Area Forecast Discussion
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FXUS62 KRAH 230542
Area Forecast Discussion
National Weather Service Raleigh NC
140 AM EDT SAT JUL 23 2016
An area of high pressure aloft will expand from the central U.S.
across the mid-Atlantic states and Carolinas through early next
week. This will bring a period of hot temperatures to central NC.
.Near Term /Overnight/...
As of 720 pm Friday...
Central NC lies on the eastern periphery of a deep upper level ridge
(centered over the lower Midwest) and on the western periphery of an
upper level trough stalled offshore the Southeast coast. Similar to
yesterday, diurnal destabilization this afternoon has been strongest
in the W/SW Piedmont (1000-2000 J/kg MLCAPE) and weakest (500-1000
J/kg MLCAPE) in eastern/coastal NC where subsidence prevails on the
backside of the upper level trough stalled offshore. Small amplitude
disturbances /DPVA/ rounding the NE periphery of the 300 mb ridge
over the central Appalachians could track into western NC this
eve/tonight, however, the `sphere of influence` of such disturbances
should remain west of central NC as they track S/SSW along the
eastern periphery of the H3 ridge. As a result, forcing for ascent
this evening will be confined to shallow convergence attendant a
weak Piedmont trough and convective outflow. With the above in mind,
expect scattered convection to largely remain confined along/west of
Highway 1 and to gradually weaken/dissipate within a few hours after
the loss of heating/insolation. Expect lows generally in the lower
70s, though a few rural/low-lying areas in the N/NW Piedmont may
fall as low as 68-70F. -Vincent
.Short Term /Saturday and Saturday Night/...
As of 345 PM Friday...
The environment on Saturday should be similar to today, although PW
values are expected to rise steadily, with thicknesses continuing to
climb. We`ll also be on the anticyclonic side of MCVs dropping
southward through the southern Appalachians, with no other dynamic
forcing mechanisms evident. So we`ll be relying on purely
thermodynamic lift, it appears, focused on differential heating in
the higher terrain as well as subtle boundaries, a few of which may
be leftover from the current convection over western NC. Will expand
the low shower/storm chances a bit from today`s pops, but still
expect coverage and upscale growth to be limited by warm and
somewhat dry mid levels. Thicknesses and new guidance indicate highs
of 94-98, and with dewpoints dropping no further than around 70 over
much of the area, heat index values should peak in the 99-104 range
for a couple of hours. This is below advisory criteria, so will
stick with a mention in the HWO for now, but this will certainly be
revisited tonight. Lows Sat night in the low-mid 70s, not allowing
much recovery from the heat stress. -GIH
.Long Term (Sunday through Friday)...
As of 245 PM Friday...
To begin the long term period, the strong upper ridge that provided
multiple days of intense heat across the Central Plains will have
dampened and became elongated in east-west fashion, extending into
the region. As it does, heights will rise over central NC through
the weekend. As such, max low level thickness values are progged to
top out in the low to mid 1440s on Sunday (slightly lower than
previous runs), with similar values on Monday. This combined with
mostly dry conditions and temps not cooling off much as night, temps
will be able to rise well into the mid 90s, maybe even the upper 90s
(warmest on Sunday). This combined with a moist air mass may
necessitate the issuance of a heat advisory, most likely across at
least the eastern half of the forecast area, where heat index values
will approach or exceed 105 degrees. With regards to precip chances,
overall they will stay rather low through early next week, but will
not be zero as there will be a persistent Piedmont trough that could
be a focus for convective development, as well as the sea breeze
and/or any weak disturbances that move through aloft.
The aforementioned ridge will continue to dampen and shift more
offshore through the middle of the week. Also, a shortwave trough is
progged to cross southern Canada and the Great Lakes Monday into
Tuesday. This will propel a cold front towards the region Tuesday
into Wednesday, but as can be expected this time of the year, there
is disagreement with just how far south it will make it and it will
likely stall near or just north of the area and then meander for a
few day. Another shortwave crossing the Ohio Valley will approach
towards the end of the week. Therefore, with us gradually losing the
influence of the upper ridge and with a cold front in the vicinity,
precip chances will start to increase, at least back to the normal
diurnal range, especially towards the middle to end of the week. The
increased cloud cover and precip chances should allow temps to
"cool" back to the low to mid 90s (however, still slightly above
.Aviation /06Z Saturday through Wednesday/...
As of 140 AM Saturday...
VFR conditions expected to prevail across central NC through Monday
as an area of high pressure aloft builds over the region. While
isolated thunderstorms will be possible each late afternoon-early
evening through Monday, probability of convection affecting a
specific TAF site is too low to mention in the terminal forecast at
this time. Patchy MVFR fog will be possible early each morning,
primarily between the hours of 10Z-12Z.
While VFR conditions will likely dominate through Wednesday, there
will be periods of MVFR conditions associated with either early
morning fog, or late afternoon/early evening convection.
Record high temperatures and the year in which the record was most
recently set at Raleigh, Greensboro, and Fayetteville.
Sat Jul 23 Sun Jul 24 Mon Jul 25
RDU 105/1952 101/2011 102/2010
GSO 99/1952 99/1914 101/1914
FAY 103/2011 105/1952 103/1914