Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0754 AM CDT Fri Aug 17 2018

Valid 171300Z - 181200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
NORTHEAST AND MID-SOUTH REGIONS...

...SUMMARY...
The most concentrated risks of severe storms today are over parts of
the inland Mid-Atlantic to western and central New England, with
damaging to severe gusts and sporadic hail, and over parts of
Arkansas and Mississippi, for damaging wind.

...Synopsis...
In mid/upper levels, a persistent area of ridging will
move/redevelop westward across the southwest through the period. 
Meanwhile, a progressive pattern will persist over the northern tier
of states, south of the belt of strongest westerlies over Canada.  A
leading, positively tilted shortwave trough was apparent in
moisture-channel imagery from the neck of ON through a weak/closed
low over northern IL, southwestward over the Ozarks.  This trough
will shift eastward through the period, becoming still more
positively tilted as its northern part moves faster.  By 00Z, the
trough should extend from the middle/lower St. Lawrence Valley of
southeastern Canada across extreme southern ON to northern IN and
southern MO.  By 12Z, the trough should extend from the Canadian
Maritimes across ME, northern NY, and OH, to the Mid-South.  An
upstream shortwave trough -- now located over the WA/OR Cascades and
coastal northwestern CA -- is forecast to move slowly eastward to
the northern Rockies in ID/MT by the end of the period. 

At the surface, A wavy frontal zone was analyzed at 11Z from Long
Island across southern ON, southern Lake Michigan, eastern IA,
south-central KS, and the TX Panhandle.  A frontal-wave low should
consolidate along this boundary tonight, over New England, as the
mid/upper trough approaches.  By the end of the period, the front
generally should extend from there southwestward down the Ohio
Valley to the Red River region of southern OK and north TX. 
However, the baroclinic zone may remain rather poorly defined with a
good deal of outflow to its south, where the bulk of convection is
expected.

...Northeast...
Scattered thunderstorms in bands and clusters are expected to
develop this afternoon and move eastward to east-northeastward
across the area, offering the risk of damaging gusts and sporadic
hail.  

Some destabilization should occur over central/eastern New England
ahead of an ongoing cloud/precip plume over NY, and an isolated
damaging gust cannot be ruled out from the most intense cores in
that regime.  The more sustained and concentrated convective
potential, with occasional damaging to severe winds, is forecast
behind the morning cloud/precip plume and along/southeast of the
frontal zone as the richly moist boundary layer diabatically
destabilizes.  MLCAPE should range from the 2000-3000 J/kg range
over southern New England, NJ and the lower Hudson Valley region
where boundary-layer theta-e and heating each will be maximized, to
1000-1500 J/kg over the northern parts of the outlook area.

Even though the mid/upper trough will be weakening with time as it
approaches the area, that approach will lead to height falls,
large-scale DCVA/cooling aloft, and strengthening of mid/upper winds
and, to a limited extent, low-level and deep-layer shear.  Forecast
soundings suggest about 25-35 kt effective-shear magnitudes, but
also, enough low-level hodograph curvature to yield marginal SRH for
at least transient supercell characteristics.  The primary storm
mode should be multicellular, with marginally severe hail and
sporadic damaging wind.

...Central Appalachians to southern Plains...
Multiple episodes of thunderstorms are expected across this lengthy
corridor through at least this evening, including several ongoing
clusters of convection that may persist through the morning long
enough to encounter a favorably heated/destabilizing boundary layer
and increase their potential for strong/severe gusts.  Additional
convection should form along outflow and differential-heating
boundaries left by morning clouds/precip.  The preconvective air
mass will be characterized by rich low-level moisture, with dew
points commonly upper 60s to mid 70s F, and pockets of sustained
surface heating to boost low-level/subcloud lapse rates.  Midlevel
lapse rates will increase with westward extent, contributing to most
of the increase in preconvective MLCAPE from around 1000 J/kg in the
central Appalachians to around 3000 J/kg over parts of OK/AR.

