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FXUS65 KBOU 211147 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 547 AM MDT Tue May 21 2024

KEY MESSAGES

- Cooler today, with another round of afternoon showers and thunderstorms. Small hail and gusty winds are possible from these storms but they will likely stay below severe limits.

- On and off snow showers across the high country through tonight, with light accumulations across the higher mountains. Some travel impacts possible along the mountain passes this morning and later this evening.

- Warming/drying trend for the second half of next week with elevated fire weather conditions likely Thursday.

SHORT TERM /Through tonight/
Issued at 333 AM MDT Tue May 21 2024

The weather has settled down a bit since Monday evening, with radar showing several areas of scattered showers and a couple of thunderstorms across the eastern plains. Water vapor satellite shows the initial shortwave lifting across northeast Colorado this morning, with the main trough axis still lingering of to our west. Meanwhile, a surface low is now located over west- central Kansas, with our cold front now draped to our south, per WPC surface analysis and recent obs.

Shower activity should decrease later this morning, with some low cloud cover persisting through most of the day. Cooler temperatures will prevail tomorrow behind the cold front, with highs remaining in the upper 50s to low 60s for the plains and urban corridor.

The trailing shortwave with this trough is expected to push across the forecast area by this afternoon, and the lift from this and the shallow but persistent upslope flow should provide the forcing for another round of showers and a few thunderstorms.
Model soundings show meager CAPE this afternoon, and severe weather is not anticipated. However, any stronger storms would be capable of producing briefly gusty winds and small hail.

Meanwhile, snow levels will hover near 8500 feet today and gradually lower later this evening. An ongoing burst of snow has produced some slushy/snow covered roads across the I-70 mountain corridor this morning... and snow showers will continue on and of through the day with light accumulations. Widespread travel impacts are not anticipated with this, but a few brief periods of slick travel conditions will be possible through the evening.

Showers and storms may linger into the evening/early overnight hours tonight for the plains with a few snow showers across the higher elevations, but drier air will quickly work into the region behind the trough. Expect clearing skies and cool overnight lows into Wednesday AM.

LONG TERM /Wednesday through Monday/
Issued at 333 AM MDT Tue May 21 2024

Wednesday will bring warmer and drier conditions to the forecast area as the upper level low shifts to the northeast and relatively weak zonal flow aloft develops. Weak ridging at the 500 mb level will quickly traverse across the area as another upper level low makes its way ashore over the PNW. High temperatures on Wednesday will be a few degrees below normal, however, still climb to the low 70s across the foothills and plains, and high 50s to low 60s for most of the mountains and valleys. Forecast soundings indicate increasing instability in the afternoon as mid level lapse rates steepen that could allow for some isolated showers or thunderstorms to develop across the eastern plains.

Southwesterly flow will develop on Thursday as the aforementioned upper level low over the PNW shifts east into Idaho/Montana/Wyoming and skirts just to the north of Colorado.
Guidance is in agreement that the main forcings from this disturbance will stay to the north of our forecast area, but we will see some increasing moisture as well as an associated cold frontal passage through northeastern colorado Thursday night.
Temperatures will be in the high 70s Thursday afternoon across the plains and foothills, and 50s to 60s for the mountains, but with the passing cold front, temperatures will drop into the 20s and 30s overnight for the mountains and valleys that could allow for some light snow showers to develop over these areas. Ahead of the cold front, warm and dry conditions will bring elevated fire weather conditions to portions of the urban corridor, South Park, and the Palmer Divide. Behind the cold front, Friday will be quite cooler than Thursday with high temperatures barely reaching the mid 60s for the foothills and plains, which is roughly 10 degrees below the norm for this time of year.

The active weather pattern will continue through the weekend with daily chances for afternoon scattered showers and thunderstorms as temperatures return to the mid to high 70s for the weekend.

AVIATION /12Z TAFS through 12Z Wednesday/
Issued at 541 AM MDT Tue May 21 2024

A batch of weak showers is pushing across the metro this morning, which has also come with a push of light westerly winds. This has been enough to push most of the stratus away from Boulder/BJC and trends suggest that we'll see a return to VFR in the next hour or two at DEN/APA. VFR should continue into the early afternoon once it does establish.

Additional showers and thunderstorms are forecast by early/mid afternoon at the terminals. Better confidence in timing for today with most guidance favoring somewhere between 20-00z this afternoon. Main concern would be gusty winds but can't rule out some small hail as well. Beyond that, showers may linger into the evening hours with the potential for some briefly lower cigs in the evening. Cloud cover should diminish quickly as we approach 06z with drainage flow establishing around that time as well.

BOU WATCHES/WARNINGS/ADVISORIES
None.

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