Issue Date: 7/12/2015
Issue Time: 9:45AM

— Low flood threat for San Juan Mountains and Southwest Slope

This morning, Colorado residents awoke to mostly clear skies and cool temperatures in the 40s and 50s. Overhead, our atmosphere is being increasingly dominated by a high pressure ridge to our southeast (see water vapor image below). However, return flow (or clockwise) around the high pressure is allowing for moisture to stream in from the subtropics. A distinct monsoonal moisture surge is noted this morning, from the Mexican Sierra Madre mountain range all the way north along the Arizona/New Mexico border. While morning precipitable water (PW) values across the state were in the 0.6 to 0.8 inch range, this surge will be carrying 1inch or greater PWs into southwest Colorado. East of the Divide, downsloping flow and subsidence from the high pressure will put a limit on rainfall rates.

For today, we expect mostly sunny skies this morning to lead to scattered thunderstorms over southwest Colorado and into the higher terrain of the Central Mountains. Most rainfall activity will be benign, with 1-hr rainfall rates up to 0.6 inches possible. However, over the southeast corner of the state, high moisture content will allow for 1-hr rainfall up to 1.0 inch. A Low flood threat has been posted for that region. In addition to the rainfall today, stronger storms will be capable of producing gusty winds up to 55 mph. Storm activity will diminish after sunset statewide.

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

Southwest Slope, San Juans:

Mostly sunny early with scattered thunderstorms developing by early afternoon. Maximum one-hour rain rates up to 1.0 inch will be possible, leading to isolated flash flooding mud flows and debris slides. Gusty winds, up to 55 mph, will also be possible. Storm activity will gradually diminish in the late evening. A Low flood threat has been posted for the area.

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

Mostly sunny early, then turning partly cloudy. Isolated to widely scattered thunderstorms will be possible from early afternoon to around sunset. Max 1-hr rain rates up to 0.5 inches will be possible, along with gusty winds up to 55 mph. No flooding is expected today.

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

Mostly sunny and warmer with a few cumulus clouds possible by late afternoon. Rainfall is not expected today, but if a storm does form, it will be more of a gusty wind threat than rainfall. Flooding is not expected today.

Issue Date: 7/11/2015
Issue Time: 10:00AM

— Flooding is NOT expected today
— Hikers: please be aware of lightning, even in weaker thunderstorms

Simply stated: the persistent upper-level low off the California coast has been wreaking havoc on weather forecasts. We have noticed that weather models have consistently been trying to dissipate the low, while it has not wavered. In the end, this will result in higher than expected precipitation chances today. However, moisture content has decreased noticeable over the state since Thursday. Morning dewpoint temperatures are in the 40s and 50s, which is relatively high. But precipitable water, a measure of total atmospheric water vapor content, has fallen into the 0.6 to 0.8 range statewide. We expect the highest thunderstorm activity today west of the Divide, over the San Juan, Grand Valley and Central Mountain regions. East of the Divide, a stray storm is possible, but rainfall rates should be relatively light. Flooding is not expected today across Colorado.

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, Southeast Plains, Palmer Ridge, Front Range, Urban Corridor, Raton Ridge, Southeast Mountains:

Mostly sunny early, then becoming partly cloudy with isolated to widely scattered possible by mid afternoon. Highest coverage will be over the highest terrain. One hour rain rates up to 0.6 inches will be possible. Flooding is not expected today.

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

Mostly sunny early, then becoming partly cloudy with isolated to widely scattered thunderstorms developing over the higher terrain. Storms will spread into valleys by later in the afternoon. Overall, highest storm coverage will be in the San Juans, Central Mountains and Grand Valley region. One hour rain rates up to 0.5 inches will be possible today, along with hail up to 0.5 inches in the strongest storms. No flooding is expected today.

Issue Date: 7/10/2015
Issue Time: 9:55AM

— Low flood threat for Northeast Plains and Southeast Plains

Even as late as yesterday, it appeared that the upper-level low pressure over California (see water vapor image below) may impact our weather today with more heavy rainfall. However, a look at this morning’s observations shows drier conditions, and warming mid/upper-level temperatures as the low pressure somewhat unexpectedly retreating northward. Both of these factors suggest a large reduction in the coverage and intensity of thunderstorm activity today. Nonetheless, there will be enough instability to produce thunderstorms capable of marginally heavy rainfall over both the Northeast and Southeast Plains. As such, a Low flood threat has been issued for these regions. For the rest of the state, expect weaker thunderstorms today and generally more sunshine.

