scholarly journals The 13–14 December 2001 IMPROVE-2 Event. Part II: Comparisons of MM5 Model Simulations of Clouds and Precipitation with Observations

2005 ◽  
Vol 62 (10) ◽  
pp. 3520-3534 ◽  
Author(s):  
Matthew F. Garvert ◽  
Christopher P. Woods ◽  
Brian A. Colle ◽  
Clifford F. Mass ◽  
Peter V. Hobbs ◽  
...  
Keyword(s):  
Liquid Water ◽  
Mesoscale Model ◽  
Heavy Precipitation ◽  
Precipitation Event ◽  
State University ◽  
Cloud Liquid Water ◽  
Aircraft Flight ◽  
Oregon Cascades ◽  
Microphysical Parameterization ◽  
Mass Concentrations

Abstract This paper compares airborne in situ observations of cloud microphysical parameters with the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) simulations, using the Reisner-2 bulk microphysical parameterization, for a heavy precipitation event over the Oregon Cascades on 13–14 December 2001. The MM5 correctly replicated the extent of the snow field and the growth of snow particles by vapor deposition measured along aircraft flight tracks between altitudes of 4.9 and 6 km, but overpredicted the mass concentrations of snow. The model produced a broader number distribution of snow particles than observed, overpredicting the number of moderate-to-large-sized snow particles and underpredicting the number of small particles observed along the aircraft flight track. Over the mountain crest, the model overpredicted depositional growth of snow and mass concentrations of snow, but underpredicted the amount of cloud liquid water and conversion of snow to graupel. The misclassification of graupel as snow and excessive amounts of snow resulted in the model overpredicting precipitation on the lee slopes and in localized areas along the foothills of the Cascades. The model overpredicted cloud liquid water over the lower windward slopes and foothills, where accretion of cloud liquid water by rain was the primary precipitation-producing mechanism.

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 Microphysical Processes and Synergistic Interaction between Frontal and Orographic Forcing of Precipitation during the 13 December 2001 IMPROVE-2 Event over the Oregon Cascades

2005 ◽  
Vol 62 (10) ◽  
pp. 3493-3519 ◽  
Author(s):  
Christopher P. Woods ◽  
Mark T. Stoelinga ◽  
John D. Locatelli ◽  
Peter V. Hobbs
Keyword(s):  
Pacific Northwest ◽  
Liquid Water ◽  
Particle Production ◽  
Microwave Radiometer ◽  
Synergistic Interaction ◽  
Orographic Precipitation ◽  
Cyclonic Storm ◽  
Cloud Liquid Water ◽  
Oregon Cascades

Abstract On 13–14 December 2001 a vigorous cyclonic storm passed over the Pacific Northwest, producing heavy orographic precipitation over the Cascade Mountains. This storm was one of several studied during the second field phase of the Improvement of Microphysical Parameterization through Observational Verification Experiment (IMPROVE). A wide variety of in situ and remotely sensed measurements were obtained as this storm passed over the Oregon Cascades. These measurements provided a comprehensive dataset of meteorological state parameters (temperature, pressure, humidity, winds, and vertical air velocity), polarization Doppler radar measurements, and cloud microphysical parameters (cloud liquid water, particle concentrations, size spectra, and imagery). The 13–14 December case was characterized by the passage of a tipped-forward lower-tropospheric front that extended upward to a preceding vigorous upper cold-frontal rainband, which produced clouds up to ∼8–9 km. An important difference between this storm and those studied previously over the Washington Cascades was that the prefrontal low-level airflow over the Oregon Cascades was characterized by strong westerly (as opposed to weak easterly) cross-barrier flow. Consequently, as the upper cold-frontal band passed over the Oregon Cascades there was both strong ice particle production aloft and significant production of liquid water at lower levels in the orographic lifting zone. Airborne in situ measurements, ground-based microwave radiometer measurements, and observations of snow crystals showed the simultaneous presence of high ice crystal concentrations and relatively large values of cloud liquid water aloft, and heavily rimed particles reaching the ground. Analyses indicate that a synergistic interaction occurred between the frontal and orographic precipitation.

scholarly journals Value of Human-Generated Perturbations in Short-Range Ensemble Forecasts of Severe Weather

2006 ◽  
Vol 21 (3) ◽  
pp. 347-363 ◽  
Author(s):  
Victor Homar ◽  
David J. Stensrud ◽  
Jason J. Levit ◽  
David R. Bright
Keyword(s):  
Short Range ◽  
Mesoscale Model ◽  
Heavy Precipitation ◽  
Severe Weather ◽  
State University ◽  
Ensemble Forecasts ◽  
Fifth Generation ◽  
Operational Forecasts ◽  
Weather Forecasters ◽  
Forecasting System

