U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 141256 
Storm Prediction Center ac 141255 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0755 am CDT Tue Aug 14 2018 

Valid 141300z - 151200z 

..there is a marginal risk of severe thunderstorms over parts of 
the Central High plains...south-Central Plains...and eastern North 

Marginally severe thunderstorms are possible this afternoon into 
evening over parts of the north-central rockies/High Plains region, 
eastern North Carolina, as well as portions of Oklahoma and southern 

The mid/upper-level pattern over the contiguous U.S. Will be rather 
disheveled through the period, with the primary belt of northern- 
stream westerlies remaining over Canada. A broad cyclone now 
covering the central/northern Appalachians and much of the northeast 
will move slowly northeastward while gradually weakening to an open 
wave late this period or early day 2. Another cyclone -- currently 
covering much of the central/Southern Plains with a primary 
circulation center over central Kansas -- will move slowly east- 
northeastward through the period, also becoming an open-wave trough. 
By 12z the trough should be near the Kansas/MO line and over eastern OK. 

An embedded vorticity lobe -- now apparent in moisture-channel 
imagery over the hys/hlc area -- is forecast to dig southeastward to 
northern OK this evening then pivot eastward toward the Western 
Ozarks. A basal shortwave trough over the northern rockies occupies 
the southwest end of a persistent/positively tilted synoptic trough 
that extends to Hudson Bay. The shortwave trough will amplify 
steadily as it moves east-southeastward across Mt, reaching the 
western Dakotas and northeastern Wyoming by 12z. 

At the surface, a weak, wavy, quasistationary frontal zone was drawn 
from the coastal mid-Atlantic across eastern/central NC, central SC, 
northern portions of Georgia/al, then northwestward arching across the 
stl and Oma areas as a warm front, then southwestward to a surface 
low near speed. A cold front associated with the northern-stream 
synoptic trough was drawn from the James Bay region to south-central 
Minnesota, becoming quasistationary to the Central High plains. 

..north-central rockies/High Plains... 
Convection evolving from an ongoing cloud/precip shield over 
southeastern Montana/northeastern Wyoming may produce isolated severe hail 
through early afternoon as it moves east-southeastward. Additional 
thunderstorms are expected to develop this afternoon over higher 
terrain of eastern Wyoming and move east-southeastward to southeastward, 
offering hail as well as isolated severe gusts. 

Convective potential will be aided by a combination of favorable 
residual moisture (surface dew points commonly 50s f), diurnal 
heating south of the morning cloud/precip area, and Post-frontal 
upslope flow. The latter will provide enhanced storm-relative 
boundary-layer winds, as well as contribute to enough veering of 
flow with height to yield 40-45-kt effective-shear magnitudes. 
Buoyancy will be on the marginal side, with MLCAPE reaching 800-1200 
j/kg, but still sufficient to support multicells and transient 
supercells moving into a favorably well-mixed boundary layer for 
sporadic hail and strong-severe gusts. Activity should weaken this 
evening as it moves into lower-Theta-E air. 

Scattered thunderstorms are expected to develop this afternoon over 
the outlook area, offering the potential for isolated severe 
hail/gusts and a conditional, lower-end tornado risk. 

Satellite imagery shows a broad clear slot across the region, over 
the southern semicircle of the mid/upper cyclone. This feature is 
related to a corridor of midlevel drying analyzed on last night's 
00z upper-air charts, and evident in available soundings this 
morning. It should persist today, north of the southwest-northeast 
plume of profuse low/middle-level moisture, cloud cover and embedded 
convective precip that covers parts of north TX, southern/eastern OK 
and into the Ozarks. Forecast soundings suggest that sustained 
heating of a favorably moist boundary layer in that slot will offset 
modest lapse rates aloft over central/northeastern OK, and act in 
concert with somewhat greater lapse rates over western/northern 
areas nearer the cyclone core and in a zone of DCVA aloft. The 
result should be around 2000-3000 j/kg MLCAPE. 

Favorable buoyancy and low-level Theta-E will be juxtaposed with a 
belt of somewhat enhanced middle-level flow to aid in storm 
organization. Anvil-level flow, low-level winds and hodographs each 
are progged to remain modest on the meso-Alpha scale. However, 
localized vorticity enhancement along outflow/differential-heating 
boundaries may promote short-lived development/tightening of 
low-level rotation on the storm scale. As such, a marginal tornado 
risk exists, as well as locally strong-severe gusts and sporadic 

..eastern NC... 
Isolated to widely scattered thunderstorms may develop this 
afternoon near a surface Lee trough and residual frontal zone, 
across the eastern Piedmont/western coastal plain. The most intense 
cores may yield marginally severe hail/gusts. 

The frontal zone, while losing baroclinicity, still demarcates very 
moisture-rich Atlantic marine air to the south from lower Theta-E in 
VA, beneath the southern rim of somewhat enhanced mid/upper cyclonic 
flow. Low-level flow/lift along these boundaries should be weak, 
but in concert with strong surface diabatic heating, still 
sufficient for at least a few sustained cells to develop. By 
early/mid-afternoon, weak mlcinh and near-70 f surface dew points 
will be in place, supporting 2000-2500 j/kg MLCAPE, amidst roughly 
35 kt effective-shear magnitudes. 

.Edwards/Peters.. 08/14/2018 


Mesoscale Discussion

acus11 kwns 132244 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 132243 

Mesoscale discussion 1284 
National Weather Service Storm Prediction Center Norman OK 
0543 PM CDT Mon Aug 13 2018 

Areas affected...parts of northeastern New Mexico 

Concerning...severe potential...watch unlikely 

Valid 132243z - 140015z 

Probability of watch issuance...5 percent 

Summary...isolated storms may be capable of brief, marginally severe 
hail and strong, gusty winds through this evening. Watch issuance is 
not anticipated. 

Discussion...ascent on the fringe of a mid-level vorticity Max has 
combined with terrain-induced circulations to produce isolated 
storms over northeast New Mexico late this afternoon. Although 
surface dew points are relatively low (in the 40s to lower 50s), 
mid-level cooling/saturation has yielded adequate elevated buoyancy 
for a couple stronger cells. As they move south, a storm or two may 
acquire transient mid-level rotation, owing to modest deep-layer 
shear provided by 20-30 kt of northerly 500mb flow. Any such cell 
will be capable of isolated hail. A few stronger gusts may be 
possible as well, given the deep/well mixed boundary layer 
environment. Despite this potential, a lack of greater coverage and 
organization is expected to preclude watch issuance. 

.Picca/grams.. 08/13/2018 

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


Latitude...Lon 34160483 34430546 34790580 35230587 35650566 36540535 
36910367 36220320 34860321 34250367 34160483