STP 05-30-2016: A few storms amidst lots of sunshine

Issue Date: Monday, May 30th, 2016
Issue Time: 9:05AM MDT

Happy Memorial Day!

Several scattered complexes of weak thunderstorms developed across mainly eastern Colorado on Sunday. Once again, despite impressive storm structure (making for very photogenic pictures), the cells had a hard time getting much rainfall to the ground. The problem? Dewpoint depressions, defined as the difference between the surface air and dewpoint temperatures, were on the order of 30-40 degrees F. As such, rainfall that began to fall out of the cloud base quickly evaporated and cooled the air around it. This “swamp cooler” effect led to widespread gusty winds, even up to 60 mph, prompting several severe thunderstorm warnings. Meanwhile, rainfall totals topped out at about 0.4 inches for a few lucky locales, but with most other observations in the 0.1 to 0.25 inch range. A few 0.75 inch hail reports were received near Manitou Springs, where the 7,000 foot elevation made it easier for hail to reach the ground with minimal melting.

Taking a step back, we have discussed previously how it has been a rather cold May statewide. The updated numbers, see the map below, show that nearly all of Colorado has been below average with a few areas east of the Divide up to 5F below normal! This has certainly been a boon to the high-elevation snowpack with many locations continuing to sport over 1 foot of snow water equivalent (SWE). Some of the more impressive numbers from SNOTEL sites: Tower in the Park Range with 42.6 inches(!), Black Mesa in the San Juans with 27.5 inches, and Never Summer in the Medicine Bow range with 19.2 inches of SWE remaining.

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No flooding reports were received yesterday. For specific rainfall estimates in your area, please check our STP map below.
STP_20160530

FTB 05-29-2016: A Lot of Sunshine, And a Few Scattered Storms

Issue Date: Sunday, May 29th, 2016
Issue Time: 9:55AM MDT

— Flooding is NOT expected today.

Today’s pattern will be a continuation of yesterday, with a temporary transient ridge setting up overhead as shown in the water vapor image below. The mid-levels of the atmosphere have warmed several degrees Celsius in the last 24-hours and additional height rise are expected. This points to subsidence above the boundary layer and should act to limit rainfall amounts. However, with ample sunshine and enough low-level moisture, expect lots of cumulus clouds to pop up and some of those to lead to scattered showers and thunderstorms. Highest coverage will be east of the Divide, and especially in the Northeast Plains. But with precipitable water values at or below their seasonal normal, rainfall is expected to remain in check. Flooding is not expected today.

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The next weather player is also seen on the water vapor image. This cut-off low, currently over southern California, is expected to propagate east and will impact Colorado’s weather on Memorial Day (Monday) and into Tuesday. An increase in shower and thunderstorm activity is expected each day.

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, scroll below the map.
FTB_20160529Zone-Specific Forecasts:

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

Mostly sunny early with isolated to scattered showers, and weak thunderstorms developing by early afternoon and lasting into the early evening hours. Storms will form in the higher terrain and move slowly eastward through the day. Flooding is not expected today. Max hourly rain rates:

0.6 inches in the Palmer Divide, Front Range, Urban Corridor and Raton Ridge

1.2 inches in the Northeast Plains and Southeast Plains

Primetime: 12pm to 8pm

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

Mostly sunny early then turning partly cloudy. Scattered showers and perhaps a thunderstorm are possible mainly over the higher terrain. Max hourly rain rates up to 0.25 inches. Flooding is not expected today.

STP 05-29-2016: Splendid Saturday With A Few Mean Looking, But Mostly Nice Thunderstorms

Issue Date: Sunday, May 29th, 2016
Issue Time: 9:05AM MDT

As expected, rainfall coverage continued to decrease on Saturday compared to previous days. True to Colorado standards, sunshine was widespread in the morning, but quickly led to scattered cumulus clouds by noon. Showers and weak thunderstorms popped up across many locations, especially east of the Continental Divide. However, with limited instability in place, most storms were much more impressive looking than what their rain totals would suggest. Highest observed 24-hour amounts ending this morning were about 0.5 inches across eastern Colorado. Between the observation sites, radar estimates up to 0.75 inches are shown for parts of the Northeast Plains.

With the warmer temperatures, snowmelt continued though in a very lethargic fashion. An overall cool May (especially when it comes to afternoon high temperature) has put snowmelt at many high-elevation locations about 5-10 days behind schedule. For example, shown below is the Columbus Basin SNOTEL site in the San Juan Mountains (source: NRCS) reading just under 15 inches of snow water equivalent. The site’s median for today is only about 2 inches, and this location is about 9 days behind its average melt schedule. Some great June river rafting seems to be in store across the state!

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No flooding reports were received yesterday.

For specific rainfall estimates in your area, please check our STP map below.
STP_20160529

FTB 05-28-2016: Near Perfect Start To The Holiday Weekend

Issue Date: Saturday, May 28th, 2016
Issue Time: 10:00 AM

— LOW flood threat today for parts of Grand Valley (landslide possible)

The trend of quieter weather will continue for Colorado after the passage of Thursday’s impressive low-pressure system. A transient upper-level ridge will build over the state today, which will promote subsidence in the mid-levels of the atmosphere. Precipitable water values, shown below, continue to fall or held steady just under their seasonal normals today. In all, a typical summer-like diurnal pattern is expected today, with scattered showers and a weak thunderstorm building in the highest elevations by early afternoon. Activity will move quickly eastward into the Cheyenne and Palmer Ridges with generally light rainfall amounts. Despite the quieter weather, hikers should be aware that even weak thunderstorms can cause dangerous lightning. A small cumulus cloud can transition into a lightning producing storm in only 20 minutes.

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We continue to point out that a Flash Flood Watch, issued by the Grand Junction NWS, remains active today for the Salt Creek landslide area (Mesa County). We urge everyone in that area to keep up to date with local officials or the NWS.

Today’s Flood Threat Map

FTB_20160529Flood Threat Legend

Zone-Specific Forecasts:

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

Mostly sunny and warmer today with isolated to scattered showers, and perhaps a weak thunderstorm, developing by early afternoon and lasting into the early evening hours. Max hourly rain rates up to 0.5 inches are possible. Flooding is not expected today.

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

Mostly sunny and warmer today. An isolated shower is possible in the early to mid-afternoon hours. Max hourly rain rates up to 0.25 inches are possible. Flooding is not expected today.