Gusty cool front late Sunday, but not really much cooler

12:20 PM, Saturday, February 18, 2017

A mild three-day weekend is underway and although there will be a cool front late Sunday, other than some gusty winds behind the front it is not expected to turn much colder. Some precipitation (snow mountains, rain valleys) is likely in western Colorado late Sunday and Sunday night, but a big storm is not expected. For the Front Range lower foothills and plains there is a small chance of a brief showery period with the front Sunday evening and even a slight chance for a rumble of thunder (that would be quite unusual for February if it does happen). Monday should be a bit cooler, but still milder than average, and maybe some gusty winds. Abnormally warm weather is likely Tuesday and Wednesday.

Will winter return?

Not in the next four days. There is increasingly consistent indications that more wintry weather may make a comeback after midweek.

More unusual warmth to end the week

12:20 PM, Tuesday, February 14, 2017

Wednesday and Thursday are likely to bring more near record warmth along the Front Range. The warmth is not expected to be as impressive as last Friday, but we may still get within striking distance of the record highs. The record highs for Wednesday and Thursday in Denver are 66 and 70, and in Boulder they are 67 and 69.

 

The three day weekend should be colder, but probably with temperatures still near or above average. Pacific moisture streaming into the central Rockies may not have a big impact along the lower elevations of the Front Range, but some precipitation is probable for the mountains and west.

More seasonable weather this weekend

12:35 PM, Friday, February 10, 2017

The strong chinook winds and record temperatures are in their final day, for this round. At noon record warm temperatures were being observed up and down the Front Range. We are likely to get close to the monthly records of 77 in Denver and 79 in Boulder.

A trend toward cooler weather will begin Saturday morning and there will probably be a distinct cold front passage during the afternoon with brief gusty north or northeast winds. The air mass behind the front is of polar-Pacific origin rather than arctic, so Sunday’s temperatures should be near average.

The north-northeasterly surge Saturday will be conducive to clouds and precipitation but the upper air setup isn’t very favorable to precipitation, especially from Denver north. Expect a brief period or rain or snow below 7000 feet and snow higher up late Saturday afternoon or night. Accumulations  are likely to be below an inch from Denver north. Accumulations south of Denver should be relatively minor too, but there is a better chance for a couple inches.

Warm through Friday, then colder Saturday

11:15 AM, Wednesday, February 8, 2017

Warm weather (although with some gusty chinook winds in and near the foothills) will be in place statewide Thursday and Friday. The mountain snow and valley rainshowers should decrease by Thursday too.

Record highs in Denver and Boulder are not likely, but it’s not out of reach for Friday. The current records on Friday are 72 in Boulder (1962) and 71 in Denver (1951).

 

A Pacific cold front on Saturday will should bring temperatures back to near-average levels  by late Saturday. It should also bring Pacific moisture resulting in more mountain snow and valley rain or snow near and west of the continental divide. For the Front Range urban corridor it does not look like the kind of setup for significant precipitation, but that can’t be ruled out yet. I’ll update on Friday.

Cold snap ending

2:30 PM, Friday, February 3, 2017

If you live in western Colorado the cold snap never started. But for the icy lower elevations of the Front Range, Saturday will see a milder Pacific airmass, but some areas of gusty winds may be the price to pay. There will probably be a bit of snow along the high elevation ridges and some strong wind gusts. But overall a dry and mild weekend is in store for the Front Range region.

How unusual is freezing precipitation in Colorado?

9:35 AM, Thursday, February 2, 2017

The local media has asked me how unusual the recent freezing precipitation is. I thought I’d share with the blog readers.

First let me  answer the question: freezing rain is quite rare in Colorado, but freezing drizzle is a rather regular visitor. What we had recently was freezing drizzle. Now you’re really confused, right?

 

What is freezing drizzle?

Drizzle is not light rain, it’s small rain. It’s the small, misty droplets that don’t make a sound when they hit the ground. It forms in low stratus clouds that don’t reach high into the atmosphere. Cloud droplets slowly grow large enough to fall to the ground as mist and drizzle. When it’s below freezing those drizzle droplets are supercooled and freeze on contact with the surface. If the cloud grows tall the top of the cloud would be cold enough to form ice crystals and those crystals then help convert the cloud droplets to snowflakes.

 

How is freezing rain different?

Rain is a larger droplet than drizzle and forms in deeper cloud layers. Most of our rain (even in summer) starts as hail or snow in the cloud and melts on its way to the ground. Freezing rain occurs when hail or snow melt into rain on the way to the ground, but then the rain enters a below-freezing layer of air near the ground and becomes supercooled. Freezing rain typically requires that a warm & moist oceanic air mass ride up and over the cold low-level air, something that rarely happens in Colorado. Freezing rain is responsible for truly devastating ice storms that we sometimes get in the central and eastern U.S. I’m not aware of any really severe ice storm along the Front Range.

 

What do we get in Colorado?

Freezing rain is rare in Colorado. But freezing drizzle, although we don’t get it every winter, is a fairly dependable occurrence.

Maybe some patchy fog and freezing drizzle tonight

3:00 PM, Wednesday, February 1, 2017

A shallow cold air mass is banked up against the lower foothills and it will probably be Saturday before it’s pushed east. During this afternoon locations such as Nederland and Idaho Springs basked in the 40s while Denver and Boulder were 20 degrees colder with low stratus. The cold air didn’t fully get over the Palmer Divide, so Colorado Springs is not quite as cold as places to the north.

 

During the night and into Thursday there may be some areas of fog, light freezing drizzle, and possible some light snow grains in and along the lower foothills mainly north of the Palmer Divide. Amounts should be quite light, but it doesn’t take much freezing drizzle to make for some icy surfaces. The overcast may thin a bit by Friday, but it will likely be Saturday before westerly winds bring a fresher air mass.