U.S. Severe Weather Forecast (Convective Outlook)

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000 
acus01 kwns 171254 
swody1 
Storm Prediction Center ac 171252 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0652 am CST Fri Jan 17 2020 


Valid 171300z - 181200z 


..no severe thunderstorm areas forecast... 


... 
thunderstorms are expected from southern and central Texas to the 
southern Ozarks today into tonight. No severe weather is 
anticipated. 


... 
A progressive upper-air pattern will feature a well-defined 
synoptic-scale trough, now negatively tilted from coastal British Columbia and the 
Pacific northwest across the Great Basin and northern Arizona. This 
trough will move eastward through the period, phasing with an 
initially weak shortwave over the Central High plains to form a 
closed 500-mb low over northern Minnesota by 12z. At that time, the trough 
should arc from the low across northeastern IA, north-central MO and 
northeastern OK. The southern extension of the leading shortwave 
trough is apparent in moisture-channel imagery across eastern nm to 
southern baja. This feature will move eastward across western OK 
and west/northwest Texas today, weakening and accelerating eastward 
across much of the Ohio and Tennessee valleys overnight. 


At the surface, 11z analysis showed a wavy cold front from Atlantic 
waters northeast of the Bahamas, across south FL, west-northwestward 
over the north-central/northwestern Gulf, becoming quasistationary 
over the middle Texas coastal plain near vct, southwestward across 
eastern nuevo Leon. The western part of the frontal zone over Texas 
will become diffuse amidst a strengthening low-level warm-advection 
regime related to cyclogenesis now occurring over the southeastern 
Montana/northeastern Wyoming region. That low should deepen and move across 
the upper Mississippi Valley around 12z, with cold front reaching 
northwestern IL, south-central MO, southeastern OK, and central/ 
southwest Texas. 


..Southern Plains... 
Isolated to widely scattered, episodic thunderstorms are forecast 
across the outlook area through the period. While a few 
thunderstorms may occur outside these regimes, the primary 
contributors to total thunderstorm coverage of at least 10% should 
be: 
1. A corridor of deep ascent currently extending from northwest Texas 
south-southwestward across west-central Texas into northwestern 
coahuila. This appears to represent a combination of modest DCVA 
preceding the leading shortwave trough with the western rim of 
low-level warm advection. This convection should shift 
northeastward and mostly weaken through the early evening. However, 
associated thunder potential in the upward vertical velocity plume may cycle back up 
again tonight ahead of the cold front, in the tail section of an 
increasingly moist, 40-60-kt low level jet developing in response to 
north-Central Plains cyclogenesis. 
2. In the last few hours of the period (pre-dawn hours tomorrow), 
the low-level cold front will encounter the same moistened sector 
and may initiate a narrow band of convection with embedded 
thunderstorms. 


In both regimes, the bulk of supportive buoyancy will be elevated 
and decreasing poleward, modulated by modest lapse rates and Low 
Cape density in the deep convective layer. Effective-shear 
magnitudes mostly should remain around 35 kt or less. As such, 
severe potential appears too low for unconditional probabilities. 


.Edwards/Gleason.. 01/17/2020 


$$ 

Mesoscale Discussion


000 
acus11 kwns 171232 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 171232 
iaz000-mnz000-nez000-sdz000-171800- 


Mesoscale discussion 0059 
National Weather Service Storm Prediction Center Norman OK 
0632 am CST Fri Jan 17 2020 


Areas affected...portions of eastern NE...western/central 
Iowa...central/eastern South Dakota...and southwestern Minnesota 


Concerning...heavy snow 


Valid 171232z - 171800z 


Summary...moderate to heavy snowfall, with rates around 1 inch per 
hour, will develop and then spread northeastward this morning. 


Discussion...within large-scale upper troughing over much of the 
western/central conus, a lead shortwave trough will continue to 
eject northeastward this morning across the Central Plains and 
towards the upper Midwest. The 12z sounding from Omaha NE shows 
strong southerly winds in the 925-700-mb layer. This low-level warm 
advection and additional large-scale ascent preceding the shortwave 
trough are promoting a broad area of precipitation this morning 
across parts of the southern/Central Plains. From roughly the NE/Kansas 
border northward, the low-level thermodynamic profile should remain 
cold enough to support snow as the dominant precipitation type. 
Strong lift is forecast to occur through 18z in the dendritic growth 
zone from eastern NE into parts of western/central IA, 
central/eastern SD, and southwestern Minnesota. Light to locally moderate 
snow ongoing across central/eastern NE and vicinity is likewise 
expected to increase in intensity through the remainder of this 
morning as this broad area of snow shifts northeastward. Snowfall 
rates around 1 inch per hour appear likely by 15z over parts of this 
region, with locally higher rates possible through 18z within the 
most intense portion of the snow band. 


.Gleason.. 01/17/2020 


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


Attention...WFO...mpx...dmx...fsd...oax...abr...Gid...lbf... 


Latitude...Lon 43029367 41939304 41329266 40919287 40719342 40659445 
40599578 40639680 41019737 41549798 42079861 42539919 
42989948 43759950 44679863 45509701 45559549 44889450 
44019380 43029367