Monthly Archives: May 2015

Cooler/showery Friday, then a taste of summer

1:00 PM MDT, Thursday, May 28, 2015.

The persistent wet pattern is slowly relaxing, but not until after a cooler Friday with numerous showers around. By the second half of the weekend we may may seeing our first above average temperatures in a long time.

There will be a scattering of showers and thunderstorms around this afternoon with a few spots experiencing a briefly heavy thunderstorm. A cold front on Friday will bring some upslope flow and result in cooler temperatures (60s lower elevations). There will likely be numerous showers and thundershowers around in the afternoon and evening, and maybe some low clouds & drizzle in some areas Friday night.

But Saturday afternoon we should be drying out. I can’t rule out the chance for a late day thundershower Saturday through Monday, but the chances should be below average (climatological average for measurable rain along the Front Range in June is about 25-30% per day).

For Sunday through Tuesday, temperatures are likely to rise above average, reaching around 80 on Sunday and in the 80s Monday and maybe Tuesday too in the Denver-Boulder-Fort Collins area.

Drier & warmer, but still some afternoon showers/thundershowers

1:15 PM, Monday, May 25, 2015

Today through Thursday should be warmer and with longer dry intervals than in recent days.  Temperatures in the urban corridor and plains will likely be around average Tuesday-Thursday, with highs in the low 70s.  There is still the risk of afternoon showers and thunderstorms, especially in the mountains. But some locations in eastern Colorado may actually experience a completely dry day.

Although the active wet pattern has relaxed for a while, it’s not gone.  Another moist disturbance near the end of the week may result in widespread rain again.

Although several locations in Colorado are approaching monthly records, we are not in the hardest hit region from the active storm track. Parts of Oklahoma and Texas continue to experience historic flooding. Meanwhile, the weather pattern that has been so persistently wet for us has resulted in persistent  warm and dry conditions in the Northeast and up in Alaska. Fairbanks, Alaska hit a record 86 degrees a couple days ago, while parts of New England went from record snowfall to drought in just a couple months.

Some sunny intervals, but also more rain

11:00 AM, Saturday, May 23, 2015

The good news is that there are now and will continue to be some breaks in the overcast letting the sun through at times this weekend. The bad news is that there will be more rain each day, and possibly in the form of a heavy thunderstorm.

The large scale pattern continues to support weak storm systems from the southwest and ample moisture from both the Gulf of Mexico and the Pacific. Intervals of partly sunny skies should occur each day. But the little bit of heating during the sunny periods should be enough to trigger more showers and thunderstorms. Some thunderstorms today (Saturday) may be  strong, with brief heavy rain and hail, especially out on the eastern plains. Both Sunday and Monday are likely to see some shower and thundershower activity along with some partial clearing intervals. The best chance for rainy periods is in the afternoon and evening, with some areas of fog or drizzle in the late night or early morning.

West slope areas are getting these rounds of showers and thundershowers too, so be prepared for lightning and rain if you are in the high country. Although the odds slightly favor a rain-free  Bolder Boulder 10K race on Monday, you should have a plan for rain (or at least drizzle) if you are going to be there.

Wet tonight, some more rain over weekend

1:15 PM, Thursday, May 21, 2015

For those wondering about the frequent occurrence of clouds and precipitation since the middle of April, the general weather pattern will stay in place into next week, but not every day should be completely overcast. A very persistent atmospheric “trof” in the Southwest has resulted in a storm track from the Southwest to the central plains, with the Front Range region receiving rain and snow with each disturbance that moves through. The storms bring upper level Pacific moisture and draw lots of low-level moisture from the Gulf of Mexico.

The next storm in the sequence will impact the Colorado/Wyoming region this evening through Friday midday (ending from south-to-north on Friday). Almost all areas should get some moderate rain (and moderate amounts of snow above 11,000 feet).  There may be a few heavier showers or thundershowers mixed in. Given the wet ground, watch for some minor flooding in localities with the heavier showers.

Much of western Colorado has seen sunny intervals yesterday and today. There is a good chance for some breaks in the overcast Friday afternoon (late afternoon up toward Wyoming) through early afternoon Saturday.  But given the moist, unstable conditions, there will likely be redevelopment of clouds and some showers or thundershowers late in the day. Temperatures will probably warm above 60 on Friday and Saturday along the urban corridor, but stay below the average which is around 70.

Saturday night into Sunday may see the coverage of clouds and showers increase as the next atmospheric disturbance moves up from the southwest. It’s too early for high forecast confidence, but most indications currently suggest another lull in activity on Memorial Day before some late-day thundershowers develop.

The numbers:

Many parts of the south-central and Southwest U.S. have had an unusually wet 5 weeks. Some stations in Oklahoma are at the 20-inch mark.  Here in Colorado there are some May monthly totals exceeding 10 inches (around Colorado Springs and in northern Weld County). Boulder is up to 6.38″ for the month, and 10.35 inches since April 16th. In the last 65 years there have been three similar periods in Boulder (all centered on May) that were just a little wetter: 1969 (10.74″), 1978 (10.38″) and 1995 (11.36″). And then there is 2013 when 18.17 inches fell in September alone, most of it in 8 days.

