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10:30am Update: Next Storm/Next Snow Forecast Discussion from the Cherrywood Observatory – June 21, 2019

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

In Brief:

The next 10 days will see all the weather types we can have near town. A strong cold front arrives in the morning Friday. Rain chances really pick up around 1pm starting a 3 day stretch of rain that will top 1 inch and may approach 2 inches total. There is severe weather possible Friday with hail and tornadoes and hail is possible Saturday.

Snow is possible in the nearby foothills and we "might" see snow flurries Sunday AM mixed in with the rain. Crazy! Rain ends before midnight Sunday and we see a stretch of 90'sF midweek into next weekend.

10:30am Update:

ANOTHER Update - now all of Denver is in the Slight Risk (2 on a scale of 1-5) and the Marginal Risk (1 on a scale of 1-5) extends far to the west into the mountains. There is no real change for Longmont.

You can keep up with the exciting changes at:
https://www.spc.noaa.gov/products/outlook/day1otlk.html

End 10:30am Update.

8:30am Update:

Everything in the forecast is on track for storm timing, lots of rain through Sunday morning with showers, now and then, into Sunday night. Very cool air in place and 3-5" snow above 10,000 feet, measurable snow probably down to 9,000 feet elevation and maybe a dusting in the lower foothills (Boulder, if they are lucky, might see early morning snows mixed with the rain.) Longmont shouldn't see snow with lows in the mid 40'sF.

For severe weather today, the SPC has decreased the threat along I-25 and westward - we have only a Marginal Risk (1 on a scale of 1-5) today for hail and high winds. There is a risk of isolated tornadoes in the Slight Risk zone to our east. They way they have drawn the risk excludes Fort Lupton, but includes Brighton, Commerce City, DIA, and Auroroa.

Figure 1 update: The severe storm weather forecast for the U.S. from the Storm Predication Center in Norman, OK. Made Friday for Friday.

End 8:30am Update.

Forecast Discussion:

The front sweeps through Friday morning and showers begin in the overrunning setup behind it (Figure 1). Rain chances this afternoon and evening are very high (Figure 2). Don't plan to play outside!

Another reason to stay inside will be the severe weather risk (Figure 3) - we'll be under a Slight Risk for high winds, large hail, and isolated tornadoes (Figure 6). Often, the risk expands in coverage once more data comes in overnight - so I may be updating this post in the AM. The cold air entering the state later today (Friday) is clear on the GFS (Figure 4).

Oh, even though I say the word snow below, welcome to the first day of Astronomical Summer - Friday June 21 at 9:54am.

The Longer Range Forecast:

Rain chances continue through late night Sunday (Figure 2) with 1 1/4th inches predicted from weatherunderground and 1 3/4th inches from the GFS (Figure 8). This is all powered by a deep trough in the upper air flow as it slowly moves by (Figure 5).

By Saturday noon, rain continues off and on with quite cold air in place across the state (Figure7). We'll even see nighttime and early morning snows in the mountains (Figure 9). Will Boulder see snow flurries? A coating??!! Will we see flurries in the rain in the early morning??

Next week the heat begins for the first time with 90'sF starting as early as Wednesday (Figure 2 - red oval) with a big ridge building overhead (Figure 10).

Figure 1: The forecast surface map for Friday noon from NCEP.
Figure 2: the graphical forecast for the next 10 days for Longmont, CO from weatherunderground.com
Figure 3: The severe storm weather forecast for the U.S. from the Storm Predication Center in Norman, OK. Made Thursday for Friday.
Figure 4: The forecast temperature departure from normal map from the GFS and weather5280.com for Colorado, Friday PM.
Figure 5: The 500mb forecast upper air analysis for Saturday AM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.
Figure 6: The severe storm weather forecast for the U.S. from the Storm Predication Center in Norman, OK. Made Thursday for Saturday.
Figure 7: The forecast temperature departure from normal map from the GFS and weather5280.com for Colorado, Saturday noon.
Figure 8: the forecast accumulated precipitation map from the GFS and tropicaltidbits.com for Colorado,over the next 5 days.
Figure 9: the forecast accumulated snow map from the GFS and tropicaltidbits.com for Colorado,over the next 5 days.
Figure 10: The 500mb forecast upper air analysis for next Thursday AM. Pink dot is Longmont. Red lines are troughs, blue lines are ridges.

Current Weather

Partly cloudy

Partly cloudy

32°F

UV Index
0 Low
Pressure
29.97 Steady
Visibility
8 miles
Dewpoint
25 °F
Humidity
75%
Wind
WNW 2.2 mph
Gust
3.8 mph
Wind Chill
32 °F

Hourly Forecast

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
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