SPC - No watches are valid as of Thu Nov 15 16:35:02 UTC 2018

No watches are valid as of Thu Nov 15 16:35:02 UTC 2018.


SPC MD 1648

MD 1648 CONCERNING WINTER MIXED PRECIPITATION FOR CENTRAL APPALACHIANS...MID ATLANTIC
MD 1648 Image

Mesoscale Discussion 1648
NWS Storm Prediction Center Norman OK
0856 AM CST Thu Nov 15 2018

Areas affected...Central Appalachians...Mid Atlantic

Concerning...Winter mixed precipitation 

Valid 151456Z - 152100Z

SUMMARY...Areas of heavy snow are likely to develop in the higher
elevations of the central Appalachian Mountains this morning. By
afternoon, a mixture of snow and sleet are likely in the lower
elevations from northern Virginia into northern New Jersey. This
corridor may changeover to freezing rain or rain this afternoon.

DISCUSSION...The latest water vapor imagery shows an upper-level low
in the mid Mississippi Valley with southwest mid-level flow over
much of the eastern Seaboard. At the surface, a large area of high
pressure is in place across the Northeast. Surface temperatures are
below freezing in most of the central Appalachians with dewpoints
mostly in the teens. As a large area of precipitation moves across
the central Appalachians this morning, the temperature profile will
support the development of snow.  Areas of heavy snow will be
possible especially in the higher elevations of the central
Appalachian Mountains where 1 inch per hour snowfall rates may
occur.

Surface temperatures from northern Virginia northeastward to
northern Maryland are currently just below freezing. At this time,
light snow is being reported along this corridor. This snow will
likely develop northeastward into southeast Pennsylvania and
northern New Jersey late this morning. As warm advection continues
over the top of the cold airmass late this morning into early
afternoon, a changeover to sleet, freezing rain and rain will be
possible from northern Virginia to northern New Jersey.

..Broyles/Hart.. 11/15/2018

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...OKX...ALY...PHI...BGM...BUF...CTP...LWX...PBZ...
RLX...

LAT...LON   38327873 38517974 39167986 40567961 41717904 42067799
            41907558 41547397 40537401 39307622 38597785 38327873 

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SPC Nov 15, 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
0656 AM CST Thu Nov 15 2018

Valid 151300Z - 161200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
EASTERN NORTH CAROLINA...

...SUMMARY...
Isolated damaging gusts and a tornado or two may occur from late
this morning through afternoon over portions of near-coastal eastern
North Carolina.

...Synopsis...
In mid/upper levels, a slow-moving, large-scale ridge will remain
just offshore from the Pacific Coast States through the period. 
Downstream, several shortwave perturbations will rapidly traverse
the northwesterly flow across western Canada and the northern
Plains/upper Midwest regions.  The leading such feature -- now
apparent in moisture-channel imagery over portions of ND -- is
expected to phase with an initially weaker/trailing trough over the
MT/SK border area.  The combined feature will amplify and move
southeastward across the upper Mississippi Valley and Lake Michigan
tonight, reaching western Lower MI and IN by 12Z.  As heights fall
ahead of this process, the strong/closed cyclone now centered near
the Mississippi/Ohio River confluence will eject/accelerate
northeastward generally up the Ohio Valley while gradually
weakening.  By the end of the period, this feature should devolve
into a compact, open-wave trough over the Mid-Atlantic.

At the surface, 11Z analysis showed a low over the Atlantic waters
off the central SC coast, with a cold front southwestward across
east-central/southwestern FL Peninsula.  A sharply defined warm
front, with strong baroclinic gradient reinforced by persistent
precip to its north, was evident from the low offshore the NC coast
just south of buoy 41013.  The low should cross eastern NC through
early afternoon, then deepen and occlude over or barely offshore
from the coastal Delmarva Peninsula through 06Z.  By 12Z, the low
should be located over Long Island or just offshore.  The cold front
is forecast to sweep off the Atlantic coast from NC-FL before 00Z,
while the warm/coastal front preceding the low oscillates inland
over eastern NC just prior to the passage of the low.

