FTB 05-19-2019: The Next Upper-Level Low Approaches

Issue Date: 5/19/2019
Issue Time: 8:55 AM

NO FLOOD THREAT IS FORECAST TODAY.
NOTE: STREAMS AND RIVERS IN THE SAN LUIS VALLEY ARE RUNNING A BIT HIGH TODAY DUE TO SNOW MELT BUT ARE NOT EXPECTED TO REACH FLOODING THRESHOLDS.

The next upper-level low will approach from the west today, becoming centered over Nevada by midnight tonight. Associated with this upper-level low is an area of broad moisture transport, highlighted in the image below, which will spread mid-level moisture across the state throughout this forecast period. For much of the day today, this southwesterly flow and ribbon of moisture will bring showers and a few thunderstorms to the High Country, spilling over into the valleys as they move towards the northeast. While the best coverage and strongest activity (relatively speaking) is expected during the afternoon and evening, this shower activity will continue overnight and into tomorrow morning.

East of the mountains, the development of a surface low pressure circulation centered near the Palmer Ridge by this afternoon will bring easterly, upslope flow to northeast Colorado. This will result in scattered showers and a few embedded thunderstorms over the Urban Corridor, Northeast Plains, Palmer Ridge, and northern portions of the Southeast Plains during the afternoon and evening. This activity will be garden-variety, with periods of light-to-moderate rainfall, gusty winds, and occasional lightning, with thunderstorms capable of producing small hail.

During the overnight/morning hours tomorrow, a few thunderstorms will develop over the far Southeast Plains due to a moisture surge from the southeast as the aforementioned surface low pressure strengthens in response to the approaching upper-level low. These storms will be capable of producing brief periods of moderate-to-heavy rainfall, hail up to 1.5 inches in diameter, and strong winds up to 60 mph.

For more details on timing and rain rates, please see the zone-specific forecast discussions below.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below (hover over threat areas for more details). For Zone-Specific forecasts, jump below the map.

Zone-Specific Forecasts

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

Conditions will be dry across much of the area, especially during the morning and early afternoon hours. By 2 PM or so, the aforementioned surface low and easterly, upslope flow will kick off a few showers and embedded thunderstorms over the Urban Corridor, Palmer Ridge, Northeast Plains, and northern portions of the Southeast Plains. This activity will be garden-variety with periods of light-to-moderate rainfall, gusty winds, and occasional lightning, with thunderstorms capable of producing small hail. This activity will diminish slowly after sunset, with a few lingering showers possible into the early morning hours tomorrow. Maximum rain rates from this activity will be 0.1-0.25 inches/hour.

After midnight, a couple thunderstorms will develop over the far Southeast Plains. These storms are expected to be on the strong-to-severe side of the scale, capable of producing brief periods of moderate-to-heavy rainfall, hail up to 1.5 inches in diameter, and strong winds up to 60 mph. Maximum rain rates for this activity will be 1-1.25 inches/hour. These storms are the early precursor to a dangerous severe weather day across Oklahoma, Texas, and Kansas tomorrow.

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

Scattered showers and a couple weak thunderstorms are expected today across the mountains, with activity spilling over valleys with time as storms move towards the northeast. A few showers are ongoing at this time; activity will increase as we move into the afternoon hours, with scattered coverage expected to continue into tomorrow. Snow levels will be around 9000-10000 feet. Most of the activity will produce rainfall rates less than 0.1 inches/hour, with maximum rain rates of 0.15-0.25 inches/hour possible from weak thunderstorms.

Timing: Isolated showers are ongoing, activity will increase after lunch time, and scattered showers and a couple weak thunderstorms will continue through the remainder of the period (11 AM tomorrow).