932 FXUS65 KBOU 170543 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1143 PM MDT Wed Apr 16 2025 .KEY MESSAGES... - Transition day Thursday with gusty winds and arrival of a significant cold front. - Critical fire weather conditions expected late Thursday morning through the afternoon from South Park & southern foothills through east central Colorado. Denver still on the edge. - Moderate to locally heavy snow for mountains, foothills Thursday night through Saturday; A few inches for the lower elevations, with minor travel impacts. - Much colder Friday and Saturday, with warming temperatures Sunday through Tuesday. && .UPDATE... Issued at 808 PM MDT Wed Apr 16 2025 High based showers along with an isold tstm have been producing gusty winds early this evening. Expect most of the activity to end over the far nern plains in the next hour or so. The nrn mtns will continue to see periods of showers overnight as that area will be in the favored left exit region of an upper level jet. && .SHORT TERM /Through Thursday/... Issued at 245 PM MDT Wed Apr 16 2025 Satellite initially showed trapped waves indicating mid level stability, but now some shallow cumuliform growth on those waves. The waves are also slowly diminishing per recent trends as the airmass stability decreases. Thus, a few showers have popped up on radar. That said, they are high based with only light precipitation/sprinkles. Given the well mixed sub-cloud layer and DCAPE near 800 j/kg, we`ll likely see a few gusts to 30-40 mph out of those into the evening hours. The northern mountains will be getting into the left exit region of an upper jet, so that should be enough to keep showers going there through the overnight. We made a slight increase in mountain PoPs and QPF, with snow amounts on a couple ridgelines expected to be near 3". Travel impacts should be minimal in all but the high passes like Rabbit Ears and Cameron. Eisenhower Tunnel area will likely see less coverage. On Thursday, a cold front is likely to sneak into northeast Colorado in the morning. It`s quite uncertain how far south it makes it, but typically a little farther than most models suggest. At this point, the front is already through southeast Montana so we`d expect it to have at least enough push to make it to about Denver by mid to late morning before stalling or washing out, and then retrograding a tad. That makes for a trick temperature forecast with a relatively high bust potential anywhere from Denver northward. That frontal location/retrograde will also affect fire weather concerns - see discussion below. South of the front, west/southwest winds will be howling with gusts to 35-45 mph expected most of the day. By late afternoon, we do expect a more significant push of the front and that will bring strong, gusty north winds across all of the plains. With gusts to 45 mph or more, there may also be some blowing dust in spots. We`ll also see a plunge in temperatures with the frontal passage - likely a quick 20 degree F drop late in the afternoon. With regard to precipitation, there is some drying aloft noted during the afternoon. Thus, a break in northern mountain precipitation is expected for a few hours, before convective showers fill in again with daytime heating and destabilization. More widespread precipitation will develop in the evening - more on that in the long term section below. && .LONG TERM /Thursday night through Wednesday/... Issued at 245 PM MDT Wed Apr 16 2025 Rain and snow will spread south across our area Thursday evening into Friday morning as moisture deepens behind Thursday`s front, with the lower elevations seeing the dominant precipitation type transition to snow mid to late evening on Thursday. Warm temperatures preceding this system should cause road temperatures to lag noticeably behind their ambient counterparts, so accumulations outside of colder surfaces are expected to be limited for the lower elevations until reinforcing cold air arrives later on Friday. Synoptically, we`ll have weak QG ascent in place, with a departing jet to our southeast along the eastern periphery of a shearing trough over Utah. At the surface, winds will maintain a prevailing northeast direction in the morning, keeping temperatures cool and in the 30`s for the urban corridor, with gradual veering towards increasingly easterly flow later in the afternoon. Combined with steeper lapse rates during the second half of the day, snowfall intensity should pick up across all areas (i.e. mountains , foothills and plains) Friday afternoon as the colder trough axis