Area forecast discussion
National Weather Service Charleston SC
110 am EDT Sat may 18 2013
Synopsis...
an upper disturbance will move north of the area through the weekend
as Atlantic high pressure builds across the region. High pressure
will be the dominant feature through much of next week before a cold
front possibly approaches on Friday.
&&
Near term /until 6 am this morning/...
Atlantic high pressure at the surface will prevail overnight...as a
short wave trough approaches from the west. Middle and high level
clouds will increase in coverage as the trough nears. The
increase in clouds and a light southerly flow will keep low
temperatures mainly in the middle 60s tonight...with upper 60s near
the immediate coast.
&&
Short term /6 am this morning through Monday/...
Saturday and Saturday night...a deep and expansive longwave upper
ridge will encompass much of the eastern half of the country with an
embedded shortwave trough positioned near the Ohio Valley. This
baggy trough caught within the larger scale ridge will slowly
meander across the Appalachians and towards the East Coast. Pieces
of vorticity energy associated with this feature will cross the forecast
area with some lowering of heights. At the surface...the forecast
area will be in the southerly flow regime around high pressure over
the Atlantic. Model soundings show the atmosphere become more
conducive to convective development in the afternoon compared to
previous days...especially along and west of I-95. Areas east of
I-95 are prognosticated to see warmer 850 mb temperatures and a cap that will
likely keep development isolated at best. Further west...the cap
erodes and with cooling/moistening profiles...scattered
showers/thunderstorms are expected. The expectation is that this
will be just garden variety showers/storms as none of the severe
weather parameters are particularly impressive. Highs will continue
a few degrees above normal reaching the middle/upper 80s.
Overnight...ongoing convection should become increasingly confined
further west and north as the seabreeze pushes inland. I have
maintained a small area of slight chances through the night closer
to the trough and better moisture. Lows will be mild and in the
middle/upper 60s.
Sunday through Monday...this will be the most active time period
with the best coverage of showers/storms. The baggy shortwave trough
and associated passing vorticity maxes will linger overhead while a moist
S/southeast flow in the low levels continues. The models continue to depict
an increasingly moist atmosphere with precipitable waters rising into the 1.7-1.8
inch range at times...which is near the 99th percentile and 2
Standard deviations above normal for middle/late may. The result is a
quite moist and uncapped scenario where showers/storms could develop
at just about any time. In fact it wouldn/T be surprising if at time
the coverage of precipitation becomes numerous. This will likely be more
closely timed with the passing of embedded energy aloft which has a
low confidence at this time. Probability of precipitation have been increased more into the
middle/high chance range for the daytime hours...with even low chances
going overnight. With considerable cloud cover around insolation
will be a bit limited keeping highs down a few degrees...but still
near or slightly above normal.
&&
Long term /Monday night through Friday/...
the upper shortwave north of the area on Monday will essentially
dissolve across the eastern Carolinas on Tuesday leaving a very weak
ridge pattern in place. Atlantic high pressure will produce an
onshore flow with sea breezes developing each afternoon. Surface
dewpoints will persist in the middle 60s with highs climbing well
into the 80s each day. Although there are no strong forcing
mechanisms...we kept isolated showers and thunderstorms in the
forecast each afternoon/evening. A cold front could move into the
area on Friday.
&&
Aviation /06z Saturday through Wednesday/...
VFR conditions will prevail at kchs and ksav through 06z Sunday.
Isolated convection could develop later this afternoon mainly
west of the I-95 corridor...probabilities of any convection
impacting the terminals are too low to include in the forecast at
this time.
Extended aviation outlook...primarily VFR. Low chances of direct impacts
from isolated to scattered mainly afternoon showers/thunderstorms
through early next week.
&&
Marine...
overnight...quiet marine conditions will prevail as surface high
pressure east of the waters remains the dominant weather feature.
Generally expect south winds less than 15 knots with seas 2-3
feet...highest in the outer waters.
Through early next week...Atlantic high pressure will be the primary
marine influence with southerly flow prevailing. Wind speeds will
persist in the 10-15 knots range with seas 4 feet or less.
&&
Chs watches/warnings/advisories...
Georgia...none.
SC...none.
Marine...none.
&&
$$
Synopsis...
near term...
short term...bsh
long term...jaq
aviation...
marine...
