wxgeek's weather-Cold and Snow This Week - Update Wed Nov 30

Update Wed Nov 30

NWS still deciding whether to issue a Winter Storm Warning or Winter Weather Advisory for much of the foothills. Based on their assessment, it will likely become a Winter Storm Warning. Models in general agreement, although snow amounts still vary from 5-10 inches with the NAM/WRF, to 4-8 inches on the GFS. I still don't see the high amounts NWS is toting, so we will see. The bottom line is a cold and snowy day on tap for Thursday with lots of wind, especially east ogf I-25 where blizzard conditions will be possible. Snow still looks to arrive between midnight and 3 am, with some moderate snow during the Thursday morning commute. Heaviest snow looks to be between 4 am and 10 am Thursday. Light snow will continue into Thursday evening. With snow and wind, travel will be difficult Thursday. Commute on Thursday will be bad, so if you can avoid driving you should.

Snow amounts, so using a blend of models, I would say 3-6 inches across the Plains and Urban Corrifdor, and 4-9 inches across the foothills, with the possibility of up to 12 inches in some favored spots. Models output between 0.5 and 0.75 of liquid equivalent, so using a 16:1 ratio for an arctic airmass, up to 8-12 inches on the high end. I'm still uncertain this event will produce this much snow, but better to be ready for a more significant event. Temps will drop during the day on Thursday, so highs only in the teens, with lows Thursday night near zero. Because today will be quite warm, it is likely initial snow will melt on asphalt roads then quickly turn to ice with snow on top. This will cause roads to be very slick from Wednesday night through the day on Thursday as crews attempt to keep up with the snow, especially Thursday morning.

Models then diverge on the wekend weather, but my general feeling is that we will see another round of cold and snow late Friday night into Saturday, with continued cold and snow fluries into Sunday, so a more winter like weekend.

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Update Tue Nov 29

NWS has issued a Winter Storm Watch for the upcoming system, although I am somewhat puzzled by their predicted snowfall amounts. They are talking about 8-17 inches in the foothills. There is currently some disagreement between the numerical models, but the more generous NAM/WRF I can only see getting up to about 8 inches of snow, and the other models like the GFS and Euro have lesser amounts.

Based on what I have recently seen, here is my forecast....

Another sunny and mild day today. Some gusty wetserly winds likely to develop tonight into Wednesday morning, which will keep temps pretty mild again on Wednesday. Upper level low will slide down from British Columbia towards the CA/AZ border on Thu. An associated arctic front will drop south across CO on Wednesday evening with a good upslope flow developing behind this front. Snow should move from north to south across the state, with snow developing in our foothills around midnight on Wednesday night. Snow will continue overnight and through the day on Thursday, ending Thursday evening. Strong north to northeast winds will accompany the snow on Wednesday night and Thursday morning with speeds in the 20-35 mph range, so substantial blowing and drifting of snow will accompany this system. Temps will also be quite cold in the modified arctic air, with temps Thursday struggling to get above the teens, and low temps Thursday night near or below zero in the foothills.

The big question now is snow amounts. I am still of the belief the smounts will be on the lighter side, with 2-4 inches on the Plains and Metro area, and 3-6 inches in the foothills and Palmer Divide. The reason for my lower snow amounts is that most arctic fronts don't produce great amounts of snow due to the extremely cold airmass, which does not hold great amounts of moisture. The upper level low will still be very far away near the CA/AZ border, so the upper level dynamics are not strong enough to support lengthy heavy snow. Of course with all of that said, I could be wrong. Time will tell. The end result will still be a cold and snowy period from Wednesday night into Thursday eveing, which will make for a pretty nasty commute on Thursday. Near whiteout conditions could exist for periods on Wednesday night into Thursday morning, so travel could become very difficult, with road closures or restrictions a possibility.

Long range progs then indicate another system will move down from the northwest on Friday night and combine some with the upper low over CA/AZ that will be ejecting east. This combination could bring anotehr round of snow, cold and wind on Friday night into Saturday. Models are not in great agreement on this evolution yet, so confidence in this time period not very high at this time. Sunday looks to be cold with some lingering flurries possible. Models then suggest next week will be dry and more seasoanl temps.

Update Nov 30th