Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
1101 am EDT Sat Jul 4 2015
Atlantic high pressure will prevail as a trough of low pressure
lingers inland through the middle of next week.
Near term /through tonight/...
today...a persistent middle level trough of low pressure will extend
across much of the eastern Continental U.S. With shortwave energy that
continues to round its southern base over parts of the deep south
and Middle Atlantic States. At the surface...the area will remain between a
Piedmont trough inland and high pressure centered well offshore in
the western Atlantic. The pattern will favor deep moisture within a
west/southwest flow...characterized by precipitable waters that approach 2.0
Some questions remain in regards to the overall precipitation potential
this afternoon and/or evening. Latest radar mosaics continue to
indicate convective complexes over parts of central Alabama and
central Georgia...likely in association with 500 mb shortwaves that
continue to shift east over the area. These complexes should
generally track just to the northwest of the area this afternoon
along a slightly building ridge of high pressure from the Atlantic.
However...outflow boundaries that push south of these complexes
could be a Focal Point of convective develop later this afternoon
and evening. Most outflow boundaries will take on a west-east
orientation based on current activity...which is parallel to the
flow off the surface. This suggests any convection that does develop
along outflow boundaries will be slow to progress eastward...thus
not impacting the area until later this afternoon or evening.
Model guidance does indicate a moderately unstable atmosphere in the
southeastern United States this afternoon/evening...with sbcapes
approaching 2500 to 3000 j/kg across much of the area. In
addition...dcape values near 800-1000 j/kg and inverted-v soundings
support a damaging wind threat. Thus...a few thunderstorms have the
potential of being strong of severe while moving over the area. Best
chances of severe weather should be over southeast South Carolina
late afternoon into early evening...mainly due to stronger shear
associated with a 30-40 knots low level jet. Overall high temperatures should
range in the lower 90s away from the coast...but cloud cover could
limit them a few degrees in some areas.
Late this evening and overnight...the upper ridge may begin to
break down a bit...with the lowering heights and some passing
upper level short wave disturbances supporting low chances of
showers and thunderstorms...with the greatest coverage near the
coast. Lows should be in the lower to middle 70s across the area.
Short term /Sunday through Tuesday/...
generally a continuation of the same pattern with high pressure over
the Atlantic and low pressure inland. The main challenge is timing
of shortwave troughs aloft which will be the main forcing for
Sunday...close proximity to the upper trough along with deep
moisture will mean above normal rain chances...highest inland closer
to possible organized convection upstream. High temperatures in the
lower 90s...mainly near and west of I-95. Some showers and storms
will linger into Sunday night with lows mainly in the lower to middle
Monday...scattered to possibly numerous showers and thunderstorms
expected again with abundant clouds likely helping keep temperatures
slightly below normal closer to 90. Severe risk appears low given
Tuesday...scattered convection again although probably not quite as
much as the upper trough weakens and high pressure exerts more
influence. Highs a bit warmer closer to normal in the lower 90s away
from the locally cooler coastal areas.
Long term /Tuesday night through Friday/...
medium range guidance is in fairly good agreement through middle week
indicating more high pressure ridging. Another trough could return
late in the week. Should see low rain chances through at least
Thursday...mainly each afternoon/evening. Temperatures will
generally be near normal...with highs in the lower to middle 90s and
lows in the lower to middle 70s.
Aviation /15z Saturday through Wednesday/...
VFR conditions are generally expected to prevail through 12z
Sunday. Scattered showers and thunderstorms should develop later
today into this evening and could impact the terminals. A tempo
group has been included at both kchs and ksav from 20-24z to
indicate the potential for thunderstorms accompanied by flight
restrictions. Gusty/erratic winds are also possible in association
with any thunderstorms that develop. Although this is the most
likely timing for any thunderstorms...a few isolated storms could
occur near kchs earlier in the day and vicinity thunderstorms
is mentioned in the taf beginning at 16z.
Extended aviation outlook...brief flight restrictions are
possible in mainly afternoon/early evening showers and
thunderstorms...with the best chances likely through Tuesday.
today and tonight...conditions will slowly improve over the
coastal waters as an enhanced pressure gradient begins to relax
between Atlantic high pressure centered well offshore and a
trough of low pressure northwest of the area. Look for south to
southwest winds to prevail with speeds upwards of around 15 knots
through tonight. Seas will could subside a bit as winds
diminish over the period...but overall should range between
2-4 feet...highest in the outer Georgia waters.
Sunday through Thursday...expect a persistent pattern featuring
Atlantic high pressure and an inland trough of low pressure. A
tightened pressure gradient between these features will maintain
elevated winds/seas through the period but conditions should largely
remain below advisory levels. Seas will be 2-4 feet on average...but
could reach 5 feet at times mostly beyond 20 nm.
Rip currents...the combination of lingering lunar influences...an
easterly swell of 2 feet every 9 seconds and gusty winds will
support a moderate risk for rip currents for the lower South
Carolina beaches today. It appears slightly lower winds from
south along Georgia coast will limit the rip current risk to a
high-end low category.