Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 220817 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 316 AM EST Sun Jan 22 2017 .SYNOPSIS... A potent low pressure system will track northeast from the Deep South into the Carolinas this afternoon into tonight, linger over the area on Monday, then track offshore the Mid-Atlantic coast on Tuesday. && .NEAR TERM /TODAY AND TONIGHT/... As of 300 AM Sunday... ...Dense Fog Advisory in effect until 10 am for the Triangle, Northern Piedmont and NE Coastal Plain... ...Severe Weather Possible late this Afternoon and Evening... Unseasonably rich moisture continues surging N/NE from the GOMEX into the Carolinas this morning as low-level flow backs/strengthens in response to height falls in advance of a potent upper level low progressing east from the lower MS river valley into the Deep South. Significant moistening has occurred over the past 24 hrs, as evidenced by PWAT values near 1.25" on the 00Z GSO RAOB (roughly double the PWAT observed on the 12Z Saturday GSO RAOB). An MCS upstream over AL/GA at 06Z is expected to progress rapidly E/NE into the Carolinas this morning, the northern portion of which should cross central NC between 12-17Z (roughly from sunrise to noon). Dense fog will erode from SW-NE between roughly 7-10 am as the aforementioned MCS (or remnants thereof) progresses across central NC. In the wake of the departing MCS, expect a lull in precipitation during the early/mid afternoon as a dry mid-level airmass /modified elevated mixed layer/ advects northeast into central NC. Chances for convection will increase from SW-NE by late afternoon as small amplitude waves rounding the base of the upper low eject NE from the Deep South into the Carolinas amidst diffluent flow aloft and increasingly favorable thermodynamics as rich low-level moisture advects poleward underneath a modified elevated mixed layer characterized by H7-H5 lapse rates on the order of 7-8 C/km. A slow moving warm front is expected to bi-sect central NC from SW-NE or WSW-ENE (i.e. along or south of CLT-RDU-RWI) this afternoon. If sufficient forcing is available to break the cap at the base of the EML in the warm sector along/south of the front this afternoon, the thermodynamic/kinematic env would favor supercells capable of producing all severe weather hazards. Thus, a conditional potential for severe weather will exist during the mid to late afternoon. Temperatures may range from the low/mid 70s south of the warm front to the mid/upper 50s north of the warm front. A squall line is expected to develop in AL/GA this afternoon, along a cold front assoc/w a rapidly deepening sfc cyclone tracking NE from the Deep South into the western Carolinas, in advance of a potent upper level low tracking ENE through the Deep South. The aforementioned squall line is expected to propagate E/NE through portions of the Carolinas this evening (00-06Z Mon). Thus, the primary severe weather threat is expected to unfold this evening (00- 06Z Mon) as the aforementioned squall line propagates across the Carolinas. While damaging straight line winds will be the primary threat with the squall line, a few tornadoes will be possible in the warm sector along the coast and in vicinity of the warm/occluded front further inland over portions of central NC. Expect lows tonight ranging from the upper 40s in the NW Piedmont to the lower 50s elsewhere. -Vincent && .SHORT TERM /MONDAY AND MONDAY NIGHT/...
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As of 317 AM Sunday... Monday and Monday night: Models have trended slower and farther south with the deepening upper low and attendant upper trough moving through the area Monday. Cold core aloft featuring H5 temps of -22 to -24C and mid-level lapse rates of 7 to 7.25 C/km will support instability showers in a southwest to northeast fashion throughout the day with rain expected to finally shift northeast of the area between 06 to 09z Tuesday. Highs Monday ranging from mid 50s NW to lower 60s east. Drier air filtering into the area with the departure of the system should lead to SW to NE clearing late Monday night into Tuesday morning. Lows Monday night in the lower 40s NW to mid 40s elsewhere.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/...
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As of 317 AM Sunday... Tuesday through Thursday: The return of sunshine will be a welcomed change during the mid-week period as shortwave ridging shifts over the region Tuesday and Wednesday. Meanwhile, northward extension of a surface high over the Deep South/GOM region will result in above normal temps, peaking Wednesday afternoon with highs 65 to 70. Shortwave energy moving through an amplifying long wave positively- tilted trough setting over the central and eastern conus could lead to scattered showers across the area late Wednesday night and Thursday as the attendant cold front moves through the area. Friday through the weekend: Below normal temperatures are expected Friday and through the weekend with the development of a deep trough east of the Rockies. Dry with no prospects for precip at this time.
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&& .AVIATION /06Z SUNDAY THROUGH THURSDAY/... As of 215 AM Sunday... 24-HR TAF Period: Conditions ranging from MVFR to VLIFR were present across central NC at 06Z this morning. The worst conditions were located at the INT/GSO/RDU/RWI terminals across the Northern Piedmont and NE Coastal Plain, north of a warm front extending SW-NE across portions of the Sandhills and SE Coastal Plain. As the warm front pushed north of the FAY terminal early this morning, conditions improved to MVFR. Expect conditions to remain relatively steady state this morning. Although dense fog will begin to lift as precipitation overspreads the area from SW-NE after ~12Z, ceilings are likely to remain in the IFR/LIFR category at the INT/GSO/RDU/RWI terminals through this afternoon as morning precip helps to reinforce an in-situ CAD wedge along and north of the Hwy 64 corridor. The FAY terminal will be situated south of the warm front and should see MVFR ceilings prevail today, though periodic IFR conditions will be possible during precipitation later this morning. A Squall line is expected to develop upstream this afternoon, then track E/NE across central NC terminals late this evening, between 00- 06Z. Isolated severe thunderstorms will be possible during this time frame, particularly at the FAY terminal. Some improvement will be possible by the end of the TAF period (06-12Z Monday) as low-level flow veers to the SW in the wake of the squall line. Looking Ahead: Any improvement late tonight and early Monday will be short-lived, however, with showers increasing in coverage and IFR/MVFR ceilings returning as a potent vertically stacked low rotates slowly eastward across the Carolinas. Gusty NW winds will be possible on the back side of the system Monday evening/night. Conditions are expected to improve /return to VFR/ sometime late Monday night or early Tuesday as the aforementioned system tracks offshore the Carolina/Mid-Atlantic coast. -Vincent && .RAH WATCHES/WARNINGS/ADVISORIES... Dense Fog Advisory until 10 AM EST this morning for NCZ007>011- 024>028-040>043-076>078. && $$ SYNOPSIS...Vincent NEAR TERM...Vincent SHORT TERM...CBL LONG TERM...CBL AVIATION...Vincent

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