Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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543 FXUS63 KDMX 092328 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 628 PM CDT Thu May 9 2024 ...Updated for the 00z Aviation Discussion... .KEY MESSAGES... - Lingering shower chances into this evening, mainly along and east of I-35. Few showers/storms possible again Friday afternoon and evening. - Fantastic spring conditions Saturday. Sunshine and 70s. - Chances for showers and storms return early next week. Severe threat low. && .DISCUSSION... Issued at 200 PM CDT Thu May 9 2024 The presence of a broad, decaying trough overhead has sustained shower activity over the forecast area through the day. The focus has generally been within a diffuse zone of low level convergence co- located with mid-level fgen forcing. RAP analysis shows pockets of 0- 3km CAPE pushing 100 J/kg beneath a cool airmass aloft. The enhanced stretching potential combined with high background vorticity may support a few funnels or brief landspouts. Dry air has really eaten into the westward extent of the precip, much more so than suggested by hires guidance. Thus the rest of the day has trended drier at many locations, save for about the eastern third of the cwa which stands the highest chance to see additional measurable precipitation before the rainfall exits tonight. Additional precip chances return Friday afternoon and evening as a compact shortwave slides through the Great Lakes region and sweeps a surface frontal boundary across the state. Synoptic forcing contributions are not well phased on the south/west periphery of the wave, and combined with dry boundary layer conditions should limit the spatial coverage and depth of the convection. Soundings show inverted-v profiles and steep low level lapse rates up to ~800mb so a few brief elevated wind gusts are possible, but overall the threat of any strong to severe convection is low. Make plans to get outside on Saturday as fantastic spring conditions are forecast. A passing surface ridge axis beneath building heights aloft will lead to dry conditions and subsidence through much of the atmospheric column, giving way to plentiful sunshine and highs in the 70s. Rain chances return early next week as cutoff upper low is kicked out of the Four Corners region. Forcing mechanisms and convergence still look rather diffuse, so it is difficult to pinpoint a particular period for higher PoPs or to provide more detail on potential precip amounts. The deterministic EC is also more aggressive with impinging dry air on the northern periphery of the upper low as it crosses the central Plains, a trend that is also reflected in the EC ENS guidance with a fair share of members now advertising no QPF over the northern half of the forecast area. Flow aloft is very lethargic with 500mb winds less than 20 kts. Any convection will be highly disorganized and likely pose little severe threat. && .AVIATION /00Z TAFS THROUGH 00Z SATURDAY/... Issued at 628 PM CDT Thu May 9 2024 Scattered convection moving into southeast sections at 2320 and diminishing. Have dropped -shra most areas sans OTM where VCTS is possible between 00 and 01z. Have left out for now. Patchy MVFR cigs continue with VFR returning aft 02z most areas. Some early morning MVFR BR from MCW to ALO and should lift by 13z. Some mixing expected aft 20z most areas from the west northwest, through end of period. /rev && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Martin AVIATION...REV