Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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258 FXUS63 KDMX 032326 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 626 PM CDT Mon Jun 3 2024 ...Updated for the 00z Aviation Discussion... .KEY MESSAGES... - Minimal shower and storm chances into Tue morning, but more widespread storms expected Tue mid-afternoon into the evening. Some of those storms may be strong to severe with large hail, damaging wind, and locally heavy rain. - Mainly dry with seasonal temperatures and lower humidities Wed-Mon && .DISCUSSION... Issued at 250 PM CDT Mon Jun 3 2024 Outside of a bit slower progression on the frontal passage later tomorrow, expectations haven`t change a whole lot over the past few days with storm chances peaking late Tuesday and followed by an extended period of more tranquil and pleasant weather into early next week. The upper trough passage driving our convection potential tomorrow should usher in an extended period of higher amplitude flow, slowed by a meandering eastern CONUS closed upper low, and keeping Iowa in prolonged mainly inactive northwest flow aloft. There wasn`t much going on by mid-afternoon with most of the precip from earlier in the day now re-firing off to the east. The airmass south and east remains conducive for some development however with uncapped 1000-2000 J/kg MLCAPEs. GOES Cloud Phase Distinction products note some enhanced development in the Waterloo vicinity, and also southeast, so there is some potential for peak heating convection into the early evening for those locations. With effective shear <=25 kts any strong to severe potential appears to be minimal. Albeit low, there is some potential for additional development south and east later into the night however. Satellite imagery continues to note a lingering MCV over eastern KS, which is expected to drift north and east overnight with its subtle vertical motion field into weak low level moisture transport, which may trigger some additional weak nocturnal warm advection response. After a brief late morning lull, vertical motion ahead of the current deep Pacific NW PV anomaly should reach the Siouxland area or beyond by early afternoon, possibly triggering some isolated convection ahead of the front. The frontal progression is a bit slower than previously anticipated, but this synoptic lift should couple with the frontal low level convergence NW-SE starting no earlier than mid-afternoon, and then gradually spread south and east into the evening. There is some severe weather potential with MLCAPE ~2,500 J/kg, but organization and maintenance will be a question with effective shear often <=20 kts. Updraft strength will be marginal too with projected mean wind storm motion only 15-25 kts until the trough approaches and corresponding associated low level storm relative inflow at those values or weaker. With these lower storm relative winds, and soundings relatively dry post afternoon mixing, experimental Entrainment Cape values are ~40% less than traditional MLCAPE reflections which also suggest tempered updrafts. This slow movement may lead to some locally heavy rains however with climatologically anomalously high moisture parameter space, including precipitable water values 1.75"+. 12z HREF localized probability matched-mean (LPMM) 24hr QPF suggests isolated 1-3 amounts are possible. Any precipitation should move off to the east approaching daybreak Wednesday starting what looks to be an extended period of little precipitation, seasonal temperatures, and atypically lower dewpoints. This will be driven by fairly uniform northwest flow surface to above keeping us with little in the way of forcing or moisture with surface high pressure progressing no further than Iowa until the weekend. The only precipitation window of note looks to be late Fri into early Saturday across central and southwest Iowa as weak waves top the Rockies ridge and induce warm/theta-e advection aloft through the MO Valley. There are a few other brief precipitation opportunities in various deterministic solutions, but right now the NBM does not reflect a sufficient signal for any mention beyond later this week. One higher confidence reflection of sensible weather will be lower humidities in prolonged northwest low level flow pushing dewpoints into the 40s at times later this week, atypically low for early June. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 624 PM CDT Mon Jun 3 2024 VFR conditions currently prevail and will continue overnight into much of Tuesday. A broken line of showers and storms are likely as a front pushes through late Tuesday afternoon and evening. Included mention of -TSRA at select terminals to highlight the most likely time of arrival of this activity, however the extent of categorical impacts at each terminal remains uncertain and will be further refined in coming TAF issuances. && .HYDROLOGY... Issued at 250 PM CDT Mon Jun 3 2024 A Flood Warning remains in effect for Estherville, with all of this morning`s river forecasts based on 24 hours worth of QPF (through 12Z Tue). While heavy rains are possible Tue afternoon and evening beyond that period per the Discussion section, additional flooding concerns beyond the current Estherville Flood Warning are not expected at this time based on recent HEFS output and RFC contingency forecasts. Neither GEFS based HEFS median to 30th percentile QPF exceedance probabilities or the 120 hour deterministic QPF suggest additional flooding beyond what is already occurring, hinting at mainly within bank rises unless rainfall greatly exceeds expectations. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Small AVIATION...Martin HYDROLOGY...Small