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FXUS65 KBOU 192331 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 531 PM MDT Fri Apr 19 2024

KEY MESSAGES

- Springtime snow in the Rockies, with accumulations expected in most locations tonight through Saturday morning.

- Slick and hazardous travel in the foothills, and possibly onto the adjacent plains into Saturday morning

- Cold through Saturday, then drier and warmer for Sunday through much of next week.

SHORT TERM /Through Saturday/
Issued at 257 PM MDT Fri Apr 19 2024

Current radar shows banded precipitation has made its way off the higher terrain and is moving eastward across the plains. While there is not one 'main' forcing responsible for this banding, there are a multitude of weaker forcings at play providing enough lift for these bands to develop. While the westerly jet stream aloft is a tad north and east of CO to supply robust lift, modest lift is occurring in northeastern CO due to its proximity to the jet's right entrance region. Within the upper level flow, a shortwave trough will pass over the forecast area tonight bringing weak PVA. Additionally, weak 600-500 mb frontogenesis is present, and light northeasterly surface winds will bring weak upslope flow to the Front Range Mountains and Palmer Divide. A Winter Weather Advisory remains in effect from 6 PM this evening through 9 AM tomorrow for these locations.

Guidance are in good agreement with location and amounts, however, banded precipitation can be tricky to pinpoint exact location, therefore there may be some localized heavier amounts mixed in with forecast totals. Lower elevations across the plains can expect 1 to 3 inches. The foothills can expect to see 3 to 6 inches, and up to 10 inches are possible for the highest mountain elevations.
Travel may be slick for tonight's evening commute underneath locations where snow bands develop. Snowfall should taper off in the morning with some lingering showers possible through the afternoon.

LONG TERM /Saturday night through Friday/
Issued at 257 PM MDT Fri Apr 19 2024

The second half of the weekend will feel much more like spring, as ridging builds across the Rockies. Guidance is in good agreement with westerly flow developing across the forecast area, with warm air advection also aiding in getting warmer temperatures back into the area. This airmass also will be drier, with cloud cover quickly dissipating through the day. Temperatures should make it back into the 60s across the lower elevations, though this may depend a bit on how quickly moisture moves out Sunday morning.

The warming trend should continue Monday, with highs likely returning to the 70s across the plains. There should be a bit more moisture embedded in the westerly flow aloft, which combined with some weak/broad ascent and instability... could lead to some widely scattered showers and perhaps an isolated thunderstorm.

A cold front is expected to drop into the region sometime Monday afternoon or Monday night, ushering in briefly cooler temperatures. However, the day to day pattern will not change significantly, as a series of weak shortwaves/pockets of moisture traverse the region over the course of the week.

By the end of next week, guidance does begin to diverge a bit.
There is broad agreement on broad upper trough axis swinging across the Pacific Northwest into the central Plains by next weekend. The GFS is a bit quicker and stronger with a lead shortwave, leading to a bit wetter end of the week, while other guidance keeps us mostly dry until next weekend. The model blend in this time period appears to be a good enough middle ground for now, and we'll hope for more model certainty on another day.

AVIATION /00Z TAFS through 00Z Saturday/
Issued at 524 PM MDT Fri Apr 19 2024

Snowbands continue to decrease visiblities at all sites between LIFR to IFR conditions. This pattern will persist due to snowbands drifting south and additional bands forming north from the foothills to plains. Expect conditions to improve by 14-16Z at all terminals as snow bands end. There is potential for lingering low clouds through 23Z thus will keep vis at MVFR conditions for potential fog. Cloud decks lift slightly near 2k ft by Saturday evening.

BOU WATCHES/WARNINGS/ADVISORIES
Winter Weather Advisory until 9 AM MDT Saturday for COZ033>036.

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