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Displaying AFOS PIL: AFDDMX Received: 2017-10-12 23:40 UTC
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689 FXUS63 KDMX 122340 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 640 PM CDT Thu Oct 12 2017 ...Updated for 00z Aviation Discussion... .SHORT TERM.../Tonight through Friday/ Issued at 319 PM CDT Thu Oct 12 2017 Low clouds that have hung around much of the day breaking up and dissipating and should continue to dissipate across the far east into the early evening hours. An elongated area of sfc low pressure stretches from the plains of Canada southward through the eastern Dakotas into central NE and the high plains of CO/KS. This sfc trough will shift south and east through Iowa late tonight into Friday. A weak shortwave trough will eject out of the western US upper trough through the central US interacting with the sfc boundary resulting in a chance for some showers/drizzle across portions of central IA Friday. Moisture looking more limited in the morning with front pushing a bit further south than previously anticipated, this have trimmed some pops across the far north/northwest and decreased pops overall through the morning hours. An overrunning type situation setting up through the day, with deeper saturation expected toward the afternoon hours with increased moisture advection/waa across much of central IA. This should result in more widespread shower chances through the afternoon hours, and maybe a an isolated thunderstorm across the far south/southeast where some weak instability is present toward late afternoon in vicinity of the frontal boundary. As for temperatures will have CAA aloft this evening, but then waa increase ahead of the shortwave late tonight as the front stalls across the forecast area. Also expect low clouds to fill back in tonight as moisture advection increases. Therefore had temps drop off fairly decent this evening, then hold steadier across the central/south late tonight. Warmest temps expected Friday across the southeast with boundary getting hung up across the central portion of the forecast area. Therefore expect highs only around 60 in the far northwest with highs in the mid 70s far southeast. .LONG TERM.../Friday night through Thursday/ Issued at 319 PM CDT Thu Oct 12 2017 The main focus on the extended was on the severe weather potential Saturday and strong winds Saturday night into Sunday. Models are good agreement with the overall synoptic setup, timing and location of the frontal boundary on Saturday into Saturday night. Friday night into Sunday...WAA wing of a fairly potent low pressure system strengthening over the Central Plains will cause some shower and thunderstorm activity across southern Iowa Friday evening and into the overnight hours towards Saturday morning. The front is expected to push back northward Saturday morning as the main surface low pushes northeast across Iowa throughout the day and continues to deepen as it moves northeast. The warm sector, generally along and south of Interstate 80 to the Missouri border, will be the focus of strong to potentially severe thunderstorms in this location late Saturday morning into the afternoon. Certainly a very conditional setup if some instability has a chance to build into the south after the overnight convection diminishes/pushes northward. MUCAPE per NAM/ECMWF/GFS suggestion that it increases by 21z to 2000-2500 J/kg over the south to southeast sections of the forecast area. Lapse rates through the column range around 6 to near 7 C/km per OTM forecast sounding. Shear is backing somewhat in this location and the 0-1km and 0-3km bulk shear range around 30 knots and 45 knots respectively. Deep layer shear looks strong to enough to allow storms to be long-lived but do have low confidence with supercells during the entire period per the lack of significant directional shear. More likely scenario is initial development in the afternoon to be supercellular but quickly transition into linear QLCS type across the south. Wind damage looks to be the primary severe threat. Heavy rain is another concern along and south of the front. PWATs over 1.5 inches which is well above normal for mid-October. WLCD around 3500m with strong moisture transport into southern Iowa should provide for efficient rain producers. Storm movement looks to be fairly fast and not perfectly oriented with Corfidi vectors, so training is possible but not as clear-cut. By 00z Sunday, the surface low deepens to around 1000mb over southern Wisconsin producing a very sharp gradient across the state Saturday evening. Strong PV anomaly punches into the state Saturday evening providing some initially strong winds/gusts across the forecast area. Winds atop the mixed layer range near 40 knots or even higher closer to the surface low. Increased winds several knots Saturday night into Sunday morning. Monday through Wednesday...CAA continues throughout the day on Sunday as a surface high pressure builds into the region by Sunday night into Monday. No significant storms systems anticipated over the work week next week with above normal temperatures forecast as large ridge over the southeast remains in place. && .AVIATION.../For the 00Z TAFS through 00Z Friday evening/ Issued at 635 PM CDT Thu Oct 12 2017 Low-med confidence forecast package. Lingering stratus to impact eastern TAF sites of KOTM and KALO. This stratus will gradually shift westward and impact KMCW tonight. KDSM will be impacted by another band of stratus sometime tomorrow afternoon. Fog potential at KMCW and KALO. Cannot rule out OVC002 or so cloud base near sunrise hours tomorrow. Will watch carefully. Confidence medium that fog/IFR may linger through more of the morning than usual at KALO. && .DMX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...Beerends LONG TERM...Podrazik AVIATION...Kotenberg