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Jonathan D. W. Kahl, Brandon R. Selbig, and Austin R. Harris

ABSTRACT

Wind gusts are common to everyday life and affect a wide range of interests including wind energy, structural design, forestry, and fire danger. Strong gusts are a common environmental hazard that can damage buildings, bridges, aircraft, and trains, and interrupt electric power distribution, air traffic, waterways transport, and port operations. Despite representing the component of wind most likely to be associated with serious and costly hazards, reliable forecasts of peak wind gusts have remained elusive. A project at the University of Wisconsin–Milwaukee is addressing the need for improved peak gust forecasts with the development of the meteorologically stratified gust factor (MSGF) model. The MSGF model combines gust factors (the ratio of peak wind gust to average wind speed) with wind speed and direction forecasts to predict hourly peak wind gusts. The MSGF method thus represents a simple, viable option for the operational prediction of peak wind gusts. Here we describe the results of a project designed to provide the site-specific gust factors necessary for operational use of the MSGF model at a large number of locations across the United States. Gust web diagrams depicting the wind speed– and wind direction–stratified gust factors, as well as peak gust climatologies, are presented for all sites analyzed.

Full access
Amin Dezfuli

Abstract

Atmospheric rivers (ARs) are responsible for some of the hydroclimatic extremes around the world. Their mechanisms and contribution to flooding in the Middle East are relatively poorly understood. This study shows that the record floods during March 2019 across the Middle East were caused by a powerful AR, originated from the North Atlantic Ocean. Iran, in particular, was substantially affected by the floods. The nearly 9,000-km-long AR propagated across North Africa and the Middle East, and was fed by additional moisture from several other sources on its pathway. Simultaneous presence of a midlatitude system and a subtropical jet facilitated the moisture supply. The AR, as passing over the Zagros Mountains, produced record rainfall induced by the orographic forcing. The resulting floods caused widespread damage to infrastructures and left a death toll of at least 76 in Iran.

Free access
K. Lagouvardos, V. Kotroni, T. M. Giannaros, and S. Dafis

Abstract

On 23 July 2018, Attica, Greece, was impacted by a major wildfire that took place in a wildland–urban interface area and exhibited extreme fire behavior, characterized by a very high rate of spread. One-hundred civilian fatalities were registered, establishing this wildfire as the second-deadliest weather-related natural disaster in Greece, following the heat wave of July 1987. On the day of the deadly wildfire, a very strong westerly flow was blowing for more than 10 h over Attica. Wind gusts up to 30–34 m s−1 occurred over the mountainous areas of Attica, with 20–25 m s−1 in the city of Athens and surrounding suburban areas. This strong westerly flow interacted with the local topography and acted as downslope flow over the eastern part of Attica, with temperatures rising up to 39°C and relative humidity dropping to 19% prior to the onset of the wildfire. These weather elements are widely acknowledged as the major contributing factors to extreme fire behavior. WRF-SFIRE correctly predicted the spatiotemporal distribution of the fire spread and demonstrated its utility for fire spread warning purposes.

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Thomas Jones, Patrick Skinner, Nusrat Yussouf, Kent Knopfmeier, Anthony Reinhart, and David Dowell

Abstract

Landfalling tropical cyclones (TCs) are among the greatest natural threats to life and property in the United States, since they can produce multiple hazards associated with convective storms over a wide region. Of these hazards, tornadoes within TC rainbands pose a particularly difficult forecast problem owing to their rapid evolution and their frequent occurrence coincident with additional hazards, such as flash flooding and damaging winds. During the 2017 Atlantic hurricane season, Hurricanes Harvey and Irma impacted the continental United States, causing significant loss of life and billions of dollars in property damage. Application of the Warn-on-Forecast (WoF) concept of short-term, probabilistic guidance of convective hazards (, ), including the potential for tornadoes within TCs, offers the ability to provide forecasters with valuable tools for prioritizing the relative risk from multiple convective threats and effectively communicating them to the public.

Open access
Clifford F. Mass, Robert Conrick, Nicholas Weber, and Joseph P. Zagrodnik

Abstract

On 27 January 2018, a highly localized, strong wind event occurred along the north shore of Lake Quinault, Washington. The resulting loss of large old-growth trees in a roughly 0.5-km2 region led to blocked roads and power outages. Nearby surface stations did not record anomalous winds, and no tree damage was reported in the surrounding region. Based on public accounts and a nearby seismometer, it appears that the strong winds lasted less than 10 min. Surface and aerial damage surveys showed that the trees fell from a different direction (northerly) than the synoptic or mesoscale f low (southwesterly to southeasterly). Based on high-resolution Weather Research and Forecasting (WRF) Model simulations, it appears that the damaging northerly winds were the result of a strong atmospheric rotor produced by a high-amplitude mountain wave. A simulation with 148-m grid spacing produced a rotor at the same time and location as the treefalls. Synoptic analysis and the high-resolution simulation showed that moderately strong southeasterly flow and a stable layer associated with the approaching occluded front interacted with a ∼750-m-high upstream mountain ridge to produce the mountain wave and associated rotor circulation. The combination of an inversion and strong shear at and above the upstream ridge were outliers in a climatology of soundings from the nearby Quillayute rawinsonde site, suggesting that such intense mountain-wave rotors are unusual in this valley.

