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FXUS65 KBOU 220121 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 721 PM MDT Tue May 21 2024

KEY MESSAGES

- Scattered showers and isolated thunderstorms continue through this evening. Small hail and gusty winds are possible from the storms.

- Ongoing light snow showers may lead to slick travel along mountain passes through Wednesday morning.

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

UPDATE
Issued at 721 PM MDT Tue May 21 2024

Updated to increase PoPs over the plains where there is a good amount of rain showers now, and one more scattered batch to come, which is crossing the Urban Corridor. Though skies are mostly cloudy to overcast now, the airmass stabilizes and drier air moves in overnight resulting in mostly clear skies after midnight.
Lowered temperatures a couple degrees, which puts overnight lows in the 30s. The typical low lying areas may fall into the lower 30s and may see frost. Therefore issued a Frost Advisory for tonight and early Wednesday morning with temperatures falling to 32-37 degrees.

SHORT TERM /Through Wednesday/
Issued at 241 PM MDT Tue May 21 2024

Radar reflectivity has increased across the foothills and plains displaying scattered to numerous showers. A few webcams along mountain passes present flurries for areas above 8,500 feet. This pattern will continue as the shortwave trough passes through northeastern Colorado. Snowfall totals for areas above 9 thousand feet range between 1-4 through Wednesday morning. Showers should become isolated by midnight tonight. With model soundings along the plains showing an inversion and low level moisture lingering through early morning Wednesday, it is possible patchy fog could occur along I-25 corridor near the Wyoming Colorado border and along I-76 near Morgan county.

Cross sections indicate drier air throughout the 500-700mb layer thus limiting any storm development Wednesday afternoon. An isolated shower or two could occur for the southern foothills and Palmer Divide but chances are low (10-15%). Wednesday afternoon 700mb ing.temperatures range between 3-6C along the foothills and plains which should lead to a slight warm up compared to yesterday. Foothills and plains range from 60-72F Wednesday afternoon; Additionally, the mountains and valleys increase near 45-60F. Partly cloud skies will begin to clear by late Wednesday afternoon.

LONG TERM /Wednesday night through Tuesday/
Issued at 241 PM MDT Tue May 21 2024

Colorado will be under the influence of a quasi-zonal flow Wednesday night through Monday with occasional upper level shortwaves and cold fronts moving across the Northern and Central Rockies. This pattern should result in near normal temperatures along with isolated to scattered afternoon and evening showers and storms across the forecast area most days. Warm temperatures combined with breezy conditions and low relative humidity may lead to fire weather concerns across South Park, the Palmer Divide and much of the plains Thursday afternoon and evening. A cold front expected to move across Northeastern Colorado Friday evening may produce wind gusts up to 35 mph across the northern sections of the plains.
Friday should be the coolest day of the week in the wake of the front with temperatures only climbing into the upper 60s on the plains. Most of the showers and storms during this period should be high based with gusty winds and brief light to moderate rain.
However, there is the potential for some stronger storms across the plains, mainly east of the Front Range Urban Corridor, both Thursday and Saturday afternoon/evening due to better available surface moisture along with increased convergence and lift associated with the passing shortwaves and cold fronts.

Warmer and drier weather is expected on Tuesday as upper level high pressure builds over the Rocky Mountain Region.

AVIATION /00Z TAFS through 00Z Wednesday/
Issued at 543 PM MDT Tue May 21 2024

Threat for showers continues through 03Z with ceilings down to 4000 feet. Chances for a thunderstorm continue to decrease as the showers stabilize the airmass. However, can't totally rule out a brief weak thunderstorm affecting the terminals. Drier moves in overnight with mostly clear skies expected by 06Z. Southerly winds should prevent fog from forming. Best chance for fog will be in the low lying areas north of Denver, in the GXY area. For Wednesday, southerly winds to continue through the morning.
Eventually expect a Denver Cyclone to form. As the cyclone progresses eastward, a wind shift from the south to the north to northwest is expected sometime after 20Z.

BOU WATCHES/WARNINGS/ADVISORIES
Frost Advisory from midnight tonight to 8 AM MDT Wednesday for COZ038-041>047-049.

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