David R. Novak

An Overview of the 2010 Hazardous Weather Testbed Experimental Forecast Program Spring Experiment

The NOAA Hazardous Weather Testbed (HWT) conducts annual spring forecasting experiments organized by the Storm Prediction Center and National Severe Storms Laboratory to test and evaluate emerging scientific concepts and technologies for improved analysis and prediction of hazardous mesoscale weather. A primary goal is to accelerate the transfer of promising new scientific concepts and tools from research to operations through the use of intensive real-time experimental forecasting and evaluation activities conducted during the spring and early summer convective storm period. The 2010 NOAA/HWT Spring Forecasting Experiment (SE2010), conducted 17 May through 18 June, had a broad focus, with emphases on heavy rainfall and aviation weather, through collaboration with the Hydrometeorological Prediction Center (HPC) and the Aviation Weather Center (AWC), respectively. In addition, using the computing resources of the National Institute for Computational Sciences at the University of Tennessee, the Center for A...

High-Resolution Observations and Model Simulations of the Life Cycle of an Intense Mesoscale Snowband over the Northeastern United States

Abstract This paper investigates the structural and dynamical evolution of an intense mesoscale snowband occurring 25–26 December 2002 over the northeastern United States. Dual-Doppler, wind profiler, aircraft, and water vapor observations in concert with the fifth-generation Pennsylvania State University–NCAR Mesoscale Model run at 4-km grid spacing are used to highlight evolutionary aspects of a snowband unresolved by previous studies. The high-resolution observations and model simulations show that band formation was coincident with a sharpening of a midlevel trough and associated increase in frontogenesis in an environment of conditional and inertial instability. Band maturity was marked by increasing conditional stability and a threefold increase in frontogenetical forcing. Band dissipation occurred as the midlevel trough and associated frontogenetical forcing weakened, while the conditional stability continued to increase. The effect of changing ascent is shown to dominate over changing moisture in ...

The Role of Moist Processes in the Formation and Evolution of Mesoscale Snowbands within the Comma Head of Northeast U.S. Cyclones

Abstract The role of moist processes in regulating mesoscale snowband life cycle within the comma head portion of three northeast U.S. cyclones is investigated using piecewise potential vorticity (PV) inversion, modeling experiments, and potential temperature tendency budgets. Snowband formation in each case occurred along a mesoscale trough that extended poleward of a 700-hPa low. This 700-hPa trough was associated with intense frontogenetical forcing for ascent. A variety of PV evolutions among the cases contributed to midlevel trough formation and associated frontogenesis. However, in each case the induced flow from diabatic PV anomalies accounted for a majority of the midlevel frontogenesis during the band’s life cycle, highlighting the important role that latent heat release plays in band evolution. Simulations with varying degrees of latent heating show that diabatic processes associated with the band itself were critical to the development and maintenance of the band. However, changes in the meso-α...

Operational Forecaster Uncertainty Needs and Future Roles

Abstract Key results of a comprehensive survey of U.S. National Weather Service operational forecast managers concerning the assessment and communication of forecast uncertainty are presented and discussed. The survey results revealed that forecasters are using uncertainty guidance to assess uncertainty, but that limited data access and ensemble underdispersion and biases are barriers to more effective use. Some respondents expressed skepticism as to the added value of formal ensemble guidance relative to simpler approaches of estimating uncertainty, and related the desire for feature-specific ensemble verification to address this skepticism. Respondents reported receiving requests for uncertainty information primarily from sophisticated users such as emergency managers, and most often during high-impact events. The largest request for additional training material called for simulator-based case studies that demonstrate how uncertainty information should be interpreted and communicated. Respondents were i...

The New York Bight Jet: Climatology and Dynamical Evolution

Abstract This paper describes the southerly New York Bight (NYB) jet (11–17 m s−1) that develops primarily during the warm season just above the surface offshore (east) of the northern New Jersey coast and south of Long Island (the NYB). Observations from two offshore buoys are used to develop a 9-yr climatology of 134 jet events from 1997 to 2006. There is a seasonal maximum (2.5 events per month) during June and July, with a skew toward the spring months. The wind directions for the jet trace out a nearly elliptical orbit for the 24-h period around the time of jet maximum at ~2300 UTC [1900 eastern daylight time (EDT)] on average. Composites reveal that the NYB jet occurs on days with southwesterly synoptic flow, and the jet is part of a larger-scale (200–300 km) wind enhancement offshore of the mid-Atlantic and northeast U.S. coasts during the early evening hours. High-resolution observations (surface mesonet, aircraft soundings, and a terminal Doppler weather radar) and Weather Research and Forecastin...

