Area Forecast Discussion
Issued by NWS Blacksburg, VA

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135 FXUS61 KRNK 180028 AFDRNK Area Forecast Discussion National Weather Service Blacksburg VA 828 PM EDT Mon Oct 17 2016 .SYNOPSIS... High pressure will take up residency along the southeast coast of the United States through at least Thursday and provide mild and dry conditions to our region. A cold front will cross the area Thursday night into Friday along with its associated showers. Gusty winds are expected behind the front Friday into Saturday. && .NEAR TERM /THROUGH TUESDAY/...
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As of 820 PM EDT Monday... Made some minor adjustments to T/Td grids to bring better in line with current observations. No major changes needed at this point. Adjusted sky grids to reflect expectation of dense fog along/near rivers after 06Z and patchy fog elsewhere, clearing around 14Z. No other changes needed at this time. As of 215 PM EDT Monday... The center of surface high pressure was off the coast of NC/SC with its associated ridge axis extending westward into AL/GA. An upper low was located over central Manitoba with is associated occluded front extending southeast into southern Ontario. The associated warm front was positioned eastward to near the NY/PA border. Finally, the associated cold front extended southwest from the triple point into MN/SD. The location of these features is allowing for a generous southerly low level flow to advect from the western Gulf of Mexico into the Mississippi and Lower Ohio River valleys. This fetch is transporting moist and warmer than normal conditions into this region of the country for this time of year. A broad upper ridge over the southeast U.S. is capping what would normally be ripe conditions for decent coverage of convection in this area. As we progress into the middle of the week, this relatively mild and moist air will work its way into our area. While we too will be under the influence of the capping upper ridge, look for temperatures to trend higher, as well as dew point readings, but precipitation is not expected. The warm air advection will have the impact of yielding warmer ridges overnight as compared to their neighboring valleys by at least five degrees. Also, most ridgetops will experience temperatures equal to or slightly greater than the typically warmer Piedmont region of VA and NC. Wind gusts of 15 to 20 mph can be expected overnight at the highest elevations. Mountain valleys and most of the Piedmont region will experience calm or light southwest winds. This will lead to another night of patchy fog within these regions. High temperatures on Tuesday are expected to be greater than those realized today. Readings of the mid 70s to near 80 are forecast for the mountains with low to mid 80s across the Piedmont. Bluefield, Blacksburg, and Danville are forecast to reach highs within one degree of their records for the date. See the CLIMATE section of this discussion for additional details.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... As of 245 PM EDT Monday... The 12Z GFS and 12Z NAM models continue to advertise a high amplitude trof deepening from the northern plains to the Mississippi Valley by Thursday evening. The GFS ensemble mean agrees with this general idea, but is slightly less amplified. For our area this means well above temperatures, and some cases, record warmth for our area on Wednesday. Temperatures will continue to be well above normal Thursday, but with low level winds backing in advance of the approaching trof and an increase in high clouds temps may be a couple of degrees cooler. Overall, increased temps through the period and continued the trend of delaying precipitation in the west on Thursday as forecast soundings continue to indicate an abundance of dry air between 700- 400 mb. With PW values increasing in southeast WV late Thursday along with weak shortwaves advecting in advance of the approaching trof in the deep southwest flow, placed highest POPS (still in the slight chance to low chance category) in this region. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 230 PM EDT Monday... Differences on the timing of the passage of a strong cold front early in the long term period are still evident in the medium range models, with the GFS still deeper and slower with the associated high amplitude upper trof. The 12z ECMWF is trending deeper, but still not as slow or strong as the GFS, while the 12Z Canadian model solution also is more progressive with this system. Leaned toward the more progressive solutions and kept highest POPS for Thursday night with rain ending in the east early Friday. Northwest winds will generate some upslope showers into the first half of the weekend. Breezy and much cooler conditions will be found for the weekend, and as the upper flow becomes more zonal early next week, temperatures will moderate. