Scientific Forecaster Discussion
fxus62 krah 191946
Area forecast discussion
National Weather Service Raleigh NC
346 PM EDT Fri Jul 19 2019
a strong ridge of high pressure will build over the mid Atlantic
region through Sunday, then begin to break down and weaken Monday.
The current heat wave will continue and worsen through the weekend.
A pattern change to wetter and cooler weather will arrive next week.
Near term /today through tonight/...
as of 155 PM Friday...
Forecast remains on track, with isolated to scattered storms peaking
in the late afternoon/early evening but lasting well into the night
as some elevated cape persists with weak residual boundaries. The
current thermal and moisture setup is similar to what it's been for
a few days, with moderate to high MLCAPE (1500-2500 j/kg), low level
lapse rates near or just over 8 c/km, and d-cape near or over 1000
j/kg, but with poor deep layer shear and unimpressive mid level
lapse rates under 6 c/km. As such, we should see another couple of
cells today with the potential for strong downburst winds but
without much high reflectivity well aloft. The subtle mid level
shear axis still extends through central NC, although the weak winds
aloft are limiting its contribution to ascent. Will maintain
isolated pops except over the far S and E, where better deep
moisture should boost coverage. Weak elevated cape should hold well
into the night, so will be slow to trail pops off overnight. The
heat advisory will be held as is for east sections through 7 PM. Lows
71-78 under fair to partly cloudy skies. -Gih
Short term /Saturday through Saturday night/...
as of 210 PM Friday...
..excessive heat warning now in effect for Saturday/Saturday night
for the eastern Piedmont, sandhills, and coastal plain, with a
heat advisory over the western Piedmont...
The extreme heat remains the big story heading into the weekend,
with a greater potential for adverse health impacts as people engage
in outdoor activities this weekend. The extended length of this heat
wave with minimal cooling at night only heightens the concern, as
studies of previous deadly heat waves have similarly been long-lived
with very muggy nights during which temps barely dip below 80f. The
mid level ridge axis builds strongly across NC this weekend, with
the low level thermal ridge holding firm from central NC northeast
across central/east Virginia and Delaware/MD, where low level thicknesses may
approach 1450 M with 850 mb temps sitting in the 19-21c range. As
the light SW low level flow ensures elevated dewpoints well into the
70s, the heat indices are expected to climb to 108-113f over the
eastern two-thirds of the central NC forecast area Saturday.
Elsewhere, readings are expected to reach near 105 for at least a
couple of hours. Will convert the existing excessive heat watch for
Sat/Sat night to an excessive heat warning for these eastern areas,
and will Post a heat advisory for the rest of central NC including
The Triad. (The watch will remain in place for the same eastern
sections for sun; see the long term discussion for details.) While
precipitable water will stay above normal, the warmth of the entire column and a
lack of substantial boundaries or triggers aloft to focus convection
should restrict storm coverage, and will leave pops as isolated.
Expect highs of 94-99 followed by lows of 73-78. -Gih
Long term /Sunday through Thursday/...
as of 345 PM Friday...
The upper ridge remains in place on Sunday with the Bermuda high in
place at the surface. This will give US yet another, but hopefully a
final day of extreme heat across central NC. An excessive heat watch
remains in place from US Highway 1 eastward for heat index values of
110 degrees and above. Points west can expect 105-109 degree heat
For Monday the pattern begins to change as an upper level trough
begins to dig into the Great Lakes region from Canada, but it is a
bit delayed compared to previous runs of the models and thus we will
still have a fairly hot day on Monday for much of the area with
temperatures in the mid to upper 90s east of Highway 1 but some
relief at least to the lower 90s in The Triad. Heat index values
will also be lower but still 100-104 across the east.
Overnight Monday night a low pressure system will begin to develop
over New York as the upper trough continues to dig through the Ohio
Valley. The surface low will track into New England Tuesday morning
and a strong frontal zone will track across the Appalachians and
into the Carolinas on Tuesday, bringing a fair amount of rain to
central NC and more importantly, extinguishing the heat as The Triad
will struggle to get to 80 degrees with mid 80s across the
southeast. The front will linger along the coast or slightly inland
through the end of the week, potentially bringing some higher rain
totals to this portion of the state with upwards of 2 inches
possible through Thursday. Temperatures are gradually expected to
warm through the 80s towards 90 degrees by the end of the week but
still much more comfortable than what we are currently experiencing.
Aviation /18z Friday through Wednesday/...
as of 1235 PM Friday...
VFR conditions will continue to dominate through the next 24 hrs
over central NC. Hot conditions will continue with deep mixing,
resulting in high-based convective clouds in the afternoon and areas
of mid and high clouds resulting from dissipated storms through Sat
morning. Isolated showers/storms and storm clusters remain possible,
mainly 20z-06z with higher chances at Fay and lower chances
elsewhere, but these should be few in number and largely
circumnavigable. Winds will be mostly light from the SW, although a
few infrequent gusts to 15-18 kts are possible this afternoon.
Looking beyond 18z Sat, isolated storms will again be possible each
afternoon/evening Sat and sun, but coverage will be low. Storm
chances will increase Mon as a cold front approaches from the NW,
and good shower/storm chances will persist Tue/Wed as the front
settles southeastward over the region. The risk of early-morning sub-
VFR fog/stratus will remain low through Mon morning, but chances
will start to inch up for Tue and Wed morning. -Gih
Record high temperatures and years for the next few days.
Rdu gso Fay
Fri 7/19 101/1902 98/1977 101/2002
Sat 7/20 102/1942 100/1977 104/1932
sun 7/21 102/2011 102/1926 105/1937
Mon 7/22 103/2011 101/1926 107/1932
Excessive heat warning from 10 am Saturday to 6 am EDT Sunday for
Heat advisory until 7 PM EDT this evening for ncz007>011-024>028-
Excessive heat watch from Sunday morning through Sunday evening for
Heat advisory from 10 am Saturday to 6 am EDT Sunday for ncz021>023-