605
FXUS63 KABR 021940
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
240 PM CDT Wed Jul 2 2025

.KEY MESSAGES...

- Heat and humidity continues through Friday, with highs of 90 to
around 100 on Thursday and upper 80s to mid 90s on Friday. Dewpoints
will range in the 60s to low 70s. Heat indices may top 100 degrees
in a few spots Thursday.

- A system late Friday/early Saturday will bring relief from the
heat and humidity in the form of showers and thunderstorms with the
highest chances (60 to 80%) along and east of the James River
Valley. The main concern is the potential for heavy rainfall.

&&

.DISCUSSION...
Issued at 236 PM CDT Wed Jul 2 2025

Main concerns in the forecast will be the ongoing heat and humidity
through Friday and the potential for heavy rain over the eastern
half of SD into MN Friday evening into Saturday morning. As the
ridge moves in overhead Thursday, 850mb winds will be out of the
south, allowing for warm and moist air to surge northward. 850mb
temps by peak heating will range from ~22 to 29C, which is about 2
standard deviations above normal per NAEFs. This warm air along with
surface winds out of the south/southeast leads to high confidence on
hot temps as NBM has finally caught up and increased the overall
temps by a couple of degrees with NBM 25-75th spread about 3-5
degrees. Deterministic NBM has highs overall in the 90s to 101 with
the upper 90s to lower 100s west of the James River, highest over
central SD. Surface dewpoints will range in the 60s to around 70.
Heat indices could reach around 100 over portions of central SD and
James River Valley, however, in collaboration with the neighboring
offices this is not widespread enough for any heat headlines as of
now so we held off. EC EFI has values of 0.6 to 0.9 and a shift of
tails of zero along and east of the Mo to James River for MaxT.

The ridge will continue its path eastward Friday with unidirectional
southwesterly/southerly flow aloft to the surface. 850mb temps won`t
be as warm but still range from 21 to 23C, which is only about 1
standard deviation above climo. Surface temps are forecasted in the
upper 80s to the mid 90s, warmest over south central SD. NBM 25-75th
spread is about 4-5 degree west of the James River Valley. We really
see an increase in moisture, especially over the eastern CWA with 16
to 17C dewpoints at 850mb. Surface dewpoints are expected to rise in
the upper 60s to lower 70s east of the Mo river and highest over
James River Valley and eastward where we have the surge of moisture
northward aloft.

Ensembles overall agree on the center of the Canadian low over
Saskatchewan/Manitoba border by 12Z Thursday (and trailing
shortwave) with its lee trough extending southward. This low will
continue its path northeast and deepen along the way. A secondary
lee low will form over ND/SD/MT border by Thursday evening. This
looks to bring a 15-20% chance of storms over the western half of
Corson County (with this area clipped by a marginal risk of severe
per SPC). This lee low will then shift northeast and over north
central ND early Friday morning with another low forming over
northern SD by Friday evening and tracking over SD/ND/MN border
early Saturday. During this time, the surface trough continues its
eastward track across the Northern Plains and becoming positive
tilted. Finally, a cold front will move northwest to southeast over
the CWA through Saturday. With this synoptic setup/ongoing moisture
and daytime heating and instability, the cap should be able to break
easily (700mb temps is only 10 to 11C). Pops of 30-45% over the CWA
during the day Friday will increase, with the bulk of the precip
Friday evening through Saturday morning, with pops of 60-80% along
and east of the James River Valley. There is the potential for heavy
rain during this time as NAEFs mean specific humidity from 850mb-
925mb is about 2-3 standard deviations above climo and PWAT around 2-
2.5 above standard deviation with values of 1.75" in this enhanced
moisture area from the James River Valley and eastward. Adding in
weak winds aloft this could lead to slow moving storms/showers,
leading to the potential for flooding or for any areas that receives
training of showers and storms. ERO still highlights a slight risk
east of a line from McPherson to Hyde Counties. EC EFI for QPF
ranges from 0.5 to 0.7 east of the Coteau into MN, with a shift of
tails of zero over far northeastern SD into west central MN. Even
though we have the moisture and instability, the wind shear will be
20kts or less making mid level lapse rates weak only around 6C or
so. So severe threat looks to be more isolated if we even get that.

For the rest of the forecast period, a "wavy" trough over the West
Coast continues which results in an ongoing active pattern. Clusters
agree well on a ridge building over the western CONUS and large mid
level high underneath it for the middle to end of next week with
northwest flow over the Northern Plains.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1227 PM CDT Wed Jul 2 2025

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are forecasted through the TAF period with overall
dry weather. Winds will be on the increase Thursday with gusts of
20-30kts by the late morning/midday.


&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&

$$

DISCUSSION...MMM
AVIATION...MMM