Winter WeatherOctober 17, 2007

Winter WeatherA winter storm is a low-pressure system that covers a large area and contains weather fronts.In the Northern Hemisphere, circulation is counterclockwiseFronts can produce rain, sleet, freezing rain, or snow

Winter CyclonesWinter cyclones are produced by (or spin off of) the Aleutian and Icelandic Lows (both semi-permanent pressure cells)They can impact weather between September and MayMost intense in January and FebruaryThe severity of the storm can be determined by checking the pressure at the storms center anything below 1000mb is severe

Winter Lows

The severity of winter cyclones depends on Latitude Distance from the oceanSource regionContinentalitySouthern Italy and Nebraska are at the same latitudeTopographyMountains alter wind patternsAltitude Influence temperature distribution

Jet StreamParks over the US during the winterCan change position and contour often, or stay in the same position for monthsPersistent winter ridges produce a warm, dry winterPersistent winter troughs produce a cold, wet winter and spring floods

Sleet and Freezing RainThe most dangerous winter weather because no one takes them seriouslyIce pellets or snowflakes that melt as they fall, but refreeze before hitting the surfaceFreezing rain freezes on the first thing it hits: power lines, roads, trees, geeseIf more than 1 in of ice forms at the surface, it is termed an ice storm

Freezing Rain

Sleet

HailHail consists of ice pellets formed in roughly concentric layersFormed when water is frozen in the atmosphere. The ice pellet falls and encounters water, which freezes to the ice pellet forming a second layerThe size of hail is determined by the strength of the updraftHail has more water volume, snowflakes have more air volume

Hailstones

SnowSnow is precipitation in the form of frozen water with a crystalline structureFor powdery snow, 8-12 inches of snow will melt into 1 inch of waterFor wet snow, 4-6 inches of snow will melt into 1 inch of water

Winter Precipitation

Drifting SnowDrift control used to prevent roads from becoming impassibleTemporary snow fences erected to capture snow blowing from the west and northwestRows of conifers also used

BlizzardsBlizzards are characterized by blowing and drifting snow, limited visibility, and cold temperaturesOccur on the polar sides of fronts behind cold frontsTemperatures below 25F and winds above 35mphBlizzards are strongest when reaching the farthest point south in the jet stream

Rain into snowPrecipitation changes from rain into snow as a cold front passesWind changes from SSW to WNW as the front passesSnow into rainWhen a center of low pressure passes over an area before the warm frontSnow is melted into rainCauses freezing rain and ice storms

NoreastersAka NortheasternsWhen trough sets up over Atlantic seaboardAtlantic Ocean feeds extreme snow storms along the coastWinds out of the NESnow 1-4 feet deep, coastal flooding, beach erosion

Cold Air DammingWhen high pressure sets up over the NE US or eastern Canada, it forces cold air into the Appalachian MountainsThe air is too dense to rise over the mountains, so it becomes trappedThis produces extreme temperatures, ice storms, freezing rain, and/or blizzardsExample, Blizzard of 1993

Cold Air Damming

FYIAlcohol increases the danger of hypothermia (which is extremely low body temperature)It impairs judgmentIt causes small blood vessels in the skin to dilate, increasing the rate of heat loss from the body

FolkloreThe wooly boogers!Their coloring predicts winter weatherHornetsPlacement of nests predicts winter weatherPunxsutawney Phil