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Office: FSD

FXUS63 KFSD 191055

Area Forecast Discussion
National Weather Service Sioux Falls SD
555 AM CDT Mon Mar 19 2018

.SHORT TERM...(Today and Tonight)
Issued at 355 AM CDT Mon Mar 19 2018

Near term issues center around abundant low level moisture, and
continued areas of fog and/or drizzle early this morning. Again
dealing with a deep, relatively dry northeast flow above this low
level moisture. Aside from some patchy drizzle, this will limit
extent to which precipitation will be able to advance into the
forecast area through the day. Thus have further trimmed pops for
today, confining to areas mainly west of the James Valley until late
in the day when upper wave drops into central South Dakota. This
will provide increased lift to eventually overcome dry layer and
allow some light precipitation to expand eastward. The moist low
level air mass should help keep surface temperatures above freezing
as the precipitation initially advances toward I-29 late in the
afternoon, limiting any potential for any minimal snow accumulation
prior to 00Z to just higher elevations in our far western counties.

Surface/boundary layer temperatures will cool below freezing this
evening as the wave slowly advances east, allowing rain to change
over to light snow through the night. Wave is rather slow-moving,
but not seeing any mid level front or deep lift that would focus a
heavier band, so still expecting just a broad light snowfall over
the area. Amounts generally 1-3 inches, with the highest amounts in
our higher elevations in southwest Minnesota/east central South
Dakota, where cooling will reach the surface more quickly.

.LONG TERM...(Tuesday through Sunday)
Issued at 355 AM CDT Mon Mar 19 2018

Light snow will be lingering near/east of I-29 by daybreak Tuesday,
generally exiting by midday, but a secondary weak wave will drop
southeast into the region Tuesday afternoon/night that will keep a
slight precipitation chance around into Tuesday night. GFS/Canadian
a bit more robust with this wave than NAM/ECMWF, and will keep pops
quite low as a result. However, will have to watch this wave for the
potential for another light dusting of snow Tuesday night for parts
of the area.

Temperatures will warm midweek as modest upper ridge builds into the
region, with highs in the 40s and 50s by Thursday. This in advance
of a lead wave bringing a good chance of precipitation to the region
late in the work week, followed by a more potent trough which could
impact the region next weekend. At this time, thermal profiles would
support either rain or snow, with minimal snow accumulations with
the first wave Friday as temperatures again warm into the 40s and

More uncertainty in strength/track and associated snow potential
with the weekend system. Current consensus would point to some
accumulation, primarily across northeast portions of the forecast
area, but ensembles show very broad range in not only precipitation
amounts, but also low-level temperatures which will be critical to
precipitation type. Will certainly be a system to monitor as we
progress through the week.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 550 AM CDT Mon Mar 19 2018

MVFR visibilities in fog and patchy drizzle through the morning
hours. Otherwise, MVFR/IFR ceilings through the TAF period. Light
rain will spread across the area later this afternoon, changing to
light snow this evening and continuing overnight.





