Observing Weather and Climate from the Ground Up A Nationwide Network of Networks (2009) / Chapter Skim
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Appendix A: A Rationale for Choosing the Spatial Density and Temporal Frequency of Observations for Various Atmospheric Phenomena
Appendix A: A Rationale for Choosing the Spatial Density and Temporal Frequency of Observations for Various Atmospheric Phenomena
Pages 185-207
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From page 185... ...
Appendixes
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From page 187... ...
The list is neither definitive nor exhaustive, but it does cover events that cause the greatest disruption, damage, and loss of life. FLOODING FROM LARGE-SCALE STORMS Definition: Steady soaking rains, sometimes with embedded showers and thunderstorms, cause flooding of small streams and larger rivers.
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In-situ observations inside of cloud systems within a day or so of reaching the West Coast would also be very helpful. Mesoscale features within the storm circulation often mark the difference between merely soaking rains (say, 0.20 inches per hour)
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SNOWSTORMS AND ICE STORMS Definition: These storms include any storm depositing enough snow or ice to disrupt road or air travel, communications, or the electrical power supply. An ice storm occurs when liquid precipitation falls at surface temperatures below freezing.
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Both snow and ice storms disrupt daily commerce and transportation, but ice storms commonly pose the additional hazard of power outages with all the collateral damage that implies, and damage to the power distribution infrastructure. The cost of major winter storms can be very high.
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The probability is lower north of Cape Hatteras. Tropical storms are virtually unknown along the West Coast, though remnants sometimes move northward into the southwest United States from the Baja region.
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The use of additional observations taken outside the targeted area in the initial conditions did not lead to further improvements in the forecast. The foregoing considerations suggest that further improvements in forecasts of track and of the extratropical transition will require targeted sounding data throughout the depth of the troposphere at roughly 100-150 km spacing and 6-h frequency.
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From page 193... ...
Outside metropolitan areas, ∆x could probably be relaxed to 20-30 km and ∆t to 30 min, but this may not be sufficient near lakeshores or the seacoast, where the meteorology is complicated by land and sea breezes. These requirements pertain to the surfacebased stable layer and the deeper mixed layer, where the pollutants reside.
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From page 194... ...
as to predict the dissipation. It is critical to know the height of the inversion layer and the strength of the inversion in order to predict dense fog or the height of a low cloud base.
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Thunderstorms resulting from gust-front interactions in the boundary layer, along stationary lowlevel convergence zones, or within horizontal convective rolls are much less predictable, even with good measurements. See, for example, Weckwerth (2000)
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Size: The area of excessive rainfall is often only a few kilometers wide, but the flood can propagate downstream for tens of kilometers. Duration: 30 min to several hours Geographical preference: Flash floods favor steep terrain, especially where the ground is relatively impermeable or the soil is already saturated.
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From page 197... ...
In flash-flood situations, the cloud base is usually lower than the climatological normal; in fact, it is often lower than 1500 m. A cloud base temperature of 10°C or higher is an indicator of high precipitation efficiency; the considerable depth of cloud below the freezing level aids the "warm rain" process (formation of many large drops by collision and coalescence)
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From page 198... ...
What combination of cloud physics and dynamics controls hail growth is still mostly a mystery (Knight and Knight, 2001) , but it is clear that convective available potential energy, a measure of atmospheric instability that is correlated with maximum updraft speed, and vertical wind shear, which governs whether or not the precipitation shaft
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From page 199... ...
Size: The damage swath is usually just a few kilometers wide but ranges from a few to more than 100 km long. Duration: a few minutes to more than an hour Geographical preference: A 4-year climatology of cold-season bow echoes over the continental United States shows them confined to east of the Rocky Mountains and south of 45°N (Burke and Schultz, 2004)
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map showing the mean number of days per century with at least one tornado, F2 intensity or greater, touching down in a grid box 80 km on a side. The maximum of 40 days exists just southeast of Oklahoma City, but the 25-day contour includes most of Oklahoma, the eastern two-thirds of Kansas, southeast Nebraska, southwest Iowa, northwest Missouri and west central Arkansas. Few F2 or greater tornadoes occur west of the Rocky Mountains or east of the Appalachians.
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WINDSTORMS WITHOUT PRECIPITATION Downslope Windstorms Definition: Downslope windstorms are usually localized in the lee of mountain barriers. Wind blowing across a mountain barrier causes waves to form in the flow, similar to water waves in a stream when it flows across a rock in the streambed.
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Forecasters look for strong cross-mountain winds, a stable layer near mountain-top level, often near 600 hPa along the Front Range of the Rocky Mountains in Colorado, and a lack of strong shear in the mid- and upper troposphere. The strong surface winds typically last for a few hours at a time and can be extremely gusty.
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From page 203... ...
For this purpose, full-tropospheric temperature and wind soundings within the broad region including the low are necessary at resolutions of ∆x=100 km, ∆z=0.5 km, and ∆t=6 h. FIRE WEATHER Definition: Fire weather refers to conditions that favor the rapid spread of brush or forest fires, whether a fire is in progress or not.
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Any supercooled cloud can produce aircraft icing. A supercooled cloud contains liquid water at temperatures below 0°C.
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Infrared measurements from space and ceilometer measurements from the ground will not detect supercooled clouds unless the cloud base or cloud top lies within the critical temperature layer. Downbursts Definition: A downburst is a strong downrush of air from a convective cloud that strikes the ground.
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They are caused by the evaporation of droplets falling into a deep layer of fairly dry air below a high cloud base in the presence of a steep lapse rate (rapid decrease of temperature with height, about 1°C for each 100 m of altitude)
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From page 207... ...
Clear-air turbulence is most common in the vicinity of upper air fronts, which are associated with strong threed imensional wind shears. Clear-air turbulence is also common, and may be severe, in mountain wave situations.
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