Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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099 FXUS62 KRAH 180745 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 345 AM EDT Wed Apr 18 2018 .SYNOPSIS... A warm front will lift northward across central NC this morning, with breezy sw winds in its wake. A cold front will cross central NC early Thursday morning, with blustery NW winds occurring behind the front. Cool high pressure will build into the Carolinas from the northwest Friday, and settle overhead on Saturday. && .NEAR TERM /THROUGH TONIGHT/... As of 340 AM Wednesday... A series of low pressure systems passing to our north and an area of high pressure anchored off of the SE U.S. coast will maintain breezy sfc winds across central NC through Thursday. These winds in conjunction with relatively low humidity values during the afternoon hours will have some impact on fire behavior (see that Fire Weather discussion below). Today, a sfc boundary bisecting central NC west-to-east this morning will lift nwd into VA later today in response to the approach of a sfc low that will cross the mid MS Valley into the lower Great Lakes. Wly flow in the mid/upper levels of the atmosphere will induce the development of a lee side trough later today in the wake of the departing sfc warm front. The resultant sw low level flow will increase by mid-late afternoon with gusts 20-25kts probable. This warm flow will advect a much warmer air mass into our region. This will lead to afternoon temperatures well into the 70s across the far north-NW, to around 80-lower 80s elsewhere. Tonight, a steady sw sfc wind will persist as a sfc cold front, attendant to the sfc low, will approach from the west. A narrow band of clouds will from immediately ahead of this front, though the column overall appears too dry and stable to generate/support any precip. The steady sw sfc wind and increasing cloudiness will support mild overnight temperatures in the 50s to lower 60s. && .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/... As of 340 AM Wednesday... Thursday, the sfc cold front will continue its east-SE track across central NC, exiting the coastal plain counties by mid-late morning. Some model guidance does depict enough lift in the lowest 10k feet of the atmosphere to potentially generate a few sprinkles across the southern counties early Thursday morning. Otherwise, expect clearing skies Thursday morning NW-SE as drier cooler air surges into the region. It will become blustery behind the departing sfc front with gusts 25-30kts probable during the morning through the early afternoon. While the initial cold air advection will be offset by the downslope component of the low level flow, this flow projected to veer to a more nly direction by late afternoon. Thus, could see temperatures slowly fall across the NW Piedmont after 3 PM in repsonse to the cold air advection. Continued cold air advection Thursday night will send temperatures tumbling through the 50s during the evening, and into the 40s prior to midnight across the Piedmont. Overnight temperatures should vary from the upper 30s across the Piedmont, to around 40 across the Sandhills and southern coastal plain. && .LONG TERM /FRIDAY THROUGH TUESDAY/...
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As of 345 AM Wednesday... The upper-air pattern on Friday will feature a broad trough over New England and the Atlantic provinces of Canada with another trough and closed low over the southwestern U.S. Broad ridging will be in place across central plains. The surface pattern will feature a cool 1035 MB surface high pressure system centered over the northern Plains on Friday morning that will shift east into the eastern Great Lakes on Saturday and then ridge south into the Mid-Atlantic. Morning low-level thickness guidance has trended cooler with some spread between the typically cooler GFS and the milder EC with values averaging on Friday morning between 1315-1305 meters and then moderate to 1325 to 1315 meters on Saturday morning. The resulting sensible weather on Friday and Saturday will include clear skies on Friday with mainly clear skies on Saturday, dry weather, and chilly temperatures between 5 and 10 degrees below normal. Highs on Friday will range in the lower to mid 60s despite bright sunshine with highs moderating into the mid 60s on Saturday. Morning lows on Saturday will range from 34 to 40 supporting the potential for some patchy frost. The upper trough and embedded closed low over the Four Corners region pushes east into the southern Plains on Sunday and then the lower Mississippi Valley on Monday as the ridge axis reaches moves over the Mid Atlantic early Monday. The upper low weakens on Monday into Tuesday as it approaches the Southeast coast on Tuesday night. Not surprisingly, NWP guidance is still struggling with this system, especially at later periods and with the surface reflection of the upper trough. As the surface high to our north shifts off the New England coast on Monday into Tuesday, a weak surface low associated with the upper-trough will push east across the Deep South/Gulf Coast region Monday into Tuesday. This will allow an easterly flow to develop across the Carolinas on Monday and then strengthen on Tuesday with breezy and cool northeast winds increasing during the period. Guidance is consistent in keeping Sunday dry across central NC with a chance of showers arriving across the southwestern portion of the forecast area on Monday morning and then slowly spread east into Tuesday. Still, forecast confidence is lower than normal for Monday and especially Tuesday, and some adjustments to the forecast in the coming days are probable. Morning lows on Sunday will range in the lower 40s with highs in the mid 60s to around 70. Lows on Monday and Tuesday mornings will be moderated by the cloud clover and wind with lows in the mid 40s to around 50 on Monday and the upper 40s to lower 50s on Tuesday. Highs both days will range in the mid 60s to near 70. -Blaes
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&& .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/... As of 150 AM Wednesday... There is a high likelihood that VFR conditions will persist across central NC through Thursday afternoon. Of note to small aircraft operators will be gusty sfc winds this afternoon, most likely after 2 PM, with gusts 20-27kts probable. While the sfc gustiness will subside just prior to sunset, a low level jet passing overhead will result in low level wind shear parameters Wednesday evening across most of central NC, and primarily along and east of highway 1 overnight. SW winds around 2000ft expected to be 40-45kts. Sfc winds will be gusty again Thursday as a cold front glides eastward across the region. Gusts in the 25-30kt range will be probable, strongest in the morning through early afternoon. VFR parameters are expected to persist into the weekend. Cool high pressure will build into the area Friday and linger overhead Saturday into Sunday. The next threat for sub VFR ceilings may occur as early as Sunday night, but may hold off until late Monday or Monday night. && .FIRE WEATHER...
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Coordination with neighboring NWS offices and the North Carolina Forestry Service has led to the issuance of Increase Fire Danger statement today across sections of western and central NC, and across the bulk of the state for Thursday. Across central NC, the most critical fire weather parameters today will be across sections of the southern Piedmont into the Sandhills as lower dewpoints and warm afternoon temperatures will yield late afternoon humidity values in the 25-30 percent range. This will occur at about the same time the strongest wind gusts will occur (19Z-22Z) with gusts 22-25kts. On Thursday, minimum humidity values in the afternoon will bottom out in the mid-upper 20s areawide with gusty westerly-nw sfc winds predicted from mid morning into the afternoon hours. Based on what fire activity occurs today, and if model dewpoint guidance comes in lower, cannot rule out the possibility of a short-fused Red Flag Warning for parts of central NC on Thursday.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...WSS LONG TERM...BLAES AVIATION...WSS FIRE WEATHER...WSS

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