910 
fxus63 kgid 022312 
afdgid 


Area forecast discussion 
National Weather Service Hastings NE 
512 PM CST Tuesday Dec 2 2008 


Aviation...the primary forecast concern will be the passage of a 
strong cold front later tonight. Late afternoon surface analysis 
had a cold front moving across southern South Dakota. This feature 
will continue to make progress south tonight and will bring gusty 
northerly winds to kgri later this evening. Will time the onset of 
the gusty winds around 04z...but obviously that time is not a 
certainty. Radars across South Dakota also indicate some light 
snow follows the cold front...however how to handle it once it 
reaches kgri is less certain with some forecast models suggesting 
it will snow...while others are dry. Have decided to keep a brief 
period of light snow late tonight into early Wednesday morning 
since it appears that even the dry looking 18z NAM/WRF run shows 
moisture increasing with sufficient vertical motion for light 
snow. Will also introduce an MVFR ceiling as the snow begins...and 
then go with a low (3500ft) VFR ceiling by middle morning on 
Wednesday. 


&& 


Previous discussion... /issued 343 PM CST Tuesday Dec 2 2008/ 


Short term...tonight through 12z Thursday. Main forecast 
concerns with precipitation and winds tonight into early Wednesday morning. 


Current satellite imagery shows the next bout of shortwave energy to 
cross the plains over The Rockies. Associated cold front on 
track...draped south from Minnesota through South Dakota and into the Panhandle of 
NE. This system will continue to make its way east across the 
plains this evening and during the overnight hours...and models 
continue to be in pretty good agreement and consistent from the past 
few runs. Looking at precipitation...increased probability of precipitation into the likely 
category...for areas east of a line from Ord to Superior along 
with best forcing. Little has changed with timing through the 
County Warning Area...which will lag a few hours behind the main surface front as 
the main forcing mechanism lies with low/middle level 
frontogenesis...but lift will also be aided by a 110+kt upper 
level jet. Still expecting things to hold off through midnight for 
all but far northern portions of the County Warning Area. Trended away from the 
NAM for quantitative precipitation forecast...as it leaves the area completley dry...and more 
towards the GFS. Am not expecting significant accumulations...as 
there is not a ton of moisture available and it is not a long 
lived event...but feel that accumulations near an inch are 
possible across the eastern portion of the County Warning Area. Upped probability of precipitation across 
the southeast for the first part of Wednesday morning for 
lingering showers...but things should be quickly moving out...with 
only flurries hanging around. Another concern for tonight lies 
with the winds. Decided to go with a wind advection for roughly all but 
the northeastern third of the County Warning Area...with best chances for 
hitting our criteria /sustained 30mph for 1 hour or any 45 miles per hour gust/ 
between 6-12z. Models in good agreement showing increasing winds 
in the lower levels off the surface overnight...along with good surface 
pressure rises behind the front. Feel that with cold air advection...ll lapse 
rates will be good enough to help transport some of that wind down 
to the surface. Keep advection going into middle morning Wednesday...but after 
sunrise think that winds will be tapering off below criteria...but 
most noticeable drop off in winds likely won't be until the 
afternoon hours. Highs for Wednesday will be quite a change from 
today...as colder air building into the plains keeps temperatures 
in the 30s across the County Warning Area. 


Long term...for 12z Thursday through next Tuesday. 


For Thursday into Thursday night...a cold but active northwest flow 
regime is shown to dominate across the region as the models reveal a 
small but potent clipper system sliding through the area Thursday 
night. Ahead of this wave...the right entrance region of a 120kt 
upper jet streak will move across northern Kansas into far southern 
Nebraska. The direct circulation associated with the entrance 
region is shown to produce a modest band of frontogenesis in the 
800-700mb layer stretching from southwest Nebraska into north 
central Kansas. This forcing along with some decent isentropic lift 
around the 285k Theta layer...will push some moisture into the 
dendritic layer across north central Kansas and far south central 
Nebraska Thursday into the first half of Thursday night. Although 
moisture will be very limited with this system...can/T rule out 
scattered flurries over north central Kansas and portions of south 
central Nebraska south of a Lexington to Superior line Thursday into 
Thursday night. 


The medium range models continue to show a very cold northwest flow 
regime remaining across the plains Friday into Saturday as a deep 
trough is carved out across the eastern Continental U.S.. this will keep the 
forecast area under a subsident and resultant dry pattern through 
Saturday night with temperatures staying near to below normal for 
highs. 


For Sunday through Tuesday...the GFS and European model (ecmwf) agree on flattening 
the upper pattern as a decent wave rides through the region. 
However...as usual the GFS is much more progressive with kicking 
this wave through the region Sunday into Monday while the European model (ecmwf) 
slows the wave down by about 12 to 18 hours. Confidence is not 
strong in either model and ensemble data is not much help. Will aim 
in the middle of these two solutions for now but this may have to be 
adjusted. Given this setup...will keep a slight chance for rain and 
snow Sunday into Monday while temperatures cool back into the upper 
30s to middle 40s for highs on Tuesday. 


&& 


Gid watches/warnings/advisories... 
NE...Wind Advisory from midnight tonight to 9 am CST Wednesday for 
nez060>062-072>076-082>086. 


Kansas...Wind Advisory from midnight tonight to 9 am CST Wednesday for 
ksz005>007-017>019. 


&& 


$$