Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Columbia SC
731 am EDT Friday Apr 18 2014

Synopsis...
moisture will increase today ahead of low pressure in the
northeast Gulf of Mexico. The low will move slowly across North
Florida and be off the southeast coast Saturday afternoon. The low
will move a little farther out to sea Easter Sunday.

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Near term /until 6 PM this evening/...
radar and satellite trends show moisture spreading into the
forecast area from the south ahead of low pressure in the Gulf of
Mexico. The models show isentropic lift increasing especially
in the southeast section today. Believe rain will overspread the
area but will be delayed especially in the north part because of
the dry air initially in place. Used the hrrr and Storm Prediction Center WRF for the
start time of the rain. Believe it will begin in the south part
this morning...the central section about midday and the north part
late in the day. Cloudiness and evaporative cooling associated
with the moisture spreading into the area should hold down
temperatures. We used the colder temperature guidance.

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Short term /6 PM this evening through Sunday night/...
the models are in agreement indicating the greatest isentropic
lift and bulk of the rain will occur tonight. High moisture should
continue through Saturday night associated with the offshore low.
There remains uncertainty with the forecast Sunday. The NAM is
slower shifting moisture eastward and may be correct since the
500 mb cut-off low may be slow to shift eastward. The guidance probability of precipitation
were close tonight through Saturday night. We used an average of
the NAM and GFS MOS for pop forecast Sunday. Cloudiness and
northeast flow supports the colder high temperature guidance. Used
the guidance consensus for the low temperature forecast. The GFS
was farther north with the position of the 500 mb cold pool and shows
temperatures lowering to near -18 over the forecast area Saturday.
The associated lapse rates would likely support a few elevated
thunderstorms late tonight into Saturday. The NAM kept the core of
the cold air aloft south of the forecast area. We held off
including thunderstorms in the forecast for now because of the model
inconsistency. The NAM and GFS plus sref mean support a soaking
rain with totals around 2 inches. If these amounts occur here and
in the headwaters...flooding may occur at some of the river
forecast points.

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Long term /Monday through Thursday/...
the GFS and European model (ecmwf) indicate warmer and drier air will return to
the region Monday with an upper ridge building and high pressure
at the surface. An upper trough will approach from the west
Monday night with increasing moisture Tuesday. The models show a
cold front moving into the area Tuesday afternoon and night.
Continued to indicate a chance of showers associated with this
feature. Dry ridging behind this front will likely dominate during
the rest of the medium-range period. The GFS...ECMWF...and ekd MOS
were in good agreement with the temperatures through the period.
Expect highs in the upper 70s and lower 80s Tuesday through
Thursday.

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Aviation /12z Friday through Tuesday/...
surface high pressure will remain entrenched along the eastern
Seaboard. Upper trough to our west will cut off along the Gulf Coast
later today and tonight. Surface low pressure developing in the Gulf
of Mexico will drift to the NE towards North Florida. This will lead to rain
gradually spreading NE towards our forecast area later today and tonight...with
resultant lowering of cigs/vsbys. In the near term...an area of MVFR
ceilings in an east-northeast low level flow off the Atlantic may spread west into
the forecast area. Current radar indicates a large area of showers spreading
up from the Gulf of Mexico across North Florida/S Alabama/S Georgia. High resolution
models bring rain towards ags/dnl by around midday to early
afternoon...spreading NE towards the other terminals during the
afternoon. Rain is expected to continue tonight and Saturday...with
ceilings expected to lower to IFR.

Extended aviation outlook...a prolonged period of rain and/or
IFR ceilings may linger through Sunday...with breezy conditions or low
level wind shear possible at times.

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Cae watches/warnings/advisories...
SC...none.
Georgia...none.
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