Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 160735 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 215 AM EST Tue Jan 16 2018 .SYNOPSIS...
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Cold high pressure will move offshore this morning. A strong upper level disturbance and associated arctic cold front will approach from the west late tonight. The system and cold front will move through our region Wednesday. This will be followed bitter cold into Thursday. A warm-up will begin Friday and extend into the weekend.
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&& .NEAR TERM /TODAY/...
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As of 215 AM Tuesday... ...Winter Weather Advisory late tonight and Wednesday in the west and in the east Wednesday... A very cold morning with widespread lows in the teens to lower 20s, sunshine will bring a fairly mild "comparatively speaking" afternoon. Clear skies this morning will give way to increasing cloudiness this afternoon. This occurs as the mid/upper level disturbance approaches from the west later this afternoon and evening. The arctic surface high is forecast to hang on over eastern NC through the afternoon. This will give plenty of sunshine to most areas today, with mostly sunny skies becoming mostly cloudy in the west this afternoon. Highs today, supported by low level thicknesses and unanimous MOS guidance agreement should top out in the mid 40s NW, 47 to 50 elsewhere, except 51-54 in the far Southern Coastal Plain. The mild sunshine this afternoon will do little to warm the very cold surfaces enough to preclude a cold enough ground for snow to accumulate during the expected event. The ground temperatures will be nearly optimal with readings in the mid 30s to near 40. Only a frozen ground leading into the evening would be optimal.
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&& .SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/...
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As of 215 AM Tuesday... ...Winter Weather Advisory all of central NC 11 PM tonight through the day Wednesday... Regardless of the "milder" afternoon, a lingering, very dry boundary layer associated with the departing arctic high pressure will set the stage for snow after midnight in the west, spreading late tonight and early Wednesday. Moderate to high confidence in 1-3 inches of snow for much of central NC later tonight through Wednesday. Models continue to converge on a snow event for much of central North Carolina tonight and Wednesday. A widespread 1 to 2 inches of snow is expected, with some locally 3 inch totals over the north-central and Northeast Piedmont and Northern Coastal Plain. This snow is fairly an atypical snow event for our region as it will be generated by a mid/upper system with a departing arctic high. Typically, for accumulating snow to occur with these typically moisture starved systems, the mid-level vorticity maximum must track just to our south and east. This appears that it is the case this time, with the models in good agreement. This will maximize the little moisture available with strong lift to produce precipitation. Given the dynamics and the expected evaporative cooling, it should be a situation that brings efficient snow accumulations, even with low QPF (0.1 to 0.3 of an inch now forecast). Snow/liquid ratios are forecast to be 10-1 at onset, becoming 15-20 to 1 with strong cooling aloft and at the surface as the precipitation ends Wednesday. Ground temperatures will be cold enough too as the precipitation will start in the west at night, and in the east by around daybreak. As far as precipitation type (P-Type), the models agree in snow as being the dominate type, with a very brief period of light rain at the onset in the SE. Even with highs in the mid 40s to lower 50s today (the very dry and chilly boundary layer will evaporatively cool quickly with the onset of precipitation in the west later tonight. Partials in the 1000/850 and 850/700 strongly support this scenario. The temperatures will quickly wet bulb to below freezing (20s). The area that may get more light rain at onset is in the SE Coastal Plain at precipitation onset Wednesday morning. This region is forecast to have a dew point recovery to near 32, with temperatures forecast in the mid 30s at onset (12z to 15z Wed). It may take a few hours of light rain for the precip to transition to snow in these areas. However, light snow is then expected as the mid level cool rapidly with the system moving overhead (dynamic cooling). The timing of snow in the west is between 100 and 400 am into the western Piedmont, and between 400 am and 700 am in the central, and 700 am and 1000 am in the