Probability of a tornado within 25 miles of a point. Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk
Area (sq. mi.)
Some Larger Population Centers in Risk Area
No Risk Areas Forecast
Probabilistic Damaging Wind Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
SPC AC 190554
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1254 AM CDT Sat Aug 19 2017
Valid 191200Z - 201200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR CENTRAL
NEBRASKA AND PORTIONS OF NORTHWEST KANSAS...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR MUCH OF
NEBRASKA AND NORTHERN KANSAS...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM CENTRAL
OHIO INTO CENTRAL PENNSYLVANIA...
Scattered severe thunderstorms are possible across parts of Nebraska
and Kansas late this afternoon and through the evening. Isolated
severe storms are possible from Ohio into central Pennsylvania
during the afternoon and ending by the early evening.
Early morning water-vapor imagery shows a vigorous shortwave trough
over the Midwest and an upstream lower-amplitude disturbance over
WY. Both features are forecast to move generally eastward during
the period and reach the Lower Great Lakes and the central High
Plains, respectively, by late afternoon. A surface trough will
sharpen during the day across the central High Plains as a low
develops east across Manitoba. A relatively ill-defined surface
pattern is forecast across the upper OH Valley with high pressure
centered over the southern Appalachians.
The influence of a mid-level ridge will abate during the day as a
mid-level vorticity maximum moves into western NE by afternoon.
Will tailor this outlook towards a NAM/SREF median moisture
scenario. The 00Z GFS is an outlier and is dry biased according to
early morning surface observations across the central Plains (1-3
degrees C too low). The dichotomy in moisture/buoyancy depictions
by the aforementioned model guidance is apparent during the late
afternoon. It seems most probable a corridor of upper 50s-lower 60s
boundary layer dewpoints will reside across NE/KS. As the mid-level
disturbance and associated weak forcing for ascent overspreads the
warm sector coupled with strong heating eroding convective
inhibition, isolated thunderstorms are likely by late
afternoon/early evening. Very steep surface-500 mb lapse rates
ranging from 8-9 degrees C/km will favor intense downdrafts with the
more robust cores. Veering flow within this same layer with modest
mid-level westerlies will yield 30-40 kt effective
shear---sufficient for some storm organization. Large hail/severe
gusts may accompany the more intense thunderstorms. As a southerly
LLJ strengthens during the evening, a continuation of some
strong/severe potential may occur farther east into east-central
NE/north-central KS through the evening.
...OH eastward into central PA...
A plume of modestly moist low levels is forecast to extend northeast
across the OH Valley ahead of a potent mid-level impulse. Weak
buoyancy will contribute to convective development as early as
midday over OH. Forecast soundings suggest some marginal storm
organization potential. The primary threats with the stronger
storms will be localized pockets of damaging gusts and perhaps a few
updrafts capable of marginally severe hail. This activity will
diminish by early evening owing to the loss of instability.
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z