Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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916 FXUS63 KDMX 272339 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 639 PM CDT Mon May 27 2024 ...Updated for the 00z Aviation Discussion... .KEY MESSAGES... - Scattered showers and thunderstorms this afternoon with strong winds being the main impact. - Additional scattered showers expected tomorrow, severe risk is low. - Quiet through mid-week before shower and thunderstorm chances return late week into the weekend. && .DISCUSSION... Issued at 300 PM CDT Mon May 27 2024 >> Shower and Thunderstorm Chances This Afternoon/Evening After the scattered showers and thunderstorms passed through the area this morning, skies cleared briefly through mid-day. This allowed for a few hours of sunshine to mix out the boundary layer and steepen lapse rates, ultimately kicking off more scattered showers and thunderstorms this afternoon. The dry low levels below these storms have resulted in strong winds at the surface as rain falls and evaporates through the layer, with some locations reporting gusts near 50 mph. A few more prominent updrafts have also produced some small hail, but with a relatively shallow 1000 J/kg of CAPE, and fairly high LCLs, storms will likely struggle to produce any severe criteria hail. That being said, if any larger hail is produced, it would likely be further south where effective shear values are around 35 to 40 kts. In addition to small hail and strong winds, the 100-200+ J/kg of 0-3 km CAPE and modest amount of low level vorticity may help to produce a few funnel clouds today but increasing LCLs this afternoon should help mitigate any touchdowns. That being said, cant rule out a very brief landspout before bases increase later this afternoon, especially given the large amounts of stretching present. Storms today will be during the peak heating period, diminishing as the surface inversion sets in and as the wave departs east. >> Additional Precipitation Chances Tomorrow A second wave will move through the overall northwest flow tomorrow morning, bringing another chance for a few showers and thunderstorms right on the coattails of todays wave. These chances will be over a similar area to todays, mainly favoring the northern and eastern portions of the state but with additional chances over southern Iowa as well. Not anticipating much for severe risks with any storms on Tuesday, with very low amounts of CAPE (less than 1000 J/kg) limiting the chance for any stronger storms. These remain scattered through the day as the wave passes, diminishing Tuesday evening. >> Quiet Before Shower and Storm Chances Return Thursday and Friday Beyond the scattered showers Tuesday, the forecast looks mostly quiet through the middle of the week with an upper level ridge and surface high pressure building in overhead. As we get later into the week, another 500 mb trough begins to dig in over the northwestern US and will bring us our next chances for thunderstorms. The arrival of the gulf moisture behind the surface high pressure looks to be Thursday into Friday, with a minor timing discrepancy between the GFS and ECMWF. The ECMWF has it arriving on Thursday morning, while the GFS holds off any precipitation in the area until late Thursday night to early Friday morning. Ensemble guidance splits these solutions, favoring towards a Thursday morning to mid-day arrival. This timing discrepancy, in conjunction with additional waves passing through into the weekend, has resulted in a prolonged period of forecasted precipitation starting Thursday morning and lasting through the end of the 7 day period. This is likely a bit overdone and will not be a consistent washout, but it does look to be an active weekend with off and on shower and thunderstorm chances possible into the beginning of next week. Severe chances through this period will be better determined in the coming days, but right now it looks like the better instability will stay west of the area on Thursday and Friday, then increase overhead on Saturday and Sunday. The Gulf stays pretty open through the weekend as well, supplying us with a good amount of moisture supportive of heavy rainfall. That all being said, this is all still a ways out and we will have to see how the pattern continues to evolve as it draws nearer. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 640 PM CDT Mon May 27 2024 Lingering scattered showers with embedded lightning are moving southeastward over north central Iowa this evening. The initial shower over MCW will clear by the start of the period and should be past ALO by 130z and will monitor for any possible amendments, but activity should be on downward trend after sunset. Removed VCSH from previous TAFs at FOD Tuesday morning with confidence not sufficient for inclusion. However, chances do remain over northern Iowa and may need to be added back in if and when confidence does increase for an impact to the terminal. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Dodson AVIATION...Ansorge