Monthly Archives: May 2017

Holiday Weekend Weather

11:55 AM, Friday, May 26, 2017

 

In a nutshell, not bad. Saturday will be the coolest of the three days with temperatures running a little below average. Saturday will also bring a chance for some showers or a thundershower, especially after noon. Sunday and Monday should be sunnier with near average temperatures for this time of year and very little chance for rain. Have a nice weekend.

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Fast moving storm later today, above average snowpack

12:20 PM, Monday, May 22, 2017

We are in for some fast changes over the next week. It’s too early to tell what the holiday weekend will bring, but the current indications are that it may start out wet.

Today

And east-west band of showers and thundershowers is likely to move from the Cheyenne area this afternoon to the Colorado Springs area near or shortly after sunset. Denver and Boulder are likely to be impacted between 5 and 8PM. A bit of snow may occur above 7000 feet.

Tuesday-Saturday

Expect a dry midweek and much warmer on Wednesday. We will probably be in for a spell of unsettled weather Thursday-Saturday, with at least some rainy periods and cooler temperatures.

Snowpack

Last week’s storm boosted the snowpack in the South Platte drainage to 132% of average. While that isn’t exceptional, it does mean there could be a period of high water over the next month in Front Range rivers and creeks depending on weather conditions. A cool, moist period followed by hot weather could cause the melting to be concentrated over a short time period. Something to watch for…

Now for the freeze, then a nice weekend

11:55 AM, Friday, May 19, 2017

Now that the storm is winding down there are only a few bands of showers occurring over the plains. New showers may develop briefly during the afternoon, but overall there is a drying trend. New snow amounts in the mountains should be minor and any showers in the low elevations are likely to be mainly rain.

With partial to full clearing tonight we are likely to see frosts and freezes in many low elevation areas. Throughout this whole storm neither Denver nor Boulder have had any record low temperatures. There is a chance tomorrow morning. The record low in Denver is 31 and in Boulder it’s 27, both from 1931.

Next cold front

The weekend should be mild after a cold start on Saturday. There is a small chance for a shower or thundershower late Sunday. There is a better chance for showers late Monday or Monday night with the next cold front. That system is much less impressive than the one we just had, but I can’t 100% rule out the chance for another frosty morning in some of the usual cold spots on Tuesday or Wednesday.

Storm Update

12:20 PM, Thursday, May 18, 2017

The bad news is that the rain changed to snow in low elevations earlier than expected. The good news is that the melting rate is higher during the day and can balance the snowfall rate. But beware, the snow is coming in bursts and accumulation is occurring in lower elevation areas during the heavier bursts. More significant accumulation is expected in the mountains (especially north of I-70).

The precipitation is likely to become more intermittent later tonight and Friday and may even change back to rain Friday. The risk of tree damage in the lower elevations (where more vulnerable deciduous trees exist) remains and may be enhanced in some areas this evening where the heavier snow is occurring.

Most likely additional snowfall amounts (after noon on Thursday)

Above 6500 feet from I-70 northward: 8-16 inches

Above 6500 feet south of I-70: 4-10 inches (less as you go south from Pikes Peak).

Below 6500 from the Denver area north: highly variable trace to 6 inches (maybe more in Cheyenne and very little in Colorado Springs).

 

Watch for freezing temperatures tonight and again Friday night.

 

 

 

Major Storm: heavy mountain snow, heavy rain then snow lower elevations

12:45 PM, Wednesday, May 17, 2017

The coming storm may be one for the record books! The storm is expected to move across southern Colorado tonight through Friday. The current track suggests the heaviest impacts are likely from the mountains and plains around Denver north to Cheyenne. Lesser impacts are likely from Colorado Springs southward. The area between Colorado Springs and south Denver will probably be on the edge of the intense part and should probably prepare for a heavy storm. The rest of this post will be referring to the likely heavy precipitation areas from Denver north to Cheyenne.

