Scientific Forecaster Discussion

000 fxus63 kdmx 180439 afddmx Area forecast discussion National Weather Service Des Moines Iowa 1139 PM CDT Mon Jun 17 2019 ..updated for 06z aviation... Discussion.../tonight through Monday/ issued at 333 PM CDT Mon Jun 17 2019 A strong shortwave trough for this time of year and an associated weak surface low pressure are moving eastward over far northern Minnesota early this afternoon. A weak boundary that is moving into northwest Iowa has been the focus in our area for showers and thunderstorms. Late this morning, 0-3km MLCAPE was maximized over northwest Iowa with a funnel cloud reported near Terril as a thunderstorm developed as stretching was enhanced. If any isolated storms can develop away from the line of convection that stretches from Mason City to around Carroll as of 300pm, then funnel clouds are still possible over the next few hours over northern Iowa. There is the potential of some sub-severe wind gusts with the storm near Fort Dodge showing a wind signature, though it may not reach the surface. Current cams show this line dissipating this evening, but with the boundary remaining over northern Iowa still potential for some lingering precipitation. Otherwise tonight, there is some potential for fog over southern Iowa with a few models lowering visibilities down to a mile. Have added some patchy fog for the time being over southern Iowa. The next shortwave trough will come out from the central rockies and track south of the state through Missouri near I-70. 00z runs were painting higher quantitative precipitation forecast amounts over southern Iowa compared to the 12z runs, which have the bulk of the heaviest rainfall over northern Missouri. NAM and regional CMC still maintain the higher rain totals over southern Iowa, but have shifted the highest quantitative precipitation forecast in the forecast south of the state at this time Tuesday into Wednesday morning. Still, upped totals from initial guidance and at times more in line with wpc through Wednesday morning. Some showers and storms may linger over the state into Wednesday, especially the southeastern half of Iowa, as the shortwave exits into the Ohio Valley. Severe weather threat looks low with weak deep layer shear and marginal instability. A brief break in the weather will occur late Wednesday into a part of Thursday before a northern stream wave drops through the region ahead of a longwave trough moving over the Pacific northwest. The wave will generate more showers and storms with the best instability and shear focused along the Iowa/Nebraska border. Cannot rule out some strong to severe storms over the western part of the forecast area at this time. This longwave trough will begin to change the pattern to southwesterly flow and a more active pattern with strong to severe storms and heavy rain potential increasing late this week into this weekend. Lending credence to this idea is the 17/00z cips analogs, which has a strong signal for at least 1 severe report and a signal for at least 5 severe reports over the region, which aligns well with the Storm Prediction Center day 5 outlook area. Further, 17/00z naefs also starts increasing specific humidity late Friday into Saturday over the region as the low level jet draws higher amounts of low level moisture over the region. With surface low still tracking primarily west of central Iowa and a warm front lifting through the state Friday into Saturday, this would mean all modes (tornadoes, hail, winds) will be possible. Precipitable water values will top out between 1.5 to 2 inches with deep warm cloud depths, which could also lead to heavy rainfall. At this time, it is a period to keep a close eye on with 12 to 16 model cycles between now and then for things to evolve and evaluate further. && Aviation.../for the 06z tafs through 06z Tuesday night/ issued at 1139 PM CDT Mon Jun 17 2019 Light rain this evening has diminished through the evening, but expect redevelopment across northwest Iowa early Tuesday morning, moving southeast through the day Tuesday with MVFR cigs possible. In addition, patchy fog is expected to develop across southeast Iowa Tuesday morning with MVFR to IFR vis possible for a short time. && Dmx watches/warnings/advisories... none. &&

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