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Thursday September 18th 2014 8:50am

Summary:

Thursday will be mostly dry, a few more showers on Friday (but not many), then Saturday will be mostly dry and the much nicer day of the weekend. Sunday through Tuesday will be showery for most of the state, then one or two colder systems could affect Colorado sometime between Friday the 26th and Tuesday the 30th.

Details:

On Wednesday there were a few showers over the mountains, but most of these were "dry" with the rain evaporating before it hit the ground. With a little more moisture over the southern mountains, more of the showers produced brief bursts of rain.

Thursday will be similar to Wednesday with most areas seeing a dry and very warm day and a few showers over the mountains, mostly over the San Juans.

Friday is now looking like a pretty nice day. Earlier in the week, Friday looked like a wet day with lots of moisture moving into Colorado from the remnants of Hurricane Odile. However, most of Odile's moisture is going to stay south of us over New Mexico, so Friday's forecast is now similar to Thursday with afternoon clouds and showers over the mountains, but really nothing of significance.

If you're looking to get outside and play this weekend, choose Saturday. I can't rule out a shower over the mountains, especially along the eastern continental divide, but for the most part it'll be a nice day in the mountains where the Aspens are beginning to turn their beautiful fall yellow. The exception to the clear weather will be in the eastern foothills and front range which could see low clouds for much of the day with an upslope wind from the east.

The turning point in our weather will start on Sunday when moisture from a storm over California works into Colorado. This storm is cut off from the main west-to-east flow of weather, so it will move very slowly and will bring showers to Colorado from Sunday midday or afternoon all the way through Tuesday evening or even into Wednesday morning/midday. 

colorado weather

Forecast for the slow moving cut-off storm later this weekend and into early next week. Source: Weatherbell.com

Next Wednesday and Thursday look like nice days next week, and then...something "interesting" will happen:-)

Between Friday, September 26th and Tuesday, September 30th, one or two colder storms should move across the the western US and Canada. The details of these storms are 100% unknown and the models are unbelievably waffley (is that a word?). We might see nothing more than cooler air for northern Colorado and some wind, while snow falls in Wyoming and Montana. Or we might see one or two strong cold fronts move across the mountains with snow falling down to 10,000ft (mid-mountain-ish) or lower. At this point, nobody knows what will happen, but it's nice to see some action on the long-range forecast. Stay tuned...plenty of time to figure out the forecast to see if we can get some widespread snow to fall on the mountains while the calendar still reads September.

JOEL GRATZ

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Wednesday September 17th 2014 7:47am

Summary:

Wednesday and Thursday will be mundane with afternoon clouds and a shower over the mountains. Friday brings a better chance of rain, but not a lot of rain. Saturday will be the drier day of the weekend (still a shower possible), while Sunday, Monday, and Tuesday look cloudy and potentially pretty wet. The second half of next week should be dry.

Details:

Tuesday was a nice day with a few afternoon showers over the mountains, with the most showers over the San Juans.

Wednesday is dawning with dry conditions across the state and some high cirrus clouds spreading up from the south. It was a beautiful sunrise from the Mt Evans webcam with the cirrus clouds visible at the top of the image.

colorado weather

Looking at the current weather across the west, there are two obvious features on the infrared satellite image (infrared sensors on the satellite measure temperature and therefore can "see" the colder clouds above the ground even though it's dark during the overnight hours).

The first feature is over Arizona, New Mexico, and northern Mexico. This is what's left of Hurricane Odile. Heavy rain of more than 3 inches is falling over AZ and NM, but the main effect on Colorado will be high clouds over southern Colorado, afternoon mountain showers over the San Juan and Sangre de Cristo mountains, and a burst of heavy rain for extreme southeast Colorado on Friday as the decaying center of Odile passes by. Most of Colorado will not see heavy precipitation from Odile.

colorado weather

Wednesday morning satellite image. Source: Weathertap.com

The second feature is the swirling mass of clouds west of California. This storm will cut-off from the main west-to-east flow of weather and it will hang out over California for a few days before finally moving east toward Colorado early next week.

What does this mean for our weather?

Wednesday and Thursday will be mostly dry with the best chance for showers over the southern mountains.

