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Area Forecast Discussion (AFD)

Issued by Aberdeen, SD (ABR)

FXUS63 KABR 232334

Area Forecast Discussion
National Weather Service Aberdeen SD
534 PM CST Tue Jan 23 2018

.SHORT TERM...(This Evening through Wednesday Afternoon)
Issued at 317 PM CST Tue Jan 23 2018

The forecast challenge tonight into Wednesday will be whether or not 
fog and/or low stratus forms over the CWA for a third consecutive 
night, and its impacts on temperature.

Currently, temperatures are holding in the 20s across the eastern 
third of the CWA, where low stratus clouds and patches of fog 
persist. The sun is shining through some high clouds across the 
western two-thirds of the CWA, where temperatures are warming into 
the 30s and 40s.

The high clouds are associated with an upper level wave working 
through the region. Once that wave/cloudiness moves southeast of the 
region, another clear sky night on light (albeit westerly component) 
winds will be in play. And, there will probably be adequate low 
level moisture still around tonight in the nocturnal boundary layer 
to aide in more fog or low stratus development, especially within 
and between the Missouri and James River valleys and up on the 
Prairie Coteau. East of the Coteau may end up being more stratus 
than fog. Since there is support from the RAP in BUFKIT, along with 
several other numerical guidance data sets, opted to stick with fog 
mention in the weather grids for tonight into the first half of the 
day Wednesday. Similar to last night, temperatures should not drop 
off much more than perhaps 5 to 10 degrees underneath cloudy areas 
tonight. Clear areas may be able to drop closer to 15 to 20 degrees 
before stabilizing in fog/stratus environment, with a slow 
temperature rebound expected on Wednesday, if fog/stratus tonight 
pans out.

.LONG TERM...(Wednesday Evening through Tuesday)
Issued at 317 PM CST Tue Jan 23 2018

When the period opens Wednesday night, a large upper level ridge of 
high pressure is beginning to build into the region. By Friday 
morning, the upper ridge has shifted east and is being replaced by a 
large/broad upper level trough of low pressure. By Sunday morning, 
we're right back where we started when the period opened, with 
another upper level ridge trying to build into the region from the 
west. However, the 12Z GSM deterministic solutions all agree today 
on this next upper level ridge being suppressed while it works into 
the middle of the country and for a brief period heading into day 7, 
there could actually be nearly zonal flow over the region.

In this continued progressive pattern of ridge/trof/nearly zonal 
flow, the forecast is still basically a dry forecast. The warming 
trend still shows up in the deterministic low level thermal progs as 
well as ensemble guidance through Friday. The onset of the broad 
longwave upper trof still progs a cold frontal passage through the 
CWA late in the week, with temperatures cooling back down to near, 
or perhaps just below, climo normal for the weekend. The suppressed 
ridge/nearly zonal flow set-up for early next week potentially 
ushers a quick turn around back into some well above climo normal 
temperatures by Tuesday.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday Evening)
Issued at 534 PM CST Tue Jan 23 2018

Confidence is growing that ABR will join ATY in the IFR category
by around 06Z tonight as additional low level moisture sinks south
from ND. MBG will be on the western edge of this low cloud/fog 
field, and am less confident that it will occur. Took out much of 
the fog potential at PIR for now, but it may be able to slip in 
around 09Z Wednesday. Winds should be around or below 10kts 
through the period.