Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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288 FXUS62 KRAH 181909 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 309 PM EDT Fri Aug 18 2017 .SYNOPSIS...
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A weak surface trough will extend from the western Piedmont of Virginia south into the Piedmont of the western Carolinas. A cold front will move across the southern Appalachians this evening and into the Piedmont of the Carolinas and Virginia overnight. The front will slow across the Coastal Plain on Saturday before pushing off the coast on Sunday.
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&& .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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As of 235 PM Friday... The latest surface analysis shows a surface trough extending from the western Piedmont of Virginia south into the Piedmont of the western Carolinas. A cold front extends from western PA southward into WV and eastern KY and TN at 18Z. A tongue of extremely high dew points in the upper 70s to lower 80s extends from the coastal region into the Coastal Plain, Sandhills and eastern Piedmont. Dew points at 2pm include 80 at Goldsboro and 79 at Halifax which combined with temperatures of 90 to 95 result in heat index values from 100 to 109 supporting the current heat advisory. Visible satellite from GOES 16 shows deep convection across the coastal region of NC, some enhanced cumulus in the northern Piedmont and Coastal Plain and scattered convection across the mountains. The air mass across the region is moderately to strongly unstable with MLCAPE values ranging from 1500 to 3000 J/Kg with modest mid-level lapse rates of 5.5 to 6.0 deg C/km. Central NC is in a region of weak forcing for ascent despite the loaded airmass. The closest forcing mechanisms include an eastward advancing shear axis with attendant cold front approaching the mountains with another short wave trough over AL/GA which slips southeastward. Still expect there will be only isolated convection across central NC into the late afternoon hours with limited forcing. A broken lines of showers and storms moving across the NC mountains will slip east and probably intensify as it experiences a relative increase in instability late this afternoon and evening. This area of convection will likely reach the Triad between 5 and 8pm. Signals are that the convection will tend to very slowly weaken as it moves into the eastern Piedmont and Coastal Plain. The best forcing will be across the northern half of the CWA with decreased coverage and intensity in the south. As the shear axis and front move slowly east overnight the threat of convection will wane and shift eastward. Portions of the area are in a marginal risk for severe weather, primarily from downburst winds. Don`t think there will be much cold advection so lows tonight will once again be in the lower to mid 70s. -Blaes
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
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As of 300 PM Friday... The cold front reaches the Coastal Plain Saturday morning and slowly slips east and moves off the coast by daybreak Sunday. An upper level trough approaches the region from the OH Valley on Saturday afternoon with the trough axis moving across central NC toward daybreak Sunday. A much drier air mass moves into the region with precipitable water values dropping into the 1.1 (west) to 1.6 (east) range by Saturday afternoon. While a small threat for a shower or storm lingers across the Coastal Plain and Sandhills near the cold front, generally dry conditions are expected elsewhere. The air mass cools slightly with highs ranging between 88 to 94 degrees Saturday afternoon. Drier air moves into the area from the northwest Saturday night, and dew points fall into the mid to upper 60s across the Piedmont and the lower 70s in the Coastal Plain. This will support much more comfortable lows in the upper 60s in the Piedmont and lower 70s in the Coastal Plain. -Blaes
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&& .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 244 PM Friday... Dry weather is expected on Sunday across all of central NC with a dissipating front now progged well to our south and rather inactive westerly flow aloft. Given the steady-state airmass combined with ample sunshine, we should easily see highs into the low 90s. On Monday we`ll see heights rise as the ridge off the SE coast builds northward. The sfc pattern will be fairly typical for this time of year with the sfc high over the western Atlantic promoting a southerly low level flow over our area. Forecast soundings show a notable inversion around H7 with dry air in the mid-levels, and in some cases (particularly across our southern and eastern counties) a fair amount of moisture above H4. Thus with heating, the forecast soundings suggest a decent amount of shallow cu may form below the inversion across much of central NC as the afternoon progresses. To make matters worse, the soundings also suggest a veil of cirrus, esp the farther south you go. If there is any good news, these soundings do not support rain or deep convection, so will keep PoPs well below climo for Monday. So in summary for the eclipse weather, neither clear nor completely overcast, but rather partly cloudy with cu briefly obscuring the sun at times, along with some high clouds. Keep in mind that if you spend any substantial time outside, be ready for highs in the low-mid 90s with heat index values in the upper 90s. Tuesday should be mostly dry as the ridge slowly moves east, but then rain chances will increase on Wednesday as the next northern stream short wave moves south and east and pushes a cold front across our area. The longwave trough will continue to deepen over the East, so look for cooler temps by late next week, and perhaps even a brief break from the high humidity for next weekend. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
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As of 230 PM Friday... VFR conditions across central NC this afternoon will give way to scattered showers and thunderstorms this evening. The convection will largely be associated with an eastward advancing cold front. Look for the greatest chances of adverse aviation conditions in the Triad (KINT and KGSO terminals) from 21 to 02Z, in the Triangle (KRDU terminal) from 23 to 03Z and in the east and southeast (KRWI and KFAY terminals). An isolated shower or storm is possible across the Piedmont and especially the Coastal Plain overnight. Don`t expect much in the way of late night or early morning low-level stratus although a BKN layer of clouds is expected overnight at around 6kft. Generally fair weather with SCT-BKN cumulus with bases around 4kft is expected on Saturday, with some scattered afternoon storms across the Coastal Plain and Sandhills impacting the KFAY terminal. Southwest winds at 5 to 10kts this afternoon will become light west overnight behind the front and light northwesterly on Saturday. Looking beyond 18Z Saturday....generally VFR conditions are expected on Saturday and Sunday with just a few showers or storms across the Coastal Plain on Saturday and dry weather on Sunday. The threat late-day storms and some early-morning fog and stratus increases on Monday into tuesday. -Blaes
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&& .RAH WATCHES/WARNINGS/ADVISORIES...
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Heat Advisory until 6 PM EDT this evening for NCZ025>028- 040>043-073>078-083>086-088-089.
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&& $$ SYNOPSIS...BLAES NEAR TERM...BLAES SHORT TERM...BLAES LONG TERM...NP AVIATION...BLAES

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