434 FXUS62 KRAH 062334 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 634 PM EST Sun Jan 6 2019 .SYNOPSIS... A weak dry cold front will move through central NC tonight. High pressure centered over southern Quebec will extend southward into the Carolinas Monday. An upper level disturbance will pass overhead Monday night through early Tuesday, followed by a strong cold front Tuesday night. Well above normal temperatures early this week will trend to below normal for the later half of the work week. && .NEAR TERM /THROUGH TONIGHT/... As of 330 PM Sunday... Mild afternoon across central NC with temperatures well above normal for early January, ranging from the low-mid 60s north to the upper 60s/near 70 south. Areas of cirrus which covered a good part of the Piedmont this morning as diminished at mid afternoon to permit mostly sunny across most of the region. A mid level s/w seen on water vapor imagery exiting the New England coast this afternoon will aid to drive a dry sfc cold front through central NC tonight. Passage of the cold front will be noted by sfc winds veering to a north-northeast direction with brief periodic gusts possible overnight. This low level northeast flow will advect a cooler air mass into the region late tonight, but it will feel more noticeable on Monday. High-mid level cloudiness will increase later tonight into Monday morning. Overnight temperatures will be a few degrees cooler than last night, ranging from the mid-upper 30s north to the upper 30s/around 40 south. && .SHORT TERM /MONDAY THROUGH TUESDAY/... As of 330 PM Sunday... Monday, a dry air sfc ridge will extend south from a parent high over southern Quebec into eastern NC. The low level flow will veer to an ely direction. This flow will aid to advect moisture off the Atlantic, which should bank up against the Blue Ridge, possibly leading to some lower cloud encroaching upon the Triad region by late morning. Regardless, the low level flow will advect/maintain a cooler air mass, leading to afternoon temperatures much cooler than this afternoon. Currently have highs ranging from the upper 40s/lower 50s north to the mid-upper 50s south. Potential for temperatures to be a couple of degrees warmer if skies remain mostly sunny through most of the day, especially across the Sandhills and southern Coastal Plain. Monday night through Tuesday morning, a s/w will cross the Great Lakes into southern Ontario, with the tail end of the s/w passing over our region. This feature will induce sly flow over a stalled sfc front lying across Georgia-southern SC. Sly flow appears to strengthen enough to enhance isentropic upglide to generate patchy light rain monday evening across the Piedmont, and overnight across portions of the Coastal Plain and northeast Piedmont. Overall spotty nature and light intensity of the precip suggest just chance PoPs warranted with expected rainfall amounts no more than a trace or a hundredth or two. This light precip should moisten the lower layers of the atmosphere enough to generate a low cloud deck, primarily over the Piedmont. This cloud deck may have an impact on high temperatures Tuesday. The low level flow becomes SW in the wake of the departing s/w and ahead of a strong sfc cold front. This flow of warmer air may be enough to erode/dissipate the deck of low clouds by mid day Tuesday, permitting temperatures to soar back into the 60s. If the low clouds fail to materialize Monday night or are rather thin and dissipate early tuesday, then temperatures Tuesday afternoon may reach well into the 60s across the NW Piedmont and reach 70-75 degrees elsewhere across central NC. Since the NAM does not appear as robust this cycle with the moisture layer as compared last night's run, have adjusted max temps up a few degrees, especially across the NW Piedmont. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... As of 245 PM Sunday... Tue night: The cold front will make its way SE through NC, with veering winds to NW and commencement of CAA. The tight MSLP gradient overnight will keep the low levels mixed. Any scattered frontal clouds should clear out early, although some incoming high level moisture and the vertical wind structure suggests some orographically enhanced cirrus is possible over our NW and N late Tue night into early Wed morning. Lows in the mid 30s to mid 40s. Wed/Wed night: Sheared energy diving through the mean trough base will cross NC late Wed, drawing the reinforcing cold front SSE through NC Wed night with little more than a few clouds. Thicknesses are projected to be just 10-15 m below normal Wed, before falling post-front to 35-40 m below normal. Highs in the mid 40s to mid 50s, then cold lows in the mid 20s to around 30. Thu-Fri night: Dry and chilly weather expected as the mean trough shifts off the NOAM E Coast, with rising heights and flattening mid level flow. The southern portion of polar surface high pressure will build into NC from the NW during this period, keeping thicknesses and temps well below normal. High clouds are also likely to be increasing and thickening with the arrival of accelerating upper flow from NC back into the central Miss Valley late Thu into Fri, producing a trend from fair to partly cloudy skies. Then, as a southern stream shortwave trough over Baja late Thu tracks E to TX, moist upglide at 300-305K is induced, and we should see increasing mid clouds as well from the west late Fri or Fri night (GFS is slower than the ECMWF with the trough but adds in a northern stream wave, making for a faster cloud arrival). But downslope flow in the low levels favor keeping the forecast dry. Highs in the 40s both days. Lows again in the 20s Thu night and in the upper 20s to lower 30s Fri night with increasing clouds. Sat-Sun: Lots of uncertainty here, as the southern stream wave's approach induces surface cyclogenesis over the Gulf and off the Southeast coast. The GFS's greater northern stream energy as compared to the ECMWF serves to suppress southern stream moisture just S of NC, keeping the weekend largely dry. But the ECMWF, along with most of its ensemble members, maintains southern stream dominance and pulls abundant moisture up across the Carolinas, enough for high precip chances late Sat into Sun. Given the important spread of solutions, will keep pops low for now, in the chance range, with a chance for rain or snow in the NW and VA border counties. Temps should struggle to reach the 40s both days. -GIH && .AVIATION /00Z MONDAY THROUGH SATURDAY/... As of 633 PM Sunday... 24 hour TAF period: High confidence VFR conditions will prevail through at least Monday afternoon. Expect high clouds to stick around much of the night and through the day Monday, with some lower cigs in the 2-5 kft range expected to spread over central NC from the southeast after 18Z. Winds will generally be variable at 5 kts or less, with some 6-10 kt winds during the day Monday, especially at the eastern terminals. -KC Looking ahead: The approach and passage of an upper disturbance Monday night will lead to a moistening of the atmosphere, and the potential for MVFR/IFR ceilings late Monday night into Tuesday morning. In addition, a period of low level wind shear may occur overnight Monday night into Tuesday morning. Sub VFR ceilings may persist through much of Tuesday, primarily over the Piedmont. A strong cold front will cross the region Tuesday night, ushering in a much cooler and drier air mass. This will initiate a period of VFR conditions that should linger through the rest of the week. -WSS && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS/Haines NEAR TERM...WSS SHORT TERM...WSS LONG TERM...Hartfield AVIATION...KC