Sunrise 5:44 AM   Sunset 8:09 PM Moonrise 10:37 AM   Moonset 12:46 AM

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FXUS65 KBOU 141131 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 531 AM MDT Tue May 14 2024

KEY MESSAGES

- Scattered afternoon showers/thunderstorms today, most numerous along/south of I-70 where a few could be strong and produce hefty outflow winds.

- 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 tonight/
Issued at 218 AM MDT Tue May 14 2024

A few light high-based showers are dotted across the high country and eastern plains at this hour embedded within the westerly synoptic flow in advance of the approaching shortwave trough.
These spotty showers may continue through the early morning hours, mainly for the northern tier of our forecast area where QG lift will be most pronounced.

Despite a fair amount of mid and high-level clouds at times today, we should still see sufficient clearing and enough compressional warming from near-surface downslope flow to push temperatures into the mid 70's for the urban corridor and locally upper 70's in the plains. Meanwhile, cold air advection will increase aloft, contributing to notably steeper low-level lapse rates by this afternoon, in excess of 9-10 C/Km in the surface to 3km layer per most CAM forecast soundings. Under a well-mixed environment, conditions will be favorable for the development of scattered to numerous elevated showers and thunderstorms, particularly after ~2-3PM MT. There's relatively good consensus as far as the bulk of today's convective activity being focused across the southern half of our forecast area, roughly aligning with and south of I-70, where MLCAPE should be maximized (with values ranging from 300-700 J/Kg).

With the aforementioned lapse rates as well as healthy DCAPE surpassing 800-1,000 J/Kg, storms will be capable of producing strong outflow winds, which in a few cases may approach 60 mph and thus marginally severe levels. This threat will be primarily confined to Douglas, Elbert, and Lincoln Counties, although locally gusty outflow winds will be possible for almost all areas.
Models don't appear to be handling the outflow wind potential all that well, so have made some upward manual adjustments to our wind gust forecasts to try and at least capture the median state.
The stronger storms are also likely to carry hail, albeit generally on the smaller side in the majority of cases. Activity will dwindle considerably by mid-evening, although isolated showers and a few thunderstorms may linger, particularly in the northeast plains. For the mountains, any snow today will generally be confined to the highest elevations, above ~11,000 ft.

Tonight, temperatures will hold mostly steady, with a healthy amount of cloud cover that will increase closer to sunrise as the surface cold front approaches from Wyoming.

LONG TERM /Wednesday through Monday/
Issued at 218 AM MDT Tue May 14 2024

A shortwave trough aloft will move across our forecast area on Wednesday providing forcing. At the surface, there will be a cold front that moves across the Colorado plains tonight through early Wednesday morning. The post-frontal airmass will be cool and moist. Highs will be in the 60s across the plains with a decent amount of cloud cover throughout the day. The moisture and forcing will combine with weak instability to create scattered to numerous showers and thunderstorms mainly in the afternoon and evening. The weak northeasterly flow in the low levels will provide slight upslope flow that will make storms more frequent over the Palmer Divide and southern foothills than anywhere else.
The instability, with mixed-layer CAPE around 500 j/kg, will not be enough for severe storms to form. However, the storms could produce small hail, gusty winds, and brief heavy rain.

There will be NVA over Colorado on Thursday as the aforementioned trough departs the area. This will lead to drier conditions as highs increase slightly due to more sunshine. There will be enough lingering moisture along with slight instability across the higher terrain that a couple of stray showers and storms could form.
However, most of our forecast area will remain dry.

An upper level ridge will move over Colorado Friday and Saturday.
This will provide subsident flow and much warmer mid level temperatures. Highs will warm to the 80s across the plains each day with only a few stray showers mainly over the higher terrain. The only minor weather concern is elevated fire weather conditions across the plains with relative humidity dropping to the teens with breezy conditions.

Some models show a cold front moving across Colorado Saturday night which would lead to slightly cooler conditions on Sunday. A broad trough will move across the western US during next work week. There will be southwesterly flow aloft which may keep temperatures above normal. There will be small shortwave troughs within this southwesterly flow that could bring storms to our forecast area.
This pattern could be conducive for severe weather and the climatology of late May begins to strongly favor severe weather.

AVIATION /12Z TAFS through 12Z Wednesday/
Issued at 525 AM MDT Tue May 14 2024

VFR conds expected to prevail for all terminals through at least 03Z Wed. Relatively light SSW drainage flow during the early morning hours today will transition to a more robust NW wind between 17-19Z with speeds 12-16 kts.

Scattered PM convection expected to develop over and south of the Denver metro starting 20-21Z Tue, with SCT-BKN clouds bases near 080. Majority of SHRA/TS activity expected to remain near and south of KDEN. An addition concern revolves around potential outflow winds from any developing convection. At this time, confidence seems high enough in relatively organized convection due south of KDEN pushing east into the evening, to warrant inclusion of some form of a S or SE wind after ~01Z. Regardless, wind direction in the evening will likely be driven not by the general synoptic (large-scale) flow, but rather from outflow winds, the direction of which will be entirely dependent on location of convection relative to the terminal. Variable wind directions are thus a reasonable expectation for the evening hours. The stronger thunderstorms should dwindle relatively quickly in the evening, with subsequent weakening of winds, however a few lingering showers or thunderstorms will remain possible through the evening in the vicinity.

Finally, will need to monitor potential for lower CIGS after 06-08Z Wed in association with an approaching surface front, with increased potential for bases 020-030 Wed AM for all terminals.

BOU WATCHES/WARNINGS/ADVISORIES
None.

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