254 FXUS62 KRAH 070918 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 418 AM EST Mon Jan 7 2019 .SYNOPSIS... High pressure centered over southern Quebec will extend southward into the Carolinas allowing for dry conditions today. An upper level disturbance will pass overhead tonight through early Tuesday, bringing a slight chance of rain to the area. A strong cold front will then cross central North Carolina 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 345 AM Monday... Backdoor cold front has cleared the zones this morning with most sites now reporting a light northeast wind. Scattered to numerous cirrus continue to overspread the region this morning in association with an upper level disturbance across the Midwest. The main story for today will be the continued mid and high level clouds with surface high pressure centered over southern Quebec extending down into central North Carolina. Low level thicknesses (1000/ 850 mb) are forecast to be only around 1330 m this afternoon and with high/ mid clouds forecast, highs only in the lower 50s to near 60 degrees (still well above normal for this time of year though) appear likely. Late this afternoon into evening the upper level trough axis supporting the parent ridge of high pressure over Quebec will pull east allowing the surface reflection to pull east as well. As this occurs low level flow will veer to the east and then southeast allowing upslope flow to commence against the Blue Ridge. NAM and GFS forecast soundings are in pretty good agreement that widespread thickening of clouds will likely occur early this evening. Simultaneously, a shortwave will cross the Great Lakes with a trailing line of PVA down over TN. Towards NC 900 mb - 800 mb flow will be out of the southwest with isentropic upglide commencing. The backdoor front will wash out at this time with a marine warm front (demarcated by ~60 degree dewpoints) over the Coastal Plain. High res models generally support this setup with a matching reflectivity field. Over central NC weak isentropic upglide is mainly shown as light rain with showers towards the coastal marine warm front. Have slightly raised PoPs here as confidence has increased in a weak rain/ light QPF event (due to the PVA and upglide). As mentioned above though, QPF will be mostly light. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... As of 400 AM Monday... Tuesday the shortwave will exit the coast with southwest flow establishing across central North Carolina. The NAM and GFS here are fairly different as the NAM shows low clouds holding in across most of the area, while the GFS has the low clouds breaking. Generally behind a shortwave weak subsidence exists which would favor at least transient trapping of some low level moisture. Through the day though low level flow turns more westerly which would favor a slow erosion of the low clouds (downslope flow). Both the GFS and NAM appear overdone on opposite sides of the spectrum (the GFS deterministic is warm compared to the ensemble). Have trended high temperatures up slightly, while favoring more of a NAM solution. If low clouds are thicker than forecast though, highs might struggle to get to 60 degrees across the Piedmont, while if low clouds are thin and quickly erode, highs in the lower 70s in the Coastal Plain will be possible. Tuesday night, a potent shortwave will dive southeast over Michigan with an accompanying cold front crossing the NC state line Tuesday evening. The GFS, ECMWF, and CMC are in fairly good agreement with the front crossing central North Carolina just around or after midnight Wednesday morning. Right behind the front a strong isallobaric wind with CAA will allow winds to quickly pickup. The GFS and NAM forecast soundings would support wind gusts in the 25 to 35 MPH range. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... As of 400 AM Monday... There is little change in forecast rationale during the medium range, with a step down to much colder conditions mid to late week, and wet to wintry ones during the weekend. A strong nwly jet now moving onshore the CA and Pacific Northwest coast will contribute to the digging/amplification of a potent shortwave trough sewd across the upr Midwest and Great Lakes through the short term, then to the Northeast, where a closed low is forecast to develop, by Wed. Downstream of, and in cyclonic flow aloft surrounding that low, a polar front will sweep sewd across cntl NC on Wed, closely following the lead front forecast to cross the region Tue night. Following 850 mb temperatures are forecast to dip to around minus 11 at GSO by 12Z Thu. Related cold air advection will support a strong nwly breeze, amidst a deeply mixed boundary layer Wed-Thu. When combined with temperatures dipping into the 20s Wed night, wind chill values in the teens are expected to result Thu morning. Although the wind will subside by Thu night, the presence of a "break-off", 1030 mb surface high over wrn NC Fri morning will support colder air temperatures - mostly between 20 and 25 degrees. High temperatures both Thu and Fri will be similarly chilly, in the upr 30s to mid 40s. While the aforementioned mid-upr low/trough will lift newd and away from the nern US through the end of the week, renewed nrn stream amplification is forecast to occur from cntl Canada to the cntl Appalachians Fri-Sun. At the same time, a srn stream shortwave trough is forecast to migrate across the srn US, with some interaction/phasing possible invof the srn middle Atlantic coast over the weekend. While the complexity of the flow will yield uncertainty regarding forecast details for the next several days, the overall pattern is one supportive of cyclogenesis from the GOM to the middle Atlantic coast, with sufficient cold air in place to support snow across parts of the middle Atlantic states, including probably the NC Piedmont, by Sat-Sat night. && .AVIATION /09Z MONDAY THROUGH FRIDAY/... As of 130 AM Monday... 24 hour TAF period: Weak backdoor cold front is currently pushing southeast and is located between KRWI and KRDU. GFS and NAM forecast soundings continue to hint at some potential gusts in the 10 to 15 kt range right behind the front, but given current gusts out there (or lack there of) have left the mention out. VFR conditions are expected through this morning into afternoon as surface high pressure remains in control and winds slowly veer around to the east and then south. Late this afternoon into evening VFR conditions will likely transition to MVFR (and possibly IFR) as an upper level disturbance approaches from the west. Looking ahead: 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. Behind the cold front Wednesday winds will be gusty in the 20 to 30 kt range. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Haines NEAR TERM...Haines SHORT TERM...Haines LONG TERM...MWS AVIATION...Haines