523 FXUS65 KBOU 191101 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 501 AM MDT Thu Jun 19 2025 .KEY MESSAGES... - Strong signal for record breaking heat from Friday into the weekend, along with potential for critical fire weather conditions. - Dry conditions through most of Sunday, but chance of storms returns along with heat relief by early next week. && .DISCUSSION /Through Wednesday/... Issued at 216 PM MDT Wed Jun 18 2025 Water vapor shows very dry air over Colorado and the Desert Southwest this afternoon. There is subsident flow over our forecast area resulting in a mostly sunny day with light winds. An upper level ridge will move eastward on Thursday with 700 mb winds becoming west-southwesterly across our forecast area. This will allow for compressional warming that will result in temperatures climbing well above normal. Most of the I-25 corridor will see a high in the mid 90s tomorrow with some locations on the eastern plains seeing a high in the upper 90s. With continued subsident flow, no showers or storms will form. A strong trough will move across the Pacific Northwest on Friday while a ridge strengths over the southeastern US. In between, strong west-southwesterly flow throughout the troposphere will develop over Colorado. This flow will advect in much warmer air from the Desert Southwest. In addition, the I-25 corridor and eastern plains will experience strong downslope winds which will increase temperatures in the low levels. Furthermore, there will be strong subsidence that will keep conditions mostly sunny for the majority of the day. All of these factors will combine to create very hot conditions which may break record highs. The record high for Denver is 99 which is well within reach as the current forecast has 100. The decision was made to issue a Heat Advisory because temperatures will be around 100 degrees across the I-25 corridor and plains, it is considered "early season heat" (which is basically anytime before July for our area), and that there will be mostly sunny conditions. However, there are a couple of factors which may help us avoid too many heat illnesses and those are windy conditions with gusts above 30 mph and very dry conditions with relative humidity around 10 percent. On Saturday, very similar conditions to Friday will exist. Models have latched onto slight cooling at 700 mb which may keep Saturday a degree or two cooler but otherwise the same high temperatures are in the forecast. The decision was made to extend the Heat Advisory through Saturday afternoon as the multiple days of heat will impact people. The aforementioned trough over the Pacific Northwest will enter northwest Colorado on Sunday. Model guidance has a much larger spread in the temperature forecast as two solutions appear possible. One solution is that the trough is slow to arrive and strong southwest winds continue to be over our entire forecast area. If this were to be the case, very hot temperatures will continue and the Heat Advisory may need to be extended to Sunday. The other solution is the trough is quick to arrive and a backdoor cold front moves through the plains. If that occurs, temperatures would be much cooler and storms would be possible across the far northeast plains. The trough will then be over Colorado Monday through the middle of next week. This will usher an active pattern of daily showers and storms in the afternoon/evening with some having the potential to reach severe limits. It will also be cooler during this period with below normal temperatures. && .AVIATION /12Z TAFS through 12Z Friday/... Issued at 501 AM MDT Thu Jun 19 2025 Mostly clear skies will prevail through the TAF period with only a FEW clouds above 12,000 ft AGL after 18Z. Winds will feature fairly normal diurnal wind patterns, with an enhanced E/SE flow picking up after 19Z. A few gusts as high as 17-22 kts possible 20Z-01Z. After a return to normal south/southwest drainage winds tonight, southwest winds will increase 15Z-18Z Friday with gusts to 20-25 kts developing. && .BOU WATCHES/WARNINGS/ADVISORIES... Heat Advisory from 11 AM Friday to 6 PM MDT Saturday for COZ038>051. && $$ DISCUSSION...Danielson AVIATION...Barjenbruch