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FXUS65 KBOU 192130 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 330 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 /18Z TAFS through 18Z Saturday/
Issued at 1142 AM MDT Fri Apr 19 2024

Continued ceiling and weather impacts through the TAF period.

Light rain/snow showers are moving east off the mountains and will be over all airports by 19Z. The Denver Cyclone is keeping winds westerly a tad longer at KDEN but they are expected to turn NE by 21Z. Precipitation is expected to turn to all snow between 1-2Z this evening. Uncertainties remain on snowfall totals as heavy precipitation is possible if a snow band sets up over the airports. Accumulations of 1-4 inches are expected on grassy surfaces and slushy accumulations are possible for runways.

BOU WATCHES/WARNINGS/ADVISORIES
Winter Weather Advisory from 6 PM this evening to 9 AM MDT Saturday for COZ033>036.

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