Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
745 am EDT Wednesday Jul 29 2015
a weak pressure pattern will persist over the region into early
Thursday. A cold front will advance into the region Friday and
will stall through early next week. High pressure will gradually
into the region by the middle of next week.
Near term /through tonight/...
disorganized low pressure will reside off the coast through tonight
and is forecast to lift slowly east-northeast or NE. Deeper moisture profiles
are mostly SW through southeast of the forecast area today but our
western and southern Georgia zones do brush the region of higher
precipitable waters and enhanced 850 mb to 500 mb moisture. Since the region
remains under the eastern flanks of an expansive upper ridge...hot
and humid weather is on tap. High temperatures will warm to the middle 90s
many areas with heat indices inland Georgia zones reaching 105-108
degrees this afternoon. Probability of precipitation capped at 20/30 percent along and
west of I-95 this afternoon...aligned with the deep moisture
gradient. Seasonably strong thermodynamics will be coupled with
marginal instability and warm middle levels to produce mostly spotty
pulse convection until middle/late afternoon when scattered
convection develops just to our west and SW. Isolated stronger storms
could crop up from east central Georgia to the okefenokee...a few
of these storms could brush locations such as Metter and
Reidsville but overall we are not anticipating much of a risk for
severe weather across inland Georgia.
A few showers and thunderstorms may linger into middle evening inland zones
west of I-95 but conditions should be quiet overnight with partly
cloudy skies and perhaps some late night fog and stratus...mainly
over inland zones.
Short term /Thursday through Saturday/...
Thursday...an east-west moisture gradient will persist over the
region. Thus...afternoon probability of precipitation are graduated from slight chance near
the coast to chance inland...highest along/west of I-95. Models
depict less than impressive inland instability. Thus...the potential
for severe weather should remain quite limited...unless a stronger
multicell thunderstorm cluster which develops inland clips far
inland counties. Outside thunderstorms/before thunderstorms
develop...temperatures in the middle 90s should become common away from
the coast...and heat index values could peak in the 100-105f range
at many locations.
Thursday night...inland thunderstorm coverage/intensity should
gradually wane. However...to varying degrees guidance depicts
sufficient moisture spreading into the region from the
north/northwest to support isolated showers/thunderstorms through
the overnight. Thus...maintained ongoing slight chance probability of precipitation after
Friday and Saturday...a cold front will advance into the region and
will stall. The associated trough at the surface and aloft will
settle over the region and will focus a pool of precipitable waters exceeding 2
inches...1-3 Standard deviations above normal...over the area. This
regime will support periods of active convection featuring likely
probability of precipitation across many areas especially Friday afternoon/evening and again
Saturday afternoon/evening. Locally greater probability of precipitation could eventually be
The potential for pulse severe weather could actually be greatest as
thunderstorms fire and expand in coverage Friday afternoon. Of
greater concern...high precipitable waters and weak tropospheric winds will
support high rainfall rates and erratic storm propagation...and the
probability for localized excessive rainfall/flooding will increase.
Otherwise...temperatures could top out in the Lower/Middle 90s before
thunderstorms develop Friday. Then...held temperatures close to 90f
Saturday...although temperatures could hold in the 80s at many
Long term /Saturday night through Tuesday/...
the stationary front...associated deep layered trough...weak
steering winds and Reservoir of above-normal precipitable waters will persist over
the region through the weekend and into early next week. This
environment will support elevated probability of precipitation and a continuing threat for
locally heavy rainfall/short fuse flooding. Likely probability of precipitation appear
reasonable for Saturday. Then...model disagreement arises regarding
the position of the trough and associated axis of deepest moisture
Sunday-Monday. If the Atlantic ridge allows the trough axis to push
off the coast...the focus for heaviest rain will shift over the
Atlantic waters. However...if the Atlantic ridge remains stronger
and holds the trough axis and rich moisture over the region as
depicted by the 29/00z European...elevated probability of precipitation/the associated
potential for locally heavy rain will persist. Due to
uncertainty...capped maximum probability of precipitation at around 50 percent Sunday and
Monday. Eventually...the trough will eventually weaken or will shift
offshore...allowing high pressure to gradually build into the region
with more typical temperatures/probability of precipitation Tuesday through Wednesday.
Aviation /12z Wednesday through Sunday/...
VFR conditions expected to prevail today and much of tonight at
both ksav/kchs. Convection is expected to develop inland from the
terminals later this afternoon and evening. Areas of low clouds
are possible overnight but fog is fairly unlikely.
Extended aviation outlook...low chance for direct impacts from
thunderstorms Thursday...then increasing thunderstorm chances
Friday through the weekend.
local waterspout checklist gave a moderate to high risk for
waterspouts this morning. Web cams from the beaches indicate
favorable cumulus lines/towers. We have issued a marine weather
statement addressing possible waterspouts along the coast this
With the weak low pressure well offshore...onshore flow will generally
persist with speeds mainly in the 10 knots range through tonight with
diurnal enhancements of 10-15 knots along coastal Charleston County
this afternoon and evening. Seas 2 to 3 feet through tonight...
highest beyond 20 nm offshore.
As a cold front approaches then stall over the region...winds will
gradually veer toward the south/southwest late week into early next
weekend. While wind speeds will generally be less than 15 knots...
the sea breeze circulation and periodic nocturnal surges could push
winds to 15-20 knots. Seas of 2 to 3 feet will remain common...
although periods of 4 feet seas could occur especially at 20 nm and
beyond. Also...thunderstorms are expected at any time late week into
early next week. Thunderstorms could greatly alter synoptic winds
and will create localized hazards...perhaps including waterspouts.
elevated high tide levels are expected through the rest of the
week and the weekend thanks to the upcoming perigean Spring tide
and full moon cycle. Onshore winds will also provide additional
enhancement at times...and shallow coastal flooding will be
possible through the weekend especially with the evening high tide
cycle. Will maintain the mention in the hazardous weather
outlook. A coastal Flood Advisory could be issued around high
tide late this afternoon into early this evening for downtown