Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Columbia SC
206 am EST sun Jan 22 2017
a warm front will extend through the forecast area today ahead
of strong low pressure. The low will be near the area tonight.
Severe thunderstorms are possible today and this evening. The
low will begin to lift north of the region Monday. Dry ridging
will move into the area Tuesday.
Near term /through tonight/...
there will be a threat of severe thunderstorms through this
A warm front will extend through the forecast area ahead of
strong low pressure today. Satellite and radar trends support
numerous showers and thunderstorms early this morning mainly
associated with a mid-level shortwave trough. Shear will be high
with h85 wind near 50 knots. Observation trends support
increasing instability associated with the low-level southerly
flow. The instability will likely remain weak this morning as
depicted by the NAM and GFS but because of the very strong shear
severe thunderstorms including tornadoes are possible. The
threat should be greater in the southeast section closer to the
more unstable air.
The high-resolution models support a lull in shower and
thunderstorm coverage as this lead mid-level feature lifts
northeast of the area later this morning. There will likely be
increased coverage late this afternoon into the evening just
ahead of the upper low. The NAM and GFS are consistent
indicating strong instability developing as the cold upper
low gets closer to the area. The models display surface-based
Li values -5 to -9 with the greatest instability in the east
section closer to greater low-level moisture. This instability
combined with continued favorable h85 and h25 jet dynamics and
a mid-level dry slow supports the potential for supercells
ahead of an qlcs. Significant tornadoes (ef2 damage or greater)
and large hail will be possible this afternoon and evening.
The severe thunderstorm threat should end late tonight as the
warm or occluded front shifts north of the forecast area with a
loss of surface-based instability. Wrap-around moisture and cold
air aloft associated with the upper low supports a continued
shower chance with graupel possible. The NAM MOS supports wind
close to lake Wind Advisory criteria.
Short term /Monday through Tuesday/...
the deep low should be lifting northeast of the area Monday.
Wrap-around moisture and cold temperatures aloft support a shower
chance mainly early. Graupel will be possible because of the
cold air aloft. The models were not consistent with the wind
speed forecast Monday into Monday night with the NAM MOS
showing the higher values. Based on the pressure gradient
associated with the strong low north of the area and forecast
consistency we followed the NAM. A lake Wind Advisory may be
needed. It should be dry with less wind Tuesday as ridging
moves into the area. The temperature guidance is likely too high
Monday because of the cold upper low close to the area. Followed
the consensus for the temperature Monday night and Tuesday.
Long term /Tuesday night through Saturday/...
a cold front is forecast to push through the forecast area
Wednesday night or Thursday supporting a chance of showers. Much
cooler yet seasonable temperatures will follow this front for
Friday and Saturday.
Aviation /07z Sunday through Thursday/...
restrictions expected for a majority of the 24-hr taf period.
A return to MVFR/IFR conditions is currently underway at all taf
sites. This is ahead of another developing round of showers and
strong thunderstorms. Current region radar shows showers and
storms across southern Alabama and Georgia. Near term guidance
indicates this activity will be pushing northward overnight, and
is expected to be nearing the csra sites between 07z-08z, and
then into the midlands sites between 08z-09z. Have trended tafs
Models are consistent showing IFR/LIFR restrictions through the
overnight period with a possible improvement to MVFR by mid
Sunday morning associated with a dry slot. Damaging winds, large
hail and tornadoes will be possible with strong storms through
Extended aviation outlook...showers and thunderstorms and associated
restrictions are likely to continue Sunday evening and into Monday
as the main upper trough crosses the region.