Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 220221 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1021 PM EDT Tue Aug 21 2018 .SYNOPSIS... A lead shortwave trough and sfc front will traverse central NC overnight, followed by the passage of a secondary upper level trough and cold front through the area late Wednesday. High pressure will then build into the region to close the work week. && .NEAR TERM /THROUGH TONIGHT/... As of 1000 PM Tuesday... A mid/upper level trough will traverse east through the area overnight. Accompanying modest synoptic scale H5 falls on the order of 20 meters, in concert with DPVA along the lead vorticity shear axis crossing the area will support a broken band of convection through the area through ~09z. Bulk of model guidance suggest that owing to increasing sfc based inhibition, from nocturnal cooling over the next few hours, this convection will as it advances east into the central Piedmont and coastal plain counties. Will keep highest(likely)pops across the western Piedmont through 03z, with pops decreasing to chance/slight as you push east. The severe and flooding threat is winding down as well, with an isolated strong to severe storm possible across the far western zones through midnight, before aforementioned BL stabilization ends the threat. Overnight lows 70 to 75. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... As of 312 PM Tuesday... Wednesday, the l/w trough will rotate through the region accompanied by a sfc cold front. This feature will lie immediately west of our region Wednesday morning, then drift across the area during the day. This feature interacting with available moisture and modest instability will trigger scattered showers and isolated thunderstorms, primarily along and east of highway 1. NW flow behind the front will usher a stable drier air mass into central NC. This will be noted by sfc dewpoints lowering through the 60s across the western Piedmont during the afternoon. A more notable surge of drier air will occur Wednesday night with dewpoints by early Thu in the 50s, with lower 60s across the far SE. Under clearing skies and a steady nw sfc wind, overnight temperatures should range from the lower 60s NW to the upper 60s. && .LONG TERM /THURSDAY THROUGH TUESDAY/... As of 230 PM Tuesday... A much quieter pattern will setup in the extended with below normal temperatures and precipitation expected through the middle part of the weekend. Towards the end of the extended global models are showing the heat returning to the area. The last couple of runs of the GEFS, GEPS, and EPS have all show anomalously high 500 MB heights. Thursday morning surface high pressure will build into the region with a potent upper level trough axis located overhead. 850 MB temperatures behind the front fall towards 12 degrees C while 1000/ 850 MB thicknesses also fall below 1400 M. This will support high temperatures in the lower to mid 80s. The air mass itself will also be much drier and the difference will be noticeable. PWATs are forecast to fall to around 0.65" (or below the 10th percentile for this time of year) and with clear skies dewpoints will likely mix out into the upper 40s in places (esp. towards the triad). Friday morning, low temperatures will dip into the 50s for most areas as the upper level trough axis moves east and the best ageostrophic convergence moves overhead. High temperatures look very similar Friday as compared to Thursday with low level thicknesses and 850 MB temperatures remaining near identical. Friday evening into Saturday the remnant energy from the upper level trough axis will pinch off and drop southwest with another upper level disturbance approaching from the west. PWATs will remain around 0.75" Saturday though and will be slow to moderate. So even though upper level lift will pass north of the region, the area should remain dry Saturday. Sunday, 850 mb temperatures will begin to quickly increase allowing highs to climb into the mid to upper 80s. PWATs will also be on the increase Sunday (esp. towards the Triad and coast) which will allow the chance of showers and thunderstorms to enter back into the forecast. The chance looks low and will be primarily confined towards the Piedmont and coastal plain. Monday into Tuesday a mid-level ridge will begin to setup over North Carolina and allow 90 degree temperatures to return to the area. The chance of precipitation looks low these days, but this can easily change given the uncertainty in the strength of the ridge. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... As of 700 PM Tuesday... Shower and storm coverage across central NC has been rather subdued so far Tuesday evening. Still expecting a slight increase in coverage around sunset with a gradual down trend through the overnight hours. Have adjusted arrival times slightly with this package, with storms arriving between 00z/03z at KINT/KGSO, between 02z and 04z at KRDU, with VCTS further east where where uncertainty remains higher. A sfc cold front will approach from the west Wednesday, and cross the region late Wednesday through Wednesday evening. Ahead of the front, a few showers and isolated thunderstorms will occur ahead of the boundary. Otherwise expect MVFR/low end VFR ceilings across the region Wednesday morning as boundary layer moisture remains high. Can`t rule out a quick dip to IFR/LIFR too, especially if a site gets hit by overnight showers/storms enhancing sfc available moisture. Drier more stable air mass will overspread the region from the west Wednesday night into Thursday. This will initiate a prolonged period of VFR parameters Wednesday night through Sunday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...CBL NEAR TERM...CBL SHORT TERM...WSS LONG TERM...Haines AVIATION...JJM

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