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The Next Storm/Next Snow Forecast Discussion from the Cherrywood Observatory – September 13th, 2018

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

Forecast Discussion:

The ridge still rules, the atmosphere is dry, there is no smoke in the state, and a cool down is visible - 8 days out from now.

Figure 1 shows the dry weather on this side of the stationary west coast trough (purple is center of moist axis). The surface map for later today shows dry conditions and high pressure over Colorado (Figure 2). The temperatures will continue to be about 10-13F above average (Figure 3). Toasty!

Figure 1: the water vapor satellite image from Wednesday afternoon. Reds/Oranges are dry air, greys/whites are moist air regions.

Figure 2: The forecast surface map for Thursday PM. From NCEP.

Figure 3: the departure from normal temperature at noon Thursday - surface temperatures from weather5280.com

The longer range forecast:

Figure 4 is the animation of the upper air pattern showing Colorado sitting under the same pattern for most of the next week.  You can see Florence drift in, die inland and zip off to the northeast on this run of the GFS. Finally, about 7 days out, you can see the ridge modify and break down. Troughs start to enter the West.

The first big cold front roars into the state the early morning of Thursday the 20th (Figure 5).  That is a 30F drop from the week between now and then.

Looking at Florence, there is coverage of this storm everywhere now, and is often updated more frequently than this column as landfall is hours away.  Figure 6 shows the push-me-pull-me of the two highs will now result in the storm drifting VERY slowly to the southwest for 48 hours or more before heading deep inland to die.  Some folks in the Carolina's will see feet of rain. The tangle of models all pretty much agree.  The pink arrow in Figure 7 is the approx. location of the earlier path.  That is quite a southward drift!!

Figure 4: The animated 500mb forecast upper air analysis for next 9 days. from tropicaltidbits.com

Figure 5: the departure from normal temperature at noon Thursday next week 9/20- surface temperatures from weather5280.com

Figure 6: the five day cone of uncertainty plot forecast from the NHC for Florence.

Figure 7: the five day multi model plot forecast from the NHC for Florence.

Current Weather

Mostly clear

Mostly clear

32°F

UV Index
0 Low
Pressure
29.98 Steady
Visibility
8 miles
Dewpoint
25 °F
Humidity
75%
Wind
WNW 1.7 mph
Gust
3.8 mph
Wind Chill
32 °F

Hourly Forecast

Today
6 AM
29°F
Intermittent clouds
Today
7 AM
28°F
Mostly cloudy
Today
8 AM
36°F
Partly sunny
Today
9 AM
42°F
Partly sunny
Today
10 AM
48°F
Partly sunny
Today
11 AM
53°F
Partly sunny
Today
12 PM
57°F
Partly sunny
Today
1 PM
60°F
Partly sunny
Today
2 PM
62°F
Partly sunny
Today
3 PM
63°F
Partly sunny
Today
4 PM
64°F
Partly sunny
Today
5 PM
62°F
Partly sunny

7 Day Forecast

Partly sunny

Thursday

64 °F

Partly sunny


Intermittent clouds

Thursday Night

35 °F

Partly cloudy


Partly sunny w/ showers

Friday

54 °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

36 °F

Becoming cloudy with a shower in spots late


Showers

Monday

50 °F

Mostly cloudy and cooler with occasional rain; windy in the afternoon


Intermittent clouds

Monday Night

31 °F

Windy in the evening; partly cloudy


Sunrise and Sunset

Sunrise
6:50 AM
Sunset
7:22 PM

Based on AccuWeather data