U.S. Severe Weather Forecast (Convective Outlook)

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Day Three

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acus01 kwns 231946 
swody1 
Storm Prediction Center ac 231945 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0145 PM CST Thu Feb 23 2017 


Valid 232000z - 241200z 


..there is a slight risk of severe thunderstorms over northeast 
Kansas... 


..there is a marginal risk of severe thunderstorms from northeast 
Kansas through southeast Nebraska...northern Missouri into Iowa... 


... 
Thunderstorms may produce isolated severe hail across portions of 
northern Kansas and far southern Nebraska into Iowa and northern 
Missouri this evening and overnight. 


... 


Previous forecast appears on track, and only minor adjustments have 
been made. Elevated thunderstorms should develop from north central 
to northeast KS, moving into southeast NE and southern Iowa this 
evening where a progressive shortwave trough and strengthening 
low-level jet will augment isentropic ascent and destabilization 
north of a warm front currently located across southern Kansas. While 
updrafts will be elevated, effective shear will be sufficient for a 
few storms to develop mid-level rotation which, in addition to steep 
mid-level lapse rates and 500 j/kg MUCAPE, will promote a modest 
threat for mainly large hail. 


.Dial.. 02/23/2017 


Previous discussion... /issued 1029 am CST Thu Feb 23 2017/ 


..Central Plains and middle Missouri Valley/Midwest... 
Limited moisture observed across the central and Southern Plains 
(per surface observed and 12z upper-air data/soundings) casts some 
uncertainty regarding the timing/extent of convective development, 
while otherwise likely limiting the overall potential for severe 
storms later today. 


This limited moisture and the existence of an appreciable elevated 
mixed layer is expected to preclude surface-based development 
through the afternoon, although an increase in elevated thunderstorm 
development may begin to occur around and after sunset (as early as 
23z-00z time frame). Aided by DPVA and increasing isentropic ascent, 
this development should mainly be focused across north-central 
Kansas just to the north of an eastward-developing surface low and 
north of a sharpening warm front. While moisture/overall buoyancy 
will be meager, very steep mid-level lapse rates and long 
straight-line hodographs within the cloud-bearing layer could yield 
some hail/locally gusty winds, with latest forecast soundings 
generally suggesting that storms should generally be rooted near or 
above 850 mb. Any such threat should be semi-focused across 
north-Central/Northeast Kansas this evening, but other 
strong/locally severe thunderstorms could occur across far southern 
Nebraska into Iowa and northern Missouri through the overnight. 


$$ 

Mesoscale Discussion


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sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 231231 
nez000-sdz000-wyz000-231700- 


Mesoscale discussion 0199 
National Weather Service Storm Prediction Center Norman OK 
0631 am CST Thu Feb 23 2017 


Areas affected...portions of western and northern Nebraska...and 
extreme south-central South Dakota 


Concerning...heavy snow 


Valid 231231z - 231700z 


Summary...heavy snowfall rates around 1 inch/hour are expected 
through the morning from part of north-central NE (in vicinity of 
Keya Paha County through Cherry and Sheridan counties, and perhaps 
into western parts of the NE panhandle). This snowfall rates should 
also develop into extreme south-central South Dakota (primarily from Bennett 
to Tripp counties). 


Discussion...trends in mosaic radar imagery indicated mesoscale 
banding developed around 09z, and has persisted through 12z so far 
across mainly northern Cherry County to Sheridan County. Surface 
observations show this precipitation is in the form of snow, with 
this region located north of the wet-bulb 0c line which at 12z 
extended from northeast to southwest NE. Northeasterly surface 
winds are expected to increase some this morning into the afternoon, 
as an area of low pressure forms across eastern Colorado and deepens, 
tracking into west/southwest Kansas this afternoon. This indicates 
cooler temperatures should be maintained across the discussion area 
today to sustain the precipitation type as snow. 


Trends in mosaic radar imagery indicated some increase in intensity 
within the snow bands. This trend should persist through this 
morning, as height falls/DPVA spread into western and central NE, 
with the approach of the Great Basin trough, further enhancing 
midlevel frontogenesis within the 600-700-mb layer. In addition, 
11z rap forecast soundings indicated the upward vertical motion in 
the 600-700-mb layer will occur within the favorable dendritic 
growth zone this morning, supporting the heavier snowfall rates. 


.Peters.. 02/23/2017 


..please see www.Spc.NOAA.Gov for graphic product... 


Attention...WFO...lbf...unr...cys... 


Latitude...Lon 43239975 42779971 42350100 42020226 41670354 41760409 
42230389 42740270 43040153 43239975