FTB 05-17-2019: Approaching Trough Returns Scattered Storms and Snow to the Forecast

Issue Date: Friday, May 17th, 2019
Issue Time: 8:45AM MDT

–Flooding is NOT expected today

Currently there is some light to moderate rainfall over western Colorado and with snow being report in Pagosa Springs. These showers are associated with another shortwave that is rounding itself around the base of the trough and some upper air support from the jet. The center of the trough is currently over Nevada and is forecast to move westward today as it becomes an open wave. This should increase rainfall chances from west to east into the afternoon and evening with storms having southwest to northeast movement. For western Colorado, the best chances for measurable rainfall will be along the Continental Divide and Flat Tops. Expect storm activity to continue into mid-afternoon with a break this evening as dry air moves in from Utah (yellow in the image below). However, a surface low is forecast to move into southwest Colorado by early tomorrow morning, so a second set of showers and snow (>8K ft) are likely over SW Colorado to start the day.

With southwest winds aloft, moisture over the southeast quadrant of the state will be minimal due to downsloping effects, so not expecting much rainfall over the Southeast Mountains and not much, if any, over the adjacent Southeast Plains and Raton Ridge. The severe thunderstorm threat will follow the dry line, which should set up well to the east of Colorado. Some better wrap around moisture exists over the Colorado and Nebraska/Wyoming border from a surface low over western Nebraska. So as the current set of storms moves to the northeast, best accumulation will be over the northern Front Range, Urban Corridor and Northeast Plains this afternoon and evening. Enhanced convergence along the Cheyenne Ridge will also help boost 24-hour totals along Colorado’s northern border. As a cold front starts to drop through the state this evening, coverage of thunderstorms may also increase in this area. Upper dynamics will likely help continue light showers over the higher terrains through midnight. Totals today and tonight are expected to remain under flood threat criteria, so there is no flood threat today.

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, Northern Mountains, Urban Corridor, Palmer Ridge, Northeast Plains:

Increased cloud cover is likely this afternoon as the storms start to form over the Front Range. With northeast movement of the storms and wrap around moisture from the surface low along the northern border, the best chance for measurable rainfall is over the northern Front Range, Urban Corridor and Northeast Plains. The best chance for a severe thunderstorm is over northern Weld and Logan County, although better dynamics will be located in the panhandle of Nebraska. Max 1-hr rain rates up to 0.5 inches will be possible (east) with 24-hr totals just over 0.5 inches (west). Flooding is not forecast.

Primetime: 12PM to Midnight

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

Expect ongoing showers through early this afternoon until the dry slot arrives. This should bring a break in precipitation until the next wave moves into southwest Colorado early tomorrow morning. This wave will bring snow to higher elevations (>8K ft) with rain at lower elevations. 24-hour totals up to 0.5 inches are possible over the Central and San Juan Mountains, with the highest accumulations along the Continental Divide and Flat Tops where 24-hour totals could reach 0.8 inches. Flooding is not forecast today.

Primetime: Ongoing to 8AM

Raton Ridge, Southeast Mountains, Southeast Plains:

Not too much moisture over the area with the southwest winds aloft. While some cloud cover and light sprinkles may form over the Southeast Mountains, they should evaporate quickly over the adjacent plains. Some strong surface winds are possible today, and with the low relative humidity, fire danger is slightly elevated. With the spring green up, large scale fire growth should be limited. Gusts up to 35 mph are forecast over the Southeast Plains and Raton Ridge, with some higher gusts over the Southeast Mountains. Best chance for precipitation is over the western Southeast Mountains, where most of the precipitation will fall as snow overnight into tomorrow morning. Flooding is not forecast.

Primetime: 2PM to 8AM