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FXUS63 KFSD 080837 AFDFSD

Area Forecast Discussion National Weather Service Sioux Falls SD 337 AM CDT Wed May 8 2024

KEY MESSAGES

- Showers and isolated storms expected today. Some storms could be strong to severe and bring another round of meaningful and locally heavy rainfall. Confidence is low in severe weather threat as well as location of heaviest rainfall.

- Warmer and mainly dry conditions move in for the weekend.
Continued warm with renewed rain chances by mid week.

DISCUSSION
Issued at 334 AM CDT Wed May 8 2024

CURRENTS: Pleasant conditions this morning with calm to light winds and some clouds across the Hwy 20 corridor and south central SD. A few weak echoes are visible on radar in these areas as well, but dry low levels is precluding any measurable precip. Temperatures through 08z/3 AM CDT are in the 40s to mid 50s, and expect widespread 40s by daybreak. Surface low is located over north central NE, with upper low across northwestern SD/southeastern MT.

TODAY AND TONIGHT: Some uncertainty today in the forecast, as models disagree on where exactly the stacked low pressure meanders and where the associated fronts are. This will impact everything from rain chances to winds to severe weather potential through today.
Guidance shows the surface low by 18z/1 PM CDT anywhere from northeastern NE to over Sioux Falls to over IA/MN border. By this time, the mid and upper low are located in central and southwestern SD, respectively, with roughly the same amount of variability as the surface low. All this to say the subtle differences are leading to lower than average confidence in precipitation forecast today.

Overall, trends in the hi-res and other guidance show showers developing by late morning into the early afternoon hours, generally isolated at first becoming more widespread through the later afternoon and early evening hours. Although risk is low, we could see a few strong to severe storms. Instability increases fairly quickly this morning into the early afternoon to around 1000 to as high as 1500 J/kg. Steep mid level lapse rates over 7 deg C/km with this instability and increasing bulk shear would support some large hail of quarter to half dollar sized. Think that damaging wind gusts to 60 mph are less of a concern with DCAPE at or less than 500 J/kg, but can't entirely be ruled out. As we sit under the upper low, funnels and/or landspouts are also possible. Landspout/non-supercell tornado threat is additionally supported by 0-3 km MUCAPE and 0-1 km MLCAPE both over 500 J/kg and steep low level lapse rates (over 8 deg C/km). This threat will also be variable in location depending on where the warm front ends up, which would provide another focus. Folks should stay weather aware today and this evening.

Regarding heavy rain potential, with the variance in model solutions, it is difficult to say exactly where the highest QPF will be realized and how much. Taking a look at the 08.00z deterministic guidance, the axis of heaviest precip ranges from the Hwy 14 corridor to north central IA. Ensemble guidance (outside of the HRRR and GFS) shows a less than 10% chance of any portion of our area seeing over 0.50" of rain. However, the GFS ensemble paints a 50% chance over the MN/IA border stretching east. The HRRR is the most bullish - with most locations across southwestern MN and northwestern IA having a 60-90+% chance of over half an inch of rain. Think that some folks will see 0.50-0.75" through Thursday, with locally higher amounts possible in thunderstorms. This could lead to localized ponding and some small rises on local creeks/streams if the heavier precip falls in our more saturated areas.

Otherwise, highs today in the 60s to lower 70s with increasing clouds. Winds will be variable as the low moves across the area, with sustained winds 5-15 mph and gusts to 20-25 mph. Showers and isolated storms continue to slowly sink south during the overnight hours. Lows fall into the 40s.

TOMORROW THROUGH THE WEEKEND: Our persistent stacked low pressure system is shoved out of the way Thursday as another wave drops south, keeping scattered shower/isolated storm chances in play.
We'll see drier weather for Thursday night into Friday. We'll remain in northwesterly flow with another wave or two skirting by to the east over the weekend which could bring the return of low end shower and storm chances. Still some variability in the timing/location of the wave(s), so have left the NBM for now. Periodically breezy winds expected. A warming trend is also expected, with highs warming into the 70s by the weekend and lows in the 40s and 50s. Some 80 degree highs are possible by Sunday.

EARLY TO MID NEXT WEEK: More zonal flow is progged to move over the Plains by early next week, with models varying widely on the tracks of waves/troughs. Generally expect near to above average temperatures to continue. Rain and storm chances also return, greatest currently expected in the middle of the week with a more robust trough.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
Issued at 950 PM CDT Tue May 7 2024

VFR conditions are forecast to largely prevail this TAF cycle.
Should see light and variable winds persist throughout the overnight period, with direction still varying a bit after daybreak as an upper level low moves overhead. Sustained speeds looks to remain between 10 to 15 MPH. Otherwise, a few showers and storms may be possible during the afternoon/evening, which may result in brief periods of reduced cigs/vsbys.

FSD WATCHES/WARNINGS/ADVISORIES
SD...None.
MN...None.
IA...None.
NE...None.

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