Friday will still be mostly dry, but there's a better chance for afternoon showers over most mountains. This is because a bit more moisture will be over the state.

Saturday will be the nicer day of the weekend as we'll be in between the two storms I mentioned above. I still can't rule out the chance of a shower over the mountains and some low clouds over the front range and plains east of the divide, but if you're heading to the hills to check out the early fall color, Saturday looks better than Sunday.

By Sunday, the cut-off storm over California will move toward us, so look for lots of showers, clouds, and cooler weather on Sunday, Monday, and Tuesday as this storm moves along at a turtle's pace.

colorado weather

Respectable rainfall totals could fall on much of Colorado on Sunday, Monday, and Tuesday according to the American GFS weather model's forecast. Source: Weatherbell.com

Yesterday I talked about how the European model showed the cut-off storm moving more slowly than the American GFS model, and how this would lead to a pretty nice weekend. That was half correct. The storm IS going to move more slowly than the original GFS forecast, which is pretty standard as the GFS is usually too fast with these storms. And the European was pretty much correct, delaying the arrival of the storm until early next week. However, the storm is going to be potent enough to pull moisture into Colorado well ahead of its arrival, and this is why Sunday is now looking like not the greatest day. In short, the European model was about right with the timing of the storm, but a bit off with its strength.

By next Wednesday the cut-off storm should move east of Colorado with improving weather. Then next Thursday and Friday should be sunny with near normal temperatures.

These cut-off storms are really a pain to forecast ... they're like a drunk person stumbling around at 2am with no direction and you can't tell where they're going to go next. I'm relatively confident in the forecast I shared above since more of the models are coming into a agreement AND the models match my previous experience of cut-off storms. But I'm not as confident as I would normally be about a 4-5 day forecast, so stay tuned.

JOEL GRATZ

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Tuesday September 16th 2014 6:54am

Summary:

Mostly dry on Tuesday, Wednesday, and Thursday with a few afternoon showers over the San Juan mountains. The best chance of rain showers will occur between Thursday night and Friday night. Next weekend's weather is still tough to call, but I think it'll be on the drier side for most mountain areas in central and northern Colorado.

Details:

A few afternoon showers popped up over many of the mountains on Monday, but on Tuesday, Wednesday, and Thursday the majority of these showers should be confined to the southern mountains, generally south of US50 over the San Juans and Sangre de Cristo ranges.

Our tranquil weather pattern will break down on Thursday night as the remnants of Hurricane Odile move toward Colorado from the south while another storm splits into two parts to our west, with one part heading for Colorado.

Between Thursday night and Friday night, look for cloudier weather with a good chance of rain showers and a few Thunderstorms.

During this time, the remnants of Odile will bring heavy rain to northern New Mexico and *maybe* to southern and southeastern Colorado, roughly from US160 south. There will be a limited path of heavier rain, and right now I'm not sure if this stays south in New Mexico or reaches up to southern Colorado.

Also on Thursday night through Friday night, part of the splitting storm to our west will move across northern and central Colorado, bringing an increase in showers and storms for most mountain and valley areas. This won't be an all-day soaking rain, but it will be a wetter day than Tuesday, Wednesday, and Thursday.

colorado weather forecast

Basemap shows the Tuesday morning Water Vapor satellite image. Source: Weathertap.com

The big question is what will happen to the second half of the splitting storm to our west after Friday?

On the map above I show it heading south toward the southern coast of California. Since these splitting storms usually move very slowly, I'll side with the European model's prediction that it will stay over southern California through the weekend and won't move toward Colorado until Tuesday of next week. This is about 1-2 days slower than the American GFS model's forecast.

Siding with the European makes our weekend look mostly dry over the northern 2/3rds of the mountains, with just a few showers over the San Juans and some cooler, perhaps cloudier weather over the eastern plains. In short, the European model says it'll be a nice weekend to look at the early fall color in the northern half of Colorado, while the American GFS model says it'll be wet for a lot of the weekend. Again, I'll side with the Euro since splitting storms usually move very slowly.

