF7.

Abstract:On the basis of the leading modes of the Meiyu frontal cloud system extracted by the empirical orthogonal function (EOF) from the black body temperatures (TBBs) in the active periods of Meiyu during 1998 to 2008, the frequency of occurrence, persistence time, and transitional characteristics are investigated. There are seven independent leading modes for TBB anomalies (EOF1 to EOF7). The statistics show that the positive phase of EOF1 has the highest frequency of occurrence and can explain the first appearance mode in 25% of the total Meiyu processes. The positive phase of EOF5 has the lowest frequency of occurrence of all of these leading modes and is often mixed with other modes as a transition mode. In addition, the longest persistence time of the negative EOF2 is 81 h and is longer than that of the other leading modes, whereas the longest duration time of the positive EOF5 is only 18 h, which is shorter than that of the other leading modes. The negative phase of EOF6 has the longest mean duration time. The conversions between the leading modes are random, whereas only the negative EOF5 and EOF6 show better directionality. Among them, the probability for the transition from the negative phase of EOF6 to the negative phase of EOF5 is 66.67%, whereas the negative phase of EOF5 often transites to the positive phase of EOF3 and the negative phase of EOF1.

Abstract:In this study, the dominant modes of winter temperature over eastern China (to the east of 100°E) are analyzed using the monthly temperature data recorded at 160 stations in China, National Centers for Environmental Prediction (NCEP) reanalysis data, National Oceanic and Atmospheric Administration-Cooperative Institute for Research in Environmental Sciences (NOAA-CIRES) 20th century reanalysis data, and NOAA Sea Surface Temperature (SST) data. The formation mechanism and precursory signals for the second (dipole) mode are primarily studied. Moreover, the prediction method for the second mode is explored by using the winter of 2012-2013 as an example. The results indicate that in addition to the unanimously colder or warmer first mode, the dipole mode, which is characterized as a colder (warmer) region over northern China and to the east of 110°E accompanied by a warmer (colder) region over southern China and to the west of 110°E, is also a main mode dominating the region over eastern China. The winter of 2012-2013 belongs to the second mode. The first mode is related mainly to the SST anomalies in the tropical eastern and central Pacific, the snow cover anomalies over the northern Asian continent, and the sea ice concentration anomalies in the Arctic Ocean along northern Asia during the previous autumn. For the second (dipole) mode, the SST anomalies have no clear influence; however the snow cover anomalies over the middle latitudes over East Asia, the sea ice concentration anomalies from the Svalbard archipelago to the Franz Josef Land archipelago of the Arctic Ocean during the previous autumn, and the surface air temperature pattern of the Arctic Ocean-East Asian temperature contrast caused by the aforementioned snow cover and sea ice anomalies seem to be important. The previous autumn Arctic Ocean-East Asian temperature contrast (AE) index, which involves the synthesized signals of snow cover and sea ice concentration, is closely related to the second mode and should be considered as an important predictor. In the autumn of 2012, several previous signals, such as the normal SST state in the equatorial Eastern and central Pacific, the warmer surface air temperature over the Arctic Ocean, and the colder surface air temperature over the middle latitudes of East Asia, are not conducive to the first mode but are favorable for the second (northern-colder-southern-warmer) mode. By using the previous AE index, the anomalous temperature pattern over eastern China in the winter of 2012-2013 can be effectively predicted.

Abstract:Numerical experiments were conducted on a squall line occurring on June 3-4, 2009, in Henan, Anhui, and Jiangsu provinces, China, that produced high winds and hail. The impact of moisture on the entire air column and that of its vertical distribution on the intensity, development process, and morphology of mesoscale convective systems (MCSs) were investigated. Analysis revealed that the amount of moisture and its vertical distribution had a significant effect on the strength of the downdraft and cold pool, which thus affected the morphology, duration, and strength of convection. The experiments on the entire air column demonstrated that the intensity of MCSs increased with moisture and that the strengths of the cold pool and the thunderstorm high increased, which led to higher winds. Conversely, the intensities of MCSs, cold pool, and surface winds decreased with moisture. Additional moisture led to a stronger cold pool, which caused the maximum winds to strengthen at the developmental stages of the MCSs. However, the cold pool and rear inflow jet weakened more rapidly, which was unfavorable for high wind development and maintenance at mature stages. Precipitable water in entire air column remained unchanged. Linear MCSs and high winds tended to occur in environments of mid-level drier air and low-level moister air that favored the development of stronger thunderstorm highs and discouraged the persistence of MCSs.

