scholarly journals High-Resolution Simulations and Microphysical Validation of an Orographic Precipitation Event over the Wasatch Mountains during IPEX IOP3

2005 ◽  
Vol 133 (10) ◽  
pp. 2947-2971 ◽  
Author(s):  
Brian A. Colle ◽  
Justin B. Wolfe ◽  
W. James Steenburgh ◽  
David E. Kingsmill ◽  
Justin A. W. Cox ◽  
...  
Keyword(s):  
Mesoscale Model ◽  
Salt Lake ◽  
Great Salt Lake ◽  
Cloud Water ◽  
Precipitation Event ◽  
Convergence Zone ◽  
Grid Spacing ◽  
Surface Precipitation ◽  
Wasatch Mountains ◽  
Precipitation Enhancement

Abstract This paper investigates the kinematic flow and precipitation evolution of a winter storm over and upstream of the Wasatch Mountains [Intermountain Precipitation Experiment third intensive observing period (IPEX IOP3)] using a multiply nested version of the fifth-generation Pennsylvania State University (PSU)––National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5). Validation using in situ aircraft data, radiosondes, ground-based radar, and surface observations showed that the MM5, which featured four domains with 36-, 12-, 4-, and 1.33-km grid spacing, realistically simulated the observed partial blocking of the 8–12 m s−1 ambient southwesterly flow and development of a convergence zone and enhanced lowland precipitation region upwind of the initial Wasatch slope. The MM5 also properly simulated the advance of this convergence zone toward the base of the Wasatch during the passage of a midlevel trough, despite not fully capturing the westerly wind shift accompanying the trough. Accurate simulation of the observed precipitation over the central Wasatch Mountains (within 25% of observed at all stations) required a horizontal grid spacing of 1.33 km. Despite close agreement with the observed surface precipitation, the Reisner2 bulk microphysical scheme produced too much supercooled cloud water and too little snow aloft. A model microphysical budget revealed that the Reisner2 generated over half of the surface precipitation through riming and accretion, rather than snow deposition and aggregation as implied by the observations. Using an intercept for the snow size distribution that allows for greater snow concentrations aloft improved the snow predictions and reduced the cloud water overprediction. Sensitivity studies illustrate that the reduced surface drag of the Great Salt Lake (GSL) enhanced the convergence zone and associated lowland precipitation enhancement upstream of the Wasatch Mountains. The presence of mountain ranges south of the Great Salt Lake appears to have weakened the along-barrier flow and windward convergence, resulting in a slight decrease in windward precipitation enhancement. Diabatic cooling from falling precipitation was also important for maintaining the blocked flow.

scholarly journals The 13–14 December 2001 IMPROVE-2 Event. Part III: Simulated Microphysical Budgets and Sensitivity Studies

2005 ◽  
Vol 62 (10) ◽  
pp. 3535-3558 ◽  
Author(s):  
Brian A. Colle ◽  
Matthew F. Garvert ◽  
Justin B. Wolfe ◽  
Clifford F. Mass ◽  
Christopher P. Woods
Keyword(s):  
Water Vapor ◽  
Mesoscale Model ◽  
Positive Impact ◽  
Cloud Water ◽  
Precipitation Forecast ◽  
State University ◽  
Microphysical Process ◽  
Surface Precipitation ◽  
Sensitivity Studies ◽  
Microphysical Parameterization

Abstract This paper investigates the microphysical pathways and sensitivities within the Reisner-2 bulk microphysical parameterization (BMP) of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) for the Improvement of Microphysical Parameterization through Observational Verification Experiment (IMPROVE)-2 field experiment on 13–14 December 2001. A microphysical budget over the windward slope at 1.33-km horizontal grid spacing was calculated, in which the importance of each microphysical process was quantified relative to the water vapor loss (WVL) rate. Over the windward Cascades, the largest water vapor loss was associated with condensation (73% of WVL) and snow deposition (24%), and the windward surface precipitation resulted primarily from accretion of cloud water by rain (27% of WVL), graupel fallout and melt (19%), and snowmelt (6%). Two-thirds of the snow generated aloft spilled over into the lee in an area of model overprediction, resulting in windward precipitation efficiency of only 50%. Even with the large amount of precipitation spillover, the windward precipitation was still overpredicted in many locations. A series of experiments were completed using different snowfall speeds, cloud water autoconversion, threshold riming values for snow to graupel autoconversion, and slope intercepts for snow. The surface precipitation was most sensitive to those parameters associated with the snow size distribution and fall speed, while decreasing the riming threshold for snow to graupel conversion had the greatest positive impact on the precipitation forecast. All simulations overpredicted cloud water over the lower windward slopes, had too little cloud water over the crest, and had too much ice at moderate-to-large sizes aloft. Riming processes were important, since without supercooled water there were bull’s-eyes of spurious snow spillover over the lee slopes.

