Area Forecast Discussion
Issued by NWS Kansas City/Pleasant Hill, MO
Issued by NWS Kansas City/Pleasant Hill, MO
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167 FXUS63 KEAX 220506 AFDEAX Area Forecast Discussion National Weather Service Kansas City/Pleasant Hill MO 1206 AM CDT Sun Sep 22 2024 .KEY MESSAGES... - Showers/Storms Continue This Evening - Conditional Severe Threat NE KS to NW MO Late Tonight - Conditional Severe Threat South of I-70 Sunday Morning/Afternoon - Cooler This Week && .DISCUSSION... Issued at 240 PM CDT Sat Sep 21 2024 The forecast continues to have several moving parts to it that leaves conditional threats and periods of higher uncertainty through Monday morning. The mid and upper-level pattern has not seen a drastic change over the past 24 hours. There is trough moving through the Canadian Prairie Provinces. There are still some influences on the mid-level pattern from this system, but the primary feature driving the rain shower activity this afternoon has been the trough currently centered just west of the Four Corners Region. Jet streak with this system has positioned stronger dCVA into the Front Range and High Plains, and has resulted in broad surface cyclone across much of the Central Plains, with secondary area of cyclogenesis in the TX/OK Panhandle Region. This has de-amplified the ridge axis across much of the Gulf Coast and lower Mississippi River Valley, and in the lower portions of the troposphere has turned flow southerly. The thermal boundary that been traversing eastern Kansas and most of Missouri the past few days has started to push back northward already as a warm front. With this, has also come isentropic ascent with some kinematic support form weak vort max passing overhead. This has helped to provide the expansive cloud cover as well as widespread shower activity across the forecast area. Elevated instability, primarily with stronger WAA has allowed the development of a few isolated thunderstorms. However, wind shear has not been overly impressive across the warm sector this morning and therefore organization for any convection has been hard to come by. Expecting this to be the case through the remainder of the evening. While there are few breaks in cloud cover that could support additional updraft development, the lack of stronger flow should continue to inhibit any robust organization. The primary threat with any thunderstorms this afternoon will be lightning, and wind gusts to around 40 MPH. Later this evening, mid-level trough will start to lift out of the Four Corners Region and will send another vort max across the Plains. This should provide another shot of dCVA and promote surface cyclogenesis primarily across the southern Plains this evening. Current deterministic guidance along with several CAMs this morning has an inverted surface trough that extends into the Ozarks and southern Missouri River Valley that should provide increasing convergence heading into the remainder of the evening. Meanwhile, an area of subsidence over the Northern High Plains will develop a stronger surface anticyclone that drops southward on the backside of the ejecting trough out of the desert southwest. This will push the thermal boundary back southward as a cold front as we head into the overnight hours, and will be the focus point for stronger updraft development from eastern Kansas into northwest and northern Missouri. The main question will be if we will see enough clearing for more robust destabilization on the warm side of this boundary through the remainder of the afternoon. 12z HREF mean CAPE values are in the ballpark of 1000-1500 J/kg across most of the forecast area heading into the late evening hours. However, there could be potential to push above 2000 J/kg if we are able to realize greater insolation. With the rain activity today, the column is more moist than it was yesterday, meaning dry air entrainment will not be as prevalent. As the mid-level vort max moves through, deep layer shear should continue to increase into the evening along the thermal boundary, with 0-6km bulk shear values reaching between 30-40 kts. The combination of forcing and deep layer shear, along with instability will lead to the potential for thunderstorms to organize, and present a threat for wind gusts to around 60 MPH and hail around quarter size. Given the strong forcing, along with low- level jet development, not expecting any storms to remain discrete for a long period of time, and although hodographs are quite lengthy the curvature will be very limited, thus limiting ability for SRH to be realized and limiting any kind of tornado threat. Given the cloud cover, we may not be able to mix out an inversion present around 900mb, meaning that most convection, even along the cold front, will more elevated and not surface based. This almost limits how much of wind shear updrafts can realize. Heavy rainfall may lead to stronger cold pools with convective clusters along the front, further supporting localized wind gusts if a line is able to develop. The cluster then moves primarily east-southeast through the remainder of the overnight hours. With respect to rainfall amounts, HREF mean values are generally around 1.0 to 1.5 inches across a large portion of the forecast area. There are few pockets of probability matched mean