FTO 09-29-2022: Unsettled Weather Pattern Heading Into The Weekend

Issue Date: Thursday, September 29th, 2022
Issue Time: 1:30PM MDT
Valid Dates: 9/30 – 10/14

Note: This is the final Flood Threat Outlook of the 2022 forecast season, but the program is scheduled to return on May 1, 2023. It has been our pleasure serving the state of Colorado for another flood season!

Event #2 from Monday’s FTO has become the main event for this final outlook period. As the Low, marked in the water vapor imagery below, becomes cut off from the steering flow, it is expected to linger north of the state for a handful of days. With plenty of upper and mid-level dynamics accompanying the Low and decent moisture in place over the state, scattered to numerous storms are anticipated for the mountains and portions of the plains through next week. Heading into next week, it looks like the Low should start to break up with increasing northwesterly flow aloft forecast. It’s likely that a cold front will drop through the state on the backside of what remains of the Low sometime between Sunday and Tuesday, which could bring some more intense rainfall to plains. Following this event, a warmer and calmer period is anticipated.

Heading into October, average PW values start to take a nosedive, which helps reduce the heavy rainfall threat amid other factors. During Event #1, above average values PW values are likely to occur both east and west, but with values remaining well below an inch, heavy rainfall is not anticipated at this time. While there may be some isolated, weak thunderstorms that can develop during the afternoon and evening hours, surface moisture, especially on the front-end of this system, should be limited. This should help to keep rainfall rates in the light to moderate range. Generally speaking, longer duration, stratiform precipitation is mostly forecast during this event, which should also help to reduce the flood threat. It is increasingly likely that snow will develop across the highest elevations (mostly above 9,500 feet), especially with any overnight precipitation that lingers over the mountains.

As far as temperature, afternoon highs should be quite enjoyable and fall-like with overnight temperatures becoming quite chilly, especially in areas that are cloud-free. So, prepare for the classic fall Colorado diurnal temperature swings. Scroll down to view more details about the event outlined in today’s FTO.

Event #1: FridayWednesday (9/3010/5)

No Apparent flood threat as an incoming Low becomes cut off and helps boost the chance for precipitation through next week.

With scattered to numerous storms forecast during Event #1, highest precipitation accumulations are anticipated over the mountains. Initially, storms are expected to develop over northwestern and northern Colorado on Friday, but with cooler temperatures, little to no CAPE is expected. So, rainfall should be stratiform with perhaps some embedded convection. By Sunday, the majority of rainfall should be over the central and southern high terrain. Again, with limited CAPE, the heavy rainfall threat remains on the lower end with max 3-6 hour totals up to 1.25 inches possible. A cold front is expected to drop through eastern Colorado sometime between Sunday and Tuesday, which may help produce some rainfall over the plains and expand mountain precipitation. Portions of the plains may be able to pick up an inch of rain along and near the front over a 1 to 3-hour period, and a couple thunderstorms may be able to develop depending on the timing of the frontal passage. All in all, there is a limited chance of flooding with cooler temperatures over the state with ongoing rainfall, so there is No Apparent flood threat issued. We’ll be sure to keep an eye on the system and produce a special off-season FTB forecast if necessary, but at this time, it is unlikely that one will be needed.