Office: UNR FXUS63 KUNR 191016 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 416 AM MDT Mon Mar 19 2018 .UPDATE... Issued at 415 AM MDT Mon Mar 19 2018 Conditions are favorable for some light freezing drizzle over northwestern parts of the area, including the northern Black Hills, so have updated the forecast to include that through this morning. && .DISCUSSION...(Today Through Sunday) Issued at 253 AM MDT Mon Mar 19 2018 The latest water vapor images revealed a continuing complex upper-level pattern, with the main low over KS/OK. A rather diffuse upper flow was over the CWA, with a few weak short-wave troughs in the vicinity. Forcing from these waves will affect mainly the eastern CWA today where the models do show modest isentropic lift, frontogenesis, and Q-vector convergence. Precipitation has transitioned to snow across most of the CWA, although there was some spotty freezing drizzle. Expect that snow will be the dominant type today. One to four inches of snow are possible over south-central SD. Have cancelled the winter weather advisory for the northwest as things are winding down there. Otherwise, it will be seasonally cold today with brisk northwest winds over the SD plains. Clouds will be widespread, with some areas of fog as well. A few more weak short-wave troughs will continue to affect the CWA tonight and Tuesday, but the result will only be isolated to scattered snow/rain showers. Low clouds and some fog also are likely again tonight. Tuesday will see some warming at 850-mb, which should translate to slightly warmer weather than today (although still tempered by snow cover). It will be dry Tuesday night and Wednesday as upper riding continues. Areas of fog may again develop Tuesday night and Wednesday night, especially over parts of northwestern into central SD. 850-mb temperatures on Wednesday rise to 2-10C, warmest over northeastern WY. There should be a fairly large contrast in highs from snow-free parts of northeastern WY to snow- covered areas of northwestern SD. The upper ridge will still be affecting the CWA Thursday, and breezy southerly winds will help mix down some of the warmer air aloft. A large trough over the western CONUS will send a weak short-wave trough across the CWA Thursday night, producing low-level theta-E advection and fostering scattered showers. Additional short-wave troughs will move across the CWA Friday and Saturday as a large upper low moves over the Pacific Northwest. Some Pacific FROPAs will occur both Friday and Saturday, bringing slightly cooler air and breezy conditions. Unsettled conditions will persist Sunday and Monday as troughiness dominates the weather pattern for the CWA. The GFS is notably warmer than the ECMWF, and given the pattern would expect the cooler ECMWF solution to be more realistic. && .AVIATION...(For the 06Z TAFS Through 06Z Monday Night) Issued At 1128 PM MDT Sun Mar 18 2018 A storm system will continue to move through the area into Monday with snow at times, especially east of the Black Hills. Some FZDZ may also occur, especially across far northeast WY into northwest SD. Areas of fog will occur with small T/Td spreads and abundant boundary layer moisture. Result will be widespread IFR conditions through early Monday afternoon with some LIFR conditions in the heaviest snow over central SD. Improvement will occur from northwest to southeast Monday afternoon and evening. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ Update...Bunkers DISCUSSION...Bunkers AVIATION...Helgeson
Office: ABR FXUS63 KABR 190849 AFDABR Area Forecast Discussion National Weather Service Aberdeen SD 349 AM CDT Mon Mar 19 2018 .SHORT TERM...(Today through Tuesday Afternoon) Issued at 347 AM CDT Mon Mar 19 2018 A vigorous upper level low pressure system currently over northern Oklahoma, along with a weak system over southern Alberta, will bring light precipitation to the region. Light snow has been ongoing west of the Missouri Valley this morning with webcams supporting 1-2 inches so far. An additional inch or two could be possible before the system begins to push eastward today. While upper level lift is not great, the slow nature of this system could produce two to three inches of snow for east SD and western MN. Surface temps around freezing could limit the snowfall amounts. Precipitation will gradually diminish from west to east late this afternoon through tonight. However a weak upper level trough will cross the region on Tuesday with additional light pcpn possible. .LONG TERM...(Tuesday Evening through Sunday) Issued at 347 AM CDT Mon Mar 19 2018 The models show a weak short wave trough leaving the region to the east on Tuesday night with some residual chances of rain/snow for this time. Otherwise, the models show 50h ridging building into the region from the west for Wednesday and Thursday bringing a short period of time of dry conditions. The models then still show a large low pressure trough moving into the western U.S. The models have been consistent with kicking an initial significant short wave trough that will move northeast across our region Thursday night into Friday night. Still have in very good chances of rain/snow with this system. The models were now less impressive with the weekend system. This time around the models show a short wave trough kicking out of the western trough and farther north across the Northern Plains for Saturday and Sunday. The models have varied on this several times. This solution would be warmer for us along with lesser chances of rain/snow which is what is in the forecast this time around. Highs through the period are expected to be near to around 5 degrees below normal mostly in the 40s and lower 50s across the cwa. && .AVIATION...(For the 06Z TAFS through 06Z Monday Night) Issued at 1245 AM CDT Mon Mar 19 2018 IFR/MVFR cigs will remain in place over the CWA through the TAF period. Precipitation will spread from west to east across the area overnight and through the day Monday. The precipitation will vary from snow to rain depending on temperatures, with vsbys likely falling into the MVFR category at times. && .ABR WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. && $$ SHORT TERM...SD LONG TERM...Mohr AVIATION...Mohr