Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 281007 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 507 AM EST Mon Nov 28 2016 .SYNOPSIS...
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High pressure will drift east of the Atlantic seaboard today as a deep area of low pressure across the mid part of the U.S. gradually shifts eastward. A cold front will move through the region Tuesday accompanied by gusty winds and much needed rain showers. Another wave of low pressure will develop across the Midsouth Wednesday spreading another round of rain showers into the region before cooler and drier conditions return for the end of the week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 430 AM EST Monday... Finally, some significant changes to the long standing dry weather pattern that will bring much needed rain into the region. Unfortunately, amounts are looking to be less than was thought just 24 hours ago. Nonetheless, a good soaking rainfall of 1 to 2 inches over a 2-3 day period appears to be a good bet for much of the forecast area. Not a significant drought buster, but which will certainly greatly reduce the fire danger. The pattern change is already underway as low pressure deepens across the central U.S. as strong short wave energy moves eastward from the eastern Pacific. A strong cold front was evident this morning from the western Great Lakes southwest into Texas along which fairly robust thunderstorms were developing even at this hour and which appears on track for a fairly significant thunderstorm outbreak across the Midsouth later today. However, with the broad low pressure area centered in the mid U.S. and shifting east only slowly along with a high pressure ridge remaining in the western Atlantic, the short wave and associated front will shear out and lift mostly northwest of the region overnight and early Tuesday. A diminishing area of showers will reach the western CWA before daybreak Tuesday and then linger further east in a continued diminishing state after daybreak. Some light rain or sprinkles may develop during the late afternoon/evening along the southeast facing slopes of the Blue Ridge from northwest NC into southwest VA, but no appreciable measurable precipitation is expected until likely well after midnight. As a result, have backed off on pops during the early part of the overnight hours trending to categorical by daybreak Tuesday. Rainfall amounts through daybreak will average 1/2 inch or less west of the Blue Ridge and likely 1/4 inch or less east of the Blue Ridge. Otherwise, look for an increasingly cloudy day with early day mid/high clouds lowering during the afternoon/evening, especially southwest and near the Blue Ridge. Wind will be the main concern through this period as a strong 50-60kt LLJ traverses the region during the 21Z-09Z time frame. This will be the typical situation where we have strong south to southeast winds in our typical western locations from Mercer county southwest into northwest NC. MOS guidance and BUFKIT soundings do not show these winds mixing well down to the surface as well as in some situations. After considerable collaboration with neighboring offices, have posted a wind advisory for the western most tier of counties from Mercer southwest to Watauga, but have noted that it is mainly for elevations above 3500 ft. 850mb temps hold mostly in the +5C to +8C range today, then surge late tonight into Tuesday into the +12C range as the strong LLJ moves across the region. Cloud cover and limited WAA during the daytime today will inhibit any significant warming, but temperatures will still top out just above normal readings. Overnight, a non-diurnal temperature trend is in order as the strong southerly winds attempt to bring the warmer mid-level temperatures down to the surface. Temperatures could rise five degrees or more from midnight to dawn Tuesday.
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&& .SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/...
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As of 400 AM EST Monday... During this portion of the forecast, two distinct shortwave troughs will progress northeast across the area along a nearly stationary cold front. The second of these two waves act as a kicker to progress the frontal boundary eastward towards the coast. Compared to 24 hours ago, model guidance is still fairly consistent with the timing of the precipitation associated with the first wave. Starting Monday night, the majority of the activity will be across the western portion of the area come sunrise Tuesday, and progress across the region during the day. By the early evening, only isolated to scattered coverage is expected across the central and eastern portions of the region. After a brief break in the action Tuesday night, precipitation associated with the second wave will start to enter the southwest portion of the area by sunrise. It is with this second wave that guidance has trended slower with the associated precipitation. For the first half of the day, the the NAM and ECMWF keep the prevailing low level flow parallel with the flow of the upper trough, thereby stalling the progression eastward until afternoon when the low level flow becomes more westerly. The Canadian solution is comparable to 24 hours ago with a more rapid entry of precipitation into the western parts of the area Wednesday morning. The GFS has trended a bit slower, but not to the degree the NAM and ECMWF have. Our forecast will reflect the trend towards a slower arrival, perhaps in line with the GFS as a consensus solution. Wednesday evening, precipitation will be exiting the eastern portion of the area while northwest flow develops in the west. This northwest flow is expected to help maintain cloud cover and upslope precipitation across parts of southeast West Virginia into Thursday. While starting out as rain showers, enough colder air is expected to make its way into the area for snow showers to occur at the highest elevations early Thursday morning. This upslope cloud cover and isolated rain/snow showers will get a bit of enhancement Thursday night as the region catches the southern end of a clipper system moving through the Great Lakes region. Temperatures through the period will trend milder through Wednesday. Anticipate a mix of low to mid 60s for high temperatures across the mountains with upper 60s to lower 70s across the Piedmont on Wednesday. Temperatures will trend cooler on Thursday in the wake of the cold front by 10 to 15 degrees. Precipitation totals through the period will average two-thirds of an inch to one inch across the region. Totals closer to one and one- half inches are forecast for along the crest of the Blue Ridge and for western Greenbrier County, WV.
