Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/15/21

Area Forecast Discussion
National Weather Service Denver/Boulder CO
730 PM MDT Tue Sep 14 2021 .UPDATE... Issued at 719 PM MDT Tue Sep 14 2021 The upper level longwave trough has pushed into the four corners region with drying upstream seen on water vapor. Pressure rises have pushed across the county warning area with increasing stable conditions across the region. This has ended convection over the area with scattering out from northwest to southeast. This will continue overnight leaving mostly clear skies and lows dipping into the mid-50s for the lower elevations and 30s for the high country. Tuesday will be the start of a warming and dry trend with the introduction of an upper ridge over the region. Current forecast is on track with highs reaching back into the lower 90s for portions of the plains and Denver metro with elevated fire conditions, especially over north and middle parks. && .SHORT TERM...(This evening through Wednesday) Issued at 250 PM MDT Tue Sep 14 2021 Strong to severe storms are ongoing over the Palmer Divide this afternoon with severe hail and damaging wind gusts the primary threats. SPC mesoanalysis shows up to 1,500 j/kg of surface-based CAPE in Elbert and Lincoln counties with effective bulk wind shear above 40 knots. These factors, along with QG ascent ahead of a shortwave trough and upslope flow, will allow a couple supercells to develop and push eastward as the afternoon progresses. A Severe Thunderstorm Watch was issued for Elbert and Lincoln counties until 9pm this evening although the watch may be able to be cancelled early as the atmosphere may be worked over by the first round of storms. Some of these storms have already split and straight hodographs would indicate splitting storms will be possible through this event. A left mover could make its way into southern Washington County and produce severe hail but the risk was not high enough to include that area in the watch. For the rest of the plains, including Denver and the northeast corner, it is too stable for much, if any, thunderstorm development. ACARS soundings show a couple inversions around 750 and 650mb which will be too much to overcome to produce severe storms. There have been one or two storms that have made it onto the plains after forming in the foothills and that`s about the most coverage that will occur north of I-70. Showers and storms come to an end this evening as instability weakens. The rest of the night will be dry with slight above normal temperatures. Our forecast area will see subsident flow under the right exit region of an upper level jet streak on Wednesday. With much drier air in place, there will be dry conditions. High temperatures will increase tomorrow due to warmer air aloft moving into Colorado and downslope flow forming over the plains. Denver will have a chance at seeing 90 degrees for a high although much of the metro area will top out in the upper 80s. The only concern on Wednesday will be elevated to near critical fire weather conditions across the northern mountains and foothills as well as North Park. This threat is discussed in the fire weather section below. .LONG TERM...(Wednesday night through Tuesday) Issued at 250 PM MDT Tue Sep 14 2021 Moisture will shift east Thursday as dry southwest flow aloft brings drier and warmer conditions to the area. High temperatures will rise a couple of degrees, particularly on the plains, reaching the high 80`s and low 90`s. Winds aloft will remain relatively healthy into the weekend, producing breezy conditions for much of the mountains and foothills each afternoon. On Friday, a weak trough brushing the area to our north will temporarily lower temperatures into the low to mid 80`s for daytime highs, with upper level winds primarily out of the west. Some enhancement in moisture is possible Friday but does not look sufficient for any precipitation. High pressure will nudge northward Saturday, resulting in a quick return to warmer and drier conditions with highs inching into the low 90`s in the plains. Warm temperatures will continue into Sunday, albeit with a slight increase in upper level moisture which could be enough to squeeze out an isolated shower or thunderstorm in the mountains. As we head into early next week, all eyes will be on the deepening longwave trough across the Intermountain West, which now features fairly prominently in most guidance. There continues to be significant uncertainty, particularly related to timing of the trough, but a notable trend toward cooler temperatures, windier conditions and possible precipitation looks likely sometime between Monday and Wednesday. Approximately 75-80% of GFS and EC ENS solutions indicate some precipitation early next week, with the GFS ENS system clearly the wetter of the two. With that, there will be some potential for mountain snowfall and possibly for foothills too if the colder and wetter solutions verify. Either way, it appears we`re in store for a little taste of fall. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 719 PM MDT Tue Sep 14 2021 Expect VFR conditions through the TAF period. The showers from this afternoon and early evening have cleared the terminals and skies should continue to clear out overnight. Dry conditions will set in and skies should remain mostly clear through the rest of the TAF period. It looks like there is a weak cyclonic circulation centered roughly over KDEN, and winds should turn to normal drainage through the evening as it breaks down. Drainage winds should be replaced by easterly upslope winds late in the day or early in the afternoon Wednesday, then around back to drainage again by Wednesday night. && .FIRE WEATHER... Issued at 250 PM MDT Tue Sep 14 2021 A dry airmass under a ridge aloft will result in relative humidities dropping to the low teens across the higher terrain and northern plains. A jet stream will be to the north of Colorado which will increase winds along the Colorado/Wyoming border. Gusts could reach up to 25 mph across Jackson and Larimer counties which will result in elevated to near-critical fire weather danger. A Fire Weather Watch was not issued since winds will be just below the threshold in most of the area. Elevated fire danger will be in place, Thursday through Saturday over Middle and North Park during the afternoon hours. && .HYDROLOGY... Issued at 250 PM MDT Tue Sep 14 2021 No threat for flash flooding. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Bowen SHORT TERM...Danielson LONG TERM...Rodriguez AVIATION...EJD FIRE WEATHER...Danielson/Rodriguez HYDROLOGY...Danielson
