Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 191502 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1100 AM EDT Wed Jul 19 2017 .SYNOPSIS...
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A weak upper level low over will drift slowly over eastern NC through tonight. A hot and dry upper level ridge will build east from the Plains to the Carolinas through Saturday, before breaking down Sunday and Monday.
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As of 1100 AM Wednesday... The latest data analysis indicated a broad and weak upper low centered over the region, with the mid level low centered around or just south of Rocky Mount. Lower pressure at the surface was hard to find, but a weak surface trough was noted near the Blue Ridge and another over the Coastal Plain. Latest satellite data indicated the small spin of the mid/upper level circulation as noted above, with the best moisture located along the coast - just ahead of the trough axis. Dew points are down a few degrees today over the Piedmont where some 60s were evident at mid-morning. There were plenty of lower to mid 70s dew points down east. Soundings from the area indicated some drying in the mid/upper levels over the Mountains with the more northerly flow on the back side of the trough axis. It appears that convection today will be much more isolated in the western zones than what occurred on Tuesday afternoon. Still, widely scattered thunderstorms will have plenty of instability to work with as highs in that region reach the upper 80s to around 90, with dew points in the upper 60s. In the central and eastern zones, scattered thunderstorms are still expected to develop near the mid/upper low over the eastern Piedmont and Coastal Plain with continued heating. The areas south and east of the Triangle appear to have the best chance of storms, with the convection expected to be highly pulse and outflow driven. MLCapes on the order of 1500 to 2000 J/KG suggest fairly intense cores capable of gusty winds that may again produce some isolated wind damage. Some hail may also occur, but it is favored to be just below severe criteria in most cases. Highs in lower 90s are favored in these areas. Ongoing convection will diminish rapidly by mid evening, with mostly clear skies overnight. Lows generally in the mid 60s over the rural Piedmont, ranging into the lower 70s elsewhere.
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&& .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 345 AM Wednesday... The mid-upper level low now over NC is forecast to drift or reform off the SC coast by 12Z Thu, before drifting swwd along the sern U.S. coast, to nrn FL by 12Z Fri. This will tend to delay the ewd expansion of the sub-tropical ridge from the MS Valley. Thu will consequently be the transition day of warming temperatures, into the middle 90s on average, that will then probably peak early in the medium range (Fri-Sat). Heat indices around 100 degrees will result Thu, except for over the nrn and wrn Piedmont where a mixing out of surface dewpoints into the middle to upper 60s, behind a lee/ Piedmont surface trough, will yield a relatively "drier" heat. The departure of the mid-upper level low and associated cold pool aloft will result in minimal diurnal convective coverage that should be limited to an isolated storm or two along the sea breeze/in the srn Coastal Plain and ern Sandhills. Mild overnight, and rain-free, with lows in the lower to middle 70s. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 400 AM Wednesday... A closed low west of Vancouver Island this morning will migrate ewd through srn Canada, reaching the Great lakes and Northeast by Mon- Tue. Vorticity associated with the remnants of the mid-upper low now crossing NC, which will have drifted wwd to the Gulf Coast or lower MS Valley by this weekend, will shear newd in swly to wswly flow downstream of the aforementioned crossing the Great Lakes. The sub- tropical ridge now over the central Plains and mid MS Valley will build esewd to the srn Appalachians through Sat, followed by weak height falls aloft, and consequent weakening, and lessening influence of the sub-tropical ridge at the base of the trough crossing the Great lakes and Northeast and within a corridor of the aforementioned sheared vorticity from the sw. This will favor increasing probabilities of mainly diurnal convection Sun-Tue, and a slow reprieve from the heat as an associated surface front settles into the srn middle Atlantic states/Carolinas by Tue. Temperatures downstream of the sub-tropical ridge will peak in the middle 90s to around 100 degrees Fri-Sat, and probably again Sun, before trending to near average by the end of the period. When combined with surface dewpoints ranging from the middle to upper 60s west of an Appalachian-lee trough (over the wrn NC Piedmont) to lower 70s to the east of that feature (over the Coastal Plain), heat index values between 100 and 110 degrees are expected to result through the weekend. The consecutive days of heat will likely warrant Heat Advisories for much of central NC. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... As of 200 AM Wednesday... 24 hour TAF period...Drier airmass in place over the western 2/3rds of the area will help limit coverage of early morning stratus/light fog, with VFR conditions except for a 3-4 hour predawn window at RWI, FAY, and possibly RDU. Upper low parked over central NC will produce scattered convection in the east this afternoon into evening, with only isolated showers west. Winds will be light, less than 6 knots, through the period. Looking further ahead...VFR conditions are expected with building high pressure aloft mid week through Friday. The will be a low probability of fog/low stratus in the predawn across the east. && .CLIMATE... RDU Records: Date | High Year | High Min Year ------------------------------------------ 20 July | 102 1942 | 76 1981 21 July | 102 2011 | 78 1932 22 July | 103 2011 | 78 2011 23 July | 105 1952 | 78 2011 24 July | 101 2011 | 79 2011 GSO Records: Date | High Year | High Min Year ------------------------------------------ 20 July | 100 1977 | 75 1986 21 July | 102 1926 | 76 2011 22 July | 101 1926 | 77 2011 23 July | 99 1952 | 78 2010 24 July | 99 1914 | 78 2010 FAY Records: Date | High Year | High Min Year ------------------------------------------- 20 July | 104 1932 | 80 1996 21 July | 105 1932 | 79 1977 22 July | 107 1932 | 79 2011 23 July | 103 2011 | 79 1998 24 July | 105 1952 | 79 1945 && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...Badgett/mlm SHORT TERM...MWS LONG TERM...MWS AVIATION...mlm CLIMATE...RAH is the U.S. government's official web portal to all federal, state and local government web resources and services.