Area Forecast Discussion
Issued by NWS Sioux Falls, SD

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

527
FXUS63 KFSD 241102
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
602 AM CDT Mon Apr 24 2017

.SHORT TERM...(Today and Tonight)
Issued at 351 AM CDT Mon Apr 24 2017

The last mild day for the foreseeable future is on tap for today,
ahead of a cold front which is slated to push across our western
forecast area this afternoon.

Boundary is located west and just north of the CWA at 08Z, with a
weak low evident between KICR/KPIR/K9V9, a stationary/warm front
arcing eastward near Hwy 212, and the cold front southwest into the
Nebraska Panhandle. Mid-upper level wave currently swinging through
western Nebraska will begin to kick the southern end of the front
eastward today, but slowly. Models showing pretty good agreement in
bringing the front into our far western counties by 18Z, then only
progressing to just east of the James River Valley, roughly near a
De Smet-Yankton line by 00Z. Eastward progress continues tonight,
with boundary reaching the Hwy 60 corridor by 06Z, and nearing Storm
Lake by daybreak Tuesday.

Stout southerly flow ahead of the boundary has already maintained
overnight temperatures in the upper 40s-50s for most of the area.
With 925mb temperatures reaching levels at or above those seen on
Sunday, expect another day of above normal highs in upper 60s-lower
70s for those areas still ahead of the front by mid-late afternoon,
despite extensive mid-high level cloud cover. Should also see good
post-frontal mixing in the far western counties, but decent cold
advection will limit highs there to lower 60s, or not too far above
current readings in some areas.

As far as rain chances, limited moisture below 700mb will result in
spotty high-based showers at best, with sprinkles or virga the more
likely scenario for most areas. Forecast soundings depict little if
any instability, with a strong inversion at/above 700mb, and only
skinny CAPE on the order of 100-300J/kg attainable for parcels
lifted from at least this level. Thus have removed the mention of
thunder for today. Any mid level showers should move east of the
forecast area by early this evening with the lead mid-level wave
well into MN/IA by 00Z. Attention then turns to approach of deeper
trough, which should begin to spread some light rain into southwest
portions of the area very late tonight. Persistent cool advection
through tonight will drop temperatures into the mid 30s-mid 40s by
daybreak, possibly a little warmer around Storm Lake, depending on
cold front timing.

.LONG TERM...(Tuesday through Sunday)
Issued at 351 AM CDT Mon Apr 24 2017

By Tuesday morning the surface front will reside just to the
southeast of our CWA, becoming nearly stationary over IA into the
afternoon. A shortwave will begin to lift out of eastern Nebraska
during the morning hours with increasing midlevel theta e advection
spreading northward across our area. With that will see increasing
rain chances through the MO River Valley into portions of
northwestern IA through the morning, then rain will become likely
over all but the northwestern portion of the CWA by afternoon as the
wave lifts north and east and the 850 mb front sets up across the
area. With clouds/showers and ensuing cold air advection, it will be
a cool day with highs only in the 40s over all but our IA zones,
where 50s will be common over that area. 850 mb temperatures cool
through the day, and may see readings fall during the afternoon,
especially in our southeast as the cold air advection gets into that
area. Northerly winds around 15 kts during the afternoon will only
add to the discomfort.

By Tuesday night the main upper level low slides across the Northern
Plains, and will see precipitation chances slowly tail off over our
area through the night. By evening, 850 mb temps will be sub 0 C in
our west, and cannot rule out any lingering precipitation mixing
with or changing to snow through the James River Valley into the
central Highway 14 corridor. Any accumulation would be minor at that
point with only a few hundredths of QPF as the system pulls away.
Northwesterly winds will remain strong overnight with skies
remaining cloudy, but with the cold air advection lows will still
drop into the lower 30s north and west, to mid/upper 30s elsewhere.

The overall trend for Wednesday will be drying out, though cannot
rule out some very light lingering precipitation, mainly northeast
as the upper level low pulls off into the Upper Mississippi Valley
late. With a decent gradient remaining over the area, still looking
at strong northerly winds during the day, perhaps trending downward
in the afternoon as the gradient slackens and mixed layer winds
decrease. Much below normal temperatures will continue to be the
rule on Wednesday with sub 0 C 850 mb temperatures over the entire
area, and looking at highs lower to mid 40s.

The remainder of the extended period will be characterized by
continuing below normal temperatures, as upper level energy dives
into the Pacific Northwest on Thursday, carving a deep upper level
trough over the western and central CONUS for the end of the week
into the weekend. Highs through the period will only be in the 40s
and 50s, with lows in the 30s. Confidence is not especially high
with regard to timing of precipitation chances for the end of the
week with model differences on the specifics, though consensus would
place the higher probabilities on Friday and Saturday night.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 602 AM CDT Mon Apr 24 2017

VFR conditions expected to dominate through much of this TAF
period, with gusty south winds again the primary concern through
the daytime hours. Locations along and east of I-29, including
KFSD and KSUX, will likely see frequent gusts at or above 25kt
after 15Z. Strongest winds will diminish toward sunset, gradually
shifting to northwest and north as a cold front moves across the
region.

Models indicate potential for MVFR ceilings developing very late
in this TAF period, but uncertainty whether this is just an impact
of cooling low level temperatures, or if the stratus will actually
be realized, so opted to stick with VFR ceilings for now.

&&

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

$$

SHORT TERM...JH
LONG TERM...JM
AVIATION...JH



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.