SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0754 AM CDT Sat Jul 02 2022
Valid 021300Z - 031200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHEAST AND MID-ATLANTIC...AND OVER PARTS OF THE NORTHERN
PLAINS...
...SUMMARY...
Isolated to scattered thunderstorms with damaging winds and hail are
expected across parts of the Northeast and Mid-Atlantic, and over
parts of the northern Plains.
...Synopsis...
In mid/upper levels, the synoptic pattern from east-west will remain
dominated by:
1. A broad cyclone, initially centered over James Bay, and forecast
to pivot across QC to near extreme western Labrador by around 12Z
tomorrow. A small shortwave trough -- evident in moisture-channel
imagery over southern MB -- is forecast to pivot southeastward over
Lake Superior by 00Z, then across southern ON and southern QC to
northern New England by the end of the period.
2. Ridging over the Rockies and from the southern Appalachians
across north TX to eastern AZ. The Rockies branch of the ridge will
move eastward slightly over WY/MT late in the period in response
to...
3. A Pacific cyclone initially located well west of Cape Flattery,
with troughing southward to near 30N. The 500-mb low should move
generally south-southeastward through the period, remaining
offshore. However, a series of shortwave troughs/vorticity maxima
over its southern semicircle should progress inland and lead to net
height falls across the Northwest.
At the surface, 11Z analysis showed a cold front from southern QC
across northern/western NY, to central OH, becoming quasistationary
across south-central IN, southern IL, central MO, and central KS.
This front is forecast to move eastward across NY, New England, and
parts of eastern PA/NJ through the period, while becoming or
remaining quasistationary (under nearly parallel flow aloft) from WV
to KS. Another cold front was drawn from far northern ON across
western Lake Superior, becoming wavy/quasistationary over
southwestern MN, and southeastern ND to northeastern MT. Only
mesoscale oscillations are expected to the position of the northern
Plains boundary.
...Southern New England to portions of Mid-Atlantic...
Scattered thunderstorms are expected to develop in a richly moist
environment along/ahead of the front, mainly south of a large area
of convective outflow covering New England and NY (that should
retreat northward into southern New England/NY today), and near
prefrontal troughs and outflow/differential-heating boundaries from
ongoing areas of clouds and precip. Scattered damaging wind (in
terms of trees/tree limbs/wires, etc.), and isolated severe/50+ kt
gusts, are possible from this activity during the afternoon and
early evening.
Boundary-layer theta-e will be quite favorable, with surface
dewpoints commonly in the upper 60s to low 70s F. Areas of either
sustained/strong surface heating, or warm advection from such areas
beneath somewhat greater antecedent cloud cover, will provide
diurnal destabilization. The result thermodynamically should be
shallow but well-mixed boundary layer with weakly inhibited (at
best) MLCAPE in the 1000-1500 J/kg range, locally/briefly near 2000
J/kg. Though directional shear will be weak, the region will reside
beneath the southern rim of stronger mid/upper-level cyclonic flow,
contributing to both favorable cloud-layer shear and around 35-45-kt
effective-shear magnitudes, in support of some downward momentum
transfer and organization of the severe potential beyond typical
warm-season pulse downbursts.
... WV/VA Appalachians to KS/northern OK...
Farther southwest and west near the front, and outflow boundaries to
its south, widely scattered to scattered thunderstorms are possible
this afternoon into early evening. Isolated severe gusts/hail will
be the main concern, with activity becoming weaker and more isolated
from late evening onward. Convection should take the form of
variably sized/organized multicellular clusters. Low/middle-level
flow and vertical shear will be weak and mainly unidirectional away
from boundaries, limiting convective organization to what can be
accomplished through low-predictability, localized boundary-
interaction processes and temporary upscale cold-pool aggregation.
Strong heating and low-level moisture should offset modest midlevel
lapse rates to support 1000-2000 J/kg peak/preconvective MLCAPE
during mid/late afternoon.
...Northern Plains to western NE...
Isolated to scattered thunderstorms are expected to develop this
afternoon near and south of the front, with a few supercells
possible in the first few hours of the convective cycle, then some
upscale expansion into one or two small MCSs over the central/
eastern Dakotas possible before activity diminishes tonight. Severe
hail and gusts will be possible.
The boundary layer over most of this region is expected to be
well-heated/mixed. Greater inflow-layer moisture content (but also
somewhat stronger MLCINH) is forecast over northern and eastern
parts of the outlook area in closer proximity to evaportanspirative
source regions. By contrast, a deeply mixed subcloud layer will
characterize much of the High Plains. Steep midlevel lapse rates
atop those layers will support MLCAPE peaking around 2000-2500 J/kg
over central SD where the greatest juxtaposition of moisture and
heating is expected, lessening with northwestward extent into cooler
air and southward extent to weaker moisture. Favorably strong
upper-level winds and veering with height from low/middle levels
will yield enough deep shear for a blend of supercells and organized
multicells. The hail threat should peak earlier and farther west,
while the wind threat continues eastward and deeper into the
evening.
...Inland Pacific Northwest...
Isolated to scattered thunderstorms are possible from midafternoon
into early evening, offering the potential for gusts/hail near
severe limits. Height falls and shots of DCVA/destabilization aloft
are expected in strengthening midlevel cyclonic flow, placing
large-scale ascent and related steepening of midlevel lapse rates
over an area of at least marginal low/middle-level moisture inland.
Lower-elevation surface dew points in the 40s to low 50s may lessen
somewhat due to mixing through the afternoon. However, surface
diurnal heating will help to drive pockets of 500-1200 J/kg MLCAPE
where dewpoints remain in the 40s to near 50 F, with a well-mixed
subcloud layer. Where not too altered by local orographic effects,
generally northeasterly to northerly near-surface winds (northwest
of the surface low) will elongate hodographs and strengthen deep
shear through strong veering with height, despite modest speeds.
This may aid in storm organization as well, with 30-45-kt
effective-shear magnitudes possible.
...Coastal southern NC...
With tropical-storm-force winds detected offshore, T.S. Colin has
been named by NHC while centered near the SC coast, between CHS-MYR.
This is a well-sheared system (with respect to the deep-troposphere
shear vectors). Accordingly, deepest convection is asymmetrically
distributed seaward, and may continue to be, given NHC's forecast of
even stronger deep shear than at present. Under those
circumstances, and being a small, marginal T.S. not forecast to
strengthen much (if at all), at most only a mesobeta-scale area of
favorable low-level kinematic fields for tornado potential
reasonably will be possible in a downshear (east-northeast) sector.
At this time, uncertainty is too great to introduce an
unconditional/categorical tornado outlook. If confidence increases
in both:
1. Favorably large overland hodographs near Cape Fear and/or Cape
Lookout, and
2. Convective trends indicate potential for landfalling supercells
in the associated wind field, a small area of tornado probabilities
may be necessary in a succeeding outlook update.
..Edwards/Goss.. 07/02/2022
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