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 Post subject: Red Flag Warning for the Foothills & Metro
Post Posted: Apr 17, 2018 7:21 am 
Whoa momma! A top Pinecam poster!
Whoa momma! A top Pinecam poster!
Joined: Dec 22, 2006 10:21 pm
Posts: 2001
Location: BFE
Synopsis: Critical to extreme fire danger will exist across portions of the area later this morning into early this evening. After analyzing the latest updates from a few of the fire managers have decided to include the Denver metro area, South Park and the southern Foothills in a Red Flag Warning just to be on the safe side. Strong winds combined with low humidity values will be in place later this morning thru the afternoon hours so if a fire gets started it could spread very rapidly.

In the mountains there will be a good chance of snow showers this afternoon as a weather disturbance moves across along with gusty winds.

High winds are expected late this morning through the early evening hours across the Plains and over the Palmer Divide. Wind gusts from 60 to 65 mph will be possible. Critical to Extreme fire danger will be in place from late this morning through early this evening across the Denver metro area, Southern Foothills, South Park, Palmer Divide extending into Lincoln county and eastern portions of Adams and Arapahoe counties. Wind gusts to 60 mph will occur along with low humidity levels. Elsewhere an upper level disturbance will bring snow to the mountains this afternoon into the early evening hours with gusty winds at times. Accumulations of 2 to 4 inches will be possible.

The long-term outlook through Friday: Wednesday through Saturday...An upper ridge is expected to move across the forecast area Wednesday and Thursday. It will be dry, but the airmass will be cooler on Wednesday, then warm up a bit on Thursday. There will be elevated fire danger over the southern areas of the forecast area Thursday afternoon. Moisture will increase significantly Thursday night and continue through Saturday as an upper closed low move eastward just south of Colorado. Widespread beneficial precipitation is expected with this storm. I am waiting to see what this morning’s computer models have in store for this storm, yesterday’s models had the storm sowing and dumping 12 to 24 inches of snow above 8,000….more info to follow.

Watches & Warnings

For the Foothills and the Denver Metro, a Red Flag Warning is in effect from 1000 hours until 1800 hours for the Foothills and 2000 hours for the metro. High winds and low humidities have spawned conditions to be favorable for new fire starts and rapid fire growth. Extreme fire behavior is possible.

For the Denver Metro, NOT including JeffCo, a High Wind Warning is in effect today.

Hazardous Weather Outlook for today and tonight: High winds are expected late this morning through the early evening hours across the Plains and over the Palmer Divide. Wind gusts from 60 to 65 mph will be possible.

Critical to Extreme fire danger will be in place from late this morning through early this evening across the Denver metro area, Southern Foothills, South Park, Palmer Divide extending into Lincoln county and eastern portions of Adams and Arapahoe counties. Wind gusts to 60 mph will occur along with low humidity levels.

Elsewhere an upper level disturbance will bring snow to the mountains this afternoon into the early evening hours with gusty winds at times. Accumulations of 2 to 4 inches will be possible.

For Wednesday through Friday: Wednesday and Thursday look dry with high pressure aloft. The next Spring storm will bring deepening moisture, cooler temperatures and widespread precipitation to all of the forecast area Friday well into Saturday. Significant snowfall may occur over mountains and foothills east of the divide. Stay tuned. Upper ridging returns on Sunday and Monday with dry weather returning.

Front Range Foothills Forecast

Today
A 20 percent chance of snow showers after noon. Mostly sunny, with a high near 53. Windy, with a southwest wind 15 to 20 mph becoming west southwest 23 to 28 mph in the afternoon. Winds could gust as high as 44 mph.

Tonight
Mostly clear, with a low around 23. Windy, with a northwest wind 20 to 25 mph decreasing to 11 to 16 mph after midnight. Winds could gust as high as 40 mph.

Wednesday
Sunny, with a high near 53. West wind 6 to 11 mph becoming light and variable. Winds could gust as high as 18 mph.

Wednesday Night
Mostly clear, with a low around 26. East wind 5 to 7 mph becoming calm in the evening.

Thursday
Mostly sunny, with a high near 60. Light and variable wind becoming southeast 5 to 8 mph in the morning.

West Denver Metro Forecast

Today
Mostly sunny, with a high near 65. Windy, with a southwest wind 16 to 21 mph becoming west 28 to 33 mph in the afternoon. Winds could gust as high as 47 mph.

Tonight
Mostly clear, with a low around 30. Windy, with a northwest wind 21 to 31 mph decreasing to 10 to 20 mph after midnight. Winds could gust as high as 44 mph.

Wednesday
Sunny, with a high near 58. West wind 5 to 9 mph becoming east in the afternoon.

Wednesday Night
Mostly clear, with a low around 32. East wind 5 to 8 mph becoming calm in the evening.

Thursday
Mostly sunny, with a high near 67. Calm wind becoming southeast 5 to 9 mph in the morning.

Fire Weather for the Western Metro Fire Districts below 6000 feet (Zone 239) –


Today...

Sky/weather.........Mostly sunny until 1200, then partly cloudy (40-50%).

Max Temperature.....59-67.
24 hr trend......Little change.

Min Humidity........10-16%.
24 hr trend......20-25% drier.

20-foot winds.......Windy. Southwest winds 12-18 mph with gusts to 35 mph increasing to west 26-38 mph with gusts to 55 mph in the afternoon.

Haines Index........4 low.

LAL.................1.

CWR.................0 percent.

15K FT MSL winds....Southwest 50-60 mph.

Mixing height.......6000-7000 ft AGL until 1200, then 11000-12000 ft AGL.

