FTB 07-26-2015: Better Moisture + Passing Disturbance = More Thunderstorms

Issue Date: 7/26/2015
Issue Time: 9:44 AM

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

The water vapor image below is a bit messier than previous days, but the same major players remain; an upper-level ridge across the central US with upper-level troughs flanking either side. One feature that hasn’t been present across Colorado the last few days is a mid-level disturbance, and one is forecast to move across the state today (marked by the black dashed line). This disturbance will be accompanied by a slight increase in mid-level moisture, mainly for southern and eastern regions. The disturbance and accompanying moisture will lead to more thunderstorms, overall, today and tonight.

07262015_WV

If one was to draw a line approximately from the Pawnee National Grassland -> Granby -> Glenwood Springs -> Grand Junction, the best chances for thunderstorms will be to the south and east where the better moisture resides. An isolated, high-based thunderstorm or two cannot be ruled out north and west of that line, but in that environment the biggest threats will be gusty winds and lightning, with very little rain.

The biggest threat for heavy rain today will be across the Palmer Ridge, Southeast Plains, and Northeast Plains regions, where the better surface moisture will be; surface dewpoints will likely remain in the 50s this afternoon. Near the mountains, i.e. the Urban Corridor and western extents of the Southeast Plains, drier air will mix down to the surface through the afternoon, creating more of an inverted-V environment; this means that the main threat will be gusty winds and lightning, with brief periods of moderate rainfall. Specifics such as rain rates and timing will be given in 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.
FTB_snapshot_20150726

Zone-Specific Forecasts

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

Scattered showers and thunderstorms are expected this afternoon and evening. A few will become strong-to-severe across the Palmer Ridge, Southeast Plains, and Northeast Plains regions. The main threat with strong-to-severe storms will be strong winds (gusts >50 mph) and large hail. Brief periods of heavy rainfall are also likely with those storms, see rain rates below.

Urban Corridor: 0.5-1.0 inches/hour
Raton Ridge and western extents of the Southeast Plains: 0.6-1.1 inches/hour
Palmer Ridge, Southeast Plains, and Northeast Plains: 1.5-2.5 inches/hour

Timing: Noon – 9 PM, with a few showers/thunderstorms lingering over the Raton Ridge and Southeast Plains until just after midnight.

Northwest Slope and Northern Mountains:

Mostly sunny and warm, with an isolated shower/weak thunderstorm over the highest terrain of the Northern Mountains possible. Gusty winds and lightning will be the impacts from any thunderstorm activity, and very little rain. Max rain rates will be less than 0.25 inches/hour.

Timing: Noon – 7 PM

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

Isolated-to-scattered showers and thunderstorms, favoring the higher terrain. The best relative chances will be across the San Juan Mountains, Central Mountains, and Southeast Mountains. Maximum rain rates will be 0.25-0.5 inches/hour for all regions except the Front Range, where rain rates could push 0.4-0.8 inches/hour. Storm motions at 20 mph ENE will limit potential flood threats.

Timing: 11 AM – 8 PM, with a few showers lingering over southern areas until the early morning hours.

STP 07-26-2015: Mostly Sunny for Most as Drier Air Worked In, Some Thunderstorms Rumbled

Issue Date: Sunday, July 26th, 2015
Issue Time: 9:00 AM MDT

Summary:

For nearly everyone, yesterday was a beautiful Saturday marked by mostly sunny skies and warm temperatures as dry air worked in from the west. A few High Country showers and weak thunderstorms were able to develop, producing less than 0.1 inches of rainfall. The best storms of the day developed in the Raton Ridge and Southeast Plains regions, near a surface boundary along the CO/NM border. They produced brief bouts with moderate rainfall and gusty winds.

There weren’t any severe storm reports from yesterday, and no flash flooding was observed.

STP_snapshot_20150726

FTB 07-25-2015: Much Drier North and West, Isolated-to-Scattered Thunderstorms Remain Possible South and East

Issue Date: 7/25/2015
Issue Time: 9:30 AM

NO FLOOD THREAT IS FORECAST.

