FTB 07-30-2016: High Pressure Shifting East

Issue Date: 7/30/2016
Issue Time: 9:20 AM

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE NORTHEAST PLAINS, PALMER RIDGE, AND SOUTHEAST PLAINS.

Current water vapor analysis (below) shows the upper-level high centered just off the southwest coast of California, an upper-level trough (red line) digging along the west coast of Canada, and the mean flow pattern of the jet stream (black line and arrows). The upper-high will shift to the east today as the upper trough digs, nudging better moisture into western Colorado. This will lead to an uptick in thunderstorms over the High Country and Western Slope, especially across the higher terrain of the Southwest Slope, San Juan Mountains, and Southeast Mountains. Further to the north and east, the atmosphere will be a bit drier, and only isolated thunderstorms are expected.

WV_20160730

With the jet stream positioned well to the north and east of Colorado, small disturbances in the flow will not have the same magnitude of effect on eastern Colorado storms. Instead, this period’s thunderstorms will mostly originate over the mountains and move generally eastward over the lower elevations. The exception to this will be over the far Northeast Plains, Palmer Ridge, and Southeast Plains, where there will be just enough forcing to kick off isolated-to-scattered strong/severe thunderstorms. Decent low-level moisture will provide the opportunity for bouts with heavy rain, but downslope winds from the west will work to dry the lower-levels. This drying will enhance thunderstorm wind gust potential, so be on the lookout for that, as well as large hail (up to 1.5 inches in diameter). For details regarding 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.
20160730_LFT

Flood Threat Legend

Zone-Specific Forecasts

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

Isolated-to-scattered showers/thunderstorms expected, with the best coverage near the mountains and across the far Northeast Plains. Most storms will be garden variety, producing moderate rainfall, gusty winds, and lightning. A few strong/severe storms over the plains will result in heavy rain, strong winds, and large hail. The areas outlined by the low flood threat are where heavy rain concerns are greatest, relatively speaking. Maximum rain rates are as follows:

Urban Corridor and Raton Ridge: 0.4-0.8 inches/hour
Palmer Ridge: 1.0-1.5 inches/hour
Northeast Plains and Southeast Plains: 1.5-2.0 inches/hour

Timing: 1 PM – 11 PM for the Urban Corridor and Raton Ridge, 2 PM – Midnight for the Palmer Ridge and Southeast Plains, and 3 PM – 2 AM for the Northeast Plains

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

Isolated-to-widely scattered thunderstorms are expected over the higher terrain today, with the best coverage expected over the Southwest Slope, San Juan Mountains, and Southeast Mountains. Moisture is mainly confined between 4 km and 6 km aloft, so not much rain is expected from any activity.

Generally speaking, the main impacts will be gusty winds and lightning. Brief bouts with moderate rainfall cannot be ruled out near the CO/NM border, or across the Front Range/Southeast Mountains, where moisture is best. Maximum rain rates will be 0.4-0.8 inches/hour across the Front Range, Southeast Mountains, San Juan Mountains, and Southwest Slope regions, and 0.2-0.4 inches/hour elsewhere.

Timing: 1 PM – 9 PM for most areas, with a few showers/storms lingering across the higher terrain of the San Juan Mountains, Southwest Slope, Grand Valley, and Central Mountains until the early morning.