Another Shot of Bitterly Cold Air Along with a bit of Light Snow

Another Arctic cold front (much like the one that pushed through during the middle of last week) will come barelling through on Monday, bringing dramatically colder temperatures along with a little bit of light snow -- though, personally, not enough to satiate this snow lover's hopes for a big dumping of the white stuff.

High temperatures today will be some 20 degrees colder than yesterday's high of 37, with northeasterly winds of 5-10mph allowing for wind chills near 0 degrees at times. A few stray snow showers or flurries are possible during the day, but the majority of the (light) snow will probably hold off until Monday evening into the early hours of Tuesday.

Detailed Forecast

Monday 1/21
Expect mostly cloudy skies with bitterly cold high temperatures near 17 degrees along with wind chills, at times, near zero. A few widely scattered snow showers or flurries are possible through the daylight hours, perhaps bringing a coating to an inch in some spots.

Monday night 1/21
Overcast skies and frigid temperatures will characterize Monday night. Occasional periods of light snow may bring up to an inch of accumulation in some spots. We'll see overnight lows from 0 to 5 above, with wind chills below zero at times.

Tuesday 1/22
The sun will return on Tuesday, with temperatures not nearly as uncomfortable as Monday's highs. Look for high temperatures around 29 degrees with cold overnight lows near 14.

ARCTIC COLD FRONT BARRELS THROUGH Bringing Bitter Cold & Light Snow

An exceptionally strong Arctic cold front will come barreling through later today which will bring, in its wake, the coldest air mass we've seen so far this entire winter. While high temperatures today (along with very gusty winds "ahead" of the cold front's passage) will be near 50, we may not make it out of the mid teens on Wednesday! And continued breezy conditions will provide wind chills near (or even below) zero for much of the day.

I expect that the cold front itself will push through sometime between 4 and 6pm today, dropping temperatures 15 to 20 degrees in a matter of 90 minutes. Thereafter, light snow will develop sometime between 6 and 10pm tonight, and linger (on-and-off) through the morning hours Wednesday. With fresh snow cover on the ground and light winds, we'll see the lowest temperatures of the season Wednesday night with overnight lows around zero degrees. (Fun meteorology/science fact: snow is a strong emitter and reflector of radiation; at night, with clear skies, snow cover enhances cooling.)

Detailed Forecast

Today 1/15:

• Mostly cloudy and windy conditions along with mild high temperatures near 50 degrees will characterize the first half of the day.
  
• By mid to late afternoon, temperatures will begin to drop through the 40s into the mid to upper 30s.
  
• By 6pm, temperatures will be below freezing.
  
• Light snow will develop between 6 and 10pm tonight as temperatures fall to the upper teens.

Tonight 1/15:

• Look for periods of light to moderate snow throughout much of the evening and overnight hours.
• Low temperatures will drop to near 10 above.
• Expect 1-3" of snow by Wednesday morning.

Wednesday 1/16:

• Overcast skies and scattered snow showers are likely during the morning hours, bringing up to an inch of additional accumulation
• The afternoon will feature partial sunshine with bitterly cold high temperatures near 16 and wind chills near zero much of the time.
• Clear and bitterly cold Wednesday night, with lows from -2 to +2

TOTAL EXPECTED ACCUMULATION:
TWO to FIVE INCHES

Thursday 1/17:

• Mostly sunny and not as frigid on Thursday
• Expect high temperatures in the mid to upper 20s
• Overnight lows will drop to near 10 above

A Look at the Weather Pattern Ahead 2nd Half of January Looks Very Cold

Though the weather thus far this month has been fairly benign -- with little snow and temperatures averaging 2.3 degrees above normal -- there are plenty of indications that the second half of the month may feature significantly more in the way of cold, along with the potential for several accumulating snow events.

I expect that we'll see seasonably cold (read: near-normal) temperatures over the next week with daytime highs generally ranging from the mid 30s to the mid 40s with overnight lows typically in the teens and 20s. And we've got a decent shot of at least a few inches of snow on Wednesday, as an area of low pressure pushes through the region.

I am more concerned, however, about the last 10 days of the month. There are several warning signs that this period may feature much below normal temperatures. Most long-range computer modeling suggests this. In fact, as I write this, one of the more reliable longer-range forecast models hints at the potential for overnight lows in the -10 to -25F degree range during the last week of January; (the lowest temperature so far this winter in downtown Boulder is about 5 above.)

Indeed, the Climate Prediction Center (where I used to work) suggests a very high probability of below-normal temperatures in their 6-10 day temperature guidance -- which would correspond to Jan 19-23. Their 8-14 day guidance (Jan 21-27) also calls for a high probability of below-normal temperatures.

Whence this potential for bitterly cold temperatures? The answer is in the jet stream -- a narrow band of fast-flowing air currents about 35,000 feet up. The jet stream dictates the source region of air masses, and typically troughs (or dips in the jet stream) correspond to cooler than normal temperatures while ridges (or peaks in the jet stream) correspond to warmer than normal temperatures.