Abstract During the spring of 2003, the Storm Prediction Center, in partnership with the National Severe Storms Laboratory, conducted an experiment to explore the value of having operational severe weather forecasters involved in the generation of a short-range ensemble forecasting system. The idea was to create a customized ensemble to provide guidance on the severe weather threat over the following 48 h. The forecaster was asked to highlight structures of interest in the control run and, using an adjoint model, a set of perturbations was obtained and used to generate a 32-member fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) ensemble. The performance of this experimental ensemble is objectively evaluated and compared with other available forecasts (both deterministic and ensemble) using real-time severe weather reports and precipitation in the central and eastern parts of the continental United States. The experimental ensemble outperforms the operational forecasts considered in the study for episodes with moderate-to-high probability of severe weather occurrence and those with moderate probability of heavy precipitation. On the other hand, the experimental ensemble forecasts of low-probability severe weather and low precipitation amounts have less skill than the operational models, arguably due to the lack of global dispersion in a system designed to target the spread over specific areas of concern for severe weather. Results from an additional test ensemble constructed by combining automatic and manually perturbed members show the best results for numerical forecasts of severe weather for all probability values. While the value of human contribution in the numerical forecast is demonstrated, further research is needed to determine how to better use the skill and experience of the forecaster in the construction of short-range ensembles.

scholarly journals Simulation of an Orographic Precipitation Event during IMPROVE-2. Part I: Evaluation of the Control Run Using a Triple-Moment Bulk Microphysics Scheme

2008 ◽  
Vol 136 (10) ◽  
pp. 3873-3893 ◽  
Author(s):  
J. A. Milbrandt ◽  
M. K. Yau ◽  
J. Mailhot ◽  
S. Bélair
Keyword(s):  
Doppler Radar ◽  
Mesoscale Model ◽  
Vertical Motion ◽  
Wave Pattern ◽  
Precipitation Event ◽  
Windward Side ◽  
Motion Field ◽  
Microphysics Scheme ◽  
Oregon Cascades

This paper reports the first evaluation of the Milbrandt–Yau multimoment bulk microphysics scheme against in situ microphysical measurements. The full triple-moment version of the scheme was used to simulate a case of orographically enhanced precipitation with a 3D mesoscale model at high resolution (4- and 1-km grid spacings). The simulations described in this paper also serve as the control runs for the sensitivity experiments that will be examined in Part II of this series. The 13–14 December 2001 case of heavy orographically enhanced precipitation, which occurred over the Oregon Cascades, was selected since it was well observed during the second Improvement of Microphysical Parameterization through Observational Verification Experiment (IMPROVE-2) observational campaign. The simulated fields were compared with observed radar reflectivity, vertical velocity, precipitation quantities from rain gauges, and microphysical quantities measured in situ by two instrumented aircraft. The simulated reflectivity structure and values compared favorably to radar observations during the various precipitation stages of the event. The vertical motion field in the simulations corresponded reasonably well to the mountain-wave pattern obtained from in situ and dual-Doppler radar inferred measurements, indicating that biases in the simulations can be attributed in part to the microphysics scheme. The patterns of 18-h accumulated precipitation showed that the model correctly simulated the bulk of the precipitation to accumulate along the coastal mountains and along the windward slope of the Cascades, with reduced precipitation on the lee side of the crest. However, both the 4- and 1-km simulations exhibited a general overprediction of precipitation quantities. The model also exhibited a distinct bias toward overprediction of the snow mass concentration aloft and underprediction of the mass and vertical extent of the pockets of cloud liquid water on the windward side of the Cascades. Nevertheless, the overall spatial distribution of the hydrometeor fields was simulated realistically, including the mean-mass particle diameters for each category and the observed trend of larger snow sizes to be located at lower altitudes.

scholarly journals The 13–14 December 2001 IMPROVE-2 Event. Part I: Synoptic and Mesoscale Evolution and Comparison with a Mesoscale Model Simulation

2005 ◽  
Vol 62 (10) ◽  
pp. 3474-3492 ◽  
Author(s):  
Matthew F. Garvert ◽  
Brian A. Colle ◽  
Clifford F. Mass
Keyword(s):  
Large Scale ◽  
Mesoscale Model ◽  
Model Simulation ◽  
Heavy Precipitation ◽  
Middle Level ◽  
Model Verification ◽  
Precipitation Event ◽  
Low Level ◽  
Baroclinic Zone