On March 16th this year Denver was 81 degrees and Boulder was 80 degrees, both records. That is still the warmest that we have been this year.

Cold & Wet, maybe frost Wed morning

12:30 PM, Monday, May 18, 2015

Since late April we have been in a colder and wetter pattern that what we had earlier in the Spring (in case you hadn’t noticed). Boulder has accumulated 8.69 inches of precipitation since April 16th, and similar wetness can be seen in many Front Range localities.

That pattern is here for at least another week. Today and tomorrow (Tuesday) are likely to be particularly wet and cool. Expect the generally cloudy and dry conditions at midday Monday to be replaced with periods of rain and drizzle (and maybe some locally heavier showers or thundershowers) later today through Tuesday. Significant snows (over 12″) are likely in the mountains above 10,000 feet. That snow level should creep down to Nederland’s elevation tonight with some accumulation (mainly in grassy areas).  Even the lower foothills and possibly Cheyenne should be prepared for some wet snow. It is unlikely that there will be measurable snow in Colorado Springs, Denver, Boulder, and Fort Collins. If the clouds break up enough on Tuesday night, there could be some frosts along the urban corridor, especially in normal cold spots (like river valleys).

Wednesday afternoon and Thursday are still likely to have showers and thundershowers, but those days are likely to be a little less damp and cool than Tuesday. Another storm in the sequence is likely to arrive at the end of the week, but it is not yet clear if it will result in more widespread steady precipitation for the Front Range.

Heavy Precip: Flooding & Wet snow thru Saturday night

10:20 AM, Saturday, May 9, 2015

Today and tonight is the peak of this storm and it will have an impact with heavy rain and flooding, and heavy wet snow making it down to the urban corridor.

Showers and some heavy thunderstorms (snow above 8000 feet) will continue today. Don’t expect the breaks in the action to last very long. As the upper level storm system moves through southern Colorado the wind through a deep layer will turn east, then northeast and then north. That should result in a large area of steady precipitation, especially from the Palmer Divide area northward to eastern Wyoming. Many creeks are at bankfull and may exceed floodstage today. The runoff to the creeks will start to decrease this evening as rain changes to snow in the Front Range foothills and the Cheyenne area. The rain will likely change to snow in the Denver-Boulder-Fort Collins corridor by midnight. The changeover in Colorado Springs may not occur until after the heaviest precipitation is over, so the chance for accumulation there is smaller. Toward daybreak Sunday the clouds and snow are likely to become more intermittent in the Denver-Boulder area too

Rain + liquid equivalent of snow:

A large area with and additional 1-2 inches is likely from the Palmer Divide area northward into eastern Wyoming Saturday afternoon and night. But local amounts of 2-3 inches are possible in the vicinity of thunderstorms within this area as well as the southern Front Range and southeastern Colorado. Be alert for flash flooding.

Snowfall:

An additional 10-18 inches in areas above 9000 feet (mainly from I-70 northward) and in the mountain ranges of Wyoming.

6-12 inches in the Cheyenne area and the Front Range foothills between 6000 and 9000 feet, and the Pikes Peak region.

1-6 inches (very variable) for the Denver-Boulder-Fort Collins corridor.

Impacts: With trees leafed out even a small amount of wet snow can cause damage to trees and power lines. Be careful around tree damage, and be prepared for power outages.

Biggest imapct: Wyoming-South Dakota; but cold & wet in Colorado too

12:45 PM, Friday, May 8, 2015

A big wet storm system to our west will keep it cloudy and rainy through tonight, with snow above 8000 feet. As the storm moves from the Four Corners Saturday morning to northeastern Colorado Sunday morning, we may see several phases of the storm play out. The strongest westward moving moisture flow may shift north into Wyoming during the day Saturday. As the storm moves into northeastern Colorado Saturday night and Sunday morning, moist northerly flow in eastern Colorado may reinvigorate the precipitation as the snow levels fall. Near freezing temperatures are likely even in many low elevation areas Sunday and Monday mornings.

Here is a regional breakdown:

Northeastern Colorado & the Front Range, including Denver, Boulder, Fort Collins and Nederland:

Through early Saturday: Clouds and rain. There may be some locally heavier showers or a thunderstorm that trigger brief minor flooding. Snow levels may lower again to 8000 feet, but the accumulating snow will be mainly above 9000 feet.

During the day Saturday: an area of slightly drier air (a dry slot) should move into southeastern Colorado and there is a chance it may move into northeastern Colorado too for a period. I think you should be prepared for a cloudy, rainy day even though I think the odds slightly favor a lull period. If the sun manages to poke through briefly, that may trigger thunderstorms during the afternoon, possibly strong thunderstorms on the far eastern plains.