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

Southeast Plains, Northeast Plains:

Mostly sunny early with scattered thunderstorms developing by mid afternoon. One hour rain rates up to 1.7 inches could cause isolated flash flooding in the extreme northeast and southeast corners of the state. A Low flood threat is in place. Storms may be ongoing through the late evening hours as higher moisture returns into the area through the low-level jet. In addition to heavy rainfall, hail up to 1.25 inches may accompany the strongest storms.

Primetime: 2PM through 11PM

Palmer Ridge, Front Range, Urban Corridor, Raton Ridge, Southeast Mountains:

Mostly sunny early, then becoming partly cloudy. Warmer temperatures are expected today. Isolated to widely scattered thunderstorms will form over the highest terrain by early afternoon and spread eastward. One hour rain rates up to 0.7 inches will be possible, but flooding is not expected.

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

Mostly sunny early with scattered thunderstorms developing shortly after noon. Highest coverage will be in the San Juans. One hour rainfall up to 0.6 inches will be possible with the strongest storms. No flooding is expected. In addition to the rainfall, gusty winds up to 60 mph and hail up to 0.75 inches may accompany the strongest storms.

Issue Date: 7/9/2015
Issue Time: 10:30AM

— Moderate flood threat for Palmer Ridge, Raton Ridge and parts of Southeast Plains
— Low flood threat for Grand Valley, Southwest Slope, San Juans, Central Mountains, Front Range, Urban Corridor and Northeast Plains

A combination of features will act in tandem to bring another day of heavy rainfall across parts of our state. Some of the players are outlined in the water vapor image below. The most prominent is the upper-level low pressure spinning over California. Over the past 3 days, this disturbance has barely budged, but appears to be gaining speed as it heads east. South and east of this low, a stout subtropical jet is entering Arizona. At the nose, or most downstream part, of the jet is a marked disturbance currently approaching the 4-Corners region. With more sunshine today, the atmosphere will have an easier time heating up, allowing this disturbance to trigger some heavy rain producing storms over Colorado later this afternoon and evening. Along with favorable dynamics, we also note relatively high moisture content. Dewpoint temperatures are once again in the 50s to near 60F statewide. Precipitable water (PW) values have dipped slightly since yesterday, now in the 0.85 to 1 inch range. However, PWs are expected to stay steady or increase throughout the day.

 

For today, we expect early breaks in clouds to quickly fill in with scattered to widespread thunderstorm activity. First, over and west of the Divide by noon and then east of the Divide shortly thereafter. The highest flood threat today will be over the Palmer Ridge where favorable winds could provide for a window of very heavy rainfall this afternoon and evening. A Moderate flood threat is in place here. A separate Moderate flood threat is also in place for the Raton Ridge and Southeast Plains where a moisture surge may produce some very heavy rainfall later this evening and into midnight. Elsewhere, a Low flood threat is in place for many parts of the state for scattered, short-term thunderstorms capable of producing flash flooding.

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

Raton Ridge, Southeast Plains, Southeast Mountains:

Partly cloudy early with scattered to widespread thunderstorm forming by mid-afternoon. One hour rain rates up to 2.4 inches will be possible, with 3-hr rain rates up to 3.5 inches. Storm activity may intensify after sunset as a low-level jet pumps a very moist atmosphere (PWs approaching 1.6 inches) into Colorado. Activity is expected to subside shortly after midnight as instability fades. A Moderate flood threat is in place for parts of the area with a Low threat elsewhere.

Primetime: 2PM through 1AM

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

Partly cloudy early, then scattered to widespread thunderstorms forming by early afternoon. Activity will form first over the highest terrain of the Front Range and Palmer Ridge. One hour rain rates up to 1.6 inches will be possible, causing isolated to scattered flash flooding. The highest threat area will be the Palmer Ridge, where south-southeast winds will create a favorable upslope component to the flow. Activity is expected to cease shortly after sunset.

Primetime: 2PM through 10PM

Raton Ridge, Southeast Mountains, San Luis Valley, Central Mountains, Southwest Slope, San Juans:

Partly cloudy with isolated to scattered thunderstorms developing by early afternoon. One hour rain rates up to 0.8 inches will be possible, but flooding is not expected. Activity will subside shortly after sunset.

Southwest Slope, San Juans, Grand Valley, Central Mountains, San Luis Valley:

Mostly sunny early with showers and thunderstorms quickly developing by noon. One hour rain rates up to 0.9 inches will be possible. Given the saturated soils in many parts of the area, this will be enough to induce isolated flash flooding, mud flows and debris slides. Numerous mud flows have been reported over the past several days. A Low flood threat is in place for all areas except for the San Luis Valley. Activity will subside around sunset.

Primetime: 12PM through 8PM

Northwest Slope, Northern Mountains:

Partly cloudy with isolated showers and thunderstorms possible from early afternoon through around sunset. Highest one-hour rain rates will be around 0.6 inches, and no flooding is expected.