scholarly journals Capabilities and Limitations of Convection-Permitting WRF Simulations of Lake-Effect Systems over the Great Salt Lake

2015 ◽  
Vol 30 (6) ◽  
pp. 1711-1731 ◽  
Author(s):  
John D. McMillen ◽  
W. James Steenburgh
Keyword(s):  
Salt Lake ◽  
Numerical Models ◽  
Great Salt Lake ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Grid Spacing ◽  
Convective Storm ◽  
Lake Effect ◽  
Object Based ◽  
The Right

Abstract Although previous studies suggest that the Weather Research and Forecasting (WRF) Model can produce physically realistic banded Great Salt Lake–effect (GSLE) precipitation features, the accuracy and reliability of these simulations for forecasting applications remains unquantified. The ability of the WRF to simulate nonbanded GSLE features is also unknown. This paper uses subjective, traditional, and object-based verification to evaluate convection-permitting (1.33-km grid spacing) WRF simulations of 11 banded and 8 nonbanded GSLE events. In all simulations, the WRF was configured with the Thompson microphysics and the Yonsei University (YSU) planetary boundary layer parameterizations. Subjectively, a majority of the simulations of banded GSLE events produce physically realistic precipitation features. In contrast, simulations of nonbanded GSLE events rarely produce physically realistic precipitation features and sometimes erroneously produce banded precipitation features. Simulations of banded GSLE events produce equitable threat scores (ETSs) comparable to other convective-storm verification studies, whereas simulations of nonbanded events exhibit lower ETSs. Object-based verification shows that the WRF tends to generate precipitation to the right (relative to the flow) and downstream of observed. These results, although based on a specific WRF parameterization suite, suggest that deterministic prediction of GSLE using convection-permitting models will prove challenging in practice with current numerical models. In addition, identifying and addressing the causes of the rightward and downstream precipitation bias is necessary to achieve optimal performance from future probabilistic and/or deterministic high-resolution forecast systems.

scholarly journals Orographic Influences on a Great Salt Lake–Effect Snowstorm

2013 ◽  
Vol 141 (7) ◽  
pp. 2432-2450 ◽  
Author(s):  
Trevor I. Alcott ◽  
W. James Steenburgh
Keyword(s):  
Snow Water Equivalent ◽  
Salt Lake ◽  
Great Salt Lake ◽  
Salt Lake Valley ◽  
Wasatch Mountains ◽  
Lake Effect ◽  
Thermally Driven ◽  
Precipitation Band ◽  
Northern Utah ◽  
Snow Water

Abstract Although several mountain ranges surround the Great Salt Lake (GSL) of northern Utah, the extent to which orography modifies GSL-effect precipitation remains largely unknown. Here the authors use observational and numerical modeling approaches to examine the influence of orography on the GSL-effect snowstorm of 27 October 2010, which generated 6–10 mm of precipitation (snow-water equivalent) in the Salt Lake Valley and up to 30 cm of snow in the Wasatch Mountains. The authors find that the primary orographic influences on the event are 1) foehnlike flow over the upstream orography that warms and dries the incipient low-level air mass and reduces precipitation coverage and intensity; 2) orographically forced convergence that extends downstream from the upstream orography, is enhanced by blocking windward of the Promontory Mountains, and affects the structure and evolution of the lake-effect precipitation band; and 3) blocking by the Wasatch and Oquirrh Mountains, which funnels the flow into the Salt Lake Valley, reinforces the thermally driven convergence generated by the GSL, and strongly enhances precipitation. The latter represents a synergistic interaction between lake and downstream orographic processes that is crucial for precipitation development, with a dramatic decrease in precipitation intensity and coverage evident in simulations in which either the lake or the orography are removed. These results help elucidate the spectrum of lake–orographic processes that contribute to lake-effect events and may be broadly applicable to other regions where lake effect precipitation occurs in proximity to complex terrain.

scholarly journals Model Forecast Improvements with Decreased Horizontal Grid Spacing over Finescale Intermountain Orography during the 2002 Olympic Winter Games

2005 ◽  
Vol 20 (4) ◽  
pp. 558-576 ◽  
Author(s):  
Kenneth A. Hart ◽  
W. James Steenburgh ◽  
Daryl J. Onton
Keyword(s):  
Mesoscale Model ◽  
Forecast Accuracy ◽  
Cooperative Networks ◽  
Intermountain West ◽  
Grid Spacing ◽  
Free Atmosphere ◽  
Wasatch Mountains ◽  
Cold Pools ◽  
Skill Scores ◽  
Horizontal Grid

