A storm system brought a brief period of light to moderate snow and strong winds to the north-central mountains of Colorado. Storm totals ranged from 5 to 9 inches.
Every event with a place to put it; 3 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS BOU wrote it up.
A storm system brought a brief period of light to moderate snow and strong winds to the north-central mountains of Colorado. Storm totals ranged from 5 to 9 inches. In addition, strong winds were observed above timberline with peak gusts ranging from 60 to 70 mph.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Denver/Boulder, CO wrote its last area forecast discussion before the first event at Dec 18, 9:37 PM MST, 1 hour 23 minutes earlier.
Area Forecast Discussion National Weather Service Denver/Boulder CO 937 PM MST Tue Dec 18 2018 .UPDATE... Issued at 934 PM MST Tue Dec 18 2018 Light snow has moved into the mountains, with lowering clouds and areas of snow in the valleys west of the Front Range as well. Touched up the forecast with higher PoPs and added an inch or less of additional snow to what we already had forecast for the overnight period. Models continue to slightly retreat on Wednesday's wind speeds, but are still close to warning criteria. UPDATE Issued at 724 PM MST Tue Dec 18 2018 No significant updates at this time. Timing of current highlights still in tact. Latest RAP shows the best period of snowfall appears to be late tonight into Wednesday morning, approximately 09-15z time frame. Although the snow may taper off, strong gusty winds will produce areas of blow snow and poor visibilities over the mountain passes into the afternoon. Current highlights in the mountains look fine, with strong winds developing across the northeast plains on Wednesday. && .SHORT TERM...(This evening through Wednesday) Issued at 322 PM MST Tue Dec 18 2018 Another warm and dry afternoon across the CWA has lead to the 12th consecutive day of above normal temperatures in Denver. This quiet weather pattern will be put to an end as a strong jet stream enters Colorado tonight. This jet stream will have peak 200-300 mb winds of 150 knots and will be positioned to the west of the northern mountains late tonight and tomorrow morning meaning that the area will be in the ascent-favored left exit region. This, combined this with strong upslope winds, will help create snow especially across the western and northern slopes of the northern mountains. Since the moist layer is not very deep and the lapse rates are marginal, amounts should be generally light to moderate. One of the most difficult parts of this storm to nail down is determining the snow rates and end time of the snow during the day Wednesday. The aforementioned jet stream will have moved over the eastern plains during the day tomorrow leaving the mountains in the subsident, right exit region of the jet stream. The typically bullish HRRR produces nearly no snow at all in the mountains from 18Z Wednesday to 00Z Thursday. I disagree with this solution and have gone with a blend of global models that produce a trace to 2 inches of snow during this time frame. By the end of the snowfall from this system, snow amounts will be on the low end of advisory criteria with 2 to 6 inches expected above 9000 feet with higher amounts on the western and northern slopes. In addition to the snow, there will be strong winds with gusts up to 70 mph possible meaning blowing snow and reduced visiblities will be likely. Consequently, there is high confidence in hazardous travel conditions in this storm and a Winter Weather Advisory has been issued for the northern mountains and I-70 corridor mountains from 11pm tonight through 5pm Wednesday. The jet streak will also create hazards over the plains. The subsidence from the jet stream and the strong surface pressure gradient the surface, will create wind gusts between 45-60 mph which is borderline High Wind Warning criteria. However, the impacts from this event, such as blowing dust and elevated fire weather conditions, will be bad enough to allow for the issuance of a High Wind Warning. There was also consideration of a Red Flag Warning for this event due to the strong winds. However, minimum relative humidities will be between 20 to 25 percent over the eastern plains which does not meet the criteria. Nonetheless, precautions should be taken as any fire that does start will be able to spread rapidly. .LONG TERM...