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Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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734 FXUS63 KFSD 071110 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 610 AM CDT Sun Jul 7 2024 .KEY MESSAGES... - Patchy fog again developing early this morning. Widespread dense fog is not expected, but areas of visibility below a mile are possible. - Unsettled weather continues through the first half of this week with spotty afternoon to early evening showers/storms Sunday through Wednesday. Severe weather is not expected. - Cooler than normal temperatures for early July through the early part of next week, but trending warmer and more humid by the end of the week. && .DISCUSSION... Issued at 355 AM CDT Sun Jul 7 2024 TODAY-WEDNESDAY: The first half of this week will be dominated by a slow moving northern stream trough in the mid-upper levels. The main trough axis resides from northern Minnesota through eastern South Dakota into Nebraska today and slides further east into the Upper Mississippi Valley on Monday. With the trough overhead today, expect to see scattered showers/thunderstorms expand in coverage through the mid-late afternoon and early evening, diminishing again after sunset. Lack of deep layer shear and weak mid level lapse rates should keep storms non-severe, with lightning and perhaps brief heavy rain the main threats. While the above transition with the northern stream upper trough is occurring, tropical cyclone Beryl will be making landfall on the Texas coast, and the track of its remnants over the following couple of days may have some impact on our weather through midweek. Modest consensus in latest deterministic models, and even in the broader ensemble view, takes the remnants of Beryl northeast toward the mid-Mississippi Valley, potentially connecting with the northern stream trough as it slides a bit further east into the Great Lakes. This ultimately slows the eastward progression of the trough, which keeps portions of our forecast area under weak cyclonic flow through Wednesday. Not seeing a significant impact on temperatures, with daily highs holding in the upper 70s-mid 80s through Wednesday. However, the cyclonic flow provides additional weak lift in support of low chances for diurnal/afternoon showers and thunderstorms, mainly near and east of the US Highway 81 corridor. NBM seems a little low on its coverage of low pops based on the more recent models, so have bumped up and/or expanded coverage of 20-30 pops for the afternoon hours Monday through Wednesday. Similar to today, shear remains quite weak through this period, so severe storms are not expected. THURSDAY-SATURDAY: As we progress through the latter part of next week, the upper ridge makes a stronger push eastward. While this should favor dry weather with regards to precipitation, it will also allow summertime heat and humidity to return to the region. We see temperatures trending upward through this late week period, with low (20-30%) probabilities of temperatures topping 90F in our far west by Friday, with moderate-high (50-80%) probabilities pushing into the James River Valley on Saturday. Along with the increasing heat, a transition to southerly low level flow will draw higher dew points northward. Ensembles indicate moderate (~50%) probabilities for dew points topping 70F Friday, and moderate-high (60-80%) probabilities of the same by late Saturday. Those with heat sensitivities will want to monitor trends for this late week-next weekend period and be prepared to take precautions to avoid heat illness. && .AVIATION /12Z TAFS THROUGH 12Z MONDAY/... Issued at 610 AM CDT Sun Jul 7 2024 Areas of fog reducing visibility to less than a mile in some locations north of I-90 at sunrise (though not impacting TAF sites). This should dissipate by 13Z-14Z. Scattered showers and thunderstorms are expected to develop this afternoon (07/19Z-21Z), diminishing by sunset or shortly thereafter (08/01Z-03Z). Light winds will prevail through the period, variable during the overnight/early morning, favoring west to northwest at or below 12kt during the late morning and afternoon. Storms may bring some stronger gusts and brief MVFR visibility. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...JH AVIATION...JH