Abstract This paper describes the large-scale synoptic and mesoscale features of a major precipitation event that affected the second Improvement of Microphysical Parameterization through Observational Verification Experiment (IMPROVE-2) study area on 13–14 December 2001. The fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) was used to simulate both the synoptic and mesoscale features of the storm. Extensive model verification was performed utilizing the wealth of observational assets available during the experiment, including in situ aircraft measurements, radiosondes, radar data, and surface observations. The 13–14 December 2001 storm system was characterized by strong low-level cross-barrier flow, heavy precipitation, and the passage of an intense baroclinic zone. The model realistically simulated the three-dimensional thermodynamic and kinematic fields, the forward-tilted vertical structure of the baroclinic zone, and the associated major precipitation band. Deficiencies in the model simulations included an attenuated low-level jet accompanying the middle-level baroclinic zone and the lack of precipitation associated with the surface front; NOAA P-3 aircraft in situ data indicated that the model required 1.33-km grid spacing to capture realistically the complex mesoscale forcing related to terrain features. Despite the relatively skillful portrayal of mesoscale and synoptic structures, the model overpredicted precipitation in localized areas on the windward slopes and over a broad area to the lee of the Oregon Cascades.

scholarly journals Assimilating X- and S-Band Radar Data for a Heavy Precipitation Event in Italy

Water ◽  
2021 ◽  
Vol 13 (13) ◽  
pp. 1727
Author(s):  
Valerio Capecchi ◽  
Andrea Antonini ◽  
Riccardo Benedetti ◽  
Luca Fibbi ◽  
Samantha Melani ◽  
...  
Keyword(s):  
Extreme Event ◽  
Wrf Model ◽  
Heavy Precipitation ◽  
Radar Data ◽  
Flash Floods ◽  
Precipitation Event ◽  
Weather Research And Forecasting ◽  
Limited Area ◽  
Heavy Precipitation Event ◽  
The Town

During the night between 9 and 10 September 2017, multiple flash floods associated with a heavy-precipitation event affected the town of Livorno, located in Tuscany, Italy. Accumulated precipitation exceeding 200 mm in two hours was recorded. This rainfall intensity is associated with a return period of higher than 200 years. As a consequence, all the largest streams of the Livorno municipality flooded several areas of the town. We used the limited-area weather research and forecasting (WRF) model, in a convection-permitting setup, to reconstruct the extreme event leading to the flash floods. We evaluated possible forecasting improvements emerging from the assimilation of local ground stations and X- and S-band radar data into the WRF, using the configuration operational at the meteorological center of Tuscany region (LaMMA) at the time of the event. Simulations were verified against weather station observations, through an innovative method aimed at disentangling the positioning and intensity errors of precipitation forecasts. A more accurate description of the low-level flows and a better assessment of the atmospheric water vapor field showed how the assimilation of radar data can improve quantitative precipitation forecasts.

Variational Assimilation of Cloud Liquid/Ice Water Path and Its Impact on NWP

2015 ◽  
Vol 54 (8) ◽  
pp. 1809-1825 ◽  
Author(s):  
Yaodeng Chen ◽  
Hongli Wang ◽  
Jinzhong Min ◽  
Xiang-Yu Huang ◽  
Patrick Minnis ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Liquid Water ◽  
Weather Prediction ◽  
Wrf Model ◽  
Liquid Water Path ◽  
Cloud Liquid Water ◽  
Water Path ◽  
Ice Water Path ◽  
Ice Water ◽  
The Impact

AbstractAnalysis of the cloud components in numerical weather prediction models using advanced data assimilation techniques has been a prime topic in recent years. In this research, the variational data assimilation (DA) system for the Weather Research and Forecasting (WRF) Model (WRFDA) is further developed to assimilate satellite cloud products that will produce the cloud liquid water and ice water analysis. Observation operators for the cloud liquid water path and cloud ice water path are developed and incorporated into the WRFDA system. The updated system is tested by assimilating cloud liquid water path and cloud ice water path observations from Global Geostationary Gridded Cloud Products at NASA. To assess the impact of cloud liquid/ice water path data assimilation on short-term regional numerical weather prediction (NWP), 3-hourly cycling data assimilation and forecast experiments with and without the use of the cloud liquid/ice water paths are conducted. It is shown that assimilating cloud liquid/ice water paths increases the accuracy of temperature, humidity, and wind analyses at model levels between 300 and 150 hPa after 5 cycles (15 h). It is also shown that assimilating cloud liquid/ice water paths significantly reduces forecast errors in temperature and wind at model levels between 300 and 150 hPa. The precipitation forecast skills are improved as well. One reason that leads to the improved analysis and forecast is that the 3-hourly rapid update cycle carries over the impact of cloud information from the previous cycles spun up by the WRF Model.

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