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Displaying AFOS PIL: AFDDMX Received: 2017-08-13 04:42 UTC
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406 FXUS63 KDMX 130442 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1142 PM CDT Sat Aug 12 2017 .SHORT TERM.../Tonight through Sunday/ Issued at 300 PM CDT Sat Aug 12 2017 Little change to forecast expected through Sunday. Subjective surface analysis at 13z shows expansive ridge of high pressure from the surface to H700. Aloft H500 wave also visible on the water vapor imagery continues to move slowly toward the region. Lower levels show lee side development taking place over South Dakota at the surface with an H850 trough beginning to take shape over the Western Plains at H850. Overall trends remain the same...with initiation to take place west of our area later today and slowly move to the east northeast tonight...tracking mainly with the low to mid level warm air advection/thetae advective processes. Both the Euro and the GFS suggest that the better forcing will again remain north of the region...with northern Iowa seeing better forcing than the remainder of the forecast area. Along with the chances for precipitation Sunday during the morning/afternoon hours north...cloud cover should hinder afternoon warming north areas while the south with some afternoon sunshine will again drift into the lower 80s by late afternoon. Instability remains rather limited...so overall either isolated to scattered thunder is anticipated over the north Sunday. Lows tonight will be similar across the east...where generally clear skies and light winds will promote decent radiational cooling with the high still influencing the region... while increasing cloud cover west will retard cooling to some extent. Typically warmer conditions will be found in the metro. Highs Sunday will struggle to reach the lower 70s north and reach the lower 80s south. .LONG TERM.../Sunday night through Saturday/ Issued at 300 PM CDT Sat Aug 12 2017 Somewhat active more summerlike weather pattern anticipated during the period...though models are not in great agreement with the details at this time. Main concerns currently are the extent of forcing and placement of best forcing. Overall both the GFS/Euro continue to trend of lingering showers/possible thunder over the western/northern sections through early Monday morning...weakening with time. The Euro suggests a weak boundary will be the focus of additional development Monday afternoon over the west/south with the GFS mainly dry. Some of the uncertainty is due to the very weak waves tracking east through the flow. With the main system passing east by Sunday night...prefer the drier solution for Monday...at least through 00z Tuesday. The GFS also develops return flow by 00z Tuesday and with a weak sfc boundary forming the better push of isentropic lift appears to be focused more over Nebraska into western Iowa than the remainder of the forecast area. Overall the best chances in the 7 day period for precipitation over a widespread area is from late Tuesday night through Wednesday. However the pattern still suggests both a southern stream/northern stream wave propagating through the flow Tuesday night into Thursday. As has been the case for many instances this summer...moisture has been limited after the southern stream wave has developed keeping the better moisture channel either east or south of the region. Despite this will maintain higher PoP Tuesday night into Wednesday night with precipitation ending on Thursday. There remain some significant differences regarding the expected wind fields/strength between the GFS and Euro for the midweek system. The GFS is much stronger with H850/H300 winds by 00z Thursday over the east half of the area while the Euro model higher amplitude winds south into Missouri. Given the lack of consensus in forcing...the risk for severe storms is not a certainty though increased instability by midweek may be enough to support stronger storms either later Wednesday or into the overnight hours. Still a few days to examine future model packages. For the remainder of the forecast period there is an additional wave/cool front that moves east into the region by Friday into Friday night. With additional upper level support and some intermodel consistency... showers and thunderstorms will be a possibility Friday into Friday evening. Highs through the period will be warming from Monday through Wednesday...then steady off in the mid 80s over the south with 70s to lower 80s over the north. Lows should remain in the 60s to lower 70s. && .AVIATION.../For the 06Z TAFS through 06Z Sunday night/ Issued at 1136 PM CDT Sat Aug 12 2017 Only aviation forecast concern through the next 24 hours will be the potential for showers and thunderstorms in northern Iowa. Chances for TSRA activity will steadily increase through the day, and is mentioned in the KMCW and KFOD taf after 00z. The potential for earlier timing will need to be resolved with future forecast issuances. Otherwise VFR conditions will prevail for the current taf period. && .DMX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...REV LONG TERM...REV AVIATION...Martin