Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 170605 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 105 AM EST Mon Jan 16 2017 .SYNOPSIS... High pressure along the Mid-Atlantic coast will gradually shift offshore tonight and Tuesday, in advance of a cold front approaching the mountains from the west. The cold front will progress east of the mountains Tuesday night, track southeast through North Carolina Wednesday morning, then southward offshore the Carolina coast Wednesday afternoon as an associated upper level disturbance tracks offshore the Mid-Atlantic coast. && .NEAR TERM /THROUGH TONIGHT/... As of 10 PM Monday... Cold air damming wedge will remain in place across Central NC overnight. Surprising, earlier in the afternoon the sub-VFR ceilings scattered out in a narrow corridor across the NW Piedmont. However, nocturnal cooling of the lingering shallow moist layer in place over central NC should result in lowering ceilings and potentially areas of dense fog overnight. Additionally, weak shortwave disturbances traversing the flat low-amplitude ridge in place across the region could support an isolated shower overnight. Temperatures the remainder of the night will be nearly steady with lows ranging from lower to mid 40s northeast to lower 50s south. && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... As of 105 PM Monday... The lingering CAD wedge is expected to undergo top-down erosion during the day Tuesday as southwesterly low-level flow strengthens in advance of a shortwave approaching the Mid-Atlantic from the W/NW. Initially overcast skies should become broken by early afternoon, perhaps scattering out entirely from the Triangle southward and eastward. Broken to overcast cloud cover is most likely to persist the longest across the N/NW Piedmont where occasional sprinkles cannot be ruled out. Challenging temperature forecast. Expect highs in the upper 50s (N/NW) to mid 60s (S/SE) Tuesday afternoon. Expect rather mild lows Tuesday night as the MSLP gradient tightens in advance of the approaching cold front and a southwest breeze persists much of the night. Expect lows in the mid to upper 50s, possibly a few degrees cooler in the Northern Piedmont/NE Coastal Plain where precipitation assoc/w the front is most likely to occur prior to sunrise Wed. It should be noted that a large amount of uncertainty persists with regard to the precise coverage/timing of precip assoc/w the upcoming cold frontal passage early Wed. -Vincent && .LONG TERM /Wednesday through Monday/... As of 230 PM Monday... Fast progressive flow through the extended period will produce several frontal passages Wednesday through early next week. The sensible airmass change behind each system will be minor as arctic air will remain blocked across the northern tier of the CONUS and we will remain unseasonably mild through the period. A rather vigorous short wave skating across the Ohio valley will nudge a backdoor front south into the area by sunrise on Wednesday, with fairly widespread rain in the morning tapering off during the early afternoon. Despite the modest cold air advection, we will benefit from a warm overnight min in the mid 50s bolstered by increasing sun as the day progresses to allow highs to reach the mid 60s over most of the area, with some readings near 70 along the southern tier. Lows Wednesday night will be cooler under mostly clear skies...40 north to 45 south. Dry weather will linger through Thursday night as upper ridging and surface high pressure migrate overhead. The modestly cooler airmass will be in place and highs on Thursday will stall within a degree or two either side of 60. Will see some light rain begin to spread into the west by late Thursday night as overrunning ensues in south to southwest flow as the stacked ridging moves offshore. Mins will remain mild in the southerly flow under increasing cloudiness... again mostly in the 40 to 45 range. A quick and perhaps vigorous round of showers is on tap on Friday as a low over the plains rotates northward and deep southwest flow lifts the stalled surface front north concurrent with reasonably supportive mid and upper dynamics. Will increase PoPs to likely across the entire area as uncertainty is on the rise with time in this fast flow regime. Highs Friday should uptick a degree or two in the warm air regime with mainly upper 50s north to lower 60s south. We then see a repeat of a short-lived dry spell with low amplitude mid level ridging Friday night and Saturday. Lows Friday night will be in the mid 40s with highs Saturday mostly in the lower 60s. Somewhat similarly, a stronger short wave moving across the mid west will reassert southerly flow Sunday, pushing another mild but potentially much wetter front across the area through Monday night. This upper low will be deepening as it moves into the Tennessee Valley, and as such, will produce more favorable conditions for convection as H85 winds are progged to 50kt and supported aloft by a favorably aligned upper jet. Will have 50-60 PoPs both Sunday into early Monday as we let the details resolve themselves. Mild temps linger both days...mid 50s northwest to lower 60s southeast. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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AS OF 100 AM Tuesday... 24 Hour TAF period: A mix of aviation conditions at this hour as ceilings have dropped below VFR levels in most locations. There is model disagreement this morning whether or not dense fog will occur. At this point have not included it in the TAFs as the HRRR had already depicted fog in the area which has not yet occurred. Low ceilings should then be the main threat to aviation conditions with everything down to LIFR possible. After sunrise, ceilings are eventually expected to break out although it may take until the afternoon to do so. Some gusty winds are possible up to 20 kts or so this afternoon. Long term: A frontal system will move through the area on Wednesday. High pressure returns on Thursday for a brief stay before the next system moves in Thursday night through Friday night. High pressure then returns once again for the weekend.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Vincent NEAR TERM...CBL SHORT TERM...Vincent LONG TERM...mlm AVIATION...Ellis

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