Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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946 FXUS62 KRAH 201159 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 700 AM EST Fri Jan 20 2017 .SYNOPSIS... An upper level trough will pivot northeast across western North Carolina into this morning. This will be followed by a brief quiet period Friday afternoon and night. A strong storm system is expected to affect the region over the weekend into Monday. && .NEAR TERM /THROUGH TONIGHT/... As of 400 AM Friday... MVFR ceilings are now showing up in the southwest as a southern stream shortwave approaches the area. Radar still shows main precipitation back across western NC and moving northeastward. The Triad will begin experiencing rain closer to 12z and with this a further drop in ceilings. Looking at the main 500 mb vorticity max associated with this feature, it tracks northeastward, brushing the Triad and continuing northeastward into VA. With that in mind the best chances for more moderate to heavy precipitation will be along the northern tier today with lighter showers to the south. High resolution models show much of the rain ending later this afternoon as the system moves eastward and out of the area. Max temps upper 50s across the northeast to mid to upper 60s across the south. Multiple guidance sources showing a high confidence fog situation later tonight into Saturday morning as dewpoints remain in the upper 40s to low 50s across the area and a very moist airmass prevails. With near 100 percent relative humidity in place, low temperatures will also be in the upper 40s to low 50s across the area. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... As of 400 AM Friday... After a brief break in precipitation, weak isentropic lift will continue on Saturday keeping a chance for rain in the forecast, with the better chances later in the day when a 500 mb vort max moves through the area. High resolution models are depicting a line of heavier showers and perhaps a an isolated thunderstorm moving through Saturday afternoon. Model forecast soundings are more wet than unstable and so moderate to heavy showers should be more of the characterization of the precipitation as opposed to more widespread thunderstorms. The line will move through and out of the CWA by Saturday evening. A quarter to a half an inch of rain will be possible but due to the linear and progressive nature of the system, the entire day should not be a washout. Despite the clouds and rain, an increase in warm air advection will help temperatures rise into the mid to upper 60s with a few 70s across the south. Precipitation chances will continue to increase on Saturday night ahead of a developing set of low pressure centers that will affect the area Sunday and Monday. Southwestern areas will be most vulnerable to precipitation. Lows in the 50s. && .LONG TERM /Sunday through Thursday/... As of 220 AM Friday... Earlier thinking remains valid. Warm and stormy weather will rule Sun through Mon, followed by dry and mild weather Tue through Wed. A pattern shift toward lower (higher) heights over the eastern (western) CONUS will commence Wed night, with cooler temps arriving for Thu. Sun through Mon night: Widespread showers and perhaps a storm or two should be ongoing across central NC early Sun, within vigorous forcing for ascent generated by DPVA with a wave tracking NNE through the area, having emanated from the deep low over the lower Miss Valley, along with a 50 kt low level jet punching into the area from the south, and intense upper divergence. PW of 200-300% of normal in conjunction with this strong lift will support a period of heavy rain Sun morning into early afternoon, as an occluded surface low tracks NE over the NC Piedmont. A slug of relatively drier mid level air will move in from the south Sun afternoon, leading to a short relative lull in coverage and intensity, and will have categorical morning pops dipping to good chance/likely for a period in the afternoon within brief shortwave ridging between the exiting wave and the upper low crossing the Gulf States. This lull will be short-lived as the upper low shifts east over AL/GA then NE over the Carolinas, bringing another round of strong deep lift. The ECMWF/GFS have come into better agreement on timing, although the ECMWF is still a bit faster than the GFS. The slightly slower GFS speed is preferred based on the strength of this system. Will ramp pops back up to categorical Sun evening into the early overnight hours, followed by another downturn in coverage and intensity late as a mid- upper dry punch arrives along with cooling low levels. Scattered to numerous showers will persist through Mon as the upper low crosses the region with ~7 C/km mid level lapse rates and lower but still above-normal PW. Precip chances will wind down Mon night as the low shifts to our north. A few strong storms remain possible, mainly from midday Sun into Sun evening, with a 70+ kt mid level jet streak accompanying powerful upper divergence and steep 700-500 mb lapse rates over 7 C/km according to the GFS. CIPS analog guidance continues to suggest more of a severe threat for FL compared to our area, historically speaking, although GFS forecast soundings for central NC still show long wavy hodographs and marginal to moderate instability, suggestive of at least a modest risk of a few strong wind-producing storms, and perhaps a tornado as well along and north of the occluding frontal system. Highs in the mid 60s to around 70 Sun, lows from the upper 40s to mid 50s Sun night, and mid 50s to lower 60s for highs Mon. Lows in the low-mid 40s Mon night. Tue through Thu: Mid level heights rise over the Southeast as a mid level ridge axis shifts over the region, while surface high pressure crosses the northern Gulf and FL. Expect fair skies Tue/Wed with slightly cooler but still above normal temps. The aforementioned pattern change will begin late Wed night or Thu morning (ECMWF brings a cold front through earlier than the GFS) as a strong EPac trough this weekend shifts eastward and begins to tap into cooler polar air that has been bottled up well to our north. Expect highs back down into the 50s Thu. A few showers are possible with the cold front, although will keep pops on the low side given the significant model timing differences. -GIH && .AVIATION /12Z FRIDAY THROUGH TUESDAY/...
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As of 110 AM Friday... 24 Hour TAF period: Conditions have come down to MVFR in most locations across the western Piedmont as rain has moved into the western half of the forecast area. This system will continue to track north and east. expect eastern sites to follow suit with lower ceilings, visibility and a period of rain. Once the system moves through conditions will gradually improve later today. Long term: Expect fog early Saturday morning and then attention turns to a stronger system expected to bring the possibility of thunderstorms to the area on Saturday. Conditions should return to VFR on Sunday.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Badgett NEAR TERM...Ellis SHORT TERM...Ellis LONG TERM...Hartfield AVIATION...Ellis

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