Area Forecast Discussion
Issued by NWS Des Moines, IA

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000 FXUS63 KDMX 292340 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 640 PM CDT Fri Mar 29 2024 ...Updated for the 00z Aviation Discussion... .KEY MESSAGES... - Scattered storms tonight with a few marginally severe - Seasonal Weekend with rain returning Sunday - Rainfall & storms continue into Tuesday; bulk of severe potential south of Iowa && .DISCUSSION... Issued at 242 PM CDT Fri Mar 29 2024 .Short Term /Tonight through Saturday Night/... Confidence Short Term: Medium to High Generally on track for some convection over the area by evening across central to eastern Iowa. Already on satellite, some destabilization is taking place aloft with the development of mid level cumulus. The surface boundary remains in place over west central to southeast Iowa. H850 analysis this morning at 12z showed a narrow plume of moisture being rapidly advected north within a 40 to 55kt low level jet. Though the moisture is still rather limited with Td of 0C to 5C, that will increase toward the evening hours as slightly deeper moisture from northern Texas begins to get closer to the area. Also, surface moisture at this time remains low with dewpoints in the 30s to lower 40s in southwest Iowa. Late afternoon and early evening will see more moisture pooling at low levels near the front in southern to eastern Iowa. This will help focus available moisture/lift from central to eastern Iowa this evening with the help of a H700 wave, another push of warm air advection and approaching weak surface low. Once storms develop, H700 flow will push them east later into the evening. Current HRRR operational runs are forecasting CAPE to peak at 700 to 1200 j/kg early in the evening from around 22z to 02z, then the area of better instability advects east with the system. It may take until 23-00z for initiation, and thereafter a short window of storm potential in our southeast to east as the storms move out. Overall, some turning in the winds will give rise to slightly better chances for larger hail and the HRRR reflects some weak helicity tracks with the elevated convection. SPC continues with a marginal risk over those areas this evening. The upper level wave will be east of our area by 12z with decreasing clouds and some sun on the way for Saturday. Lows tonight will drop to the lower 30s northwest while the southeast will hold in the upper 40s. Though tomorrow will feature some weak northwest flow, little if any cold air advection will follow the system tonight. Thus, expect another pleasant day to round out the last few days of March. Highs tomorrow ahead of the more robust large scale trough will warm to the upper 40s far northwest to the lower 60s in the south. A sun/cloud mix is on the way for Saturday. As we approach Saturday night, low pressure will begin to gather strength over Kansas as the frontal boundary just pushed south of the state will become more focused again over northern Missouri. Models are beginning to diverge somewhat on the timing and placement of the first round of showers and scattered storms Sunday. There is now a little better consensus on a more southern track of the next storm system with the GFS deterministic more closely mirroring the Euro of the past couple of days. As anticipated, the southern stream is still dominating the preferred path of synoptic energy. With the lessening chances for precipitation for most of Saturday night, have cut back on PoPs through the period to 15 to 30%; and mainly south. Saturday night mins will remain mild with upper 20s north to the lower 40s in the south. .Long Term /Sunday through Friday/... Confidence: Medium With the models now coming into better consensus of a more southern track, the risks of any additional severe weather over our area is lessening. The main challenge now is the evolution of the system and how rapidly the low strengthens. This will make the difference between 1 to 1.5 inches of rainfall versus 2 to 3 inches of rainfall. The GFS continues to quickly amplify the H850 system prior to it tracking near Iowa, rather than the Euro which deepens the low as the low is exiting east of the Mississippi River. The 12z deterministic Euro continues to amplify the low later with the bulk of the expected qpf east of Iowa. The 12z GEFs supports some heavier totals in the southeast/eastern areas of Iowa including a portion of our southeast. That being said, the trends continue to suggest a slightly slower amplification which would keep rainfall totals roughly between 1/2 inch to 2 inches across the south while the north receives a couple of tenths to up to a half inch in some areas. The Euro deepens the system much more as it gets into northern Ohio with a decent cyclone and stronger area of low pressure. Temperatures will be cooler with the low tracking farther south. Highs Sunday are anticipated to mainly in the 50s and with higher chances for showers and some thunder Sunday night into Monday night, highs are again likely to remain in the 50s for Monday. Breezy conditions will also develop within northwest flow Monday as the deepening low departs. By Tuesday there is a hint of a northern stream trough possibly swinging around the parent upper low. Due to the differences in model spread progression east of the region, this feature may not impact Iowa at all. If it does, an area of light rain or snow would accompany the weak wave. Our blended approach keeps a chance of light precipitation east, otherwise the remainder of the forecast sees a drying trend until late week. With that temperatures will initially be rather cool in the lower to mid 50s for Tuesday and Wednesday, then transition to a moderating trend by late week. We may need to trim back expectations a bit and delay the rapid warming depicted by the NBM with todays model runs slowing the large system across the eastern CONUS. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
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Issued at 633 PM CDT Fri Mar 29 2024 VFR ceilings were widespread across central IA due to expansive mid and high cloudiness at 00z. This should persist through the evening with scattered showers and a few storms developing southeast, mainly near KOTM, during the evening. Thunder is possible there, but has been omitted for the time being until confidence in location and occurrence increases. A brief period of MVFR stratus may brush KALO Saturday morning, but otherwise confidence is fairly high for VFR conditions later in the day.
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&& .DMX WATCHES/WARNINGS/ADVISORIES...None. && $$ DISCUSSION...REV AVIATION...Small

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