FTB 10-02-2018: Flood Threat Bulletin Special Edition as Remnants of Hurricane Rosa Move into Western Colorado

Issue Date: Tuesday, October 2nd, 2018
Issue Time: 09:55AM MDT

NOTE: This is a special edition of the Flood Threat Bulletin. At this time, we do not foresee a threat needing to be issued after today. However, if a flood threat appears additional Bulletins will be produced as warranted.

— A MODERATE flood threat has been issued for the flood threat has been issued for the Bull Draw, Plateau, Burro and 416 burn scar areas

— A LOW flood threat has been issued for the Southwest Slope, San Juan Mountains, Central Mountains, Grand Valley, Northern Mountains and Northwest Slope

The main axis of subtropical moisture associated with the remnants of Hurricane Rosa will make its way into southwest Colorado and move NNE throughout the day. This will bring widespread showers and thunderstorms to western Colorado as well as over the higher terrains through tomorrow morning. While the threat for rainfall is widespread today, the largest totals will be confined to higher terrains over the Grand Valley, Central Mountains, Southwest Slope and San Juan Mountains. The snow line is expected to be somewhere between 12,000 and 13,000 feet, so only the highest peaks will have a dusting of snow by tomorrow morning. As anticipated, Precipitable Water (PW) has increased drastically over Grand Junction, and PW was measured at 0.98 inches in the 12Z sounding. This surpasses the daily record, but the October record of 1.05 inches remains (for now).

This morning, the first wave of showers has made its way over the Southwest Slope and San Juan Mountains associated with the shortwave marked in the water vapor imagery below. This feature and associated stratiform rain will continue to move to the NNE throughout the morning into this evening. Expecting showers to become lighter and less widespread as they move into the Northern Mountains and Northwest Slope. None the less, 24-hour totals just under 1 inch will be possible over the Northern Mountains. A second wave of showers is expected to move into the southwest corner of the state this afternoon associated with the second shortwave marked in the water vapor imagery below. Widespread stratiform rainfall is forecast with some embedded convection (limited instability) through early tomorrow morning. Some light, isolated showers will likely continue over the Central and San Juan Mountains into Wednesday. Normally, stratiform rain and steering winds around 20 knots would keep the flood threat low. However, the multiple rounds of storms in a high moisture environment and convection embedded in the showers will warrant flood threat today. Recent burn scars will be especially susceptible to flash flooding, mud flows and debris slides. A Low flood threat has been issued for western Colorado with a Moderate Flood threat for the Plateau, Bull Draw, Burro and 416 burn scars.

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.

Flood Threat Legend

 

Zone-Specific Forecasts:

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

Multiple rounds of showers with embedded convection this afternoon are expected over these regions with the highest totals favoring the southern high terrains and their southwest facing slopes. However, 24-hour totals just under 1 inch are possible over the Northern Mountains as well with max 1-hr rain rates up to 0.5 inches. The more stratiform nature of the showers to the north should bring some relief to fire crews in the area and limit the overall flood threat. 24-hour totals up to 2.25 inches will be possible over the San Juan Mountains with max 1-hr rain rates up to 0.7 inches due to embedded convection. These rain rates and totals will put the region and recent burn scars at risk for local flash flooding, debris slides and mudflows. A Low and Moderate flood threat has been issued.

Primetime: 10AM to 3AM

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

While not at the main center of action today, some isolated afternoon showers will be possible over the higher terrains this afternoon as moisture moves into the area from Rosa. A couple of these storms may wander into the adjacent plains, but storms are expected to be high-based with limited rainfall totals. Storms this afternoon will also be capable of producing brief, gusty winds. Max 1-hr rain rates up to 0.25 inches will be possible with 24-hour totals up to 0.6 inches over the Southeast Mountains.

Primetime: 12PM to 12AM