Issue Date: 8/9/2015
Issue Time: 9:55AM

— LOW flood threat for the Palmer Ridge and parts of Southeast Plains
— An elevated flood threat is likely tomorrow east of the Continental Divide

Today’s weather map (see water vapor image below) shows most of the same players as yesterday. Monsoonal flow around the subtropical high continues to stream northeastward. Today the trajectory of that flow implies that only southeast Colorado will be meaningfully impacted. This is also well captured by morning precipitable water values (PWs). For most of the state, PWs are in the 0.6 to 0.85 range, but Pueblo sits at 1.2 inches. As the high pressure ridge will build to the northwest today, we expect some further lowering of PWs. However, the southeast quadrant of the state will likely maintain the critical 1.0 inch PW threshold that we use as a rough proxy for the heavy rainfall threat. At the surface, dewpoint temperatures are in the 40s to mid-50s, except in the southeast where low 60s are found. Meanwhile, also note a strong low pressure seen off the west coast. This will become a player in our weather over the next few days (see our Flood Threat Outlook).

This morning, most of Colorado sits under clear skies. Cumulus clouds will quickly develop and then build into thunderstorms by early afternoon. Highest storm coverage will be from the San Juans eastward through the south face of the Palmer Ridge. But even in these areas, we expect isolated to scattered coverage. The expected surface circulation will favor drying/downsloping flow north of the Palmer Ridge. To the south, however, a weak upslope component to the flow combined with high moisture will support a Low flood threat. In this small region, 1-hr rain rates up to 1.9 inches will be possible. Elsewhere, storms are not expected to amount to much rainfall. That will change tomorrow.

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.

Zone Specific Forecasts

Palmer Ridge, Southeast Plains:

Sunny early, then partly to mostly cloudy with isolated to scattered thunderstorms developing by early afternoon. Max 1-hr rain rates up to 1.9 inch will be possible, causing isolated flash flooding and street flooding. Gusty winds up to 45 mph may accompany the strongest storms. Storm coverage will likely be highest from mid-afternoon through around sunset. However, the flood threat will persist through the early morning hours due to anticipated upslope moving outflow boundary.

Primetime: 1pm to 1AM

Northeast Plains, Urban Corridor, Front Range, Southeast Mountains, Raton Ridge, San Juans:

Partly cloudy early, then isolated to scattered showers and thunderstorms forming around noon and lasting through early evening. Max 1-hour rain rates up to 0.6 inches will be possible. No flooding is expected. Gusty winds up to 45 mph could accompany the strongest storms. East of the Divide, an isolated storm or two may pop up in the late evening and early morning hours.

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

Mostly sunny early, then partly cloudy with isolated to showers and a weak thunderstorm possible from early afternoon through early evening. Max 1-hr rain rates up to 0.3 will be possible, thus, flooding is not expected.

Issue Date: 8/8/2015
Issue Time: 9:45AM

— LOW flood threat for the Palmer Ridge and parts of the Northeast and Southeast Plains

Yesterday’s disturbance has raced all the way across Kansas overnight. However, as shown in the water vapor image below, another much weaker disturbance is seen this morning over northern Utah. This disturbance will progress east/northeastward within the flow. As it is also transporting in some very dry air from the west, heavy rainfall will effectively be prevented west of the Divide today. Case in point: in Grand Junction’s morning atmospheric sounding, the relative humidity values between 10,000 and 14,000 feet ranged between 2 and 5%. Meanwhile, east of the Divide, a surface low circulation was noted on the CO/KS border. This will help to maintain a weak surface front roughly along the Palmer Divide. A monsoon surge continues to send pulses of moisture northeast, supporting a rainfall threat across eastern Colorado today. However, coverage and intensity should be much weaker/lower than Friday. Finally, the morning moisture check reveals dewpoints in the 50s and low 60s east of the Divide and precipitable water values near 1 inch. These readings are certainly conducive for at least isolated heavy rainfall.

For today, we expect the cloud deck over central and northeast Colorado to thin out a bit by afternoon. Thunderstorms are expected to develop over the San Juans stretching east/northeast across the Palmer Ridge. West of the Divide, rain rates will be low enough to ease any flooding concerns. East of the Divide, rain rates could approach 2.2 inches an hour over the Palmer Ridge and Northeast Plains. A Low flood threat is warranted here. However, storm motion will be fast enough to prevent a prolonged heavy rain threat. Due to the dry air impinging from the west, there will likely only be one round of thunderstorms today (unlike yesterday). Hail and gusty winds will once again be a threat, but we do not expect hail over 1.5 inches.

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.

Zone Specific Forecasts

Northeast Plains, Palmer Ridge, Southeast Plains:

Partly cloudy early with scattered thunderstorms developing shortly after noon. Coverage will be highest over the Palmer Ridge as well as far northeast Colorado. Max 1-hour rain rates up to 2.2 inches can be expected. A Low flood threat is in place for isolated flash flooding, and street flooding. Wind shear in the lowest 6-km will vary between 30-35 knots, supporting hail up to 1.5 inches in the strongest storms. However, atmospheric instability will be limited (and decrease by late afternoon), tempering this threat. Gusty winds up to 55 mph will be possible with the strongest storms. Most activity will cease around sunset, but an isolated storm or two could persist through midnight.

