SPC - No watches are valid as of Sun Jul 22 13:39:02 UTC 2018

No watches are valid as of Sun Jul 22 13:39:02 UTC 2018.


SPC - No MDs are in effect as of Sun Jul 22 13:39:02 UTC 2018

No Mesoscale Discussions are in effect as of Sun Jul 22 13:39:02 UTC 2018.


SPC Jul 22, 2018 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook
      
Day 1 Outlook Image
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0759 AM CDT Sun Jul 22 2018

Valid 221300Z - 231200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHEAST AND NORTHERN/CENTRAL PLAINS...

...SUMMARY...
Severe storms, primarily capable of damaging winds and large hail,
will be possible across parts of the Southeast and northern/central
Plains this afternoon and evening.

...Synopsis...
In mid/upper levels, the pattern will remain dominated by three
synoptic- to meso-alpha-scale features:
1.  A large, stacked cyclone -- now centered over OH -- forecast to
fill slowly but also expand southward over the Southeast through the
period.  This will occur as a series of mesoscale vorticity lobes
orbit the southern semicircle, leading to net height falls across
most of GA, SC, AL, and FL.
2.  A strong northern-stream trough -- now evident in
moisture-channel imagery from a 500-mb low over northwestern SK
across north-central/southwestern MT.  As the northern SK cyclone
moves slowly eastward, the basal trough will change from positively
to negatively tilted and decrease in amplitude, ejecting
northeastward across MT to central ND by 00Z.
3.  Persistent ridging over the south-central and southwestern
CONUS, rooted in a strong high that will retrograde slowly across
NM.

At the surface, a low analyzed at 11Z near IPT will eject further
inland and weaken today across the lower Great Lakes and southern
ON, in tandem with a mid/upper-level vorticity lobe.  The associated
warm front is forecast to move northward over eastern NY and parts
of southern/western New England, generally becoming more ill-defined
with time.  Farther west, a cold front was drawn initially from a
low between GGW-GDV, southwestward cross northern WY.  By 00Z, this
front should reach eastern ND, south-central SD, north-central NE,
and eastern WY, with a prefrontal trough from central SD to eastern
CO.  By 12Z the front should advance to north-central MN,
northeastern NE and southeastern CO. 

...Southeast...
The main severe threat will be associated with scattered to numerous
thunderstorms that should develop quickly from midday through early
afternoon over northern FL, and later in the afternoon near
sea-breeze and confluence boundaries across the FL
Panhandle/southern AL region.  Damaging gusts and large hail are
expected, and a tornado cannot be ruled out.

Favorable low/middle-level lapse rates will overlie strong surface
heating, 70s to near 80 F surface dew points, PW to near 2 inches,
and mean mixing ratios 19-20 g/kg.  Forecast soundings in the
preconvective environment accordingly show strong to extreme
buoyancy, with MLCAPE 3500-4500 J/kg, locally near 5000 J/kg.  These
buoyant profiles will be deep also, with equilibrium levels near 50
kft and max parcel levels potentially topping 60 kft.  As such, both
water-loaded severe pulses and upscale cold-pool organization appear
possible in support of the convective-wind hazard.  Directional
shear should be small, given the westerly boundary-layer wind
component.  However, deep-layer speed shear will be favorable for
organized multicells and at lest transient/heavy-precip supercells,
with effective-shear magnitudes ranging from 30-35 kt over the
northern FL Peninsula to 40-45 kt across the western Panhandle and
adjoining parts of AL.  As such, a large-hail risk exists also. 
Given the lack of larger ambient hodographs, tornado potential is
more conditional on storm-scale processes and to mesobeta-scale
convection/boundary interactions.

Evolution of one or two primary complexes is possible from initial
convection over northern FL and/or activity moving southeastward out
of the western activity into northwestern FL later.  Damaging wind
will become the main concern as any such upscale organization
proceeds.

...Northern/central Plains...
Scattered thunderstorms are forecast to develop along/ahead of the
front and near a prefrontal trough this afternoon.  First activity
should be over parts of ND where large-scale/deep-layer ascent will
arrive sooner and stronger ahead of the ejecting mid/upper
perturbation -- then over SD and NE where heating, low-level
instability and theta-e will be greater.  Large hail and severe
gusts are possible.

A well-defined axis of low-level moisture extends from northeastern
OK north-northwestward across the central Plains to western SD and
central/northwestern ND, per surface analysis.  Dew points should
remain commonly in the 60s F under modest capping through much of
the preconvective time period, in a narrow corridor near the trough,
and ahead of the front.  Satellite imagery indicates cloud debris
from earlier convection is breaking up over NE and SD, with a swath
of clearing northward into ND,  This should allow sustained surface
heating through afternoon, helping to boost MLCAPE into the
1500-2500 J/kg range in a narrow, north/south-elongated
preconvective corridor over the outlook area.  Deep shear will be
marginal over most of this region, with effective-shear magnitudes
generally 30-40 kt, and a blend of multicells and short-lived
supercell structures possible.  The severe threat (especially hail,
later wind) should wane with eastward extent as modes get messier
and inflow-layer theta-e diminishes this evening.

..Edwards/Peters.. 07/22/2018

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