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The Next Storm/Next Snow Forecast Discussion from the Cherrywood Observatory – October 7, 2017

This content was originally published by the Longmont Observer and is licensed under a Creative Commons license.

Forecast Discussion:

Things are on track for a warm weekend and a cold/wet/snowy Columbus Day. We have gusty down-slope winds buffeting Longmont Friday evening and it may still be breezy at times on Saturday.  Temperatures will be in the mid to upper 70's east of the mountains (Figure 1).

Figure 1: Saturday late afternoon 6 foot above ground level forecast temperatures from the GFS. Longmont is the pink dot.

In the Longer Range:

Our next storm is coming more into focus (there is more model agreement at least). The trough is barreling over us on Monday as seen in Figure 2. The GFS total liquid (rain and melted snow) forecast for this storm in Longmont (Figure 3) seems to be in the 0.25 to 0.5" range. The total snowfall (Figure 4) looks to be in the 2-3" range. The National Weather Service is calling for 1-4" along I-25 and 5-10" up in the higher mountains.

The timing seems to have the front hit Longmont around 7pm with rain chances picking up around 9pm and a change over to snow after midnight Sunday.  The snow (or rain/snow mix) should taper off later Monday morning with rapid clearing behind the trough Monday afternoon. Temperatures should be in the mid to lower 20'sF Monday night into Tuesday morning. We'll go back to the 20's F Wednesday morning as well.

Tropical Storm Nate (in Figure 5) is already about to graze the Yucatan and will be dangerously close to New Orleans - in the present forecast- Saturday night as a Category 1 storm.   More on Nate and our snow as the weekend goes on!

Figure 2: the Monday midday 500mb upper air map model forecast from the GFS. Troughs are red lines, ridges blue lines.

Figure 3: total accumulated precipitation (liquid) between Fri PM and Tuesday PM from the GFS. Longmont is the pink dot.

Figure 4: total accumulated snow (10:1 ratio) between Fri PM and Tuesday PM from the GFS. Longmont is the pink dot.

Figure 5: NHC official 5 day forecast for tropical storm Nate.

Current Weather

Heavy rain

Heavy rain

50°F

UV Index
0 Low
Pressure
29.75 Rising
Visibility
5 miles
Dewpoint
46 °F
Humidity
85%
Wind
N 3.3 mph
Gust
7.1 mph
Wind Chill
50 °F

Hourly Forecast

Today
9 PM
49°F
Thunderstorms
Today
10 PM
48°F
Thunderstorms
Today
11 PM
48°F
Thunderstorms
Tomorrow
12 AM
47°F
Cloudy
Tomorrow
1 AM
47°F
Cloudy
Tomorrow
2 AM
46°F
Cloudy
Tomorrow
3 AM
45°F
Rain
Tomorrow
4 AM
45°F
Cloudy
Tomorrow
5 AM
45°F
Rain
Tomorrow
6 AM
44°F
Rain
Tomorrow
7 AM
44°F
Rain
Tomorrow
8 AM
44°F
Cloudy

7 Day Forecast

Mostly cloudy w/ t-storms

Friday

69 °F

Variable cloudiness with a couple of thundershowers this afternoon; gusty winds and small hail can accompany any downpour


Thunderstorms

Friday Night

41 °F

Cloudy; a couple of showers and a thunderstorm this evening followed by periods of rain late; gusty winds and small hail can accompany any downpour


Rain

Saturday

44 °F

Chilly with periods of rain and a thunderstorm; travel in the foothills and mountains will be slippery due to snow


Rain and snow

Saturday Night

36 °F

Cloudy with rain, mixed with a little snow late; travel in the foothills and mountains will be slippery due to snow


Mostly cloudy

Sunday

61 °F

Mostly cloudy and warmer


Intermittent clouds

Sunday Night

36 °F

A thunderstorm in spots in the evening; otherwise, partly cloudy


Partly sunny

Monday

71 °F

Partly sunny, pleasant and warmer


Partly cloudy

Monday Night

45 °F

Partly cloudy


Mostly sunny

Tuesday

73 °F

Pleasant with sunshine and patchy clouds


Partly cloudy

Tuesday Night

40 °F

Partly cloudy


Sunrise and Sunset

Sunrise
6:06 AM
Sunset
7:51 PM

Based on AccuWeather data