Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 221803 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 203 PM EDT Sun Apr 22 2018 .SYNOPSIS... High pressure will stay anchored from the Great Lakes to the Middle Atlantic through Sunday night, while low pressure shifts from Arkansas to eastern Tennessee. This low will then track over the Ohio Valley on Wednesday. && .NEAR TERM /THROUGH TONIGHT/... As of 1255 PM EDT Sunday... About the only notable adjustment for the forecast this afternoon is a small increase in the high temperatures for parts of the area. With the cloud cover remaining on the thin side for many locations, surface heating is outpacing the forecast by a degree or two. Have adjusted upward by a similar amount the high temperature for mainly eastern sections of the region. As of 950 AM EDT Sunday... Mid to high level cloud cover continues to thicken and spread eastward across the region. This trend will continue through the afternoon hours. Have adjusted the hourly sky cover grids to reflect the latest satellite imagery across the area with this coverage advecting eastward along the 500 mb flow. For temperatures, dew points and winds, have only needed to tweak values to better reflect the current conditions, and kept the trends heading into and through the afternoon the same. Have added a small chance of light rain to parts of the Northern Mountains of North Carolina. The 12Z/8AM HRRR offers a solution that paints a hundredth or two in this area during the afternoon, and adding a slight POP matches well with the POP/wx grids GSP has along our common border in that area. As of 300 AM EDT Sunday... For today, an upper low will be in Arkansas, while an inverted trough extends northeast into Kentucky, from a surface low over Mississippi. Meanwhile, over the Mid Atlantic, two surface high pressure systems will join forces to keep rain out of the area for one more day. We will see an increasing in high clouds as moisture from the upper low rides over the merged surface ridge. Despite thickening high clouds, temperatures across the mountains will be slightly warmer than normal with highs in the mid to upper 60s, with the exception of higher ridges being in the upper 50s. The foothills and piedmont counties will experience slightly cooler than normal temperatures today. With a cool light southeast breeze, highs in the east will range in the upper 60s to lower 70s. Clouds will continue to lower tonight as the upper low moves over eastern Tennessee and closer to the area. Saturation of the environment will take some time as the dry high over the Mid Atlantic holds off rain from entering the area until later Monday morning. Some light rain from southeast upslope flow may fall by sunrise, but the bulk of the heavier rain is not scheduled until later in the day. With moisture continuing to pump into the region overnight, temperatures will remain mild with lows ranging in the 40s. && .SHORT TERM /MONDAY THROUGH WEDNESDAY/... As of 150 AM EDT Sunday... Upper low becomes vertically stacked and drifts from the Tennessee Valley into the Ohio Valley during this time frame. At the surface a triple-point low forms Tuesday then moves northeast to the Virginia coast Tuesday night and Wednesday. Upper pattern is somewhat blocky with a ridge preventing much eastward movement of the upper low. But timing of precipitation similar to last several runs with steady rain filling in from southwest to northeast across southwest Virginia, southeast West Virginia and northern North Carolina on Monday. This a favorable scenario for a classic upslope heavy rain event along the Blue Ridge and foothills to the east. With deep and very strong isentropic lift and upslope bringing precipitable water values around 1.5 inches into the region, anticipate 0.5 to 1.0 inches of rain every 6 hours from 18Z/2PM Monday through 18Z/2PM Tuesday. Will stay on the cool side of guidance for maximum temperatures on both Monday and Tuesday due to very limited solar insolation and a strong in-situ wedge. Once the surface low reaches the Virginia coast, surface winds will become west then northwest eroding the wedge. At this time, models have this occuring on Tuesday night. Not particularly meaningful cold air advection behind this system but there may be enough of a downslope component to the wind along with the deeper moisture pulling out of the area, that there may be some breaks in the clouds east of the Blue Ridge on Wednesday. Breaks or not, will still have Wednesday warmer than Tuesday. && .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... As of 320 PM EDT Saturday... The upper low over the Great Lakes will get caught up in the northern stream jet, open as a wave, and eject eastward with the prevailing flow. Its associated cold front/trough axis will cross our region, and help bring winds around the the northwest Wednesday into Wednesday night. This will result in our winds shifting northwest, and allowing for upslope rain showers across the west, and decreasing coverage of precipitation east of the Blue Ridge. Our weather pattern will remain quite progressive through the remainder of the forecast period. Two additional northern stream shortwave troughs are expected to zip through the region. Each will bring a return of showers to the area, with the greatest concentration across the mountains. The first will be Wednesday night into Thursday. The second will occur either Friday or Saturday, as model agreement isn`t as strong on this second one. Our forecast will reflect the quicker of the two solutions with enough colder air arriving in its wake for the potential for some snow showers along the highest peaks and ridges of southeast West Virginia, south into the Northern Mountains of North Carolina. Temperatures during this portion of the forecast will trend colder with readings by Saturday some five degrees below normal. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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As of 145 PM EDT Sunday... VFR conditions continue to prevail across the vast majority of the region. The exception would be currently be between KGEV- KTNB where some MVFR ceilings have developed, and they are expected to continue through the afternoon, and gradually work their way north into parts of far southwest Virginia. As we progress through the overnight hours, MVFR ceilings will slowly work their way northeast into the region along with rain with sub-VFR visibilities, but it is likely the TAF forecast locations will remain VFR until mid-morning Monday. A broad swath of rain will continue to overspread the area tomorrow with ceilings dipping into the IFR/MVFR range by the conclusion of the valid TAF period of 18Z/2PM Monday. The light and variable winds most locations are experiencing today, will gradually trend southeast, and start increasing in speed overnight. Very gusty conditions are expected in the KBLF region by Monday, near 40 kts. Extended Aviation Discussion... Sub-VFR ceilings and visibilities associated with a broad region of moderate to heavy rain are expected for most locations by late Monday afternoon. These conditions, along with very gusty conditions in the west, will continue in and through Monday night and early Tuesday. Tuesday afternoon and night, the low pressure responsible for the wet weather will shift east of the area. This will bring our winds to the northwest, and allow for the precipitation to trend showery in the west. The weather pattern will remain unsettled Thursday into Friday as a series of disturbances crosses the area, each with the potential for providing showery precipitation and localized sub-VFR conditions.
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&& .HYDROLOGY... As of 530 AM EDT Sunday... Collaborated with WPC on covering the southern Blue Ridge in a Marginal/Slight Risk of Excessive Rainfall for Monday through Tuesday night. Total rainfall amounts will range from 1.5 to 3 inches with locally higher amounts along the Blue Ridge. If this amount of rainfall in realized some small streams and creeks will likely flood, then mainstem rivers will rise. Based on the expected rainfall the lower reaches of the Dan and Roanoke Rivers and along the James River from Lick Run to Scottsville have to potential to rise to Action Stage. While the official river forecast does not yet contain the expected rainfall, this discussion highlights an above average potential for flooding within these river basins. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...RCS NEAR TERM...DS/RCS SHORT TERM...AMS LONG TERM...DS AVIATION...DS HYDROLOGY...AMS is the U.S. government's official web portal to all federal, state and local government web resources and services.