FTB 07-04-2019: Hot Temperatures for the 4th of July with a Chance of Thunderstorms over the Northeast Plains

Issue Date: Thursday, July, 4th, 2019
Issue Time: 8:55AM MDT

–A LOW flood threat is issued for the Arkansas River at Avondale

Still quite the dry air mass over the majority of the state as shown by the yellows and orange below. There is some dense fog and a couple light showers over the northeast corner of the state to start the day. A surface low is pulling in some very high dew points into the area behind a weak front, but this should begin to mix out and burn off the fog after a couple hours of heating. The upper trough driving our weather pattern the last couple of days is currently over Nevada, and it will continue to move eastward throughout the day. This will tighten the pressure gradient over the western border and produce gusty southwest surface winds again today. Paired with a very dry air mass, a Red Flag Warning has be issued from noon today to 8PM tonight for the Northwest Slope and Grand Valley. Please use extra caution with any open flames.

As far as rainfall chances, there’s not quite enough moisture over western Colorado today for storms. An isolated weak shower or two may be possible along or near the Continental Divide further south, but other than increased cloud cover over the San Juan Mountains this afternoon, it’s going to be another hot, dry day. To the east, the surface low over the Southeast Plains will continue to pull in low level moisture over the northeast quadrant of the state on its north and east side. There is a very strong moisture gradient from Denver to North Platte, so not surprised about the dense fog reports. However, dry air above the surface will likely mix out a lot of this surface moisture, limiting the chances for afternoon storms.  Downsloping winds over the Southeast Mountains and Raton Ridge should help setup a dryline to the east. Right now this moisture gradient looks to set up over the KS/CO border, so that should keep the rainfall and severe weather threat east of the Southeast Plains. Storm motion to the northeast today will be fairly quick, and with high bases once again on the storms, flooding is not forecast.

Riverine:

The NWS Flood Warning continues for Avondale as dam releases at Pueblo have the Arkansas River running high. Minor flooding is forecast for low lying areas along the river, so a Low flood threat has been issued. While there are still some high flows throughout the state (Eagle, Rio Grande, Los Pinos and Crystal River to name a few), flows from snowmelt are anticipated to decrease today and into this weekend over most areas. However, dam releases are likely, so this may cause swollen rivers and minor flooding on rivers downstream of the releases. Increased chances for rainfall this weekend may also cause some minor flooding issues if storms track over elevated rivers and creeks. Please tune into your local NWS for the latest on Flood Advisories and Warnings, but here are a list of the current Flood Advisories (as of 9AM): Blue River below Dillon, Colorado River at RMNP and downstream of Grand Lake, Roaring Fork River, Fry Pan River, Crystal River near Redstone, Gore Creek and the Eagle River near Gypsum.

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:

Northeast Plains, Palmer Ridge, Front Range, Urban Corridor:

Best chance for measurable rainfall today will be over the Northeast Plains over the counties bordering Nebraska. As weaker storms move off the higher terrains (mountains and Palmer Ridge) this afternoon, they will encounter better moisture over this area as well as a front that will continue to drop south overnight. This will help create more widespread storm activity later tonight with the main threats being moderate rainfall and gusty outflow winds, but some large hail may be possible, too. Max 1-hour rain rates up to 0.85 inches are forecast. Storms back to the west will look a lot like yesterday, so plentiful virga with some light showers mixed in. Max 1-hr rain rates up to 0.25 inches may be possible with most storms producing 0.10 to 0.15 inches in their cores. Should be a great night for fireworks along the Front Range!

Primetime: 3PM to 3AM

Southeast Mountains, Raton Ridge, Southeast Plains, San Luis Valley:

It’s going to be a hot one with the century mark likely being hit over the Southeast Plains. Dry air should keep the rainfall threat at bay with only a few high clouds expected this evening. Surface winds will increase over the San Luis Valley this afternoon, but critical fire weather is not anticipated at this time. With the front passing through overnight, some morning cloud cover will be likely to start Friday morning.

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

The Red Flag Warning is in place over the Northwest Slope and Grand Valley from noon today until this evening when the upper and lower atmosphere uncouple. Winds today will be in the 15-25 mph range from the southwest with gusts up to 35 mph possible. Please use extra caution with open flames and anything that could cause a spark. High temperatures today will be in the 90°Fs over the lower elevations with 80°Fs for the mountain valleys.