Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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524 FXUS63 KDMX 251140 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 640 AM CDT Sat May 25 2024 ...Updated for the 12z Aviation Discussion... .KEY MESSAGES... - Highs today once again in the 70s with rain and storms likely (>80%) tonight. Marginal risk in the southern half of the state for large hail and damaging winds. - Rainfall amounts tonight totaling between 1 and 2 inches south with locally higher amounts possible. Confidence lower (20%) in flash flooding due to progressive storm motion. - Additional rain chances Monday, but with light amounts. Rain will return next weekend. && .DISCUSSION... Issued at 329 AM CDT Sat May 25 2024 There was a noticeable dryness yesterday afternoon and overnight due to the surface high moving across the Plains. 00z upper air analysis showed the main low level moisture axis veered to the east with the system that impacted the state on Friday. Some recovery will occur as a wave moves off the Rockies today and pulls the low level jet up into Nebraska during the day. An instability axis will build into Iowa. CAMs have an MCS forming at the nose of the jet later today over Nebraska, but its progression and severity as it moves east has some questionable factors. Mainly, the low will be positioned over Kansas and Nebraska and will be pushed due east in the upper jet, keeping the brunt of development south. Additionally, the speed of that upper jet will make warm sector storms advance quickly to the east. This may cut off the advancement of the instability axis further north and cause the MCS to either decay or dive south. All that being said, a pocket of MUCAPE values nearing 2000 J/kg will focus over the southern half of the state and wane with time tonight along with PWAT values around 1.5". Deep layer shear is favorable for storm organization, particularly before midnight. Plenty of synoptic energy at play to develop showers and storms over the state. As long as the warm front stays in Missouri, storms in the state would be elevated in nature with large hail and damaging winds being possible, hence the Marginal Risk. The tornado threat is negligible with elevated storms as well. Rest assured that winds and hail will not be at the magnitude we saw Thursday night into early Friday, justified mostly by the warm sector and brunt of the kinematics being displaced to the south for places like Oklahoma. We will see efficient rainfall out of this system, but with fast storm motions limiting efficiency. Plenty of isentropic ascent over the warm front. The CAPE profile is elongated with warm cloud depths hovering around 10kft. Areas across the south can expect between 1 and 2 inches. The HREF PMM has a secondary swath of higher precipitation amounts near the Highway 20 corridor, likely from simulated decaying convective elements from Nebraska. Lower confidence (~40%) in this secondary area of QPF at this time. The aforementioned progressive nature of storms will spread the QPF over 6 hours and keep areas out of flash flooding troubles, but locally higher amounts can lead to ponding and increased river levels, especially for areas impacted the most from rains this week. An upper level low in Canada will continue to churn additional waves Sunday night as well as Monday, but with less and less moisture to work with. One last wave comes through on Tuesday where the addition of PoPs may be needed in further issuances. Otherwise, the upper level trough will deepen over the northeast and build in by midweek with high pressure settling in over the Plains. This will block the Gulf from us until at least Friday, tempering our rain chances. Highs will be near 80 for the week which is right near average for this time of year. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 637 AM CDT Sat May 25 2024 VFR conditions expected for the daytime hours today with generally southerly winds. Winds become southeasterly after 00z. Showers and thunderstorms arrive after 06z tonight with MVFR and IFR cigs and vsbys. Severe winds possible as storms reach KOTM. Have added prevailing SHRA FM groups to reflect time of highest confidence of storm arrival. Timing to be refined in future issuances. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Jimenez AVIATION...Jimenez