FTO 09-12-2019: Warm and Dry Weekend with Rainfall Returning Next Week

Issue Date: Thursday, September 12th, 2019
Issue Time: 12:40PM MDT
Valid Dates: 9/13 – 9/27

Should be almost completely rain free through this weekend, although there may be some isolated storms possible over the mountains during the afternoon hours. Zonal flow will produce westerly winds aloft, so a couple storms my wander into the adjacent plains. However, dry air will also be in place, so not thinking these storms will produce much, if any, rainfall. Temperatures also start to climb as the ridge builds over the state. A trough starts to develop and deepen to our west on Sunday, which will change flow aloft to southwesterly. This will possibly pull in disturbances on Monday/Tuesday, and with an increase in moisture, some weak afternoon thunderstorms will be possible over the mountains and western Colorado (Event #1 pt 1).

Wednesday is looking to be quiet as the trough pulls northward and subsidence is over the state. There will likely be cooler temperatures as well. The low re-digs back over the Great Basin for Thursday, which may push some mid-level lift into the state ahead of the trough. As the system pulls to the northeast sometime on Thursday and Friday, this will return the chances for more widespread showers and thunderstorms. Storm motion will again be swift (similar to this last system), and with limited moisture, there is No Apparent Flood Threat at this time. This may be upgraded for one of the days as confidence increases for the timing of the event. Linger moisture on Saturday my produce some showers over the mountains, and depending on where the convergence line ends up, the Southeast Plains may get a couple thunderstorms as well.

PW is quite low through the weekend for both Grand Junction (west) and Denver (east). The jet still looks to be mostly north of the state and without any mixing of strong winds down to the surface near the northern border, not thinking there will be any fire danger tomorrow and into this weekend. PW starts to creep up with the first part of Event #1 early next week. Thinking this will be more of a western Colorado/mountain event. However, a couple weak storms over the far Southeast Plains can’t be ruled out. Model members aren’t in full agreement with the moisture return, but right now thinking storms (to the west) will look similar to the system that just passed through. Tune back in on Monday as model agreement will likely better align.

Event #1: Monday (9/16) – Saturday (9/21)

No Apparent Threat as a shortwave and large trough moves across the state.

There will be a nice break in rainfall until the next system moves through and increases PW temporarily. Again, looking like a mountain and western Colorado event. Flooding is not anticipated at this time due to lower levels of moisture associated with the system. The main threats will be small hail and gusty winds from thunderstorms if the shortwaves line up with peak heating. At this time, thinking storm motion will be fast enough and rain rates low enough (fewer pockets of decent instability) that flooding will be avoided. Recent burn areas over western Colorado will be watched closely in the FTB on Monday into Tuesday.

The stronger system likely moves through sometime between Thursday and Friday next week. This will bring better chances of statewide rainfall. Not a ton of confidence in this forecast yet as it’s a bit far out. Right now, not looking like a huge moisture surge, and with fast storm motion once again, flooding should be avoided. Excepting the first day to be more of a threat over western Colorado, and the rainfall transitioning to the east on the second day. Rain rates look to have the potential to cause flooding issues if storms track over a recent burn area. So, this will be monitored in the FTB and updated in Monday’s FTO as confidence is again on the lower end for this forecast for now.