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Office: FSD

FXUS63 KFSD 141746

Area Forecast Discussion
National Weather Service Sioux Falls SD
1146 AM CST Thu Dec 14 2017

.SHORT TERM...(Today and Tonight)
Issued at 331 AM CST Thu Dec 14 2017

Current water vapor image shows the next short wave diving southeast
near where ND, SD and MT meet. Deterministic models are all in good
agreement in tracking this wave primarily along and west of the
James River valley today when following the PV and mid and upper
level QG forcing. There is not much in the way of surface features
to follow with this wave. A broad area of weak low pressure exists
in central ND which weakens as tries to move southeast. At any rate,
moisture depth is still pretty robust across our western zones where
saturation exists through about 5km, and a thermal profile cold
enough to produce ice crystals. High pops for a low QPF event are
warranted in our southwest corner where around a half inch of snow
may fall this morning before warming up a bit this afternoon.
Heading to the east, pops rapidly drop off heading toward the I 29
corridor this morning. However, another weak mid level wave which
shows up in the 700-500mb QG forcing field dives southeastward this
afternoon and evening impacting the eastern half of our forecast
area. Just enough instability and a favorable thermal profile of
-12C at the top of the cloud layer may produce a few light snow
 showers/flurries, or sprinkles depending on temperature.
 Therefore some locations in east central SD, parts of southeast
 SD, extreme northwest IA and southwest MN could receive a dusting
 of snow this afternoon although some of it may melt. These light
 snow showers or flurries will likely linger into the evening
 hours as the wave departs. Concerning temperatures, highs today
 will be in the 30s, followed by lows tonight mainly ranging from
 20 to 25 degrees.

.LONG TERM...(Friday through Wednesday)
Issued at 331 AM CST Thu Dec 14 2017

In the longer range, the next system to watch continues to be on
Saturday night. Basically a three pronged upper wave takes shape
with the northern stream wave moving into the Dakotas, a second
wave near the four corners area, and a closed low off the
California Baja. The latest ECMWF is a little less aggressive with
the hookup between the southern and northern stream waves and is
in closer agreement to the NAM and GFS. There may be a bit of
light snow Saturday night in our west when initially, there is
some saturation in the confluent region of the northern and
southern stream jets. But as the northern stream takes over on
Sunday, the moisture supply cuts off and basically leaves our
forecast area dry. The surface low and associated inverted trough
angling from northeast to southwest in the central and southern
plains is fairly robust, but just does not have enough saturation
to work with this far north. At this time, next week looks
seasonably mild. In fact we may not be warm enough on Monday and
Wednesday, especially in our western and southern zones if some of
these 925mb temperatures pan out. Winds could be pretty strong on
Tuesday following a very weak cold frontal passage, with strong
subsidence and drying present for that day.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1144 AM CST Thu Dec 14 2017

Scattered light showers are expected this afternoon and evening
across the area, with MVFR ceilings likely. South and west of the
James River, mid-day temperatures will be warm enough to allow
falling snow to partially melt and create a rain snow mix. North and
east of the James River valley, snow will be the dominant
precipitation type, with only light accumulations under half an inch
expected. Most will see only a dusting to a couple tenths of an
inch. Winds will be light today, with precipitation ending around
15/0300z. Friday looks dry with breezy southwest winds developing
during the afternoon, gusting in the 20 to 25 kt range.





