Area Forecast Discussion
Issued by NWS Kansas City/Pleasant Hill, MO
Issued by NWS Kansas City/Pleasant Hill, MO
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287 FXUS63 KEAX 181051 AFDEAX Area Forecast Discussion National Weather Service Kansas City/Pleasant Hill MO 551 AM CDT Fri Oct 18 2024 .KEY MESSAGES... - Elevated Fire Weather Concerns Friday - Warm, Mostly Dry Through The Weekend - Rain Chances Return Monday into Tuesday && .DISCUSSION... Issued at 356 AM CDT Fri Oct 18 2024 H5 ridge axis has shifted eastward into the Central Great Lakes Region along with the associated surface anticyclone, now centered east of the area. Deep trough is digging toward the Four Corners Region this morning with stronger dCVA present over the Front Range. Lee surface cyclogenesis has been ongoing. With this developing west of the area, and the stronger surface anticyclone east, low- level flow has turned southwesterly from the Central Plains into the lower Missouri River Valley. This is promoting a WAA regime, and is expected to increase temperatures Friday afternoon into the lower and mid 70s. Amongst NBM members and other ensemble suites, the inner-quartile range spread is fairly narrow with most points in the lower to mid 70s. Only far northeast reaches of the forecast area may only hit the upper 60s. Subtle height falls will start ahead of the trough axis in the western CONUS but overall forcing and kinematics will not be overly robust. The lack of moisture transport will keep conditions dry today. Diurnal heating should lead to stronger boundary layer mixing, that will help boost temperatures, as well as maintain lower dewpoints with southwest flow brining in drier plateau air. With air temperatures in the lower 70s, and dewpoints expected to remain in the lower to mid 30s this afternoon, relative humidity values between 20 and 30 percent are expected. In our northwestern counties, winds at the top of the mixed layer may be around 20-22 kts. There is some spread amongst various guidance on the strength of winds. For southeast counties, winds at the top of the mixed layer between 17-20 kts appear favorable in various model soundings. Have went ahead and increased wind gusts slightly from NBM guidance to account for stronger mixing this afternoon. These warm and dry conditions will lead to elevated fire weather concerns, but are not currently forecast to reach headline criteria this afternoon. There are essentially two different regimes divided geographically. Stronger winds in our northwest with slightly lower dewpoints depressions (and thus slightly higher RHs), and then larger dewpoint depressions (lower RHs) but weaker winds in our southeast. Saturday, jet streak begins to wrap around the trough axis over the desert the southwest, and puts dCVA at a standstill across the Front Range. Current expectation is for a closed-low in the mid to upper- levels of the troposphere, while the associated surface cyclone is unable to advance with lack of upper-level support moving downstream. The surface anticyclone to the east remains in tact, keeping the WAA regime in place that should provide another day of temperatures in the mid 70s across most of the area. Most inner- quartile ranges amongst ensemble suites are clustered around this range. Current deterministic guidance depicts subtle backing of the surface winds, which may help our area tap into slightly better moisture transport. Dewpoints are currently progged to reach back into the lower 40s by Saturday afternoon. However, will need to continue to monitor boundary layer mixing potential again, as some guidance seems to be too high with dewpoint output the past few days. Even with the possibility of moisture transport, most of the column remains very dry, therefore, precipitation chances are not expected on Saturday, as all of the forcing and large scale ascent are tied out west with a closed-low system. Ensemble suites hold less than 10 percent probabilities for any measurable rainfall through Saturday evening. Sunday, a weak short-wave off the west coast is progged to get the closed-low system over the desert southwest moving again but progress will be slow. Previous WAA regime will actually build a secondary mid-level ridge axis early Sunday that will have to move eastward before any substantial height falls can start. This eventually does push east, and with another area of dCVA promoting cyclogenesis over the Front Range and High Plains, stronger southerly flow should increase WAA and boost temperatures into the upper 70s across most of the forecast area. While a few short-waves and vort maxima may try to ride through the ridge, the lack of moisture will continue to limit precipitation chances. Ensemble probabilities for measurable precipitation Sunday are also below 10 percent for most of the forecast area. Like with Saturday, will continue to monitor local boundary layer mixing and dewpoint trends to determine if any kind of elevated fire weather concerns will be present during this warm and dry spell. Next rain chances return mid-day Monday and continue through Tuesday as the mid-level system gets another kick and begins to lift out of the desert southwest, dragging a surface cyclone across the Plains. Mid-level height falls begin to take place Monday afternoon, and at the surface should promote meridional flow that helps transport more moisture back to the area. The strongest forcing remains west of the area for most of Monday, but there may be enough convergence out ahead of the main trough axis to promote some shower activity into the western portion of the forecast area. Ensemble probabilities for precipitation are generally around 50-60 percent, then decrease eastward. The stronger mid-level kinematic support moves through late Monday into Tuesday as the main lobe of vorticity passes overhead, where Q-vector convergence is concentrated within the vicinity of low convergence along a weak thermal boundary. 24 hour precipitation total probabilities by the end of Tuesday are around 40 to 50 percent to exceed 0.10 inches, but very low for anything 0.50 inches and greater. While any rain would be welcomed, current forecast amounts would only provide minimal relief to drought conditions. Even the outlier members amongst ensemble guidance struggle to reach much above one inch of rainfall. Instability is not currently progged to be very robust as this feature moves through the start of the next work week, therefore looking at the favored mode of precipitation to be general showers. Perhaps if we realize elevated instability, a few isolated thunderstorms could get going, but current pattern evolution is only favoring general showers. As for temperatures Monday and Tuesday of next week, continued WAA will support ranges from the upper 70s to lower 80s. Tuesday will have bit more uncertainty, as cloud cover will play large role in controlling the insolation. For the remainder of next week, the short-wave trough exits our area, and a few mid-level perturbations are progged to move southwestward out of Canada. This will promote generally northwest flow through the end of the forecast period. There are some low end ensemble probabilities for isolated rain showers through the middle of next week as these weak disturbances move through the flow, but generally are only around 15 to 20 percent for any measurable rainfall (and not widespread across the forecast area either). Temperatures will likely be cooler compared to the weekend. Ensemble spread for temperatures through the middle of next week are larger, and this looks to mainly be due to precipitation production and cloud cover differences associated with the short-wave perturbations in the northwesterly flow. Overall QPF projections are very low though, most models clustering around just a few hundredths of an inch. && .AVIATION /12Z TAFS THROUGH 12Z SATURDAY/... Issued at 552 AM CDT Fri Oct 18 2024 VFR conds are expected thru the TAF pd with clr skies. Winds will be out of the south btn 7-12kts thru 15Z when winds will increase to 10-15kts with gusts to 25kts. Winds are expected to diminish aft 23Z becmg SSE btn 5-10kts. && .EAX WATCHES/WARNINGS/ADVISORIES... MO...None. KS...None. && $$ DISCUSSION...Krull AVIATION...73