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Forecast discussion:
A quick (late) snow and Halloween weather update:
With the western ridge inching eastward briefly, we rocket to a beautiful (nearly) 70F on Sunday - only to have it robbed by a couple of short wave troughs racing through Monday and Tuesday. Temperatures plummet below freezing on Monday which may only have a high of 32F (Figure 1). Precipitation moves in with it as well with some models showing snow again on Halloween. Matt Makens posted a graph of all Halloweens from 1872 to 2016 and snow amounts that fell (Figure 2). There are 15 days out of 144 years or 10% of the time snow has fallen on Halloween. That is pretty special if it happens!
The weatherunderground 10 day graph shows a good chance of snow Monday morning and a bit of a chance on Tuesday morning - but a serious drop in temperatures. The red line on 10/31 are the conditions at 7pm Halloween night Temperatures will be around 38F with partly cloudy conditions and a small (6%) chance of precipitation. I'll have my telescope open for Trick or Peak at the corner of Cherrywood Dr. and Cherrywood Way in NE Longmont showing whatever I can get through the clouds- as long as there isn't any precipitation falling.
A quick look at the total snowfall through midnight Tuesday/Wednesday (after trick or treating is over)... the GFS paints a coating to 1/2" for Longmont (Figure 4). The NAM paints the foothills to our west with an inch or two of snow, but Longmont is in the trace to coating amount here as well.
In the longer range:
After Tuesday, things get very steady and quiet with highs in the mid 50's to mid 60's overall and some clouds almost all the time. Lows hover just above or below freezing, but nothing extreme for this time of year (Figure 3 again).