Office: UNR FXUS63 KUNR 141720 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 1020 AM MST Thu Dec 14 2017 .DISCUSSION...(Today Through Wednesday) Issued at 208 AM MST Thu Dec 14 2017 Initial shortwave is moving over the Rockies and through the Four Corners region, while the secondary upper wave is approaching the CWA from the north. Skies across the CWA are mostly cloudy, and some bands of snow are moving through parts of western SD. At the surface, winds are northwesterly around 10-20 kts, and temperatures are in the upper 20s and 30s. Upper wave will slide through the northern plains this morning, bringing gusty winds, light snow, and cooler air. Pressure rises, CAA, and 850 mb winds are not as strong as they were in previous days, but forecast soundings are indicating the potential for some strong winds mixing down. Still expecting 20 to 35 mph winds, with gusts to 50 mph from northwestern into west central SD. Will expand Wind Advisory into a few more zones. Froude number shows good upslope enhancement of snow through 18Z, before it gradually decreases in the afternoon. Another 1 to 4 inches of snow will be possible for the northern Hills, mainly in the morning hours. Parts of south central SD could see an inch or two of snow, but other areas will receive less than an inch. Gusty winds may create some patchy blowing snow at times. Highs today will be mainly in the 30s, with 20s in the Black Hills. Upper ridge will shift over the central states on Friday, as a trough pushes into the western CONUS. Temperatures will warm into the 50s. Under partly cloudy skies, westerly winds will be around 10 to 20 mph. The upper trough will begin crossing the Rockies Friday night into Saturday, and chances for precip will increase. Light snow will spread over the CWA through Saturday night, with accumulations around an inch or less. Colder air will also accompany this trough. Highs both days will be in the 30s to lower 40s, with lows in the 20s. Mild and mostly dry weather is expected for the beginning of next week, as an upper ridge moves over the region. Both the GFS and ECMWF are showing a trough digging into the western CONUS towards the end of next week, which could bring much colder weather to the area for next weekend. && .AVIATION...(For the 18Z TAFS Through 18Z Friday) Issued At 1020 AM MST Thu Dec 14 2017 Light snow will gradually end from west to east today. MVFR/local IFR conditions expected with the snow. Gusty northwest winds will continue into the afternoon, strongest east and north of the Black Hills with gusts to 45kts. && .FIRE WEATHER... Issued At 208 AM MST Thu Dec 14 2017 As temperatures warm into the 50s Friday, relative humidity will drop to 20 to 30 percent. Westerly winds will be breezy, gusting above 25 mph at times. Current forecast does not warrant headlines, but if min RH values drop into the teens, critical fire weather conditions may result. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...Winter Weather Advisory until noon MST today for SDZ024. Wind Advisory until 3 PM MST this afternoon for SDZ001-002- 012>014-026-030>032-043-072>074. WY...Winter Weather Advisory until noon MST today for WYZ057. && $$ DISCUSSION...Pojorlie AVIATION...JC FIRE WEATHER...Pojorlie
Office: ABR FXUS63 KABR 141747 AAA AFDABR Area Forecast Discussion...UPDATED National Weather Service Aberdeen SD 1147 AM CST Thu Dec 14 2017 .UPDATE... Issued at 1139 AM CST Thu Dec 14 2017 Light precipitation will continue sliding southward across the region over the next few hours. Based on a report in our northeast, plus a webcam observation, have added patchy freezing drizzle in the far northeast portion of the CWA. The rest of the forecast for today looks good overall. && .SHORT TERM...(Today and Tonight) Issued at 400 AM CST Thu Dec 14 2017 Another day, another 500mb embedded wave sining in from the northwest. This one is just to our northwest early this morning, and will sink southeast through mid afternoon. Current sfc set up shows a stationary front over our eastern counties, extending from 1016- 1018mb pressure center over eastern ND/northeastern SD and much of MN. This feature will slide east as a ridge of high pressure temporarily builds overhead through this evening, before becoming surpressed to our south as the next trough nears from the north (extending from the low over northwestern Canada). Went closer to the RUC13 with the top down method, which reduced the probability of ice over our eastern counties shortly past 12Z, and kept a higher chance of freezing drizzle with any of the light radar returns shown over that area. Even through we seem to be in a lull, it looks to be temporary as additional light precipitation slides in from western SD and ND. Continue to monitor upstream observations where have been mainly reporting SN, although the Glen Allin station did briefly report UP. Extended the Winter Weather Advisory until 9am for the lingering freezing drizzle with icy conditions on untreated roadways. After 9am there will be a better chance of mainly snow. Total snowfall amounts today should be around an inch or less, with the best chance of accumulation over our southwestern counties. Couldn't rule out some lingering flurries over the east (mainly Sisseton Hills) tonight. Another concern today will be the breezy winds developing west of the Missouri River. Winds are expected to stay below advisory criteria. .LONG TERM...(Friday through Wednesday) Issued at 400 AM CST Thu Dec 14 2017 It appears a pattern change will likely take place in the long term, particularly toward the middle and end of next week. The recent west conus ridge and east conus trof is forecast to retrograde with troffing gradually taking shape over the western conus as mid level ridge develops over the eastern Pacific. Most models, especially ensembles, indicate as much. Deterministic runs offer less confidence, but that's probably to be expected at this time range. During the long term, probably the best chc for measurable pcpn will occur Saturday and Saturday night as a system tracks across the region; and again by the middle to latter part of next week as the mid level pattern goes through some sort of re-alignment. Temperatures overall will favor near to above normal for the vast majority of the forecast. But, a change to colder temps is likely toward the end of next week. && .AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon) Issued at 1139 AM CST Thu Dec 14 2017 Light precipitation will continue sliding southward across the region through mid afternoon. Visibility will be impacted briefly with heavier snowfall rates. Otherwise, expect MVFR cigs to continue through this evening with a gradual improvement possible tonight. && .ABR WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. && $$ UPDATE...SD SHORT TERM...KF LONG TERM...TDK AVIATION...SD