Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
420 PM EDT sun Apr 19 2015
Synopsis...a warm front over South Carolina will lift northeast
across North Carolina this evening as an area of low pressure moves
northeast into the eastern Great Lakes on Monday. A cold front will
move into the mountains from the west Monday afternoon and then
track east to the Carolina coast late Monday night. High pressure
will build into the region for Tuesday and Wednesday.
Near term /tonight/...
as of 345 PM Sunday...
Complicated forecast for this evening and overnight with a threat of
heavy rain and flooding issues and threat of severe weather across
the southern Piedmont and coastal plain. Widespread area of mainly
light to moderate rain shifting across central NC this afternoon is
largely associated with a northward advancing warm front in a
veering wind profile. Boundary layer dew points continue to rise
with dew points in the upper 60s across the southern Piedmont and
sandhills. Another region of convection extends from southwestern NC
southward to coastal Georgia. This area of convection is being supported
by a middle level short wave approaching a region of moderate
instability. This area has shown an increasing trend in terms of
coverage and intensity as it moves east and northeast. Convection
allowing models bring this area of convection northeast into central
NC this evening through a little after midnight. Most of the
precipitation should have cleared central NC by around 200 am.
A low-end severe weather threat...mainly in the form of a damaging
wind gust or brief tornado is possible between 22-06z...mainly
across the southern portion of the County Warning Area. A Tornado Watch is currently
in effect through 800 PM just to the southwest of the rah County Warning Area. In
addition to the limited but non-zero tornado threat...a transitory
area of heavy rain is expected to move northeast across central NC
this evening into the early overnight hours with a one or two hour
period of heavy rain. While widespread flash flooding is not
expected...urban areas and typically susceptible areas in the
western Piedmont and Yadkin Valley areas are most at risk.
Temperatures will show a limited diurnal trend tonight with the
cloud cover...precipitation and southeast breeze at 10-15 miles per hour that
becomes southwesterly overnight. Lows will range in the lower to middle
Short term /Monday and Monday night/...
as of 420 PM Sunday...
A cold front will approach the Appalachians during the afternoon and
then move through central NC Monday night before moving offshore
toward daybreak Tuesday. Lingering stratus across central NC on
Monday morning will give way to increasing intervals of sunshine
during the late morning and early afternoon hours. Boundary layer
dew points will range in the lower 60s. With afternoon heating and
surface temperatures expected to rise into the upper 70s to lower
80s...the atmosphere will become moderately unstable with MLCAPE
values in the 1000-2000 j/kg range by afternoon. Scattered
convection is expected to develop during the middle to late afternoon
across the foothills and western Piedmont as the cold front
approaches. The westerly flow may act to limit convective coverage
and recent convection allowing models suggest that the convective
coverage will be more limited than previously noted. However...if
convection can develop there is a severe weather risk mainly from
the 21 to 06z time frame as a narrow corridor of convection pushes
east. The main threat will likely be associated with damaging wind
gusts but if a less linear and more discrete convective Mode
occurs... more likely earlier in the event...than a increasing
threat of large hail will be present. Highs on Monday will range
in the 78 to 84 degree range with lows in the 52 to 60 range.
Long term /Tuesday through Sunday/...
as of 330 PM Sunday...
Tuesday through Wednesday...cold front will have moved offshore by
Tuesday morning with dry conditions returning to central NC. High
pressure will shift across the southeast US Tuesday into Tuesday
night...before moving offshore by Wednesday morning/early afternoon.
During this time frame...dry conditions will persist with temperatures
running near to slightly below normal.
Wednesday night through Thursday night...another cold front will
approach the area late Wednesday into Thursday. However...limited
moisture return ahead of this system will keep precipitation chances on the
low end. Nevertheless...will keep a slight chance pop in the
forecast for early Thursday...but mainly confined to the southeast
half of the forecast area. Highs on Thursday will range from the
upper 60s across the north (earlier frontal passage) to the
middle/upper 70s further south.
Friday through Sunday...there is fairly high uncertainty with regard
to the end of the week and especially into next weekend. The overall
pattern indicates the aforementioned cold front will stall just
south of the region for the end of the week. Then...as a southern
stream system approaches...multiple waves of low pressure will ride
along this boundary...spreading precipitation back into the area.
However...as can be expected this far out...details have yet to be
worked out. Regardless...will show probability of precipitation for early in the weekend
with (as of now at least) drier conditions by Sunday. Temperatures will
generally be near to slightly below normal.
Aviation /18z Sunday through Thursday/...
as of 245 PM Sunday...
24 hour period...multiple rounds of showers and possibly embedded
thunderstorms across the south will move across central NC this
afternoon and evening resulting in widespread adverse aviation
conditions with ceilings dropping to IFR and LIFR levels at times
and MVFR visibilities becoming IFR in heavy rain. A lull in precipitation
and a brief relaxing of ceilings/visibilities will move from southwest to
northeast late this afternoon and evening before the second round of
likely. Heavier precipitation impacts the area roughly between 22z
and 05z. Generally light rain showers are expected after 06z...most
commonly across the northern Piedmont and northern coastal plain
with dry weather expected from the pre dawn hours on Monday through
early Monday afternoon. Low clouds will persist overnight with ceilings
generally below 1kft and frequently less than 500 feet. Ceilings will
improve on Monday morning with VFR conditions expected by late
morning with a scattered-broken cumulus layer developing and ranging between
Looking further ahead...scattered showers and thunderstorms will
develop Monday afternoon across the foothills and spread east into
the western Piedmont very late in the afternoon and then move across
central NC during the evening hours. Adverse aviation conditions
including gusty winds ahead of the front and accompanying convection
with areas of MVFR/IFR ceilings and visibilities are expected. A return
to VFR conditions are expected Monday night through Thursday as high
pressure builds in.