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Area Forecast Discussion
Issued by NWS Kansas City/Pleasant Hill, MO
Issued by NWS Kansas City/Pleasant Hill, MO
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259 FXUS63 KEAX 120843 AFDEAX Area Forecast Discussion National Weather Service Kansas City/Pleasant Hill MO 343 AM CDT Mon Aug 12 2024 .KEY MESSAGES... - Showers/Storms Through Late Morning Today - More Showers and Storms Tuesday through Middle of Week - High Heat Index Values Possible Wednesday Southwest CWA && .DISCUSSION... Issued at 343 AM CDT Mon Aug 12 2024 Mid-level short-wave axis is close to the IA-MO-NE triple point and has been forcing a group a showers/storms from NW Missouri into west- central Iowa during the overnight hours. Warm front currently sits in far eastern Kansas from just west of the KC Metro toward Fort Scott KS. The first round of rain that brought a swath of 1.5 to 2.5 inches of rainfall in the western KC metro utilized much of the instability close to the warm front. As of 08z, MUCAPE in our counties has dipped to around 500 J/kg. There is still some activity on-going in south-central Kansas where instability has been higher as this is deeper into a rich theta-e airmass. For the remainder of the morning, expecting large scale ascent to maintain showers/storms primarily north of Interstate 70, and this will push mainly eastward. At this point, efficient rainfall is still possible with amounts of 1-2 inches possible, but the lack of favorable thermodynamics is expected to keep storms sub-severe. HREF mean QPF north of Interstate 70 is around 1.25 to 1.5 inches. There are a few pockets where HREF output depicts a 40 percent probability of exceeding 1.5 inches of rainfall. As for flooding in north-central Missouri, does not seem favorable at this point. Flash flood guidance suggest a rainfall rate of 3+ inches in 3 hours is needed for widespread flooding. For areas closer to Interstate 70 and southward, there is potential for additional shower activity to fill in along the warm front as the short-wave continues to dig and large scale ascent increases. CAM solutions this morning have not been consistent with development through the remainder of the morning. It is a situation where the forcing and moisture is there, but the thermodynamics may struggle to support a convective structure. As mentioned before, there is some activity in south-central Kansas that could continue eastward within a wing of stronger insentropic ascent, but given the lack of any further diabatic heating or other source of instability, hard to confidently declare robust development. The greater instability axis dives toward the Ozarks, so any new development along the leading short-wave may dive south of the area if it develops. PWATs throughout most of the area are still around 2.00 inches, and with stronger storms we certainly saw efficient rainfall production. The good news for the western KC metro is that most activity should stay north as the warm front slowly advances toward the northeast. However, should there be more robust development that finds a way to maintain itself, another inch of rainfall through Wyandotte and Johnson [KS] Counties could result in some minor flooding. Once the short-wave passes through, we should see a break from precipitation for the remainder of Monday afternoon. Currently expecting temperatures in the western part of the area to reach the lower 80s as stronger WAA pushes temperatures upward. Northeast portions of the forecast area likely remain much cooler with dense cloud cover and precipitation keeping temperatures in the lower 70s. Late tonight and into Tuesday morning, another mid-level short-wave works through the mid-level ridge pattern that will provide additional kinematic forcing for shower and thunderstorm development. Another area of dCVA over the Front Range will continue to provide modest surface pressure falls from the Central Plains into the lower Missouri River Valley with a thermal boundary likely somewhere over Central Missouri. Expecting another higher theta-e airmass at least within the boundary layer to be in place, though overall instability may still be lower with a saturated column and weaker lapse rates. Current HREF mean MUCAPE does not exceed 1000 J/kg. Current CAM guidance depicts the bulk of the forcing on the southwestern third of the CWA, moving through primarily in the mid to late morning hours of Tuesday. Deep layer shear is coming in weaker with this short-wave Tuesday compared to the one experienced early Monday morning. Overall severe threat appears limited. QPF will also be progged lower given that lack of organization, HREF mean values generally between 0.25 and 0.75 inches from just west of KC to Springfield, MO. HREF probability matched mean (PMM) values for Tuesday morning along this QPF axis is around 1.25 inches. The strongest forcing and mid-level support exits the forecast area between 18-20z on Tuesday, but continued isentropic ascent and higher theta-e airmass may support linger activity. Most ensemble probabilities maintain at least 20 to 30 percent probability for some measurable rainfall for the remainder of the afternoon and evening on Tuesday. Wednesday, broad warm sector sets up from the eastern Plains into the mid-Mississippi River Valley, as the ridge axis pushes eastward. A series of short-waves and vort maxima on the backside will continue to promote cyclogenesis across the Plains and should see a steady uptick in surface pressure falls through the afternoon on Wednesday. Higher theta-e airmass pushes eastward and should start to see better CAPE, with potential for EML from 700mb-500mb to be in place that could steepen lapse rates and yield higher CAPE values. The primary question will be deep layer wind shear through, especially from eastern Kansas into Missouri. Weaker flow may result in weaker shear. However, with increasing surface convergence and pressure falls along an axis of destabilization, could support a few stronger updrafts. This is largely conditional on early morning isentropic shower activity clearing in time for this destabilization to occur. Primary threat would be for storms to produce severe hail and some damaging wind gusts. Given the high uncertainty of how Tuesday activity spills into Wednesday morning, will not attempt to pinpoint mesoscale details at this time. Will also need to keep an eye on QPF trends heading into Wednesday, as the ground across much of the area may remain saturated, meaning flooding and other hydro issues become more problematic. In addition to storm chances, the push of strong WAA along with higher humidity may have the potential to yield heat index values in the triple digits, primarily for the western and southwestern portions of the forecast area. Confidence at this time is medium-low, as cloud cover and lingering precipitation drag could greatly keep temperatures much lower. For the end of the week, additional short-waves may bring more precipitation chances, with temperatures generally in the upper 80s. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1224 AM CDT Mon Aug 12 2024 First round of showers is moving eastward, more development is expected heading into the overnight hours. Ceilings will gradually drop to IFR by the early morning hours of Monday. Most precipitation activity should between 12z-14z. There is still moderate amounts of uncertainty with thunderstorm trends and timing through the overnight hours. && .EAX WATCHES/WARNINGS/ADVISORIES... MO...None. KS...None. && $$ DISCUSSION...Krull AVIATION...Krull