values that exceed 2.5 inches. Will need to watch rainfall rates for issues related to flooding. However, antecedent dry conditions the past few weeks should help to mitigate most flooding effects. Expecting the thermal boundary to also remain progressive enough with stronger mid-level trough moving through that should limit training showers/storms across most of our area. If the stronger thunderstorm threat does not unfold as currently anticipated, the amount of moisture and forcing present will still result in rainfall across a large portion of the forecast area. Both CAM and coarser ensemble suites continue depict probabilities above 70 percent for at least 0.50 inches of QPF along the cold front through the overnight hours. Sunday morning, lingering showers and storms are expected especially south of Hwy. 36, though most of the activity should eat into the instability that greatly limits any kind of severe threat, especially past 10-11z timeframe. The mid-level trough continues to move eastward. Most guidance depicts the surface cold front being somewhere in the southeastern third of the forecast area, essentially from Bates County Missouri to Cooper County Missouri. There is some potential for the boundary to stall during the late morning hours here, that could result in some training. This time frame late morning into the afternoon hours of Sunday is where most of the forecast uncertainty still remains. A few CAM solutions keep the boundary further to the northwest along the Interstate 70 corridor, while others push it much closer to Interstate 44 in southern Missouri. Therefore, this is leading to spread in solutions for recovery on the warm side of the boundary for the southern portions of area. With the mid-level wave still nearby, the boundary should still have decent deep layer shear present, that if there is recovery and further destabilization on the warm side of the boundary, new development could organize and produce a few stronger to marginally severe storms. Once again, the main concerns would be wind gusts around 60 MPH and hail around quarter size. With that being said, ensemble probabilities seem to favor a more southeastward position of the front and better surface convergence closer to the Interstate 44 corridor for most of Sunday afternoon, concentrating the more favorable severe threat outside of our forecast area. As for rainfall amounts, our southeast counties still hang onto elevated probabilities for at least 0.50 inches of QPF, and HREF probability matched mean values have a few pockets of an additional 2-3 inches of rainfall. This would be the higher end of expected totals, but if the boundary does stall for a few hours while activity is still ongoing, this could result in event totals closer to 4 inches of rainfall. Current Flash Flood Guidance depicts that most of the area can handle in excess of 3 inches, so this amount spread over 36 hours would indicate only a minimal flooding threat. However, if the higher end of the probability matched mean values as indicated by the 12z HREF are realized over a shorter time, localized flooding may become possible, and will need to be monitored. For the remainder of the week, medium range deterministic guidance is quite spread with how the pattern evolves. GFS develops a stronger closed-low system centered more over the Great Lakes Region, while ECMWF keeps it much further west. This greatly impacts timing of southerly flow vs northerly flow, and what this means for temperatures during the middle of this week. Inner-quartile ranges amongst various ensemble suites is large, between 68 and 81F for many points across our forecast area. For now, will stick with temperatures in the official forecast closer to the median of these values. Regardless, with the passage of the Sunday cold front and mid-level wave/low parked somewhere nearby if not directly overhead, temperatures will be cooler this upcoming week then what was experienced last week. The uncertainty is whether we will be well below normal, or perhaps right around it depending on the positioning of the closed-low system and how much progress any kind of ridging along the western CONUS makes. Although there may be some large scale lift available, most of of the moisture still gets pushed southeastward of the area by Monday, setting up drier conditions through the middle of this week. Though if we continue to see a denser cloud shield, cannot rule out periods of sprinkles or light showers through the middle of this week. Currently though, ensemble probabilities for measurable rainfall in our forecast area remain quite low through at least Thursday. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1159 PM CDT Sat Sep 21 2024 On going stormy weather will continue to impact the Kansas- Missouri state line terminals through the rest of the night and much of Sunday. VFR showers and thunderstorms continue to advect east from Kansas into Missouri ahead of a cold front that will sweep south Sunday morning. Thunderstorms and showers will prevail ahead of the front with showers and lowering CIGs behind the front as it settles south. Conditions should improve as we move through the morning into the afternoon hours of Sunday. && .EAX WATCHES/WARNINGS/ADVISORIES... MO...None. KS...None. && $$ DISCUSSION...Krull AVIATION...Cutter