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 Post subject: Red Flag Warning for ABOVE 6,000 feet today.
Post Posted: Sep 29, 2018 8:21 am 
Whoa momma! A top Pinecam poster!
Whoa momma! A top Pinecam poster!
Joined: Dec 22, 2006 10:21 pm
Posts: 1996
Location: BFE
Synopsis: After a couple of days of fall weather we return to summer as a warm and very dry airmass will combine with strong westerly winds to bring very high to extreme fire danger across the northern Colorado mountains today. The winds and low humidities will develop in some areas this morning and become widespread by early afternoon. The Ryan and Silver Creek wildfires will be impacted by these conditions. There will be a slow improvement in humidity this evening, with winds decreasing in the valleys, but it will remain windy over the ridges overnight tonight.

Warm and dry air will be over the area today, with increasing westerly flow aloft. There is some shallow moist and cool air over the plains that will continue to retreat eastward as the day goes on, with warm dry air moving in from the west. Areas near the foothills may be near Red Flag conditions for a few hours this afternoon.

In the mountains, the ridges and higher slopes did not fully decouple overnight, and Red Flag conditions will develop in these areas this morning, then spread into the valleys and lower foothills by early afternoon. The humidities will gradually rise this evening, with winds diminishing in the valley areas. Ridges and higher slopes will remain fairly windy overnight.

The long-term outlook through Tuesday: Southwesterly flow aloft is expected over the forecast area through Wednesday. Moisture will slowly increase starting Sunday night and continuing through mid week. There should be enough moisture for a chance of precipitation, mainly in the mountains Tuesday and Wednesday.

Watches & Warnings
For the Front Range Foothills and Mountains ABOVE 6,000 feet there is a Red Flag Warning in effect from 1000 hours to 1900 hours.
Winds...West 15 to 25 mph with gusts up to 45 mph.

Timing...Today from 1000 to 1900 MDT. Strong winds and low humidities will develop over the higher ridges and east slopes this morning, then spread into the valleys and lower foothills by early afternoon.

Relative Humidity...As low as 11 percent.

Impacts...Fires will start easily and spread rapidly.

Hazardous Weather Outlook for today and tonight: After some low clouds and patchy fog on the eastern plains early this morning, warm and very dry air will spread from the mountains onto the plains. The combination of warm dry air and increasing west winds will create very high to extreme fire danger over the mountains from late morning through the day. Wind gusts of 30 to 40 mph will be common in the mountains this afternoon, with gusts to 50 mph over the higher areas. Temperatures will warm quickly by midday over the western portion of the plains including the Denver area, while the eastern plains will warm more slowly. The fire danger will ease with increasing humidities this evening, though some wind will continue in the mountains through the night.

For Sunday through Friday: Moisture will increase later Sunday, and better moisture will stick around much of the week. There will be enough moisture for a chance of showers and a few thunderstorms, mainly in the mountains, on Tuesday and Wednesday. There will be a chance of precipitation across the forecast area Thursday and Friday.

Front Range Foothills Forecast
Today
Mostly sunny, with a high near 75. West wind 8 to 14 mph, with gusts as high as 22 mph.

Tonight
Mostly clear, with a low around 47. West wind 5 to 8 mph.

Sunday
Sunny, with a high near 71. Light and variable wind becoming south southeast around 6 mph in the afternoon.

Sunday Night
Partly cloudy, with a low around 47. South wind around 6 mph becoming west southwest after midnight.

Monday
Mostly sunny, with a high near 71. West southwest wind around 6 mph becoming light and variable in the afternoon.

West Denver Metro Forecast

Today
Partly sunny, with a high near 83. Southwest wind 5 to 9 mph becoming west northwest in the afternoon.

Tonight
Mostly clear, with a low around 50. West northwest wind 3 to 7 mph.

Sunday
Sunny, with a high near 75. Calm wind becoming east northeast around 6 mph in the afternoon.

Sunday Night
Partly cloudy, with a low around 52. East northeast wind around 5 mph becoming light and variable.

Monday
Mostly sunny, with a high near 79. West southwest wind around 6 mph becoming east southeast in the afternoon.

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

Today...

Sky/weather.........Mostly cloudy (60-65%) until 1200, then partly cloudy(40-50%).

Max Temperature.....80-84.
24 hr trend......25-35 degrees warmer.

Min Humidity........10-14%.
24 hr trend......More than 50% drier.

20-foot winds.......West winds 5-11 mph.

Haines Index........5 moderate.

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

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

15K FT MSL winds....West 25-35 mph.

Mixing height.......4000-5000 ft AGL until 1200, then 8500-9500 ft AGL.

Transport winds.....Light winds until 0800, then west 10-15 mph until 1100, then 20-25 mph until 1700, then around 15 mph.

Smoke dispersal.....Poor until 1100, then good until 1200, then excellent until 1700, then good.

Tonight...

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

Min Temperature.....46-50.
24 hr trend......10-15 degrees warmer.

Max Humidity........67-77%.
24 hr trend......10-15% drier.

20-foot winds.......Northwest winds 4-8 mph.

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

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

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

15K FT MSL winds....Southwest 20-30 mph.

Mixing height.......1500-2500 ft AGL.

Transport winds.....Northwest 10-15 mph until 0100, then light.

Smoke dispersal.....Poor.

Sunday...

Sky/weather.........Mostly sunny until 1500, then partly cloudy (30-40%).

Max Temperature.....69-75.
24 hr trend......10-15 degrees cooler.

Min Humidity........30-40%.
24 hr trend......25-35% wetter.

20-foot winds.......East winds 4-7 mph.

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

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

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

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

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

Transport winds.....Light winds until 1400, then southeast around 10 mph until 1600, then light.

Smoke dispersal.....Poor.

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

Today...

Sky/weather.........Partly cloudy (40-50%).

Max Temperature.....71-81.
24 hr trend......15-20 degrees warmer.

Min Humidity........10-14%.
24 hr trend......More than 50% drier.

20-foot winds.......
Valleys / lower slopes...West winds 10-16 mph with gusts to 30 mph.
Ridges / upper slopes....West winds 12-18 mph with gusts to 30 mph.

Haines Index........5 moderate.

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

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

15K FT MSL winds....West 25-35 mph.

Mixing height.......4500-5500 ft AGL until 1200, then 10000-11000 ft AGL.

Transport winds.....West 20-25 mph until 1600, then around 15 mph.

Smoke dispersal.....Poor until 1000, then good until 1200, then excellent until 1700, then very good.

Tonight...

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

Min Temperature.....44-50.
24 hr trend......7-10 degrees warmer.

Max Humidity........44-54%.
24 hr trend......35-50% drier.

20-foot winds.......
Valleys / lower slopes...West winds 6-12 mph.
Ridges / upper slopes....West winds 9-15 mph.

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

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

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

15K FT MSL winds....Southwest 20-30 mph.

Mixing height.......2500-3500 ft AGL.

Transport winds.....West 10-15 mph.

Smoke dispersal.....Good until 2000, then poor.

Sunday...

Sky/weather.........Mostly sunny until 1500, then partly cloudy (30-40%).

Max Temperature.....66-76.
24 hr trend......2-4 degrees cooler.

Min Humidity........16-26%.
24 hr trend......4-7% wetter.

20-foot winds.......
Valleys / lower slopes...Southwest winds 6-12 mph. Gusts up to 20 mph in the afternoon.
Ridges / upper slopes....Southwest winds 8-14 mph with gusts to 20 mph.

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

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

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

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

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

Transport winds.....Southwest 15-20 mph.

Smoke dispersal.....Poor until 1100. excellent after 1300.

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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