Abstract Forecasts produced for the 2002 Olympic and Paralympic Winter Games (23 January–25 March 2002) by a multiply nested version of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) are examined to determine if decreasing horizontal grid spacing to 4 km improves forecast accuracy over the finescale topography of the Intermountain West. The verification is based on high-density observations collected by the MesoWest cooperative networks, including approximately 200 wind and temperature sites and 100 precipitation sites across northern Utah. Wind and precipitation forecasts produced by the 4-km MM5 domain were more accurate (based on traditional measures) than those of its parent 12-km domain. The most significant improvements in wind speed forecasts occurred at night in valleys and lowland locations where the topography of the 4-km domain produced more accurate nocturnal flows. Wind direction forecast improvements were most substantial at mountain sites where the better topographic resolution of the 4-km domain more accurately reflected the exposure of these locations to the free atmosphere. The 4-km domain also produced quantitative precipitation forecasts that were either equally (small events) or more (large events) accurate than the 12-km domain. Precipitation bias errors varied substantially between the two domains since the representation of the region’s narrow, steeply sloped, basin-and-range topography improved dramatically at 4-km grid spacing. Curiously, the overall accuracy of temperature forecasts by the 4-km domain was not significantly better than that of the 12-km domain. This was due to an inability of the MM5 to properly simulate nocturnal and persistent cold pools within mountain valleys and the lowlands upstream of the Wasatch Mountains. Paradoxically, the added resolution of the 4-km domain, coupled with the failure of this version of the MM5 to fully capture the nocturnal and persistent cold pools, resulted in poorer skill scores. At upper elevations, which are typically above the cold pools, the 4-km domain was substantially more accurate. These results illustrate that decreasing horizontal grid spacing to less than 10 km does improve wind and precipitation forecasts over finescale Intermountain West topography. It is hypothesized that model improvements will ultimately enable the advantages of added model resolution to be fully realized for temperature forecasts over the Intermountain West.

The Impact of Coastal Boundaries and Small Hills on the Precipitation Distribution across Southern Connecticut and Long Island, New York

2007 ◽  
Vol 135 (3) ◽  
pp. 933-954 ◽  
Author(s):  
Brian A. Colle ◽  
Sandra E. Yuter
Keyword(s):  
New York ◽  
Gravity Wave ◽  
Doppler Radar ◽  
Mesoscale Model ◽  
Long Island ◽  
Heavy Precipitation ◽  
Radar Data ◽  
Surface Precipitation ◽  
The Impact ◽  
Precipitation Enhancement

Abstract The modification of precipitation by the coastal land areas of Long Island (LI), New York, and southern Connecticut (CT) is examined for an extratropical cyclone over the northeast United States on 1 December 2004, which produced strong southerly flow (15–30 m s−1) below 900 mb and heavy precipitation over LI. The differential surface roughness at the coast and the hills of LI (30–80 m) and southern CT (100–250 m) enhanced the surface precipitation by 30%–50% over these regions compared with the nearby water region of LI Sound. The three-dimensional precipitation structures are shown using composite Weather Surveillance Radar-1988 Doppler radar data interpolated to a Cartesian grid, which is compared with a 4-km simulation using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5). As the low-level stratification and flow increased at low levels, the MM5 produced a terrain-forced gravity wave over LI and CT upward through 6 km MSL. Precipitation enhancement (2–3 dBZ) occurred from the surface upward to around the freezing level (3 km MSL) across central LI and southern CT, while there was a localized precipitation minimum over LI Sound. A factor separation on a few sensitivity MM5 runs was performed to isolate the impact of small hills and differential friction across the LI coastline. Both the hills and frictional effects have similar contributions to the total precipitation enhancement and the vertical circulations below 3 km. The hills of LI enhanced the gravity wave circulations slightly more than the differential friction above 3 km, while there was little flow and precipitation interaction between the hills and differential friction. A sensitivity simulation without an ice/snow cloud above 3 km MSL revealed that the seeder-feeder process enhanced surface precipitation by about a factor of 4.

Bibliographic notes on H. Stansbury's Exploration and survey of …/ Expedition to the valley of the Great Salt Lake

2003 ◽  
Vol 30 (2) ◽  
pp. 317-330 ◽  
Author(s):  
L. J. Dorr ◽  
D. H. Nicolson ◽  
L. K. Overstreet
Keyword(s):  
Salt Lake ◽  
Great Salt Lake ◽  
Title Page ◽  
Classic Work ◽  
Us Government ◽  
Multiple Issues ◽  
Title Pages

Howard Stansbury's classic work is bibliographically complex, with two true editions as well as multiple issues of the first edition. The first edition was printed in Philadelphia; its 487 stereotyped pages were issued in 1852 under two different titles with three variant title-pages (an official US government issue and two trade issues). A second edition was printed in Washington in 1853 and had 495 typeset pages (with corrections and additions in the appendices). The issue of 1855 is identical to the 1852 trade issue, except for the change of the date on the title-page. Each issue and edition, with its bindings and plates, is described.

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