272
FXUS63 KFSD 121941
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
241 PM CDT Fri Jul 12 2024

.KEY MESSAGES...

- Wildfire smoke continues to stream overhead through the
  weekend into early next week. Surface impacts are currently
  not expected.

- Showers and thunderstorm chances are low tonight through the
  weekend. However, if a storm is able to develop, strong to
  severe storms may occur.

- Temperatures and dew points increase for the weekend. Heat
  Advisory in effect for Saturday. Moderate (40%-60%) chance of
  exceeding criteria Sunday.

- Unsettled pattern continues early next week, with periodic
  shower and storm chances. Temperatures near climatological
  averages.

&&

.DISCUSSION...
Issued at 239 PM CDT Fri Jul 12 2024

CURRENTS THROUGH TONIGHT: Additional diurnal cumulus clouds
have developed today, with hazy skies due to continued wildfire
smoke. We`ve climbed into the 80s and with dew points in the 60s
to lower 70s, heat indices are in the lower 90s for some folks.
Showers have been trying to develop but are struggling due to
the cap and lack of moisture. Winds increased through the early
afternoon with now southerly winds gusting to around 30 mph.
Gusts taper off after sunset, with southerly winds around 5-10
mph overnight. Although a couple of hi-res models hint at valley
fog developing, think winds remain just strong enough overnight
to preclude development. Lows tonight "drop" into the upper 60s
and lower 70s. Capping in place should keep us dry overnight,
but can`t entirely rule out a very isolated storm.

THIS WEEKEND: With the ridge in place over the southern US, our flow
pattern generally remains west-northwesterly through the weekend.
Not only does this allow the heat and humidity to build (more on
that in a minute), we`ll see hazy skies continue as wildfire smoke
streams eastward. The HRRR guidance brings in some periodic higher
concentrations through the weekend, but with the strong inversion
limiting mixing and low level southerly flow, impacts at the surface
are not expected.

Guidance has underdone dew points for today so with that in mind,
have continued to try to trend those values up. Combined with above
average temperatures (highs in the 90s), have issued a Heat Advisory
for the entire area for Saturday afternoon and evening with heat
index values near/above 100 degrees F. Models did come in cooler for
Sunday, but think this is due to the models struggling with
convection. Bumped up the NBM a couple of degrees closer to the
previous forecast using some of the NBM 75th; however, held off on a
headline for now to determine if the "cooler" temps are a trend in
the models or a fluke this run. Headline or now, hot and humid again
Sunday, with highs near/in the 90s. Lows through the weekend in the
upper 60s to lower 70s.

We`ll also be keeping an eye on convective chances through the
weekend with a few waves moving through (continued disagreement in
the models in timing/location). 925/850 mb temperatures both in the
20-30 degree C range leads to a stout capping inversion. Once again
this afternoon, CAMs continue to struggle with evolution and
development of convection through the weekend. Again, think that
capping will prevent most development in our area, and also cause
storms which advect into our area to struggle. However, robust
instability thanks to the heat and humidity, increasing shear, and
steep mid level lapse rates would all favor strong to severe storms
*if* a storm can develop. Ping pong ball sized hail, wind gusts to
70 mph, and locally heavy rain are the main hazards although again,
convective chances are very low.

Given the heat, humidity, and isolated storm risk, folks with
outdoor or travel plans should keep an eye on the forecast for the
latest information. Plan now for heat impacts and have a plan in
case storms develop.

MONDAY ONWARD: High pressure continues to spin over the southwestern
US through at least the middle of next week. Upper troughs and
stronger waves toward mid week bring a return to more northwesterly
flow aloft than the westerly flow we will see over the weekend. This
will likely keep periodic rain and storm chances around, but should
allow temperatures to moderate back to near climatological normals.
After Monday, highs return to the lower/mid 80s (possible as cool as
the mid 70s for some) and lows fall into the 50s and 60s.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1140 AM CDT Fri Jul 12 2024

VFR conditions prevail through the period. Southeasterly winds
gust around 20 to 25 knots this afternoon, with gusts dropping
off after sunset. Winds will be light overnight, but think
they`ll be just strong enough to preclude fog development.
Southerly winds around 10 knots expected into tomorrow
afternoon.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory from 1 PM to 8 PM CDT Saturday for SDZ038>040-
     050-052>071.
MN...Heat Advisory from 1 PM to 8 PM CDT Saturday for MNZ071-072-
     080-081-089-090-097-098.
IA...Heat Advisory from 1 PM to 8 PM CDT Saturday for IAZ001>003-
     012>014-020>022-031-032.
NE...Heat Advisory from 1 PM to 8 PM CDT Saturday for NEZ013-014.

&&

$$

DISCUSSION...SG
AVIATION...SG