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218 FXUS65 KBOU 190542 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1142 PM MDT Mon May 18 2026 .KEY MESSAGES... - Rain and mountain/foothill snow will gradually decrease through this evening. A few wet snowflakes may still mix in for the I-25 Corridor. - Near freezing temperatures and frost/freeze highlights for most of the plains, but some uncertainty as to how cold with more lingering cloud cover. - Still unsettled Tuesday through Thursday with scattered to numerous showers and a few storms, most numerous in/near the Front Range. - Warming and drying trend for the weekend. && .DISCUSSION /Through Monday/... Issued at 123 PM MDT Mon May 18 2026 Satellite shows the upper level trough ejecting east/northeast across the forecast area this afternoon, with an enhanced band of precipitation and even a couple thunderstorms moving east across the forecast area. The precipitation will weaken as it moves onto the eastern plains as the upper level trough continues to shear and weaken, and upper level support is replaced by weak subsidence. After the trough passage, we still have some weak upslope to work with so we`ll delay the dissipation of showers in/near the Front Range overnight. In fact, a few light showers could linger well past midnight, with the last of them dissipating in/near the southern foothills toward daybreak Tuesday. All existing Winter Storm Warnings and Advisories will remain in tact through 9 pm, but any travel impacts should be waning as precipitation rates decrease. Still can`t rule out a few snowflakes mixing in with the snow down toward the I-25 Urban Corridor during heaviest convective showers this afternoon and then this evening as temperatures aloft cool slightly. With regard to the potential freeze across the plains tonight. The latest trends are for more clouds and higher low level moisture, making it more difficult for temperatures to drop. We think most of the Denver/Boulder metro area will stay just above freezing due to mostly cloudy skies persisting through the night, while the plains north and east of Denver could see areas of frost with partial clearing but still some light northerly winds. The Palmer Divide should still end up colder so went with a Freeze Warning there, but even then only the higher elevations above 6500 feet would be most prone to sub freezing temperatures. On Tuesday, the airmass will be more stable but there`s still enough moisture and shallow instability for late day shower/isolated storm development in/near the higher terrain. That shower development and coverage will also be supported by weak QG forcing. Temperatures will remain well below normal, with highs only in the 50s over most of the plains. Wednesday should see an uptick in convective shower/storm coverage in the afternoon as lapse rates aloft become moist adiabatic, and we continue to see weak forcing as the mean upper level trough axis holds off to our west. Temperatures will only moderate a few degrees, and still be 10-15 degrees below normal. The trend for Thursday has been toward more active and stronger convective development. The main reason behind this is a stronger and deeper upper level trough dropping southeast across the Rockies. That will support steeper lapse rates, and combined with moderate low level moisture means increasing instability. MLCAPE from various more reliable progs indicate 500-1000 J/kg across most of the plains and I-25 Corridor, so there will be potential for a couple severe storms. As long as this trough passes by Thursday night (and the slower passage has continued in the latest ensemble means), Friday should finally trend drier. Temperatures will then start a warming trend for this weekend with more zonal flow advertised in the ensembles, so eventually we should return to near or above normal temperatures. && .AVIATION /06Z TAFS through 06Z Wednesday/... Issued at 1125 PM MDT Mon May 18 2026 MVFR and IFR conditions are still prevalent across the area, with isolated to scattered light rain and drizzle near the TAF sites. Isolated light showers are expected to continue on and off for the next few hours before we see a brief break in precip chances in the late morning and early afternoon. This break will be short lived as additional scattered showers move over the area in the mid afternoon through the late evening. High res models are showing slightly better rain coverage for the 00Z to 06Z time frame, compared to a bit earlier in the afternoon. MVFR and IFR conditions are expected to continue overnight, with CIGs around 600ft to 2000ft. Ceilings will start to lift tomorrow late morning and afternoon, but CIGs will still remain around 3000ft to 5000ft at their max before starting to lower again for Tuesday night. Winds during this TAF package will generally remain on the lighter side,with speeds mainly staying below 12kts. Wind directions are a bit uncertain in the late morning and afternoon as some models are showing outflow boundaries from overnight and morning convection moving through the area. && .BOU WATCHES/WARNINGS/ADVISORIES... Frost Advisory until 8 AM MDT Tuesday for COZ038-042>051. Freeze Warning until 8 AM MDT Tuesday for COZ041. && $$ DISCUSSION...20 AVIATION...AP