Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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645 FXUS62 KRAH 190918 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 512 AM EDT Thu Oct 19 2017 .SYNOPSIS... Surface high pressure over the Mid-atlantic will extend across the region into the weekend. A cold front will approach the area from the west early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 510 AM Thursday... A quick updated to the forecast to lower temps across the piedmont this morning and add some patchy frost to the forecast. Otherwise, skies will remain mostly clear/clear with seasonably cool/cold temps this morning. Previous discussion at 220 AM: A weak mid/upper level disturbance is currently moving across the region this morning. However, with generally a dry atmo in place, only a scattering of high cirrus is accompanying the weak disturbance this morning. Otherwise, surface high pressure will remain in place with slowly moderating temperatures. Model guidance has trended cooler with high temps today, and have such lowered highs by a couple of degrees from previous forecasts. Thus, expect high temps will generally be in the lower to mid 70s today. Mid level ridging will begin to build eastward and into the area tonight, with surface high pressure holding over the area. This will result in a continuation of dry and cool conditions with clear skies. Low temps are expected to range from around 40 in the coldest rural locations to the mid to upper 40s in the urban areas and far SE. && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... As of 235 AM Thursday... Mid level ridge axis will build overhead on Friday into Friday night, resulting in little change in the weather across central NC, other than temps will be a bit warmer. Expect high temps will generally be in upper 70s to around 80. Lows temps are expected to range from the mid 40s in the cold spots to the lower 50s in the urban areas and SE. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 315 AM Thursday... Little change in forecast rationale described well by the previous shift. Mid-upper ridging now over the wrn GOM is forecast to amplify as it builds east, across and offshore the sern US coast through the weekend, and downstream of a powerful trough forecast to amplify across the Rockies and Plains states. The models continue to indicate that this initially meridional trough will separate and yield a closing off of the srn portion of the trough, as an increasingly active srn stream jet in split flow aloft noses across the lower MS Valley by Sun night. Model spread increases with respect to the geometry and progression of a new trough forecast to amplify from the ne Pacific to the Great Lakes vicinity by the middle of next week, and consequently how quickly this trough may serve as a "kicker" to cause the aforementioned lead srn stream wave to lift and accelerate through the Appalachians Mon-Tue. At the surface, high pressure centered over the middle Atlantic states Sat will strengthen, beneath the building ridge aloft, and move off the nrn middle Atlantic and Northeast coast by Sun. A warm front will retreat nwd, in return flow around the high, across the Carolinas Sun-Sun night. This will occur ahead of a deepening surface cyclone and accompanying lead cold front related to the aforementioned srn stream closed low, forecast to migrate ne through the srn and central Appalachians late Mon-Tue. A secondary cold front, one related to the trailing trough forecast to reach the Great Lakes vicinity by the middle of next week, will likely sweep east of the Appalachians and across NC late Tue-Tue night. Sensible weather resulting from the pattern outlined above will include mild and dry conditions this weekend, followed by the passage of a band or bands of showers, and probable QLCS thunderstorms, Mon night-early Tue. Strong and coupled QG and mesoscale forcing for ascent, and strengthening lower and deep- tropospheric flow, will support an associated risk of severe storms over the Carolinas during that time. Much cooler conditions, and variably cloudy ones, with a chance of "instability" showers in cold, cyclonic flow aloft, will follow for Tue night-Wed. && .AVIATION /10Z THURSDAY THROUGH TUESDAY/... As of 515 AM Thursday... 24-Hour TAF period: VFR conditions will generally continue for the 24 hour TAF period. The one exception will be at fog prone KRWI, where some pre-dawn fog is expected early this morning. Visbys at KRWI are expected to range from MVFR-LIFR early this morning through around sunrise. Otherwise, VFR conditions will continue with light and variable to calm winds and mostly clear/clear skies, as surface high pressure remains over the region. Patchy sub-VFR visbys will again be possible on Saturday morning at KRWI, but confidence is too low to include in the TAFs at this time. Looking ahead: VFR conditions will prevail through the first half of the weekend, with brief periods of sub-vfr conditions in the pre- dawn hours possible near KRWI. Upslope flow in the west late Sunday night or Monday ahead of an approaching cold front could result in some sub-VFR conditions. However, the next chance for widespread sub- vfr conditions will come with pre-frontal convection between Monday afternoon and Tuesday night as the front moves into and through the region. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...BLAES NEAR TERM...BSD SHORT TERM...BSD LONG TERM...MWS AVIATION...BSD/KC is the U.S. government's official web portal to all federal, state and local government web resources and services.