Area Forecast Discussion


176 
FXUS63 KFSD 131002
AFDFSD
Area Forecast Discussion
National Weather Service Sioux Falls SD
402 AM CST Wed Dec 13 2017
.SHORT TERM...(Today and Tonight)
Issued at 401 AM CST Wed Dec 13 2017
Strong short wave showing up very well on water vapor imagery 
currently diving quickly southeastward in central and western SD. At 
the surface, low pressure is positioned over central MN with the 
wind shift through southwest MN and extreme northwest IA. The PV 
surge at the 1.5 pressure surface is quite robust early today, 
before moving to the southeast later this morning. In the meantime, 
strong surface pressure rises are noted this morning coupled with 
cold air advection in the surface to 925mb layer greatly adding to 
wind speeds along the PV surge behind the initial wind shift. Wind 
speeds are already gusting over 40 mph in our western zones for 
instance, and these types of winds will move quickly eastward early 
today. Therefore no changes needed to the wind advisory. Some of the 
higher terrained areas, such as the Buffalo Ridge in southwest MN 
and lower Brule areas, will experience gusts of 45 to 50 mph at 
times late this morning and early afternoon, when deep mixing for 
this time of year is coincident with low level cold air advection. 
By mid afternoon, the strongest gusts will begin to subside as the 
gradient relaxes a bit, coupled with less wind in the mixed layer 
and an absence of pressure rises. 
Measurable precipitation will be hard to find with this system. 
Stratocu will enter our forecast area this morning. However the 
moisture depth is thin, with the deepest moisture in southwest MN 
midday and early this afternoon at about 100mb deep. Soundings are 
dry adiabatic due to low level instability, so would not rule out 
scattered flurries or light snow showers once the temperatures both 
at the surface and aloft cool this afternoon. But measurable 
snowfall will be hard to find, especially with the windy conditions. 
This morning, any light precipitation will be primarily of the 
liquid variety. Concerning temperatures, they are a challenge today. 
Conditions have warmed up dramatically as expected right along the 
strongest winds, with lower 50s currently at Chamberlain and 
Mitchell. Therefore temperatures will warm elsewhere as the winds 
increase early today, then will begin to slowly cool off before 
steadying out as the mixing potential battles the cold air 
advection, likely to a stalemate. At any rate, highs today will 
likely be realized early in the day during the initial surge of 
wind, noting that the models really struggle with the degree of 
warming as the winds increase.
Tonight, the winds will decrease dramatically. There could be some 
leftover flurries over parts of southwest MN and northwest IA in the 
evening under lingering stratocu and a favorable thermal profile 
aloft. But again measurable snowfall will be virtually non existent 
due to a lack of deep moisture. Skies will then become partly cloudy 
in our eastern zones helping to produce lows in the teens. 
Conversely, another round of increasing mid and high level cloud 
cover will put the brakes on temperatures from falling very much in 
our western zones, with lows in the upper 20s likely in our south 
central SD zones. 
.LONG TERM...(Thursday through Tuesday)
Issued at 401 AM CST Wed Dec 13 2017
On Thursday, a weaker short wave will move southward. Mid and upper 
level QG forcing as well as PV are consistent amongst the 
deterministic models in showing the track of the wave primarily 
along and west of the James River valley, mainly through the midday 
hours. Moisture with this wave is quite robust, through about 5 km, 
and the thermal profile shows a steady cooling through this layer 
with no inversions to worry about. Chances for light snow appear 
likely in our extreme west toward central SD with amounts possibly 
between a half inch and one inch. Snow amounts wane to a dusting at 
most toward I 29 moving too far east of the wave influence. The 
isobars and winds aloft our fairly relaxed on Thursday except 
conditions could become quite breezy Thursday afternoon in south 
central SD behind low pressure which is moving southeast through 
eastern Nebraska, and building high pressure over the northwestern 
plains. Therefore the gradient is a bit strong toward central SD. 
Blowing snow Thursday afternoon in south central SD should not be a 
concern as the precipitation rate decreases and temperatures warm 
into the upper 30s producing a light rain or snow mix. 
On Thursday night, QG forcing shows another weak short wave moving 
southeastward across Minnesota. For now, left out the mention of 
flurries in our far eastern zones as the stratus depth is quite thin 
once again. The next system to watch is Saturday night. The various 
models are in pretty good agreement with the large scale in showing 
a split wave. The GFS is strongest with the northern stream 
throughout the northern plains and cuts off the moisture supply, 
whereas the ECMWF and GEM Global show some hookup with the southern 
stream energy. Therefore the ECMWF and GEM develop low pressure over 
the central and southern plains, elongated from northeast to 
southwest, with light snow developing across the favored northwest 
quad throughout much of the forecast area as mid level temperatures 
are cold enough to produce ice. For now, compromised between the 
models and kept low pops confined to our western and southern zones, 
noting that the GFS is totally dry in our area. Otherwise highs this 
weekend will likely to continue to trend above normal, with 
seasonably mild weather continuing into early next week.
&&
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1056 PM CST Tue Dec 12 2017
Cold front working through the area. Behind the front, winds are
rapidly increasing aloft, and will mix to the surface on
Wednesday. Stratocumulus is expected to develop Wednesday morning
in the 2500-3500 foot range. Strong northwest winds will decrease
Wednesday night. 
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory until 6 PM CST this evening for SDZ067-070-071.
     Wind Advisory until 3 PM CST this afternoon for SDZ038-050-052-
     053-057>059-063-064.
     Wind Advisory until 3 PM CST this afternoon for SDZ039-040-
     054>056-060>062-065-066-068-069.
MN...Wind Advisory until 6 PM CST this evening for MNZ072-080-081-089-
     090-098.
     Wind Advisory until 3 PM CST this afternoon for MNZ071-097.
IA...Wind Advisory until 6 PM CST this evening for IAZ001>003-012>014-
     020>022-031-032.
NE...Wind Advisory until 6 PM CST this evening for NEZ013-014.
&&
$$
SHORT TERM...MJ
LONG TERM...MJ
AVIATION...BT