Relative maxima in severe potential may develop within this swath,
dependent on mesoscale developments such as favorable boundary
intersections/interactions and/or upscale cold-pool organization of
one or more of the ongoing clusters.  One increasingly concerning
candidate for just such organization is the loosely organized
complex now crossing the southeastern KS, southwestern MO,
northwestern AR, and northeastern OK area.  This activity will have
a boundary from preceding convection astride which to forward-
propagate over AR.  The complex then could move southeastward into a
favorably destabilizing, large-buoyancy air mass by early afternoon
over central AR and beyond, with mainly a wind threat.  Otherwise,
any relative foci/maxima for severe potential remain too uncertain
in timing/morphology to lay out another 15% unconditional threat
area at this time. 

...Central/southern High Plains...
Scattered primarily afternoon thunderstorms are expected to develop
over the Front Range, foothills and adjacent elevated terrain,
moving east-southeastward to southeastward over the adjoining High
Plains for a few hours before weakening this evening.  The mature
phases of this activity will pose a risk for isolated severe
gusts/hail.  A narrow meridional corridor of preconvective MLCAPE
1000-2000 J/kg is progged to develop amidst steep low/middle-level
lapse rates and adequate residual moisture.  Forecast vertical wind
profiles show pronounced veering with height (directional shear);
however, low/middle-level speeds will be weak, limiting bulk shear. 
Still, given the steep lapse rates and a belt of 40-50-kt anvil-
level flow forecast to cross the area north of the anticyclone
aloft, some of the convection may become organized, with aggregated
outflow production possible. 

...ID and vicinity...
Favorable destabilization is expected following morning
clouds/convection to support additional/afternoon development 
The approaching mid/upper-level trough will yield increasing
large-scale ascent/cooling aloft related to DCVA and lift in the
left-exit region of a cyclonically curved upper-level jet streak. 
As the associated steepening of mid/upper lapse rates spreads over a
diabatically heated/destabilized boundary layer, sufficient
low-level moisture should remain through the mixing process to
support 500-1500 J/kg MLCAPE.  A narrow corridor of favorable
buoyancy also may develop over portions of northern ID and western
MT ahead of morning convection persisting into afternoon.  Also,
mainly over the southern part of the outlook area where mid/upper
winds will be strongest, increasing deep shear is forecast. 
Well-mixed subcloud layers will promote a predominant threat of
isolated severe gusts.  Dry lightning also is possible under young
bases and off the edge of cores in this regime for fire-threat
purposes; see the SPC day-1 fire-weather outlook for more details.

..Edwards/Broyles.. 08/17/2018

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1130 AM CDT Fri Aug 17 2018

Valid 171630Z - 181200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF
THE NORTHEAST STATES AND THE LOWER MISSISSIPPI VALLEY REGION...

...SUMMARY...
Threat for severe storms with damaging wind is expected primarily
over the Northeast States as well as the lower Mississippi Valley
this afternoon. Other more isolated strong to severe storms are
possible over the central and northern Rockies.

...Northeast States...

Widespread showers accompanying a low-amplitude lead shortwave
trough will move through New England through midday and early
afternoon. Despite weak mid-level lapse rates, partial clearing in
the wake of the morning showers will promote destabilization of the
very moist boundary layer, supporting 1500-2000 J/kg MLCAPE. A belt
of modest southwest winds aloft with 25-35 kt between 850-500 mb
exists between the leading impulse and a more substantial shortwave
trough centered over Lake MI. The more significant destabilization
will occur between these two systems, and given minimal cap and
moist thermodynamic profiles, storms are expected to redevelop
during the afternoon from central PA through central NY and spread
east. Lake breezes, the higher terrain and residual boundaries will
all serve as potential initiating mechanisms. While vertical shear
will remain weak promoting multicell storm modes, activity will be
embedded within sufficient flow for a threat for locally strong wind
gusts as low-level lapse rates steepen. Stronger low-level shear is
present in vicinity of a warm front currently located from southern
New England through eastern NY, but instability along and north of
this boundary will likely remain limited.

...Lower Mississippi Valley region...

