Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Columbia SC
735 PM EDT Mon Jun 26 2017
a front will linger near the coast through Tuesday. Deeper
moisture ahead of the front will remain east of the forecast
area. Surface high pressure will extend through the region
Wednesday with the front farther off the coast. Diminished
relative humidity will be associated with this pattern. The
ridge will be in the Atlantic late in the week and circulate
increased moisture into the forecast area, leading to
increasing chances of storms over the weekend.
Near term /until 6 am Tuesday morning/...
an upper trough axis will remain west of the area overnight while
surface high pressure ridges into the area from the west. A dry
night is in store due to a relatively dry air mass over the
region. Dew point temperatures this evening are in the middle to
upper 50s for most locations. Precipitable water values will
remain below 1.25 inches through daybreak Tuesday. With the
unseasonably cool and dry airmass over the region, below normal
overnight lows are forecast in the middle 60s.
Short term /6 am Tuesday morning through Tuesday night/...
main concern during this time frame is the passing of an upper
trough axis during Tuesday afternoon and evening. Deeper
moisture remains well offshore with the old frontal boundary
and the lack of moisture is the limiting factor for
precipitation and limiting instability. The positively tilted
trough axis should cross the forecast area around 00z with best
positive vorticity advection crossing the region during the afternoon hours and 500mb
temperatures around -12c. Forecast soundings indicate a
generally dry atmospheric column and an inverted-v signature
with a shallow saturated layer between 700mb and 850mb
depending on the model. Precipitable water values rise to just
below 1.5 inches before the trough axis passes which may be
sufficient enough with weak instability to support
isolated/scattered showers mainly across the northern and
eastern half of the forecast area during the 18z-00z time
frame. Max temperatures will be slightly below normal ranging
from the lower 80s northern midlands to upper 80s southeastern
midlands and csra.
Much drier air will move into the region behind the trough
Tuesday night as high pressure builds in from the north and
dewpoints fall into the 50s and precipitable water values drop
below an inch. This will provide well below normal overnight
lows, nearly 10 degrees below normal, in the upper 50s to lower
Long term /Wednesday through Monday/...
spectacular weather expected across the forecast area for late
June with a seasonably cool surface ridge in place Wednesday
morning providing below normal temperatures and low humidity.
Atmospheric moisture will remain low Wednesday with precipitable
water values less than an inch providing mostly clear skies and
little chance of precipitation.
The upper level pattern transitions from nearly zonal 500mb
flow early in the period to more southwesterly flow for the
remainder of the extended forecast period with broad upper
troughing across the northern portion of the country. The
surface ridge will shift offshore Thursday and further away on
Friday allowing a moist southerly flow to return over the
forecast area with increasing dewpoints and humidity and
precipitable water values pushing back to near 2 inches by
Friday, tapping into the Gulf of Mexico. Generally expect an
increase in diurnal convection Friday through the weekend with
increasing moisture and possible weak shortwave energy
enhancing convection Sat/sun when highest pops are expected. An
upper ridge tries to build into the southeastern states on
Monday with the deepest atmospheric moisture shifting east of
the forecast area which may lead to lower chances of convection
but still will keep some rain in the forecast.
Temperatures through the period will generally be near normal
for highs in the upper 80s to lower 90s with slightly below
normal low temperatures early in the period then becoming near
Aviation /00z Tuesday through Saturday/...
a dry atmosphere is expected to ensure VFR conditions overnight into
Tuesday morning. Some guidance indicating MVFR fog at ogb late
tonight/early Tuesday morning. However, with late afternoon
dewpoints in the upper 50s there, think it is too dry. Some mid
level cloudiness may stream across the region overnight. Upper
energy and a surface trough is expected to traverse the region
Tuesday afternoon. Moisture will be limited. However, some guidance
is indicating a few showers and isolated thunderstorms possible with
these features in the afternoon. For now, will handle with vcsh
and a broken cloud deck above VFR level.
Extended aviation outlook...no significant impacts to aviation
expected through Wednesday. A return flow and increasing low level
moisture may provide a late night/early morning stratus threat
Thu/Fri. Scattered thunderstorms expected Fri/Sat.