Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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030 FXUS63 KDMX 081849 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 149 PM CDT Sat Jun 8 2024 .KEY MESSAGES... - Sprinkles, a fleeting shower west or south this afternoon or early this evening - Ample sunshine, comfortable temperatures and humidity Sunday, Monday - Warmer weather Tuesday through Friday, storm chances return && .DISCUSSION... Issued at 149 PM CDT Sat Jun 8 2024 GOES-East upper level water vapor imagery shows a broad trough with embedded closed lows and shortwave troughs sprawled over the southern provinces of Canada into the Northeastern US with this resulting in northwest flow over Iowa. This places Iowa in the squeeze between the northern jet stream flow around the broad trough close by to the north with the southern jet stream of shortwaves far enough away to keep our forecast more tranquil with any severe threat remaining south of the state through early next week. At the moment, we reside beneath nebulous shortwave energy as well as the right entrance region of a departing 115 knot jet streak. These are the impetus for the clouds entering the western part of Iowa this afternoon. Radar has shown light returns over parts of Siouxland and there have a been a few mPING reports in Plymouth County. However, the farther east towards Cherokee/CKP and Storm Lake/SLB, there have not been any reports from automated sites or ground observers whether mPINGs or parents in this same area. The lack of surface reports is due to plenty of dry air below 700mb/sub cloud layer that is shown in forecast soundings this afternoon and with surface dewpoint depressions of 10 to 15F, have trimmed back PoPs a bit more this afternoon into this evening. As the jet streak farther departs and the shortwave energy sinks away as the broad trough breaks apart with one piece deepening over the Eastern US, this will result in continued northwest to westerly flow with mostly dry conditions and comfortable temperatures and humidity by early June standards through Monday. At the same time, heights will be rising over the western US and as the Eastern US trough moves away, these higher heights will arrive replacing comfortable conditions with temperatures above normal Tuesday through the end of the week. Highs during this period will be well into the 80s to around 90 degrees. Latest NBM puts the probability of exceeding 90 degrees on Thursday at 60% or higher roughly south of Highway 30. While temperatures will be on the rise, chances for storms will also return to the forecast. A shortwave trough aloft and a surface low will ride along the US/Canadian border while a cold front draped to its south approaches Iowa on Tuesday. MUCAPE of 500-1000 J/kg will build ahead of this front by mid-afternoon with a marginal amount of shear for storm organization. While this would result in thunderstorm potential, any severe risk appears low at this time with this supported by the SPC day 4 outlook and Colorado State University`s (CSU) machine learning random forest outlook. While the cold front will push into Missouri, a warm front and attendant warm air advection return on Wednesday along with additional storm chances, especially over northern Iowa into Minnesota and the Dakotas. CSU outlook does have a broadbrush area of severe probability, but the jet streak and better forcing will reside over the Dakotas. More chances may return on Thursday as the front pushes through the state. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1152 AM CDT Sat Jun 8 2024 A few lingering MVFR ceilings at the start of the period at ALO and OTM will give way to VFR conditions, which should then prevail through the period. A fleeting sprinkle or brief shower could occur this afternoon or early this evening at FOD, DSM, or OTM if it can overcome the dry subcloud air. With chances remaining at or less than 10%, have maintained a dry forecast. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Ansorge AVIATION...Ansorge