Area Forecast Discussion
Issued by NWS Pueblo, CO
Issued by NWS Pueblo, CO
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881 FXUS65 KPUB 202331 AFDPUB Area Forecast Discussion National Weather Service Pueblo CO 531 PM MDT Thu Jun 20 2024 .KEY MESSAGES... - Strong storms possible through this evening across the mountains and adjacent northern I-25 corridor. - Flash flood concerns increase tonight through Friday night for the Continental Divide and burn scars in the southeast mountains as anomalously moist airmass spreads up from the south ahead of an approaching trough. - Isolated afternoon thunderstorms will be possible on Sunday, with an uptick in thunderstorm activity thereafter through the mid part of next week. - Continued warming trend this weekend through the mid part of next week. && .SHORT TERM /THROUGH FRIDAY NIGHT/... Issued at 209 PM MDT Thu Jun 20 2024 A strong southerly moisture fetch ahead of the approaching trough out west has brought precipitable waters of 100-125% of normal across southern CO according to satellite measurements this afternoon. Moisture advection continues tonight with Precipitable Waters increasing to up to 250% of normal funneling into the southwest mountains. Dew points in the 40s across the mountains and valleys are already yielding CAPE values of up to 1000 J/kg. Combined with deep layer shears of 20-30 kts (greatest values to the north) a few strong to near severe thunderstorms will be possible across the mountains and valleys where hail up to 1 inch in diameter and wind gusts up to 60 mph will be possible. Locally heavy rainfall capable of producing rock slides and flash flooding will be the primary risk however and burn scars and areas with susceptible soils will be monitored closely. There will likely be one or more rounds of showers and embedded thunderstorms continuing over the mountains through tonight with the focus for sustained precipitation across the Eastern San Juan mountains given southwesterly orographic forcing. Question will be how intense thunderstorms and rainfall rates will be overnight with the risk shifting more towards flash flooding as soils become saturated. Model blends show mean QPF values of up to 1.5 inches across the eastern San Juans through tonight with most areas elsewhere in the 0.25 to 0.5 inch range across the mountains. 90th percentile shows some areas of up to 3 inches of rain across the eastern San Juans. There is likely some convective feedback leading to some of these higher values within the model spread (as we saw last night with convection forecast to spread into El Paso county), but there is an upslope signal that could lead to higher precipitation amounts from the model blends which can`t be completely discounted. Given the dry antecedent soil moistures will hold off on any Flash Flood Watches at this point, but tonight`s rainfall may prime the pump for a greater flash flood risk on Friday. Another round of showers and thunderstorms will redevelop early on Friday as forcing increases ahead of the next upper trough. Once again, flash flooding will be the primary concern across the mountains with high precipitable waters (250%+ of normal) still over the region. CAPE values look a little lower but still ranging up to 750 J/kg if we can get enough afternoon heating with the residual convective cloud cover. So another round of strong to marginally severe thunderstorms will be possible across the mountains. Deep layer shears will be stronger tomorrow given increasing flow aloft so if we can realize sufficient instability there could be a better chance for severe thunderstorms. Once again convection will linger well into the night as the upper trough slowly moves across CO with focus shifting southward with time. The southeast plains will feel little impact from this system as the majority of the forcing and instability stays over the mountains. An isolated storm or two will be possible as they drift off into the adjacent plains with gusty winds and brief heavy rainfall the primary risks for Friday. Meanwhile, temperatures for eastern areas will continue the warming trend with highs back in the mid 90s across the lower elevations. The valleys and mountains will stay cooler given the early onset to convection with highs in the 60s and 70s. -KT && .LONG TERM /SATURDAY THROUGH THURSDAY/... Issued at 209 PM MDT Thu Jun 20 2024 Friday night through Saturday... An upper level trough is going to be transitioning over the region by later in the evening on Friday, and the axis will move overhead right around midnight and through the early morning hours over the CWA. This will translate to the possibility of showers and thunderstorms continuing over much of the region during the overnight hours. With an abundance of moisture in the mid-levels and even low levels with upsloping, PWAT values have been between 200- 300% of normal and the risk for excessive rainfall and possible flash flooding will still be in place as a result. Heavy rains possible with some of these storms could also exacerbate snow melt and also lead to water levels potentially reaching action stage for rivers within the San Luis Valley. The other areas of concern will be burn scar areas, as well as Monarch Pass and the Chalk Cliffs/Cottonwood Pass. After the trough moves through, it will be relatively stable behind the wave with subsidence occuring, and therefore mostly dry by later in the day on Saturday. There could still be a couple an isolated shower or storm developing later in the afternoon over the higher terrain with daytime heating and some residual moisture in place, otherwise it will be predominantly dry by later in the day for most of southeast Colorado. It will be slightly warmer as well since upper level ridging will move over behind the exiting trough. Sunday through Thursday... The longwave ridge over the inner-mountain west will slowly propagate eastward with the axis over the region on Sunday. Meanwhile, there will be some moisture advected up in the mid-levels from the southwest. This will allow for the development of afternoon and evening showers and thunderstorms, mainly over the mountains, with westerly flow pushing some of the storms out over the plains by later in the day. With the ridge axis moving over, it will also cause temperatures to continue to warm with temperatures approaching the 100 degree mark for locations within the lower Arkansas River Valley. The ridge will flatten and move east with another larger longwave ridge moving over in its wake towards the middle of the week. This will result in a continuing warming trend with temperatures over 100 degrees becoming more likely during the day over much of the plains from Monday through Wednesday. There will also be some subtropical moisture advected up in the ridge over the Four Corners area which will help increase chances of afternoon and evening thunderstorms over the mountains, with some of these moving out into the plains by later in the day. In addition, some of the deterministic models are also cueing in on a potential tropical system moving out over the Pacific Ocean south of Baja California, which might get tapped into the southwesterly flow and increase mid-level moisture over the region towards the middle of next week which may also help to increase thunderstorm chances, although this is still quite far out in the forecast and therefore subject to change. By Thursday, an approaching trough from the northwest will help break down the ridge and also increase southwesterly flow ahead of it. This may help to pull up more mid-level moisture form the southwest but also cause gusty surface winds to present fire weather concerns over portions of the CWA during the afternoon through early evening on Thursday. -Stewey && .AVIATION /00Z TAFS THROUGH 00Z SATURDAY/... Issued at 526 PM MDT Thu Jun 20 2024 KALS...expect showers and isolated thunderstorms to move off the mountains and spread across the San Luis Valley overnight. Thunderstorms initially, around 3-6z this evening will be followed by light rain, low CIGS and reduced VIS through Friday morning. Generally VFR conditions are expected Friday late morning into the afternoon hours. KCOS and KPUB...a rogue shower or thunderstorm may be possible through 2z this evening, but confidence in a storm hitting the terminals is low at this time. Expected precipitation to remain banked over the mountains to the west, with mid and high level clouds across the region overnight into Friday. Very similar conditions are forecast for Friday afternoon. Mozley && .PUB WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...KT LONG TERM...KT AVIATION...MOZLEY