Monday, January 18, 2010

January fluke: ice & rain

What could be more unlikely than the Vikes going to the Superbowl? How 'bout a cold rain during what is (on average) the coldest week of winter. Unusual, rare, but hardly unprecedented. Unusually strong storms roaring out of the Gulf of Mexico are often accompanied by not only copious moisture, but a surge of warm air capable of turning snow over to ice, even rain. Granted, this is far more typical in mid March than mid January, but we've all come to expect the unexpected in this neck of the woods, right? Nobody ever said this would be boring...

Forecast for Sunday in New Orleans: a jubilant sea of purple & gold, thunderous cheers, lightning-fast sacks, slippery (Saints) turnovers, high probability of a very quiet local crowd in the fourth quarter, significant risk of a rout. Degree of confidence: moderate to high. (check out the eye on that beast! Hurricane Brett is coming ashore. Time to warn the local residents).

We salvage one more dry, storm-free, blue-sky day, enough sun dribbling through for highs well up into the 20s, a good 5-10 degrees warmer than average. A weak bubble of high pressure hangs on long enough to ensure a dry commute into work or school Wednesday morning, but clouds quickly stream in tomorrow, the atmosphere capable of a light mix of wet snow, sleet, and freezing rain Wednesday night into Thursday. This will just be the first shot, the atmospheric appetizer, but roads may become slushy and slippery Thursday, highs holding a few degrees below freezing. My hunch: freeways and major state highways (treated) will probably be mostly-wet, but the side-streets may become glazed with ice.

Potential for Thursday icing. Ice potential forecast valid midnight Wednesday night. Many of the ingredients are coming together for significant freezing rain and sleet (ice pellets) Thursday morning as the first wave of moisture/energy pushes northeastward across the Plains. The only saving grace: temperatures will be in the upper 20s, so freeways and major state highways (that are treated by MnDOT) may be mostly-wet. But secondary roads could - in theory - be coated with glaze ice.

We catch a brief break on Friday, in-between storms, but it still looks like the main event, the most significant slug of moisture, arrives next weekend. Computer models have been printing out some very impressive, 1.5 to 2" liquid amounts by Monday. Were that all snow it would pile up to about 15-20" of the white stuff. The trouble is: it won't be all snow. Our weekend storm will be vigorous enough to pull unusually mild air northward, warming up the lowest mile to 8,000 feet of the atmosphere, able to turn falling snow into rain, possibly rain freezing on contact with cold surfaces for a time (freezing rain). The bulk of the precipitation may fall as rain Saturday and Saturday night, but as the storm tracks toward Wisconsin into the Great Lakes the airmass overhead will cool off, turning rain over to (mostly) snow on Sunday. Throwing around inch-amounts more than 48 hours before the storm would be reckless and highly premature, but it still looks like a potential for a "plowable" snowfall for much of Minnesota Sunday into Monday morning.

No more arctic air in sight - yet. The most bitter, subzero air has shifted north of the Arctic Circle (these temperatures in Celsius). Steering winds blowing predominately from the Pacific (and from the Gulf of Mexico this weekend) will keep temperatures above average through the end of the month. The 15-day GFS model keeps daytime highs in the 20s and 30s through the first few days of February.

An Olympic-size mess. For much of the last 1-2 weeks daytime highs have been in the 40s and 50s in Vancouver, British Columbia, site of the upcoming Winter Olympics. To make matter worse, unusually mild weather on the slopes has been accompanied by frequent rains, accelerating snow melt. Just when you thought things couldn't get any worse for NBC. Nothing But Controversy. The forecast for this week doesn't look promising, highs mostly in the 40s to near 50 (temperatures below are in Celsius).

Paul's Outlook for the Twin Cities

Today: Partly sunny, still dry. Winds: SE 5-10. High: 29

Tonight: Patchy clouds, chilly. Low: 14

Wednesday: Sunny start, clouds increase during the day. High: 28

Wednesday night: Light snow, mixing with freezing rain (ice). Slippery in time for AM Rush on Thursday. Low: 19

Thursday: Period of mixed wintry precipitation, wet snow, ice and rain. Slushy accumulation possible, especially outside the metro area. Freeways: mostly wet, very icy across greater MN. High: near 30

Friday: Overcast - better travel. High: 31

Saturday: Sleet and freezing rain, capable of icing early. Mostly rain by midday/afternoon. Roads may be very slippery far northern/western suburbs, especially early. High: 32

Sunday: Changeover back to mostly snow, potential for a couple inches, possibly enough to plow/shovel by Sunday night. High: 31

Monday: Light snow slowly tapers off to flurries, little additional accumulation by afternoon. High: 28

No comments:

Post a Comment