FTB 09-23-2020: Weak Convective Showers for Southern Mountains

Issue Date: Wednesday, September 23rd, 2020
Issue Time: 09:55AM MDT

— Flooding is NOT expected today

Today Colorado is between large-scale drivers of weather as the mid-level high pressure dome is centered along the southern California coast and post-tropical cyclone Beta swirls over southeastern Texas (see image below). An elongated area of clouds & showers associated with some mid-level lift stretches from central Colorado northeast into the Dakotas. This does not appear to be associated with a well-defined Low pressure system, but rather just mid-level convergence in the upper-level flow. Mid-level winds are more northwesterly/northerly to the west of this elongated feature, whereas southwesterly winds exist within it. This bit of energy is moving its way eastward out of the state, and it will create some weak showers over the northern plains regions this morning and afternoon. Mid- and upper-level moisture remains over the state as PW from the Denver (Grand Junction) morning sounding shows 0.63 (0.66) inches, similar to yesterday. Surface dew points are near 40F for most low-elevation locations across the state, increasing to the mid 40Fs along eastern Colorado. Daytime heating will allow some weak instability to build, which will initiate some convective showers and maybe a thunderstorm over the mountains south of I-70. This convective precipitation should remain weak and high-based, so mainly gusty winds are expected. No flooding is expected today.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. Hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

Northeast Plains, Urban Corridor, Palmer Ridge, Raton Ridge, & Southeast Plains:

Some morning showers and clouds will begin the day for the northern half of the plains regions, but little rainfall is expected. Some convective showers could drift off the higher elevations this afternoon into the adjacent plains, but limited moisture will keep rain rates below 0.2 in/hr. Temperatures will again climb well above average into the mid and upper 80Fs, which will keep surface relative humidity low (10-20%) and favor plenty of evaporation for any showers that do move over the area. This evaporation will allow gusty winds up to 40 mph to be generated from showers as they dissipate. No flooding is expected today.

Some smoke from the active Mullen, Middle Fork, and Cameron Peak wildfires may be transported into the northern Urban Corridor and Northeast Plains today. The NWS has an Air Quality Alert in place over this area. See your local NWS for more information.

Primetime: 10AM to 8PM

Grand Valley, Northwest Slope, Northern Mountains, Front Range, Central Mountains, Southwest Slope, San Juan Mountains, Southeast Mountains, & San Luis Valley:

Convective showers are possible for most mountain regions, but chances for accumulating rainfall largely exists south of I-70. Rain rates should stay below 0.2 in/hr with these showers due to the limited moisture and high-bases, which will favor plenty of evaporation and gusty winds up to 40 mph. The southern Front Range and Southeast Mountains have the highest chances for showers and possibly a weak thunderstorm. Some moderate 20 mph mid-level north/northwest flow should keep showers moving, limiting total rain accumulations to under 0.3 inches by morning. No flooding is expected today.

The valley locations along western Colorado should stay dry and warm today, with high temperatures reaching into the low 80Fs. Smoke levels may increase as westerly/northwesterly winds transport west coast wildfire smoke into the state.

Primetime: 12PM to 8PM