textproduct: Aberdeen

KEY MESSAGES

- The Northern Plains will see an active pattern, and chances for showers and thunderstorms are in place through the weekend and into the start of next week.

- Through Sunday evening, chances of 0.25" of rain or more is 70-90% west of the James River. Chances of 0.5" of rain or more is 50-85%, highest along and west of the Missouri River. Amounts may be higher with any stronger storms.

- There is a Marginal Risk (Level 1 of 5) for severe weather Saturday evening into Saturday night across central and parts of north central South Dakota. Jones County, as well as parts of Lyman and Stanley Counties reach a Slight Risk (Level 2 of 5). Damaging wind gusts of 60-70 mph and hail of 1" in diameter are the main threats. A tornado or two can not ruled out in the slight risk area.

- There is a Marginal Risk (Level 1 of 5) for severe weather Sunday, mainly along and west of the James River Valley. Damaging wind gusts of 60 mph and hail of 1" in diameter are the main threats.

DISCUSSION

Issued at 225 PM CDT Fri May 29 2026

Omega block pattern continues with a highly amplified ridge now over east-central CONUS (return flow) with an upper level low over Canada/New England and upper trough over the western CONUS by 00Z Saturday. WAA at 850mb to surface will continue to be breezy out of the southwest with ongoing open access to the Gulf as dewpoints are ranging in the mid 50s to the mid 60s. This is shown well by RAP 1000-500mb RH as RH by this evening ranges between 80-90+% and will continue through the weekend. At the surface, high pressure system is off to our east over Indiana with a north to south oriented lee trough/stationary front setting up to our west. With return flow/moisture along with weak pulses of upper level energy here and there tracking northward over the CWA from the gulf, CAMs continue to show scattered rains showers here and there mainly along and east of the Missouri River. Daytime heating may allow for weak thunderstorms to occur with the possibility of pea size hail, however, mid level lapse rates are rather weak, CAPE 500j/kg and under, and no bulk shear. Through the overnight into Saturday morning, the center the trough becomes a closed low where it will track more northeast and over UT/CO/WY which will bring the chance of thunderstorms over central to western SD (as CAMs indicate this) while scattered rain showers continue east of here with better moisture advection over the area and higher PWAT's. Latest NBM indicates pops of 50 to 75% west of I29 between 00-12Z Saturday.

Saturday morning through Saturday afternoon, return flow continues at 500mb along with southeasterly flow/moisture at 850mb to surface as dps are forecast to be in the mid 50s to lower 60s. 850mb to surface, an elongated area of low pressure will extend from MT through CO with one low spinning over MT/WY and one over CO by Saturday afternoon with a northwest to southeast converging line/frontal boundary from western SD through western KS with a dryline west of here. This setup will bring ongoing scattered showers and thunderstorms moving in from the south/southeast here and there across the CWA. Storms during this time should stay below severe limits through the early afternoon as CAPE will be under 1000 j/kg through the early afternoon, and lack of shear and lapse rates.

By 00Z Sunday, the upper closed low will be over WY with an embedded negative tilted shortwave over eastern CO and western KS/NE where it will track northeast and over the western half of Dakotas by early Sunday morning. At the surface, this weakening low over MT and its occluded front will be over southwestern SD through NE as another area of low pressure will develop over KS/NE border and shift a bit eastward by 12Z Sunday. So with this setup, NamNest, HiRes Cams, and HRRR all indicate discrete cells turning into a north to south line (or broken line) of storms, east/northeast of a dryline, over western SD through western NE Saturday evening. It will then track east and over our western CWA (central SD) between ~03-06Z where it will continue to track east/northeast across the CWA. If a cold pool develops, this outflow part of the storm will track southeast.

HRRR/HiRes FV3/NSSL WRF indicate the possibility of a bowing line, however, the apex of the bow placement differs. For example, FV3 shows the bow more south of the CWA with HRRR more northward across south central SD pushing eastward, and HiRES ARW further north. So still uncertain on exact path for now. HREF 700-500mb lapse rates will increase to 6-7C/km, highest over south central SD late Saturday afternoon with SFC/MU CAPE increasing between 1000-2000j/kg over central SD with the highest over far south central SD through about 06Z as bulk shear increases to around 30-40kts by this time along and west of the Mo River. 0-3 and 0-1 SRH is forecast to range between 100-200m2s2 over central SD after 00Z Sunday. Due to this setup SPC continues with a marginal risk (level 1/5) along and west of a line from Mcintosh to Miller with a slight risk (level 2/5) over the southern portions of Stanley, Jones, and western Lyman (which is on the northern axis of better instability) Saturday evening/overnight. The main threat will be large hail (size of quarters), wind gusts of 60-70 mph (could be higher if a bow echo forms) and the threat for a tornado or two (in the slight risk area).

By Sunday, winds aloft will be out of the south/southwest with the 850mb low over MT and tracking over MT/southern Canada by Sunday evening with winds out of the southwest to southeast. Northwest to southeast convergence over the western CWA along with ongoing low level moisture, and some instability, isolated severe storms are possible with hail up to quarters and wind gusts of 60 mph as the spc has highlighted a marginal risk (level 1/5) along and south and west of a line from Eureka to Watertown Sunday afternoon and evening.

Mean QPF amounts 00Z Saturday to 12Z Monday ranges from 0.3 to 0.7" west of the James River and highest along and west of the MO. 75th percentile would be around 0.8 to 1.0". However, any stronger storms will produce localized brief heavy downpours, increasing overall QPF for any one location. With this upper low/trough pretty much hanging out over the Northern Rockies, we will continue with chances of precip off and on pretty much through most of next week. Temps will be cooler for the weekend in the 70s and 80s through Monday, and ranging in the 80s Tuesday through the end of next week.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

Issued at 1211 PM CDT Fri May 29 2026

Terminals KABR,KATY,KPIR,KMBG

VFR cigs are forecast to continue at KABR/KATY before dropping to MVFR cigs by the late morning/midday hours on Saturday. KPIR/KMBG will consist of VFR/MVFR cigs with PIR dropping to IFR by ~09Z or so Saturday. With ongoing south/southeasterly winds at the surface to 850mb, this has allowed for low level moisture to increase with this uptick in moisture continuing through the TAF period. This results in scattered showers that will continue to move in from the south and southeast through the rest of the TAF period with the possibility of a thunderstorm or two late this afternoon/evening and again Saturday afternoon. Surface winds will increase late tonight/overnight with gusts of 25-30kts

ABR WATCHES/WARNINGS/ADVISORIES

SD...None. MN...None.