448
FXUS63 KFSD 221056
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
556 AM CDT Sun Sep 22 2024

.KEY MESSAGES...

- Temperatures trend downward to below normal levels for today
  and Monday.

- Temperatures trend back to normal to above normal levels for
  next week, with limited chances for precipitation through the
  period.

&&

.DISCUSSION...
Issued at 348 AM CDT Sun Sep 22 2024

Surface high pressure continues to settle into the region very early
this morning. In a cold air advection regime, temperatures have
already falling into the 40s over east central SD through the
northern James River Valley, with 50s elsewhere across the area.
Rainfall has remained south of our CWA overnight, with current radar
indicating showers located through east central NE into southern IA.
This activity is expected to remain to our south, thus a dry
forecast is on tap for area today. The aforementioned surface ridge
axis will slide directly over our area through the day, and with a
decreasing surface pressure gradient winds will trend downward into
the afternoon. With 850 mb temperatures running 8-10 degrees C
over our area, it will be a cooler day with highs in the upper
60s to around 70.

The surface high drifts into the Mississippi Valley tonight, with
light winds transitioning to southeasterly overnight on the back
side of the high. While there is no strong model guidance indicating
fog tonight, with the nearly calm in winds in a southeasterly flow,
cannot completely rule out patchy shallow fog in some of the lower
lying areas - though confidence is low for this scenario. With the
light winds and skies becoming mostly clear overnight, conditions
will be optimal for radiational cooling. In response, we are looking
for lows in the lower to mid 40s - perhaps into the upper 30s
through east central SD where ensembles show a 60% probability of
temperatures less than 40 degrees.

The southerly flow increases on Monday as the surface high finally
moves into the Great Lakes/eastern Canada region as a surface trough
approaches from our west. With warm air advection, highs will climb
a bit - into the lower to mid 70s.

A weak cold front tracks across the region on Monday night into
early Tuesday. Not much in the way of sensible weather with this
system (other than turning winds around from the northwest). The
deterministic ECMWF wants to produce some precipitation with this
feature on Tuesday, though this is not supported by any other model.
In addition, the ECMWF ensembles indicate a 10% or less chance of
receiving a tenth of an inch of precipitation in or area - so will
remain with a dry forecast for now. Highs on Tuesday will once again
be in the lower to mid 70s.

For the remainder of next week into the weekend, models indicate
rising upper level heights over our area for mid to late week. This
will keep temperatures above normal with deterministic and ensemble
guidance favoring highs in the mid to upper 70s through the period.
Mainly dry conditions are expected through at least the end of the
week, then some uncertainty creeps in by later on Friday and
Saturday with models differing in the evolution of a cut off low
over the Mississippi Valley. Related to this, the ECMWF solution
would bring a chance of rain to our area by Saturday of next week -
though this is not supported by other models.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 555 AM CDT Sun Sep 22 2024

VFR conditions expected through the TAF period.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.

&&

$$

DISCUSSION...JM
AVIATION...JM