U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 180455 
Storm Prediction Center ac 180453 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1153 PM CDT Tue Oct 17 2017 

Valid 181200z - 191200z 

..no severe thunderstorm areas forecast... 

thunderstorm potential today will focus across portions of the 
Florida Peninsula as well as over parts of western New Mexico and 
far West Texas. No severe storms are expected. 

Predominately zonal upper pattern is expected across the Continental U.S. For 
the majority of the period. Some modest pattern amplification is 
possible after 00z west of The Rockies as a strong shortwave trough 
approaches the Pacific northwest. Shortwave trough currently moving 
through Saskatchewan is expected to continue eastward into western 
Ontario while maturing. Associated surface low will take a similar 
path while an attendant cold front moves eastward/southeastward 
across the Central Plains and upper Midwest. By 00z Thursday, this 
cold front will likely extend from western Upper Michigan southwestward 
into western Kansas. Thereafter, frontolytic processes, encouraged by a 
deepening Lee trough across the northern High Plains, will lead to a 
weakening of the portion of the front across the Central Plains. 

Dry and stable conditions are anticipated across much of the Continental U.S.. 
isolated to scattered thunderstorms are possible across Florida as modest 
surface convergence occurs amidst a moist and unstable airmass. 

Farther west (across southwest nm), increased mid-level moisture 
associated with a weak shortwave trough (currently moving across 
baja california) combined with modest low-level moisture and steep 
low-level lapse rates will support 100-300 j/kg of MLCAPE during the 
afternoon. Lift provided by the shortwave trough, in tandem with 
favorable orographic circulations, will interact with this 
instability to support isolated to widely scattered thunderstorms. 

.Mosier/Elliott.. 10/18/2017 


Mesoscale Discussion

acus11 kwns 151903 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 151903 

Mesoscale discussion 1719 
National Weather Service Storm Prediction Center Norman OK 
0203 PM CDT sun Oct 15 2017 

Areas affected...from eastern Ohio across Pennsylvania and into 
western/central New York 

Concerning...severe potential...watch possible 

Valid 151903z - 152000z 

Probability of watch issuance...40 percent 

Summary...a narrow line of low-topped showers and thunderstorms will 
develop eastward with a threat of strong to severe wind gusts this 

Discussion...multiple segments of low-topped showers and storms are 
developing from southwest Ontario into eastern Ohio along an 
intensifying cold front. The strongest area of lift currently exists 
over Canada, and this is where sporadic lightning activity is 

Surface observations show gradually warming temperatures, with 
dewpoints in the lower 60s. The deeper moist plume exists mainly 
just ahead of the front, with drier air/lower precipitable water values from the 
Appalachians into New England. Temperatures aloft are not very cold 
except for well behind the front into Michigan, leading to only weak 
cape values. In addition, much of the instability exists mainly in 
the parts of the atmosphere. 

With mean winds in excess of 40 kt in the lowest few km, these 
showers and storms along the cold front will likely Transfer 
momentum to the surface with 40-50 mph wind gusts possible, and 
perhaps an isolated severe gust. The most likely area for severe 
winds would appear to be over New York where mean wind speeds are 
strongest, and in closest proximity to the shortwave trough. In 
addition, veering winds with height and sufficient srh may result in 
embedded areas of rotation in qlcs fashion. This, however, will be 
dependent on sufficient instability being present. Ample heating 
over New York lends some confidence of this possibility. 

.Jewell/Hart.. 10/15/2017 

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


Latitude...Lon 45137382 44617383 43857421 42877523 41847651 40797811 
40338016 40308120 40628143 41138132 41808085 42798018 
43597918 43997754 44407616 44927537 45137464 45137382