textproduct: Columbia

SYNOPSIS

Warm weather continues with a chance for showers this afternoon and into Wednesday. A very dry and cold air mass moves in behind the front for the remainder of Thanksgiving week. Temperatures return to seasonal values late in the weekend but the chance of rain also returns by early next week.

NEAR TERM /THROUGH TONIGHT/

Key message(s):

- Showers and a few thunderstorms will move across the Southeast today and tonight.

Shortwave moving across Ga this morning has brought a line of heavy showers into the northern CSRA. This line will continue to track eastward into the early afternoon hours. While the southern end of the line has slowed and weakened, the central/northern portions continue tracking east/northeast. This should bring the activity into the central/northern Midlands, with mainly a brief period of moderate rainfall possible. Lingering scattered light rain expected behind this line through the afternoon. In addition to this activity, additional light showers will be moving inland from the coastal plain, with that activity nearing the far eastern counties during the afternoon too. Afternoon high temperatures will reach the mid to possibly upper 70s in many areas prior to the rain, then temperatures cool into the mid to upper 60s behind the line of rain showers for a period. during the afternoon.

Later this evening and overnight, break in the rain early this evening, then another round of showers will become possible late tonight ahead of an approaching cold front. This rain is not expected until after midnight, with highest pops closer to sunrise Wednesday morning. Overnight lows still on the mild side, with readings around 60 due to warm advection and cloud cover.

SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/

Key message(s):

- Scattered rain showers and isolated storms into early afternoon ahead of cold front.

- Breezy and warm Wednesday before cold front moves through.

- Much colder and drier Wednesday night through Thursday night

Wednesday and Wednesday Night: Strong upper low/trough moves into the Great Lakes and Ohio Valley driving a cold front through the forecast late Wednesday into Wednesday night. A line of scattered showers is expected to be ongoing at the start of the forecast period with the axis of highest PWATs around 1.5 inches moving through the forecast area and strong moisture convergence along and ahead of the front. Isolated thunderstorms also possible with MUCAPE values as high as 500 J/kg but mainly across the eastern half of the forecast area. Overall rainfall totals are not expected to be very high with most locations receiving a tenth of an inch or less but isolated locations could see up to a quarter inch.

Breezy conditions are expected with an increased pressure gradient and 850mb winds around 25 to 35 knots resulting in wind gusts of 25 to 30 mph at times. Strong winds also expected with the surge of cold advection that arrives Wednesday evening behind the front and a lake wind advisory may be needed although it looks marginal at this time. Temperatures will continue to be warm with above normal highs as the cold air lags a bit behind the front and surges in during the evening hours. Highs should again be in the 70s but temperatures plunge Wednesday night with lows falling into the 30s with the cold advection, despite non-ideal radiational cooling.

Thursday and Thursday Night: A significantly colder and drier air mass settles over the forecast area on Thanksgiving day with dewpoints in the low to mid 20s and possible upper teens by Thursday afternoon. This will likely result in near critical RH (25%) but winds should be quite a bit lower than on Wednesday. High temperatures will be well below normal with 850mb temp anomalies 5 to 10 degrees below normal resulting in highs in the 50s with continued cold advection. Overnight lows expected to drop into the upper 20s to lower 30s under mostly clear skies but still not ideal radiational cooling as the center of the surface high remains to our west over the MS Valley.

LONG TERM /FRIDAY THROUGH TUESDAY/

Key message(s):

- Cold and very dry air mass remains in place into the weekend.

- Temperatures moderate some late in the weekend into early next week with possible increasing rain chances.

The upper trough axis shifts east of the area on Friday with 500mb heights and flow becoming more zonal as strong surface high pressure migrates eastward to the east coast Friday night and Saturday. The cold and dry air mass will remain over the forecast area Friday and Saturday with high confidence in below normal temperatures with highs struggling to get out of the 40s and low 50s both Fri/Sat. Friday night looks to be the coldest night with near ideal radiational cooling with calm winds and clear skies and very dry air mass resulting in lows well into the 20s. NBM may still be on the warm side for lows as the NBM 50th percentile is several degrees colder and MOS guidance is also a few degrees colder.

Ensemble mean 500mb flow Saturday into early next week shifts more southwesterly across the southeastern states in response to upper level troughing over the western part of the country. This upper flow pattern should support a transition to more near normal temperatures with increasing moisture and chances of rain. While details remain uncertain that far out, ensemble PWATs rise to 150-175 percent of normal Sunday into early next week which would favor increased chances of rain with any shortwave energy moving through the southwesterly flow aloft.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Variable conditions as rainfall moves through the region the next 24 hours.

A line of showers will be moving into the CSRA and central Midlands at initial taf issuance timeframe this afternoon. This could bring a brief period of mvfr visibilities along the leading edge in areas of heaviest rainfall. Have started off ags/dnl/cae/cub with at least vcsh and a tempo group through 20z. May still see some isolated to scattered light rain behind the main area of precip, so will hold onto vcsh through 00z at most of those sites for now. At ogb, confidence is lower in regards to rainfall due to the southern end of the line slowing and weakening. If it holds together it may be just west of ogb around 18z. Will make final decision on whether to include vcsh and tempo at that site closer to actual 18z issuance time period. In addition to the showers, skies will go from mostly sunny and vfr, to overcast with ceilings low end vfr behind the line. Broken vfr ceilings then expected overnight ahead of the next approaching cold front for Wednesday. There should be another round of rainfall late tonight, some time after 06z and through 14z at least on Wednesday. This will bring an additional period of lower mvfr ceilings and visibilities as it moves through. Drier air then moves in after 15z, with some lifting of ceilings near the end of the taf period. Winds today out of the south ahead of showers, then turning more southwest behind the rainfall. Winds on Wednesday will turn more westerly as the front move through, with wind speeds and gusts picking up near the end of the period.

EXTENDED AVIATION OUTLOOK...Return of VFR expected Wednesday evening and through the remainder of the period.

CAE WATCHES/WARNINGS/ADVISORIES

SC...None. GA...None.