FTB 08-14-2019: No Flood Threat, but Isolated Severe Thunderstorms are Forecast for the Northeast Plains

Issue Date: Wednesday, August 14th, 2019
Issue Time: 9:05AM MDT

Marked in the water vapor imagery below are the shortwaves in the area (orange X’s) as well as the direction of their movement today (black arrows). Exiting the state to the southeast is the shortwave that brought widespread, heavy rainfall to the eastern plains yesterday afternoon and overnight. There are still a few moderate showers over the far Southeast Plains associated with this feature as well as decent cloud cover over the southeast quadrant of the state in the wake of the rainfall. Northwest flow aloft is forecast continue today with less moisture and minimal to no mid-level energy moving through the state. With drier air mass in place (really dry above 400mb in the Denver and Grand Junction soundings), storms this afternoon over the mountains and adjacent plains should be fairly isolated. There is also a noticeable inversion in place around 400mb (Denver), which should keep rainfall out of the forecast for the Denver Metro area. As far as western Colorado, storm chances will again be confined to the eastern San Juan Mountains with only trace amounts of rain likely.

Looking for storms to fire under upslope flow around 2PM mainly over the southern Front Range and Southeast Mountains. As the high-based move off the higher terrains, they have a better chance of producing measurable rainfall over the adjacent plains, especially along the elevated terrains of the Palmer and Raton Ridges. It is likely that a storm or two fires over the Cheyenne Ridge/dry line that sets up moves through the Northeast Plains. A smaller ribbon of high CAPE and shear values over the area may produce a severe thunderstorm or two, although it’s important to note the threat for severe thunderstorms is over a much smaller area than yesterday. The severe storm or two will have the potential to produce large hail (around egg size), gusty winds and an isolated tornado. Storm motion is slightly faster than yesterday and moisture a little lower, so not expecting storms to reach flood threat criteria. All storms should exit the state by 11PM, and flooding is not forecast.

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:

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

Max 1-hour rain rates up to 0.2 inches will be possible over the adjacent plains with storms over the eastern mountains producing only trace amounts to no rainfall. Gusty winds will be the main threat with storms (west) today as they form and quickly dissipate. If storms make it to the southeast corner before falling apart, totals closer to 0.75 inches will be possible. The severe thunderstorms over the Northeast Plains will have max 1-hour rain rates closer to 0.9 inches with an isolated total around 1 inch possible. Once again, these storms may produce large hail, gusty winds and an isolated tornado or two. Flooding and overnight storms are not forecast. Cloud cover over the southeast quadrant of the state should knock down high temperatures a few degrees as well.

Primetime: 2PM to 11PM

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

Similar set up to yesterday with little change to high temperatures. Dry air continues to be entrained from the west, so storm chances will be limited to the eastern San Juan Mountains. These storms will likely only produce trace amounts of rainfall with a couple isolated totals up to 0.1 inches possible. Also expect some brief, gusty winds from the storms that do form. Cloud cover will also be similar to yesterday, so only minimal relief from the heat is forecast.

Primetime: 2PM to 8PM

FTB 08-13-2019: Severe Thunderstorms Forecast for the Northeast Plains Along with Overnight Rainfall for the Southeast Plains

Issue Date: Tuesday, August 13th, 2019
Issue Time: 10:25AM MDT

–A LOW flood threat has been issued for the Northeast Plains, Palmer Ridge, Southeast Plains and eastern Raton Ridge

Upper level flow has not changed much since yesterday, and with high pressure continuing to build over the desert southwest, westerly flow aloft will continue to pull in the dry air mass from Utah (see the lack of clouds in the visible satellite imagery below). There is some residual moisture over the San Juan Mountains, so some high-based light showers and weak thunderstorms may be possible this afternoon as a shortwave moves in from Utah and enhances weak upslope flow. The main threat from storms will be gusty winds. New to today’s forecast is a mid and upper level jet over the Colorado and Wyoming border, which will keep steering flows very fast over Northeast Colorado. It feature may also help break the cap this afternoon with the northeast corner of the state being in the right entrance region of the jet. The dry air from Utah and westerly winds off the eastern mountains will help reinforce a very strong dry line (marked in orange below) over the eastern plains. Dew points will drop by 30-35°F on the west side of this line, which will help cause convergence. Paired with convergence on a southward moving boundary, there is a threat for severe thunderstorms over the Northeast Plains from about 3PM through this evening. These severe thunderstorms will be capable of producing very large hail, strong outflow winds (>60 mph), an isolated tornado or two and brief, heavy rainfall. With the high shear, high CAPE environment and slightly lower freezing level than Sunday, storms have the potential to produce hail greater than the size of baseballs.

