Area Forecast Discussion
Issued by NWS Aberdeen, SD
Issued by NWS Aberdeen, SD
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795 FXUS63 KABR 190821 AFDABR Area Forecast Discussion National Weather Service Aberdeen SD 321 AM CDT Sun May 19 2024 .KEY MESSAGES... - Rain showers and a few thunderstorms (20-45%) will continue over the area this morning, moving east/northeast. A second wave of showers and thunderstorms are forecasted to form over north central to south central SD late this afternoon through this evening (30-65%). - There is a slight risk (2/5) for some of these storms to become strong to severe storms this evening from north central to south central SD. Main threats include up to quarter size hail and wind gusts between 60-70mph. A marginal risk (1/5) extends eastward into northeastern SD. - An active pattern continues next week with additional rounds of showers and thunderstorms for Tuesday-Friday. Near to slightly below normal temperatures are expected Tuesday-Friday as well. && .SHORT TERM /TODAY THROUGH MONDAY AFTERNOON/... Issued at 319 AM CDT Sun May 19 2024 As of 3AM, scattered rain showers and isolated thunderstorms (15- 25%) continue to push northeast over the CWA. Short term models agree on a surface trough positioned over the western parts of SD early this morning as the main trough deepens over the Pacific Northwest into the Northern Rockies. On the PVA side of this trough, shortwave energy will be pushing northeast over the area with a LLJ forming over south central SD (30-40kts) and pushing northeastward into the afternoon (30-35kts). CAMs indicates showers/few storms becoming more widely scattered, east of the Mo River, late morning through midday (20-45%). Precip is forecasted to move out of the eastern CWA by late this afternoon/evening. Our attention then turns to later on in the day as we expect a second round of thunderstorms. An embedded negative tilted shortwave moves over the Northern Plains, with southwesterly winds increasing. At 850mb to the surface through the day, a low pressure system will form over western SD as low level winds remain out of the south ahead of it. The warm front lifts north through 18Z, leaving the CWA in the warm sector and on the northern edge of a dryline. By this evening, the center of the low is forecasted to be over northern SD with much of the low level moisture from north central to south central SD between the fronts. Through the overnight, the low will track east/southeast with the cold front trailing and forecasted to be out of the CWA by Monday morning. RAP indicates a cap setting up over central and western SD through the morning into the midday and over northeastern SD by the evening. This cap looks to erode from north central to south central SD late this afternoon as HREF indicates a narrow area of CAPE increasing to 1000-2000 j/kg in this area. Mid level lapse rates will increase to 7-8C over the CWA and bulk shear between 40-50kts out of the west then southwest. CAPE does weaken with sunset with a cap setting back in over central SD and continuing over northeastern SD. With dp`s rising into the 50s, instability, and lift, it`s all there for convective inhibition (assuming the cap breaks). HREF 4hr max 2- 5 UH>75m2s2, indicates organized convection, as cells start firing up over north central to south central SD between 22Z-00Z and spreading eastward. UH>150m2s2 indicates a few discrete cells could form in this area of higher instability, where shear is perpendicular to the front. CAMS show cells merging and becoming more of a messy linear system (as bulk shear becomes more parallel) ahead of the cold front, pushing east across the CWA. HRRR, HIRES ARW/FVE, and NSSL-WRF show this transition where NAM NEST and Rap show more of a messy scattered threat and no linear transition. So confidence remains lower on the exact outcome and far south the line could get. Depending on the LLJ, storms may stay strong as they march east into MN, otherwise less instability will be over the area giving way to just general showers/storms as it pushes into MN. The SPC has upgraded to a slight risk (2/5) from parts of north central to south central SD with a marginal risk (1/5) spreading eastward over much of the CWA. Main threats is up to quarter sized hail and wind gusts (60-70mph). Behind the system, the CWA looks to remain dry most of the morning but that will be short lived as a surface trough forms overhead and a low pressure system to the south. With shortwave energy aloft, we could see lift for more rain/storms. Latest NBM has a 15-30%, highest west of the Mo River Monday afternoon. && .LONG TERM /MONDAY EVENING THROUGH SATURDAY/... Issued at 319 AM CDT Sun May 19 2024 No break from the active pattern. The first system in the extended is a subtle southwest flow shortwave coming in from the southwest of the state Monday night. Just some mid level moisture/ascent with this one, with stable north/northeast low level flow out of weak high pressure to the north. Really not much to write home about, but it does precede a stronger system that will definitely overshadow any moisture that falls Monday night. By Tuesday morning this Colorado Low will deepen around Sioux City before tracking northeast to Minneapolis. 990mb is a little out of place for May, as the surface pressure falls to 2 standard deviations below climo. Thankfully no Arctic airmass gets pulled into the region so the primary p-type is rain, with the bulk of that in the eastern CWA associated with a deformation zone/wrap around. Forecast QPF ranges from essentially nothing for north central South Dakota, to +2" potential for eastern SD/western MN. Our numbers are a little shy of the NBM 48-hour 75th percentile. The GFS shows just a slightly farther east bullseye for QPF and GEFS plumes run lower for the most part though a few members do have as much QPF as the official forecast. The point is that there is still some wiggle room, in addition to what will be a sharp contrast with the western gradient in moisture over the CWA. Not only will it be wet, it will also be cool and windy on the back side of the system with 850mb temperatures down to as low as +3 to +6C. The gradient and low cloud potential should keep temperatures from bottoming out Wednesday morning, with lows in the low/mid 40s. Then we have a system for Thursday/Friday timeframe. Deterministic models still have a hard time with timing/intensity of the system which is associated with shortwave that takes a more typical late spring trajectory across the northern Rockies. Clusters are pretty spread out on this one, so will continue to advertise low confidence on what this system will bring. As we have brought up across several discussions, this overall pattern will continue to keep us below normal with respect to temperatures throughout the extended. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1223 AM CDT Sun May 19 2024 Terminals KABR,KATY,KPIR,KMBG VFR conditions prevail for the TAF period at KPIR/KMBG with MVFR cigs moving in for KABR/KATY between ~04 to ~10Z Monday. Winds will turn south/southeasterly through the day and shift out of the northwest across KMBG/KPIR towards the end of the TAF period, behind a cold front. Gusts of 20-30kts possible this afternoon and evening. A few showers and thunderstorms possible early this morning with another round of storms forming from north central to south central SD this afternoon and evening, pushing eastward. && .ABR WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. && $$ SHORT TERM...MMM LONG TERM...Connelly AVIATION...MMM