Sunrise 5:43 AM   Sunset 8:07 PM Moonrise 10:30 AM   Moonset 1:12 AM

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FXUS65 KBOU 132017 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 217 PM MDT Mon May 13 2024

KEY MESSAGES

- Scattered showers and isolated thunderstorms over the mountains and foothills with isolated showers and storms over the nearby plains.

- Scattered afternoon/evening showers and thunderstorms Tuesday.

- Front brings cooler and wetter weather on Wednesday. Light snow for elevations mainly above 10,000 feet.

- Warmer and generally drier starting Thursday, with lesser but at least isolated daily afternoon showers/thunderstorm coverage, highest for the mountains.

SHORT TERM /Through Tuesday/
Issued at 217 PM MDT Mon May 13 2024

Radar showing scattered showers over the mountains and foothills.
Best instability resides over the higher terrain with ML CAPE to around 500 J/kg, so still expect isolated storms to form.
Instability decreases eastward onto the plains. Weak ridging will move across Colorado this evening and tonight. Expect this to keep convection weak and isolated to scattered. The stronger storms will be capable of produce small hail (pea sized), wind gusts to 40 mph, and brief heavy rain. Convection dies off early to mid evening with the loss of daytime heating stabilizing the airmass.

For Tuesday, westerly flow aloft will prevail behind the exiting ridge and in advance of a wave dropping southeast across Wyoming.
This wave should help produce at least scattered convection (more than today). Instability will slightly increase with ML CAPE up to 700 J/kg. Still expect storms to stay sub severe, with brief heavy rain and small hail under the stronger storms. Wind gusts may be slightly stronger, up to 50 mph. Airmass warms a little more with some locations topping 80F degrees over northeast Colorado.

LONG TERM /Tuesday night through Monday/
Issued at 217 PM MDT Mon May 13 2024

Tuesday evening into Wednesday, an upper level trough approaches from the west with weak QG lift ahead it. An associated cold front moves across the region, likely early Wednesday morning (midnight- 6am). North to northeasterly flow persists during the day Wednesday post-front. The upslope component will provide an addition source of moisture, especially in the favored areas such as the Palmer Divide, Front Range, and adjacent plains. This will bring a cooler and more unsettled day. In the cooler post-frontal airmass, high temperatures likely stay in the 60s across the plains, considerably cooler than Tuesday's highs. Sounding profiles and instability fields show marginal instability Wednesday afternoon (MLCAPE < 500 J/kg). Within the weak upslope environment, this could support convective showers and embedded storms.

With respect to amounts, ensemble means show a range of 0.20" to 0.60". There is notable small variations happening from run to run and the GFS is appearing to be the wetter suite of solutions. The higher amounts will likely be focused in those upslope favored areas (Front Range, Palmer Divide, south foothills, Denver metro).
The cooler air stays north with the trough, but it be should enough to bring snow levels down to 10,000 during the day and around 9500 overnight. As a result, snow showers are possible for the higher mountains/mountain passes. Ensembles show light accumulations, so at this point not major impacts are anticipated.

On Thursday, the upper trough exits to the east putting northeast Colorado under northwesterly flow aloft. Subsident flow should keep dry out much of the region from Wednesday. Model cross sections show some residual moisture in the high country with marginal instability building in the afternoon to support scattered showers/storms. Given the limited instability/moisture, coverage/chances will be less (< 25%) and mainly over the higher terrain. Temperatures recover from Wednesday with highs pushing back into the upper 60s/low 70s for the lower elevations and 40s/50s for the high country.

Friday into the weekend, expect weak ridging to zonal flow in the upper level pattern. 700mb temperatures warm a degree or two each day, supporting a gradual warming trend. Highs in the upper 70s to low 80s Fri/Sat. Daily heating/instability should support scattered afternoon showers and thunderstorms in the mountains with a low chance for a few to stray onto the adjacent plains. Friday through the weekend will be drier across the plains with relative humidity values dropping into the 20 percent range in the afternoons.

AVIATION /18Z TAFS through 18Z Tuesday/
Issued at 1123 AM MDT Mon May 13 2024

VFR to prevail through tonight and Tuesday. There will be a chance for gusty winds around the showers and storms that form, otherwise light diurnal winds will prevail. Scattered showers and isolated thunderstorms are expected to form over the higher terrain west of Denver after 18Z. Isolated showers/storms will be possible in the Denver area. There's about a 10 percent chance for a thunderstorm at the airports. Gusty outflow winds will accompany some the showers and storms that develop, and could produce a wind shift.

BOU WATCHES/WARNINGS/ADVISORIES
None.

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