Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 132328 AAA
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
628 PM CDT Wed Mar 13 2024

.KEY MESSAGES...

- Rainfall chances for tonight are 10-25% for areas mainly south of
  a line from Onida to Milbank, while weak low level cold air
  advection overnight into Thursday sets the stage for slightly cooler
  conditions.

- Gusty west to northwest winds of 25 to 35 mph on Friday and
  Saturday will lead to an elevated fire weather concern.

- Temperatures will cool down into the 30s for Sunday, which is 5 to
  10 degrees below average for this time of year.

&&

.UPDATE...
Issued at 625 PM CDT Wed Mar 13 2024

See updated aviation discussion below.

&&

.SHORT TERM /THIS EVENING THROUGH THURSDAY NIGHT/...
Issued at 145 PM CDT Wed Mar 13 2024

At 1 PM CDT, temperatures are slowly working up through the
upper 40s to upper 50s under a partly to mostly cloudy sky. There
are even a couple of low 60s dotting the map this afternoon. Wind
direction and speed is a function of inverted surface troffing over
the western CWA. East of this feature, east-southeast breezes (10-
20mph gust to 30mph) are occurring, while west of this feature,
northerly breezes are occurring (10-20mph gusts to 30mph). Aloft,
southwesterly flow remains in tact, for the moment, with a couple of
shortwaves noted in water vapor imagery making their way out onto
the central plains.

The forecast trend is for the separation of jet-streams to persist,
as the upper level longwave trof over the inter-mountain west
continues to dig south into the southwestern CONUS overnight and on
Thursday, and the weaker northern stream upper level steering flow
takes over across the northern plains. During the tonight period,
the upper level flow will go from weak southwesterly, to very little
wind aloft. Then on Thursday, the upper level flow will transition
from very light winds aloft to a light northwesterly steering flow.
While all this is happening, at the surface, the inverted surface
trof is forecast to shift south, allowing surface winds CWA-wide to
become north-northeasterly CAA winds. Cooler air will begin
advecting into the CWA tonight and persist all the way through to
late Thursday night.

As the CWA becomes the northern edge of the deformation zone
tonight, mid-high clouds will stream up as far as, basically, the
southern half of South Dakota before running out of steering wind.
This will continue to be the case on Thursday until that light
northwesterly steering flow aloft kicks in. So, overnight low
temperatures could be a little bit cooler across the northern half
of the CWA where clearer skies are expected, with somewhat warmer
readings possible under any bkn/ovc mid and high cloudiness reaching
this far north. Ensembles spread is relatively small, with low
temperatures expected to be mainly in the 30s overnight. Similarly
on Thursday, ensembles spread supports high temperatures in the 40s
and 50s (a good 10 degrees or more cooler than today`s readings).
Short-range ensemble guidance supports there being some CAA stratus
working down from North Dakota on Thursday, possibly persisting into
Thursday night. A lot depends on those low clouds Thursday night, as
to whether or not low temperatures drop as low as the low to mid 20s
or stay up (under cloud cover) closer to 30 degrees.

The only place in the short term that (ensemble) PoPs are showing up
is tonight (10 to 25% chance), and that is generally south of a line
from Onida to Milbank, and is tied to that deformation zone that
develops overnight. PoPs have been on the decrease over this CWA
over the past couple of days for tonight/Thursday, as this
split/separation in the flow pattern has been becoming more clear-
cut in the guidance. Any remaining PoPs are likely tied to the
previously mentioned deformation zone that forms overnight, which
continues to slowly show up in the guidance forming further south
and taking PoPs with it. Otherwise, stable/dry surface high pressure
is progged to build into the CWA from late tonight through Thursday
night.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 145 PM CDT Wed Mar 13 2024

The long term begins on Friday with a storm system passing north and
east of the region with warm temperatures invading the CWA. The NBM
shows a 40 to 85% chance of wind gusts exceeding 25 mph, mainly
along and north of Highway 12, and the favored higher terrain area
of the Prairie Coteau. The winds, along with dry conditions will
cause elevated fire weather concerns, especially in north central SD
where RH values drop below 30 percent. Higher winds are expected on
Saturday with the NBM showing a 20 to 60 percent change of gusts
exceeding 35 mph. While highs on Saturday will be cooler behind a
cold front, the atmosphere remain dry with afternoon RH values
dropping below 40 percent for most of the CWA. Thus, Saturday will
be another elevated fire weather day.

Colder air will invade the area on Sunday with 925 mb temps dropping
to the single digit below zero C. High temperatures may only warm
into the 30s and low 40s, or 5 to 10 degrees below average. With
steep low level lapse rates, isolated to scattered snow showers
still appear possible Sunday afternoon, mainly over the eastern half
of the CWA. Warmer air may move back into the area as soon as
Tuesday. However, model spread is rather large with some guidance
showing temps in the low 30s, while others show mid to upper 50s.
The mean suggest highs will range from the upper 30s, in western MN,
to the mid 50s, west of the Missouri River valley. The ensemble
spread remain large Tuesday and Wednesday, with mean temperatures
warming through midweek.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 625 PM CDT Wed Mar 13 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions will prevail across the area tonight. Look for MVFR
cigs to reach north central South Dakota early Thursday morning,
then gradually spread to the south and east across the area during
the daytime hours. Far northeastern South Dakota and west central
Minnesota will likely not see these lower cigs before the end of
the TAF period.

&&

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

$$

SHORT TERM...Dorn
LONG TERM...SD
AVIATION...Parkin


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