River Flood Warning 157, NWS Sioux Falls, SD

AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
628 AM CDT Fri Apr 26 2019

.SHORT TERM...(Today through Saturday Afternoon)
Issued at 412 AM CDT Fri Apr 26 2019

Tricky forecast for tonight into this Saturday with a dynamic wave
set to emerge from the northern Rockies and track east through the
northern Plains.

For today, mid level frontal boundary lifts northeast into south
central SD this morning, before weakening in the afternoon. The main
impact will be increased mid and high clouds, however there could be
enough support for a few sprinkles in the Missouri Valley through
midday. With cooler northwest flow and mostly cloudy skies,
temperatures will be cooler than yesterday, with highs in the mid
50s to lower 60s.

Winds shift to the east-southeast Friday evening with the
aforementioned system arriving in the northern High Plains. Warm air
and moisture advection will allow light rain to quickly spread
across the region in the evening. As the surface low deepens over
the western SD/NE border and the shortwave digs into eastern
Wyoming, strong forcing will allow rain to become moderate to heavy
at times in the early morning hours Saturday, especially across east
central SD into southwest MN. With the increased precipitation
rates, dynamic cooling will allow temperatures to cool late tonight,
with thermal profiles suggesting near or just above freezing surface
temperatures in the highway 14 corridor or just north by daybreak
Saturday. Near 0C 850MB temperatures along our northern border will
likely allow rain to begin mixing with snow in east central SD,
extending into the Buffalo Ridge region of southwest MN where the
slightly higher terrain may allow for rain to switch to snow
quickest.

Thermal profiles remain marginal for snowfall into Saturday morning
across far east-central SD into southwest MN and the Iowa Great
Lakes as the enhanced precipitation rates suggest that 1 to 2 inches
of snow per hour would be possible through mid morning. The big
question is how quickly the rain transitions to snowfall and how far
south the strongest forcing sets up. Models are in relatively good
agreement, however the ECMWF does dig slightly further south and is
slightly faster than the GFS and NAM. Did blend in a little of the
NAM's cooler surface temperatures to force the dynamic cooling. Also
continued to lower snow ratios, with the likelihood that any
snowfall will be slushy/high moisture content. Lots of uncertainty
in the timing of the change to snow with marginal temperatures, so
went with 2 to 4 inches in southwest MN and the Iowa Great Lakes,
with up to 2 inches in far east central SD (Brookings). If the track
of the low changes even slightly, expect these numbers to change.
Overall QPF amounts of around 1 inch is expected in our northern and
eastern counties, however the bulk of that should fall as liquid.
The uncertainty is how much will fall within the snowfall window
Saturday morning.

In addition to wet weather, winds will become quite gusty as the low
center deepens and tracks through our southern forecast area late
tonight into Saturday. Northerly winds behind the exiting low will
likely gust to 35 or 40 mph on Saturday. The gusts combined with
falling snow will create reduced visibility. Additionally, will
need to keep monitoring river flooding impacts with an inch or
more of precipitation expected in areas where rivers are already
in flood stage.

.LONG TERM...(Saturday Evening through Thursday)
Issued at 412 AM CDT Fri Apr 26 2019

Below normal temperatures and an active weather pattern continues
into next week. The next trough tracks through the northern Plains
Sunday afternoon into Sunday night bringing the next chance of rain.
Split southwest flow aloft directs yet another wave into the central
US mid week, however models are uncertain whether the northern or
southern stream is the more active. Although temperatures will be
cooler than normal, it looks like rain will be the main
precipitation type.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 627 AM CDT Fri Apr 26 2019

Light and variable winds are expected through the daytime hours
today. High clouds will move in from the west and southwest.
During the early overnight, then these cloud decks will lower,
eventually bringing widespread rain after 27/0500z. Snow could
mix with rain during the early morning hours Saturday over
southwest Minnesota. Area-wide, easterly winds will be increasing
in strength Saturday morning, with gust to 35 kt by the afternoon
Saturday.

&&

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

SHORT TERM...
LONG TERM...
AVIATION...VandenBoogart

Hazardous Weather Outlook
National Weather Service Sioux Falls SD
509 AM CDT Fri Apr 26 2019

IAZ001-002-012>014-020>022-031-032-MNZ098-NEZ013-014-SDZ038-050-
052>054-057>071-271015-
Lyon-Osceola-Sioux-O'Brien-Clay-Plymouth-Cherokee-Buena Vista-
Woodbury-Ida-Rock-Dixon-Dakota-Beadle-Gregory-Jerauld-Sanborn-
Miner-Brule-Aurora-Davison-Hanson-McCook-Minnehaha-Charles Mix-
Douglas-Hutchinson-Turner-Lincoln-Bon Homme-Yankton-Union-
509 AM CDT Fri Apr 26 2019

This Hazardous Weather Outlook is for portions of northwest Iowa,
west central Iowa, southwest Minnesota, northeast Nebraska,
central South Dakota, east central South Dakota, south central
South Dakota, and southeast South Dakota.

.DAY ONE...Today and Tonight

Rain returns to the area this evening, becoming heavy at times
overnight. Snow may mix with rain at times mainly north of I-90
late tonight.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Rain will continue into Saturday, possibly mixing with snow at
times in the morning. Total rainfall amounts approaching one inch
may lead to localized rises in area streams in rivers. Little to
no snow accumulation is expected.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

IAZ003-MNZ071-072-080-081-089-090-097-SDZ039-040-055-056-271015-
Dickinson-Lincoln-Lyon-Murray-Cottonwood-Nobles-Jackson-Pipestone-
Kingsbury-Brookings-Lake-Moody-
509 AM CDT Fri Apr 26 2019

This Hazardous Weather Outlook is for portions of northwest Iowa,
southwest Minnesota, and east central South Dakota.

.DAY ONE...Today and Tonight

Rain returns to the area this evening, becoming heavy at times
overnight. Snow may mix with rain at times late tonight.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Rain will continue into Saturday, switching to wet, heavy snow at
times in the morning. Snowfall accumulations of 1 to 4 inches
will be possible, with the highest amounts expected in southwest
Minnesota. Winds will gust up to 40 mph on Saturday, reducing
visibility during snowfall.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.