Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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179 FXUS63 KFSD 091907 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 207 PM CDT Sun Jun 9 2024 .KEY MESSAGES... - Periodic chances for showers and storms return Monday night and continue off and on through much of the week. - Uncertain severe weather risks focused mainly on Wednesday afternoon and evening. - Temperatures rise above normal by the middle of the week. High probabilities (>80%) of highs above 80 degrees Wednesday and Thursday, with low-moderate (30-60%) probabilities of highs at or above 90 degrees for areas near/west of the James River Valley on Wednesday. && .DISCUSSION... Issued at 205 PM CDT Sun Jun 9 2024 TONIGHT-MONDAY: Surface high pressure sitting across our western forecast area early this afternoon. Decent mixing east of the ridge axis is allowing for moderate wind gusts, generally 15-25 mph though slightly higher in our far east. As the ridge axis slides east this evening and tonight, expect gusts to diminish quickly with loss of heating as we approach sunset, followed by light & variable winds through the overnight. The ridge axis shifts east of the forecast area on Monday, allowing for some increase in south-southeast winds, strongest along and west of the James River Valley where afternoon gusts 25-30 mph are expected. A bit of mid-high level moisture may produce high-based (near-above 10kft AGL) clouds at times but precipitation is not expected. High temperatures look to be similar or slightly warmer than today, from mid 70s to lower 80s most areas. MONDAY NIGHT-TUESDAY: Mid-upper level trough and an associated cold front will move east across the forecast area through this period. Strong-severe storms are expected to develop across the High Plains of western South Dakota mid-late afternoon Monday, with increasing storm chances sliding east into central South Dakota through the evening. As storms approach our western counties, most likely after 11/00Z, they will be encountering more stable air which is still trying to recover from the departing surface ridge, and will be stabilizing further with loss of daytime heating. If the storms in western SD can develop strong enough cold pools to accelerate the storms eastward into south central SD more quickly (as seen in 12Z HRRR), could not rule out an isolated stronger wind gust. But given the lack of instability/shear expected across our forecast area, think the risk of severe weather is low. Greater consensus among the CAMs is for showers/storms to decrease in coverage as they encounter the more stable air across southeast SD after sunset Monday evening, with scattered showers and a few non- severe thunderstorms continuing east into southwest MN/northwest IA through Tuesday morning before exiting off to the east by midday. Tuesday should be a slightly warmer day than Monday, though in our eastern areas this may depend on how quickly the lingering showers and/or clouds move out. NBM highs for Tuesday may be a touch on the warm side given low (10-30%) probabilities for temperatures topping 80F across the northeast half of the forecast area. However, given uncertainty mentioned above, did not alter NBM highs significantly at this point. WEDNESDAY-THURSDAY: This looks to be the warmest period of this forecast, especially Wednesday as a strong thermal ridge builds north ahead of an approaching cold front. Ensembles are showing better than an 80% chance of temperatures topping 80F across most of the forecast area Wednesday afternoon. Low-moderate (30-60%) probabilities for highs topping 90F are confined to our western areas, along/west of the James River Valley, which is supported by high (>80%) probabilities for 850mb temperatures exceeding 20C in this area. Similar high probabilities of 80+F persist across at least southern parts of the forecast area for Thursday, though seeing more variance among the different ensembles, leading to somewhat lower confidence. This building of warmer air northward coincides with low level moisture advection as well, with the broad ensemble showing moderate (50-70%) probabilities for surface dew points rising above 65F by late Wednesday (though only low 10-30% probabilities of exceeding 70F). The heat and humidity support moderate MLCAPE values of 1500- 2000J/kg seen in the deterministic models, which are consistent in showing deep layer shear of 40+kt across the forecast area as well, though the broader ensemble indicates low (10-30%) joint probabilities of SBCAPE>1000J/kg and shear>40kt coincident with each other. Timing of the mid-upper level shortwave may also throw some uncertainty into the mix, as some deterministic models show the wave moving through earlier in the day where it would not be able to take advantage of peak heating. Thus still some uncertainty in severe weather chances for Wednesday-Wednesday night, but will be a period to monitor as we progress through the next few days. As many or more questions regarding potential for Thursday, as models vary in how far south the low level boundary will progress in the wake of Wednesday`s activity. Shear remains moderate-strong with mid-upper level jet across the northern Plains, but instability is highly uncertain. FRIDAY-SUNDAY: Low confidence in details for the outer periods of the forecast, though trends seem to support seasonable temperatures settling back into the region. Modest consensus showing a trough sliding northeast across the region this weekend, perhaps favoring Saturday-Saturday night for increased precipitation chances. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1227 PM CDT Sun Jun 9 2024 Moderately gusty north-northwest winds prevail along and east of the I-29 corridor this afternoon, with gusts ranging 15-18kt along I-29, to 20-25kt near and east of KMML-KOTG-KSLB line. These gusts should quickly diminish as sunset approaches, with light/variable winds anticipated overnight into Monday morning. VFR conditions will continue through the period. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...JH AVIATION...JH