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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

Mostly clear

Mostly clear

64°F

UV Index
0 Low
Pressure
30.2 Rising
Visibility
5 miles
Dewpoint
50 °F
Humidity
60%
Wind
NW 2.2 mph
Gust
6.5 mph
Wind Chill
64 °F

12 Hour Forecast

Today
6 AM
67°F
Mostly sunny
Today
7 AM
70°F
Mostly sunny
Today
8 AM
72°F
Mostly sunny
Today
9 AM
77°F
Mostly sunny
Today
10 AM
82°F
Mostly sunny
Today
11 AM
86°F
Mostly sunny
Today
12 PM
89°F
Partly sunny
Today
1 PM
93°F
Partly sunny
Today
2 PM
95°F
Partly sunny
Today
3 PM
97°F
Partly sunny
Today
4 PM
98°F
Partly sunny
Today
5 PM
98°F
Partly sunny

7 Day Forecast

Partly sunny

Thursday

98 °F

Partly sunny and hot; poor air quality from high ozone levels


Intermittent clouds

Thursday Night

65 °F

Partly cloudy and mild


Partly sunny w/ t-storms

Friday

96 °F

Mostly sunny and very warm; a thunderstorm in spots in the afternoon


Thunderstorms

Friday Night

63 °F

Mostly cloudy and mild with a heavy thunderstorm


Thunderstorms

Saturday

82 °F

Cloudy and cooler; a thunderstorm in the afternoon; much cooler than recent days


Thunderstorms

Saturday Night

61 °F

Overcast with a couple of showers and a thunderstorm


Mostly cloudy

Sunday

79 °F

Mostly cloudy with a thunderstorm in the afternoon


Intermittent clouds

Sunday Night

60 °F

Partly cloudy


Intermittent clouds

Monday

83 °F

Intervals of clouds and sun with a thunderstorm in the afternoon


Intermittent clouds

Monday Night

62 °F

Increasing clouds


Sunrise and Sunset

Sunrise
5:55 AM
Sunset
8:18 PM

Based on AccuWeather data