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FXUS65 KBOU 252109 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 309 PM MDT Thu Apr 25 2024

KEY MESSAGES

- Ongoing severe threat across northeast Colorado will continue for a couple hours this afternoon, with a hail and tornado threat. Less organized rain showers occasional showers and an isolated thunderstorm or two across the mountains and metro

- Red Flag conditions continue across portions of Elbert and Lincoln county this evening

- Cooler on Friday, with scattered showers continuing.

- Significant snowfall likely (70-80% chance) in the mountains Friday night through Saturday night, widespread rain showers over the plains

- Warmer and drier early next week

SHORT TERM /Through Friday/
Issued at 233 PM MDT Thu Apr 25 2024

Satellite shows a potent/negatively tilted trough axis centered near the Four Corners region. This trough is expected to continue to deepen as it ejects into the central plains later this evening.
Meanwhile... a few thunderstorms have developed in Washington county in the last hour or so. The edge of our CWA is also roughly the edge of the favorable environment for severe weather. This threat should continue through the next few hours before shifting east into Nebraska/Kansas.

Further west, some weak showers have developed across the high country and foothills, though this activity has remained fairly weak so far. This should gradually become a bit more organized this evening as the trough axis pivots across the state. There's still some uncertainty if Denver/I-25 corridor get into any showers/storms later this evening, with CAMs offering many solutions but zero answers. At least some scattered showers will continue overnight in the wake of the trough, especially across the mountains. Some light mountain snow is also expected with a couple inches of slushy accumulation possible above 10000ft.

Friday will be a bit of a transition day in between systems, as the first trough axis cuts off and stalls over the central Plains/Midwest, while another trough approaches from the west.
Cool northwesterly flow on the back of the initial trough will keep temperatures cooler and breezy across the plains. With moisture increasing again in advance of the second trough, there should be a gradual increase in showers later in the afternoon yet again. Still this won't compare to the rain and snow coming this weekend... which you can read more about below.

LONG TERM /Friday night through Thursday/
Issued at 233 PM MDT Thu Apr 25 2024

Much cooler and wetter weather is expected over the weekend as a closed upper low tracks from the Four Corners Region across Southern and Central Colorado. Snowfall rates should increase in the mountains during Friday evening as QG ascent and moisture increase ahead of the upper low. Precipitation should also increase across the plains as upslope flow develops behind the passage of a weak cold front. The heaviest precipitation Friday night should be focused from the Continental Divide eastward across the foothills and Front Range Urban Corridor. Models are suggesting enough convective instability during the evening to produce a few thunderstorms leading to higher precipitation rates.
There may be a lull in the precipitation during the early morning hours with precipitation ramping back up again by sunrise as the flow around the mid and upper level low results in increasing moisture and easterly upslope flow along and east of the mountains. Widespread precipitation is expected to continue across most of the forecast area through the Saturday evening as the upper low slowly drifts east to northeast across the state. Models are showing 2 to 3 inches of QPF from the Front Range Mountains eastward across the Front Range Urban Corridor and Palmer Divide with lesser amounts further east across the plains. The mountains should see snow amounts from 6 inches to possibly over 2 feet with the heaviest amounts over the Front Range Mountains above 10,000 feet. Therefore, have issued a Winter Storm Watch for these areas effective Friday evening through late Saturday night. There is also the potential for a few inches of snow across the higher portions of the Palmer Divide as well.

Precipitation should decrease across Northeastern Colorado on Sunday with some gusty winds to 30 mph as the upper low moves into the Northern Great Plains States. Across the high country, periods of snow showers should continue due a moist westerly flow aloft.
Warmer and drier weather is expected Monday through Wednesday due to some weak ridging aloft. However, scattered (25%- 40%) snow showers will still be possible each day over the higher mountains.

AVIATION /18Z TAFS through 18Z Friday/
Issued at 254 PM MDT Thu Apr 25 2024

Difficult aviation forecast. Ongoing weak showers are producing gusty outflow, and this could continue through the evening hours across the Denver metro. Cloud bases will briefly drop with some of these showers as well. The predominant flow will be east/northeasterly through the afternoon, with a shift to north/northwesterly flow later this evening. Scattered showers will remain possible through the overnight period. Can't rule out a brief period of TSRA but wasn't confident enough to include in the TAFs.

Afternoon showers are possible again on Friday, with similar hazards of briefly lower cigs and gusty winds.

FIRE WEATHER
Issued at 233 PM MDT Thu Apr 25 2024

Moisture has been slow to mix out along and south of I-70 this afternoon, but recent trends over the past couple of hours suggest that rapid drying is ongoing. Some unofficial stations across southern Lincoln county have approached RFW criteria in the past hour, and this is expected to be the case across the current Red Flag Warning area through mid/late afternoon. Will keep the current highlight in place.

Cooler weather is expected on Friday. Despite increasing northwesterly winds, RH values should remain high enough to avoid critical fire weather conditions.

BOU WATCHES/WARNINGS/ADVISORIES
Winter Storm Watch from Friday evening through late Saturday night for COZ033-034.

Red Flag Warning until 8 PM MDT this evening for COZ246-247.

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