SPC Oct 11, 2018 0600 UTC Day 1 Convective Outlook



SPC 1200Z Day 1 Outlook

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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1244 AM CDT Thu Oct 11 2018

Valid 111200Z - 121200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE EASTERN
CAROLINAS AND SOUTHEAST VIRGINIA...

...SUMMARY...
Tornadoes are possible across eastern portions of the Carolinas and
southeast Virginia throughout the day and into the evening.

...Synopsis...
A relatively complex atmospheric pattern is currently in place
across the CONUS. Most prominent feature is tropical cyclone
Michael, which is forecast to remain at tropical storm strength
throughout the day today. Forecast track provided by the National
Hurricane Center takes the center of the system through central SC
and eastern NC and off the Mid-Atlantic coast by 06Z on Friday.
Other features within the upper pattern include: 1) a strengthening
shortwave trough expected to drop through the northern and central
High Plains this evening and overnight, 2) a shortwave trough moving
southwestward off the central/southern CA coast, eventually
transitioning to an upper low off the central/southern CA coast, and
3) the shortwave trough currently moving through the central Plains,
which is expected to eject quickly northeastward through the Upper
Great Lakes. Evolution of this central Plains shortwave will
encourage a further eastward push of the cold front currently
extending from Lower MI southward off the central Gulf Coast. By 00Z
Friday, this cold front is expected to extend from VT
south-southwestward through the Carolina Piedmont and off the
Florida Big Bend coast.

...Mid-Atlantic...
Despite the gradual weakening anticipated, the low to mid-level wind
fields surrounding tropical cyclone Michael will remain quite
strong. An area of 850 mb winds near 60 kt will likely persist just
east of the center as the system moves across the Carolinas and far
southeastern VA. Consequently, large, looping low-level hodographs
and high storm-relative helicity values indicate a kinematic
environment supportive of tornadoes. The air mass is also quite
moist, with mid-70 dewpoints already in place as far north as
eastern VA. Warm mid-level temperatures may mitigate instability
somewhat but the air mass will still be unstable enough to support
persistent updrafts and low-topped supercells. Combination of
favorable thermodynamics and kinematics will result in a threat for
tornadoes across the region.

Several factors (i.e. speed of the system, relatively higher
instability) suggest a somewhat higher tornado risk. However, the
system has struggled to maintain well-developed rain bands away from
the center. Recent development of the band across southern SC is the
first such development noted throughout the evening. Additionally,
recent high-resolution guidance does not show much banding. The
tornado threat still appears high enough to merit a 5% threat area,
but low confidence in well-developed rain bands precludes higher
probabilities with this outlook.

A related but somewhat separate threat for damaging wind gusts
exists across northern portions of the Mid-Atlantic where the
eastward progressing cold front will interact with the moist and
moderately unstable air mass around the tropical system. Some
interaction between storms along the front and those surrounding
Michael may lead to brief updraft augmentation and the potential for
isolated damaging wind gusts.

..Mosier/Leitman.. 10/11/2018

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