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The synoptic-scale atmospheric patterns and the most extreme 13-day rainfall periods during the 1993 and 2008 historic Midwest flood events are compared. Over the north central part of the United States, these two 13-day periods were the two wettest during the warm season over the past 60 years. The 500-hPa geopotential height, mean sea level pressure, 250-hPa u-wind and 850-hPa v-wind component anomaly patterns associated with the two periods were found to be remarkably similar. A correlation of .939 was found for the 500-hPa height anomalies between the two periods. The synoptic patterns associated with both periods facilitated the development of a plume of anomalously high precipitable water and moisture flux around the periphery of the subtropical high that then intersected a quasi-stationary baroclinic zone, thereby supporting the development of frequent mesoscale convective systems (MCSs). Frequent low pressure waves along the front, as well as the presence of a nearby exit or entrance region of an upper tropospheric jet streak, enhanced synoptic scale ascent. Early detection of these extreme events might be possible by both medium and short range forecasters using ensemble guidance to ascertain the potential likelihood of similar patterns and features to the aforementioned 13-day periods. On the global climate scale, the late winter and spring season preceding both summer floods featured anomalously wet conditions over the central United States, which contributed to high antecedent soil moisture conditions. Despite the anomalously wet pre-flood periods, there were no similarities in pre-flood monthly El nino Southern Oscillation (ENSO) anomalies, yet both years did feature a negative North Atlantic Oscillation (NAO) signal two months prior to and during the floods. [ABSTRACT FROM AUTHOR]

A significant East Coast Storm affected New England on 29-30 March 2010. The storm brought heavy rainfall and record flooding to portions of southeastern New England. Providence, RI set a daily rainfall record of 135.1 mm (5.32 inches) on 30 March 2010 and had a two-day total rainfall of 223.3 mm (8.79 inches) setting a new record. Many sites in southern New England set daily and monthly rainfall records. The heavy rain event was relatively well predicted by the National Centers for Environmental Predictions (NCEP) Ensemble forecast systems (EFS). The forecasts of this event depicted a pattern conducive for heavy rainfall. Standardized anomalies aided in identifying the potential impact of this event. Initially, the NCEP models and ensemble forecast systems predicted a surge of high precipitable water with strong southerly winds over southern New England. As the event unfolded, a second surge of rainfall was predicted with strong easterly winds over the same region as a surface cyclone developed and moved up the coast. This created a unique situation where a Maddox-type synoptic heavy rain pattern evolved into a frontal type event. The two periods of heavy rainfall produced the record two-day totals and contributed to the flood problems. Both forecast and analyzed anomalies associated with this historic storm will be presented. These data will show how the synoptic-scale anomalies were well correlated with the heavy rainfall. The anomalies facilitate putting this event into a historical perspective relative to previous events. This case demonstrates the utility of using anomalies to increase forecaster confidence and situational awareness. Improved anomaly-based situational awareness combined with probabilistic ensemble quantitative precipitation forecasts can facilitate forecasts of and decisions related to future significant events such as this. [ABSTRACT FROM AUTHOR]

Extreme rainfall events contribute a large portion of wintertime precipitation to northern California. The motivations of this paper were to study the observed differences in the patterns between extreme and more commonly occurring lighter rainfall events, and to study whether anomaly fields might be used to discriminate between them. Daily (1200–1200 UTC) precipitation amounts were binned into three progressively heavier categories (12.5–50.0 mm, light; 50–100 mm, moderate; and >100 mm, heavy) in order to help identify the physical processes responsible for extreme precipitation in the Sierra Nevada range between 37.5° and 41.0°N. The composite fields revealed marked differences between the synoptic patterns associated with the three different groups. The heavy composites showed a much stronger, larger-scale, and slower-moving negative geopotential height anomaly off the Pacific coast of Oregon and Washington than was revealed in either of the other two composites. The heavy rainfall events were also typically associated with an atmospheric river with anomalously high precipitable water (PW) and 850-hPa moisture flux (MF) within it. The standardized PW and MF anomalies associated with the heavy grouping were higher and were slower moving than in either of the lighter bins. Three multiday heavy rainfall events were closely examined in order to ascertain whether anomaly patterns could provide forecast utility. Each of the multiday extreme rainfall events investigated was associated with atmospheric rivers that contained highly anomalous 850-hPa MF and PW within it. Each case was also associated with an unusually intense negative geopotential height anomaly that was similarly located off of the west coast of the United States. The similarities in the anomaly pattern among the three multiday extreme events suggest that standardized anomalies might be useful in predicting extreme multiday rainfall events in the northern Sierra range. [ABSTRACT FROM AUTHOR]

Since late 1995, NCEP has made available to forecasters hourly model guidance at selected sites in the form of vertical profiles of various forecast fields. These profiles provide forecasters with increased temporal resolution and greater vertical resolution than had been previously available. The hourly forecast profiles are provided for all of NCEP's short-range models: the Nested Grid Model, Eta Model, and Mesoscale Eta Model. The highresolution forecasts aid in the timing of frontal passages, low-level jets, and convective initiation. In addition, through time-height cross sections of Richardson numbers, forecasters can alert pilots to the potential for clear air turbulence several hours to a day in advance. Further, the profiles are useful in prediction of cloudiness and the dissipation of low-level stratus and fog. Time-height cross sections of wind velocity have proven extraordinarily useful in visualizing and forecasting inversion heights, frontal passage timing, boundary layer depth, and available environmental and storm-relative helicity during convective events. The hourly model forecasts were found to be exceptionally helpful when combined with hourly surface observations to produce enhanced real-time analyses of convective parameters for use in very short term forecasting. High-resolution analyses of lifted index, CAPE, convective inhibition, moisture flux convergence, and 2-h changes in these fields aid the forecaster in anticipating convective trends. The introduction of model forecast error into these real-time analyses was minimized by using the latest available Eta or Mesoscale Eta Model runs. Therefore, the model data used to enhance the analyses are typically no more than 6-12 h old. [ABSTRACT FROM AUTHOR]

The article focuses on the objectives at the first forum of human in the Forecast Process in the U.S. Among the major themes identified at the forum were improved communication within the profession and users, improved task delegation and time management in forecast production, increased understanding and usage of probabilistic forecasts, and ability to improve on numerical weather prediction (NWP) model guidance. It generated interesting follow-up ideas on credible and meaningful ways of expressing uncertainty and educating people about it. It is noted that forecasts without verified accuracy may lead to misleading results. Forecasters' cognitive styles go beyond the length of forecasting experience.