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FXUS65 KBOU 032125 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 325 PM MDT Fri May 3 2024

KEY MESSAGES

- A few showers and storms across the eastern plains this afternoon into tonight.

- Warmer and windy on Sunday.

- Active, cooler, and mainly windy pattern from late Sunday through most of next week. A few chances of accumulating snow across the mountains with isolated/scattered showers across the plains.

SHORT TERM /Through Saturday/
Issued at 303 PM MDT Fri May 3 2024

Current analysis shows a lee cyclone across the Palmer Divide area.
From the north, a cold front is advancing southward with a push of gusty northerly winds behind it. Gusts 35-45 mph are being reported across the region from the front. Along this front, a line of thunderstorms moves across the northeastern plains. SPC mesoanalysis shows an axis of marginal instability across the far east plains (< 500 J/kg SBCAPE). This is overall supported by an shortwave trough moving eastward just north of the Colorado border. For the remainder of the afternoon and into the evening expect showers in the mountains with another round of showers moving across the northern border onto the plains. Areas such as Lincoln County remain unstable ahead of the advancing front, so can't rule out any shower or storm development in those areas in the next hour.

Showers linger across the mountains this evening with remaining showers/storms exiting the eastern plains. Behind the front, temperatures cool sufficiently overnight with lows in the low to mid 30s across the plains. We are approaching Frost/Freeze headline territory for areas on the plains; however, given its current rating of mixed susceptibility for vegetation and closeness to average last freeze, we decided to hold off on headlines. For tomorrow, expect cooler temperatures with highs in the 60s across the plains, 50s for foothills/mountain valleys, and 40s for the mountains. Expect another round of showers and a few storms in the afternoon (marginal CAPE), mainly over the higher elevations and south of I-70.

LONG TERM /Saturday night through Friday/
Issued at 303 PM MDT Fri May 3 2024

A strong upper low will be located near northern California on Sunday morning, with increasing south-southwesterly flow over our forecast area through the day. The result will be a warm, dry, and breezy end to the weekend as the dryline shifts towards the CO/KS/NE border. Temperatures should warm into the mid to upper 70s. Model soundings suggest boundary-layer average winds of 30-45kt, which would lead to wind gusts of 45-55 mph.
Some guidance keeps just enough moisture out in the far eastern plains for an isolated shower or storm, though the models that keep some moisture here also maintain a strong cap through the day.

The closed upper low is expected to transition to a sharp, negatively tilted trough axis by Monday morning... which then ejects into the northern Great Plains from Monday into Tuesday. A quick round of mountain snow is likely with the passage of the trough axis, though cross-sections show somewhat sparse moisture on this side of the trough. For the plains, a few showers will be possible, but the main story will be wind. A bora-like event appears likely as a colder westerly flow develops. Temperatures will hover in the upper 50s/low 60s. Gusty winds will continue, especially across the high country.

Zonal flow is expected to persist Tuesday into Wednesday as the upper trough stalls over the far northern Great Plains. Guidance shows a bit of moisture lingering in this flow, which would lead to scattered snow showers across the high country while the plains remain generally dry. With fairly strong mid-level flow, gusty winds will be slow to subside in this period.

As we get into the latter half of next week, there is increasing uncertainty in the overall synoptic pattern. Recent guidance attempts to stall out the trough or even retrograde it back to the south and west. Unsurprisingly, ensemble guidance lacks a clear, definitive signal, with a substantial amount of spread for T/QPF as we get into Thursday/Friday of next week. We'll likely have a ways to go until we see better agreement in this timeframe... but at the very least, it does appear that a cool and unsettled pattern will continue.

AVIATION /18Z TAFS through 18Z Saturday/
Issued at 1155 AM MDT Fri May 3 2024

VFR conditions expected for the TAF period. Breezy S/SSE winds being observed at the terminals early this afternoon. This puts a slight delay on the forecasted SW winds. Within the next 1-2 hours winds should turn more SW ahead of the incoming front. Front will likely across the terminals in the 21-23z timeframe with a brief push of gusty N/NNE winds behind in (Gust 25-35kts). Winds turn more NE after 00z with weaker gusts than the initial push (G20-25 kts). Showers and storms develop on the plains around the front timeframe. Although they should remain clear of the terminals, can't rule out the potential for outflows/variable gusts from showers set up to the north and east. Overnight, winds decrease becoming light ENE/NE. Saturday morning winds turn SE increasing to 8-10 kts by late morning.

FIRE WEATHER
Issued at 303 PM MDT Fri May 3 2024

Increasing fire danger is expected late this weekend into early next week behind the strong storm system. Gusty winds should develop on Sunday and continue daily through at least mid-week, with a gradual drying trend from Sunday through Tuesday. Near- critical to critical fire weather conditions appear likely across portions of the lower elevations at times, especially south of I-70. However, recent rainfall and ongoing green-up across the plains may limit overall fire danger. Still a couple of days out at this point, so no watches have been issued... but we'll be watching closely as we get into the weekend.

BOU WATCHES/WARNINGS/ADVISORIES
None.

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