Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
1103 am EDT Thursday Jul 10 2014
a weak cold front will approach the region tonight and will
dissipate by the weekend. Another cold front will approach from
the west by the middle of next week. This front will likely stall
and dissipate over the region. Otherwise...the region will remain
situated between Atlantic high pressure and an inland trough of
low pressure through the period.
Near term /until 6 PM this evening/...
this afternoon...high pressure will gradually retreat over the
western Atlantic as a broad trough of low pressure tracks from the
Midwest to the northeast. This trough will likely force a weak surface
front toward the southeastern United States throughout the day
before arriving sometime late tonight. Ahead of the front...a
south/southwest flow appears to be replacing dryer air with deeper
moisture...which should support shower and/or thunderstorms during
peak heating. The atmosphere remains strongly capped as indicated by
the latest 12z chs sounding from this morning...suggesting shower
and/or thunderstorms should hold off until early afternoon. Hires
models indicate convective development mainly along an inland
moving seabreeze early this afternoon...before coverage expands
inland as convective temperatures in the lower 90s are met. Afternoon high
temperatures are expected to reach the low 90s away from the coast...highest
in locations that remain rain-free for a longer period of time.
Given the current setup...have maintained the overall trend in the
precipitation forecast for today...with probability of precipitation near 60 inland where boundary
interactions between showers and thunderstorms as well as the
seabreeze and approaching weak front occur this evening. Slightly
lower chances of showers and thunderstorms will remain near the
coast. Although overall coverage of activity appears slightly less
than what previous model runs depicted...moisture convergence
along/ahead of the approaching front suggest increasing precipitable waters up
to around 2.00 inches this evening. Weak wind fields along with
poor middle level lapse rates during the time of deepest moisture
levels support slower moving showers and thunderstorms capable of
producing gusty winds and locally heavy rainfall...mainly inland.
Although widespread severe weather is not anticipated today...a
few pulse type storms could become strong/severe
initially...before more coverage of showers and thunderstorms
potentially depletes available energy.
Short term /6 PM this evening through Sunday/...
latest guidance suggests that due to upper troughing...a
dissipating stationary front at the surface and various mesoscale
boundaries produced by earlier convection will support some degree
of convection will persist through most/all of tonight. While
precipitation/diurnal stabilization could translate to sparse
coverage overnight...slight chance to chance probability of precipitation appear
reasonable...highest near the central/northern coast.
Friday...a weak front will be stalled over the region...and along
with sufficient deep layer moisture /pws around 2 inches/ and a weak
upper level trough...expect mainly afternoon and evening
scattered...to possibly numerous showers and thunderstorms.
Temperatures close to climatology...with highs in the lower 90s and
and lows in the lower 70s.
Saturday...a deep layer...broad ridge builds from the west. Deep
layer moisture begins to decrease...with mean rhs generally less
than 50% north and slightly higher south. A weak trough of low
pressure at the surface still lingers inland...which along with the
afternoon seabreeze...will be the main trigger for any convection.
Trended probability of precipitation lower compared to Friday to to lower moisture and
building upper ridge...but still in the the chance range.
Temperatures near to slightly above normal.
Sunday...the middle and upper level ridge continues to build from the
west. Deep layer moisture will once again be marginal...but still
enough to keep chance probability of precipitation for mainly afternoon and evening
convection. With the presence of the middle and upper level ridge and
low level flow veering to southwest...expect temperatures to be hotter than
previous days. Highs in the lower to middle 90s and lows in the middle 70s
Long term /Sunday night through Wednesday/...
a deep layer ridge begins to sag south of the area through the
period as a broad upper trough...which covers the eastern half of
the u... sinks toward the region from the north. Expect
scattered afternoon and evening convection Monday and Tuesday. The
flow at lower levels will be southwest...which will keep temperatures a few
degrees above normal...with highs the middle 90s and lows in the middle to
Wednesday looks to be the wettest day of the period as a weak cold
front sags into the area along with the associated upper trough.
Given the uncertainty at this point...went with higher end chance
probability of precipitation for now.
By Thursday...the weak cold front/surface trough seems to stall and
dissipate over the region. The upper trough starts to flatten as
the deep layer moisture decreases some. Thus...climo/chance probability of precipitation for
diurnally based convection seems reasonable at this time. Temperatures near
Aviation /15z Thursday through Monday/...
thunderstorms will develop this afternoon and will persist
through this evening. Will continue to cover with cumulonimbi/thunderstorms in the vicinity within
12z tafs. Since the potential for direct impacts appears greater
at ksav...introduced a tempo group for thunderstorms there 18-22z.
Outside any thunderstorms...mainly VFR expected through tonight.
Extended aviation outlook...
mainly VFR through early next week with brief periods of flight
restrictions possible with scattered afternoon showers/thunderstorms.
By middle week...chances for convection increase as a weak cold front
approaches the area and deep layer moisture increases.
this afternoon...winds/seas will remain below Small Craft Advisory
levels. A weakening pressure pattern will generally support
west/southwest winds less than 15 kts and seas no higher than
2-4 feet. Winds should be strongest this afternoon as a seabreeze
develops along the coast but likely will not be as strong as
Tonight...south/southwest winds less than 20 knots should
prevail...although local winds could vary near thunderstorms.
Seas will range from 2-4 feet within nearshore waters to as high as
4-5 feet beyond 20 nm from the coast.
No highlights expected through at least Monday as the region remains
between Atlantic high pressure to the east and south and a weak
trough of lower pressure inland. This will keep mainly south to
southwest winds of 15 kts or less and seas 4 feet or less. Slightly
stronger winds possible near the coast east afternoon/evening as the
background winds combine with the sea breeze.
By Tuesday...the pressure gradient begins to tighten as stronger
lower pressure moves in from the northwest along with a broad upper
trough...but Atlantic high pressure tries to hold on to the
southeast. This sets up a good southwest pressure gradient. Have
kept winds 15 to 20 kts for now with seas 5 feet or less.
the early Thursday evening high tide...close to 7 PM...will be
elevated but is expected to remain below coastal Flood Advisory
levels. However...if heavy rain falls near the coast this evening
localized flooding could occur.
Astronomical high tides due to the full moon/perigee and light to
moderate onshore winds could result in minor coastal flooding near
the times of high tide during the evening hours Friday through
early next week.