Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 170311 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 1011 PM EST Mon Jan 16 2017 .SYNOPSIS... Strong area of low pressure over the central United States will move northeast and into the Great Lakes by Tuesday. A cold front trailing south from the low will move east, and cross the Mid Atlantic Region Tuesday night. && .NEAR TERM /THROUGH TUESDAY/... As of 955 PM EST Monday... Will be making no changes this update period to the timing of the approaching precipitation. A late night/early morning timing of arrival in the western portions of the area is still looking promising based upon the latest radar trends and mesoscale model updates. The biggest adjustment made was to the forecast low temperatures. The region of the forecast area deepest in the cold air damming, the Lynchburg area, has already experienced temperatures falling to below forecast low temperature values. Readings the past couple of hours have been in the upper 30s. Suspect these readings will hold nearly steady the remainder of the night, and have adjusted the forecast low to similar values. Not as drastic, but slightly cooler nonetheless, are values heading south into Southside Virginia and neighboring north central North Carolina. Have adjusted slightly lower overnight low forecasts for the Danville to Reidsville regions as well. Patchy dense fog continues over parts of southwest Virginia and northwest North Carolina. Coverage do not appear broad enough or persistent enough to warrant a Dense Fog Advisory. Will continue to highlight the potential in a Special Weather Statement. Current Hazardous Weather Outlook also highlights the fog potential tonight in general. As of 645 PM EST Monday... The biggest forecast adjustment this evening is a delay in the arrival time of the main area of precipitation across western portions of the region. Based upon the latest guidance and radar trends, will have most of the area precipitation-free until almost daybreak Tuesday. At this point, areas between Richlands, VA and Lewisburg, WV can expect the arrival of the main line of showers in advance of the cold front. Also, some area between roughly Danville and Lynchburg, VA saw some clearing of the low clouds right before sunset. Low clouds are expected to redevelop this evening, and this trend has been reflected in the forecast. AS OF 345 PM EST Monday... Vigorous upper level low is spiraling northeast through the Central Plains and into the upper Mid-West. As of 18Z/1PM the surface low was near Kansas City with a cold front trailing south into east Texas. A warm front extended east from the low into the lower Ohio Valley. Southerly winds ahead of this system was advecting warm moist air northward from the Gulf Coast Region and into the Tennessee Valley where temperatures were in the 60s/70s. This warm air was trying to spill across the Appalachian Divide from the west, but was only making it as far east Bluefield WV...Marion VA...and Boone NC. East of the Divide, the airmass was cool and stable with temperatures in the 40s. The only exception was a sucker hole in the clouds vicinity of Martinsville...Greensboro...and Danville where temperatures squeaked into the 50s. For tonight, the cool wedge east of the divide (which covers 3/4ths of our CWA) will remain in place with stratus and areas of fog persisting through the overnight. Temperatures will change very little within this airmass. West of the divide, Tazewell and Smyth Counties, and for the higher mountain peaks (which will be above the stable air), the warming southwest winds from the Tennessee valley will keep temperatures mild through the overnight with readings not dropping much lower than 50. Models are in relatively good agreement for the mid-CONUS surface front to move east Tonight and Tuesday with deeper moisture arriving across our mountain counties by daybreak Tuesday, then overspreading the rest of the forecast area during the morning. Greatest POPs and QPF are expected across the northern CWA closer to the surface low which is headed for the Great Lakes. Rainfall amounts of a half inch or so are expected across the northern CWA with generally a quarter inch or less across the south. The cool wedge is expected to finally get displaced by Tuesday afternoon, so in spite of the increasing rain threat, temperatures should be 5 to 15 degrees warmer. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 330 PM EST Monday... A vigorous northern stream short wave will move through the upper midwest and penetrate the broad southern stream ridge over the eastern US. This will allow a surface low moving through the Great Lakes region to push a cold front through the area Tuesday night, with a good chance of precipitation mainly west of the Blue Ridge. The low level wind field will become amplified and with the passage of the cold front, cold air advection will aid downward momentum transfer and create quite windy conditions Tuesday night into Wednesday. The upper pattern will then begin to amplify substantially with a sharp southern stream ridge taking shape in the eastern US. This will allow high pressure to build over the region, and after some lingering upslope showers west of the Blue Ridge Wednesday we can expect generally quiet weather through Thursday. However by Thursday night, the ridge axis will pass to our east and allow low pressure moving up the Mississippi valley to push increasing isentropic lift over the region with the chance for precipitation increasing substantially. Despite the passage of the front on Tuesday night the air behind the front is only modestly colder, resulting in a continuation of above normal temperatures through midweek. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 330 PM EST Monday... The upper pattern will be in a state of flux for the end of the week and through the weekend, as one closed low over the upper midwest dissipates on Friday and is replaced by a very large closed low which dominates the eastern US by Sunday night. This will keep a progression of weather system s affecting our region through Monday. First, a dissipating low pressure system moving northward into the Great Lakes region will push a warm front through the Appalachians and central mid Atlantic region with a good chance of precipitation for Friday. Then in response to the changing upper pattern, another low will develop over the mid Mississippi valley and push what appears to be a dynamic occluded front into the area on Sunday. By this time deep moist southerly flow will be well established above the boundary layer, and when coupled with the dynamics of the front has the potential to produce a significant amount of rainfall. Guidance also indicates the presence of some instability which would support a chance for some thunder in an environment of robust low level winds. This is still quite a ways off but well worth keeping an eye on in the coming days. We eventually get into the dry slot, but moisture and colder air wrapping well around the vertically stacked system will keep a good chance of rain around through Monday. Temperatures will remain well above normal through the weekend, but colder air wrapping around the vigorous low on Monday will bring temperatures down a bit west of the Blue Ridge. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... As of 630 PM EST Monday... The coverage of the IFR/MVFR ceilings dissipated Monday afternoon along and near a KLYH-KDAN line. This void in sub-VFR conditions is only expected to be temporary heading past 00Z/7PM. The cold air damming wedge is still in place, and moisture under the nocturnal inversion is expected to again materialize as IFR/MVFR stratus overnight. Most of the rest of the region already is experiencing sub-VFR conditions, and this trend will continue through the night. About the only region that may see more VFR conditions than sub-VFR will be areas near and west of KMKJ. Rain showers will move into the region late tonight in advance of an approaching cold front. Coverage will continue to increase during Tuesday morning, especially across the western and northern parts of the region. Increasing southwest flow in advance of the cold front will advect warm air over the cold air damming, helping to slowly erode it from the top to bottom. However, this feature that will terminate the wedge will be the passage of the cold front in the afternoon. VFR conditions are expected at all terminals by the mid afternoon. A brief period of low level wind shear is expected just in advance of the cold front near a KBLF-KLWB line Tuesday morning. Extended Aviation Discussion... Clearing may take place behind the front on Wednesday with potential period of VFR Wednesday into early Thursday. However, this is expected to be short-lived per return of unsettled weather by weeks end as moisture returns from the southwest. No precipitation type issues are expected through the end of this week...just plain ol rain. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...PM NEAR TERM...DS/PM SHORT TERM...MBS LONG TERM...MBS AVIATION...DS/PM

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