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In Brief:
A major winter storm dropping feet of snow in places along I-25 and the Foothills will begin to impact the area by mid-afternoon with rapidly deteriorating road and travel conditions by evening. A winter storm warning is in place and blizzard warnings will probably be issued for areas just east of us later today. Skies clear Tuesday afternoon with windy conditions. Thanksgiving looks dry and cold (and white). A small snow storm will re-coat the snow Friday before a dry and cold weekend.
Forecast Discussion:
The NWS leads again today:
Winter Storm Warning Issued: 7:06 AM Nov. 25, 2019 – National Weather Service
...WINTER STORM WARNING REMAINS IN EFFECT FROM 8 PM THIS EVENING TO 5 PM MST TUESDAY... * WHAT...Heavy snow expected. Total snow accumulations of 8 to 16 inches. Winds gusting as high as 40 mph. * WHERE...From the Denver metro area and Castle Rock north to Boulder and Longmont, Greeley, and Fort Morgan. * WHEN...Snow will develop this evening and will become heavy by late evening. The heavy snow will continue into Tuesday morning, then diminish. * IMPACTS...Travel will become very difficult to impossible tonight. This may occur in areas north of Denver and near the foothills by mid evening, and will be a bit later across the rest of the area. Road closures and impassable side streets and rural roads are likely. PRECAUTIONARY/PREPAREDNESS ACTIONS... Prepare for a period where travel is impossible late tonight and Tuesday. Travel during the period of heavy snow is strongly discouraged. If you must travel, carry a shovel. Keep an extra flashlight, food, and water in your vehicle in case of an emergency. The latest road conditions can be obtained by calling 5 1 1 or visiting www.cotrip.org. (Graphic in Figure 1)
The crippling amount of snow seems a certainty. The timing has me spooked. The warning starts at 8pm tonight, but I've seen many of these systems blow in early (and there is snow falling in SW and south-central Wyoming already). Be ready for rapidly deteriorating conditions and increasing winds. Snowfall rates this evening and on into late morning will reach 2-3 inches an hour with vigorous up-slope east winds and very strong upward motion in the atmosphere at 700mb. This really is coming together optimally for a big snow.
The weather map for Tuesday AM (Figure 2) shows the deep surface low down to our southeast with one foot in the tropical moisture coming up the Plains and the other foot pulling down a cold front behind it taking temperatures down to just below freezing (not too cold and not too warm - just right). A blizzard warning will probably be issued for much of the NE Colorado Plains today.
Going back to timing, weatherunderground shows precipitation starting as early as 2pm (rain) and switching to snow by 4pm. This will occur earlier in Ft. Collins and a couple of hours later in Denver (Figure 3). I'm nervous about the normal evening commute. Keep an eye on your weather apps! Be ready to get home early if you are out and about.
Snowfall Roundup:
The Weatherunderground model (Figure 3): 12-13 inches.
The weather5280 forecasters (Figure 4): 8-14 inches.
The GEM model (Figure 5): 14-16 inches (or more? We are near the bullseye!).
The NAM model (Figure 6): 12-13 inches (the bullseye is a bit north of us)..
Channel 7 (not shown) has us int the 12-14ish inches area.
Channel 9 (not shown) has us in the 19-20 inch area.
And finally (Figure 7) the GFS assuming a 10:1 powder to liquid content ratio: 16-18 inches.
The (Figure 8) GFS assuming a 15:1 powder to liquid content ratio: 24-36 inches (the intervals spread out a lot more at this extreme).
Note how quickly the snow fall amounts drop off as you go south. Castle Rock is only expected to see 4-6 inches (only, sheesh!).
Thanksgiving Day Forecast: It looks quiet and cold (and coated with snow) around here for Thanksgiving Day. You may have to dig a snow pit for your deep fried Turkey in the backyard.
The Longer Range Forecast:
Another system, sliding up out of the desert southwest may drop 1-3 inches of new snow on us Friday. We remain cold, much below normal, through much of the following weekend and beyond. More on that later.