Lamar, CO Weather

Key Messages

- Periods of moderate to heavy rain expected over the southwest mountains through Friday, with the heaviest rainfall occurring Thursday night.

- A Flood Watch is in effect until Friday afternoon for the eastern San Juan mountains and the Upper Rio Grande Valley, with stream/river flooding and rock/mud slides possible.

- Over the remainder of the Continental Divide rainfall be lighter, with amounts around 1 inch possible. Scattered showers and much lighter rainfall forecast for the eastern mountains/interior valleys and I-25 corridor.

- Generally warm and dry across the plains through Friday, then a new weather system is forecast to bring much cooler and wetter weather to all of southern Colorado from Saturday into Sunday.

Short Term

Issued at 118 PM MDT Wed Oct 21 2026

Lead short wave lifting out ahead of the West Coast upper low was firing widespread convection over nern AZ/nwrn NM at midday, with showers and storms moving into much of CO west of the Continental Divide early this afternoon. Expect precip to continue to move/expand e-ne across the Divide for the remainder of the day and overnight, with potentially some stronger storms and heavy rain moving across the eastern San Juans this evening. Rainfall amounts of over an inch are possible by early Thu morning, as snow level remains very high, generally above 12000 feet. Showers spread north along the Divide and across interior valleys overnight as well, though rainfall amounts here will be much lighter, with only a couple tenths of rainfall at most. CAMs, especially HRRR, show some light showers surviving their trek over the mountains, possibly reaching the I-25 corridor early Thu morning. Nudged up pops slightly along and west of the Interstate to account for this possibility, though expect any precip here to be light, mostly sprinkles/light rain with a couple hundreths of an inch at most.

On Thursday/Thursday night, West Coast low moves onshore with strong s-sw flow continuing across CO. Models suggest potential heavy precip over the San Juans early Thu morning, then perhaps a lull from mid-morning into the afternoon, before precip cranks up again from late afternoon into Thu night as stronger upward motion moves into the region. Daytime precip amounts in the eastern San Juans may stay generally under an inch during the day Thu, then heaviest precip of the entire system arrives Thu night, with 1-2 inches of rainfall possible by early Fri morning. Biggest watch-out period for river/stream flooding from this system will likely by from Thu evening into Fri morning, as saturated soils/high rainfall rates combine to increase flood potential. Snow levels will eventually drop Thu night as cold air aloft moves in, perhaps falling to between 10k-11k feet by Fri morning, suggesting bulk of heaviest precip will fall as rain. Much lighter precip elsewhere across the area Thu, with perhaps an upturn in precip intensity/coverage Thu night as stronger wave of upward motion moves through the region. Rainfall chances and amounts decrease rapidly over the eastern mountains, with little if any rainfall east of I-25. Despite cloud cover, high temps on Thu will remain mild, with readings into the lower 80s across the plains.

Long Term

Issued at 321 PM MDT Wed Oct 21 2026

Friday... Rain continues in the San Juans on Friday, but degrading over the course of the day as moisture leaves the area and the low pressure center over CA splits. A Flood Watch remains in effect for the eastern San Juans through 0Z Saturday and the current end time looks to be on track. The plains stay dry through Friday with high temperatures climbing up into the low to mid 80s. A sfc trough sets up over eastern CO which will aid precipitation chances as we move into Saturday.

Saturday into Sunday...The southern low will begin to deepen over AZ and help moisture return to CO. This moisture along with WAA and good synoptics will support more widespread precipitation across the region. Light to moderate rain is expected, but a locally heavy shower cannot be ruled out. WPC's Day 4 (Sat) Excessive Rain Outlook includes parts of SE CO in the SLGT risk area. Day 5 also has part of the region in a SLGT risk, but a much smaller area in far SE CO. There is the potential for flash flooding in areas which experience locally higher rainfall totals for both Saturday and Sunday. Severe thunderstorms are not expected, given limited instability, but at least isolated to widely scattered thunder remains a possibility. The northern low will help push a cold front into CO on Saturday with high temperatures dropping into the 50s and 60s in the plains. These colder temps will persist through the weekend and into Monday.

For the remainder of the period, generally dry with more seasonably type temperatures in place.

Aviation

Issued at 522 PM MDT Wed Oct 21 2026

Thickening clouds will spread over the mountains affecting all three TAF sites with persistent VFR cloudiness. KALS will see off and on rain showers with cigs/vis possibly dropping into the MVFR category, especially during the overnight hours. KPUB and KCOS could see a round of showers spread into the terminals for a couple hours around 12z Thu, but conditions should remain VFR. After a bit of a break late morning, another round of showers and thunderstorms will spread off the mountains into all 3 TAF sites in the afternoon. Cigs and vis will be predominantly VFR but could drop into the MVFR category at KALS if a stronger storm impacts the terminal. Otherwise, winds will be dominated by southerly flow which will become gustier tomorrow afternoon as the system out west approaches the area. -KT