Saturday night and Sunday: northerly flow is likely to bring moisture back from the north along with colder temperatures. Rain will likely change to snow down to 7000 feet Saturday night, and possible all the way down to the lower elevations Sunday morning as the precipitation becomes more intermittent.  Snow totals of 1-6 inches should be expected from 6000-800 feet, with 6-12 inches above 8000, and maybe some local areas of 2 feet in the mountains of Larimer and northern Boulder County. I cannot yet rule out some accumulation in the Denver-Boulder-Fort Collins corridor. I will update tomorrow.

Wyoming:

Cloudy and rainy through Saturday (snow above 8000 feet), with snow levels dropping to the lower elevation areas Saturday night. Total snow accumulation through Sunday is likely to be 10-20 inches in the higher ranges of eastern Wyoming and the Black Hills of South Dakota. Even the Cheyenne area is likely to see 6-10 inches.

Southeastern Colorado, including Colorado Springs:

Rainy with some thunderstorms into tonight. Slightly drier air coming up the east side of the storm circulation is likely to result in a lull Saturday. But thunderstorms may develop in the afternoon, and some may be severe on the far eastern plains. A surge of colder, moist air out of the north Sunday will likely result in mostly cloudy conditions and some showery rain and snow.

Big, wet storm this weekend; mountain snow

12:55 PM, Thursday, May 7, 2015

A cool, moist pattern will continue into Sunday for the whole Front Range region. A large, wet storm system is likely to move slowly through the region Friday night to Sunday morning. At this point I am confident that the weekend storm will be major (2-3″ liquid equivalent) for eastern Wyoming and western Nebraska including Cheyenne and Laramie. I am also confident that southern Colorado will likely be south of the heaviest precipitation. I have a lot less confidence about the impacts for northeast Colorado, including Denver-Boulder-Fort Collins. Current indications are for significant precipitation, but less than what is likely immediately to the north. But we will have to watch the development closely.

Thursday evening through Friday: Dry periods, but mostly cloudy with rainy periods too. There may be some heavier showers or thundershowers that trigger minor local flooding in the late afternoon or evening both days. Snow levels are likely to stay near tree line. Thunderstorms are a little more likely south of Denver where the sun is poking through.

Friday night through Sunday:

Denver-Boulder-Fort Collins:

As the storm moves from the Four Corners to eastern Colorado Friday night to early Sunday we can expect a wet period, with snow levels lowering by Saturday night from near treeline to between 6000 and 7000 feet, and possibly all the way down to the plains Sunday morning. Because it appears that the Denver-Boulder area may be south of the heaviest precipitation, snow accumulation, if any, will probably be minor because much of the precipitation will fall as rain. The Front Range foothills have the potential to see 6-12 inches, with more in the higher mountains and passes.There is a small chance that the heavier part of the storm will shift south, so pay attention to the weather before venturing out. Either way, freezing temperatures by Monday morning are likely to damage unprotected annuals.

Southeastern Wyoming:

For southeastern Wyoming and the northern parts of Larimer and Weld counties in Colorado, heavier amounts are probably, with a couple feet of snow from Rocky Mountain Park north into the Medicine Bows and the Laramie Range. Even Cheyenne has a good chance for getting more than 6 inches of snow after a couple inches of rain. Be prepared for rough driving along I-80 and I-25 north of Fort Collins.

Colorado Springs and south:

Unsettled here too, but less chance that the weekend storm will be really big. But watch out for a few heavy thunderstorms today and Friday.

Staying wet for the near future

1:05 PM, Tuesday, May 5, 2015

Today and tonight: An upper level storm system over Colorado combined with lots of atmospheric moisture will increase the coverage of rain this afternoon in Colorado and southeastern Wyoming. As was the case yesterday, there will probably be some localized heavier showers or thundershowers, so watch out for brief minor flooding. The snow level should be up around treeline, so even the foothills should see rain.

Wednesday-Thursday: The upper storm system will move away but drier air is not really sweeping in behind. So showers and thundershowers remain likely, especially late day, but there will probably be dry periods when the overcast breaks as well.

Friday-Sunday: Another storm system is likely to impact Colorado and Wyoming this weekend (maybe as early as Friday) and draw in even more moisture from the Gulf of Mexico. The track is still uncertain, but parts of central/eastern Colorado and/or southeastern Wyoming may see heavy rain (heavy snow in the mountains).

Moist week for Colorado and Wyoming

12:55 PM, Monday, May 4, 2015

A moist and somewhat unstable weather pattern should continue through the week for the central Rockies region. An organized atmospheric disturbance within that pattern should make for mainly cloudy conditions and periods of rain with perhaps a thunderstorm today through Tuesday.

By Wednesday-Thursday there will probably be more breaks in the overcast, but still a good chance for showers and thunderstorms. And it now appears that by the end of the week another organized disturbance may enhanced the coverage of rainy weather.