...NC near-coastal/Tidewater/Outer Banks region...
Widely scattered to scattered thunderstorms are expected to form
along the cold front near the low, and over the warm sector, through
this afternoon.  Activity will occur in a favorably sheared and
moist environment overlain with low/middle-level lapse rates only
slightly greater than moist adiabatic, keeping buoyancy marginal but
sufficient.  Greatest shear should be near the warm-frontal zone,
with effective-shear vectors of 45-50 kt and effective SRH 300-500
J/kg.  The most unstable scenarios near the central/southern Outer
Banks and southeastern NC beaches yield MLCAPE 500-1000 J/kg with
dew points briefly reaching upper 60s, perhaps low 70s F.  This
buoyancy/shear parameter space will support tornado potential from
any supercells that can form, as well as wind/tornado risk in bowing
modes.

Even this close to the event, short-term guidance differs
importantly on the inland penetration of the favorable warm sector
prior to the passage of the surface low, and to some extent, differs
with the track of the low.  Based on a sampling of forecast
soundings, and modification to the 12Z MHX RAOB, this likely is
related to different treatment of the precip-reinforced static-
stability profile.  Regardless, the threat appears somewhat more
compressed eastward than in the previous outlook, given the
cold-sector precip situation, and supported by guidance consensus. 
The lines are slightly adjusted eastward accordingly.

..Edwards/Marsh.. 11/15/2018

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SPC Nov 15, 2018 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook
      
Day 1 Outlook Image
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1002 AM CST Thu Nov 15 2018

Valid 151630Z - 161200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
OVER FAR EASTERN NORTH CAROLINA...

...SUMMARY...
Isolated damaging gusts and a tornado or two may occur from late
this morning through afternoon over portions of near-coastal eastern
North Carolina.

...Eastern NC...
Only minor changes have been made to the ongoing forecast.  Latest
surface analysis shows a deepening surface low just off the NC coast
near Cape Fear, with a warm front extending eastward out to sea. 
Several significant supercells are noted on radar along this
boundary.  Observational trends suggest that destabilization over
eastern NC is occurring slightly slower than anticipated due to this
widespread convection.  The back edge of the convection is also
progressing eastward faster than guidance.  Present indications are
that the Outer Banks and coastal counties of far eastern NC may be
briefly in the warm sector this afternoon.  If this occurs, very
strong low-level shear will pose a threat of damaging wind gusts and
perhaps a tornado in any persistent convective core.  However, the
area and time period of potential is decreasing.

..Hart/Kerr.. 11/15/2018

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SPC Nov 15, 2018 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook
      
Day 2 Outlook Image
Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1032 AM CST Thu Nov 15 2018

Valid 161200Z - 171200Z

...NO THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Severe thunderstorms are not forecast across the Lower 48 states on
Friday.

...Synopsis...
A series of mid-level shortwave disturbances will quickly move from
coastal New England and the OH Valley into the Canadian Maritimes
during the period.  A surface low will likewise develop northeast
from Long Island to Nova Scotia during the day.  High pressure at
the surface will influence conditions across a large part of the
remaining CONUS.  Thunderstorms are not forecast.

...MAXIMUM RISK BY HAZARD...
Tornado:  <2%     - None
Wind:     <5%     - None
Hail:     <5%     - None

..Smith.. 11/15/2018

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SPC Day 1 Fire Weather Outlook

SPC Day 1 Fire Weather Outlook
          
Day 1 Fire Weather Outlook Image
Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
1031 AM CST Thu Nov 15 2018

Valid 151700Z - 161200Z

Occasional critical conditions have been observed at the highest
terrain (3-5 kft) sites in southern California. At lower elevations,
elevated conditions are present at a few locations. Given these
current observations and improving conditions expected during the
day, no changes have been made to the ongoing elevated area.

..Bentley.. 11/15/2018

.PREV DISCUSSION... /ISSUED 0142 AM CST Thu Nov 15 2018/

...Synopsis...
An upper-level ridge and associated surface thermal trough will be
in place across California at the start of the period, with the
trough breaking down to a more quasi-zonal flow pattern, with weak
west-northwesterly flow expected. 

...Southern California...
A weak surface pressure gradient will be in place across California,
mainly during the morning hours. 15-20 mph east-northeasterly
offshore winds are expected, along with critically low RH. With very
dry fuels receptive to fire spread present across the area, an
elevated delineation was continued for the morning hours. Critically
strong winds (20+ mph) may briefly occur along the higher terrain of
the southern California foothills, but the spatially/temporally
constricted nature of these stronger winds precludes a critical
delineation. From the afternoon to the end of the period, surface
conditions will become less favorable for fire spread.

...Please see www.spc.noaa.gov/fire for graphic product...

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