 

Precipitation

Rain should develop this evening and there may even be some areas that get a heavy thunderstorm. Rain should change to snow above 8500 feet this evening, and the snowline is likely to descend to the lower foothills by morning, with some heavy snow during the night. It is unlikely that there will be snow below 6000 feet, but there could be some heavy rain and an occasional mix with snow.

 

As the storm makes its close approach late Thursday through early Friday the temperatures should drop a few more degrees and that may be enough to bring the snowline down to the urban corridor.  There is a lot of uncertainty for the lower elevations.

 

Amounts through Friday

1-4 inches of liquid (rain and melted snow) throughout the region

Above 7500 feet: 1.5 -3 feet of snow

6000-7500 feet: 6-20 inches of snow (very variable depending on elevation and convective snow bursts)

Below 6000 feet: most likely a trace-3 inches with some areas of 3-6 inches (we cannot rule out more widespread amounts of 6+ inches and will re-evaluate tomorrow)

**Some model guidance suggest there could be some localized high elevation areas of the Front Range with more than 4 inches of liquid and 3 feet of snow.

 

Impacts

Difficult travel in the mountains and foothills

Although it’s less likely, if a 6-inch snowfall does occur in the lower elevations, that would result in serious tree damage and power disruptions. Be prepared for power outages and don’t park under trees.

 

Freezes

A hard freeze is not likely in the lower elevations through Thursday afternoon. There is a good chance for temperatures near or below freezing Thursday night.

With clearing expected Friday night, areas of frosts and freezes are likely Saturday morning. If there is snow cover the chance for a freeze increases.

 

Winter’s last stand

12:15 PM, Tuesday, May 16, 2017

A slow moving storm system in the Southwest and an unseasonably cold air mass from the north will affect the Front Range region from Wednesday to Friday. This weather pattern is threatening to bring measurable snow, even in the lower elevations.

Snow

The first threat of snow will begin Wednesday night into Thursday morning. There will likely be some heavy wet snow for the upper foothills and mountains, with a chance for that snow reaching down the plains by Thursday morning. The storm system probably won’t move to the east of the Front Range until Friday, so there may be addition chances for snow Thursday evening.

At this time of year enough of the sun’s energy gets through the cloud cover to make it difficult (but not impossible) for accumulating snow during the day. The things to watch for are whether the storm center will pass just to the south of the Front Range and whether the heavier precipitation will occur during the evening through early morning hours.

Keep in mind that only a few inches of snow at this time of year can cause damage to trees and power lines. Although there is still uncertainty about the snow, it’s not a bad idea to check that your flashlights have good batteries.

 

Temperature

Depending on the evolution of the storm, both Thursday and Friday mornings could see temperatures around freezing. If the skies clear out Friday night, Saturday morning may be at risk for areas of frosts and freezes as well.

 

Historical Context

Although it is unseasonably late for snow and freezes, it is not rare. In Boulder there have been at least two measurable snows recorded in June (the latest was 1.0 inch on June 12, 1947). On May 20-21, 1931 there was a 19-inch snowfall in Boulder (the trees must’ve loved that). Record lows below freezing extend into the early part of June.

More frosts yet to come?

5:50 AM, Monday, May 15, 2017

The next organized storm system to impact the Front Range is likely to move slowly through the Southwest Wednesday night through Friday night. It appears that it may drag down a polar air mass from the north which could result in temperatures of around 32F later this week or Saturday morning. For those who have tender annuals outside this is not a high-confidence forecast yet, but you should probably have a plan to cover vulnerable plants.

Precipitation this week

There is only a small chance for an afternoon shower/thundershower today and Tuesday, and most areas will likely remain dry. As the next storm system approaches the coverage of afternoon/evening showers is likely to increase a bit Wednesday. It’s too early for details, but sometime in the period Thursday thru late Friday we may experience a period of overcast and steady precipitation. If the storm system passes south of Colorado it may be associated with enough¬†cold air to help drag the rain/snow line down into the lower foothills or plains. More on that later this week.