517 
fxus63 kabr 082115 
afdabr 


Area forecast discussion 
National Weather Service Aberdeen South Dakota 
315 PM CST Thursday Jan 8 2009 


Short term...tonight through 12z Sunday 
forcast challenge facing the long term deals with expected 
precipitation/type/coverage through the next 36 hours. 


Msas shows surface low sitting in southeastern Montana/northestern Wyoming with warm front 
draped southeast into NC Nebraska. Across western Nebraska/eastern Wyoming and far southwestern 
South Dakota...temperatures have warmed into the middle 50s...with single digits above 
zero still in place across the northestern part of South Dakota. Models all agree 
on this surface low dropping southeast across southwestern South Dakota through the next 24 
hours. 850 mb/7h Theta-E analysis shows strong warm push to continue through 
06z across the eastern/southern part of the County Warning Area before Theta-E forcing 
tapers off. This lines up well with 850 mb-7h q-vector convergence 
highlighting the area of maximum warm air advection forcing through the night. 
850 mb/925mb temperatures show deep enough cold air in place across the northestern 
part of the County Warning Area to keep any freezing precipitation at Bay...and bufr 
soundings confirm that kabr and Katy should experience only 
snow...no fzra/fzdz. Further west...brief bit of snow has been 
replace by freezing rain/sleet in the mbg/pir areas. This appears to be 
with the first surge of warm air advection..and distinct back edge seen to precipitation 
on various radars. Next surge coming in...and appears on the 
kunr/kbis radars would lead one to believe its freezing rain/sleet judging 
from the mottled appearance on radar. GFS shows that 850 mb-7h 
frontogenesis and Omega maximizes across the NE part of the County Warning Area 
from 00-06z tonigh...with spec humidities in that layer from 4.0 
to 4.25 g/kg...with is plenty of moisture. BUFKIT soundings for 
kabr and Katy show good Omega passing through best dendritic 
zone...leading to effecient snow production through the evening. 
Models also agree on downglide setting up across the western 
counties by 09z with precipitation tapering off quickly. However...85h-7h 
Theta-E ridges take a negative tilt to them through the day Friday 
across eastern South Dakota...and well defined trowal feature seen at 850 mb 
through at least 18z Friday across the eastern counties. Given that 
the GFS shows good 850 mb-7h layer Omega drops south across the eastern 
County Warning Area through the day Friday...coupled with the trowal 
feature...have expanded the area of likely snow for the east on 
Friday. Winds will increase across the western County Warning Area as high pressure 
rises move in...and headline will most likely be needed. Didn't 
want to clutter up the zones with multiple headlines...so have 
opted to wait to issue any wind headlines and will let later 
shifts handle. 


Northwest flow remains in place Friday night through rest of the short 
term...with 850 mb temperature analysis showing warm air advection trying to move back into 
the area for the weekend. Models advertise a minor wave sliding 
down in the flow Saturday night...but limited moisture with the 
feature should result in only an increase in middle/hi level 
cloudiness. With a bit of 850 mb temperature recovery...have continued with 
warming temperatures Saturday/Saturday night...with some above zero lows 
possible Saturday night. 




Long term...Sunday through Wednesday 
upper level pattern takes on a +pna look during the extended 
period with a ridge across the far western Continental U.S./Eastern Pacific 
and a trough across the central/eastern Continental U.S.. looks like our 
region will see north/northwest flow aloft with a couple fairly 
potent and fast moving waves moving south over the area...dropping 
snow and bringing wind. Cold temperatures look to dominate 
throughout. 


First wave looks to track southeast across the area Sunday night 
and Monday. Rather good agreement amongst the GFS/ec/Canadian in 
bringing a couple inches of snow across the area...along with 
decent winds behind this system. Have increased probability of precipitation into the 
40/50 range given the good agreement with the models. Next wave 
comes down Tuesday-ish and have maintained low probability of precipitation for this. A 
bit more uncertainty in regards to timing with this system...but 
little doubt in there actually being a system in the area. Will 
more than likely have to increase probability of precipitation for this wave also...but 
will need to refine timing a bit in later model runs. This wave 
also has the potential to drop a couple inches of snow with fairly 
breezy winds behind it. 


As for temperatures...looks like an Arctic airmass will invade the 
region later in the period as 850mb temperatures drop into the -20s c 
below zero. Dropped temperatures further from HPC guidance. Will 
more than likely see temperatures well below zero...probably teens and 
20s below zero at night...with highs struggling to reach zero in 
some locations. More specifically...looks like coldest of air will 
arrive Tuesday night and stays in the area through the end of the 
week. Will probably also experience periods of extremely cold wind 
chills. 






&& 


Aviation... 
areas of -fzdz/-fzra will affect kmbg/kpir taf sites late this 
afternoon and through the evening hours before changing to -sn/snow 
late tonight. Farther east across kabr/Katy...expect -sn/snow to 
move into the region late this afternoon and persist overnight. 
Small chance for -pl in this area but main precipitation type will be 
-sn/sn. Ceilings will be in the IFR/MVFR range across the entire area. 
Although...kpir will not experience as low of ceilings as the rest of 
the taf sites...perhaps not even reaching MVFR at times. Visibilities 
will drop to around 1/2sm at times in areas of heavier 
precipitation. 






&& 


Abr watches/warnings/advisories... 
South Dakota...Winter Weather Advisory until midnight CST /11 PM MST/ tonight 
for Campbell-Corson-Dewey-Edmunds-Faulk-McPherson-Potter- 
Walworth. 


Winter Weather Advisory until 4 PM CST Friday for Brown-Clark- 
Codington-day-Deuel-Grant-Hamlin-Marshall-Roberts-Spink. 


Minnesota...Winter Weather Advisory until 4 PM CST Friday for Big Stone- 
traverse. 


&& 


$$ 
Short term...Hintz 
long term...tmt 
aviation...tmt 


Weather.Gov/Aberdeen