Sunrise 6:03 AM   Sunset 7:53 PM Moonrise 11:18 PM   Moonset 7:05 AM

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FXUS65 KBOU 270826 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 226 AM MDT Sat Apr 27 2024

KEY MESSAGES

- Significant snowfall (1 to 3 feet) for the mountains and foothills through tonight.

- Snow level falling to 6000 to 7000 feet MSL.

- Rainfall amounts through tonight of 1 to 3 inches for the lower foothills, Urban Corridor, and eastern plains.

SHORT TERM /Through tonight/
Issued at 208 AM MDT Sat Apr 27 2024

Today, widespread precipitation will drop anchor across the forecast area. The next upper low over the Great Basin early this morning, is progged to shift into central CO by this evening then into southwest NE by 12z Sunday. Moderate mid/upper level QG ascent will develop over the northeast CO this morning, in a diffluent and deep south/southeasterly layer. It will be moist adiabatic through the layer, with enough instability to produce thunderstorms as well. Consequently, heavy snow will develop in the mountains and foothills, with the snow level around 8,000 feet and down to around 6500 feet by later this afternoon. After coordination with the PUB office, we moved up the timing of the Winter Weather Advisory over the Palmer Divide to 3 AM vs 6 AM this morning. Otherwise, no other changes to the highlights at this time. 24-hr qpf still generating anywhere from 1 to 3 inches of water across the forecast area.

The HRRR models do indicate a few strong storms developing over Lincoln County this afternoon, with an upper level jet passing to the south and east of there. SPC has a marginal risk of severe thunderstorms this afternoon, with the main threat hail up to quarter size. By 00z this evening, the strongest QG ascent will shift towards NE/KS and the flow aloft should start to shift to the north/northeast. Widespread precipitation should continue through the evening, but the intensity should decrease. Once the precipitation tapers off, could see patchy fog late tonight into Sunday morning but not enough confidence in this outcome to include it in our grids yet.

LONG TERM /Sunday through Friday/
Issued at 208 AM MDT Sat Apr 27 2024

Upper level low will move into the Nebraska panhandle early Sunday morning and continue to pull away from Colorado Sunday.
Wrap around rain showers are expected to linger into Sunday morning over far northeast Colorado. In addition to this, scattered snow showers will continue Sunday in the mountains.
Northwest flow behind the low will produce downslope conditions along the Front Range and nearby plains. This is expected to lead dry conditions for most of Sunday, though isolated to scattered showers are expected to develop during the afternoon when it gets a little unstable. Scattered snow showers continue through the day in the mountains with up to 3 inches of snow possible.
Temperatures rebound into the upper 50s to lower 60s over northeast Colorado.

Weak ridging in the westerly flow aloft will prevail Monday. This will produce mild and dry conditions. Highs are expected to warm up into the mid to upper 60s. Right behind this ridging, an upper level trough will track across Montana and Wyoming. This wave and the left exit region of the jet may bring showers late Monday and Monday night to northern Colorado. A shallow cold front will also drop south across eastern Colorado Monday night. Though highs behind it Tuesday don't change much from Monday. There will be a chance for showers and storms Tuesday afternoon over the plains.

For Wednesday and Thursday, an upper level low over Idaho and Montana digs southeast. Models are still zeroing in on the track.
This system could stay north of Colorado and track east across Wyoming, or like the ECMWF, it could dive farther southeast into Colorado. With this being a stronger system, even if it stays north of Colorado, the cold front and moisture associated with it should produce scattered showers and storms late Wednesday and into Thursday. If this system digs farther south, a widespread rain and mountain snow event will be possible. Temperatures trend cooler and by Thursday and highs may only be in the 50s over northeast Colorado.

AVIATION /06Z TAFS through 06Z Sunday/
Issued at 1122 PM MDT Fri Apr 26 2024

Persistent rainfall and low cloud decks through the period. MFVR conditions early in the period will deteriorate to IFR shortly (after 08z) and continue through the period. There is a low probability of a rain/snow mix at APA or BJC, which could lower the ceilings/vsbys further. Surface winds will transition from NNW to NE after 08z and continue that way through the rest of the period. Sustained winds in the 8-12kt range can be expected. Once the precipitation settles down by the end of the period, fog may also need to be addressed in the outlook period for DEN (06-12Z Sunday).

BOU WATCHES/WARNINGS/ADVISORIES
Winter Storm Warning until midnight MDT tonight for COZ033-034.

Winter Storm Warning until 6 AM MDT Sunday for COZ035-036.

Winter Weather Advisory until midnight MDT tonight for COZ037-COZ041.

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