A Weather Singularity over the U. S. in October

1954 ◽  
Vol 35 (8) ◽  
pp. 351-356 ◽  
Author(s):  
Eberhard W. Wahl
Keyword(s):  
United States ◽  
Sea Level ◽  
The United States ◽  
Sudden Increase ◽  
Sea Level Pressure ◽  
Pressure Pattern ◽  
Level Pressure

A sudden increase in the probability of snow occurrence during the month of October at Denver, Colorado, had been reported. It is shown that this increase can be associated with the development of a widespread weather singularity occurring at that time of the year. The normal sea-level pressure-pattern changes derived from 40 years of data over the United States show the synoptic development of this singularity. This development leads to peculiarities in various weather elements at that time.

Comparison of Model Forecast Skill of Sea Level Pressure along the East and West Coasts of the United States

2009 ◽  
Vol 24 (3) ◽  
pp. 843-854 ◽  
Author(s):  
Garrett B. Wedam ◽  
Lynn A. McMurdie ◽  
Clifford F. Mass
Keyword(s):  
United States ◽  
Sea Level ◽  
West Coast ◽  
Mesoscale Model ◽  
The United States ◽  
Model Forecast ◽  
The West ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
East And West

Abstract Despite recent advances in numerical weather prediction, major errors in short-range forecasts still occur. To gain insight into the origin and nature of model forecast errors, error frequencies and magnitudes need to be documented for different models and different regions. This study examines errors in sea level pressure for four operational forecast models at observation sites along the east and west coasts of the United States for three 5-month cold seasons. Considering several metrics of forecast accuracy, the European Centre for Medium-Range Weather Forecasts (ECMWF) model outperformed the other models, while the North American Mesoscale (NAM) model was least skillful. Sea level pressure errors on the West Coast are greater than those on the East Coast. The operational switch from the Eta to the Weather Research and Forecasting Nonhydrostatic Mesoscale Model (WRF-NMM) at the National Centers for Environmental Prediction (NCEP) did not improve forecasts of sea level pressure. The results also suggest that the accuracy of the Canadian Meteorological Centre’s Global Environmental Mesoscale model (CMC-GEM) improved between the first and second cold seasons, that the ECMWF experienced improvement on both coasts during the 3-yr period, and that the NCEP Global Forecast System (GFS) improved during the third cold season on the West Coast.

scholarly journals Spatial and Temporal Variability of Nonfreezing Drizzle in the United States and Canada

2006 ◽  
Vol 19 (15) ◽  
pp. 3629-3639 ◽  
Author(s):  
Addison L. Sears-Collins ◽  
David M. Schultz ◽  
Robert H. Johns
Keyword(s):  
United States ◽  
Sea Level ◽  
The United States ◽  
Seasonal Migration ◽  
Eastern United States ◽  
Eastern Canada ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
Wind Speeds ◽  
Wide Range

Abstract A climatology of nonfreezing drizzle is created using surface observations from 584 stations across the United States and Canada over the 15-yr period 1976–90. Drizzle falls 50–200 h a year in most locations in the eastern United States and Canada, whereas drizzle falls less than 50 h a year in the west, except for coastal Alaska and several western basins. The eastern and western halves of North America are separated by a strong gradient in drizzle frequency along roughly 100°W, as large as about an hour a year over 2 km. Forty percent of the stations have a drizzle maximum from November to January, whereas only 13% of stations have a drizzle maximum from June to August. Drizzle occurrence exhibits a seasonal migration from eastern Canada and the central portion of the Northwest Territories in summer, equatorward to most of the eastern United States and southeast Canada in early winter, to southeastern Texas and the eastern United States in late winter, and back north to eastern Canada in the spring. The diurnal hourly frequency of drizzle across the United States and Canada increases sharply from 0900 to 1200 UTC, followed by a steady decline from 1300 to 2300 UTC. Diurnal drizzle frequency is at a maximum in the early morning, in agreement with other studies. Drizzle occurs during a wide range of atmospheric conditions at the surface. Drizzle has occurred at sea level pressures below 960 hPa and above 1040 hPa. Most drizzle, however, occurs at higher than normal sea level pressure, with more than 64% occurring at a sea level pressure of 1015 hPa or higher. A third of all drizzle falls when the winds are from the northeast quadrant (360°–89°), suggesting that continental drizzle events tend to be found poleward of surface warm fronts and equatorward of cold-sector surface anticyclones. Two-thirds of all drizzle occurs with wind speeds of 2.0–6.9 m s−1, with 7.6% in calm wind and 5% at wind speeds ⩾ 10 m s−1. Most drizzle (61%) occurs with visibilities between 1.5 and 5.0 km, with only about 20% occurring at visibilities less than 1.5 km.

