Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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133 FXUS63 KDMX 200837 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 337 AM CDT Thu Jun 20 2024 .KEY MESSAGES... - Rain focusing primarily northeast through this morning. Non- zero chance of redevelopment this afternoon. Main round of rain arrives in the north tonight. - Rain lingers in the north through the day Friday and becomes more intense for the overnight. Some storms strong to severe with gusty winds and hail early on. Heaviest rain looks to remain in MN at this time. - Another push of rain and storms Saturday with some storms becoming strong to severe. Dry period expected at least through Monday with temperatures returning to near 90 degrees. && .DISCUSSION... Issued at 308 AM CDT Thu Jun 20 2024 A stalled out front remained over southeast Iowa overnight. With high pressure to the north, LLJ moisture was redirected into the Northern Plains and away from the front. Despite the weak kinematics, plenty of moisture and some instability allowed for some showers and storms to fire off the front overnight. With 2 inch PWATS, thunderstorms along this line could produce localized amounts up to a half inch as they lift northeast through the morning. Moisture transport will remain focused west of the state today which will work to keep most of the area dry today. Cannot completely rule out some precipitation along the boundary in central Iowa today as diurnal destabilization takes place, but confidence is low (<20%) due to the lack of synoptic forcing nearby. At the very least, cloud cover will linger along the front today and make high temperatures underperform. Have lowered high temperatures to reflect this possibility with cool sector sites in the upper 70s to low 80s. The southeast will have the least residence time of the front today and will be allowed to rise into the mid 80s this afternoon. For tonight, the LLJ strengthens and generates an MCS across Nebraska. This MCS will follow along the instability gradient which will be somewhere near the IA-MN border, per model consensus. The northern extent will depend on how far north the boundary gets today. The LLJ will also veer eastward overnight tonight, adding to the heavy rain potential through the day Friday. Right now, model consensus keeps the heaviest rain in southern Minnesota, but local convective elements can alter the final location of boundaries, meaning a heavy rain scenario in northern Iowa cannot be completely discarded. In what feels like a broken record this week, the cold pool will drop the boundary into Iowa with rain chances lingering in northern Iowa throughout Friday. Have also lowered highs Friday in response, but expecting rain cooled areas in the north to have highs lower than currently forecasted. The LLJ will angle across the state overnight Friday with the highest precipitation occurring along the aforementioned front. At this point, synoptic forcing from an approaching lee side cyclone will increase coverage. Shear will also increase beneath the influence of the jet, so some storms could become severe with primarily damaging winds and hail early in the evening. Primary threat will transition to primarily heavy rain overnight. The LLJ from the southwest will shove the boundary north through the night, with current model output keeping its residence time in Iowa fairly short. Far northern counties could see 1-2 inches of rain with locally higher amounts with higher amounts remaining in MN. Trends will continue to be monitored. The upper level ridge will begin to pivot westward this weekend, allowing the low to trek northeast Saturday. Its trailing cold front will move across Iowa. Instability will build ahead of the front. Deep layer shear of around 30kts will aid in organization and make some strong to severe storms possible. As for the threat of heavy rain, this round will be more progressive in nature, keeping rainfall amounts under an inch (some higher amounts from thunderstorms). We will be afforded a dry period to into early next week until the ridge nestles over the desert southwest and opens up the Gulf to the Plains next week. The southwest flow during this time, barring rain chances, will push highs back to near 90 degrees. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 1148 PM CDT Wed Jun 19 2024 No dramatic changes within this TAF issuance. Chances for thunder remain relatively low, so have limited precipitation mentions to VCSH mainly in/around KDSM/KOTM/KALO. More pertinent will be the MVFR/IFR ceiling progression across the area as hi- res guidance continues to suggest expansion and northward lift through the period. Have continued to hold back on the most aggressive (IFR) depictions and kept current prevailing mentions to MVFR. That will need to be monitored though as there is an area of IFR ceilings over southern Iowa and northern Missouri, just uncertain how expansive that will truly become. && .HYDROLOGY... Issued at 213 PM CDT Wed Jun 19 2024 Little change in thinking from previous discussion. Heavy rain still poised to fall over basins in the north and west over the next few days. Main concern remains the West Fork Des Moines River Basin with heavy rain possible in its reaches in northwest Iowa as well as into Minnesota. Ensemble output brings sites nearest the state line into minor flood stage from a mix of local rain and upstream runoff. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Jimenez AVIATION...Curtis HYDROLOGY...Jimenez