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The Next Storm/Next Snow Forecast Discussion from the Cherrywood Observatory – September 10, 2017

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

Forecast Discussion:

We have a ridge over us currently (Figure 1) with a west coast and east coast trough in place. These are just a bit closer to each other than the distance that is equal to the width of the United States mainland... so they should move forward west to east over time. There is a moderate amount of tropical moisture that has slipped into the ridge as you can see in the water vapor satellite image Figure 2.  Irma is clearly on the map approaching Florida at the time of writing (late late Saturday night). Figure 3 is a future surface frontal/pressure system/rainfall chances map that shows afternoon showers over the mountains of Colorado with a few slipping east again onto the Plains.  Cross fingers for Longmont rain!  Irma has hit Florida by this time. Yikes.

Our smoke situation in Longmont is getting better. Figure 4 shows a LOT less smoke in the Western US that we've had in more than a week at the surface levels.  Figure 5 shows a bit of smoke in the sky above us, but you can begin to breath clearly again.

Figure 1: 500mb upper air map for Saturday PM.

Figure 2: Water Vapor satellite image for Saturday PM.

Figure 3: NCEP forecast surface analysis map with rain chances for Sunday PM.

Figure 4: HRRR model smoke forecast surface levels Sunday Midday.

Figure 5: HRRR model smoke forecast all levels Sunday Midday.

Longer Range:

Figure 6 is another upper level map, this time for Tuesday PM.  Irma's remains have stalled over the Tennessee Valley by this time and are dropping a lot of rain. Jose is still out there wandering in the Atlantic.  The ridge is sort of on our heads still, but a weak cool front may knock a few degrees off our temperatures for a day or two.

Figure 7 shows the current (nearly midnight) Irma forecast and statistics. Due to a day of interacting (destroying) the north side of Cuba, it has been downgraded to a category 3 storm.  Very warm water is still in its path and some meteorologists are thinking it will briefly hop back to a category 4 or maybe even a 5 just before landfall near Tampa. Figure 8 shows widespread 7 to 17" of rain over most of Florida over the next couple of days.

Looking WAY out to the upper air pattern NEXT Saturday night, Jose is still out there and wandering back sort of close to the east coast (Figure 9). We'll have to keep watching it all week!

Figure 6: Tuesday PM 500mb GFS forecast of upper levels.

Figure 7: Late Saturday PM Hurricane Irma stats and forecast map

Figure 8: Rainfall estimates based on the NCEP NDFD for Florida through Monday PM

Figure 9: 500mb Upper Air forecast map from the GFS valid NEXT Saturday PM 9/16.

Current Weather

Mostly cloudy

Mostly cloudy

36°F

UV Index
0 Low
Pressure
29.82 Rising
Visibility
8 miles
Dewpoint
29 °F
Humidity
74%
Wind
N 2.2 mph
Gust
3.9 mph
Wind Chill
36 °F

Hourly Forecast

Today
7 AM
37°F
Mostly cloudy
Today
8 AM
38°F
Intermittent clouds
Today
9 AM
41°F
Intermittent clouds
Today
10 AM
44°F
Intermittent clouds
Today
11 AM
47°F
Intermittent clouds
Today
12 PM
49°F
Intermittent clouds
Today
1 PM
51°F
Intermittent clouds
Today
2 PM
52°F
Intermittent clouds
Today
3 PM
52°F
Intermittent clouds
Today
4 PM
51°F
Intermittent clouds
Today
5 PM
50°F
Intermittent clouds
Today
6 PM
47°F
Mostly cloudy w/ showers

7 Day Forecast

Partly sunny w/ showers

Friday

52 °F

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


Showers

Friday Night

34 °F

A couple of showers this evening; otherwise, cloudy


Mostly cloudy

Saturday

60 °F

Mostly cloudy


Intermittent clouds

Saturday Night

34 °F

Partly cloudy


Intermittent clouds

Sunday

62 °F

Periods of clouds and sun


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


Mostly sunny

Tuesday

61 °F

Mostly sunny and milder


Clear

Tuesday Night

29 °F

Clear


Sunrise and Sunset

Sunrise
6:48 AM
Sunset
7:23 PM

Based on AccuWeather data