274 
fxus63 kgid 172038 
afdgid 


Area forecast discussion 
National Weather Service Hastings NE 
338 PM CDT Wednesday Mar 17 2010 


Short term...tonight through 12z Friday. Biggest forecast 
challenge will be chances of precipitation Thursday night. 


Water vapor reveals a positively tilted high amplitude ridge 
stretching from the southern rockies into the northern plains. A 
developing longwave trough is just entering the West Coast region. 


The remaining stratus in the central/southeastern County Warning Area should 
continue to shrivel with strong subsidence occurring behind a 
shortwave trough that moved through earlier today. 


Strong subsidence will ensure a dry forecast for tonight and 
tomorrow. By Thursday night...the aforementioned trough approaches. 
The trend is toward an earlier arrival to the chance of 
precipitation with more progressive solutions being favored. 
Still...air and soil temperatures will make it more difficult for 
snow to both fall and stick respectively...so not expecting any 
accumulation of snow through Thursday night. 


Knocked down temperatures just a tad for Thursday highs and 
tightened up the temperature gradient for Thursday night as the cold 
front approaches. 


Long term...starting 12z Friday through Wednesday. Model 
consensus continues to indicate an upper level trough will push 
across the central Continental U.S. Friday into Saturday...with an associated 
surface front pushing across the Central Plains late Thursday 
into Friday. Frontal passage across our County Warning Area should be complete by midday 
Friday. Strong model agreement also suggests a strong push of cold 
air will follow Post-fropa...with 850mb temperatures plummeting to 
around -8 c by 12z Saturday. Strong low to middle level frontogenesis 
along and behind the surface front will promote wide spread 
precipitation across the County Warning Area Friday into early Saturday. 
Precipitation will then come to an end across the County Warning Area from 
northwest to southeast as the band of frontogenesis also pushes 
off to the southeast of the area during the day Saturday. 
Precipitation type at the beginning of the event will likely be 
rain or a rain and light snow mix. As cold air quickly filters in 
behind the surface front during the day Friday...thermodynamic 
profiles will quickly cool to levels conducive for snowfall. Quantitative precipitation forecast 
fields from the ec...GFS and Gem all indicate three to four tenths 
of an inch of liquid precipitation across our Nebraska 
zones...with closer to a tenth of an inch across our Kansas zones 
on Friday. Another three to four tenths of an inch of liquid 
precipitation is then indicated across our Kansas zones Friday 
night...with perhaps an additional tenth of an inch across our 
Nebraska zones. Additional light precipitation will linger on 
Saturday...especially across our southeast. Assuming a 10:1 snow 
ratio would yield 2-4 inches of storm total snowfall across much 
of the County Warning Area through Saturday...with locally 5 inches possible 
farther south. There are however several mitigating factors to 
achieving these snowfall accumulations. First off will be the very 
warm temperatures in the days leading up to the event. High 
temperatures in the 50s and 60s Wednesday and Thursday will help 
warm ground temperatures. Soil temperatures across the County Warning Area are 
already well above freezing. Finally...with the onset of the event 
providing rain and much of the early snowfall melting...the moist 
content of the surface will only further inhibit snowfall 
accumulations. We will be well into the event before these 
mitigating factors are overcome...and currently expect some 
snowfall accumulations across our extreme northwest by midday 
Friday...with the rest of the County Warning Area following later in the day 
Friday into Friday night. Assuming this timing holds true...and 
assuming snow ratios closer to 8:1 to account for wet content of 
the snow...currently believe snowfall accumulations in the 1-3 
inch range will be possible across the County Warning Area...with three inches 
certainly being on the high end. Previous forecast had this well 
in hand and so only made minor tweaks to the current snow 
forecast. As if Friday and Saturday wont be dreary enough...strong 
pressure rises Post-frontal passage will promote strong northerly winds 
Friday and Friday night. With met and mav guidance suggesting 
sustained wind speeds in the 20-25 kts range...have no problem 
believing we could see gusts in excess of 30 kts. Should these 
winds occur during periods of moderate snowfall...visibilities 
could certainly be restricted to near a half mile. Should this 
occur...the need for a Winter Weather Advisory could present 
itself...despite the fact we may not be seeing all that much snow 
accumulation. 


A tight temperature gradient is anticipated across the County Warning Area Friday as 
the front pushes through the area. Kept 30s and low 40s going across 
the northwestern two-thirds of the County Warning Area...with low to middle 50s across 
our southeast. Will need to continue evaluating temperatures across 
our southeast should frontal passage occur ahead of schedule. Kept lows on 
Friday night in the 20s through most locations. With northwest 
surface flow and continued cold air advection at the surface as high pressure moves into 
the area...kept Saturday diurnals in the 10-13 degree 
range...yielding Saturday highs in the low to middle 30s. 


Upper level ridging and return flow at the surface commence on 
Monday and continues through Tuesday. This should lead to a nice 
warm up for the early part of next week with mex guidance suggesting 
highs soaring into the 50s and 60s. There are some indications of 
another system pushing through by middle next week...so went ahead and 
increased cloud cover for next Wednesday as well as introduced 
slight chance probability of precipitation. 


&& 


Aviation...18z kgri taf. LIFR stratus should be on its way out 
quickly this afternoon as large scale subsidence take place. A 
middle-level deck of cloudiness will move in by late morning Thursday 
in advance of the next wave moving in. Light and variable wind 
will eventually become southwest tonight...but will remain light. 
VFR visibility is expected along with light wind. 


&& 


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


$$ 


Heinlein 

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