scholarly journals Diagnosing Santa Ana Winds in Southern California with Synoptic-Scale Analysis

2013 ◽  
Vol 28 (3) ◽  
pp. 704-710 ◽  
Author(s):  
John T. Abatzoglou ◽  
Renaud Barbero ◽  
Nicholas J. Nauslar
Keyword(s):  
Sea Level ◽  
Southern California ◽  
The United States ◽  
Fire Weather ◽  
Synoptic Scale ◽  
Sea Level Pressure ◽  
Mean Sea Level ◽  
Santa Ana ◽  
Level Pressure ◽  
Santa Ana Winds

Abstract Santa Ana winds (SAW) are among the most notorious fire-weather conditions in the United States and are implicated in wildfire and wind hazards in Southern California. This study employs large-scale reanalysis data to diagnose SAW through synoptic-scale dynamic and thermodynamic factors using mean sea level pressure gradient and lower-tropospheric temperature advection, respectively. A two-parameter threshold model of these factors exhibits skill in identifying surface-based characteristics of SAW featuring strong offshore winds and extreme fire weather as viewed through the Fosberg fire weather index across Remote Automated Weather Stations in southwestern California. These results suggest that a strong northeastward gradient in mean sea level pressure aligned with strong cold-air advection in the lower troposphere provide a simple, yet effective, means of diagnosing SAW from synoptic-scale reanalysis. This objective method may be useful for medium- to extended-range forecasting when mesoscale model output may not be available, as well as being readily applied retrospectively to better understand connections between SAW and wildfires in Southern California.

scholarly journals Large-Scale Influences on Summertime Extreme Precipitation in the Northeastern United States

2016 ◽  
Vol 17 (12) ◽  
pp. 3045-3061 ◽  
Author(s):  
Allison B. Marquardt Collow ◽  
Michael G. Bosilovich ◽  
Randal D. Koster
Keyword(s):  
United States ◽  
Sea Level ◽  
Tropical Cyclones ◽  
Extreme Precipitation ◽  
Potential Temperature ◽  
Northeastern United States ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
Extreme Precipitation Events ◽  
Precipitation Events

Abstract Observations indicate that over the last few decades there has been a statistically significant increase in precipitation in the northeastern United States and that this can be attributed to an increase in precipitation associated with extreme precipitation events. Here a state-of-the-art atmospheric reanalysis is used to examine such events in detail. Daily extreme precipitation events defined at the 75th and 95th percentile from gridded gauge observations are identified for a selected region within the Northeast. Atmospheric variables from the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), are then composited during these events to illustrate the time evolution of associated synoptic structures, with a focus on vertically integrated water vapor fluxes, sea level pressure, and 500-hPa heights. Anomalies of these fields move into the region from the northwest, with stronger anomalies present in the 95th percentile case. Although previous studies show tropical cyclones are responsible for the most intense extreme precipitation events, only 10% of the events in this study are caused by tropical cyclones. On the other hand, extreme events resulting from cutoff low pressure systems have increased. The time period of the study was divided in half to determine how the mean composite has changed over time. An arc of lower sea level pressure along the East Coast and a change in the vertical profile of equivalent potential temperature suggest a possible increase in the frequency or intensity of synoptic-scale baroclinic disturbances.

scholarly journals Evaluation of a Mesoscale Short-Range Ensemble Forecast System over the Northeast United States