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&& .LONG TERM /FRIDAY THROUGH SUNDAY/...
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As of 115 pm EST Sunday... Colder air pours in for Friday-Saturday as northwest flow continues. Appears that there will be enough moisture to support a slight chance of snow or rain showers Thu night into Friday night for western Greenbrier. Shortwave ridging sets up by Saturday-Sunday and another wave shows up in the area Sunday-Sunday night with small chance of rain/snow showers. Highs Thursday close to normal will drop to 5 to 8 degrees below normal Friday-Sunday with highs in the 40s west to lower 50s east. Low temperatures should be at or slightly below normal through the period.
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&& .AVIATION /10Z MONDAY THROUGH FRIDAY/... As of 1130 PM EST Sunday... VFR conditions including light winds to prevail under high pressure overnight with a thickening canopy of high clouds continuing to increase from the west through dawn Monday. Moisture should continue to slowly increase on Monday as the surface high exits offshore allowing the flow to veer more south and southwest by the afternoon. Expect this to moisten things enough to allow the development of some cumulus /strato-cu Monday afternoon with this cloud field beneath sheared mid/high clouds arriving from the west. Some potential for spots near the Blue Ridge to lower to near high end MVFR levels by late Monday but iffy given dry air in place. Otherwise keeping it VFR for now with any lower canopy mainly above 4k feet under lowering mid deck above. Winds should also bump up a bit with speeds increasing to 8-15 kts, with a few gusts to 20-25 kts possible on the ridges as the low level jet picks up under increasing warm advection aloft. Flying conditions will deteriorate Monday night as moisture deepens ahead of a band of showers that should arrive from the west around midnight and continue into early Tuesday morning. Expect this combined with upslope flow along the Blue Ridge to result in conditions lowering to MVFR across most sites during the evening, and possible IFR in low cigs and restricted vsbys in rain/fog espcly mountains after midnight into the early morning hours of Tuesday. Since appears most of the rainfall will be just south and west of the TAF sites Monday evening, will only include a shower mention in the far western locations for now ending 06z/1AM Tuesday. In addition, strong southeast winds with gusts to 30-40+ kts may occur around KBLF Monday night as well as some of the higher ridges along the western slopes through dawn on Tuesday before diminishing. Extended aviation discussion... Initial wave of rainfall will exit later Tuesday with leftover sub-VFR conditions in place before a more significant batch of rain arrives later Tuesday night and continues into Wednesday evening. This likely to keep widespread sub-VFR ceilings and visibilities in place until a cold front passes through the region early Thursday. Drier air behind the front should result in a return to VFR east of the mountains while upslope sub- VFR cigs likely linger across the southeast West Va locations, where rain or snow showers appear possible. Broad northwest flow looks to keep this scenario in place on Friday as well with upslope driven sub-VFR cigs western mountains and mainly VFR to the east. && .FIRE WEATHER... As of 800 PM EST Sunday... Humidity slowly recovering across the valleys and east of the Blue Ridge but remains very dry on the ridges where values remain below 30 percent early tonight. However winds are quite light most spots so expect moisture to continue to edge up espcly valleys as temps cool, while may take most of the night for the ridges to recover above 50-60 percent per latest arid evening soundings. Better push of moisture advection to take shape Monday with the low level southerly jet pushing into the area by Monday night. This should help lift dewpoints up enough to alleviate the ongoing low humidity although some of the ridges may still stay below 30 percent until later Monday afternoon. Winds will pick up after dark Monday night and gusts to 40 mph or more over the higher ridges of southern WV to NW NC are likely. At the same time RH will be rising into the 40s and 50s as rain starts to initiate over the mountains Monday night. Still looking for two good rain events, though amounts are trending lower, but still in the 1-2 inch range Tuesday-Wednesday. && .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...Wind Advisory from 1 PM this afternoon to 7 AM EST Tuesday for VAZ007-009-015. NC...Wind Advisory from 1 PM this afternoon to 7 AM EST Tuesday for NCZ001-018. WV...Wind Advisory from 1 PM this afternoon to 7 AM EST Tuesday for WVZ042.
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&& $$ SYNOPSIS...RAB NEAR TERM...RAB SHORT TERM...DS LONG TERM...DS/WP AVIATION...JH/RCS FIRE WEATHER...JH/RAB

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