east. A window of accumulating snow should last around 6 hours in most areas ending from west (noon or so NW) and elsewhere mid to late afternoon. Temperatures should begin warmest as the precipitation starts. So, highs for the calendar day should end up being before the snow hits Wednesday. Temperatures should start in the mid to upper 30s tonight with thickening and lowering clouds. Temperatures (according to wet bulb forecasts etc... ) should cool into the 20s during the evening. Readings may recover a degree or two in the Yadkin Valley (far west) as skies clear mid to late afternoon. However, the arctic air will be pouring in on increasing NW winds, so do not expect anything more than possibly 28 or 30 in the Triad around 300 or 400 PM, before falling quickly again by sunset. Readings in the Triangle may not recover from the mid 20s during the event Wed. afternoon, before falling into the teens at night. In the SE Coastal Plain Wednesday, expect any light rain to quickly change to snow between 12 and 15z. Then snow is likely through the day, ending by late afternoon. Highs in the upper 30s at onset, falling quickly into the lower 30s during the day. So, an Advisory for 1-2 inches is needed all the way through the Interstate 95 corridor again. Alternate scenarios include the potential for lower QPF, as these systems are often moisture starved. The snow accumulation forecast uses the most likely outcome when examining all available data. There is a 20-30 percent chance of lower snow totals, but 1 inch appears to be the low end for the Triangle area, and 0.5 in the Triad, with trace to 0.1 in Fayetteville and Goldsboro. Conversely, there is a chance (20 percent) of higher totals that those officially forecast. This would be 2 to 2.5 inches in the Triad, 3-4 from the Triangle to Halifax, and 1.5 inch in Fayetteville and Goldsboro. The P-type is high confidence of snow in all but the SE, with 70 percent chance of accumulating snow in the SE, after some light rain to start. Wednesday night... Rapidly clear skies along with the gusty NW winds will bring wind chills into play. Actual lows should be 10- 20 NW to SE, with wind chills zero to 10.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/...
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As of 200 AM Tuesday... Thursday and Thursday night will continue to be very cold. Highs Thursday should be only in the 30s to lower 40s. Lows Thursday night in the teens to lower 20s. We will undercut MOS guidance by several degrees given the very low thickness, especially NE zones. A moderating trend will begin Friday as highs warm into the 45 to 55 range. This warming trend will continue Saturday through Monday as the upper level pattern "flips" from cold trough to warm ridge over the SE states. Lows will moderate into the 20s Friday, 30s Saturday, and mid 30s to lower 40s Sunday and Monday. Highs will warm into the 50s Saturday, then mostly 60-65 Sunday and Monday!
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&& .AVIATION /06z TUESDAY THROUGH SUNDAY/...
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As of 100 AM Tuesday... 24-Hour TAF Period: High confidence VFR conditions through 00z/17 January. High pressure will bring clear skies and calm conditions through 12z. High pressure will move east, with a weather system to approach from the west late today and tonight. An increase in high clouds today, then mid clouds later today in the west. Looking ahead: Tuesday night and Wednesday, Light snow is expected to develop/overspread central North Carolina from the west between 06z and 10z at KGSO and KINT, then into the KRDU/KRWI areas between 10z and 15z, and KFAY around 15z. There may be a brief period of light rain at KFAY at onset of precipitation, but it is expected to change to light snow by early afternoon. MVFR VSBYS AND CIGS will become IFR CIGS and VSBYS with light snow and fog. Most TAF sites will have a 6 hour window of precipitation, ending from the west by 18z KGSO, 21z or so at KRDU and KFAY/KRWI around 00z/THU. Wednesday night through Sunday... A quick return to VFR with a breezy NW wind is forecast after the system departs Wednesday afternoon and evening. VFR conditions expected Wed through Sun.
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&& .RAH WATCHES/WARNINGS/ADVISORIES...
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Winter Weather Advisory from 11 PM this evening to 7 PM EST Wednesday for NCZ007>011-021>028-038>043-073>078-083>086-088-089.
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&& $$ SYNOPSIS...BADGETT NEAR TERM...BADGETT SHORT TERM...BADGETT/BSD LONG TERM...BSD AVIATION...BADGETT

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