Area Forecast Discussion
Issued by NWS Des Moines, IA
Issued by NWS Des Moines, IA
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566 FXUS63 KDMX 010808 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 308 AM CDT Wed May 1 2024 .KEY MESSAGES... - Brief Break then Showers/Storms Return This Afternoon. - Periods of storms overnight/Thursday/Early Friday with 1 to 3 inches of rainfall possible. - Another System on Saturday with Scat Showers/Isolated Thunder and again by late Sunday into Monday. && .DISCUSSION... Issued at 308 AM CDT Wed May 1 2024 .Short Term /Today through Thursday/... Confidence Short Term: High Active pattern continues for the next several days. Elongated trough and sharp wave now lifting northeast of region early this morning. Sfc map shows a weak lagging trough/front over our area which will be the focus for renewed showers and lift by late morning into the afternoon. In the wake of todays system, we have some patchy fog developing over northeast Iowa and this will last into the early morning. The next main wave will arrive tonight. Aloft at H850, height fields show the exiting H850 wave and the sharp trough that brought the large hail and wind damage to our area on Tuesday. Upstream another wave in the TX Panhandle is recharging the Southern Stream already at 00z with an open stream of moisture from the Gulf. Though we are temporarily in northwest flow, we will be back in south southeast flow already by late afternoon. Some scattered showers will form along the lingering boundary over the west/north this afternoon. By evening, stronger warm air advection/moisture will begin to ascend the main H850 frontal boundary to our south. This will create a widespread area of showers and thunderstorms tonight. With instability remaining limited, the better chance of any organized convection will be over the southwest/west with areas of showers and isolated storms over the remainder of the region through 12z Thursday. At this time, there is only a limited risk of some severe storms over the south/southwest after midnight. After highs today in the mid to upper 60s north and in the lower 70s south, tonight will be mild south with lows in the mid 50s and in the 40s north. Tomorrow the main wave will track through western Iowa, bringing most of the region into the warm sector. The best dynamics/lift will be from northern Iowa to MN/WI as the warm front pulls north and along the trailing cool front over central/western Iowa. By afternoon MUCAPE should exceed 1000 j/kg, but shear remains just around 35 to 40kts nearer the boundaries and lesser southeast. The best H500/H300 wind support lags the front, which is a better forcing mechanism for moderate rainfall than severe weather. PWATs are forecast to increase to 1.5 inches by 12z Thursday and remain in that area for most of the day in the warm sector. Scattered rainfall amounts of 1 to 3 inches will be possible from late tonight to early early Friday as the system moves east. We continue to be outlooked for a slight risk of excessive rainfall over the region. If any hydro issues arise, they should be mainly from urban runoff and some minor flooding of low lying areas. In the next 5 days, the HEFS guidance shows a potential for some of our northern main stem rivers to go into action stage or perhaps reaching minor flooding. A lot will depend on the extent and location of the rainfall from tonight through Saturday. By late Thursday afternoon, most of the showers/storms will be over in the far northwest and still ongoing in the east. The passage of the front around noon will limit any stronger convection in the afternoon hours and we continue only with a marginal risk tomorrow. Highs tomorrow will range from some cooler upper 50s northwest to the lower 70s in the southeast. .Long Term /Thursday Night through Tuesday/... Confidence: Medium The gradual shift east of the system Thursday night will bring most of the rain to an end between 06 and 10z. Friday will be a pleasant day with a weak ridge of high pressure edging east over the region. Highs will reach the lower 70s with modest northwest winds. Some fair weather cumulus are likely, given the recent rainfall. By early Saturday morning, a weak cool front/trough will enter northwest Iowa. This extends from a low over Manitoba/Quebec south into the Central Plains. Moisture will be limited and only by late day will some instability possibly result in some isolated thunder southeast. Friday night will see mins in the mid 40s northwest to the lower 50s south with highs Saturday in the lower to mid 60s over the area. Saturday will not be a washout, but scattered showers will make it feel cooler and add somewhere between a tenth to a third of an inch of rainfall scattered across the south/west. By Saturday night, we again dry out with high pressure building into the area Sunday morning. Most of Sunday will be pleasant, but already another active wave is developing in the Rockies. This will be spreading clouds back into the region by late day, along with some showers southwest. Highs will climb back to the 60s to lower 70s. Medium range guidance is showing that a ridge over the eastern CONUS will limit the progression of the Rockies system into the Central Plains. We will get in the eastern edge of the moisture field with some showers Sunday night and early Monday; and again late Monday and Monday night as a warm front swings northeast. With the system occluding Monday night, Tuesday should be dry as we get into the dry slot of the western system. With H850 temperatures averaging 10 to 12C Sunday through Tuesday, afternoon highs should remain in the 70s with lower to upper 70s expected later in the period. Mins will be in the upper 40s and 50s. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 1131 PM CDT Tue Apr 30 2024 Conditions have improved across all sites late tonight as convection has pushed east of the area. Overnight and into the day Wednesday the primary change in weather will be shifting winds between the departing low tonight and the incoming low on Wednesday night. Scattered showers will move into the area Wednesday afternoon, becoming more widespread through the evening and overnight Wednesday night. Current impacts are at the end of the TAF period and additional detail will be added in subsequent updates. && .DMX WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...REV AVIATION...Hagenhoff