Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
416 PM EST Monday Dec 22 2014
an inland wedge of high pressure will prevail through tonight...
before beginning to erode on Tuesday as a warm front lifts north
into the area. A strong cold front will then approach from the
west on Wednesday and move through early Wednesday night. High
pressure will then build from the Gulf Coast region on Thursday
and settle over the southeast United States Friday into Saturday.
Another cold front could shift through late in the weekend.
Near term /until 6 am Tuesday morning/...
a wedge of high pressure will remain entrenched across much of the
area tonight though a warm front will begin to lift north into
coastal sections late. The widespread rain with isolated thunderstorms
that has moved through the area this afternoon is associated with
a slug of isentropic Omega and weak shortwave that is traversing
the forecast area. This forcing is prognosticated to shift northeast of the
area late this afternoon with negative vorticity advection moving
in overnight. Although the brunt of the forcing will be gone for
the overnight hours...given the in-situ wedge and continued moist
southerly flow aloft we cannot completely rule out some patchy
rain persisting. We show the highest probability of precipitation through early evening...
tapering back overnight to chance. Temperatures will fall slightly
as the night wears on...except perhaps rise a few degrees in far
southern areas as the warm front tries to lift.
The primary concern tonight is fog development. The setup is ripe
for stratus build-down fog given the strong in-situ wedge...drier
air moving in aloft...and the warm front with moist low-level air
trying to lift north. We included areas of fog overnight and will
discuss dense fog potential in the hazardous weather outlook.
Short term /6 am Tuesday morning through Thursday/...
Tuesday and Tuesday night...the middle and upper level pattern will
begin to amplify as a trough digs across the plains states then
slowly advances eastward over the Mississippi Valley. Meanwhile at
the surface an inland wedge of high pressure will begin to
erode...likely slower than models depict...as a warm front gradually
lifts into the area on Tuesday and to the north of the area Tuesday
night. Unsettled conditions will prevail as deep moisture pushes
precipitable water values upwards of 1.75 inches and numerous
disturbances aloft cross the area within a deep south-southwest
flow. There appears to be a bit of a lull in terms of precipitation
around daybreak...but then rain/showers will increase in coverage
through the morning...becoming widespread Tuesday afternoon and
Tuesday night. Models indicate there there could be some mainly
elevated instability...so have mention of slight chance
thunderstorms across coastal and southern portions of the forecast
area in the afternoon. There is expected to be a significant
gradient in temperatures on Tuesday...with highs in the upper 60s to
around 70 near the coast and across southern areas...and in the middle
50s to around 60 in northwest parts of the forecast area where The
Wedge is likely to persist. Lows Tuesday night should be in the middle
50s to lower 60s...with temperatures potentially rising in northwest
portions of the area as the warm front lifts north.
Wednesday and Wednesday night...a deep middle and upper level trough
will advance east of the Mississippi Valley...driving a strong cold
front at the surface toward the southeast coast. The front is
expected to move through the area Wednesday evening into the early
overnight hours. Deep moisture and enhanced forcing for ascent will
support widespread showers with embedded thunderstorms Wednesday
ahead of the front. Despite impressive wind fields aloft...limited
instability at the surface due to widespread rainfall will
significantly reduce the severe weather potential and the Storm
Prediction Center only has the area highlighted in a marginal risk
for severe thunderstorms at this time. If for some reason some
surface based instability can develop...then there would be a small
potential for isolated damaging wind gusts Wednesday afternoon into
Wednesday evening. Showers will then begin to taper off from the
west-southwest overnight as the cold front shifts offshore.
Temperatures on Wednesday should surge into the lower 70s as the
southerly flow strengthens and some compressional heating occurs
ahead of the front. Lows Wednesday night will be in the upper 40s to
Thursday...surface high pressure will build into the region from the
Gulf Coast region...with westerly winds resulting in rain-free
conditions. Skies will gradually clear through the day...with highs
reaching the middle and upper 50s.
Long term /Thursday night through Monday/...
quiet weather will prevail into the weekend as high pressure becomes
centered over the southeastern United States. Overall high temperatures
should gradually warm each day as high pressure continues to slide
east late weekend...allowing a light southerly flow to return to the
area. In general...temperatures will reach the lower 60s on Friday...then
to the middle 60s on Saturday. Overnight lows should range in the the
low/middle 40s into the weekend. The next best chance of precipitation should
occur early next week with a cold front that approaches the region.
However...confidence in timing and strength of pattern is quite low
given large discrepancies in model solutions.
Aviation /20z Monday through Saturday/...
we expect both terminals to remain tanked at IFR or lower through
the majority of the 18z taf period. Widespread moderate to heavy
rain will spread across both terminals this afternoon with
occasional visibility reductions. A strong wedge of high pressure will
remain in place at least through tonight. However a warm front is
expected to lift north late tonight with increasing low- level
moisture approaching the terminals. Ongoing LIFR stratus will
likely build-down this evening with visibilities dropping to LIFR.
Conditions do not support much recovery on Tuesday...though surface
visibilities should improve a few hours after daybreak. IFR or lower
ceilings likely to persist through much of the day Tuesday.
Extended aviation outlook...MVFR or lower conditions are likely
Tuesday afternoon into Wednesday evening due to low ceilings and
occasionally reduced visibilities in fog and showers. Low level wind shear will be
a possibility Tuesday night as stronger wind fields shift over the
area in advance of an approaching cold front. VFR conditions
should prevail Thursday through Saturday.
fairly weak gradient will affect the waters tonight as the coastal
trough weakens and shifts toward the coast. Winds may swing around
to south-southeast late tonight over portions of the waters but speeds will
remain at or below 15 knots. Sea fog is the main concern. The setup
is ripe for stratus build-down fog overnight...especially across
the nearshore waters and harbors/ports. We included areas of fog
in the forecast and continued mention in the hazardous weather
outlook for dense marine fog that could affect navigation.
Tuesday...a warm front will begin to lift north and west of the
waters as an inland wedge erodes. This will allow for a southerly
flow with winds less than 15 knots.
Tuesday night through early Thursday...conditions will deteriorate
late Tuesday night into early Wednesday as the pressure gradient
tightens and strong low level wind fields spread over the waters
ahead of an approaching cold front. Small Craft Advisory conditions
are expected to develop across all waters Wednesday...then continue
into Wednesday night as the cold front moves offshore and strong
cold air advection develops in its wake. Winds will reach upwards of
around 20 knots across the near shore waters and 25 knots across the outer
Georgia waters...with higher gusts. There is a small potential for a
period of gale force gusts over the outer Georgia waters Wednesday
night into early Thursday as the cold air advection peaks. Seas will
build up to 5-8 feet Wednesday before winds shift offshore.
Thursday afternoon through Saturday...conditions will improve
quickly over all waters as high pressure becomes centered over the
southeast. Winds/seas should lower below Small Craft Advisory levels
for all waters Thursday afternoon...then continue to improve
through the weekend as the center of high pressure slides offshore.
Sea fog...mariners are advised that low stratus decks and periods of
rain or drizzle will equate to reduced visibilities Tuesday until
Wednesday...but the best chance of classic sea fog could develop as
warmer air arrives atop middle/upper 50 degree shelf water temperatures
early Tuesday prior to winds increasing enough to scour it out
late Tuesday night.
the Tuesday morning high tide is predicted at 6.4 feet MLLW in
Charleston Harbor and conditions look pretty favorable for another
bout of shallow coastal flooding along the lower South Carolina
coast. Will continue to highlight the potential in the hazardous