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FXUS65 KBOU 082120 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 320 PM MDT Wed May 8 2024

KEY MESSAGES

- Continued light snowfall in the mountains with some blowing snow over the higher passes

- Cool and unsettled weather Thursday through Friday, with accumulating snow in the Front Range mountains, higher foothills, and Park County

- Gradual warming this weekend into early next week, but still somewhat unsettled with scattered showers and storms most days

SHORT TERM /Through Thursday/
Issued at 245 PM MDT Wed May 8 2024

The latest radar scans currently show rain showers over the Northern Rockies of Montana and Wyoming this afternoon associated with an elongated upper level low. This low will shift southwestward into Colorado and Utah overnight funneling moisture into the forecast area.

For this afternoon and tonight, SPC mesoscale analysis shows mid level lapse rates have increased enough this afternoon creating enough instability to bring a slight chance of thunderstorms to areas mainly west of I-25 while rain showers are possible across the plains. Precipitation will develop along the northern state border and spread south as a cold front passes from north to south later on tonight bringing a chance for snow showers to develop in the mountains and foothills. Temperatures will be a few degrees below normal across the plains and foothills, and 10 to 15 degrees below the norm for the higher elevations.

By tomorrow morning, snow levels will drop to between 6000'-7000'as the elongated low splits into two and upslope flow develops across the Front Range mountains. Max temperatures will be well below normal as widespread 50s will be seen across the plains, 40s for the foothills, and 30s and 40s for the mountains. See the long term forecast below for specifics on snow amounts.


LONG TERM /Thursday night through Wednesday/
Issued at 143 PM MDT Wed May 8 2024

The models have trended wetter with the elongating trough dropping across our area, and the impacts of this could last through Thursday night and even into early Friday morning. There is persistent QG lift through this period, but the bulk of it will stay to our south. That said, there is more of an upslope component now advertised to last through Thursday night as the elongated trough redevelops into a slightly deeper closed low in the Great Basin. Thus, with all those ingredients we increased PoPs and QPF/Snow forecasts for locations in/near the Front Range through tomorrow night. Regarding snow levels, we think most of the accumulating snow should stay above 7,000 feet per latest forecast soundings, but we did have to nudge snow levels down down to account for the upslope component and potential enhanced precipitation rates and latent heat of melting. Thus, we would not be surprised to see some accumulation down to ~6,500 feet should the more significant precipitation/upslope develop. We could certainly need Advisories for the Park/Summit County areas, and possibly into portions of the foothills in updates to follow.
Current potential shows upward of 6-12" possible for Park County and east facing slopes above 7,000 feet.

By later Friday and Friday night, we'll turn to neutral forcing or weak subsidence. Precipitation coverage will be on the decrease, although there is still some weak upslope and potential for shower redevelopment with sufficient daytime heating. There's not a lot of heating, however, with high temperatures likely struggling to reach 60, and most likely holding in the 50s closer to the foothills.

For the weekend, there seems to be more ensemble agreement that weak troughiness will remain over the forecast area. This will lead to only gradual warming, but a continuation of scattered showers and a few thunderstorms each day. Instability is limited, so there is little if any threat of severe.

We finally expect a return to above normal temperatures by early next week. That's when we begin to transition to more of a zonal flow with downslope aiding the warmup. It is springtime, however, so we'll continue to see a chance of showers and storms most days.
The severe storm threat will remain limited due to a lack of instability. It's not impossible, however, that we start to see a little stronger convection toward Tuesday or Wednesday if we can build enough low level moisture.

AVIATION /18Z TAFS through 18Z Thursday/
Issued at 1152 AM MDT Wed May 8 2024

Current VFR conditions will continue through today before transitioning to MVFR by 12Z tomorrow morning. Gusty winds will continue to lighten through the afternoon today. A cold front will pass through the area overnight tonight that will shift winds to the N/NE around 3Z. Light rain showers will be possible in the morning which could lead to the chance of IFR conditions developing if higher precipitation rates occur, with BJC having the highest probability of this happening. There is a low probability of a few snow flakes falling at KAPA but no accumulations are expected.



BOU WATCHES/WARNINGS/ADVISORIES
None.

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