FTB 08-22-2019: Garden Variety Storms Forecast for Thursday

Issue Date: Thursday, August 22nd, 2019
Issue Time: 9:40AM MDT

— Flooding is NOT expected today

The trough continues its migration eastward today, which will start to bring some enhanced lift (“Jet” area) to the state this evening, and will help keep widespread, weak thunderstorms in the forecast for the next couple of days. The jet, associated with the trough, will also bring critical fire weather to the Northwest Slope. Moisture this morning remains limited over western Colorado (PW at 0.6 inches with the most moisture in the mid-levels) and increased southwest surface winds (tightening gradient) has caused a Red Flag Warning to be issued through this evening. There is a slight increase in the chance of measurable precipitation over the higher terrains of the Central and southern Northern Mountains (along with the San Juans) with the enhanced lift in the area. Overall, the threat is looking to be more cloud cover, virga and gusty winds. Light rainfall accumulations are also forecast with the highest QPF south.

Back east, PW has dropped off to 0.77 inches at Denver this morning with a pretty good dry layer above the surface, which means storms will have higher bases and produce less rainfall than yesterday. Best moisture and lift will be east of I-25, so expecting the higher accumulations of rainfall here. Storms are forecast to form over the high terrains just after noon, and westerly steering winds will help storms move into the adjacent plains by 1 or 2PM. Over the Urban Corridor/immediate adjacent plains, the largest threat will be gusty outflow winds from the storms and small hail. Parameters are indicating a severe thunderstorms or two are possible over the Northeast Plains (near the northern CO border) early this evening with the main threats again being gusty winds, local, heavy rainfall and severe hail. Better moisture is also hanging on near the CO/NE/WY border, so if a storm tracks in the state from the Cheyenne Ridge, it has the potential to drop some local, heavy rainfall. Not thinking this heavy rainfall will be widespread enough to issue a flood threat, and storms should be moving fast enough to the ESE that flooding thresholds aren’t likely to be exceeded by much.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

Front Range, Urban Corridor, Northeast Plains, Palmer Ridge, Raton Ridge, Southeast Plains, Southeast Mountains:

Scattered, weak thunderstorms are anticipated to develop over the higher terrains early this afternoon, driven by diurnal flow. Totals up to 0.8 inches will be possible over the southern Front Range and Palmer Ridge regions with totals to the north closer to 0.3 inches over the northern Front Range. Storms will quickly move off the high terrains into the Urban Corridor with the storms mostly producing cloud cover and some gusty outflow winds. Over the Urban Corridor (east of I-25), max 1-hour rain rates up to 0.5 inches will be possible. Heaviest rainfall is forecast over the Northeast Plains and northern Larimer and Weld Counties where max 1-hour rain rates just over 1 inch will be possible. Flooding is not anticipated.

Primetime: 12PM to Midnight

Northwest Slope, Grand Valley, Southwest Slope, Northern Mountains, Central Mountains, San Juan Mountains, San Luis Valley:

Critical fire weather continues for another day with a Red Flag Warning issued over the northwest corner of the state. Surface winds are forecast from the southwest and expected to be in the 10 to 20 mph range with gusts up to 35 mph. Mixed with low humidity values, fires will be in an environment they can spread quickly. So, please use caution with any open flames. Increasing cloud cover is also anticipated this afternoon, which will bring relief to temperatures that are still a few degrees above average for late August. Max 1-hour rain rates over the northern high terrains will be under 0.1 inches with isolated totals up to 0.4 inches over the San Juan Mountains.

Primetime: 12PM to 8PM