Evolution of Mesoscale Precipitation Band Environments within the Comma Head of Northeast U.S. Cyclones

Abstract This paper explores the mesoscale forcing and stability evolution of intense precipitation bands in the comma head sector of extratropical cyclones using the 32-km North American Regional Reanalysis, hourly 20-km Rapid Update Cycle analyses, and 2-km composite radar reflectivity data. A statistical and composite analysis of 36 banded events occurring during the 2002–08 cool seasons reveals a common cyclone evolution and associated band life cycle. A majority (61%) of banded events develop along the northern portion of a hook-shaped upper-level potential vorticity (PV) anomaly. During the 6 h leading up to band formation, lower-tropospheric frontogenesis nearly doubles and the conditional stability above the frontal zone is reduced. The frontogenesis increase is primarily due to changes in the kinematic flow associated with the development of a mesoscale geopotential height trough. This trough extends poleward of the 700-hPa low, and is the vertical extension of the surface warm front (and surface...

Precipitation and Temperature Forecast Performance at the Weather Prediction Center

AbstractThe role of the human forecaster in improving upon the accuracy of numerical weather prediction is explored using multiyear verification of human-generated short-range precipitation forecasts and medium-range maximum temperature forecasts from the Weather Prediction Center (WPC). Results show that human-generated forecasts improve over raw deterministic model guidance. Over the past two decades, WPC human forecasters achieved a 20%–40% improvement over the North American Mesoscale (NAM) model and the Global Forecast System (GFS) for the 1 in. (25.4 mm) (24 h)−1 threshold for day 1 precipitation forecasts, with a smaller, but statistically significant, 5%–15% improvement over the deterministic ECMWF model. Medium-range maximum temperature forecasts also exhibit statistically significant improvement over GFS model output statistics (MOS), and the improvement has been increasing over the past 5 yr. The quality added by humans for forecasts of high-impact events varies by element and forecast projecti...

Extreme Quantitative Precipitation Forecast Performance at the Weather Prediction Center from 2001 to 2011

AbstractExtreme quantitative precipitation forecast (QPF) performance is baselined and analyzed by NOAA’s Hydrometeorology Testbed (HMT) using 11 yr of 32-km gridded QPFs from NCEP’s Weather Prediction Center (WPC). The analysis uses regional extreme precipitation thresholds, quantitatively defined as the 99th and 99.9th percentile precipitation values of all wet-site days from 2001 to 2011 for each River Forecast Center (RFC) region, to evaluate QPF performance at multiple lead times. Five verification metrics are used: probability of detection (POD), false alarm ratio (FAR), critical success index (CSI), frequency bias, and conditional mean absolute error (MAEcond). Results indicate that extreme QPFs have incrementally improved in forecast accuracy over the 11-yr period. Seasonal extreme QPFs show the highest skill during winter and the lowest skill during summer, although an increase in QPF skill is observed during September, most likely due to landfalling tropical systems. Seasonal extreme QPF skill d...

Improving Flash Flood Forecasts: The HMT-WPC Flash Flood and Intense Rainfall Experiment

AbstractDespite advancements in numerical modeling and the increasing prevalence of convection-allowing guidance, flash flood forecasting remains a substantial challenge. Accurate flash flood forecasts depend not only on accurate quantitative precipitation forecasts (QPFs), but also on an understanding of the corresponding hydrologic response. To advance forecast skill, innovative guidance products that blend meteorology and hydrology are needed, as well as a comprehensive verification dataset to identify areas in need of improvement.To address these challenges, in 2013 the Hydrometeorological Testbed at the Weather Prediction Center (HMT-WPC), partnering with the National Severe Storms Laboratory (NSSL) and the Earth System Research Laboratory (ESRL), developed and hosted the inaugural Flash Flood and Intense Rainfall (FFaIR) Experiment. In its first two years, the experiment has focused on ways to combine meteorological guidance with available hydrologic information. One example of this is the creation ...

The Value of Dual-Polarization Radar in Diagnosing the Complex Microphysical Evolution of an Intense Snowband

The northeast U.S. extratropical cyclone of 8–9 February 2013 produced blizzard conditions and more than 0.6–0.9 m (2–3 ft) of snow from Long Island through eastern New England. A surprising aspect of this blizzard was the development and rapid weakening of a snowband to the northwest of the cyclone center with radar ref lectivity factor exceeding 55 dBZ. Because the radar reflectivity within snowbands in winter storms rarely exceeds 40 dBZ, this event warranted further investigation. The high radar reflectivity was due to mixed-phase microphysics in the snowband, characterized by high differential reflectivity (ZDR > 2 dB) and low correlation coefficient (CC < 0.9), as measured by the operational dual-polarization radar in Upton, New York (KOKX). Consistent with these radar observations, heavy snow and ice pellets (both sleet and graupel) were observed. Later, as the reflectivity decreased to less than 40 dBZ, surface observations indicated a transition to primarily high-intensity dry snow, consistent wi...