fxus63 koax 192318 

Area forecast discussion 
National Weather Service Omaha/valley NE 
518 PM CST sun Feb 19 2017 

Short term...(tonight through wednesday) 
issued at 307 PM CST sun Feb 19 2017 

A low-latitude short-wave trough over the southern rockies and 
northwest Mexico this afternoon will phase with a polar-branch 
disturbance over the High Plains tonight with an elongated 
vorticity ribbon translating through the central and northern 
plains Monday into Monday night. In the low levels, strengthening 
south winds ahead of a deepening Lee trough over the High Plains 
have hastened the poleward flux of an increasingly moist 
boundary-layer into the mid MO valley with 20z dewpoints commonly 
in the upper 40s to lower 50s. 

Latest short-term convection-allowing model guidance suggests that 
initial thunderstorm development will occur across the Southern 
Plains this afternoon into evening with activity spreading north 
through central and East Kansas into portions of east NE and southwest 
Iowa after 08-09z. Steepening mid-level lapse rates coupled with the 
continued moistening of the environment and strengthening dynamic 
forcing for ascent will be supportive of isolated thunderstorms 
embedded within the broader precipitation shield. The showers and 
thunderstorms are expected to shift to the east of the area by 
late morning or early afternoon with no additional convective 
activity anticipated along the trailing wind shift/weak cold 
front which will advance across the area during the afternoon. 
Skies should clear from west to east Monday afternoon, allowing 
temperatures to warm to near or above record values for the day 
(see the climatology section below). 

The mid-level pattern will transition to quasi-zonal in the 
Tuesday-Wednesday time frame with an unseasonably warm and moist 
low-level air mass residing across the mid MO valley ahead of a 
cold front which will move into the area on Wednesday. A number of 
temperature records could be challenged through the first half of 
the work work (again, see the climatology section below) before a 
cooler air mass filters into the region from the north by 

Long term...(wednesday night through sunday) 
issued at 307 PM CST sun Feb 19 2017 

The primary feature of interest in the extended range is a 
vigorous short-wave trough and associated surface low which will 
track from the Central High plains through the mid and lower MO 
valleys Thursday into early Friday. We continue to see model 
fluctuations in track and amplitude of this synoptic system. The 
European model (ecmwf) has remained the most consistent of the available data, 
indicating the surface low developing from southeast Colorado Thursday 
morning to north-central or northeast Kansas by Thursday evening, 
prior to undergoing occlusion over central or eastern Iowa by 
12z/Friday. The deterministic GFS and gefs mean depict similar 
(albeit slightly farther south) evolutions, while the 12z 
Canadian model has now become the outlier with a farther north 
and slower solution. 

Under a scenario similar to the ECMWF, the chance of rain will 
increase from northwest to southeast across the area on Thursday. 
By Thursday night into early Friday, intense dynamic forcing for 
ascent coupled with rapidly deepening cold air on the backside of 
the surface cyclone will yield a change over to snow within the 
evolving deformation precipitation band. While exact amounts 
remain uncertain, current model trends suggest the potential for 
several inches of snow across parts of east-central and northeast 
NE into west-central Iowa. In addition to the snowfall, winds will 
strengthen considerably from the north Thursday night into Friday 
with areas of blowing and drifting snow possible. The snow is 
currently expected to taper off Friday evening with additional 
chances for light snow on Saturday into Sunday. 

Temperatures late this week into next weekend will be notably 
colder with afternoon readings generally in the 30s north and 
central with 40s southeast. 


Aviation...(for the 00z tafs through 00z Monday evening) 
issued at 518 PM CST sun Feb 19 2017 

Low clouds will increase from the south this evening, with MVFR 
conditions likely at least part of the night into Monday morning. 
The may also be some restriction to visibility with fog. The chance 
for precipitation is highest at koma and did mention a period of 
showers there. Isolated thunder is possible, but coverage seemed 
like it would be too low to mention at this time. Will amend if 
needed and address this again in the 06z tafs. 


issued at 307 PM CST sun Feb 19 2017 

Given the unseasonably warm conditions expected, the following are 
the record high and maximum low temperatures: 

Monday/20th: Omaha - 67/1930, 50/1930 
Lincoln - 71/1991, 51/1930 
Norfolk - 66/1930, 37/1996 

Tuesday/21st: Omaha - 72/1977, 53/1930 
Lincoln - 74/1991, 51/1930 
Norfolk - 74/1995, 40/1930 

Wednesday/22nd: Omaha - 71/1982, 42/1933 
Lincoln - 74/1982, 46/1896 
Norfolk - 72/1995, 37/1998 


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