The Weather Wire
December 2005 Volume 13 Number 12
Avg High 57.5
Avg Low 27.5
Snow - 1.0"
Season Snow - 10.6"
Precipitation - 0.48"
Avg High 51.5
Avg Low 23.5
Avg Snow - 10.7"
Avg Precip - 0.98"
What Causes El Nino... |
There has been a lot in the media about El Nino and the effects it has on our weather so we thought some basic information on this Phenomena would be helpful. To understand El Niño, you've got to fathom the planetary "heat engine." Heat engines -- there's one in your car -- use heat to create motion. In your car, heat from burning gasoline creates motion so you can cruise for burgers. On Earth, heat from the sun warms the equator much more than the poles, and then the atmosphere and oceans move this heat toward the poles.
The motion in the atmosphere is powered by heat from evaporating sea water. The warm, moist air rises, pulling in dry air and creating giant atmospheric loops called convection cells that transfer heat away from the equator.
Normally, when El Niño is not operating, a giant convection cell forms in the western Pacific, around Indonesia and Australia. During an El Niño, the convection cell moves east, altering the entire pattern of wet-and-dry weather in the Pacific. The huge amounts of heat released by the thunderstorms in convection cells affects the circulation of the global atmosphere, so when those thunderstorms are shifted from their normal position, the global circulation is also changed. And by changing atmospheric circulation, including the jet streams that circulate planet wide, the effects spread far beyond the Pacific basin.
Since it's heat that drives the weather -- differences in temperature and pressure literally move air and moisture around the sky -- if you change the source of heat, you change the entire weather system.
Climatologists call this changing pattern of winds and clouds the Southern Oscillation, so you'll often see El Niño called "El Niño-Southern Oscillation." If you don't mind, we'll call the combined changes in the ocean and atmosphere "El Niño." It's simpler and more elegant.
The heat engine we've been describing operates whether or not El Niño is occurring -- otherwise the tropics would fairly fry and the poles fully freeze even more than they do. As far as our weather is concerned, the key change in El Niño is the changed position of the pool of hot water and the convection cell it creates.
Perhaps this is confusing, so let's go through it in more detail. When El Niño is not operating, trade winds in the Pacific push water west, away from South America, toward Australia and Indonesia. Using satellites, scientists found that the sea surface is actually two feet higher around Indonesia than it is near the South American coast.
As hot water evaporates from the ocean in the western Pacific, it creates convection cells that make clouds and bring "normal" rains to surrounding regions.
The water that blows westward across the ocean is replaced by deep, cold, nutrient-laden water that rises to the surface near South America, feeding a vibrant fishery along Peru and Ecuador and cooling the sea surface.
That's the average condition in the Pacific, but in reality conditions oscillate between El Niño and its opposite, dubbed La Niña, when it's abnormally cool in the eastern tropical Pacific. In other words, what's really normal is change.
Every now and then, these westward winds weaken, and the ocean sloshes back toward the east, seeking to level itself out, and the warm water moves eastward. The upward movement of cold water along South America stops and the fishing industry takes a bath, deprived of its supply of nutritious, cold water.
That's El Niño.
Once the warm spot moves eastward, the winds change, and the currents change. And that causes weather upheavals around the world.
Online Forecasts Available Again
Skyview Weather is happy to announce that online forecasts and snow reports are again available on our sister www.anythingweather.com website. Forecasts and snow reports are password protected, but an email to Tim@Skyview-WX.com requesting your forecast and/or snow reports be available online will result in an account being setup for you. As always, forecasts and snow reports are for client use only, but with the online access, forecasts and snow reports are just a click away from any computer with an internet connection!
Little change in drought conditions across most of Colorado, with few areas of drought remaining..
The map below shows forecasted temperature deviances for December 2005. As can be seen, above normal temperatures are expected for Colorado for December 2005.
The map below shows forecasted precipitation deviances for December 2005. Normal or near normal precipitation is expected for Colorado for December 2005.
As can be seen in the below map, most of the state has come out of the widespread drought conditions of a year ago, with drought not expected to redevelopment in the near term..
November is normally Denver’s second snowiest month, however November 2005 turned in only a total of 1.0 inch for the entire month and puts it in the record book as the 7th least snowiest Novembers. Normal for the month is 10.7 inches so that we were 9.7 inches below normal. There were only two days with measurable snow, with 0.7 inch registering the maximum amount in 24 hours on the 17th. It again should be noted that many areas along the Urban Corridor faired much better with 8-12 inches for the month.
With snow below normal the precipitation followed suite and we were 0.50 inch below normal. Normal for the month is 0.98 inch. Five days recorded measurable precipitation of which most was in the form of snow. For the year itself we continue below normal with 12.45 inches, which is 2.73 inches below the normal of 15.15 inches.
If you thought the month felt fairly mild you were right. We finished the month with an average temperature of 42.5 degrees, 5 degrees above normal. The average maximum temperature was 57.5 degrees, six degrees above normal. Temperatures ranged from a high of 75 degrees down to a low of 7 degrees. There were no new temperatures records tied or set for the month.
Although winter does not officially arrive until December 21st, under normal conditions, by December 21st, Denver has usually experienced a taste of winter.
Normally prolonged cold spells are more frequent in January, however, 2 of Denver’s longest cold spells occurred during December. In 1983, the temperature dropped below zero on the 20th and did not return above zero until Christmas day, a record 115 hours. The temperature was below zero for 85.5 hours during December 1990 and during that period, the mercury dropped to 25 degrees below zero on the 22nd, tying the record for the lowest ever Denver December temperature.
Even though December ranks as Denver’s 6th snowiest month, some of Denver’s biggest and most memorable snowstorms occurred in December. The Christmas blizzard in 1982 rates as one of the most vicious snowstorms in Denver’s history. Snow began on the 24th and by midday on Christmas day, in a period of 24 hours, 23.6 inches of snow fell at Stapleton airport. The most snow from one storm (45.7 inches) occurred in 1913 when snow fell for the first six days of the month. Just over 37 inches of that total fell on the 4th and 5th.
December can have several occurrences of Chinook winds, mostly near the foothills. These winds rarely cause problems in Denver, however, in the foothills cities like Boulder and Fort Collins, wind speeds during a Chinook event can exceed 100 miles per hour. In December of 1990, a wind gust of 120 mph was recorded in south Boulder, just to the northwest of Metro Denver.
Sunrise/Sunset (Denver area)
October 2005 to April 2006