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Displaying AFOS PIL: AFDDMX Received: 2017-09-20 04:59 UTC
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241 FXUS63 KDMX 200459 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 1159 PM CDT Tue Sep 19 2017 .SHORT TERM.../Tonight through Wednesday/ Issued at 349 PM CDT Tue Sep 19 2017 Synoptic pattern aloft continues to be defined by a broad longwave trough with several embedded shortwaves over the western two-thirds of the conus. One such shortwave was noted on water vapor passing through WY/MT, which will quickly eject over the northern Plains tonight and pivot northward into Canada. At the surface, a cold front extends through the central Dakotas into the western High Plains. The front will progress eastward through the forecast area tonight into Wednesday. Shower and thunderstorm activity is likely along the frontal axis as it tracks out of the Dakotas, but how far south and east this activity will be supported is in question due to the presence of a strong capping EML. Several hi-res models continue to advertise some convection in north central Iowa late tonight into early Wednesday morning, mostly north of Hwy 20. Any threat for severe weather should be limited due to weakening instability overnight, but can't rule out the potential for a few strong wind gusts given DCAPE values around 1000 J/kg. Otherwise, southerly winds and abnormally humid conditions will keep temperatures very mild overnight with lows in the 60s to near 70. The aforementioned cold front will push through central Iowa tomorrow morning and afternoon. A much drier air mass will advect in behind the front, bringing a brief reprieve from the unseasonably high humidity. A strong capping inversion will likely inhibit convection along the front until late in the day, at which point the front will be starting to stall out near the southeastern periphery of the forecast area. Maintained mention of slight chance pops in our far southeastern zones to cover any potential for late afternoon development, but confidence is low at this time due to strong capping aloft and uncertainties in frontal position. For any storm that does develop, strong instability and steep mid-level lapse rates will promote the potential for hail and strong wind gusts. .LONG TERM.../Wednesday night through Tuesday/ Issued at 349 PM CDT Tue Sep 19 2017 Will see renewed warm advection on Wednesday night along with increasing moisture advection as front begins lifting northward. The increased theta-e advection and associated destabilization may lead to the development of isold/sct convection across southern/central Iowa during the night and have continued Pops during this time, mainly south of Highway 30. The warm sector will slide quickly northward on Thursday with very warm readings returning along with unusually high moisture values for late September. The upper pattern will amplify into the late week and weekend with a large western trof and equally impressive eastern ridge. Not much movement is expected as both Jose and Maria edge up the western Atlantic. Iowa will mostly be in the warm sector during this time frame with much above normal temperatures from Friday into Sunday along with the humid conditions persisting. With little forcing and the atmosphere essentially capped, the threat of precipitation will be minimal during this time. By late in the weekend into early next week, ridge in the east will finally begin to shift eastward and weaken allowing the western trof to advance as well. The front that will be in the Plains through the weekend will advance toward Iowa on Sunday night into Monday with heightened chances for storms during this time. Once the boundary slips through, temperatures will be cooler into the middle of next week. && .AVIATION.../For the 06Z TAFS through 06Z Wednesday night/ Issued at 1157 PM CDT Tue Sep 19 2017 A few thunderstorms still possible over far northern Iowa tonight and may pass near vicinity of KMCW. A storm may also be possible in the KOTM area late in the period. Expect breezy winds to persist the next several hours then diminish on Wednesday as high pressure moves into NW IA. Localized MVFR cigs possible late tonight into early Wednesday morning over the north. && .DMX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...Martin LONG TERM...Cogil AVIATION...Donavon