It’s been a busy storm chase season so far being out on the road a good portion of the time between April 22 and May 25. I’ve been home for nearly a week now and had time to upload some photos. We’ve seen many tornadoes so far this season with highlights of the year being May 22nd intercepting an EF-4 wedge tornado near Bowdle, SD and multiple tornadoes near Meadow, SD on May 24th including an EF-2 that destroyed a school. Fortunately there were no deaths or major injuries with these tornadoes. I’ve uploaded some pictures of the May 22nd chase here.

It’s been a while since I’ve posted a blog entry… been busy with family in town for Thanksgiving, vacation to Florida and Disney World in early December, then Christmas and New Years… but the weather in Northern Colorado has been quite wintry since my last post. A solid snow pack has been on the ground here in Greeley for much of this winter season. We had a surprisingly heavy snowfall on Dec 23 when about 8-9″ of snow fell (by the way we were the big winners in Colorado on this storm as most places got 2-4″). A Denver cyclone-type meso-low formed just south of Greeley causing our winds to be easterly with a convergence boundary in place just south and east of town, which kept heavy snow falling for several hours. Then as a large low pressure system wound up over the Great Plains and stalled for a couple of days and our winds became north at 20-40 mph with ground blizzard conditions lasting through Christmas day. As of January 4th, we’ve only been slightly above freezing during maybe 2 afternoons since our last snowfall and most of the snow remains on the ground.

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The temperature plunged to -6 F on Monday morning at Greeley Airport, which shattered the record low of 6 F for November 16th by 12 degrees. A combination of a fresh 10″ blanket of snow along with clear, calm overnight conditions contributed to these extremely cold temperatures.

Snow started falling right on queue Saturday evening in Greeley shortly after the winter storm warning went into effect. Snow began to fall heavily by 7pm and it continues to fall moderate to heavily as of midnight. Total snow accumulation in Greeley has already reached 9″ near the intersection of 14th avenue and 20th street. If significant snow continues to fall for the next few hours, Greeley will likely surpass the 1 foot mark.

A cold front moved through Northern Colorado this afternoon dropping temperatures into the 30s. A light to moderate band of snow will quickly move through the area and deposit a quick inch of snowfall Friday afternoon and evening. Another more significant snowstorm will move into the region on Saturday and Sunday. Weather forecast models are now in better agreement and are forecasting a significant snowfall for Greeley starting Saturday afternoon and continuing into Sunday. Forecast models are predicting a favorable easterly surface wind to accompany the upper level storm system, which was lacking during our last 10″ snowfall before Halloween (north to northwest winds dried us out and prevented us from getting 2 feet of snow). Easterly surface winds will keep the lower atmosphere sufficiently moist to allow heavy snowfall to accumulate. At this time it appears anywhere from 8″ to 12″ of snow will fall by Sunday afternoon over the Northern Colorado Plains.

The Boulder NWS is not talking much about this storm at the moment, but both the NAM and GFS models predict over 1″ of liquid precipitation for the Front Range Urban corridor during the next 60-84 hours. The NAM solution shows the potential for a big snowstorm here in Greeley on Sunday, while the GFS doesn’t look so promising. There’s a trough of low pressure developing over the Western US at the moment and the first wave and jet max will push a cold front through Northern Colorado with some snow bands forecast to develop Friday evening over the area generally from Boulder north to Fort Collins and east to the Greeley area. Looks like a general 2-4″ with this initial cold front / snow band Friday evening is possible with maybe up to 6″ in places. After a lull in the action on Saturday, another storm system will track from the Pacific NW, dive down through Utah, and then turn east and track over southern Colorado or northern (or central) New Mexico depending on the model solution you look at. The NAM is forecasting 1.5″ to 1.75″ of liquid between now and Sunday night over the northern urban corridor (including Greeley), with over an inch of that falling on Sunday. If most of this falls as snow, we could be in for a foot to foot and a half of snow with these 2 systems from Friday – Sunday. The GFS is slightly drier for the period, but is still showing 1″ to 1.25″ of liquid by Sunday night. The models have been flip flopping quite a bit over the last couple of days trying to resolve this system. So in reality we could get a big snow or a whole lot of nothing.

With the 2010 Winter Olympics being held in Vancouver, BC let’s take a look at the potential impact that El Nino might have on snow conditions. El Nino tends to cause temperatures to be warmer than normal in the Pacific Northwest plus it contributes to a weather phenomena called the “Pineapple Express”. This could wreak havoc on the snow quality at Cypress Mountain who will host freestyle skiing (aerials, moguls, and ski cross), and all 2010 snowboard events (half-pipe, parallel giant slalom, snowboard cross) and at Whistler Blackcomb who will host all alpine ski events plus bobsleigh, luge and skeleton. During a Pineapple Express event, warm moist air from Hawaii slams into the Pacific Northwest causing heavy rain and snow levels to rise as high as 10,000 ft in the middle of winter. If enough cold air is present and the snow levels stay below ski area levels, heavy snows can be expected. Whistler’s elevation ranges from 2,140 ft at Whistler Village to 7,160 ft at mountain top level. Lower parts of the mountain will be prone to experiencing periods of rainfall more frequently during El Nino due to warmer than average temperatures. Annual snowfall totals for the higher elevations of Whistler actually are greater than normal during El Nino years. The average annual snowfall for the 1982-2008 period was 398″, but the average annual snowfall for El Nino years during that same period was actually 408″. So, even though there’s lots of talk of gloom and doom for the 2010 Winter Olympics due to El Nino, there may actually be significant snowfall this winter given past weather history (if you don’t mind the occasional heavy rainfall mixed in to slush up the snow). But hey… after all, we are talking about relatively low altitude mountains along the Pacific coast and sloppy, concrete-like snow comes with the territory.

After our exciting snowstorm last week, the first week of November is shaping up to be pretty nice in the weather department for Northern Colorado. A ridge of high pressure will be building into the region through Saturday with fair conditions and temperatures topping out in the 50′s and 60′s during the daytime hours and bottoming out right near freezing each night. While it’s a bit far away, the long range weather forecast model (GFS) is forecasting a cold front to move through the region on Sunday (November 8th). At this time it appears to be a fast moving system with a quick shot of snowfall associated with the cold front and upper level low pressure system. If the forecast verifies, Northern Colorado could get a couple of inches of snow Sunday afternoon or evening. I will keep an eye on this system.