SPC Jul 12, 2018 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1252 AM CDT Thu Jul 12 2018

Valid 121200Z - 131200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON AND EVENING ACROSS PARTS OF THE MID MISSOURI VALLEY
THROUGH PORTIONS OF THE UPPER MIDWEST...

...SUMMARY...
Thunderstorms may pose a risk for strong wind gusts and perhaps some
hail late this afternoon and evening in a corridor across parts of
the mid Missouri Valley into the Upper Midwest.  Additional strong
storms accompanied by a risk for potentially damaging wind gusts are
possible across South Carolina and adjacent portions of the south
Atlantic Coast region.

...Synopsis...
Models indicate that the stronger mid-latitude westerlies will
remain generally zonal and confined to latitudes near/north of the
Canadian/U.S. border through this period.  Within this regime, a
vigorous short wave trough and associated fairly deep cyclone are
forecast to progress across northwestern Ontario into Hudson Bay by
late tonight.  It appears that a trailing cold front, now advancing
southeastward into/across the northern Plains, will stall and weaken
across the Upper Midwest/upper Great Lakes region and northern
Plains.

Downstream, the westerlies may become increasingly split, with
troughing in the weaker southern branch amplifying east of the
northern/middle Atlantic coast.  An influx of cooler/drier low-level
air associated with this feature may advance southward to the east
of the central/southern Appalachians, and perhaps south of the lower
Ohio Valley into the Tennessee Valley.

Otherwise, mid/upper subtropical ridging will prevail across much of
the central and southern tier of the U.S., with a prominent embedded
mid-level high gradually shifting across and east of the middle
Mississippi Valley.  Seasonably strong heating and residual
monsoonal moisture may once again support considerable afternoon and
evening thunderstorms across much of the Southwestern deserts into
the southern Rockies.  Thunderstorms may also become widespread in a
corridor along the front across the northern Plains into the upper
Great Lakes region, with at least somewhat more scattered
thunderstorms possible across the Gulf and south Atlantic Coast
region.

...Middle Missouri Valley into Upper Midwest/Great Lakes region...
Models indicate considerable modification of the plume of elevated
mixed layer air emanating from the Great Basin, in the wake of the
aforementioned vigorous short wave trough and associated surface
cyclone.  However, beneath the remnants of this plume, a corridor of
strong surface heating near/just south of the stalling surface front
may once again contribute to moderate to large CAPE.  This will be
aided by the lingering presence of mid 70s+ surface dew points along
the front.  Given this instability and weakening mid-level
inhibition, considerable thunderstorm development appears possible
late this afternoon into this evening.  Generally south of the
mid-latitude westerlies, mid/upper forcing to support activity
remains somewhat unclear, but a perturbation now over eastern
Colorado could augment convection across the middle Missouri Valley
late this evening as it progresses around the subtropical high. 
Although west southwesterly deep layer mean flow may remain somewhat
modest, 30 kt in the 850-500 mb layer may be enough to contribute to
the evolution of organizing convective systems accompanied by a risk
for strong surface gusts, before convection weakens overnight.

...South Carolina and adjacent portions of Georgia/North Carolina..
Seasonably strong surface heating may yield a relatively deeply
mixed boundary layer characterized by moderately large CAPE by late
this afternoon, ahead of the southward advancing surface front. 
Aided by forcing for ascent along/ahead of the front, there appears
at least some potential for an upscale growing cluster of
thunderstorms, supported by consolidating cold pools.  Although
embedded within generally weak wind fields, a northerly component at
mid/upper levels is expected to contribute to an eventual general
southward propagation, with the surface cold pool perhaps becoming
strong enough to support potentially damaging surface gusts into
this evening.

..Kerr/Wendt.. 07/12/2018

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