688 FXUS62 KRAH 031708 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1208 PM EST Sun Mar 3 2019 .SYNOPSIS... An area of low pressure will move across central North Carolina this evening bringing the threat of heavy rain as well as an isolated severe storm towards the southern Coastal Plain. Much cooler and drier weather will prevail for early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 1155 AM Sunday... Just some minor adjustments made to hourly temperatures and dewpoints, and resultant slightly cooler high temperatures across cntl NC, amidst a widespread, lowering overcast and expansion of initially patchy light/stratiform rain today. Otherwise, two notable forecast concerns will result from the track of a primary surface cyclone from e-cntl MS at 17Z, enewd across cntl Al and GA this afternoon and cntl SC and e-cntl NC this evening and early tonight: 1) a small spatio-temporal risk of damaging wind gusts and/or an isolated tornado over the far srn Sandhills and srn Coastal Plain, along and south of the track of the foregoing cyclone, and 2) a moderate to high probability of a stripe of one to one and a half inches of rain focused over the sern half of cntl NC, in the deformation axis immediately north of cyclone - both of which have been described in detail below. Previous discussion as of 430 AM Sunday... A stalled surface front remains across central South Carolina this morning with weak isentropic upglide occurring over central North Carolina. On water vapor the next upper level disturbance to affect the area can be seen over Kansas. This morning the wave will eject east through Missouri with surface cyclogenesis occurring across Mississippi/ Alabama in response to the DCVA and corresponding 500 MB height falls. As the surface low is forming this morning the stalled boundary, currently across central South Carolina, will begin to move north as a warm front. Latest runs of the GFS/ ARW/ NMM all show pretty good coverage of weak rain in the warm air advection wing, but dry air continues to be advertised in the forecast soundings. High res models are also indicating pretty good coverage right now of light rain, but this has not materialized. Overall thinking is that the initial morning precipitation as advertised by the high res models is overdone. By the early afternoon hours embedded pockets of PV in the southwest flow, will traverse the region which will likely help to get slightly better coverage. The NAM shows this occurring earlier (late morning). This afternoon the wave will be moving into Tennessee with the surface low deepening across Georgia/ South Carolina. The current suite of global models has the warm front making it into central North Carolina before stalling. The NAM Nest, ARW, NMM have the warm front stalling across the Sandhills and Coastal Plain. This appears to be the most likely scenario given the track of the wave. The surface low will then track northeast along the stalled baroclinic zone. North of the stalled front, elevated instability does exist for isolated thunder with the main threat being heavy rainfall. The upper level support with this feature is impressive. The jet streak is forecast to strengthen over central PA to near 150 kts with central NC in a RRQ. Widespread DCVA and 500 MB height falls will also be occurring at this time. PWATs at this time are forecast to be around 1.40" or at max values. Along and just northwest of the surface low track global models are advertising a swath of QPF in the 1 to 1.50" range. Given the strong forcing mentioned above and ample moisture these totals make sense. The latest GEFS and EPS means are slightly on the lower end of the totals mentioned above. With area creeks and streams already running high, this may produce additional river flooding across the area. The other concern here will be the potential for severe storms. The main threat at this time appears to be well south of the region. Forecast soundings do advertise a brief window were an isolated storm or two could become severe across our far southeastern counties. SFC to 1 KM bulk shear values are near 50 kts at this time as LLJ quickly strengthens. SB CAPE is limited here though. Temporally the window is also small with only a brief overlap in shear and instability. SPC has brought the marginal risk across our far southeastern counties given the forecast track of the warm front. Due to the forecast shear, instability, and track of the surface low there is a marginal risk for severe weather across the far southeast. Have included a mention in the HWO for this. Late Sunday night, the surface low will quickly pull northeast with a surface cold front sweeping through the counties. && .SHORT TERM /MONDAY/... As of 430 AM Sunday... Drier and cooler weather is in store for Monday as the upper level trough axis will swing east of central North Carolina. Strong CAA will take hold Monday morning with 850 MB temperatures falling towards 5 degrees C below zero. NAM forecast soundings are showing some mid-level moisture remaining across the region Monday afternoon while the GFS has mostly clear skies. For now have raised sky cover a bit, but thinking is that skies will remain more clear than not. Given the above, the thinking is for high temperatures to be near 50 degrees with mid 50s towards the Sandhills. This would be about 5 to 10 degrees below normal for this time of year. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... As of 400 AM Sunday... Monday night: DCVA resulting from a series of low-amplitude disturbances rotating east through the base of the mean upper trough Monday night and into Tuesday will result in renewed lift that will lead to clouds re-developing across the area Monday night and Tuesday. The GFS has backed off considerably with precip across the area Monday night/early Tuesday, with the model consensus now keeping the bulk of measurable precip south/southeast of the area, in proximity to weak surface low development across SC. Added a slight chance pop across the far SE zones(Sampson and Cumberland counties) around daybreak Tuesday; and with sfc wet-bulbs right around freezing and the absence of any warm air aloft, could see a brief period of very light snow or flurries with no expected impacts. Lows ranging from near 30 north to mid 30s south. Tuesday through Wednesday night: An expansive surface high from Canada will advect significantly colder air into the region during this period. H8 temps are forecast to bottom out between -10 to -15 C on Wednesday, which is a good 1 to 2 S.D. below normal. Temperatures during this period will average a good 10 to 20 degrees below normal, with highs Wednesday, despite abundant sunshine, struggling to make it into the upper 30s to lower 40s. Overnight lows well down into the 20s, with some teens possible in the typically colder spots Tuesday night and again Wednesday night. Thursday through Saturday: Eastern US trough lifts out of the region on Thursday with a transition to a more zonal and progressive flow pattern to end the week. Temperatures will begin to moderate, but will stay remain below normal on Thursday as the parent high across the area begins to break down. Significant model differences arise Friday and into the weekend-in the handling of a pair of Pacific shortwave troughs ejecting east across the CONUS. The EC is significantly more sheared/weaker with the lead shortwave trough into the eastern US on Friday, delaying the better rain chances until late Friday and into Saturday. Meanwhile, the GFS brings precip chances into the area as early as Thursday night and Friday. Given antecedent cP airmass in place, wet- bulb cooling and favorable nocturnal timing of precip could support a brief period of frozen or freezing precip at onset across northern portions late Thursday night/early Friday morning, before changing over to all rain. Given all of the uncertainty will maintain low chance pops Fri through Saturday with temperatures moderating to near or above normal by the weekend as southerly return flow becomes established. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... As of 700 AM Sunday... 24 hour TAF period: MVFR conditions are slowly progressing in from the southwest this morning as isentropic upglide commences. Most of the morning hours will likely remain dry as forecast soundings take sometime to moisten up. This afternoon a boundary that is currently stalled across central South Carolina will drift north as a warm front with ceilings continuing to lower across the TAF sites. Latest high res guidance has the warm front making it to just around KFAY before stalling. South of the warm front, thunder will be likely with an isolated threat just north of the boundary where some elevated instability exists. A surface low is then forecast to move across the Sandhills/ Coastal Plain this evening along with heavy precipitation. The surface low looks to be far enough north to require the mention of thunder in KFAY with the potential for some gusty winds as well with the convection. There will also be a brief window here with the strengthening LLJ to allow for low level wind shear to be present. In fact, at 2 kft AGL the NAM is showing winds approaching 60 kts. As the surface low exits the region to the northeast a surface cold front will sweep through the TAF sites. The 925 MB front is slightly lagging behind which might delay clearing a bit, but an overall recovery to VFR early Monday morning is expected. Behind the cold front winds will pick up with gusts of 20 to 25 kts possible. Looking ahead: Mostly VFR conditions are expected through the week, though some transitory MVFR will be possible Tuesday morning. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Haines NEAR TERM...MWS/Haines SHORT TERM...Haines LONG TERM...CBL AVIATION...Haines