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FXUS65 KBOU 180239 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 839 PM MDT Fri May 17 2024

KEY MESSAGES

- Warm through Sunday. Isolated to scattered high based showers and storms this evening, and then again Saturday.

- Breezier Sunday into Monday.

- Cooler, unsettled pattern with increasing precipitation chances across the region early next week.

UPDATE
Issued at 832 PM MDT Fri May 17 2024

Only minor changes needed at this time as very weak convection continues west of the Front Range, and over the northern border and east central Colorado. There's little rain actually reaching the ground and we've likely seen the last of the lightning.
Grids have been adjusted for current conditions, with more clouds now and then better clearing by morning.

SHORT TERM /Through Saturday/
Issued at 259 PM MDT Fri May 17 2024

Satellite shows shallow cumulus developing across the area. There is a little deeper growth noted over northwest Colorado, with a few showers starting to develop. With just enough destabilization but dry low levels, we expect isolated to scattered high based light showers/sprinkles in the high country/northern border area through this evening, with only a rumble or two of thunder possible. The rest of the plains and I-25 Corridor will only see some virga, but can't rule out some gusty outflow winds due to well mixed and relatively deep sub-cloud layer.

On Saturday, both moisture and instability build a little more with a weak shortwave noted in the QG fields. At the surface, a weak cold front backdoors across the plains late tonight/early Saturday morning. There is slight cooling noted in the boundary layer, but enough daytime heating still expected to weaken the cap and allow scattered showers/storms in the mountains to eventually spread onto part of the plains late in the afternoon. There is a little more MLCAPE with 200-400 J/kg noted, so expect a few more lightning strikes and rumbles of thunder. The most favored locations would stay generally south of I-76. Temperatures should be a few degrees cooler behind the front, but still a few degrees above normal. Southeast breezes will increase through the afternoon.

LONG TERM /Saturday night through Friday/
Issued at 259 PM MDT Fri May 17 2024

Scattered showers and thunderstorms should continue along areas south of Denver Saturday evening. It is likely areas will lack instability especially after the front thus leading to weak high based showers spreading into the plains through southerly flow until Sunday night. Low temperatures range between 45-55F for the Palmer Divide and plains. For the higher elevations, temperatures drop between 30-39F. Partly cloudy skies persist through Sunday.

Cross sections display drier air and weak mid-level moisture mainly in the high country Sunday. Zonal flow will increase resulting in wind gusts up to 25-35 mph for foothills below timberline through Sunday afternoon. NBM retains too much PoPs for weak mid-level moisture afternoon for the foothills and plains thus this forecast update reduced PoPs for likely (35-50%)chances of showers mainly in Jackson and northern Larimer counties.
Expect light rain and gusty winds up to 40-45 mph if a shower collapses.

High uncertainty lingers for Monday night and Tuesday synoptic pattern. 500mb heights across ensembles favor a shortwave trough entering no eastern Colorado mainly Monday through Tuesday. ECMWF seems to favor a less robust system with an open broad trough sweeping north of our region while the GFS favors a deeper trough entering the western mountains then pushing into the center of our CWA Timing seems to be delayed where majority of this system occurs Tuesday. Given this pattern, it is possible PoPs may have to be reduced Monday afternoon. Higher confidence remains in the general outcome of numerous showers and storms Monday night into Tuesday late morning. This pattern would likely lead to impacts such as brief heavy rainfall and small hail. Additionally, cooler temperatures are possible each afternoon Tuesday and Wednesday.
Overall, this cool down seems short lived as temperatures bounce back near normal Thursday.

AVIATION /00Z TAFS through 00Z Sunday/
Issued at 832 PM MDT Fri May 17 2024

VFR through Saturday. West winds will decrease and may become a bit more southwest by 06z. A weak cold front will produce north winds on the plains Saturday morning, but struggle to get into Denver making the morning wind forecast tricky. It will likely become east to southeast by 18z and then more south to southeast later in the day at 10 to 20 knots, but the direction may be northeast for a few hours in the morning at KDEN. Scattered showers and a few thunderstorms are expected after 21z.

BOU WATCHES/WARNINGS/ADVISORIES
None.

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