


Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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037 FXUS65 KBOU 061845 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1245 PM MDT Sun Jul 6 2025 .KEY MESSAGES... - Scattered afternoon/evening thunderstorms today and Monday. - Some strong to severe storms are possible with large hail and damaging wind gusts today and Monday, mainly across the eastern plains, but a few are possible across the urban corridor. - Hot temperatures expected Wednesday with the upper 90s expected across the plains. It is possible the hot temperatures extend into Thursday. && .UPDATE... Issued at 248 AM MDT Sun Jul 6 2025 Huge model differences regarding moisture and instability continue with the 06Z model runs. The 06Z NAM shows a stronger northeast surge this morning with dew points in the lower 50s this afternoon as far west as the base of the foothills. MLCAPE values reach 1000- 2000 J/kg if we keep low 50s dew points into the afternoon. The 06Z RAP and HRRR show drier mixing down (likely too much mixing of the drier air) and dew points in the lower 20s across the Denver area. CAPE values in this drier airmass only reach 200-400 J/kg. Zooming out, a large area of thunderstorms have persisted much of night across southwest South Dakota. Radar is showing a strong outflow boundary diving south and southwest into Wyoming and Nebraska. At its current pace this outflow boundary would reach northeast Colorado around sunrise and advance south through the area this morning. The NAM looks like the best model at this time capturing this stronger northerly surge. Northeasterly winds this afternoon increase the shear as well, likely leading to at least a few severe storms today. SPC`s Day One Convective Outlooks has Slight Risk for severe storms as far west as I-25 with Marginal Risk into the Front Range mountains. This seems very reasonable with the northerly outflow marching towards the area, which will increase low level moisture and instability. Large hail, possibly slightly bigger than golf balls and damaging winds will be the main severe threats. A similar scenario is expected for Monday with another chance for severe thunderstorms. A shortwave trough tracks across the northern plains Monday, which is expected to increase the number of storms, especially over the northeast corner of Colorado and northward into Nebraska. && .DISCUSSION /Through Saturday/... Issued at 222 PM MDT Sat Jul 5 2025 Scattered storms have formed across our CWA this afternoon and have been sub-severe so far. Instability is modest with surface- based CAPE values around 1,000 j/kg. Deep layer shear is rather low with values generally around 25 knots. The main concern with storms that form this afternoon and evening will be strong wind gusts due to steep lapse rates and large dew point depressions in the boundary layer. However, DCAPE values are around 1,400 j/kg which suggests most downdrafts will be capable of gusts up to 50 mph and not necessarily severe gusts of 60 mph. We have collaborated with SPC and we are in agreement that no Severe Thunderstorm Watch will be needed at the time of this writing. If a more organized MCS were to form, then a watch may be needed. On Sunday, there is a decent chance that an outflow boundary from overnight convection in Nebraska will keep easterly winds over northeast Colorado for much of the morning and afternoon. This would advect much better dew points into our area which would lead to higher instability. In addition, the low level easterly winds would increase deep layer shear. All factors seem to be pointing towards Sunday having a much better severe weather threat than Saturday with large hail and damaging wind gusts expected out of strong storms over the I-25 corridor and eastern plains. On Monday, conditions will be very similar to Sunday. Healthy dew points should stay in our area across northeast Colorado. If that is the case, another day of strong to severe storms with large hail and damaging wind gusts will occur. We break the pattern of daily strong to severe storms on Tuesday as ridging strengthens aloft with more capped conditions. We will then begin talking about heat on Wednesday as a 597dm 500 mb high will form over our forecast area. With strong subsidence and little cloud cover, temperatures will have the chance to get to the upper 90s and around 100 degrees across the plains. GFS MOS has 101 for Denver and the ECMWF ensembles have roughly half the members at 100 or above. If these warmer solutions appear more and more likely in the coming days, a Heat Advisory may be needed. There is a good deal of uncertainty with Thursday`s forecast as a trough will be quickly approaching from the west. If the trough is quicker to move through, cooler temperatures near seasonal normals can be expected with scattered storms. However, if the trough is slow to move through, another very hot day with temperatures near 100 degrees across the plains is possible. && .AVIATION /18Z TAFS through 18Z Monday/... Issued at 1158 AM MDT Sun Jul 6 2025 VFR conditions expected through the TAF period. The main concern today will be outflow boundaries from nearby storms producing winds up to 35 knots. High resolution models show that a direct hit from any storms is unlikely but the potential for winds from surrounding storms is high enough that a PROB30 was kept in the forecast. Instability will stick around into the overnight hours tonight and a shower or storm can`t completely be ruled out but the chance is not high enough to include a PROB30. There is also a very small chance that low clouds develop late tonight. If any of the potential overnight storms produce an outflow boundary that moves west over the terminals, there is a chance stratus clouds develop. On Monday, the chance for storms in the afternoon is roughly around 40-50%. At this time a PROB30 was added for thunderstorm wind gusts but an increase to a TEMPO may be necessary. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Meier DISCUSSION...Danielson AVIATION...Danielson