Transport winds.....Southwest 15-20 mph until 0900. west 40-50 mph after 1300.

Smoke dispersal.....Poor until 0900, then good until 1000, then very good until 1100, then excellent.

Tonight...

Sky/weather.........Mostly clear.

Min Temperature.....27-31.
24 hr trend......15-20 degrees cooler.

Max Humidity........49-53%.
24 hr trend......4-7% wetter.

20-foot winds.......Breezy. Northwest winds 19-29 mph with gusts to 50 mph decreasing to 12-18 mph with gusts to 30 mph after midnight.

Haines Index........3 very low.

LAL.................1.

CWR.................0 percent.

15K FT MSL winds....Northwest 35-45 mph.

Mixing height.......3000-4000 ft AGL.

Transport winds.....Northwest 45-55 mph until 2000. around 20 mph after 0500.

Smoke dispersal.....Excellent until 1900. poor after 0500.

Wednesday...

Sky/weather.........Mostly sunny.

Max Temperature.....56-60.
24 hr trend......4-7 degrees cooler.

Min Humidity........15-19%.
24 hr trend......4-7% wetter.

20-foot winds.......Southwest winds 4-13 mph shifting to the east 5-8 mph in the afternoon.

Haines Index........3 very low.

LAL.................1.

CWR.................0 percent.

15K FT MSL winds....Northwest 35-45 mph.

Mixing height.......7500-8500 ft AGL.

Transport winds.....West 10-15 mph until 1600, then light.

Smoke dispersal.....Poor.

Fire weather for the foothills fire districts above 6000 feet (zone 216) - Today...

Sky/weather.........Mostly sunny until 0900, then partly cloudy (40-50%) until 1500, then mostly cloudy. Chance of snow showers after 1200 until 1500, then slight chance of snow showers.

Max Temperature.....47-57.
24 hr trend......7-10 degrees cooler.

Min Humidity........11-21%.
24 hr trend......2-4% wetter.

20-foot winds.......
Valleys / lower slopes...Windy. West winds 21-31 mph with gusts to 50 mph.
Ridges / upper slopes....Windy. West winds 23-33 mph with gusts to 60 mph.

Haines Index........3 very low.

LAL.................1.

CWR.................0 percent.

15K FT MSL winds....Southwest 55-65 mph.

Mixing height.......10000-11000 ft AGL.

Transport winds.....Southwest 30-35 mph until 0800, then west 45-55 mph.

Smoke dispersal.....Fair until 0800, then very good until 1000, then excellent.

Tonight...

Sky/weather.........Partly cloudy (35-45%) until 0300, then clear. Slight chance of snow showers until 2400.

Min Temperature.....19-27.
24 hr trend......10-15 degrees cooler.

Max Humidity........44-54%.
24 hr trend......15-20% wetter.

20-foot winds.......
Valleys / lower slopes...Breezy. Northwest winds 13-23 mph. Gusts up to 50 mph decreasing to 30 mph after midnight.
Ridges / upper slopes....Breezy. Northwest winds 16-26 mph with gusts to 45 mph decreasing to 10-16 mph with gusts to 30 mph after midnight.

Haines Index........2 very low.

LAL.................1.

CWR.................0 percent.

15K FT MSL winds....Northwest 40-50 mph.

Mixing height.......3500-4500 ft AGL.

Transport winds.....Northwest 40-50 mph until 0100. around 25 mph after 0500.

Smoke dispersal.....Excellent until 2000. fair after 0500.

Wednesday...

Sky/weather.........Mostly sunny.

Max Temperature.....46-56.
24 hr trend......Little change.

Min Humidity........13-19%.
24 hr trend......Little change.

20-foot winds.......
Valleys / lower slopes...West winds 5-9 mph with gusts to 20 mph shifting to the southeast 4-7 mph in the afternoon.
Ridges / upper slopes....West winds 6-12 mph with gusts to 25 mph shifting to the southeast 4-7 mph in the afternoon.

Haines Index........3 very low.

LAL.................1.

CWR.................0 percent.

15K FT MSL winds....Northwest 30-40 mph.

Mixing height.......8000-9000 ft AGL.

Transport winds.....Northwest 15-20 mph until 1200, then southwest 10-15 mph.

Smoke dispersal.....Fair.

Fire weather terms and abbreviations

LAL – Lightning Activity Level:
LAL 1 - No thunderstorms
LAL 2 - Isolated thunderstorms. Light rain will occasionally reach the ground. Lightning is very infrequent, 1 to 5 cloud to ground strikes in a five minute period.
LAL 3 - Widely scattered thunderstorms. Light to moderate rain will reach the ground. Lightning is infrequent, 6 to 10 cloud to ground strikes in a 5 minute period.
LAL 4 - Scattered thunderstorms. Moderate rain is commonly produced Lightning is frequent, 11 to 15 cloud to ground strikes in a 5 minute period.
LAL 5 - Numerous thunderstorms. Rainfall is moderate to heavy. Lightning is frequent and intense, greater than 15 cloud to ground strikes in a 5 minute period.
LAL 6 - Dry lightning (same as LAL 3 but without rain). This type of lightning has the potential for extreme fire activity and is normally highlighted in fire weather forecasts with a Red Flag Warning.

Haines Index (HI) - Is a numerical value that indicates the potential for large wildfires to experience extreme fire behavior. The HI combines both the instability and dryness of the air by examining the lapse rate between two pressure levels in the atmosphere and the dryness of one of the pressure levels.
HI 2 or 3…..Very low
HI 4………..Low
HI 5………..Moderate
HI 6………..High

CWR – Chance of Wetting Rain. Measurable rain above 0.10 inches.

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