Scientific Forecaster Discussion
fxus62 krah 220115
Area forecast discussion
National Weather Service Raleigh NC
915 PM EDT Thu Jun 21 2018
a mid to upper level disturbance will lift northeastward across the
southern Appalachians this afternoon and southern Middle Atlantic
States tonight. A back-door cold front will drift southward and
stall near the Virginia and NC border through Friday, while a surface
trough will otherwise linger over NC through the weekend.
Near term /through tonight/...
as of 915 PM Thursday...
The stalled frontal boundary across the Ohio Valley and virginias
has provided a source of lift for some showers and thunderstorms to
our north. While cams generally mishandled convection across the
area, some scattered showers and thunderstorms are ongoing in west-
central NC and across eastern NC. Convection to our west will
continue moving east-northeastward and may impact The Triad and
Triangle in the next few hours, but severe potential is relatively
low with weak shear and modest lapse rates. A few outflow boundaries
from earlier convection in southeastern Virginia could make it into
northeastern counties and become a catalyst for some showers and
storms later this evening. Rain, heavy at times may cause some
localized flooding mainly in urban and poor drainage areas.
The front across central Virginia will remain north of the NC border
allowing for warm, humid conditions to continue with temperatures in
the low to mid 70s overnight. While fog and low stratus is
generally not expected to be a problem, pockets of low visibilities
could show up in places that receive convection.
Short term /Friday and Friday night/...
as of 355 PM Thursday...
An unseasonably strong mid-upr level low is forecast to wobble from
S-cntl Illinois to nrn Ohio from 12z Fri to 12z Sat. Glancing height falls
aloft accompanying the low will overspread wrn NC/Virginia on Fri, along
with a belt of 30-40 kts of of swly mid level flow. The surface
front will meanwhile remain quasi-stationary over srn Virginia or nrn NC,
where a weak frontal wave is likely to develop late Fri afternoon-
early evening, before tracking enewd to far ern Virginia or the Chesapeake
Bay by 12z Sat.
It will consequently again be relatively hot, with limited
convective coverage over much of cntl and especially srn NC, with
high temperatures, despite multi-layer cloudiness that may be mostly
cloudy at times, in the lwr to middle 90s. Cooler temperatures in
the mid-upr 80s are meanwhile likely over nrn counties, in closer
proximity to the front and focus for convection/clouds.
The presence of the aforementioned, unseasonably strong swly flow
aloft will strengthen environmental shear profiles, particularly
those in the vicinity of the surface boundary along the Virginia/NC
border. A few supercells, at least transient ones, are expected to
develop along that front, with an associated risk of damaging wind,
large hail, and even a tornado or two. Elsewhere, semi-organized/
multi-cells would pose a risk of primarily damaging wind gusts. Lows
again mostly 70 to 75 degrees.
Long term /Saturday through Thursday/...
as of 255 PM Thursday...
The closed low over the Ohio Valley will be absorbed into the longer
wave pattern on Saturday as it lifts northeast into the Great Lakes.
A lingering Lee surface trof and general westerly flow will provide
meager forcing, but there will be strong instability sufficient for
scattered diurnally driven convection both Saturday and Sunday as
highs reach mostly low to mid 90s. Expect increased convective
coverage Sunday afternoon through Monday morning as moisture will
increase in deeper southwest flow as the broad trof over the eastern
Continental U.S. Amplifies in response to a short wave digging into the Ohio
The East Coast trof axis will shift east, pushing a surface front
south of the area on Monday, with modestly cooler high pressure
settling south down the Atlantic coast Tuesday. Convection will
diminish/end from the northwest behind the front on Monday and highs
Monday will depend on the timing of the front. Highs in the north
are expected to stall in the upper 80s in Post-frontal cool air
advection, while the south should have time to reach mid 90s. The
high pressure area will transition offshore to establish a classic
Bermuda high configuration towards the mid week. The high pressure
will effectively cap/limit convection Tuesday through Thursday, with
widely scattered late day storms becoming a little more numerous
each day as temperatures creep from the mid and upper 80s Tuesday
back into the lower 90s on Thursday.
Aviation /00z Friday through Tuesday/...
as of 815 PM Thursday...
24 hour taf period: VFR conditions are generally expected to
continue through the 24 hour taf period, outside of any convection.
Isolated to scattered showers and storms will be possible this
evening into early Friday morning. The strongest storms or clusters
of storms will have the potential to produce gusty winds and sub-VFR
Southwesterly flow is expected to increase on Friday afternoon, with
wind gusts of around 20 mph possible. In addition, isolated to
widely scattered showers and storms will be possible again on Friday
afternoon/evening, though expected coverage is too low to include
mention in the tafs at this time.
Outlook: mainly diurnal convection and related sub-VFR conditions
will continue until a cold front, and following cooler and more
stable high pressure, arrive late Mon.
Max temperature and high-minimum temperature records...
day maximum yr min yr
06/21 100 1933 75 1924
06/22 100 1914 75 1981
day maximum yr min yr
06/21 101 1933 75 1933
06/22 100 1981 78 1933
day maximum yr min yr
06/21 105 1933 84 1928
06/22 101 1990 84 1928