Area Forecast Discussion
Issued by NWS Topeka, KS
Issued by NWS Topeka, KS
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680 FXUS63 KTOP 300524 AFDTOP Area Forecast Discussion National Weather Service Topeka KS 1224 AM CDT Tue Apr 30 2024 .KEY MESSAGES... - A period of active weather is expected Tuesday through Thursday with several chances for thunderstorms, including the potential for severe weather. - Additional rounds of thunderstorms could lead to heavy rainfall and the potential for flooding. && .DISCUSSION... Issued at 304 PM CDT Mon Apr 29 2024 Quasi-zonal upper level flow exists across the Central Plains this afternoon between a trough over the Northern Plains and another system located over the Pacific Northwest and British Columbia. It has been a quiet and pleasant day across the region behind yesterday`s cold front with mostly sunny skies, light southwest winds, and temperatures warming into the 70s. By this evening, a surface trough becomes more pronounced across the area with subtle perturbations moving through the zonal flow. Increasing mid-level ascent and moisture along with steepening lapse rates could lead to isolated showers and even a rumble of thunder this evening into early Tuesday. Forecast soundings show abundant dry air below 700mb, leading to most of this precipitation evaporating before reaching the ground. Inverted-v soundings do support some stronger wind gusts reaching the surface if a storm does impact the area. The Pacific Northwest trough quickly advances east overnight, taking on a negative tilt as it progresses across the Northern Plains during the day Tuesday. The surface pressure gradient tightens ahead of this feature with strong southerly winds boosting dewpoints into the upper 50s and low 60s. A dryline is progged to make it into central Kansas before a southeast moving cold front overtakes the dry line during the late afternoon or early evening. A capping inversion will likely preclude convective initiation through the morning and early afternoon, but models show this cap eroding sufficiently by the late afternoon to support convection. While the best dynamics will reside north of the area, lift along the boundaries, particularly near the triple point, and modest large- scale ascent is expected to be enough to generate scattered thunderstorms in the 5-7pm timeframe. Surface based CAPE of 2000- 2500 J/kg along with 30-35kt of bulk shear will support supercells capable of producing large hail and damaging wind gusts. Low-level hodographs show good curvature as well, supporting a tornado risk. The front stalls from west to east somewhere across central/southern Kansas Tuesday evening with the low-level jet continuing to pump moisture into the region. Flooding is becoming more of a concern Tuesday evening into early Wednesday, especially for areas where the boundary stalls and storm motions become more parallel to the front. The favored location for this to occur looks to be south of Interstate 70 and could extend into east central Kansas which remains very saturated from recent rains. The low-level jet works to lift the front and associate convection north during the early morning hours Wednesday. The front is progged to be into Nebraska by Wednesday afternoon as a surface low deepens across southeast Colorado and a dryline sets up across southwest Kansas. Uncertainty remains in some of the details of this round of storms, but a cap may limit convection during the afternoon until better forcing arrives during the evening. Any isolated storms in the warm sector will have the potential to produce all severe weather hazards. With large-scale forcing increasing during the evening and overnight hours, upscale growth of any dryline convection seems likely with the potential for an MCS to move across the central Plains. Damaging wind gusts would be the main hazard with any MCS that develops. Additional rounds of storms could lead to heavy rain and flooding across the area. The surface low moves northeast into Iowa by mid-morning Thursday with a trailing cold front remaining across northeast Kansas. Previous rounds of convection and the timing of the cold front will determine the strength of any storms, but the environment could support another round of convection Thursday afternoon ahead of the cold front before it shifts east of the area Thursday evening. Model spread increases by the end of the week, although the daytime hours on Friday are trending drier behind the cold front. Yet another trough ejects across the Plains Friday into Saturday, increasing chances for showers and storms. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1224 AM CDT Tue Apr 30 2024 VFR conditions are expected for much of the period. A line of TSRA is forecast to develop near MHK around 22Z then progress southeast to TOP and FOE in the 23Z-02Z time period. Added VCTS for now as convection will be scattered in that period. Winds increase to around 15kts with gusts to 24kts by 15Z, then increasing to around 23kts with gusts to 34kts by 19Z. Winds decrease as the front approaches and become southwest. At MHK winds will shift to the west then northwest around 10kts by 00Z Wednesday as the front moves through. Winds decrease at TOP and FOE by 02Z from the southwest around 10kts. && .TOP WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Flanagan AVIATION...53