Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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717 FXUS63 KFSD 020346 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1046 PM CDT Wed May 1 2024 .KEY MESSAGES... - Additional rainfall is expected tonight across the area with the highest amounts from a half an inch to an inch expected along and southeast of a line from Slayton, MN to Canton, SD to Vermillion, SD. Severe weather is not expected but minor flooding is possible. - Another chance for rain is possible Friday night into Saturday. The probability is moderate to high (50-80% chance) for rainfall amounts exceeding a tenth of an inch. - A strong low pressure system looks to bring renewed storm chances on Monday but details are uncertain as of now. && .DISCUSSION... Issued at 334 PM CDT Wed May 1 2024 High pressure dominates the area this afternoon along while cloud has expanded aloft. Outside of a few sprinkles across the area, high temperatures have warmed to the upper 50s to low 60s while winds remain light beneath the surface high. The surface high will push off to the east this evening, turning winds easterly. A mid/upper level wave will push into the Northern Plains this evening, setting the stage for another round of rain. Yesterday`s surface front resides well south of the area in Kansas. However, the front will push northwards in response to the incoming wave. The low level jet (LLJ) will strengthen which will strengthen warm air advection (WAA) across the area and kick off rain after midnight. The LLJ will also push the 850 mb boundary across northwest Iowa while also tightening the thermal gradient. This will create a solid area of frontogenesis (FGEN) which will also for a band of rain to develop. With the right entrance of an upper level jet overhead, negative equivalent potential vorticity (EPV) is possible above the frontal circulation which could allow for the band of rain to be a bit more narrow and intense. This will result in the strongest lift and bulk of the rain falling approximately between 4 am to 8 am Thursday morning. Any chance for rain will push east of the area come noon, allowing dry conditions to prevail for the rest of Thursday. Rainfall amounts between a half an inch and an inch are expected along and southeast of a line from Slayton, MN to Canton, SD to Vermillion, SD. Isolated higher amounts are possible in this area. Lower rainfall amounts from a tenth to a half an inch are expected northwest of the line. Rainfall rates do not look impressive with this system which should prevent any flash flooding from occurring. However, ponding on roadways along with minor flooding on some streams and rivers is possible. With rain finally east of the area, Thursday will be a much quieter and cooler day. High temperatures will only warm to upper 50s to 60s during the afternoon and lows down to the upper 30s to low 40s overnight. A surface ridge will be passing through the forecast area during the overnight hours. Clear skies will accompany the ridge`s passing which suggest that fog may be possible. Latest HREF probabilities only show a 20-30% chance for fog development. As such, have kept any mention of fog out of the forecast but will continue to monitor this potential. An active pattern continues aloft on Friday, brining another chance for rain. This chance for rain looks to come Friday evening and night as a strong cold front pushes through the northern and central Plains. Good news is that the daylight hours on Friday will be dry with seasonal high temperatures into the 60s. The bulk of the rain looks to be tied to the front itself, especially as this front will lie again in the right entrance region of an upper level jet. As such, negative EPV above the frontal surface is possible, thus increasing confidence in a tight band of rain passing through the area. Ensembles support this as they show a broad 50-80% chance for rainfall totals to exceed a tenth of an inch. Low temperatures will fall to the 40s overnight. The weekend will be dry as shortwave ridging takes over aloft. High temperatures will remain seasonal in the 60s and 70s with mostly sunny skies. With only marginally breezy winds expected, the weekend looks like a great time for outdoor activities! The pleasant conditions will end on Monday though as medium range guidance is very consistent in a strong upper level wave ejecting off the Rockies and into the Plains. While there is agreement in the overall synoptic setup, mesoscale details remain uncertain at this time. Have left model blended PoPs due to this uncertainty. Severe weather may also be possible but again, too much uncertainty to say for sure at this time. Rain chances will continue through the middle of next week along with near seasonal temperatures. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 1032 PM CDT Wed May 1 2024 Although ceilings are remaining at VFR levels longer than anticipated, expect MVFR/IFR conditions to advect in with showers and thunderstorms from NE through the overnight hours. Reduced visibility has been observed this evening with locally brief and heavy rainfall. This looks most likely along and east of I-29, especially over northwestern IA. Stratus with MVFR/IFR ceilings continue through the early afternoon Thursday, with widespread rainfall ending through the morning hours. However, latest guidance this evening shows the potential for isolated showers through Thursday afternoon, as well as patchy drizzle with the low cloud deck. Have not included any afternoon showers in the TAFs, as confidence in coverage is low at this time. Winds increase overnight with gusts around 20-25 knots. Evening model runs have backed off with the potential for LLWS across northwestern IA as the LLJ increases; however, have continued to include at KSUX through 02.09z as gusts have currently dropped off. Wind direction varies through this forecast period, becoming northwesterly to westerly by late Thursday morning/early Thursday afternoon. VFR conditions are currently expected to return by the end of the period. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...Meyers AVIATION...SG