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/... As of 745 PM EDT Monday... High pressure, both at the surface and aloft, will remain over the region for a couple more days. The surface high is located to the southeast in a Bermuda High position, providing the region with a warm southwest flow. With a strong subtropical upper ridge evident over the area, model cross sections show little to no moisture or clouds at any levels of the atmosphere, outside the immediate surface layer near the ground. This has equated to SKC at all TAF sites with no upstream cirrus slated to spread across the CWA during this TAF valid period. Thus, the only concern to other VFR cigs/vsbys through the TAF valid period is late night/early morning fog as a result of the stagnant air mass and decoupling at the usual spots. KLYH, KBCB, and KLWB all saw several hours of LIFR conditions in fog this morning (Monday) and KDAN saw several hours of MVFR conditions in BR. While this afternoon was on average 5 degrees warmer than what was observed Sunday afternoon, temperatures are already cooling down into the 60s and dewpoints are in the lower 60s. Thus, expect another night of fog and attendant low clouds/cigs at many locations, with the exception of KBLF and KROA which will have west flow just off the surface and where fog development is not expected. Expect the fog and low cigs/vsbys at KLWB, KBCB, and KLYH roughly in the 06Z to 13Z time frame, with KDAN likely seeing at least MVFR conditions in the 08Z-12Z time frame. All of these sites should become VFR no later than 14Z Tue. Through much of the night, winds will be light SSW-SW at the surface at speeds 3-5kts. Conditions will decouple, as noted above, at KLWB, KBCB, and KLYH and winds should become calm at these locations. While the 850mb winds do increase from the west late tonight/Tue morning, indications are that winds will not reach or exceed 30kts within the 2000 ft. layer. Conditions for LLWS shear appear to marginal to include at this point. KBLF will have stronger surface winds, so there is definitely no need to include LWWS there. Extended aviation discussion... Through Thursday morning, VFR conditions are expected during the daylight hours, with redevelopment overnight of river and mountain valley fog and associated IFR to LIFR stratus layers/ceilings. Fog will be more widespread each night as the week progresses due to rising surface dew points and increasing low level moisture, however increasing winds and mid/high cloud cover may decrease fog development somewhat Thu morning compared to Wed morning. A cold front is expected to move through the region Thursday night into early Friday. Expect the initial onset of scattered showers across western sections by Thursday afternoon. A southwest to northwest wind shift is expected to occur Thursday night across the region with gusty winds behind the front continuing into Friday night and possibly Saturday. Areas of sub-VFR conditions will likely accompany the front and precipitation associated with it. A return to VFR conditions is expected for most areas Friday night into Saturday. The exception may be western parts of the region where a healthy northwest upslope flow, and lingering low level moisture, may prolong an IFR/MVFR ceiling during this time period. && .CLIMATE... As of 125 AM EDT Monday... Temperatures will be above seasonal levels for most of the week, though our record highs may be hard to reach, except for perhaps for Blacksburg or Bluefield, mainly Wednesday. Record maximum temperatures through Thursday, Oct 20. Oct 17 Location Record Max Bluefield.....78 in 2000 Danville......88 in 1989 Lynchburg.....88 in 1908 Roanoke.......86 in 1938 Blacksburg....80 in 1989 Oct 18 Location Record Max Bluefield.....79 in 2007 Danville......86 in 2007 Lynchburg.....91 in 1938 Roanoke.......91 in 1938 Blacksburg....80 in 1953 Oct 19 Location Record Max Bluefield.....81 in 1984 Danville......85 in 1953 Lynchburg.....88 in 1938 Roanoke.......91 in 1938 Blacksburg....80 in 1991 Oct 20 Location Record Max Bluefield.....79 in 1993 Danville......88 in 1984 Lynchburg.....85 in 1993 Roanoke.......84 in 2005 Blacksburg....82 in 1985 && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...DS NEAR TERM...DS/RAB SHORT TERM...PH LONG TERM...PH AVIATION...DS/RAB CLIMATE...AMS is the U.S. government's official web portal to all federal, state and local government web resources and services.