Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
1045 PM EDT Thursday Jul 2 2015
Synopsis...a cold front will approach from the north..and stall
over the Middle Atlantic States tonight through the Holiday weekend.
Meanwhile a series of upper level disturbances will cross
overhead...bringing periods of showers and thunderstorms.
Near term /through tonight/...
as of 1045 PM Thursday...
Only a small line of showers/isolated thunderstorms remained from
near Troy to near Clayton... moving slowly east-NE at 1000 PM. This
area stretches along the old outflow boundary. A recent uptick in
showers along this boundary was occurring with low topped
convection... very little cloud-to-ground lightning. We will follow the mesoscale-
analysis and radar trends which indicate an area of weak surface
moisture convergence in this region along with some residual MLCAPES
around 500-1000 j/kg and keep likely pop going a bit longer. Trends
do suggest locally 1 to 2 inches of additional rainfall from near
Clayton to Wilson and south of Tarboro in a narrow axis. Some
trailing low topped convection may get going for a few hours along
the west edge of the outflows as well back over in the northwest Piedmont.
Otherwise... the organized convection has roughly moved offshore and
was approaching the western slopes of the Appalachians from the Tennessee
Valley. The activity over the Tennessee Valley may hold together into the
mountains. Otherwise... conditions are less favorable now east of
the mountains. We will carry a slight chance overnight. Partly
cloudy to mostly cloudy skies are expected with lows in the upper
60s to lower 70s.
Short term /Friday and Friday night/...
as of 300 PM Thursday...
Friday...water vapor imagery this afternoon depicts a well defined
convectively induce vorticity maximum moving southeastward on the backside of the
baggy upper level trough. Model guidance has a fairly good handle on
this feature. This system projected to round the base of the trough
late tonight/early Friday then cross the Carolinas later Friday. Based
on current timing...should see scattered convection develop a few
hours earlier than normal...possibly as early as 10-11 am...with the
majority of the convection occurring between noon and 8 PM.
The low level atmosphere expected to be slight-moderately unstable
along with effective bulk shear values approaching 30kts...
supportive of organized convection. Wind profile fairly
unidirectional (sw) so expect convection to evolve into broken
bands...producing strong/locally damaging winds.
Maximum temperatures Friday dependent on when convection develops and extent of
cloud cover overhead. Expect more clouds than sun north as well as
more convection across the north so should see a temperature range of low-
middle 80s north to upper 80s/around 90 south. Earlier initiation of
convection will likely have an effect on maximum temperatures (2-3 degrees
Currently appears bulk of energy associated with the vorticity maximum exits
our region by early evening. This suggest that convection should
slowly wane/diminish between 7-10 PM across the region. Similar to
tonight...presence of of a moist air mass...a stalled low level
trough and perturbations aloft suggest a few showers may linger into
the overnight hours. Min temperatures upper 60s-lower 70s.
Long term /Saturday through Thursday/...
as of 245 PM Friday...
The general overall pattern will be dominated by general troughiness
in the upper levels over the eastern U.S. With a few shortwave
disturbances progressing through the area. At the surface...a
stalled boundary will linger in the vicinity of central NC...with
generally low pressure over the area through the period. What this
means weather-wise is the typical summertime higher chances for
convection during the day/evening hours and less overnight/early
morning. However...small variations in this pattern will have big
impacts on the chances...timing...and location of convection...thus
confidence is still not terribly high in that respect. As of the
latest model runs...highest precipitation chances will be on Sunday.
Temperature-wise: highs will generally be in the middle 80s to low 90s
through the period...with overnight lows steady in the upper 60s to
low 70s. Forecast soundings continue to indicate precipitable waters in the 1.5-2
inch range through the period...thus there is still the threat of
some minor flooding resulting from developing storms. As of this
afternoon...central NC is under just a general thunder threat for
Saturday. A shortwave traversing the area on Monday may bring the
best chance for strong storms...with GFS bufr soundings indicating
modest instability...but weak shear. Given how things can change
between now and then...will leave mention out of severe weather potential statement for now.
Aviation /00z Friday through Tuesday/...
as of 800 PM Thursday...
24 hour taf period: convection is beginning to wane this hour but
showers and storms will still remain in the vicinity of krwi for the
next couple of hours. All other sites may see a lingering shower but
otherwise mostly VFR conditions. As with the past couple of
nights...there exists a chance of fog or low stratus near daybreak
but guidance is not picking it up particularly well and confidence
is only medium at this time. Triad sites and krwi which is getting
some extended precipitation may be the best locations for fog/low
stratus overnight. Expect another round of convection tomorrow
afternoon but outside of convection...VFR conditions should prevail.
Long term: a prolonged period of unsettled
weather will lead to periods of adverse aviation conditions for the
next several days.