PW over Denver this morning measured 0.63 inches, but as mentioned above, it increases to over 1 inch over the eastern plains. This is a good indicator of the potential for heavy rainfall this afternoon. The flood threat for the severe thunderstorms over the Northeast Plains will only be about 1 hour due to storm motion between 20 and 25 mph to the southeast. There is the possibility for multiple storms to track over the same area of the Northeast Plains, but storms will likely dissipate due to lack of instability as they move into a cold pool. Thus, only the Low flood threat.

 

 

Interesting set up back to the west. The severe thunderstorms over the Northeast Plains look to send a strong outflow boundary back towards the Front Range this evening. This may cause an evening severe thunderstorm or two over the southern Urban Corridor. The one uncertainty is a slight inversion at about 600mb in this morning’s sounding at Denver, which would need to be broken for these isolated storms to occur. Not seeing a flood threat with these storms, due to higher moisture back to the east, but worth mentioning as to not catch anyone off guard.

Lastly, there is an additional Low flood threat issued for the Southeast Plains. The low level jet looks to set up over the area, which would help fuel overnight storms that form along outflow boundaries and other boundaries in the area. In a high-moisture environment, storms may be capable of producing local, heavy rain totals over a 2-3 hour period. There is a little uncertainty with instability (more gradual rain rates vs very high rainfall rates), so only issuing Low flood threat for this area. Flood threats today include arroyo flooding, road flooding, local stream/creek flooding and 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, scroll below the map.

Flood Threat Legend

 

Zone-Specific Forecasts:

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

Severe thunderstorms are forecast to begin around 3PM over the Northeast Plains. Max 1-hour rain rates up to 1.75 inches will be possible with the fast moving storms. The severe thunderstorm threat over the Northeast Plains is expected to end by 8PM, but a weak MCS over the Southeast Plains is forecast overnight. These storms will likely produce some smaller hail and gusty winds as well. As mentioned above, there is some uncertainty with the heavy rainfall potential with instability. However, there is a slight chance for some very local 2-3 hour rainfall totals up to 2.25 inches, so the Low flood threat has been extended south.

Back to the west, the outflow boundary will provide a chance for an isolated storm over the southern Urban Corridor and Front Range. A quick 0.5 inches in 30 minutes will be possible if the storms break the cap. Lastly, a few storms will fire this afternoon with upslope flow over the Palmer Ridge/Front Range intersect. Storms will produce mostly cloud cover over the mountains with max totals up to 0.3 inches possible over the Palmer Ridge.

Primetime: 2PM to Morning

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

A deep layer of dry air over the area will limit storm chances today. Slightly higher levels of residual moisture over the San Juan Mountains will provide a chance for afternoon thunderstorms over the highest elevations. Storm bases will be very high, so expecting rain rates to remain under 0.1 inches with gusty winds and a few lightning strikes possible. High temperatures look to be similar to yesterday and increasing, broken cloud cover from the passing shortwave is expected to help provide some shade from the heat.

Primetime: 2PM to 8PM

FTB 08-12-2019: Mostly Dry Weather Today after an Active Weekend

Issue Date: Monday, August 12, 2019
Issue Time: 9AM MDT

— Flooding is NOT expected today

Chances of precipitation will drop significantly today after a weekend of active weather. The subtropical high has moved to the southeast and is now centered over the Gulf Coast of Texas. This has shifted the southerly flow of moisture to the east, cutting off Colorado from its primary moisture source today. Westerly flow of dry air aloft (yellow line in the water vapor imagery below) will continue to dry out western Colorado and the high country, keeping chances of precipitation low over most areas. A weak shortwave to our south will keep some residual moisture over southern Colorado, giving the area the highest chance for precipitation today. Moisture is high over the eastern plains this morning after yesterday’s rain, with dew points measuring in the upper 50°Fs and low 60°Fs. However, a cold front (blue dashed line below) is forecast to come in from the north, which will mix out moisture over the northern half of the state throughout the morning and into the early afternoon. Weak isolated thunderstorms are forecast early this afternoon over the southern mountain ranges, however fast storm motion and dry surface conditions will keep rain rates well below flood threat criteria. Another round of weak storms is forecast to form over the southernmost Urban Corridor and Southeast Mountains around sundown, moving over the Southeast Plains tonight. No flooding is forecast for today.

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.

Zone-Specific Forecasts:

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

The highest chances for precipitation today will be over the southern Urban Corridor, southern Front Range and eastern Palmer Ridge.  Storms are expected to begin over the area early this afternoon, moving quickly to the southeast.  Another round of storms is expected over the Southeast Mountains, Southeast Plains and Raton Ridge tonight.  Storms are expected to dissipate as they move to the east.  Max 1-hour rainfall rates of 0.4 inches are forecast over the area, with isolated totals up to 0.6 inches possible over the Palmer Ridge.  Flooding is not forecast today.