Primetime: 1pm to midnight

Urban Corridor, Front Range, Southeast Mountains, Raton Ridge, San Juans:

Partly cloudy early, then isolated to scattered showers and thunderstorms forming around noon and lasting through early evening. Max 1-hour rain rates up to 0.8 inches will be possible. No flooding is expected. Gusty winds up to 45 mph could accompany the strongest storms.

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

Mostly sunny early, then partly cloudy with isolated to scattered showers and weak thunderstorms possible from early afternoon through early evening. Max 1-hr rain rates up to 0.5 will be possible, thus, flooding is not expected.

Issue Date: 8/7/2015
Issue Time: 9:40 AM

A MODERATE FLOOD THREAT IS FORECAST FOR PORTIONS OF THE NORTHEAST PLAINS AND PALMER RIDGE.

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE SOUTHWEST SLOPE, SAN JUAN MOUNTAINS, GRAND VALLEY, URBAN CORRIDOR, SOUTHEAST PLAINS, RATON RIDGE, AND PALMER RIDGE.

Today will be quite the change from the last two days with scattered thunderstorms expected across much of the state. A quick glance at the water vapor imagery shows the increase in moisture from southwesterly flow aloft as the upper-level high pressure has been pushed back to the east by the approaching upper-level low. This increase in moisture will provide the fuel for thunderstorm development. A disturbance (marked by the red line over NV/UT/AZ) will rotate across Colorado today, providing background support for a fairly active day. Severe thunderstorms will be possible across Southwest Slope and Grand Valley regions (mainly a severe wind threat), and across the Northeast Plains, Southeast Plains, and Palmer Ridge regions. Severe storms over eastern Colorado will hold a mixed bag of threats thanks to ample instability/moisture/wind shear, with isolated tornadoes, severe winds, large hail, and heavy rain capable of flash flooding.

Most of the activity will follow the typical diurnal pattern and diminish after sunset, but isolated-to-scattered showers will likely continue overnight across the Grand Valley, Central Mountains, San Juan Mountains, and Southwest Slope regions. Additionally, as storms work eastward across the plains towards KS/NE, it could be midnight, or just after, before they exit the state.

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.

Zone-Specific Forecasts

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

Scattered strong-to-severe thunderstorms expected across the Northeast Plains, Palmer Ridge, and Southeast Plains, with isolated thunderstorms (some strong) expected elsewhere. Maximum rain rates will vary:

Urban Corridor and Raton Ridge: 0.8-1.2 inches/hour
Southeast Plains and Palmer Ridge: 1.2-2.0 inches/hour
Northeast Plains: 2.0-3.0 inches/hour

Timing: 2 PM – Midnight

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

Isolated-to-scattered showers and thunderstorms, but lesser moisture than other regions will keep coverage and rain rates down a bit. Maximum rain rates will be 0.4-0.6 inches/hour.

Timing: Currently – 11 PM

San Juan Mountains, Southwest Slope, and Grand Valley:

Scattered-to-widespread showers and thunderstorms, some will produce locally heavy rainfall. Cloud cover this morning will limit instability this afternoon, especially if it persists into peak heating hours. The depth of moisture suggests efficient precipitation processes will occur, so a low flood threat has been issued. Maximum rain rates will be 0.8-1.1 inches/hour.

Timing: Currently – Midnight, with isolated-to-scattered showers continuing into tomorrow morning.

Issue Date: 8/6/2015
Issue Time: 9:05 AM

NO FLOOD THREAT IS FORECAST.

Mother Nature has decided to turn off the faucet and turn on the heat for today, resulting in a day full of sunshine and basically devoid of precipitation. The upper-level ridge will be centered over New Mexico today, leaving a subsident air mass over Colorado and continue the drying trend seen over the last few days. There just simply will not be support for thunderstorms today or tonight. An isolated shower or two over the higher terrain will be possible, but the chances are less than 10% and will produce very little rainfall at the surface, if any. High temperatures today will be a few degrees above average for this date.

The next monsoonal surge will arrive tomorrow as the upper-level ridge slides to the east in response to an approaching upper-level trough. Tune into the Flood Threat Outlook this afternoon for more information on this storm, and what conditions the next 15 days hold, overall. And, as always, check back in with tomorrow’s Flood Threat Bulletin.

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.

Zone-Specific Forecasts

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

Mostly sunny and hot, with high temperatures upper-80s/low-90s along the Urban Corridor and across the Palmer/Raton Ridge, ranging into the mid-/upper-90s across the plains regions. Locations in the Arkansas River Valley near the CO/KS border will flirt with 100 degrees.

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

Mostly sunny and hot, with high temperatures a few degrees above average for this date. An isolated shower or two over the higher terrain cannot be ruled out this afternoon, but probabilities are less than 10%. Little to no rainfall at the surface will result, and the only potential impact will be weak, cooler wind gusts.