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Update 11/1 12pm: Next Storm/Next Snow Forecast Discussion from the Cherrywood Observatory – Oct. 31-Nov. 2, 2019

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

In Brief:

We are dry and warming to above freezing levels each day for the next 10 days. Very low rain/snow chances pass late Thursday night and again next Monday. No significant weather is visible in the models for the next week. We stay below normal, temperature-wise, for this entire time period.

12pm Update 11/1:

I was poking around weather stations in town Thursday morning just before sunrise and found 0F on Main St. and -4F in South Longmont and over around County Rd 1. So it got cold. I had about 65 trick-or-treaters visit the observatory last night. A few clouds did move through but it was clear 90% of the time. I think the cold and ice scared a few folks away (I had about 140 two years ago and 120 three years ago). We did enjoy Jupiter, Saturn, the Moon, Neptune, and the Andromeda Galaxy.

Things will remain chilly and dry this week. The big story is the upper air pattern (Figure 1 update). There is a large ridge off the west coast and a big trough over the eastern U.S. This give us northwest flow aloft with a steady stream of colder northerly air feeding in. Small cool fronts will pass (almost one a day) for at least the next 5 days and keep our temperatures below normal.

We'll do an analysis of the forecast for October made at the start of the month and the October that resulted - I believe it ended up being much cooler than was forecasted! Can we believe the November forecast I'll post?

Figure 1 update: The 500mb forecast upper air analysis for Sunday AM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.

End 12pm Update 11/1.

Forecast Discussion:

The storm has passed. My yard (adding the last 5 days of new-snowfall measurements together) received at least 9.2 inches in NE Longmont. The snowfall analysis from NOAA confirms this putting Longmont in the yellow shading that represents 8-12 inches of 72 hour accumulation (Figure 1).

It's Halloween! Last week, we had a giant discrepancy between forecasts with the GFS giving us a high on Halloween in the 60'sF while the European model put us in the low 20'sF. Weatherunderground had us in the upper 40'sF. It now looks like weatherunderground won the Halloween temperature-smack-down (Figure 2). But the same model brings in some clouds and a tiny chance of rain/snow overnight. Other sources don't see this happen.

For those who want to stop by and look through the telescopes, come on by the Cherrywood Observatory during trick-or-treating hours for Trick or Peek. I'm east of Alpine and south of 17th Ave. on Cherrywood and Cherrywood. Come in through the gates on the side-yard. I'll have signs and lights set up.

The 7! Timer (GFS based) model shows clear skies and temperatures around freezing in the evening (figure 3). Clear Sky Chart, out of Canada, has clear skies as well (Figure 4). Both do show a batch of clouds coming through during the 8-9pm hour.

The high temperature on Halloween will be a bit warmer just west of I-25 with a high around 40F (according to the GFS (Figure 5)). It will drop to below freezing between 6 and 7pm.

The Longer Range Forecast:

Things are cooler than normal and quiet for the next week and beyond (Figure 2). There is a hint of 'something' next Monday/Tuesday but it isn't much at this point. I need to catch up on grading and life stuff - I'll post updates as needed over the next couple of days! Have a fun spooky night.

Figure 1: The 72 hour snowfall analysis from NOAA for north central Colorado.
Figure 2: the graphical forecast for the next 10 days for Longmont, CO from weatherunderground.com
Figure 2: The 2.5 day sky conditions forecast from 7! Timer (the GFS). Light green line is peak trick-or-treating time.
Figure 4: The Clear Sky Chart sky conditions for the next 2 days from the Canadian model. Light green line is peak trick-or-treating time.
Figure 5: The high surface temperature in F for Colorado for Thursday/Halloween Day.

Current Weather

Mostly clear

Mostly clear

51°F

UV Index
0 Low
Pressure
29.79 Rising
Visibility
8 miles
Dewpoint
25 °F
Humidity
36%
Wind
W 3.8 mph
Gust
7.7 mph
Wind Chill
51 °F

Hourly Forecast

Today
11 PM
45°F
Cloudy
Tomorrow
12 AM
43°F
Intermittent clouds
Tomorrow
1 AM
41°F
Intermittent clouds
Tomorrow
2 AM
39°F
Intermittent clouds
Tomorrow
3 AM
38°F
Intermittent clouds
Tomorrow
4 AM
37°F
Intermittent clouds
Tomorrow
5 AM
36°F
Intermittent clouds
Tomorrow
6 AM
34°F
Intermittent clouds
Tomorrow
7 AM
35°F
Intermittent clouds
Tomorrow
8 AM
37°F
Intermittent clouds
Tomorrow
9 AM
41°F
Intermittent clouds
Tomorrow
10 AM
44°F
Intermittent clouds

7 Day Forecast

Partly sunny

Thursday

65 °F

Partly sunny


Intermittent clouds

Thursday Night

34 °F

A shower in spots this evening; otherwise, partly cloudy


Partly sunny w/ showers

Friday

53 °F

Cooler with times of clouds and sun; a couple of showers late in the afternoon


Showers

Friday Night

33 °F

A couple of showers in the evening; otherwise, cloudy


Mostly cloudy

Saturday

60 °F

Mostly cloudy


Intermittent clouds

Saturday Night

36 °F

Partly cloudy


Intermittent clouds

Sunday

62 °F

Times of sun and clouds


Mostly cloudy

Sunday Night

33 °F

Becoming cloudy


Showers

Monday

52 °F

Cloudy and cooler with occasional rain; windy in the afternoon


Intermittent clouds

Monday Night

29 °F

Windy in the evening; partly cloudy


Sunrise and Sunset

Sunrise
6:50 AM
Sunset
7:22 PM

Based on AccuWeather data