FTB 09-26-2018: Fall Finally Takes Hold over Colorado

Issue Date: Wednesday, September 26th, 2018
Issue Time: 08:25AM MDT

— Flooding is NOT expected today

After a long stretch of hot weather to begin September over much of Colorado, a series of cold fronts over the past few days have finally begun to usher in more fall-like temperatures. In fact, many locations in the plains had their coldest temperatures of the new cold season so far today, ranging from just below freezing in spots to the low 40s °F across the southern plains. The cooler temperatures are the result of Canadian surface high pressure, which has been shunted southward into the region by northwesterly winds aloft. A compact and fast-moving shortwave trough (dashed red line) is embedded in the upper-level flow, providing just enough lift to produce a few clouds from the Front Range and Denver metro to points southeast. These features are illustrated in the annotated map of satellite water vapor imagery below.

As this shortwave zips off to the east this morning, drier air will take hold, leading to mostly clear skies across much of the state for the middle part of the day. The exception to this will be along the southern tail of this feature, which may still have enough energy and moisture with it to fire up some isolated thundershowers across the far southern tier of counties in the state. A few forecast models indicate convection starting late this morning that should push rapidly off to the southeast, possibly visiting the northern portions of the Raton Ridge and before pushing out of the state. The limited moisture and strong winds aloft will limit both the intensity and persistence of these showers and storms, and therefore no flood threat is anticipated. Additionally, more clouds may work their way into the northern reaches of the state by this evening, associated with the next push of shortwave energy.


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:

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

Cloudy and seasonably cool to start with this morning. Isolated to scattered showers may build late this morning, initially across the higher terrain. These may survive the push off the mountains onto adjacent lower terrain in the San Luis Valley, Raton Ridge, and western Southeast Plains. Any rain that does develop will be pushed along by robust winds aloft, thereby limiting any flooding potential. Rainfall rates will generally be in the 0.05 to 0.25 inches per hour range, and isolated spots along the New Mexico border that receive the most frequent showers today may approach 0.5 inches of total rainfall.

Primetime: 11AM to 6PM

Northwest Slope, Southwest Slope, Grand Valley, Northern Mountains, Central Mountains, Front Range, Urban Corridor, Northeast Plains, Palmer Ridge:

Clearing skies this morning with temperatures running just a few degrees below seasonal normals. Expect a strong warm up today with plenty of sunshine and winds turning westerly over western portions of the state and southeasterly on the eastern plains. Mid- and high-level clouds may begin working their way into northern portions of the state by the evening, but no precipitation is anticipated.