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Displaying AFOS PIL: AFDDMX Received: 2021-10-19 11:34 UTC
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567 FXUS63 KDMX 191134 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 634 AM CDT Tue Oct 19 2021 .SHORT TERM.../Today through Tonight/ Issued at 256 AM CDT Tue Oct 19 2021 .Short Term /Today through Wednesday/... Forecast Challenges: ...Extend of precip and thunder/svr chances Wednesday ...Cool Down into late week ...Changing evolution of weekend/early next week storm Confidence through Wednesday: Medium Little impactful weather expected today. Retreating high over the lower Ohio River Valley will continue drifting east today as low pressure over the Rockies begins to get more organized. Weak system over Colorado now with a surface low with a 2 part H850 low over central and western Colorado. Both aloft and at the surface, a weak warm front/trough is pushing north across Iowa tonight with patchy mid to high level clouds moving through presently. These clouds should be nearly east of the area by 18z with generally mostly sunny skies for the balance of the afternoon hours. Despite these high clouds, H850 temperatures are expected to warm about 3C higher this afternoon than Monday afternoon. Though we will not realize the entire warm nose in the sounding, mixing up to about 865 mb should help push afternoon highs well into the 70s again this afternoon; especially given the generally continued dry conditions across the region. By tonight, the Colorado low will be tracking into eastern Nebraska between 00 and 06z with rather strong warm air advection and H850 low level jet of 35 to 40kts across southern Iowa. As the low tracks northeast overnight into northwest Iowa, elevated convection is anticipated to break out along the upper level warm front in northern Iowa and southern MN, southeast South Dakota. There may be some shower or isolated thunderstorm activity also flaring east into central and eastern Iowa between 06 and 12z, and again from 12 to 18z, though chances will remain low there. There remains some uncertainty as to the exact track of the low across northern Iowa Wednesday. Most of the models take it between US 20 and the Iowa MN border. The proximity of the low/occluded front will be key to afternoon thunderstorm redevelopment. SPC has included a marginal risk in northwest Iowa through 12z Wednesday as lift near the center of the upper level low may enhance a low risk of hail. As we move into the late morning and afternoon, the low tracking in northern Iowa will have the same impact as strong mid level warm air advection, 500 to 1000 j/kg mucape and 40kts shear combine for a threat for a few rotating storms with hail. Again, with the varying tracks of the low, the higher risk of the elevated storms will be along the occluded front near the sfc low and that will need to be narrowed down a bit in the next 24 hours as the track of the low becomes more certain. There will also be an area of storms developing along and ahead of the cold portion of the front over eastern Iowa. The bulk of that activity will likely occur just east of our forecast area. Highs Wednesday will be cooler over the region with upper 60s to lower 70s east and lower 60s northwest and west as the cooler air sweeps into the area behind the low. Winds will also pick up in the afternoon with westerly winds gusting to near and over 30 mph from I35 and west. .LONG TERM.../Wednesday through Monday/ Issued at 256 AM CDT Tue Oct 19 2021 Confidence: Medium...Lowering into the Weekend As the elongated trough/low continues to pull northeast into Wisconsin and northeast Iowa by 12z Thursday, wrap around moisture and colder air will swing through Iowa. Clouds will again fill in across the region Wednesday night with the advancing cold air and some showers/drizzle will also be possible. A secondary cool front or trough will be across central Iowa at 12z with clouds lingering for most of the day over central sections, all day in the southeast and through about noon over the north. H850 temperatures drop to 5C in the southeast and remain about 3-4C in the north by late day. With some mixing expected, highs will be capped in the lower to mid 50s north and in the mid to upper 50s in the south. The GFS, Euro and GEM all shoot another weak short wave southeast into the area already on Friday. Clouds, a small chance for sprinkles and cool H850 temperatures will hold afternoon highs to near 50 north while central Iowa nears the mid 50s and the southwest the upper 50s by days end. The bulk of the clouds are likely to clear northeast areas by sunset with another band of clouds moving into western and southern areas as some warm air advection aloft tries to return into Saturday morning. We continue to monitor the chances for frost and freeze conditions Friday night into Saturday morning. At this time, the most likely areas would be the north and northeast valley areas with temperatures around 30 north to the lower 30s into the Iowa and Cedar River Valleys. As the weekend rolls around, the operational models begin to diverge. The GFS is now speeding up the southern stream low and pulling it rapidly north into Iowa by Sunday morning, while the Euro is still 24 hours slower. The GEFs, like the GFS, has rain rapidly expanding into Iowa by 12z Sunday as well. The GEM is also swinging the low more quickly north into Sunday with a broad area of warm air advection rain/potential thunder through the day. With differences becoming more stark between the Euro and the other guidance, its safe to say that rain will occur between Sunday into Monday, but the timing still needs to be addressed in more detail. With warmer air aloft following the push of warm air advection, highs Monday will begin to tick up again and should reach the mid 60s southwest, while areas central and north will reach the lower to mid 60s by late day with lingering showers. && .AVIATION.../For the 12Z TAFS through 12Z Wednesday morning/ Issued at 634 AM CDT Tue Oct 19 2021 VFR conditions expected through the period with mid level deck arriving aft 08z north sites. Warm air advection showers possible aft 08z northwest and 10z east. Otherwise, winds mix to near 20kts aft 17z today, relaxing around 00z. /rev && .DMX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...REV LONG TERM...REV AVIATION...REV