Abstract:On the basis of National Centers for Environmental Prediction /National Center for Atmospheric Research (NCEP/NCAR) reanalysis data, and through artificial identification and comparison of weather maps, the climatic characteristics of the Tibetan Plateau Vortex (TPV) in summers of 1981 to 2010 are analyzed in this paper, and the characteristics of the atmospheric circulation and low-frequency component field are comparative studied in high-and low-frequency years of the TPV, respectively. The main results are summarized in the following points:
(1) During the past 30 years, 32 TPVs were generated over the Tibetan Plateau in summer, and the occurrence frequency of the TPV presents an obvious increasing trend and a strong interannual variability. The vortex frequency appears as significant mutations in 2000 and 2005, shifts from an increasing trend to decreasing trend in 2002, and converts into a growing trend in 2005. Moreover, the vortex frequency has significant potential for quasi-periodic oscillations to occur in periods of approximately 5, 9, and 15 years. The TPV frequency generated in June shows a decreasing trend that increase in July and August.
(2) The generating sources of the TPV in summer appear mainly in the regions of Shuanghu and Nagqu in Tibet and Zarenkewu in Qinghai in the central, western, and eastern plateau respectively accounting for 50.8%, 27.0%, and 22.2% of the total. The TPVs in summer generated in June, July, and August respectively account for 44.7%, 29.9%, and 25.4% of the total. The warm TPVs in summer make up the vast majority, accounting for 90.7% of the total. About 1.3 TPVs could develop strongly and move out of the plateau every summer during the past 30 years, which produce heavy rainfall in a wide range of downstream areas. The TPVs moving out of the Tibetan Plateau with east,northeast, and southeast shifting accounted for 56.4%,20.1%, and 20.5%,respectively.
(3) During the high-incidence years of TPV, the atmospheric circulation and low-frequency components of the atmospheric circulation at low levels show strong horizontal convergence and southerly airstream, and the Tibetan high is stronger than the climatology within the main body of the plateau at high levels. The opposite occurs in low-incidence years of the TPV. The configuration of cyclones over the Iranian Plateau, a trough over the Tibetan Plateau, and an anticyclone in the south side of the plateau have important roles in the occurrence of the TPV.

Abstract:In this paper, we study the radar echo evolution patterns and other features of short-term intense precipitation-producing mesoscale convective systems (MCSs) by examining 58 heavy rainfall events associated with the Meiyu front in East China during May to July in 2010 and 2011. Short-term intense precipitation events are deemed as such when the 1-h precipitation total exceeds 30 mm. The results show that the four most common radar echo evolution patterns of MCSs leading to short-term intense precipitation are the zonal, meridional, turning (from zonal to meridional), and combined patterns. MCSs are linear in the zonal and meridional patterns and in 70% of the turning pattern, whereas the combined pattern is oval. Although MCSs in the zonal pattern, turning pattern, and combined patterns commonly propagate backward, the characteristics of their lifetimes, movement, and durations differ significantly. In the zonal pattern, the lifetime is longest, and the intense precipitation duration is shorter than that in the turning pattern in which MCS movement is fastest and the intense precipitation duration is longest. In the combined pattern, MCS movement is slowest and the lifetime and duration are shortest. Conversely, MCSs in the meridional pattern commonly propagate forward and move more quickly than those in the other three patterns. Their lifetime is approximately half that of the zonal pattern, and their duration with more than 30 and 50 mm h^-1 precipitation approximately are one-third and one-fifth of those in the turning patterns, respectively. MCSs move eastward or southward in the zonal pattern, eastward or westward in the meridional pattern, and toward all directions in the combined pattern. That is, MCSs can move northward only in the combined pattern. Although the intense precipitation persistence is long-or short-term in the four patterns, differences in radar echo intensity and radar echo depth are rare. It is deduced that the intense precipitation duration is closely related to propagation type. A larger proportion of forward propagation corresponds to a shorter lifetime and shorter duration in the meridional and combined patterns; similarly, a larger proportion of backward propagation corresponds to longer duration in the turning and zonal patterns. Forward propagation associated with the longest intense precipitation in the turning pattern is rare.