Lastly ... a quick look at the long-range forecast shows the possibility of a cooler system affecting northern Colorado and areas east of the divide during the last 3-5 days of September. I'll keep ya posted ... don't put too much confidence in 10 day forecasts:-)

JOEL GRATZ

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Monday September 15th 2014 9:21am

Summary:

Mostly sunny and warm on Monday, Tuesday, Wednesday, and Thursday with a low chance for a few mountain showers each afternoon. More numerous rain showers are likely on Friday, then the weekend might be drier but I have little confidence in the forecast beyond 4 days.

Details:

Yesterday, Sunday, was typical of a late-summer day with a few showers over the mountains but little rain reaching the ground due to pretty dry air at the surface. On Sunday night, a cold front brought cooler air to the plains east of the divide, but the low clouds are confined to the farmland well east of I-25 and did not push further west into the urban areas and against the foothills.

Monday through Thursday will be similar to Sunday with enough moisture over the mountains to form afternoon clouds and a few showers, but still dry enough at the surface that the storms will produce more wind than rain. Temperatures will be a few degrees above normal each day.

Things change on Friday, though, as the combination of the remnants of Hurricane Odile and a weak storm along the west coast will push moisture into Colorado. Look for lots of showers and a few thunderstorms between Thursday night and Friday night, mostly over the mountains but perhaps affecting the eastern plains as well.

colorado weather forecast

Both storms will pull moisture into Colorado on Friday. Source: Weatherbell.com

After Friday, I have little confidence in the forecast for the weekend and into early next week.

The remnants of Hurricane Odile will be gone to our east, however the storm to our west that is cut-off from the main west-to-east flow of weather will meander about. These cut-off storms usually move more slowly and erratically than the models forecast, so it could stay near us through the weekend and into early next week. If it moves a bit closer to Colorado, we could see showers each day of the weekend through next Tuesday. If it stays just a bit further away, we'll see a drier weekend. At this point, I have no clue about the details and feel that I cannot give the "all clear" for the weekend because this storm will be too close for comfort. Stay tuned...

JOEL GRATZ

PS - For folks in the Denver area, check out the "First Frost" event on Friday, November 7th. It's a gathering to benefit CAIC and there's also a photo contest for those of you who do a great job of capturing images that define skiing and riding in Colorado. More information here.

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Sunday September 14th 2014 11:05am

Summary:

Sunday through Thursday will be mostly dry with a low chance for an afternoon shower over the mountains. We'll see a better chance for rain showers on Friday, with dry weather likely returning for next weekend. I do not see any strong cold fronts or widespread snow for at least the next 10 days.

Details:

Saturday was a beautiful day across the state without many weather issues. There were a few rain showers over the eastern San Juan mountains in southwest Colorado, and the northern mountains along the front range saw some gusty winds up to 30-40mph, but that's relatively standard for fall, winter, and spring for this area. I was up on Rosalie Peak near Mt Evans and verified that it was a bit gusty at 13,500ft with winds around 30mph.

This morning on Sunday, the visible satellite image shows a few things worth mentioning though none of them are a big deal. The wave clouds over northern Colorado show that there are still some strong winds over that part of the state with turbulence likely for planes flying over the area.

colorado weather forecast

Source: Weathertap.com

For Sunday, Monday, Tuesday, Wednesday, and Thursday, look for mostly dry weather, plenty of sun, temperatures at or above normal, and just a low chance of an afternoon shower over the mountains with the best chance for these showers to form over the San Juan mountains as there will be a bit more moisture in southern Colorado. The only other weather action this week will be a weak cold front that will hit the front range east of the mountains on Sunday night into Monday morning. Look for a bit cooler temperatures (60s) on Monday with some low clouds to start the day, maybe lasting through afternoon.

On Friday, a surge of moisture and a weak storm will likely move across Colorado, increasing the likelihood for showers and storms for both the mountains and the eastern plains. Temperatures will likely stay warm enough on Friday to keep any snow confined to the highest peaks above 13,000ft. 

At this point, I think next weekend will turn out to be dry which will be perfect for viewing the fall colors across northern Colorado. However, there's still some ambiguity in the models around how next Friday's storm will play out and how fast it will move, so stay tuned as I likely won't be able to give the "all clear" for next weekend until Tuesday of this week.

JOEL GRATZ

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