The same general upper-air pattern remains across the continental US, generally characterized by a high pressure ridge across the central US, flanked by a trough on either coast. The upper-level high pressure is expected to stay centered over Texas today; this is a bit further east than yesterday, thanks to the upper-level low pushing onshore over the Pacific Northwest. This will force drier air into the state today as flow becomes more westerly, but decent mid-level moisture will hang to the south and east of a line bisecting the state from southwest to northeast.

07252015_WV

For High Country areas underneath the drier air, i.e., the Northwest Slope, Northern Mountains, Grand Valley, and Southwest Slope, sunny skies and hot temperatures will be the main story today, with fair weather clouds breaking up the sunshine. A bit better moisture will hang out over the Central Mountains and Front Range, so a couple isolated showers/weak thunderstorms cannot be ruled out, especially across southern portions.

Isolated-to-scattered coverage of thunderstorms is expected over the higher terrain of other western Colorado regions (San Juan Mountains, San Luis Valley, and Southeast Mountains). With precipitable water values running below average for this time of year, rain rates will not be particularly impressive, and the biggest impacts will be gusty outflow winds and dangerous lightning.

For eastern Colorado, mostly sunny skies and hot temperatures will be the name of the game for most. Near the interface with the higher terrain, a few isolated showers/weak thunderstorms will move overhead off the mountains for southern portions of the Urban Corridor and western portions of the Southeast Plains. The best chance for thunderstorms today will be along the CO/NM and CO/KS borders, where a surface boundaries will enhance thunderstorm development a bit. With relatively dry air still in place below cloud bases, the main threats will be strong winds and large hail. Brief moderate rainfall will attend the strongest storms near the CO/KS border across the Southeast Plains and southeastern portions of the Northeast Plains, but dry air and storm motions will limit the impacts to minor street/field ponding.

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.

Flood Threat Legend

Zone-Specific Forecasts

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

Mostly sunny and hot will be the main story, with a few isolated-to-scattered showers and thunderstorms breaking the heat near the mountains south of I-70, and near the CO/KS and CO/NM borders (as described above). Temperatures will be a degree or two cooler than yesterday, so not really a noticeable change. Max rain rates break down like this:

Urban Corridor and Palmer Ridge: 0.25-0.5 inches/hour
Northeast Plains: 0.8-1.2 inches/hour
Raton Ridge: 0.9-1.3 inches/hour
Southeast Plains: 1.0-1.8 inches/hour

Timing: Noon – 9 PM, with a few isolated showers/thunderstorms lingering until midnight before crossing into Kansas.

Northwest Slope, Northern Mountains, Southwest Slope and Grand Valley:

Hot and dry, with a few fair weather clouds breaking up the otherwise sunny sky. Today would be a great Saturday to get outside and enjoy the summer. Remember to drink plenty of water and take breaks from the sun, when necessary.

Front Range, Central Mountains, Southeast Mountains, San Luis Valley, and San Juan Mountains:

Isolated storms for the Front Range and Central Mountains, becoming more scattered to the south. Main impacts will be gusty winds and lightning, with only light rainfall expected. Rain rates will be 0.2-0.4 inches/hour.

Timing: 11 AM – 9 PM

STP 07-25-2015: Cloud Cover Limited Instability, Most Showers and Thunderstorms were Garden Variety

Issue Date: Saturday, July 25th, 2015
Issue Time: 9:00 AM MDT

Summary:

More subtropical moisture was pulled into Colorado yesterday, resulting in fairly abundant high- and mid-level clouds across the High Country and portions of the lower elevations of Eastern Colorado. The cloud cover limited instability, which resulted in showers and weak thunderstorms that didn’t produce much more than light rain. The exception was across far eastern Colorado, where a bit more sunshine combined with a surface convergence zone to develop stronger thunderstorms. One thunderstorm in particular reached severe threshold by producing 1.5 inch hail, 12 miles N of Burlington (Kit Carson County).

As far as rainfall observations are concerned, most locations reported less than 0.1 inches of rainfall. Cheyenne County had the highest report of the day at 1.68 inches. Some of the other higher reports include:

Summit County: 0.39 inches
Gunnison County: 0.38 inches
Lake County: 0.27 inches
Kit Carson County: 0.25 inches
Ouray County: 0.21 inches

No flash flooding was reported.

07252015_STPImage
Storm Total Precip Legend