Area Forecast Discussion
Issued by NWS Columbia, SC

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000 FXUS62 KCAE 061454 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 954 AM EST Tue Dec 6 2016 .SYNOPSIS... Complex low pressure extending from the Ohio River Valley to Southeast Coast will move northeast and be mainly off the Mid- Atlantic Coast late tonight. Dry high pressure will briefly build across the forecast area for Wednesday. Another cold front will cross the region Thursday bringing much colder air for the end of the week. && .NEAR TERM /THROUGH TONIGHT/... The RAP surface-based LI pattern suggests the wedge of cool air will linger through today supporting continued high low-level relative humidity and associated low ceilings and fog. Radar and satellite trends support much of the lift ahead of a mid-level shortwave trough will shift east of the forecast area around midday. There will be cooling aloft associated with the trough which will help support continued scattered showers. There may be enough instability for thunderstorms but based on radar and satellite trends with the colder cloud tops well southeast of the forecast area the thunderstorm chance is low. There will be strong shear associated with the low-level jet just above the surface wedge. If instability can possibility develop then severe thunderstorms could occur. Complex low pressure extending from the Ohio River Valley to Southeast Coast will move northeast and be mainly off the Mid- Atlantic Coast late tonight. The models show a weak pressure gradient in the forecast area. Expect continued high low-level moisture and with drying aloft and nocturnal cooling significant fog will likely develop as indicated by most of the NAM and GFS MOS and a significant number of SREF members. Followed the guidance consensus for the temperature forecast. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... Dry and fair weather expected across the forecast area Wednesday in the wake of the departing system with weak high pressure trying to build into the region. Temperatures will be slightly above normal with highs in the 60s Wednesday as 500 mb flow remains southwesterly with 850 mb temperatures relatively mild around +8 C to +10 C. The next weather system will begin to take shape late Wednesday as an upper trough moves east across the middle of the country and drives a cold front across the forecast area Thursday. Moisture is marginal along the front with precipitable water values rising up to near 0.9 of an inch and the 850 mb flow becomes westerly to slight northwesterly as the front approaches further limiting the rain chances, despite favorable upper dynamics with the right entrance region of the jet present. Will continue to carry slight chance to low chance pops late Wednesday night into Thursday. Temperatures will warm ahead of the frontal passage Thursday with highs ranging from the upper 50s western Midlands to lower to mid 60s eastern Midlands. Strong cold advection Thursday night under clearing skies should allow temperatures to fall into the upper 20s to lower 30s. && .LONG TERM /FRIDAY THROUGH MONDAY/... The extended period will feature dry weather and well below normal temperatures early in the period as a continental polar air mass settles over the region, followed by increasing chances of rain by day 7 Monday as the next weather system approaches. The upper trough axis will cross the region Friday with 500 mb flow becoming slightly northwesterly while neutral to slight cold advection continues near the surface as Canadian high pressure builds in from the northwest. This air mass will be the coldest we have experienced this season with highly anomalous 850 mb temps around -6 C and surface dewpoints falling into the teens. Surface high pressure will reside over the area Saturday before shifting offshore Saturday night in response to shortwave energy moving eastward across the middle of the country with cyclogenesis occurring over KS/OK Saturday night, then deepening and lifting northeastward into the Great Lakes region Sunday. There remain some timing differences among the deterministic medium-range models but the ensembles push a cold front across the area sometime Monday, tapping moisture off the Gulf of Mexico. Will continue to highlight increasing pops Sunday night and peaking on Monday but keeping pops in the chance range. Temperatures during this period will be cold with highs Friday and Saturday struggling through the 40s to possibly lower 50s Saturday with lows in the low to mid 20s Saturday morning and only slightly warmer Sunday morning. Cannot rule out possible record lows Saturday morning. Temperatures will moderate warmer Sun/Mon back to near normal values with highs in the upper 50s into the 60s and lows in the 40s. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/...
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Expect widespread IFR/LIFR conditions through much of the TAF period. The RAP surface-based LI pattern suggests the wedge of cool air will linger through today supporting continued high low- level relative humidity and associated low ceilings and fog. Radar and satellite trends support much of the lift ahead of a mid-level shortwave trough will shift east of the forecast area around midday. There will be cooling aloft associated with the trough which will help support continued scattered showers. There may be enough instability for thunderstorms but based on radar and satellite trends with the colder cloud tops well southeast of the area the thunderstorm chance is too low to include in the terminal forecasts at this time. There should be significant shear associated with the low-level jet just above the surface wedge. Based on the NAM and KCAE 88D trends we have included LLWS in the terminal forecasts. Drying aloft with continued high low-level moisture plus light wind and nocturnal cooling supports IFR fog overnight as indicated by most of the NAM and GFS MOS and a significant number of SREF members. EXTENDED AVIATION OUTLOOK... A cold front with little moisture will move through the area Thursday. Breezy conditions may be associated with the front.
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&& .CAE WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. && $$ SYNOPSIS...99 NEAR TERM...99 SHORT TERM...99 LONG TERM...99 AVIATION...99

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