Primetime: 1PM to 10PM

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

Dry air will reduce chances of precipitation to near zero over the northern two-thirds of the area today.  The greatest chance for measurable rainfall will be over the eastern San Juan Mountains, with chances for high-based isolated storms this afternoon and into the early evening.  Max 1-hour rainfall rates of 0.2 inches are forecast for today.  Expect mostly sunny skies and high temperatures in the upper 80°Fs and low 90°Fs.

Primetime: 12PM to 7PM

FTB 08-11-2019: Severe Thunderstorms Forecast for the Northeast Plains along with Very Heavy Rainfall

Issue Date: Sunday, August 11th, 2019
Issue Time: 9:10AM MDT

— A MODERATE flood threat has been issued for the Northeast Plains
— A LOW flood threat has been issued for the southern Urban Corridor, Palmer Ridge, 416 burn area and the Spring Creek burn area

The active weather pattern will continue to round out the weekend with the 500mb high remaining in a favorable position for a northward moisture surge. Marked in the visible satellite imagery below (orange X’s) are the shortwaves, which are expected to help enhance today’s rainfall. The one currently over the state is helping create moderate rainfall over the SW high terrains. To our east is a larger shortwave that passed overhead yesterday, which helped cause some heavy rainfall overnight in Kansas. Today, the Pacific trough will begin to move to the east throughout the day (to our north). This will start to pull in the dry air seen in Utah (cloud free) over western Colorado by this evening with more westerly flow aloft forecast. Southwest flow is forecast east of the Continental Divide as the 500mb only moves slightly eastward from the approaching trough. High moisture is marked in the green line below and denotes where dew points are 60°F or greater. This high moisture is helping produce some thick fog over the northwest corner of the state as well. While some of this moisture will mix out west to east, high PW values will remain over the Northeast Plains. Paired with a decrease in steering winds over this area, storms will be capable of producing very heavy rainfall.

More widespread storms over the mountains with higher rain rates are forecast as morning heating occurs. There should be good coverage of storms, associated with the shortwave, by 11AM to noon. By about 2PM these storms will move into the Urban Corridor and eventually the Northeast Plains. Increased instability and shear over the Northeast Plains should create a couple severe thunderstorms (large hail, strong winds and possible isolated tornado) and an eventual N-S oriented line of storms. More scattered storms are anticipated over the southern high terrains this afternoon with a storm or two possible over the adjacent plains. The most likely region to receive rainfall over the adjacent plains from these storms is the climatological hot region, the Palmer Ridge.

All storms should exit into Kansas and Nebraska by 10PM or so, but a couple late night showers may be possible over the Southeast Mountains. These would be fueled by a moisture rich environment and the next shortwave moving around the ridge and into the southern tier of Colorado. A Moderate flood threat has been issued for the Northeast Plains and a Low threat has been issued for 416 and Spring Creek burn area, since storms in the area will be able to produce rain rates that have been known to cause flooding issues.

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.

Flood Threat Legend

 

Zone-Specific Forecasts:

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

Max 1-hour rain rates up to 0.5 inches (northern mountains) and 0.8 inches (southern mountains) will be possible. Over the adjacent plains, trailing storms may cause totals up to 1 inch by tomorrow morning. Max 1-hour rain rates up to 2.25 inches will be possible over the Northeast Plains (Moderate threat area) with isolated storm totals around 3 inches possible by tomorrow morning. Threats include local stream and creek flash flooding, field ponding and road flooding. A couple of severe thunderstorms will be possible with large hail, damaging winds and an isolated tornado. The flood threat should decrease after midnight or a little before. With trailing storms capable of producing such high rain rates over the Southeast Mountains, a Low threat has been issued for the Spring Creek burn area.

Primetime: 11AM to Midnight

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

High moisture holds on over the San Juan and south Central Mountains for one more day. Storms will widespread in coverage, since dry air won’t move into the state from the west until late tonight. Current showers and thunderstorms will likely limit instability for stronger storms this afternoon, but 1-hour rain rates up to 0.6 inches will be possible. With rain falling near the 416 burn area the last couple of days and rain rates greater than 0.4 inches possible, a Low flood threat has been issued for this scar. The threat for mud flows, debris slides and flash flooding over the burn area should end by 10PM. The San Luis Valley will also likely get some rain again with isolated totals up to 0.75 inches by morning with more widespread max 1-hour rain rates closer to 0.5 inches.

Primetime: 11AM to 10PM