2007 ◽  
Vol 22 (1) ◽  
pp. 36-55 ◽  
Author(s):  
Matthew S. Jones ◽  
Brian A. Colle ◽  
Jeffrey S. Tongue
Keyword(s):  
United States ◽  
Wind Speed ◽  
Sea Level ◽  
Short Range ◽  
Warm Season ◽  
Ensemble Forecast ◽  
Cool Season ◽  
Forecast System ◽  
Sea Level Pressure ◽  
Level Pressure

Abstract A short-range ensemble forecast system was constructed over the northeast United States down to 12-km grid spacing using 18 members from the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5). The ensemble consisted of 12 physics members with varying planetary boundary layer schemes and convective parameterizations as well as seven different initial conditions (ICs) [five National Centers for Environmental Prediction (NCEP) Eta-bred members at 2100 UTC and the 0000 UTC NCEP Global Forecast System (GFS) and Eta runs]. The full 18-member ensemble (ALL) was verified at the surface for the warm (May–September 2003) and cool (October 2003–March 2004) seasons. A randomly chosen subset of seven physics (PHS) members at each forecast hour was used to quantitatively compare with the seven IC members. During the warm season, the PHS ensemble predictions for surface temperature and wind speed had more skill than the IC ensemble and a control (shared PHS and IC member) run initialized 12 h later (CTL12). During the cool and warm seasons, a 14-day running-mean bias calibration applied to the ALL ensemble (ALLBC) added 10%–30% more skill for temperature, wind speed, and sea level pressure, with the ALLBC far outperforming the CTL12. For the 24-h precipitation, the PHS ensemble had comparable probabilistic skill to the IC ensemble during the warm season, while the IC subensemble was more skillful during the cool season. All ensemble members had large diurnal surface biases, with ensemble variance approximating ensemble uncertainty only for wind direction. Selection of ICs was also important, because during the cool season the NCEP-bred members introduced large errors into the IC ensemble for sea level pressure, while none of the subensembles (PHS, IC, or ALL) outperformed the GFS–MM5 for sea level pressure.

An Error Analysis of LFM-II Forecasts During the 1982–1983 Winter Season

1984 ◽  
Vol 65 (10) ◽  
pp. 1073-1080
Author(s):  
Randy Schechter
Keyword(s):  
United States ◽  
Boundary Layer ◽  
Relative Humidity ◽  
Sea Level ◽  
Gulf Coast ◽  
Winter Season ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
Temperature Boundary Layer ◽  
Temperature Boundary

An analysis of average errors (bias) in forecast variables of the National Meteorological Center (NMC) LFM-II model has been completed for the winter season of 1982–1983 (23 November 1982–31 March 1983). The forecast variables evaluated were sea level pressure, 1000-500 mb thickness, boundary layer temperature, boundary layer relative humidity, mean relative humidity, and boundary layer winds. Average errors were calculated from forecasts contained in the Forecast United States (FOUS) 60-78 bulletins for 89 stations around the United States and adjacent waters. Forecasts were stratified into runs initialized with 0000 GMT or 1200 GMT data. Verifications were produced for 12-, 24-, 36-, and 48-hour forecasts. The results substantiate certain geographically dependent error characteristics (biases) in the model. Sea level pressure is generally forecast too low east of the Rockies, particularly in the upper Mississippi valley, and too high west of the Rockies, particularly in the far southwest. Errors of 1000-500 mb thickness are generally small and tend to be forecast too high in the central United States and too low in the Rockies. For mean relative humidity, the model is too moist over the northern Rockies and too dry from Texas northward to Wisconsin. With the exception of the Rocky Mountain states, forecasts of boundary layer relative humidity are too dry nationwide. The largest dry bias is centered on the Texas Gulf coast. Boundary layer temperature forecasts are too warm along the Gulf coast and Florida and too cold near the Great Lakes. While errors are usually small for boundary layer winds, the error vectors have cyclonic curvature in the east and a northerly component in the nation's midsection. There is a pronounced diurnal variation in the model bias for some of the forecast variables examined (boundary layer temperature, boundary layer relative humidity, and, to a lesser degree, 1000-500 mb thickness). This is demonstrated by the differences in the average error fields at 0000 GMT and 1200 GMT.

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