Plaincast

Messages

Record heat today, with highs 100-106 across the plains and I-25 Corridor. Heat Advisory expanded to Palmer Divide.

Scattered afternoon/evening thunderstorms, mostnumerous over the higher terrain.

Increasing chances for thunderstorms with locally heavy rain Monday, Tuesday, and Wednesday. Some relief to extreme heat.

Discussion

Just when you think it couldn't get any hotter, we're staring into the face of what looks to be the hottest day of the year today. The heart of both the upper level ridge and mid level thermal ridge will be centered across the Front Range. 700-600 mb temperatures warm another 0.5-1.0C, which means we'll tack on another degree or two to yesterday's highs that exceeded 100F over most of the plains and I-25 Corridor. That means record temperatures are forecast for many stations, with a sampling below;

Denver: 102100 in 1910 Fort Collins: 102100 in 1910 Boulder: 101 98 in 1935 Greeley UNC: 105102 in 2003 Fort Morgan: 106106 in 1910 Akron: 101104 in 2003 Julesburg: 105105 in 1894 Limon: 100 98 in 2023

Given a further uptick in temperatures, we've expanded the Heat Advisory to also include the Palmer Divide where more significant heat impact levels are forecast. Warm overnight lows, and in some places record high minimums, are only further intensifying the heat impacts today.

With regard to any storm chances, the mid level water vapor loop and latest ACARS soundings show similar to just a slight uptick in moisture values across the area. Therefore, we expect a similar day to yesterday when we saw scattered showers and a few storms in the afternoon, with the highest coverage over the mountains and Palmer Divide, and lower chances as we head to the east with blazing sunshine expected through the afternoon. At least there will be a little heat relief due to clouds and shower outflows in/near the mountains late in the day.

For tonight, it'll be another warm one as cloud cover is expected to increase with a push in mid/upper level monsoonal moisture. Some areas near the lower foothills and Denver metro area may only reach the mid 70s for overnight lows. Fortunately, it appears the clouds will help limit heating for Monday, with some of the short term guidance showing sufficient cloudiness to keep us away from another day of Heat Advisories. The clouds may also impact convective development, but typically enough heating occurs to get late day showers and storms going. This time, they may linger well into the overnight hours Monday night which would be more typical of a monsoonal moisture surge. As precipitable water (PW) values increase to 150-200% of normal, some of the storms will be capable of producing locally heavy rainfall.

That threat may very well grow into Tuesday as we'll be approaching climatological maxes for PW. At the same time, warm cloud depths increase a little to 3,000-4,000 feet but that's still less than optimal given the very warm airmass and still deep subcloud layer. All other parameters are more favorable including slow storm motion (15 mph or less), high PW, and potential for skinny storm energy profiles above the LCL. Thus, we'll continue to watch for locally heavy rainfall and any flash flood threat. Wednesday could be another similar setup with scattered to numerous showers and storms with locally heavy rainfall, although storm motions will likely increase as the ridge flattens and a shortwave moves through. Temperatures are expected to settle closer to normal (still above, though) as we head into this more unsettled pattern and a couple backdoor "cool" fronts are expected.