Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 220120 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 920 PM EDT Tue Mar 21 2017 .SYNOPSIS... A cold front will push slowly southward through the area tonight. A secondary, back-door cold front will surge through NC on Wed. Cool high pressure will build into the region from the north Wednesday through Thursday night, then shift off the East Coast on Friday. && .NEAR TERM /Through Tonight/... As of 705 PM Tuesday... Quick update to nudge low precip chances a bit farther northward, in accordance with convection-allowing model trends and depictions of low level moisture convergence along and ahead of the incoming 850 mb trough. Still expect likely showers and storms across the extreme southern CWA, although will need to monitor trends, given that the low level theta-e ridge is weakening, with decreasing 850 mb winds, which may yield lower coverage or a suppression of better coverage to the south. -GIH Earlier discussion as of 115 PM... Overview: In the upper levels, small amplitude disturbances embedded in NW flow aloft are progged to traverse the Carolinas this evening/ tonight. 16Z WV imagery, radar imagery and RAP data show several disturbances upstream over the central MS river valley (IA/MO) this afternoon. The northern disturbance is progged to track through the Mid-Atlantic invof the mason-dixon line late this eve/tonight, while the southern disturbance/MCV is progged to track through TN into GA/SC. A cold front progressing SE into the Appalachians this morning will track slowly S/SE into central NC late this aft/eve. Strong insolation /diurnal pressure falls/ will enhance a pre-frontal trough downstream of the front (east of the mountains) and aid in the development of a weak surface low invof the NC/SC border by ~00Z. The surface low is progged to track ESE toward Cape Fear overnight as the cold front progresses S/SSE through central NC and an upper level disturbance tracks SE through TN to the Southeast coast. Today: Expect dry conditions to prevail through mid to late afternoon given weak forcing, marginal low-level moisture and a strong cap associated with an unmodified elevated mixed layer (H7-H5 lapse rates ~8C/km) advecting over the region from the west. The low- level airmass over central NC has been modified by warm advection during the past 12-18 hrs. This, in combination with skies and unimpeded Spring insolation will result in highs ranging from the mid/upper 70s to lower 80s. Tonight: Strong insolation and low-level moisture advection from TN into northern GA and Upstate SC is expected to erode the cap and result in convective development within the pre-frontal trough over southeast TN and Upstate SC (perhaps as far NE as CLT) by 21-00Z this afternoon. With the best low-level moisture expected to advect into GA/SC this afternoon, airmass destabilization/cap erosion in central NC late this aft/eve may be confined to the SC border counties, primarily in the SW Piedmont/Sandhills. North of Hwy 64, forecast soundings show a capped atmosphere in place the entire day, with little or no destabilization in advance of FROPA. With the above in mind, convection is expected to develop ~00Z in the SW Piedmont, with activity progressing E/ESE invof the NC/SC border overnight. Chances for convection will decrease from W-E after midnight as activity progresses toward Cape Fear and, ultimately, offshore the Carolina coast. Confidence in convective development/ coverage decreases heading north toward the Hwy 64 corridor, and portions of the N/NW Piedmont and NE Coastal Plain may ultimately remain dry during/after FROPA late this evening. Severe Potential: The potential for severe weather late this aft/eve and early tonight appears to have diminished for much of central NC, except invof the NC/SC border where destabilization/cap erosion is still anticipated and environmental conditions remain supportive of organized (multicellular or supercellular) convection with an attendant threat for damaging winds and hail up to the size of quarters. The potential for severe weather will be greatest along the NC/SC border between ~7 pm and ~3 am. -Vincent && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... As of 115 PM Tuesday... Expect a clearing trend in the morning as a drier airmass advects into the region from the north, with clear skies during the afternoon and evening. Cold advection is expected to persist for the majority of the diurnal heating cycle on Wed as Canadian high pressure builds into the Mid-Atlantic from the NW. Expect highs much cooler than today, in the mid/upper 50s N/NE to lower 60s S/SW. Lows Wed night may be tempered by increasing mid/upper level cloud cover after midnight. Will indicate lows ranging from the upper 20s (rural and low-lying areas east of I-95) to lower/mid 30s. -Vincent && .LONG TERM /THURSDAY THROUGH TUESDAY/... As of 243 PM Tuesday... With the cP airmass centered over the area Thursday and Thursday night, temperatures through the period will average a good 10 to 15 degrees below normal. A potentially opaque canopy of high clouds Thursday morning should diminish in the wake of the exiting NW flow disturbance, allowing for afternoon sunshine. Highs 50 to 55. High level moisture/cirrus blow-off advecting downstream from the closed cyclone over the Central US could produce fair to partly cloudy skies Thursday night, which could impede radiational cooling a bit. Lows in the lower to mid 30s. The modified Canadian parent high will shift east and offshore on Friday, with southerly return flow allowing for a quick moderation into the 60s on Friday and then into the 70s by Saturday. Meanwhile, ridging aloft will keep it dry through the day on Saturday. Strengthening warm moist air advection on the eastern periphery of the closed mid/upper level cyclone moving east-northeast into the Ohio Valley and Lower Great Lakes will result in increasing pops in the form of showers and possibly a few thunderstorms Saturday night and into the day on Sunday. The most recent 12z/21 GFS has trended farther north than previous runs, and is significantly less wet than previous runs. As such, will keep pops at chance, and highest in the west. If this more northern track solution is realized, Saturday night and Sunday could end up being mostly dry across central NC, with mostly in the way of clouds across the area. Additionally, with the low farther removed from the area, resultant weak forcing will not bode well for any severe weather. Highs Sunday in the 70s. On the heels of the dampening wave moving off the Mid-Atlantic coast Sunday night, another shortwave trough, of lower amplitude, will skirt quickly east across the Central US on Monday and will approach the area late Monday night and into the day on Tuesday. Between these two systems, expect to see a lull in precip chances on Monday, with rain chances ramping back up again Monday night and Tuesday. Continued mild with highs in the 70s. Lows in the 50s. && .AVIATION /01Z Wednesday through Sunday/... As of 915 PM Tuesday... A lead frontal zone now stretching from near EWN to JNX to JQF, and associated focus for scattered showers and storms and sub-VFR conditions mainly at FAY through 09, will settle Swd tonight. Generally Nly winds, between 6-12 kts, will develop behind the front overnight. A secondary cold front and leading edge of strong continental polar high pressure will surge Swd through central NC early Wed; and this will result in strong and gusty NEly winds in strong surface pressure rises and cold air advection between 12-18Z Wed, with lessening winds during the afternoon. Outlook: There will be a chance of MVFR-IFR visibility restrictions in radiation fog in SErn NC Fri morning, including at FAY and perhaps RWI, then again forecast area-wide on Sat morning. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield/MWS NEAR TERM...Hartfield/Vincent SHORT TERM...Vincent LONG TERM...CBL AVIATION...MWS

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