Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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493 FXUS65 KBOU 172056 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 256 PM MDT Mon Jun 17 2024 .KEY MESSAGES... - Critical fire weather conditions expected into this evening - Cooler Tuesday and Wednesday with a chance of showers and a few storms - Scattered thunderstorms Thursday into Friday - Hot and drier again by early next week && .SHORT TERM /Through Tuesday/... Issued at 142 PM MDT Mon Jun 17 2024 Current surface observations show a notable N-S temperature/dewpoint gradient across much of northeast Colorado early this afternoon. Across areas such as the southern Foothills and east to Lincoln County, SW winds have mixed down resulting in breezy conditions, low relative humidity (< 15%), and hot temperatures (90F+). Locations north of Denver have been slower to mix out. ACARS soundings still show a weak stable layer along with persistent easterly flow keeping temperatures cooler (80s) and dewpoints higher (50s). The current trend is that gradually the environment will mix out resulting in drying and warming from south to north for the remainder of the afternoon. There is some uncertainty in how far north things will mix/dry out. The main impact this will have is on the fire weather conditions (Red Flag Warning). Most of this uncertainty will be if conditions end up hitting criteria for in spots. See fire weather discussion for more details. There is a Slight Risk for the far northeast corner through tonight for severe thunderstorms; however, this is still looking like a low chance (<20%) given the capped environment. If something initiates, a few severe storms with large hail, severe wind, isolated tornado are possible given the environment. A cold front moves across the region overnight with easterly upslope winds setting up behind it across the plains for much of tomorrow. This will bring much cooler temperatures for tomorrow with highs in the 70s across the plains. Model soundings show a stable and fairly dry environment for most of the region. An axis of marginal instability over the higher terrain, mainly south of I-70 will support a few high-based showers/storms in the afternoon. && .LONG TERM /Tuesday night through Monday/... Issued at 230 PM MDT Mon Jun 17 2024 Just enough mid level moisture and instability should be present for a few showers and isolated thunderstorms Tuesday night. This appears to be aided by the right entrance region of an upper level jet streak, so showers could linger overnight. Overall, we could see scattered coverage with the showers shifting slowly east across the plains overnight with the departing speed max. However, it all looks fairly weak at this point with rather meager low level moisture. For Wednesday, moisture values increase along/east of the Continental Divide with a return flow of moisture in southeast low level flow. Instability is still limited, but overall the additional moisture should contribute to a little more intensity, but still scattered coverage. Temperatures will remain on the cooler side with a fair amount of clouds and cooler high pressure locked in east of the Divide. Thursday could see a threat of stronger thunderstorms due to a combination of increased low level moisture and warmer temperatures. There is reasonable agreement in the ensembles that MLCAPE grows to 1000-1500 J/kg, although it`s a weakly sheared environment so mainly pulse type storms expected. Convective coverage should be about the best of the week ahead should the moisture and instability come together as advertised. And the same could be said for Friday as ensembles are pointing to a surge of subtropical moisture arriving from the south and southwest. That would support a deeper moisture profile more favorable for locally heavy rainfall, so something to watch over the next couple days to see if that plume remains consistent. For next weekend into early next week, there is excellent agreement between the GEFS and EPS that an upper level ridge will be building over the Central Rockies. This would support a return of hot and dry weather, with the hottest temperatures (mid to upper 90s for the plains) likely returning by Monday. && .AVIATION /18Z TAFS through 18Z Tuesday/... Issued at 1202 PM MDT Mon Jun 17 2024 VFR conditions expected for the TAF period. SE winds transition to gusty SW winds early this afternoon at the terminals with gusts up to 25 kts. SW winds decrease in the 01-03Z timeframe. A weak front moves southward overnight in the 08-10Z timeframe. It should attempt to transition winds light northerly. BJC may tap into a weak mountain wave with enhanced westerlies after midnight then becoming light northerly early Tuesday morning. E/SE winds are likely Tuesday morning, increasing into the afternoon at 10-15 kts. && .FIRE WEATHER... Issued at 142 PM MDT Mon Jun 17 2024 Areas across the southern Foothills, Park County, Grand County, Elbert and Lincoln counties have been approaching/hitting Red Flag criteria this afternoon. Areas north such as Denver, Boulder, northern Jefferson, Washington, Morgan counties still remain unmixed resulting in dewpoints in the 50s. From south to north, this "boundary" should slowly move northward with the environment mixing down drier air and gusty SW winds. However, there is some question on how "north" this boundary goes. Counties such as east Boulder, Morgan, Washington counties may struggle to mix out quick enough with peak heating keeping them out of RFW criteria. && .BOU WATCHES/WARNINGS/ADVISORIES... Red Flag Warning until 9 PM MDT this evening for COZ213-214-216- 239>241-244>247-249. && $$ SHORT TERM...Mensch LONG TERM...Barjenbruch AVIATION...Mensch FIRE WEATHER...Mensch