Abstract:In this paper, the interdecadal variations of rainfall over North China, the Yangtze River valley, and South China during the past 100 years are examined using weather station data. The results show that the rainfall over these three regions underwent simultaneous shifts in the early 1910 s, the early 1920s, the middle 1940 s, the middle 1960s, the late 1970 s, and the early 1990 s, although there are different interdecadal shifting periods. During the past 100 years the distribution patterns of summer rainfall over eastern China are primarily characterized by dipoles, such as "positive south and negative north" or "positive north and negative south" in different interdecadal periods. Furthermore, the probability of the totally reverse distribution patterns during two adjacent interdecadal periods is higher (60%) whether they are dipolar or tripolar. In addition, summer Pacific Decadal Oscillation (PDO), winter Arctic Oscillation (AO), and spring arctic sea ice also showed synchronous shifts around the late 1920s, the middle 1940s, the late 1970s, and the middle 1990s, consistent with the shifting periods of summer precipitation over three regions of eastern China, suggesting that PDO, AO, and arctic sea ice have played a synergetic role in the interdecadal variation of summer rainfall over eastern China during the past 100 years.
At interdecadal time scales, PDO in summer is significantly negatively correlated with summer rainfall in North China. The interdecadal variability of PDO may generate interdecadal wave trains of Pacific-Japan (PJ) interconnection pattern at 500-hPa geopotential height and atmospheric circulation in the 850-hPa wind field, which is similar to that affecting the interdecadal variation of summer rainfall over North China. Consequently, summer rainfall over North China showed interdecadal variation. The AO in wintertime is significantly positively correlated with summer rainfall over the Yangtze River valley. When AO enters its positive interdecadal phase from winter to spring, it causes an increase of precipitation and a decrease in temperature over the southern Eurasian continent. The cold and wet state over the southern Eurasian continent persists from winter to summer because of the memory of soil humidity. It causes the weakening of sea-land contrast in summer. As a result, the East Asian summer monsoon experiences interdecadal weakening. Correspondingly, the rainfall over the Yangtze River valley shows interdecadal increase. Spring Arctic sea ice is significantly negatively correlated with summer rainfall over South China. Interdecadal variation in Arctic sea ice can generate interdecadal wave trains of the Eurasia-South China interconnection pattern associated with the anomalous propagation of stationary Rossby waves at 500-hPa geopotential height, which affects the interdecadal variation in rainfall over South China.

Abstract:Using empirical orthogonal function (EOF) expansion, this paper analyzes the Weather Research and Forecasting (WRF) simulative data of the torrential rain occurring on August 25 of 2008 to explore the possibility of EOF expansion for diagnosing a meso-βscale torrential rain system. The conclusions show that when sufficiently fine data are consistent with real data, it is possible to diagnose mesoscale systems with EOF expansion. The preceding three modes of EOF expansion reflect the evolvement characteristics of various-scale weather systems and correspond to various wave trains with various wavelengths and oscillation frequencies: ambient mode, torrential rain system mode, and rain clusters mode. The various waves are attributed to quasi-geostrophic Rossby, quasi-equilibrium eddy, and non-equilibrium gravity inertia waves, respectively. The physical essence of EOF expansion for a weather system is that a transformative weather system with locomotion can be separated to several mutually unattached modes, or wave trains, that differ in physical characteristics, which contributes to a better understanding of the weather system. Scale separation for weather systems is an advantage of EOF expansion because separate weather systems are unattached and have particular physical characteristics. When the space-time indices of different wave trains are in phase lock, a strongly convective precipitation will occur in the appropriate weather condition.

Abstract:Topography is an important external forcing factor on the atmosphere and has orographic thermal and dynamic impacts on the evolution of atmospheric long waves and the emergence of extreme weather. In this study, numerical calculation with the forced β plane quasi-geostrophic potential vorticity equation considering linear Rossby waves with and without the influence of basic flow is used to investigate the possible impacts of topography on the adjustment of long waves. The results show that without the basic flow, the phenomenon of long-wave adjustment was accompanied by the forcing of zonal nonuniform topography, which is also an important mechanism for the adjustment. The adjustment is closely related to topographic amplitude and zonal structure. As the amplitude of topography increases, the phenomenon of wave-number adjustment in the evolution of linear Rossby waves becomes more obvious. However, the adjustment is difficult to identify in topography with a high zonal wave number. Long-wave adjustment is also associated with latitude. High latitude relates to a low β value in which the influence of topography is strong and adjustment of the wave number is simple. On the contrary, the wave number of a linear Rossby wave with a large β effect in low latitudes is not easily changed. Long-wave adjustment is associated with the structure of the initial field and is not sensitive to the amplitude of the initial fluctuation. Moreover, when the basic flow is considered, the forcing of topography is also an important factor in producing a solitary Rossby wave. The structure of this solitary wave is determined by the distribution of the topography and is independent of the structure of initial fluctuation.

Abstract:In this study, a total of 23 winter snow-ice storms in southern China were determined based on the homogenized daily minimum temperature series and precipitation datasets at 549 stations from 1960 to 2008. By decomposing atmospheric variables into four components, the synoptic-scale atmospheric anomalies of these storms were analyzed. The centers of negative geopotential height anomalies and negative temperature anomalies were found at 300 hPa and 850 hPa, respectively, when surface weather events occurred. The centers of these anomalies can be traced as early signals to indicate the occurrence of surface snow-ice storm events. On an average, the early signals of 11 major snow-ice storm events were identified 11.2 days earlier.