There are indications that a strong TROUGH will setup over much of the US during the last 10 days of January, allowing for a direct Arctic discharge of air into our region. Model guidance for 8 days from now (Jan 21) shows exactly what I'm talking about:


Note the ridge south of Alaska and the trough over much of the country. The air (the blue arrow) will be coming almost directly out of the Arctic; note, red dot represents central Colorado.

And while cold does not necessarily ensure snow, I do think we have the potential for several accumulating snow events in the last 10 days to two weeks of January.

Stay tuned...

Light Snow Likely Today 1-2" Accumulation

This past weekend, the vast majority of the snow that fell Colorado west remained in the mountains to our west -- though I did see a two brief snow showers in Boulder on Sunday. However, as ripple of atmospheric energy moves through the today, we are likely to see periods of light to moderate snow, especially during the second half of the day.

Today 1/7
We'll wake up to mostly cloudy skies on Monday with chilly temperatures in the 20s. Clouds will begin to increase by mid to late morning. I expect that scattered snow showers will develop between 1pm and 5pm. Depending somewhat on when the snow starts, afternoon highs will probably make it to 32. Snow showers will increase in coverage and intensity as the evening wears on. They will likely taper off around midnight. Partial clearing will allow overnight lows to drop to the low to mid teens in most spots. Brrr!

TOTAL EXPECTED ACCUMULATIONS:
ONE to TWO INCHES

Tuesday 1/8
We'll see a blend of clouds and sun on Tuesday with afternoon highs reaching the mid to upper 30s. Partly cloudy and cold Tuesday night with lows dropping into the upper teens.

Wednesday through Friday
Looks to feature plenty of sunshine with dry conditions and seasonably cool high temperatures from the upper 30s to low 40s and overnight lows primarily in the upper teens to near 20.

Unsettled Weather over Next Few Days Little Snow Expected in Boulder

The cold front associated with a deep upper-level trough which has brought significant rains and mountain snows (up to 5 feet in some places!) in California is poised to push through our region Saturday night. This will bring noticeably colder weather to our region over the next few days. However, it is looking more and more likely that the vast majority of the accumulating snow will stay in the mountains (where 12-20" may fall through the weekend!), with little or no accumulating snow here in Boulder -- partly because of a lack of moisture and partly because temperatures will only be marginally cold enough for snow.

THE FORECAST FOR BOULDER

Tonight 1/5:
Look for breezy conditions and temperatures falling from the mid 40s (at 6pm) to the mid 30s by late evening, and eventually to a low in the upper 20s. A stray shower of rain or wet snow cannot be ruled out. Needless to say, no accumulation.

Sunday 1/6:
Expect mostly cloudy and breezy conditions with temperatures some 15-20 degrees colder than Saturday's high of 60 -- in the low to mid 40s. A shower of rain or wet snow is possible during the late afternoon or early evening but it will be too warm for anything to stick. Cloudy and turning colder Saturday night with a slight chance of a snow shower here or there, bringing at most a coating. Lows will be near 20.

Monday 1/7:
The best chance for (accumulating) snow is on Monday. Plan for overcast skies and cold highs in the low to mid 30s. We've got a 50/50 shot of light snow during the daylight hours which may bring up to an inch of accumulation. Partly cloudy and much colder Monday night, with lows in the low to mid teens.

Tuesday 1/8:
Look for a blend of clouds and sun on Tuesday with afternoon highs in the mid to upper 30s and overnight lows, under mostly clear skies, in the upper teens to near 20.

Mild Weather Lingers Through Saturday Colder with Snow Possible Thereafter

With a ridge of high pressure over the western third of the United States, and mild southwesterly flow aloft over our region, we'll see a continuation of Thursday's mild temperatures on Friday and Saturday. However, an upper-level trough and associated area of low pressure are likely to bring noticeably cooler conditions for Sunday into the start of next week. In addition, some light snow is possible on Sunday and Monday.

Friday 1/4

Expect more clouds than sun during the day (like Thursday), with continued mild high temperatures reaching the low 50s. Partly cloudy and a bit cooler on Friday night, with overnight lows dropping to around 30 in most spots.

Saturday 1/5

Look for mostly sunny and breezy conditions on Saturday with unusually mild high temperatures making a run for the 60 degree mark! Get out and enjoy this balmy weather before it turns cooler. Saturday night will feature increasing clouds and noticeably windy conditions with lows once again near 30.

Sunday 1/6

Under mostly cloudy to overcast skies and breezy conditions, temperatures on Sunday will likely be 20-25 degrees colder than those on Sunday! I expect highs in the low in the mid 30s to near 40 with some wet snow showers possible. Breezy and colder Sunday night with some light snow (coating to an inch?) possible and lows in the mid 20s.

Monday 1/7

Look for cloudy and cold conditions on Monday with some scattered snow showers possible. High temperatures will probably remain in the low to mid 30s with overnight lows in the upper teens to low 20s.

Long-Range Outlook

Expect drying and seasonably cold temperatures on Tuesday with the likely return of sunshine. Wednesday, too, looks dry and seasonably cold. The next precipitation-maker may bring snow back into the forecast by Thursday or Friday.