Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Columbia SC
1013 PM EDT Thursday Aug 21 2014
a strong upper ridge will lead to continued hot conditions
Friday. A back door cold front will move SW into the northern and
central midlands Saturday...and shift towards the csra Sunday.
This will lead to a chance of thunderstorms along and ahead of the
front...with temperatures returning to more normal levels behind
it. The front will shift to our south early to middle next
week...leading to generally fair weather with near normal
Near term /until 6 am Friday morning/...
upper ridge and surface high pressure centered over the lower
Mississippi Valley/Gulf Coast continue to dominate the weather
across the midlands and csra. This will continue into Friday. 88d
regional radar composite shows decaying line of showers moving
southeast across central/east NC. This was once a part of a larger
line of showers and thunderstorms that both the hrrr and WRF
indicated would weaken through the evening hours. Satellite loop
shows some debris clouds from this convection that will be
spreading across the region overnight...especially along the NC/SC
border. Otherwise...skies will remain mostly clear and
temperatures falling into the Lower/Middle 70s by sunrise.
Short term /6 am Friday morning through Sunday night/...
little change Friday. Upper ridge will remain centered just to our
west...with surface trough across the coastal Carolinas. This and
a low level downslope flow will lead to continued hot maximum temperatures.
Models continue to indicate maximum temperatures near 100 degrees again most
areas...and also continues to indicates dew points mixing down
into the 60s across most of our forecast area to near 70 southeast forecast area...keeping heat
indices below our heat advisory criteria of 110f. Only isolated to
slight chance diurnal thunderstorms at best due to building ridge
aloft...and fairly dry low level air leading to high levels of
free convection/high convective temperatures.
Main issue for Saturday and into Sunday is timing of approaching
back door front. Latest NAM a little faster than GFS. Guidance
blend and short range ensemble suggest front with associated band
of thunderstorms moving into the northern and central forecast area Saturday
afternoon. Chance probability of precipitation should generally suffice.
Warm maximum temperatures still possible Sat ahead of the front...with
warmest temperatures favoring the csra where temperatures could reach 100 again.
With NAM being slightly faster than GFS with the back door front...the
NAM MOS is slightly cooler than the GFS MOS for Sat maximum
temperature...especially north and central. Even if temperatures near 100
reached again Sat...guidance still suggests dewpoints low enough
to preclude heat index values from reaching our heat advisory
criteria of 110f.
Front expected to shift SW through the forecast area Sat nt through sun nt. Expect
chance probability of precipitation near and just ahead of the front...with cooling temperatures
along and north of it. So...probability of precipitation Sun afternoon favoring the csra. High
temperatures Sunday should be noticeably less behind the front.
Long term /Monday through Thursday/...
front to push to our south early to middle next week with surface high
pressure building down the eastern Seaboard...with upper ridge
aloft. Slightly cooler and drier air behind the front along with
ridge aloft will reduce convective chances...to slight chance at
best. Temperatures expected to be generally near normal.
Aviation /22z Thursday through Tuesday/...
VFR conditions expected to dominate the period.
Satellite loop shows convective debris clouds will continue to
cross the area overnight...which will again work to prevent fog
development. GFS lamp still indicating MVFR fog at ags/ogb
06z-13z. Given expected dry airmass and high clouds...will not
include in fog in the forecast. Expect light and variable/calm
winds overnight. On Friday...winds will be from the northwest/west
around 5 kts through the day.
Extended aviation outlook...MVFR or IFR conditions possible in late
night and early morning fog Saturday through Monday. Isolated
afternoon and evening thunderstorms may also bring restrictions.