FTB 05-19-2020: Increase in Afternoon Storm Activity for the Mountains & Adjacent Eastern Plains

Issue Date: Tuesday, May 19th, 2020
Issue Time: 8:40AM MDT

— Flooding is NOT expected today

Hot temperatures and critical fire weather will once again be the main weather stories, and western and far eastern Colorado will likely see a slight uptick in highs when compared to Monday. The low pressure and associated jet start to move slightly westward and northward throughout the day, which will once again cause critical fire weather over western and southern Colorado. As these higher wind speeds mix down to the surface and dry continues to be entrained from the southwest (PW was only 0.25 inches in Grand Junction), relative humidity values are forecast to drop into the low teens.

There is a nice, albeit weak, axis of subtropical moisture marked with the green dashed line below. As this feature moves eastward, it will be met by more humid, southeast surface winds over the adjacent eastern plains thanks to a developing lee trough. Together, this moisture will allow some showers and weak thunderstorms to pop up over the mountains with a few stronger storms possible over the plains. Quick storm motion to the NNE and overall limited atmospheric moisture will keep the flood threat away, although the stronger storms over the plains will likely produce impressive winds gusts and small hail.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, 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:

Front Range, Northern Mountains, San Juan Mountains, Central Mountains, Southeast Mountains, Urban Corridor, Palmer Ridge, Raton Ridge, Northeast Plains & Southeast Plains:

The ribbon of moisture from the Gulf of Mexico will help spark scattered afternoon thunderstorms over the mountains and adjacent plains. Storms over the mountains will likely produce some gusty winds due to the high bases and dry air aloft. Expecting the best accumulations along and near the Continental Divide with max 1-hour rain rates up to 0.30 inches possible.

Over the adjacent eastern plains, storms will favor the southern Palmer/Raton Ridge and western portions of the Northeast/Southeast Plains for accumulations. Isolated 1 to 2-hour rain totals up to 0.75 inches will be possible with max 1-hour rain rates around 0.50 inches. A couple severe storms are possible over the western portion of the eastern plains with the main threats being strong winds and hail up to 1-inch in diameter. The far eastern plains should remain capped, so we won’t be able to tap into that moisture today. Light rainfall may linger over the Northeast Plains into the early hours of the morning. Flooding is not forecast.

Primetime: 1PM to 3AM

Grand Valley, Northwest Slope, Southwest Slope, & San Luis Valley:

Critical and enhanced fire weather returns today (and again tomorrow) with a Red Flag Warning issued from 11AM to Midnight for the majority of these regions. With the jet moving over the area, southwest surface winds are expected to increase. Generally, winds will be in the 20 to 30 mph range with gusts up to 50 mph possible. Relative humidity values are forecast to drop into the low teens, so please use caution with any activity that can cause a spark. Be sure to tune into your local NWS office for the latest.