Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 171815 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 115 PM EST Tue Jan 17 2017 .SYNOPSIS... A cold front will approach from the northwest this evening, then track southeast through central North Carolina Wednesday morning. In the wake of the front, high pressure will build into the region from the northwest Wednesday night and Thursday. && .NEAR TERM /THROUGH TONIGHT/... As of 100 PM Tuesday... Surface observations indicate visibilities have risen above 3 miles in most locations as of 16Z, indicating that top-down erosion of the CAD wedge has commenced in assoc/w insolation and strengthening SW low-level flow in advance of a shortwave trough /DPVA/ approaching the Mid-Atlantic from the W/NW. Overcast skies should thin and may become broken this afternoon, though current trends would suggest breaking out entirely is unlikely except near the NC/SC border. As such, expect highs ranging from the upper 50s to ~60F in the North to mid 60s in the far SW Piedmont. Forcing this aft/eve will be limited to weak low-level warm advection, primarily in the NW Piedmont and VA border counties where a few periods of light rain will be possible through this aft/eve. Precipitation chances overnight remain difficult to ascertain. Low-level forcing will largely be absent overnight, with central NC in a relatively homogeneous warm sector characterized by unidirectional /SW/ flow. As a result, expect dry conditions with the best chance of rain between 06-12Z to the north in southern VA. Broken to overcast cloud cover and a 10-15 mph SSW/SW breeze should result in mild temperatures tonight, i.e. little diurnal variation from this afternoon. -Vincent && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... As of 115 PM Tuesday... Expect some chance for showers along the cold front progressing into central NC Wed morning given a modest plume of SFC-925 mb moisture in the presence of low-level convergence within the low-level trough. In the immediate wake of the front late Wed morning through early Wed afternoon, strong DPVA progged to track ESE through VA into northeast NC may encounter lingering low-level moisture across central/eastern NC. As a result, a period of anafrontal precipitation will be possible in central NC, primarily from the Triangle east into the Coastal Plain. Expect a clearing trend mid/late afternoon in assoc/w subsidence in the wake of the shortwave and the onset of low-level cold advection in the wake of the front. Given the timing of the front and the potential for precipitation /evap cooling/ late Wed morning through early Wed afternoon, high temps on Wed will vary little from overnight lows except perhaps in the far S/SE where temps may reach the mid 60s prior to cold advection post-fropa. Lows Wed night will be driven by a combination of cold advection and radiational cooling, ranging from near 40F at the VA border to the mid 40s SC border. -Vincent && .LONG TERM /Thursday through Monday/... As of 330 AM Monday... This time frame will feature above normal temps and alternating wet and dry periods. Polar air will hold well to our north, affecting only northern and eastern Canada into Maine, leaving NC in a mild pattern with low level thicknesses staying well above seasonal normals. A very wavy and progressive flow across the southern CONUS will bring bouts of unsettled weather reminiscent more of early spring than of the heart of winter. Thu/Thu night: A brief dry period is expected as the front settles just to our south and a weak continental high builds over the area from the west, beneath a prominent mid level ridge in the wake of Wednesday`s potent shortwave trough swinging out over the Atlantic. Expect fair to partly cloudy skies Thu, with increasing clouds late Thu into Thu night as the next shortwave trough (now over Baja California) pushes east then lifts NE, approaching NC from the SW as it takes on a negative tilt. As this trough moves in, falling mid level heights and a preceding low level jet nosing into central NC will foster deepening of moisture and an increasing chance of rain overnight, affecting the western CWA first. Highs 55-60 and lows in the mid-upper 40s. Fri/Fri night: Rain is likely early Fri morning, particularly over the northern and western forecast area, as the combination of upper divergence, mid level DPVA and height falls, and low level moisture transport appears to peak around 12z Fri. As the negatively tilted and deamplifying shortwave trough shift to our NNE, the front to our south should shift back northward as a warm front, as another round of shortwave ridging follows, persisting through Fri night. Expect rain chances to decrease SW to NE Fri afternoon as drying aloft punches in from the WSW, with dry weather but low clouds likely Fri night. Expect highs Fri from the mid 50s north to mid 60s south, where the northward-moving warm front will first arrive. Lows 45-50. Sat into Mon: Expect fair and warm weather Sat as the mid level ridge shifts overhead and over the East Coast. Thicknesses are projected to be well above normal, perhaps by as much as 40 m, although shallow mixing may mean that the thickness values could be overestimating the warming realized at the surface. Expect highs of 60-67. By Sun, attention turns to quickly deepening low pressure over the southern Plains, within the active and progressive southern stream. As this low shifts through the Mid-South and NNE into the Ohio Valley, a strong negatively tilted trough will approach our area from the W and SW. The GFS and ECMWF remain in remarkably good agreement on timing and evolution of this feature as well as with the corresponding surface frontal configuration, with a primary low tracking into the Ohio Valley, an occluded low moving into the western Carolinas, and a trailing front shifting E then NE through GA and the Carolinas Sun night. There remains the threat for a few strong storms late Sun into Sun night in our area, with this risk supported by a highly energetic and strengthening system featuring vigorous upper divergence, intense DPVA, strong kinematics with a sweeping curved hodograph, and abundant moisture with PW over 1.5". Will mention isolated thunder, with minimal CAPE values and subdued lapse rates limiting the coverage. Will trend the high pops down from SW to NE Sun night into Mon morning as the dry slot arrives, but will keep scattered showers late Mon as the trough axis shifts through the area. Highs in the upper 50s NW to mid 60s SE Sun, then around 60-65 Mon. -GIH && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... As of 100 PM Tuesday... 24 Hour TAF period: IFR ceilings are expected to improve to MVFR this afternoon. Any improvement in conditions this aft/eve should be short-lived, however, as conditions are expected to deteriorate from N/NW to S/SE (earliest at Triad and latest at FAY) tonight/Wed morning as an upper level disturbance tracks through the central Appalachians into the Mid-Atlantic and an attendant cold front /low- level trough/ progresses east of the mountains through VA/NC. Expect the best potential for rain and low ceilings between 09-17Z Wed as the front progresses SE through central NC. Breezy SW flow in advance of the front tonight and early Wed will give way to breezy NW flow in the wake of the front Wed aft/eve. Looking Ahead: Expect a clearing trend in the wake of the front with a brief return to VFR conditions Wed night/Thu. A pattern similar to the one affecting the region today is progged to develop over the region again late this week. With this in mind, expect ceilings to begin deteriorating Thu night/Friday. -Vincent && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Vincent NEAR TERM...Vincent SHORT TERM...Vincent LONG TERM...Hartfield AVIATION...Vincent is the U.S. government's official web portal to all federal, state and local government web resources and services.