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fxus63 kgid 211114 
afdgid 


Area forecast discussion 
National Weather Service Hastings NE 
514 am CST Sat Nov 21 2009 


Aviation...12z taf. Early morning satellite imagery shows a large 
area of stratus moving north across central and eastern Kansas. 
At its current pace...it should arrive at kgri around 15z. There 
is still some disagreement among the various short term forecast 
models on how long the stratus will then persist at kgri. Will 
still side with a more optimistic approach which moves the thicker 
clouds to the east of kgri later this afternoon and returns the 
terminal to VFR conditions. Winds will also be on the increase 
today...and expect them to become gusty from the south by 18z. 
Moisture will continue to surge into the region ahead of a cold 
front tonight. This will bring a fairly good chance of IFR 
conditions to kgri towards late evening. Will show an IFR ceiling 
developing around 04z...with LIFR conditions becoming possible 
early Sunday morning. 


&& 


Previous discussion... /issued 309 am CST Sat Nov 21 2009/ 


Discussion...aloft...shortwave ridging was in place across the 
Central Plains while to the west...a trough stretched from British 
Columbia south through The Rockies. The shortwave ridge axis will 
shift eastward today as the western trough advances to the east. At 
the surface the associated trough will deepen in the Lee of The 
Rockies and the gradient will tighten...resulting in increasing 
southerly winds to the breezy category at times. Cloud cover for 
today is challenging as an area of stratus currently located 
across central/southeast Kansas will work its way northward during 
the day. Our southern County Warning Area may see some fog development this 
morning and will continue to monitor trends of this in the next 
few hours. Whether or not the low clouds mix out today remains in 
question as the NAM suggests this is more probable than the GFS 
which maintains cloud cover across the majority of our County Warning Area for 
much of the day. Confidence is not high in this regard and did opt 
for a conservative approach with some clouds around. 


Tonight...the trough axis begins to push east of The Rockies and 
southwesterly flow aloft is enhanced across the plains. Moisture 
continues to advect north ahead of the surface boundary which 
approaches our western County Warning Area Sunday morning. Stratus is expected to 
settle in across our County Warning Area ahead of the surface boundary. Winds will 
be light along the boundary axis and the NAM is the most 
aggressive in suggesting the potential for the development of 
dense fog vs the GFS. Sref probabilities lend credence to the NAM 
and have included some low visibility potential in the grids but 
stopped short of advisory criteria for now. Weak lift over the 
shallow low level moisture may lead to the development of some 
drizzle. 


The trough/wave moves through on Sunday and this system may generate 
some light precipitation in the afternoon in our east where better moisture is 
present. The wave does not effectively scour the low level moisture 
and have some concerns that the stratus will remain Sunday night and 
fog may develop again. Have introduced some patchy fog for now as 
a start. 


The forecast turns more interesting on Monday as another trough digs 
south from the northern rockies and is forecast to close off across 
the plains on Monday. Models have varied on where the low will 
close off/track with the GFS remaining farther north than the 
NAM/ECMWF/Gem. Have trended toward the southern solution for now 
with precipitation chances increasing on Monday ahead of the system and 
continuing Monday night/Tuesday in the deformation/wraparound. The 
predominate precipitation type should be rain initially but a r/S mix or a 
changeover to snow west/east on the back side of the system is possible 
Monday night into Tuesday. In addition the precipitation potential...very 
strong winds on the back side of the system will buffet our region 
Monday night/Tuesday with wind gusts over 40 miles per hour possible. 


&& 


Gid watches/warnings/advisories... 
NE...none. 
Kansas...none. 
&& 


$$