Memorial Day weekend has been hot and dry so far for Denver, as we outlined in Friday’s post. While the lack of thunderstorm activity has been a bonus for holiday weekend outdoor activities, temperatures have been a little too hot outside of the mountains. The high temperature on Saturday peaked at 93 in Downtown Denver and 94 at DIA, falling just shy of the record high for the date of 95. Following another very warm (but not quite as hot) day on Sunday, the pattern will turn cooler and more active on Memorial Day.
A trough of low pressure has been spinning over the Great Basin since yesterday, resulting in active weather for areas west and north of Colorado. A very similar setup to what we have seen all month long! Late tonight and into Monday, this trough will be pushing into Colorado, as can be seen in the image below, setting the stage for more active weather to close out the holiday weekend.
As the trough approaches, a surface cold front will also arrive late tonight, ushering in more clouds and cooler temperatures on Monday. Temperatures on Monday will be much more comfortable after the past few days of hot weather, with highs in Denver about 20 degrees cooler compared to Saturday and Sunday! However, behind this cold front winds will turn northeasterly, ushering in low level moisture from the Gulf of Mexico. The upslope winds, increase in low level moisture, and cooling temperatures aloft will allow for the airmass to destabilize Monday afternoon. Below is a look at the projected surface dewpoints Monday afternoon. Dewpoints in the 50s across Northeast Colorado, and even into the low 60s across the far northeast corner of the state.
The key ingredients for severe thunderstorms are all coming together across Northeast Colorado for Monday afternoon. Colder temperatures aloft associated with the approaching trough will result in greater instability (as will terrain lift due to upslope winds), and increasing low level moisture will also provide the fuel necessary for strong to severe thunderstorms. In addition, the presence of wind shear will be another primary factor into severe thunderstorm development. Low level winds will be northeasterly, whereas winds will shift with increasing altitude to southwesterly, and also increase in speed with height. This type of wind profile with height will support rotating supercell thunderstorms. The Storm Prediction Center has already highlighted Northeast Colorado under a risk for severe thunderstorms on Monday.
As is typical, the best chance of severe thunderstorms will be across the plains of Northeast Colorado on Monday afternoon. However, the I-25 corridor from Denver to Ft. Collins, extending west to the lower foothills, will all be very much in play for severe thunderstorms, so be prepared tomorrow afternoon if you have outdoor plans in the metro area. The primary threat with thunderstorms tomorrow will be large hail and strong straight-line winds. In addition, there will likely be a tornado threat Monday afternoon, especially east of the metro area.
The one limiting factor Monday afternoon will be the cooler surface temperatures, with a “capping” inversion that could inhibit thunderstorm development – especially if cloud cover lingers. However, as an upper level disturbance tracks across the region during the afternoon, it could be enough to allow the cap to break and for thunderstorms to quickly develop. Bottom line, be sure to keep your guard up on Monday afternoon for the possibility of a strong or severe thunderstorm!