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The Next Storm/Next Snow Forecast Discussion from the Cherrywood Observatory – September 11th, 2018

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

Forecast Discussion:

With a big ridge over the middle nation, we have bone dry weather with near record to record high temperatures expected much of the rest of this week. Figure 1 shows that big ridge axis to our east with southwest flow locally. That flow is bringing in clearer air (with some smoke and haze stuck in the downwind side of the Rockies - Figure 2). That's all I've got to say about our home town.

Let's look out into the future for the next cool down and off to the East Coast and Florence...

Figure 1: The 500mb forecast upper air analysis for Tuesday noon. Pink dot is Longmont. Red lines are troughs, blue lines are ridges. From weather5280.com

Figure 2: The HRRR (high resolution rapid refresh) model forecast of smoke at all levels for Tuesday early AM.

The longer range forecast:

The 500mb map for Saturday afternoon is shown in Figure 3. The ridge axis shifts east to possibly trap Florence in North Carolina and Virginia (more on this below) but the ridge is still holding strong in the western U.S. as well. A narrow trough is hanging out on the West coast with short waves breaking off and traveling up into Canada over the ridge. That is quite a blob of high pressure!

The next trough that will push in appears to approach Monday/Tuesday next week (Figure 4). We have a while to wait for that possible taste of Fall. Note that moisture from Florence is still hanging out around North Carolina and Virginia into the middle of next week.

The current National Hurricane Center (NOAA) forecast for Hurricane Florence (Figure 5) shows that southern and central parts of North Carolina are under the gun for the storm's damage. The landfall spot is looking like it will be located along the northern South Carolina coast or southern North Carolina coast (at category 4 strength). With the storm coming in as the big U.S. ridge rocks east, it might lose its steering winds abruptly, sit, spin, die, and dump rain over SC, NC, and western VA. Figure 6 (if it verifies) shows a wide area of 20-48 inches of rainfall. Some forecasters are rightfully describing that outcome as the greatest potential disaster for the region in recorded history. Please keep an eye on it if you know of anyone living in those states.

That is not the only hit the U.S. is expecting either... Hurricane Olivia is expected to hit the Hawaiian Islands (as it weakens) Tuesday night/Wednesday morning with torrential rainfall on the mountain slopes. According to WeatherBell forecaster Joe Bastardi, though, after the next week or two, he expects the tropics to calm down a lot with El Niño effects showing up. That is a ray of hope!

Figure 3: The 500mb forecast upper air analysis for Saturday noon. Pink dot is Longmont. Red lines are troughs, blue lines are ridges. From weather5280.com

Figure 4: The 500mb forecast upper air analysis for next Tuesday night (9/18). Pink dot is Longmont. Red lines are troughs, blue lines are ridges. From weather5280.com

Figure 5: the five day cone of uncertainty plot forecast from the NHC for Florence.

Figure 6: The total precipitation predicted by the ECMWF model for the next 10 days from weatherbell.com public video. Max value in the purple region is 47.86 inches.

Current Weather

Partly cloudy

Partly cloudy

35°F

UV Index
0 Low
Pressure
29.99 Steady
Visibility
8 miles
Dewpoint
23 °F
Humidity
63%
Wind
WNW 2.3 mph
Gust
4.9 mph
Wind Chill
35 °F

Hourly Forecast

Today
3 AM
31°F
Partly cloudy
Today
4 AM
30°F
Intermittent clouds
Today
5 AM
28°F
Intermittent clouds
Today
6 AM
26°F
Mostly cloudy
Today
7 AM
29°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

7 Day Forecast

Mostly sunny

Wednesday

54 °F

Sunny to partly cloudy and warmer


Mostly cloudy

Wednesday Night

26 °F

Increasing cloudiness


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


Sunrise and Sunset

Sunrise
6:51 AM
Sunset
7:21 PM

Based on AccuWeather data