textproduct: Aberdeen

KEY MESSAGES

-Red Flag Warning remains in effect through 8 PM CDT this evening for east central and far northeastern South Dakota as well as west central Minnesota due to gusty winds (up to 25-40 mph) and low relative humidity values. Fire weather concerns continue Wednesday as well.

- Record or near record warm temperatures in the upper 80s to lower 90s are expected on Wednesday.

- There is a 30-70 percent chance of showers and thunderstorms Wednesday night into Thursday, mainly throughout central and north central South Dakota.

- Strong sustained west winds 25 to 35 mph with gusts up to 50 mph are expected on Thursday. These windy conditions may last all the way through Friday into Friday night, especially along and north of U.S. Highway 212.

- After a warm start to the day Thursday, cold air will establish control of the temperature forecast from Thursday afternoon through the end of the weekend. High temperatures Friday through next Monday are expected to be near to around 5 degrees below normal; low temperatures 5 to 10 degrees below normal (below 32F).

DISCUSSION

Issued at 120 PM CDT Mon Apr 20 2026

At 1 PM CDT, skies are sunny/mostly sunny and temperatures are warming into the 60s and 70s (20 to 25 degrees warmer than this hour yesterday). Winds are south at 15 to 25 mph with gusts up to 40 mph at times. Relative humidity values are falling through the 20 to 30 percent range as well.

Northwest flow aloft is forecast to persist through Wednesday. A cold front will pass southward through the forecast area tonight, but there will not be much of a cool down expected on Tuesday given the rather limited time for low level CAA tonight into Tuesday morning. Today's really dry airmass gets shunted down into far southern South Dakota/Nebraska on Tuesday, and by peak heating/mixing on Tuesday, the I-90 corridor of this CWA could be dealing with relative humidity as low as 15 to 20 percent, although the east-southeast wind expected in that area on Tuesday is not expected to gust to 25+mph.

A strong low level jet develops Tuesday night and persists into Wednesday night in response to the strong low level WAA expected over the central/northern plains heading into Wednesday. Presently, there is no notable tongue of Gulf moisture surging up into the CWA on Wednesday. With 925hpa and 850hpa temp progs supporting upper 80s to mid 90s (which are record or near record high temps) on Wednesday, and a dry airmass advecting back into the CWA on strong (20 to 35+mph sustained/40-45 mph gusts) southerly winds, the CWA is primed for very high or higher Grassland Fire Danger indexes. Circling Wednesday as a potential Fire Weather Watch day once today's Red Flag Warning event is over.

The upper level steering flow will switch around to the west/southwest Wednesday night as a large/cold upper level low/longwave trough heads east across the nation's mid-section. Both the NAM and GFS in BUFKIT showcase more than enough mid-level moisture (at or above 2km) availability Wednesday night into Thursday morning to support thunderstorm mention (Elevated CAPE at or above 750J/kg). At times, deep layer (cloud bearing) shear appears to produce straight-line hodographs at or above 35 knots. So, there is that potential for updrafts to rotate/split. Wouldn't be surprised if some hail is produced Wednesday night into Thursday morning. Still fairly cold aloft, too, in April, when convection happens, adding to the favorability of updrafts to be able to make hail. The probability of one quarter inch or more of rainfall occurring Wednesday afternoon through Wednesday night is 20 to 35 percent and is presently centered on Sully, Hughes and Hyde Counties.

Still looks like the upper low will run up against an upper level steering flow blockade as it makes its way through Montana/the Dakotas into southern Canada. A rather blocky steering flow pattern is set for the end of the week into the weekend, which should stall this upper low's progression across NOAM. There continues to be a signal in both the deterministic GSM's and all the various ensemble model camps for rather strong westerly- component winds to develop on Thursday, at least across the northern two-thirds of the CWA, continuing through Friday night before diminishing.

Becoming anomalously cold Friday and Saturday in the wake of this large upper low, while the strong westerly-component winds are occurring. Thursday is expected to be the transition day from warm at the start of the day to getting cold at the end of the day. Beyond that, the rest of the 7-day forecast boasts of high temperatures only reaching the 50s (so long as post-system stratus/strato-cu isn't widespread over the region), with night-time temperatures falling below the freezing mark Thursday night through Sunday night.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1223 PM CDT Mon Apr 20 2026

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are forecast through the TAF period. Strong south-southwest winds 15 to 25 knots with higher gusts are beginning to diminish, first across central and north central South Dakota (KPIR/KMBG). Over the next 3 to 6 hours, a gradual draw down in wind speeds/gusts will commence at KABR and KATY as well. With a cold frontal passage forecast overnight, winds will eventually switch around to the north-northeast before re- grouping out of the east-southeast later in the day on Tuesday.

ABR WATCHES/WARNINGS/ADVISORIES

SD...Red Flag Warning until 8 PM CDT this evening for SDZ008- 019>023. MN...Red Flag Warning until 8 PM CDT this evening for MNZ039-046.