Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 182008 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 308 PM EST Mon Dec 18 2017 .SYNOPSIS...
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High pressure was centered over Mississippi, all while a frontal boundary was stalled between Louisiana and North Carolina. High pressure will remain centered to our south on Tuesday as a dry cold front crosses the area and stall to our south. This front will act as the focus for an upper level disturbance to cross the area on Wednesday.
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&& .NEAR TERM /THROUGH TUESDAY/...
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As of 230 PM EST Monday... The region will remain sandwiched within a split flow pattern overnight into early Tuesday. Southwest flow will help maintain a moisture fetch into the region. A return of low level stratus across mainly the mountains is expected overnight after this afternoon`s scattering of the cloud cover over a generous portion of the mountain region. A shortwave trough is expected to track eastward through the northern stream jet overnight into early Tuesday. This will help to tighten the pressure gradient across the region, allowing for ridge tops to remain gusty overnight, will allow locations seeing gusty winds due to mixing during the course of Tuesday. We are also watching the potential for a very shallow band of clouds to develop over central North Carolina and inch their way north overnight. Areas near and south of Danville, VA may see these clouds arrive during the overnight hours. An associated surface cold front is expected to cross the area on Tuesday, but with limited moisture. No precipitation is forecast, but after some morning clearing of clouds in the west, look for an increase in cloud cover across the mountains during the afternoon. Temperatures will be mild for this time of the year, averaging about 15 to 20 degree above normal. Look for low temperatures tonight in the mid to upper 30s across the region. The higher ridge tops will benefit from the stronger winds with temperatures only dipping to readings around 40 degrees. High temperatures on Tuesday will range from the mid to upper 50s across the mountains to the low to mid 60s across the Piedmont.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
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As of 130 PM EST Monday... Short wave coming out of the southwest United States will be over northern Arkansas Wednesday morning then move east off the Carolina coast by Thursday morning. Also some isentropic lift on Wednesday afternoon and evening. No major changes needed to timing or forecast rainfall amounts through Thursday. Several SREF plumes and other meteograms show minimal temperature rises on Wednesday during the day which is reasonable given the expected cloud cover and precipitation. Models consistent in showing a weak wedge of high pressure east of the Blue Ridge Thursday and Thursday night which will erode on Friday. Precipitation ends before 1000-850 thicknesses forecast would support mixed precipitation type on Thursday morning.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/...
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As of 130 PM EST Monday... Models continue to advertise an amplification in the pattern with a deep trough developing over the central United States. The strength of upper ridging over the Southeast and the eventual location of the baroclinic zone which will be the focus for precipitation is more in question for Sunday and Monday. Next piece of energy lifts out of the southwest Friday, reaching the Great Lakes by Saturday. Low pressure over the Central Plains will track into the Great Lakes by Saturday morning. Warm air advection, strong southwest winds and increasing cloud cover Friday night will lead to mild overnight lows. Plan on trending toward warmer guidance for minimum temperatures. Prefer the timing of the ECMWF which brings the associated cold front through the Mid Atlantic region on Saturday. At this time will keep region in the warmer air through Monday.
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&& .AVIATION /20Z MONDAY THROUGH SATURDAY/... As of 1245 PM EST Monday... VFR conditions prevail across the area generally along and east of of the crest of the Blue Ridge. This trend is expected to continue through tonight into Tuesday morning. The exception may be some patchy IFR/MVFR stratus late tonight near KDAN. Likewise, some patchy MVFR fog may also develop overnight in this area nearest the river valleys. Across the mountains, the story is a bit different. IFR/MVFR ceilings were eroding this afternoon, but coverage is still expected to be greatest in areas between roughly KLWB-KBLF-KJFZ. As we head into and through the overnight hours, look for a bit of resurgence of in the cover over the IFR/MVFR ceilings, to an area east to near the crest of the Blue Ridge again. Some patchy drizzle will also be possible across parts of southeast West Virginia, near and west of KLWB. Winds will start to increase a bit this afternoon, especially in areas without, or with decreasing, cloud cover as low level mixing takes place. Some gusts, especially across and near the mountains, will reach 15 to 20 kts. Overnight, we expect a westerly low level jet to increase. While the mountain valleys and Piedmont region will remain decoupled, 15 to 25 kt gusts will be common at the higher ridge tops. There also may be some low level wind shear across the Northern Mountains of North Carolina where the increasing low level jet is not too far above the higher elevated mountain valleys of that region. On Tuesday, westerly winds will be generally a little stronger than those of today across the region once the morning inversion breaks. Cloud cover in the west will erode as Tuesday morning progresses. Extended Discussion... Sub-VFR conditions will return to mainly central and southern sections of the area on Wednesday as a disturbance heads east through Tennessee and North Carolina. VFR returns briefly on Thursday in advance of our next cold front that will approach the area on Friday. Look for flight conditions to gradually worsen during the day Friday, especially in the west. Sub-VFR conditions will be probable for most areas Friday night into, and through, Saturday with the arrival and passage of a potent cold front. Winds will also become gusty to very gusty immediate in advance and then post cold frontal passage. A distinct abrupt wind shift is also expected late Friday night or early Saturday morning across the area with the passage of the cold front. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...DS NEAR TERM...DS SHORT TERM...AMS LONG TERM...AMS AVIATION...DS

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