Storms continue developing along southward-advancing outflow
boundary across west central through central AR. As of late morning
updrafts remain elevated on cool side of this boundary. However,
temperatures are warming through the 80s F over the southern half of
the state where dewpoints are in the low 70s, and MLCAPE should
climb to 2500-3000 J/kg this afternoon. Storms will remain embedded
in weak vertical shear, but with 20-30 kt west-northwest winds
between 850-500 mb within base of an upper trough. This environment
should support few severe multicells with line segments along the
outflow boundary as low-level lapse rates steepen and storms become
surface based this afternoon. 

...Central/southern High Plains...

Scattered primarily afternoon thunderstorms are expected to develop
over the Front Range, foothills and adjacent elevated terrain,
moving east-southeastward to southeastward over the adjoining High
Plains for a few hours before weakening this evening.  The mature
phases of this activity will pose a risk for isolated severe
gusts/hail. A narrow meridional corridor of preconvective MLCAPE
1000-2000 J/kg is progged to develop amidst steep low/middle-level
lapse rates and adequate residual moisture.  Forecast vertical wind
profiles show pronounced veering with height (directional shear);
however, low/middle-level speeds will be weak, limiting bulk shear.
Still, given the steep lapse rates and a belt of 40-50-kt
anvil-level flow forecast to cross the area north of the anticyclone
aloft, some of the convection may become organized, with aggregated
outflow production possible.

...ID and vicinity...

Favorable destabilization is expected following morning
clouds/convection to support additional/afternoon development. 
The approaching mid/upper-level trough will yield increasing
large-scale ascent/cooling aloft related to DCVA and lift in the
left-exit region of a cyclonically curved upper-level jet streak. 
As the associated steepening of mid/upper lapse rates spreads over a
diabatically heated/destabilized boundary layer, sufficient
low-level moisture should remain through the mixing process to
support 500-1500 J/kg MLCAPE. A narrow corridor of favorable
buoyancy also may develop over portions of northern ID and western
MT ahead of morning convection persisting into afternoon.  Also,
mainly over the southern part of the outlook area where mid/upper
winds will be strongest, increasing deep shear is forecast. 
Well-mixed subcloud layers will promote a predominant threat of
isolated severe gusts.  Dry lightning also is possible under young
bases and off the edge of cores in this regime for fire-threat
purposes; see the SPC day-1 fire-weather outlook for more details.

..Dial/Gleason.. 08/17/2018

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1203 PM CDT Fri Aug 17 2018

Valid 181200Z - 191200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE HIGH
PLAINS FROM WYOMING AND SOUTH DAKOTA INTO NEW MEXICO AND TEXAS...

...SUMMARY...
Isolated severe storms will be possible across the High Plains
region on Saturday afternoon and evening.

...Synopsis...
With an upper high centered over California, a shortwave trough will
move southeastward across the central and northern Rockies into the
Plains, with substantial height falls/cooling aloft along with
increasing wind fields. Low pressure will develop over the Dakotas,
with a cold front extending southwest from the low into western
Nebraska and northeast Colorado by 00Z. Preceding this front across
the warm sector will be an expansive area of 60s F dewpoints, which
will contribute to moderate instability favorable for potentially
widespread thunderstorms from the Dakotas into the central and
southern High Plains.

To the east, a weaker upper level trough will move from the Ohio
Valley toward the Mid Atlantic, where a weak surface trough will
also exist along with a moist air mass.

...WY and SD southward into NM and the TX Panhandle...
Large-scale lift will quickly overspread the northern High Plains,
resulting in thunderstorm development by midday over southeast MT
and northeast WY, then spreading into SD by afternoon and expanding
southward into northeast CO. The potential for widespread storm
coverage, combined with relatively meager shear profiles preclude a
Slight Risk at this time. However, marginally severe hail and wind
will be possible due to pockets of strong instability especially
from SD into NE, aided by heating.

Farther south, a relatively cool and moist air mass with possible
ongoing precipitation will exist across southwest KS into TX, and
this may stave off strong storm potential until evening. The best
chance for a few severe storms in this region will be across
southeast CO and northeast NM during the late afternoon, with
marginal hail and wind possible, along with heavy rain.

...MAXIMUM RISK BY HAZARD...
Tornado:  <2%     - None
Wind:      5%     - Marginal
Hail:      5%     - Marginal

..Jewell.. 08/17/2018