Area Forecast Discussion
National Weather Service Louisville KY
1001 PM EDT Tue Sep 14 2021 .Forecast Update... Issued at 1001 PM EDT Tue Sep 14 2021 A narrow broken band of showers and thunderstorms has developed this evening along and just ahead of a cold front stretching roughly from Detroit to St Louis to Wichita in conjunction with a weakly digging 5H trough. The convection is within a corridor of 1.7-1.9" precipitable water values that will sink southward with the front tonight, eventually meeting up with a similarly humid atmosphere already in place over Kentucky by morning. An upper jet from the Midwest to the eastern Great Lakes will intensify overnight and the Ohio Valley will increasingly be under its right entrance region...especially on Wednesday. ACARS sounding out of SDF a couple of hours ago still showed a healthy mid-level cap overhead, but sounding progs show it weakening overnight with cold air advection in the 5H-7H layer associated with the advancing upper trough to our northwest. RAP data accordingly show CIN decreasing overnight. Fortunately any low level jet tonight looks to be weak, effective bulk shear will be very weak, and lapse rates are weak at the surface and aloft with CAPE on soundings showing up as tall, thin, and slightly elevated. So, given the forcing, moisture, and available instability ahead of the advancing front, will hold on to scattered showers and storms in the forecast during the late night hours. Not everyone will see rain, as evidenced by the large gap that has opened up in the line over the Wabash Valley. The latest HRRR and 3km NAM capture this well and actually bring little if any rain into the LMK CWA...but would prefer to keep PoPs in the forecast given the aforementioned moisture, forcing, and instability. Given the latest, will reduce PoPs but not entirely eliminate. && .Short Term...(This evening through Wednesday) Issued at 245 PM EDT Tue Sep 14 2021 Isolated to widely scattered showers have developed across south- central and western Kentucky this afternoon. Capping near 700mb has limited overall growth and strength of these convective showers, resulting in most echo tops not going beyond 20kft. Up to this point, very little to no lightning activity has been detected in this precipitation, and environmental conditions will not change much over the next several hours, so expect any thunderstorm activity to be largely isolated. One thing to keep an eye on this afternoon is high DCAPE (>1,000J/KG) values across the region where gusty winds could be possible in the stronger showers or isolated storms, assuming they can overcome the warmer air/cap around 700mb. We should see a break in the action near sunset as diurnal heating wanes and convective showers taper off. A broken line of storms forming ahead of a cold front this evening will then race toward our region, potentially arriving after midnight. Much of this activity will weaken by the time it approaches us, and any severe threat will be very low with the line. Though unlikely, it is entirely possible the line could dissipate before it reaches our southern IN counties as a couple of CAMs show (3km NAM, WRF ARW). Model soundings do show elevated instability persisting through much of the overnight and early morning hours tomorrow, so will keep mention of storms in the forecast as outflow boundaries from weakening convection could generate new storms. The cold front should reach our southern Indiana counties close to sunrise tomorrow and gradually push through the region during the day. As the front moves through, we could see additional development of showers and storms along it. Depending on how much clearing we see in the wake of the first round of showers/storms, there may be a low-end severe threat for gusty winds and small hail with storms that fire off along the cold front. SPC Day 2 Marginal covers that threat area well. .Long Term...(Wednesday night through Tuesday) Issued at 255 PM EDT Tue Sep 14 2021 At the start of the extended period, expect to find the upper level trough exiting east out of the area while the associated surface front initially draped along the Ohio River Wednesday night gradually sinks southward through the Commonwealth, likely washing out in our vicinity. Showers and storms will be ongoing Wednesday night ahead of and along the cold front with precip chances tapering off from north to south overnight as the frontal boundary moves through. The end of the week will then feature ridging off of the East Coast over the Atlantic while an upper trough lifts northeast across central Canada, placing our region in relatively weak flow aloft. Although the remnants of Nicholas are expected to remain well to our south, will see lingering moisture across southern portions of the area on Thursday associated with the washed out frontal boundary then increasing moisture across the area Friday as we return to southerly flow, keeping PWATs in the 1.2 - 1.6 inch range through the remainder of the period. In a warm and marginally unstable environment, cannot rule out isolated to scattered showers and storms during the afternoon and evening hours Thursday into the weekend. PoPs on Thursday will be confined to southern KY where the better moisture is with precip chances then spreading across the entire area the other days. By Sunday, as broad upper ridging moves in over the east-central CONUS, expect mostly dry weather. Temperatures will warm slightly through the period, with highs initially in the lower to mid 80s Thursday then into the mid to upper 80s by Sunday. Low temperatures will generally be in the mid to upper 60s. && .Aviation...(00Z TAF Issuance) Issued at 731 PM EDT Tue Sep 14 2021 This evening a cold front is stretched out along a APN-CMI-SGF line with a narrow broken band of showers and thunderstorms along and just ahead of it. These features will sink southward tonight, bringing showers and scattered storms to southern Indiana and central Kentucky in the early hours of Wednesday. Showers and storms will decrease in intensity and slightly in coverage during the daylight morning hours Wednesday but then renewed convection may develop in the afternoon, primarily affecting LEX and BWG. Forecast confidence is low on ceilings. Timing of showers and storms will need to be adjusted as the system approaches. && .LMK WATCHES/WARNINGS/ADVISORIES... IN...None. KY...None. && $$ Update...13 Short Term...DM Long Term...KDW Aviation...13