Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 171819 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 120 PM EST Wed Jan 17 2018 .SYNOPSIS... A strong upper level disturbance and associated arctic cold front will move through our region today. This will be followed bitter cold arctic high pressure tonight into Friday morning. A warm-up will begin Friday and extend into the weekend. && .NEAR TERM /TODAY AND TONIGHT/... As of 923 AM Wednesday... ...Winter Storm Warning for most of Central NC through 900 PM tonight... ...Winter Weather Advisory for the SE Coastal Plain (Wayne and Sampson through 900 PM... Review of some of the latest 06z to 12z model guidance is coming into collaboration(always a good thing as it increases confidence) with what we are seeing in satellite data of cooling cloud tops east of the mountains; a deeper more wrapped up mid/upper level system along with additional supportive evidence in observational/boots on the ground data of 2 inches already on the ground in the Triad and impressive-slowing moving snow band over the Piedmont, in an axis just east of the Triad and just west of the Triangle, extending from Troy to Siler City to Hillsborough to Roxboro/Oxford, that will likely produce snowfall rates locally up to 1 inch per hour. And let`s not overlook the deep moist cold snow sounding at GSO. All of which will supportive of wetter-snowier/slower/more robust system, with great set-up for CSI mesoscale banding across central NC Piedmont as suggestive by the 06z later this morning between 15 to 21z. This band will move slowly east throughout the remainder of the morning and afternoon hours, eventually shifting east and out of the area by the early evening. Given all the supporting evidence, will be increasing the snow amounts from 5 to 6 inch to 5 to 8 inches across much of the NC Piedmont, tapering off to 2 to 4 inches across the central and northern Coastal Plain counties, to 1 to 2 across the far SE counties. Although slower than previous forecasts, due to the deeper more wrapped system, once precip develops, temps will cool into the 20s. Previous forecast discussion... We will have the Winter Storm Warnings and Winter Weather Advisories run through 900 PM this evening and raise snowfall forecast amounts in the Warning area to between 3-6 inches. Forecast trends continue to advertise a deepening/stronger and more cut off mid-level circulation/trough that is forecast to track east across NC this afternoon and evening. This in turn results in a slower system which allows more QPF. Partial thicknesses support snow as the main P-Type over the Piedmont into the Northern Coastal Plain, arriving between 09z and 12z in the western Piedmont, spreading east into the Triangle area by mid morning. To the southeast of the Triangle area, the precipitation is expected to be delayed a few hours, especially along the Interstate 95 corridor, arriving late morning or early afternoon. The delayed system down east means that the precipitation is expected to begin as rain, then transition to snow as the cold air wins out mid to late afternoon. Current data indicated the arctic front had reached through the Mountains and extended NE across central VA. Bitterly cold temperatures behind the front ranged from near zero over TN and in the 20s into Mountains of NC and over northern VA. Temperatures were mainly in the 30s over central NC, with dew points in the 20s. The partial thicknesses and wet bulb temperatures were already supportive of snow over most of the Piedmont, and that is before the arctic air begins to be pulled into the region after 12z. In addition, a low pressure was developing along the arctic front over north Georgia. A light southerly flow into the low pressure has aided in the increase of boundary layer moisture (dew points in the 30s along the Savannah River in GA/SC and nosing up into northern SC. This moisture will be transported into the system as the mid/upper trough sharpens and cuts off through the day and the low pressure tracks along the front. The strengthening upper feature is responsible for the introduction of more lift/moisture transport/QPF. This QPF is expected to be maximized over central NC late morning into the afternoon with moderate to heavy snow. Snowfall details... As for the snowfall forecasts, it appears that a QPF of 0.30 to 0.50 liquid equivalent is most likely across central NC. This uses a blend of the models. Using the 10:1 becoming 15-18:1 snow to liquid ratios would give most of the Winter Storm Warning area between 3-5 inches in the northwest, 3-6 inches from SW to NE through the center of the Piedmont into the Northern Coastal Plain, and lesser 1-3 totals in the SE Coastal Plain (which occurs at the end of the event). The least totals should be in the Clinton to Goldsboro areas where 1-2 inches is expected. Snowfall rates of 0.5 to nearly 1 inch an hour will be possible for 4-6 hours given the latest guidance through the Piedmont and Northern Coastal Plain. Temperatures, precipitation timing, and P-Type details... Snow is expected to develop over the Triad and Yadkin Valley region by 12z, with the heaviest snow between 12z and 18z, gradually tapering to flurries mid to late afternoon. Temperatures will fall into the lower to mid 20s. Snow is expected to spread into the Triangle and western Sandhills region this morning, with the heaviest snow expected between 10 am and 4 pm. Temperatures will fall into the mid to upper 20s this afternoon. The snow will likely begin as a period of rain in the Central and Southern Coastal Plain late morning, then gradually transition to snow from NW to SE as the cold air works in. Dynamical cooling associated with heavier precipitation rates will also aid in the change-over to snow from Fayetteville to Goldsboro mid to late afternoon. Temperatures in the mid to upper 30s will fall quickly by mid to late afternoon into the lower 30s in the Advisory Area. The temperatures will drop quickly today as the arctic air surges in from the north as the precipitation reaches maximum intensity. Expect the snow to taper off from the west late this afternoon and evening. Clearing skies will lead to bitterly cold conditions tonight. Lows 8-18. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
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As of 120 PM Wednesday... H5 west to northwest flow and surface ridging will result in mainly clear weather. Temperatures will start very cold with highs on Thursday in the upper 30s to lower 40s. After lows in the teens to lower 20s Thursday night, temperatures will moderate to near seasonal normals on Friday.
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&& .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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As of 120 PM Wednesday... The warmer weather will continue into the weekend as the upper level pattern transitions to more ridging in the SE and a trough in the western US. A storm system will move northeastward from the central plains Sunday to the western Great Lakes on Monday. This system`s attendant cold front will cross our region Monday night with a chance of showers. Temperatures in the 50s Saturday afternoon will climb to around 60 on Sunday, and 60 to 65 on Monday. After the cold front passage, temperatures Tuesday and Wednesday will fall back into the 50s.
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&& .AVIATION /18z WEDNESDAY THROUGH MONDAY/... As of 1247 PM Wednesday... 24-Hour TAF period: The IFR/LIFR conditions will continue as the snow continues to fall. KRWI is just now starting to come down (currently MVFR) and KFAY is still VFR but should start a downward trend as the precipitation moves in. With the snow, visbys are 1/4 to 3/4 SM and cigs range from 3-8 KFT. Winds in the 8-12 kt range, with increasing gustiness in the east will continue into tonight, even after the snow ends. Snow should taper off from west to east between 00Z and 12Z Thursday, accompanied by a return to VFR conditions. Looking ahead: VFR conditions will persist through Saturday. Forecast soundings hint at some low-level moisture Saturday night, otherwise the next chance for adverse aviation conditions will occur Monday night into Tuesday. && .RAH WATCHES/WARNINGS/ADVISORIES...
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NC...Winter Weather Advisory through 9 PM EST Wednesday for NCZ078-089. Winter Storm Warning through 9 PM EST Wednesday for NCZ007-021>025-038>040-073>076-083-084. Winter Storm Warning through 9 PM EST Wednesday for NCZ008>011-026>028-041>043-077-085-086-088.
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&& $$ SYNOPSIS...Badgett NEAR TERM...Badgett/BSD SHORT TERM...Franklin LONG TERM...Franklin AVIATION...KC

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