(Wednesday night through Tuesday) Issued at 322 PM MST Tue Dec 18 2018 All of the weather activity from Wednesday afternoon will be winding down through the evening as the strong upper level jet slides eastward and heights begin rising over the state. Subsident forcing under the building ridge should cut off most snow shower activity in the mountains and begin the process of clearing out the skies. Surface pressure gradients should also begin relaxing and winds will diminish as they de-couple from the flow at mid- levels. Thursday and Friday will then be less windy with gradually warming temperatures. Friday is expected to be the warmest day of the week with afternoon highs in the mid 50s to lower 60s across the plains. Medium range models show the upper ridge breaking down by Saturday as the first of a series of Pacific troughs move into the northern Rockies Friday night. This will bring periods of mountain snow back to the forecast through the weekend. The upper pattern will be progressive with pieces of Pacific energy moving through every 24 hours or so. Cooler air is also expected to move back in from the north, with temperatures through the weekend around seasonal normals. Another upper disturbance will move through Saturday night. Snow amounts in the mountains should remain light as the upper disturbances move across the state rapidly. Early next week there are indications of a deeper trough carving out over the western United States, beginning to impact Colorado by Tuesday or Wednesday. This will keep weather fairly unsettled and may eventually bring a stronger surge of cooler air to eastern Colorado in the middle of the week. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 724 PM MST Tue Dec 18 2018 VFR conditions will continue through Wednesday evening. The winds are light at all airports through the evening as drainage takes over. The wind will increase substantially tomorrow. Gusts will be highest at KDEN and KBJC with peak gusts around 40 knots. There is a small chance that blowing dust created by the gusty winds, could reduce visibilities Wednesday afternoon. Due to the low chance of this, no visibility restrictions are included in the terminal forecasts. && .BOU WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 5 PM MST Wednesday for COZ031-033- 034. High Wind Warning from 8 AM to 5 PM MST Wednesday for COZ038- 042>049. && UPDATE...Gimmestad SHORT TERM...Danielson LONG TERM...Dankers AVIATION...Cooper
Hazardous Weather Outlook National Weather Service Denver/Boulder CO 1059 AM MST Tue Dec 18 2018 COZ030>051-191800- Jackson County Below 9000 Feet- West Jackson and West Grand Counties Above 9000 Feet- Grand and Summit Counties Below 9000 Feet- South and East Jackson/Larimer/North and Northeast Grand/ Northwest Boulder Counties Above 9000 Feet- South and Southeast Grand/West Central and Southwest Boulder/ Gilpin/Clear Creek/Summit/North and West Park Counties Above 9000 Feet-Larimer and Boulder Counties Between 6000 and 9000 Feet- Jefferson and West Douglas Counties Above 6000 Feet/Gilpin/Clear Creek/Northeast Park Counties Below 9000 Feet- Central and Southeast Park County- Larimer County Below 6000 Feet/Northwest Weld County- Boulder And Jefferson Counties Below 6000 Feet/West Broomfield County- North Douglas County Below 6000 Feet/Denver/West Adams and Arapahoe Counties/East Broomfield County- Elbert/Central and East Douglas Counties Above 6000 Feet- Northeast Weld County-Central and South Weld County-Morgan County- Central and East Adams and Arapahoe Counties- North and Northeast Elbert County Below 6000 Feet/North Lincoln County- Southeast Elbert County Below 6000 Feet/South Lincoln County- Logan County-Washington County-Sedgwick County-Phillips County- 1059 AM MST Tue Dec 18 2018 ...HIGH WIND WARNING NORTHEAST COLORADO WEDNESDAY... ...WINTER WEATHER ADVISORY NORTH CENTRAL MOUNTAINS TONIGHT AND WEDNESDAY... This hazardous weather outlook is for northeast and north central Colorado. .DAY ONE...Today and Tonight Snow and strong gusty winds will develop tonight in the high country with a powerful jet stream moving over the area. Snowfall will light across the mountain valleys and will be moderate across the high mountain passes and west facing slopes. Totals by Wednesday morning will range from 2 to 5 inches, with lighter amounts on the valley floors. Gusty northwest winds of 50 to 70 mph may also produce areas of blowing snow over higher elevations late tonight, creating hazardous travel conditions. East of the mountains, dry and mild weather will persist through tonight. .DAYS TWO THROUGH SEVEN...Wednesday through Monday Snow and windy conditions will continue over the mountain passes Wednesday morning before decreasing in the afternoon. Up to 3 inches of additional snow can be expected. On the plains, strong and gusty northwest winds are expected to develop Wednesday morning and last through much of the day. The strongest winds should stay east of the Interstate 25 corridor where gusts of 45 to 60 MPH may produce areas of blowing dust. The northern Front Range foothills could also experience similar winds. Drivers of lightweight and high profile vehicles will be especially vulnerable to the strong, gusty winds. Winds will diminish Wednesday evening, then dry and warmer weather are expected for the end of the week. Over the weekend, the mountains could see a little bit of snow while the plains remain dry with temperatures around normal. ...SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed today or tonight.
The national radar mosaic for the moment the first event began.
3 winter weather. Local standard time, as filed.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Colorado in 2018Every state in 2018This day in weather historyWarnings in Colorado, December 2018
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 795317, 795318, 795319.