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Area forecast discussion 
National Weather Service Hastings NE 
533 am CST Friday Nov 21 2008 


Aviation...12z taf. Quiet...VFR conditions expected through this 
taf period. High pressure at the surface will continue to 
dominate the pattern...and will slowly shift to the southeast 
through the day. This will bring an increase in southerly 
winds...with speeds increasing to near 20 miles per hour this afternoon before 
tapering off this evening. As far as clouds go...scattered 
middle/upper level clouds will bring mostly clear/partly cloudy 
skies...with lowest ceilings expected to remain at/above 7k feet. 


&& 


Previous discussion... /issued 429 am CST Friday Nov 21 2008/ 


Discussion...latest water vapor imagery from this early morning 
reveals a weak ridge sitting over the central and northern plains 
while upstream...a small but potent short wave is seen plowing 
across the northern rockies. Recent surface analysis shows an 
Arctic like dome of high pressure positioned from southern Canada to 
the Gulf Coast region of Texas. Much colder and drier air is 
entrenched behind this boundary with 850mb temperatures of -5 to 
-20c seen from the Central Plains into the Great Lakes region. 


For today into tonight...the aforementioned wave over the northern 
rockies...will slide east into the plains by late this afternoon. 
Ahead of this wave...the Lee trough will deepen quickly over the 
High Plains this morning to early afternoon while the surface high 
shifts eastward into the MS River Valley. This will allow winds to 
turn around to south and increase to around 20 to 25 miles per hour range with 
BUFKIT momentum Transfer showing gust potential up to 30 miles per hour by 
early afternoon. Despite the strong south winds making it look 
favorable for warmer temperatures this afternoon...only some weak 
warm air advection is shown for the forecast area as mainly cold air 
recycled around the back side of the high is shown to occur. Given 
850mb temperatures of -2 to -6c across the area and only shallow 
mixing...will aim for highs in the middle to upper 30s near Grand 
Island and Hastings...to the lower 40s near Cambridge and 
Phillipsburg. 


As the region heads into tonight...the influence of the upper wave 
will increase across the region from middle evening into the overnight 
hours as a 90-100 knots upper jet streak rounds the base of the short 
wave. Although the majority of the energy from this wave will stay 
closer to the middle level circulation across the Dakotas...some 
features from this wave may still bring a slight threat for 
precipitation. Modest isentropic lift around the 285k layer in 
combination with a tropopause fold down to 500mb providing for a rapid 
increase in middle level vorticity and hence stronger positive vorticity advection...are shown 
to push some moisture into the dendritic layer across the 
northeastern half of Nebraska and subsequently clipping areas north 
of a Loup City to York line. However...a very dry lower 5 to 7 kft 
of the atmosphere will remain across the area and suspect any precipitation 
falling over central Nebraska will end up as virga. 


For Saturday into Saturday night...the wave will slide east of the 
region with a relatively flat but progressive flow pattern remaining 
behind across the plains. With little middle to upper forcing...a dry 
forecast still looks on track for this period. The pattern will 
allow the Lee trough to continue deepen across the High Plains which 
will subsequently push the colder air northeast out of the area. 
Will aim for highs in the upper 40s to middle 50s for highs on Saturday. 


A clipper system is then shown to slide southeast across the area 
Sunday night with a weak front kicked out ahead of the system and 
across the County Warning Area on Sunday. This system looks to have little middle to 
upper support across the Central Plains and with moisture remaining 
very limited...this system will likely result only in some cloud 
cover. Nonetheless...the orientation of the upper jet streak from 
the central rockies into the plains will produce a nice plume of 
cirrus streaming off the mountains for most of the day. Their is 
some potential for this cirrus to highly limit any heating behind 
the boundary with temperatures not warming more than 10 to 15 
degrees from the morning lows. Will keep temperatures only a few 
degrees below guidance values at this point...but this will to be 
watched very closely over the next 48 hours as temperatures could end up 
much colder than prognosticated. 


&& 


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


$$