812 FXUS62 KRAH 090803 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 303 AM EST Tue Jan 9 2018 .SYNOPSIS... Weak high pressure will linger over NC today, then yield to a stronger high that will meanwhile build across the middle Atlantic states, then ridge south into NC tonight and Wednesday. && .NEAR TERM /THROUGH TONIGHT/... As of 910 PM Monday... Main concern overnight will be temperatures hovering near freezing and the potential for residual moisture on area roadways to freeze. 00Z upper air analysis depicts deep west-swly flow over the Carolinas with speed convergence noted at 850mb, aimed toward northwest NC/southeast VA. GSO sounding quite moist, nearly saturated through 500mb with PW of 0.74 inches (compared to 0.05 inches 48 hours earlier). A trough at 700mb currently crossing central NC. Low-mid level winds veer to the west with the passage of this feature. This veering is likely the reason why precip is waning in coverage and intensity. Thus, with precip decreasing and temperatures remaining above freezing, the threat for freezing rain has greatly diminished. Evening temperatures have lowered into the mid-upper 30s with a few spots in the far southeast still around 40. Meanwhile dewpoints have shot-up into the mid-upper 20s. Overnight, temperatures will gradually lower into the low-mid 30s. A few spots will cool to near or slightly below freezing by daybreak. Where this occurs, cannot rule out a slick spot or two developing on the pavement. For now will handle this with a SPS. Finally, potential for areas of fog to develop, with model guidance favoring our coastal plain as well as counties bordering the Yadkin river. With the cold ground and the slightly warmer air above the surface, conditions for fog development are there. After further investigation, may adjust the weather grids to depict fog early Tuesday across most of the region. Tuesday and Tuesday night: Coming soon! && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... As of 250 AM Tuesday... At the surface, high pressure over the northwest Atlantic will ridge southwestward, setting up a hybrid CAD wedge on Wednesday through at least Wednesday night. Strong moisture advection in the east- southeasterly return flow and the subsequent isentropic lift will result in cloudy and cool conditions on Wednesday. However, at this time models have trended drier for this period, thus have delayed onset of stratiform rain until Thursday. Have adjusted forecast highs downward to account for the damming. Highs now topping out in the low 40s NW to mid 50s SE. Lows Wednesday night in the mid 30s northeast to mid 40s south. && .LONG TERM /THURSDAY THROUGH TUESDAY/... As of 300 AM Tuesday... High confidence a cold front will approach from the west and move through the Mid-Atlantic late in the week into the early weekend. Expect increasing temperatures and chances for convection through Friday night, both decreasing thereafter. Lower confidence in the precipitation and temperature forecast for Thursday. Thursday through Saturday: The CAD wedge is expected to linger into Thursday in a more in-situ damming scenario as the high moves away to the northeast. Chances for stratiform rain increase Thursday with the continued moisture advection and isentropic lift. The CAD wedge will likely stick around into (if not all the way through) Thursday, with stratiform precipitation likely across Central NC. As a result, have also trended downward with highs on Thursday. Currently forecasting highs in the low 50s NW to mid 60s SE. The strong east- southeasterly flow into the region may finally erode the wedge Thursday night into Friday ahead of the approaching front (though models tend to be a bit on the quick side with the erosion). As a result, lows Thursday night and highs on Friday should be the warmest of the period, lows in the upper 40s NW to mid 50s SE and highs generally ranging from around 60 degrees NW to near 70 degrees SE. With regard to the approaching front, a low will develop along the front over TN Thursday night and propagate northeastward along the front Friday and Friday night. The medium range models still differ significantly with respect to this low and as a result, lowers confidence in the forecast for Friday and Friday night. How close the low gets to Central NC will have a significant impact on forcing and chances for thunder across Central NC Friday and Friday night. Cannot completely rule out some thunder and isolated strong wind gusts with the convection along the front, thus have kept chances for isolated thunder in the forecast. The main line of pre-frontal convection should be relatively quick hitting, moving in Friday aft/eve and exiting the area early on Saturday. Saturday Night through Tuesday: A return to dry weather and below normal temperatures is expected in the wake of the front as high pressure builds into/over the region. Highs in the upper 30s to mid 40s and lows generally in the 20s expected. && .AVIATION /06Z Tuesday through Saturday/... As of 115 AM Tuesday... Low confidence forecast for this morning. A mid level trough and associated mid level ceilings are forecast to move east this morning, resulting in a generally west to east clearing. This clearing, atop a marginally moist surface layer, except a very moist one within remaining snow pack at RWI, will introduce the possibility of LIFR conditions in the several hours centered around 12Z. This likelihood would appear to be highest at INT and GSO, where the clearing, and associated radiational cooling and increasing near surface relative humidity values, will occur first and be most long-lasting. The current MVFR range cloudiness at those TAF sites does not appear to have a strong forcing mechanism, so any resultant MVFR ceilings are expected to be fleeting, as it appears now. Winds will be light and variable, as weak high pressure lingers over cntl NC through the TAF period. Outlook: VFR conditions are likely to hold through this evening. A return to MVFR, then IFR CIGS, is likely later tonight, first in the GSO and INT areas, then spreading eastward across the remainder of central NC, on Wed. These sub-VFR cigs should dominate well into Fri night, with a chance of showers limiting VSBYS. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...WSS SHORT TERM...KC LONG TERM...KC AVIATION...MWS/Badgett