591 
fxus63 kgid 210345 
afdgid 


Area forecast discussion 
National Weather Service Hastings NE 
945 PM CST Thursday Nov 20 2008 


Aviation...06z taf. Skies have cleared or are nearly clear for 
the kgri area...much like the models depicted. Winds have also 
died off as surface high pressure comes into the area. Those 
light and variable winds tonight...will give wave to a south 
breeze by dawn...before those south winds increase dramatically 
by midday thanks to a tightening pressure gradient. Sustained 
20kt south winds are likely...with gusts near 30kts through 
the afternoon. Generally looking for clear to scattered high 
clouds the rest of the night...before high level VFR ceilings 
develop early Friday. That level of clouds will prevail much 
of the day Friday with a wave moving by to the north. No visibility 
restrictions is expected nor any precipitation. 


&& 


Previous discussion... /issued 536 PM CST Thursday Nov 20 2008/ 


Aviation...00z taf. Though precipitation is not expected...there 
are quite a few changes in the weather through this forecast 
period. The big picture will have cold high pressure moving across 
the kgri tonight...and then quickly moving east of the area during 
the day Friday. That will mean north winds will quickly drop off 
this evening...then become light and variable overnight. The light 
winds will not last...as a tight gradient sets up by Friday 
afternoon with south winds of 20 to 30kts likely. Low VFR ceilings 
this evening should break up...leaving just high cirrus level 
ceilings at best. Some middle clouds will start coming into the kgri 
area late in the forecast period as a short wave moves across 
South Dakota. 


Previous discussion... /issued 249 PM CST Thursday Nov 20 2008/ 


Short term...tonight through 12z Saturday. The primary issues will 
be temperatures tonight and a small chance of light precipitation 
on Friday. 


Afternoon surface analysis placed a ridge of high pressure 
stretching from the Dakotas southward into West Texas. The ridge 
will continue to build into the Central Plains tonight...and by 
06z...the axis is expected to generally reside across the forecast 
area. This should bring diminishing winds late this afternoon...and 
light winds for later tonight. Clouds across the area which are 
nicely depicted in the 12z NAM 850 mb relative humidity forecast...should also 
diminish this evening...leaving a mainly clear sky for a period of 
time before high clouds begin to arrive from the west. All of this 
will help temperatures fall off quickly tonight...and have gone for 
low ranging from 10 to 15 north...and 15 to 20 south. 


The surface ridge will move east on Friday as an 500 mb low moves from 
the northern plains into northern Iowa/southern Minnesota Friday 
night. This will bring warmer air to the Central Plains with 850 mb 
warm air advection taking hold Friday and Friday night. Isentropic 
lift also increases in the 280-290k layer while qg convergence is 
noted in the 700 mb-5 layer. Model generated vertical velocities also 
increase in the dendritic layer on Friday with relative humidity values of 80-90 
percent in northern parts of the forecast area. However...low level 
moisture is sparse across central/south central Nebraska and 
northern Kansas. The 12z NAM and GFS both keep it dry across the 
forecast area Friday into Friday night...and for now will opt to not 
add any precipitation to the forecast. There should be quite a bit 
of virga on Friday and will carry high levels of cloud 
cover...especially in the northern portion of the forecast area. 


Long term...12z Saturday through Thursday. Main forecast concern 
will be temperatures. 


Temperatures will be somewhat variable through the period as a 
couple of cold fronts move through the forecast area. On Saturday 
strong warm advection with south winds ahead of a low pressure 
system will allow for temperatures to warm quite a bit. Have a 
little concern that there will be enough mixing to get the warmer 
850mb temperatures down to the surface...but still temperatures 
should be able to be warmer than highs on Friday. The warmer 
temperatures should continue Saturday night but a cold front moves 
through on Sunday. The cold air is slow to follow the front but 
slowly sags into the forecast area Sunday night. An upper wave moves 
into the area Sunday night and precipitation forms well to the east 
of the forecast area along the front. 


Warm advection returns to the area Monday but there will be little 
mixing so Monday will remain a little cooler. Temperatures aloft 
continue to be warm Tuesday and Wednesday and surface temperatures 
should continue to be mild. By late Wednesday night into Thursday 
another cold front moves into the area. The latest model runs are 
starting to have some differences. The GFS has developed a strong 
trough across the area while the European model (ecmwf) has a ridge. The GFS seems to 
be an outlier with the trough. Will continue with a dry and mild 
forecast at this time. Despite the cold fronts moving through the 
temperatures will continue to be at or above average for this time 
of year. 


&& 


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


$$