Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 160104 RRA AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 800 PM EST Mon Jan 15 2018 .SYNOPSIS...
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Arctic high pressure will retreat northeast tonight as a low pressure area begins to organize over the Great Lakes region. This will allow for a brief warmup to near normal conditions Tuesday, but a cold front will be racing in to introduce good chances for an inch or two of snow late Tuesday night into Wednesday.
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&& .NEAR TERM /THROUGH TUESDAY/...
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As of 800 PM Monday... Seeing slowly falling pressure and rising dew points as high pressure ridged down the Atlantic seaboard retreats northeast. Only modest tweaks to hourly trends are needed at this point. Previous discussion: Clear skies across the area as central NC remains sandwiched between an exiting coastal low to the east and a low pressure system over the Great Lakes region. Was a little concerned about temperatures undercutting the forecast earlier this morning, but with optimal insolation, they have recovered nicely over the last couple of hours and appear to be on track for today`s highs topping out in the upper 30s to low 40s from north to south. No precipitation is expected through the short term. Overnight tonight expect low temperatures to plunge into the low 20s with a few upper teens possible giving the optimal radiational cooling conditions. For Tuesday, clouds will begin to filter in from the northwest as the upper low propels the positively tilted upper trough to dig further south into the Mississippi Valley region. This will be the driving force behind the potential winter weather moving into the area but this activity will hold off through 00z Wednesday with the increasing cloud cover the main concern for Tuesday afternoon. This will keep temperatures from reaching their full potential. Expect highs in the mid 40s across the north to low 50s in the extreme southern counties.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 255 PM Monday... ...Snow Accumulations of 1 to 2 Inches Possible Across the Piedmont and Northern Coastal Plain Late Tuesday Night Through Wednesday Afternoon... Closed upper low over the Upper MS Valley will transition into an open but still highly amplified shortwave trough as it progresses east through the region on Wednesday. On the heels of a strong Arctic cold front crossing the area Tuesday night, the chance for snow will increase across central NC late Tuesday night (western Piedmont/Triad)and into the day on Wednesday(central and northern Coastal Plain), as an ana-frontal precip band, driven in response to the accompanying vigorous shortwave dynamics and deep layer frontogenesis, moves west to east through the area. Confidence is increasing slightly as NWP model guidance is starting to come into better agreement in both timing and liquid equivalents. Current timing suggest precip onset and transition to all snow between 06 to 09z in the Triad, around 12z(daybreak) in the Triangle, and then 12 to 15z in the east/southeast, with a 6 to 9 hour window of precip expected thereafter before significant/aggressive drying aloft overwhelms the area, ending precip. Deterministic model guidance is right in line with the the SREF ensemble mean of a 0.10 to 0.20" liquid qpf across the area, 20-30 percent of which will likely not go to frozen accumulation owing to rain or rain/snow mix expected at onset. However, given strong column cooling, once precip changes over to all snow, snow ratios are apt to be high, averaging 12-15:1. This would result in the potential for a swath of light snowfall accumulations across the northern two-thirds of the forecast area, with amounts ranging from a half inch along a line extending from Albemarle to Southern Pine to Goldsboro, to as much 1.5 to 2.0" across the far northern- Virginia bordering counties. Potential other scenarios that could unfold are: If more progressive solutions similar to that of the GFS verify, which quickly dries out the <-10C ice nucleation layer, we could see more sleet or snow mixed with sleet, which would significantly reduce snow accumulations across the area. Barring no major forecast/model changes, a winter weather advisory will likely be needed for these areas for Tuesday night through Wednesday evening. Additionally, the Arctic high building in the Southern US in the wake of this system will support very cold temperatures and wind chill Wednesday and Wednesday night, especially across the NC Piedmont. Temperatures during the day on Wednesday will range from upper 20s/near 30 NW to mid/upper 30s SE, with NWLY wind gusts in the teens to lower 20s making it feel like more like teens to lower 30s. Lows Wednesday night are expected to be in the teens to lower 20s, with wind chill values approaching the single digits across much of central NC. With temperatures this cold, any snow on roads and bridges/overpasses will make road conditions treacherous Thursday morning. && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 255 PM Monday... As the low pressure system exits to the east, upper level flow will become much more zonal for the rest of the week and even transition to upper level ridging over the southeast by the weekend. With surface high pressure over the deep south and then translating eastward with time, expect much of the long term to be dry with a significant warming trend through the period. Expect high temperatures on Thursday to remain fairly chilly with highs in the low 40s, quickly rising to the low 50s by Friday, mid 50s by Saturday and into the 60s for Sunday. Lows will moderate through the period from the low 20s to the mid 40s. Despite the majority of the long term being dry, a frontal system will be on the doorstep for early next week but with temperatures well above normal, there won`t be any winter weather threat. && .AVIATION /00z TUESDAY THROUGH SUNDAY/... As of 620 PM Monday... 24-Hour TAF Period: High confidence VFR conditions will persist through the TAF period. Winds will generally be light and variable, becoming southwesterly around 5 kts by the end of the period. Skies will be clear, though some scattered low clouds could approach KRWI overnight, for now they are expected to remain east of there. Increasing high clouds will approach from the west ahead of the next weather system, but remain VFR until after 00Z Wednesday. -KC Looking ahead: The main concern will be the threat of winter weather mainly on Wednesday morning with the threat evolving from west to east into Wednesday afternoon. Expect precipitation to being as rain and then transitioning over to snow with a potential period of wintry mix during this transition. The greatest threat will be for northern terminals but it is possible that all terminals could see accumulating snow. During this time both ceilings and visibilities could be hampered. Precipitation is expected to end on early Thursday morning and then a return to VFR conditions as high pressure takes over. -Ellis && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...JJM/mlm NEAR TERM...Ellis/mlm SHORT TERM...CBL LONG TERM...Ellis AVIATION...KC/Ellis

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