passes overhead. The lower elevations will have better potential for accumulations on all surfaces early Friday morning and later in the day, but unless temperatures trend a few degrees colder, travel impacts should remain minor for most of the I-25 corridor. However, will need to keep an eye on areas closer to the foothills and the Palmer Divide, which may creep into Winter Weather Advisory territory. By daybreak Saturday, mid-level dry air will rapidly intrude and put an end to most of the snow by midday. Storm-total snowfall of 6 to 12" is expected to be quite widespread for our central foothills and the mountains, with locally higher amounts possible. Highlights have been posted for these areas through early Saturday afternoon. Several inches can be expected for the urban corridor, but with melting, compaction, and marginal temperatures, travel impacts will be reduced (although impacts to vegetation will likely be more notable). Lastly, robust south/southeast flow Friday and Friday night across Park County will present a favorable upslope environment for moderate snowfall, so have extended winter weather headlines into South Park as well. Only modest warming is expected Saturday as we hold on to some cloud cover and cool easterly flow over the plains, so temperatures shouldn`t climb out of the low/mid 40`s outside of the northeast plains. As flow aloft turns more zonal Sunday through Tuesday, temperatures will warm back to near-normal values, with breezy conditions across much of the region. The flow pattern would sustain some chances (20- 50%) of showers mainly in the high country most days, with dry conditions prevailing across the lower elevations. && .AVIATION /06Z TAFS through 06Z Friday/... Issued at 1143 PM MDT Wed Apr 16 2025 VFR will prevail through Thursday morning and most/all of Thursday afternoon. Southwest winds to prevail into Thursday morning 15Z, then the wind forecast becomes very uncertain. A weak front pushes into northeast Colorado Thursday morning, possibly as far south as DEN. Some models show this front stalling out with variable winds into Thursday afternoon. Other models show southwest winds prevail through the day until the main cold front arrives. The main cold front plows south through the Denver area bring northeast winds to 40 knots. Northeast winds continue through Thursday and slowly decreases behind the front. Showers a possibly a thunderstorms (10% chance) will be possible, mainly after 00Z Friday. It becomes cold enough for all snow after 06Z Friday. However, cross sections only show the airmass saturated up to 700mb until 12Z Friday. If this happens to be the case, we could see a brief period of freezing drizzle. Air temperatures will be in the upper 20s during this time. This would limit impacts to elevated surfaces. && .FIRE WEATHER... Issued at 245 PM MDT Wed Apr 16 2025 While fuel status is somewhat mixed with patchy greenup over the Palmer Divide and east central plains, we`ve upgraded to a Red Flag Warning for those locations due to still dry fuel loads from last season and the magnitude of winds and low humidity. We`ve also included South Park and the Southern Front Range Foothills. Gusts of 35-45 mph are expected, with humidity dropping to 9-14%, lowest in southern Lincoln County. Farther north, there is much more uncertainty with how winds evolve due to a cold front. That front is likely to stall near I-70 on the plains in the mid to late morning, and then retreat northward a bit before plunging south late in the afternoon. Thus, there`s still uncertainty with regard to the wind forecast. At this time, we still think a narrow corridor (south of I-70) will blow quite strong for a little while with RH down to criteria, but that`s only about half of the zone and still plenty of uncertainty with regard to how long that would occur (need 3 hours for Red Flag issuance). Thus, we kept zones 240 and 245 (Denver and rural Adams and Arapahoe Counties) in a Fire Weather Watch until more certainty can be achieved. && .BOU WATCHES/WARNINGS/ADVISORIES... Winter Storm Watch from Thursday evening through late Friday night for COZ031-033-034. Winter Weather Advisory from 4 AM Friday to 6 AM MDT Saturday for COZ035-036. Red Flag Warning from 10 AM to 7 PM MDT Thursday for COZ214-216- 241-246-247. Winter Weather Advisory from 9 AM Friday to 6 AM MDT Saturday for COZ037. Fire Weather Watch from 10 AM MDT Thursday through Thursday evening for COZ240-245. && $$ UPDATE...RPK SHORT TERM...Barjenbruch LONG TERM...Rodriguez AVIATION...Meier FIRE WEATHER...Barjenbruch