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FXUS65 KBOU 182053 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO Issued by National Weather Service Pueblo CO 253 PM MDT Thu Apr 18 2024

KEY MESSAGES

- Cool and cloudy with rounds of snow through Saturday morning.

- Best chance of accumulating snow Friday afternoon into Saturday morning.

- Drier and warmer early next week.

SHORT TERM
(This evening through Saturday)
Issued at 242 PM MDT Thu Apr 18 2024

Post frontal upslope flow continues which will lock stratus in across the plain as periods of overrunning associated with passing disturbances move through westerly flow aloft. Snow bands redevelop overnight across the front range and spreads eastward bringing some additional light snow through early Fri morning. A stronger round of upper lift associated with the next wave in westerly flow spreads in late Friday through Saturday morning.
This will bring another more widespread snow event to the region, with HRRR probabilities of 3 inches in the 40-60% range across a large portion of NE CO through early Saturday morning, though warmth of ground and pavement surfaces may mitigate impacts to some degree across the lower elevations. Probabilities for 6" or more really tail back quickly across the lower elevations though some HRRR probs do show an area of 50% probs along front range mountains. Some light snow continues into Saturday morning before drying spreads in behind the wave through the day. Stratus may hang in most of the day across the plains as focus for precipitation shifts southward. Temperatures will remain below normal through the period.

LONG TERM
(Saturday night through Thursday)
Issued at 242 PM MDT Thu Apr 18 2024

Upper ridge builds in then flattens as the next closed low passes to the north on Monday. Temperatures rebound back into the 60s to around 70 across the plains for Sunday and into the 40s and 50s for the mountain communities. This wave brings another brief round of snow Sunday night across the mountains but accumulations stay light.
Monday gets windy and warm again which could bring some near critical fire weather conditions to portions of the plains. For now RH values stay above the 15 percent critical thresholds. A minor drop in temperatures expected for Tuesday behind another front which drops through the region Monday night. Post frontal upslope flow may generate some mountain showers across the region Tuesday afternoon and evening.

Timing of the next system in southwest flow for mid to late week is still in question among the models/ensembles. For now it looks like we enter another dry and windy southwest flow pattern with another uptick in mountain precipitation late week.

AVIATION
(For the 00Z TAFS through 00Z Saturday afternoon)
Issued at 242 PM MDT Thu Apr 18 2024

Active pattern with low ceilings, periodic drizzle or light rain, with eventually snow returning to the TAF sites at the every end of the forecast period Friday evening.

Latest radar imagery depicting continued drizzle and light rain across all of the terminals, with observational data indicating any snow remaining confined to the higher terrain. While coverage of the drizzle or light rain should decrease this evening, still think it will be occasionally observed for much of the night. Some guidance showing a possibility for a small window of snow very late tonight into early Friday morning, but think there is a very low chance of this occurring at this time. Vis under this precip should be 6 miles or more but by late evening, will see vis begin to fall, with vis 3- 5sm appearing likely under additional BR development later tonight into Friday morning. The improvement to higher end MVFR ceilings this afternoon should be the last of any improvement, as a slow downward trend is likely once again tonight into Friday morning.
While can't completely rule out a return to IFR ceilings, think a more likely solution at this point is MVFR ceilings in the 1kft to 2kft range. A general light easterly wind component looks to remain in place into this evening, however, more variable winds are possible later tonight before shifting to the north Friday morning.

Drizzle or rain chances look low Friday morning at this point, but if lower ceilings are in place than currently forecast, would not be surprised to see continued development. A slow improving trend with ceilings and vis is likely through early to mid afternoon Friday, as northerly winds steadily increase. Rain will return to the terminals by mid to late afternoon and will assist with lowering ceilings during that time, with this trend continuing into the evening as snow becomes more likely.

BOU WATCHES/WARNINGS/ADVISORIES
None.

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