Scientific Forecaster Discussion

000 fxus63 kdmx 231136 afddmx Area forecast discussion National Weather Service Des Moines Iowa 633 am CDT Tue Apr 23 2019 Short term.../today through tonight/ issued at 330 am CDT Tue Apr 23 2019 Relatively quiet day today with the upper trough pushing into the Great Lakes area. This will put the upper Midwest in a northwest flow with a surface high nosing in from the northwest. The forecast problems today revolve around the lingering stratus behind the system from yesterday. Currently the far northwest into west central part of Iowa is clear but the rest of the state has ceilings on the order of a few hundred feet above the ground to around 1200 feet above the ground. As the surface high noses further into the state later this morning, it will bring in some very dry air and the low clouds should erode and push east. As far as the forecast GOES, a different model blend was used today to better capture the drier air especially across the northwest half to third of the state. The surface high will slowly shift east tonight and the upper flow will be quite light over the area and remain west to northwest over the state. A shortwave over the Southern Plains will eject to the east/northeast and as it does it will bring precip up into Missouri. At this point it looks as though the precip will remain south of the border but some mid/high clouds are likely from this over the south central to southeast part of the state. I would not be surprised if Chariton to Ottumwa got a sprinkle late tonight as the shortwave lifts out but confidence in that is far to low to include in the forecast. On Wednesday the upper flow GOES more zonal and a low pressure system over the U.S. Canadian border will drop a frontal boundary across the northern plains and northern reaches of the upper Midwest. This will turn the low level flow more southerly and temps will warm on Wednesday into the mid to upper 70s west with upper 60s east...where the influence of the low and frontal boundary will be less. Not much moisture to work with so we are not looking at precip chances at this point and even cloud cover looks pretty sparse. Wednesday will definitely be the warmest day of the work week and winds will be light...on the order to 10 to 15 mph or less. Long term.../Wednesday through Monday/ issued at 330 am CDT Tue Apr 23 2019 /Wednesday night through Friday/ Confidence: medium After a mild afternoon Wednesday, an approaching northern stream shortwave will drag a cool front southeast across the region into early Thursday morning. There remains some uncertainty as to the extent of any rain showers occurring as the front passes southeast of the area by Thursday afternoon. Currently the NAM is the driest of the models, while both the GFS/Euro paint a wetter picture with some thunder potential as the front pushes through. There remain subtle differences in the strength of the h500 wave that helps initiate and sustain the convection. The Euro is slightly farther south into Iowa with the forcing and accounts for the more southerly occurrence of showers/iso thunder than the GFS. For now will continue with a blended approach until the picture becomes a bit more clear. Clouds will be on the increase during the night with the approaching system, but still with some radiational cooling anticipated, lows will drop into the mid to upper 40s over most of the region. Thursday's highs are somewhat uncertain with the spread of solutions, potential cloud cover and showers. If the h500 wave is farther south as the Euro depicts, highs could easily be some 5 degrees cooler than currently forecast. Once the quick moving system passes south of Iowa, cooler and breezy conditions will envelop the region Thursday night into early Friday morning. There is less divergence of solutions between the GFS/Euro on Friday. Both are already bringing isentropic lift with some showers north toward Iowa as the warm front begins a northerly retreat and Lee side troughing commences over the Western Plains. Clouds should be on the increase and with lingering cold air at h850; about 1c to 5c from northeast to southwest by 00z Saturday, Friday is likely to be general near to slightly below normal in the upper 50s north to the lower to mid 60s south. /Friday night through Monday/... Confidence: low to medium An active weather pattern is setting up for the weekend with low pressure deepening just to the west of Iowa. Again, the GFS/Euro are diverging on specifics with the Euro now farther north with the h805/sfc low couplet. Late Friday into early Saturday, showers and thunderstorms will overspread the region with the low quickly moving east by the afternoon hours. Despite the rapid exodus of the storm, clouds will likely linger for the remainder of the day as cold air advection settles into the region. Highs will fall back to the lower 50s north and in the lower 60s in the south with brisk north winds for much of the day. Another storm will already take its place on Sunday with more clouds, showers and some potential again for thunder Sunday into Sunday night as a series of weather systems tracks east across the plains. It's too early to determine any impacts from the thunderstorms, but with an active pattern expected, there will be some potential for stronger storms near Iowa. && Aviation.../for the 12z tafs through 12z Wednesday morning/ issued at 1158 PM CDT Mon Apr 22 2019 IFR to MVFR stratus will continue to erode/move east through 15z-16z over the southeast taf's including kdsm and kotm. Kalo will be on the northern fringe of the low cloud deck and will likely bounce between IFR and VFR during this time. VFR conditions aft 17z over all taf locations. Sfc wind will be north then become northeast at 10-20kts. && Dmx watches/warnings/advisories... none. &&

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