Area forecast discussion 
National Weather Service Omaha/valley NE 
640 PM CDT Sat Apr 19 2014 

Short term...(tonight through tuesday) 
issued at 309 PM CDT Sat Apr 19 2014 

Rain/thunderstorm chances through Monday morning are the primary 
forecast concerns. 

Frontal boundary has slipped into northeast Nebraska this afternoon. 
Ahead of the front...temperatures have climbed well into the 70s on 
brisk south to southwest winds...however moisture has been slow to 
return. Dew points were generally in the middle and upper 40s...with 
lower 50s readings well south in central Kansas and Oklahoma. A 
weak middle level wave as seen in water vapor imagery and rap height 
fields was moving through northeast Nebraska...and was triggering 
middle level returns on radar across northeast Nebraska and eastern 
South Dakota. However only virga is expected there as low 
humidities exist below middle level cloud layer. Congestus clouds 
were also noted in south central Nebraska in area of increasing 
but still weak instability. 

Meanwhile...upper trough drifting east through Arizona will 
gradually work toward the plains overnight and eventually east of 
the area Monday. Ahead of this trough...a couple of middle level waves 
will ripple northeast across Nebraska...and should trigger 
scattered showers or storms focused near surface front. Best 
chance for thunderstorms appears to come later this evening and 
overnight as convection expected to develop in north central 
Kansas or south central Nebraska moves into our area. The slow 
moisture return was holding instability in check this afternoon 
but is expected to increase late in the day or early evening. Middle 
level lapse rates of 8.5-9 c/km were already in place in western 
Kansas/Nebraska over top of increasing low level convergence 
northeast of surface low in eastern Colorado. Various synoptic and 
mesoscale scale models (nam/GFS/rap/hrrr/hopwrf) indicate convection 
popping in north central Kansas and south central Nebraska 
sometime in the 23z to 02z timeframe...and develop/spread this 
northeast along frontal zone during the evening. Severe parameters 
are not impressive when storms arrive overnight...elevated cape 
800 j/kg and 0-6km shear near not expecting more than 
small hail and gusty winds. Chances will decrease from southwest 
to northeast after midnight as this complex rolls out of our area. 

Then chances begin to increase again Sunday morning with the 
approach of upper trough. Surface dew points will continue to 
rise...likely into the middle to upper 50s by afternoon...with cold 
front bridging north toward the South Dakota border. Afternoon 
surface convective available potential energy should approach 1500 j/kg but shear is limited. So 
again severe chances are small...but continued development of 
showers/storms appears likely through the afternoon and evening 
given cooling aloft from upper trough. Will have fairly high precipitation 
chances Sunday afternoon and night for much of the southern two- 
thirds of the County Warning Area before front finally begins moving southeast late 
Sunday night. Lingering showers/storms near I-80 and south will 
remain in the forecast Monday morning...then clearing skies with 
surface high pressure and ridging aloft building in will rule the 
forecast into Tuesday. 

Long term...(tuesday night through saturday) 
issued at 309 PM CDT Sat Apr 19 2014 

The longer term period will begin with upper ridge axis shifting off 
to the east with the approach of another trough sliding into The 
Rockies. That trough will work through the plains Wednesday and 
Thursday before lifting through the Great Lakes Friday and Saturday. 
Will have precipitation chances in the forecast until that passes 
by...with a chance for severe storms at middle week. 

Thunderstorms are possible Tuesday night as warm advection commences 
under diffluent middle level flow ahead of western trough. Middle level 
instability is not that strong then...but scattered showers/storms 
are certainly possible. On Wednesday...surface low pressure will 
intensify in the High Plains with dryline setting up in western 
Nebraska. Warm advection continues over our area leading to 
lingering chance for showers/storms. But better chances come 
Wednesday night as low/front/dryline move into eastern Nebraska 
under dynamic middle level flow and 60kt low level jet. Timing and 
magnitude of these features will still have to be fine-tuned with 
later forecasts...but this certainly bears watching. 

Most of the thunderstorm activity will be exiting Thursday 
morning...but could see some redevelopment of showers especially in 
our north and east during the afternoon as middle level cold pool 
rotates through the region. Cooler air will follow with highs 
generally in the 60s to end the week. 


Aviation...(00z tafs for kofk...klnk and koma.) 
Issued at 634 PM CDT Sat Apr 19 2014 

Surface cold front is very near kofk as of 23z and will remain 
nearly stationary through most of the night before lifting back to 
the north late tonight. The front will be the focus for some scattered 
rain showers overnight and will include a prevailing group at kofk during 
the time when models indicate the lift is strongest. We will leave 
the koma/klnk tafs dry at this time as most of the precipitation should focus 
near the front. Southerly flow will continue on sun and we may see 
isolated-scattered rain showers again develop during the afternoon but timing and 
placement of activity is to uncertain to include at this time. 


Oax watches/warnings/advisories... 



Short term...dergan 
long term...dergan 

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