No watches are valid as of Tue Aug 14 18:16:01 UTC 2018.No Mesoscale Discussions are in effect as of Tue Aug 14 18:16:01 UTC 2018.SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
0910 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
CORRECTED FOR NDFD THUNDERSTORM GRID IN NEW ENGLAND
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 KS -- will move slowly east-
northeastward through the period, also becoming an open-wave trough.
By 12Z the trough should be near the KS/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 WY 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 GA/AL, then northwestward arching across the
STL and OMA areas as a warm front, then southwestward to a surface
low near SPD. A cold front associated with the northern-stream
synoptic trough was drawn from the James Bay region to south-central
MN, becoming quasistationary to the central High Plains.
...North-central Rockies/High Plains...
Convection evolving from an ongoing cloud/precip shield over
southeastern MT/northeastern WY 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 WY 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
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.
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1127 AM CDT Tue Aug 14 2018
Valid 141630Z - 151200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
A few severe thunderstorms are possible this afternoon into evening
over parts of the north-central Rockies/High Plains region. Other
strong storms may occur over eastern North Carolina, portions of
Oklahoma and southern Kansas, and southern Arizona.
Morning water vapor loop shows a deepening upper trough over western
MT/WY. This feature will track eastward across WY today, providing
large scale forcing for ascent and scattered thunderstorm
development. Southeasterly low level winds east of the Big Horns
will maintain ample moisture, with afternoon heating yielding steep
low level lapse rates and MLCAPE values of 1000-1500 J/kg. Given
the favorable vertical shear profiles, steep mid-level lapse rates,
and consensus of 12z guidance that several storms will form, have
upgraded portions of this region to SLGT risk for large hail.
Activity may persist well into the evening, spreading eastward into
parts of western SD/NEB before diminishing.
Several vort maxima continue to rotate around an upper low over
western KS. Broken cloud cover will help to destabilize a corridor
over much of OK and southeast KS today, leading to moderate CAPE
values and scattered thunderstorm development. Deep layer shear is
marginal. However, strengthening low level flow this
afternoon/evening and ambient vorticity beneath cyclonic flow field
may be sufficient for a few rotating cells capable of damaging wind
gusts, an isolated tornado or two, and perhaps hail.
Full sunshine and dewpoints in the 70s are leading to MLCAPE values
of 1500+ J/kg over eastern NC today, beneath moderately strong
westerly flow aloft. Scattered thunderstorms will continue to
develop in this region and spread eastward toward the coast. Steep
low-level lapse rates and sufficient CAPE will lead to a few
multicell clusters capable of gusty/damaging wind gusts. Refer to
recent MCD #1285 for further details.
12z guidance is becoming more consistent in the likely development
of clusters of thunderstorms forming in southeast AZ later this
afternoon and spreading eastward across southern AZ overnight.
Ample low level moisture and CAPE, coupled of steep low level lapse
rates, will promote strong outflow winds in the stronger cells.
SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1231 PM CDT Tue Aug 14 2018
Valid 151200Z - 161200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
A few severe storms will be possible mainly over the central High
Plains Wednesday afternoon and evening. Isolated strong to severe
storms will also be possible over the middle Mississippi Valley
region and parts of New England.
A closed mid/upper-level low over NY/PA today will develop into a
open shortwave trough as it moves eastward off the East Coast
Wednesday morning. A separate shortwave trough over Ontario is
likewise forecast to move eastward across southern Quebec by
Wednesday evening. An upper trough/low initially over IA/MO will
continue east-northeastward across the mid MS Valley and Lower Great
Lakes as it slowly de-amplifies through the period. Another upper
low with a 40-50 kt embedded west-northwesterly mid-level jet should
develop eastward across SD/NE as upper ridging remains over much of
the western CONUS. At the surface, a cold front will slowly advance
southeastward across parts of New England, while a weak low develops
northeastward across the mid MS Valley/Lower Great Lakes in tandem
with the previously mentioned devolving upper trough/low. An
ill-defined cold front attendant to this surface low should stall
over parts of the southern/central Plains by Wednesday afternoon.
Modest east-northeasterly low-level winds should reside to the north
of a weak cold front across western SD/NE Wednesday afternoon. As
large-scale ascent associated with an upper low overspreads this
region, isolated to scattered thunderstorms should form along
along/south of this boundary across western/central NE. With MLCAPE
up to 1500-2000 J/kg expected owing to diurnal heating and at least
modestly steepened mid-level lapse rates, and effective bulk shear
of 40-50 kt, supercells will probably be the predominant initial
storm mode. Isolated large hail and damaging winds should be the
main severe threats, although a tornado or two may be possible along
the weak boundary where surface winds are backed to an
easterly/northeasterly direction, locally enhancing 0-1 km SRH. A
southerly low-level jet may strengthen by early Wednesday evening
across NE, and some potential for upscale growth into a small bowing
line segment may exist.
Farther south across eastern CO/western KS and parts of the southern
High Plains, additional thunderstorms should develop over the higher
terrain and then spread eastward through the early evening.
Mid-level flow will be weaker across these areas, and resultant
effective bulk shear will be limited to mainly the 25-35 kt range.
Still, multicells will probably pose an isolated strong/damaging
wind threat, along with some potential for large hail. The severe
threat will likely wane with eastward extent Wednesday evening as
convective inhibition increases.
...Eastern OK into the Mid MS Valley and Lower OH Valley...
Mid-level lapse rates will be very poor across much of the mid MS
Valley into the lower OH Valley and vicinity on Wednesday as a
subtropical airmass characterized by precipitable water values of
1.75-2+ inches remains in place. Thunderstorms will also likely be
ongoing at the start of the period over parts of these regions,
which coupled with substantial cloudiness and the poor lapse rates
should generally limit surface heating and related instability. Even
so, a belt of 30-40 kt flow in the 850-500 mb layer may allow for
some transient storm organization. Isolated strong/gusty winds may
occur with any thunderstorms that can redevelop Wednesday afternoon
and spread east-northeastward in one or more small line segments.
Isolated to perhaps widely scattered thunderstorms should develop
along/ahead of a cold front by Wednesday afternoon across southern
Ontario/Quebec, and subsequently spread eastward into parts of
northern NY/VT/NH and ME. Although surface temperatures may not
become overly warm as mid-level cloudiness somewhat limits surface
heating, a moist low-level airmass is expected to remain in place
across this area, with surface dewpoints in the mid to upper 60s
common. Even though mid-level lapse rates should remain weak,
sufficient diurnal heating coupled with the moist low levels should
result in MLCAPE up to 1500 J/kg by peak heating. The strongest
mid-level winds associated with a shortwave trough may lag the cold
front slightly, but around 30-35 kt of effective bulk shear should
prove enough to support at least modest storm organization, with
multicells capable of producing isolated strong to locally damaging
winds probably the main severe threat.
...MAXIMUM RISK BY HAZARD...
Tornado: 2% - Marginal
Wind: 15% - Slight
Hail: 15% - Slight