Sunrise 6:08 AM   Sunset 7:47 PM Moonrise 7:51 PM   Moonset 5:54 AM

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FXUS65 KBOU 230530 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 1130 PM MDT Mon Apr 22 2024

KEY MESSAGES

- Cooler Tuesday, but then above normal temperatures again for Wednesday and Thursday.

- Stormier weather pattern in the works, starting late Thursday and peaking next weekend.

- Stronger storms possible northeast plains Thursday afternoon/evening.

UPDATE
Issued at 903 PM MDT Mon Apr 22 2024

Minor adjustments to precip chances this evening to cover isolated virga/high-based showers in the mountains and northern plains.
Front still slated to push through the plains during the early morning hours, but no precipitation associated with it.

SHORT TERM /Through Tuesday/
Issued at 122 PM MDT Mon Apr 22 2024

For the rest of the afternoon, a few weak showers are possible across the high country and northeast corner of Colorado. Snow levels are all the way up to the highest mountain passes. Any precipitation that reaches the ground will be very light, and no precip is expected to reach the ground across the I-25 corridor.
Virga and gusty winds look to be the main impacts, though there are already WNW winds gusting 20-30 mph across portions of the plains. Winds will die down after 7 PM with decoupling.

Tonight a cold front moves across the plains from north to south between 2-4 AM, and will probably reach up to 8500 ft across the eastern foothills. We use the word "cold" lightly because temperatures behind the front should only be 10 degrees cooler initially. Lows across the plains should remain above freezing, with 30s across most of the plains, but 40ish across the I-25 corridor, lowest foothill locations, and the urban heat islands.
The front does not impact the West Slope whatsoever, and with partly to mostly cloudy skies, lows will be warm in the low 30s across the mountain valleys. The air behind the front is dry so we are not expecting any post frontal precipitation through late morning Tuesday. Just ahead of the 500 mb ridge, there is weak synoptic scale lift in place across the area, and above the frontal boundary enough heating should result in isolated afternoon/evening showers and thunderstorms. The snow level should again be above 10kft, and with 100-300 J/kg SBCAPE in place, there is a chance of a few rumbles of thunder. All told, the chances of measurable precip are still pretty low across the high county, between 20-40% for the valleys, and close to 50% above 10kft. Amounts will be light.

Across the plains on Tuesday, behind the front light east winds 5-15 mph are expected throughout the day. Dewpoints will remain in the low to mid 30s, and with the strong frontal inversion near 700 mb, there is zero SBCAPE and effectively no MUCAPE east of the Rockies, so any convection that moves off the mountains will be hard pressed to generate enough precipitation for it to reach the ground. Virga and a few sprinkles may occur across the I-25 corridor. Increasing QG lift occurs Tuesday evening with better precip chances across the plains (covered immediately below in the long term section). With ample cloud cover and a cool post- frontal airmass, expect highs Tuesday to remain in the low 60s across most of the plains. The northern tier of counties should be mostly clear to party cloudy, and thus a little warmer in the mid 60s. The mountain valleys will be above the frontal inversion, blocked by the Rockies, and highs should be in the upper 50s to around 60 until showers/isolated storms web bulb the temperatures into the 40s where/when precip falls.

LONG TERM /Tuesday night through Monday/
Issued at 122 PM MDT Mon Apr 22 2024

Scattered showers and isolated storms will linger into the evening hours in the post frontal airmass. The loss of daytime heating will stabilize the airmass, causing the convective activity to weaken as it progresses eastward. Could see a few showers linger past midnight over the far eastern plains. By sunrise Wednesday morning, northeast Colorado will be dry.
Temperatures warm back up Wednesday as an upper level ridge moves over the Central Rockies. Mostly sunny skies will help temperatures climb into the mid to upper 70s. A weak wave rounds the top of the ridge, and could bring a few weak showers and storms to far northern Colorado Wednesday afternoon/evening.

Flow aloft turns southwesterly as the an upper level trough over the Desert Southwest pushes the ridge east of the region. This is expected to keep temperatures mild with highs in the 70s again. At the surface, pressure lowers along the Front Range in advance of the upper level trough. Southeast winds over the plains will advect moisture into eastern Colorado pushing dew points into the 40s, and possibly lower 50s. Expect an area of decent instability (SB CAPE 750-1500 J/kg) over eastern Colorado Thursday afternoon.
Lift from the trough will trigger showers and storms, some of which could become strong to severe over the northeast plains.

For Friday, weak ridging will bring a dry start to the day.
Models show the airmass becomes unstable during the afternoon with showers and weak storms possible. Expect cooler temperatures for Friday with cold air advection behind Thursday's system.

For the weekend, a large better organized system will be tracking across the western half of the country. Temperatures are expected to continue to cool off. We will likely (60-80%) see a round of showers and mountain snow on Saturday. Some models (like the ECMWF) speed up this system with dry conditions possible for Sunday, so will have the highest PoPs on the Saturday. Heavier precipitation (1-2 inches) remains possible this weekend, though if the faster solutions pan out, amounts may end up on the lighter side.

AVIATION /06Z TAFS through 06Z Wednesday/
Issued at 1129 PM MDT Mon Apr 22 2024

VFR expected to prevail for all terminals this period. Another frontal surge is expected to arrive around 09Z with a northerly wind shift. Then winds may relax to more NW or even W 12Z-15Z, before daytime heating/mixing allow a more northeast and eventual easterly wind to persist most of the 15Z-03Z period. There is still potential for enough low level moisture for mainly SCT clouds around 3,000 ft AGL, but the upstream observations are not very moist so the odds of a ceiling at that level are quite small (<20%).

We'll see scattered but mainly high based showers develop in the area late in the afternoon and evening (21Z-05Z), and there's enough chance to warrant a PROB30 in the TAFs. The ceilings are expected to hold mostly around 8,000 ft AGL, but with the scattered showers around local ceilings down to 5,000 ft are possible with Instrument Meteorological Conditions (IMC).

BOU WATCHES/WARNINGS/ADVISORIES
None.

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