Open access
Vlado Malačič and Nedjeljka Žagar

Abstract

The marine icicles that form on coastal constructions (e.g., piers and railings) are very common in polar and subpolar areas. The occasional formation of icicles in the coastal zones of the Mediterranean Sea occurs in relation to cold-air outbreaks from the polar region, such as the one presented in this paper in February 2018. The air temperatures over the northern Adriatic Sea, the northernmost part of the Mediterranean, dropped below –2.1°C, a necessary condition for seawater to freeze, with salinity between 38.0 and 38.5 PSU. The formation of icicles on the coastal structures was further enabled by the bora wind and related high seas along the coast. Measurements presented in this paper confirm that the icicles in the Bay of Piran in the Gulf of Trieste (45.55°N) were formed from the seawater. The measured salinity level of the melted icicles, around 9 PSU, is a typical value reported for marine icicles in polar regions.

Open access
Alan W. Black, John A. Knox, Jared A. Rackley, and Nicholas S. Grondin

Abstract

We examine the trajectories of four historical markers displaced during an enhanced Fujita scale 2 (EF2) tornado at the Fort Pulaski National Monument located on Cockspur Island, east of Savannah in southeast Georgia. The careful work of National Park Service employees in cataloguing the origin and landing points of the debris allows for an unusually accurate analysis of tornado debris trajectories for heavy objects. These markers, weighing around 68 kg (150 lb) each, traveled intact for distances of up to 220 m (750 ft). One of the historical markers was fractured into at least three pieces, the larger of which traveled 300 m (1,000 ft). Understanding the travel for these relatively heavy items is important, as they are similar in weight to household appliances that could commonly be part of a tornado debris field.

Open access
Daniel T. Lindsey, Dan Bikos, and Lewis Grasso

Abstract

Geostationary Operational Environmental Satellite-16 (GOES-16) was launched into geostationary orbit in late 2016 and began providing unprecedented spatial and temporal resolution imagery early in 2017. Its Advanced Baseline Imager has additional spectral bands including two in the “clear” window and “dirty window” portion of the infrared spectrum, and the difference of these two bands, sometimes called the split window difference, provides unique information about low-level water vapor. Under certain conditions, low-level convergence along a boundary can cause local water vapor pooling, and the signal of this pooling can sometimes be detected by GOES-16 prior to any cloud formation. This case study from 15 June 2017 illustrates how the technique might be used in an operational forecast setting. A boundary in western Kansas was detected using the split window difference more than 2 h before the first cloud formed.

Open access
Yanluan Lin, Yuanlong Li, Qingshan Li, Minyan Chen, Fanghua Xu, Yuqing Wang, and Bin Huang
Open access
Arunas P. Kuciauskas, Peng Xian, Edward J. Hyer, Mayra I. Oyola, and James R. Campbell

Abstract

During the spring and summer months, the greater Caribbean region typically experiences pulses of moderate to heavy episodes of airborne African dust concentrations that originate over the Sahara Desert and propagate westward across the tropical North Atlantic basin. These dust episodes are often contained within the Saharan air layer (SAL), an elevated air mass (between 850–500 hPa) marked by very dry and warm conditions within the lowest levels. During its westward transport, the SAL’s distinct environmental characteristics can persist well into the Gulf of Mexico and southern United States. As a result, the Caribbean population is susceptible to airborne dust levels that often exceed healthy respiratory limits. One of the major responsibilities within the National Weather Service in San Juan, Puerto Rico (NWS-PR), is preparing the public within their area of responsibility (AOR) for such events. The Naval Research Laboratory Marine Meteorology Division (NRL-MMD) is sponsored by the National Oceanic and Atmospheric Administration (NOAA) to support the NWS-PR by providing them with an invaluable “one stop shop” web-based resource (hereafter SAL-WEB) that is designed to monitor these African dust events. SAL-WEB consists of near-real-time output generated from ground-based instruments, satellite-derived imagery, and dust model forecasts, covering the extent of dust from North Africa, westward across the Atlantic basin, and extending into Mexico. The products within SAL-WEB would serve to augment the Advanced Weather Interactive Processing System (AWIPS-II) infrastructure currently in operation at the NWS-PR. The goal of this article is to introduce readers to SAL-WEB, along with current and future research underway to provide improvements in African dust prediction capabilities.

Open access