Scientific Forecaster Discussion
fxus62 krah 210806
Area forecast discussion
National Weather Service Raleigh NC
405 am EDT sun Jul 21 2019
a strong ridge of high pressure will remain over the mid Atlantic
region will begin to break down and weaken on Monday. A cold front
will move into the region Tuesday.
Near term /through tonight/...
as of 400 am Sunday...
..dangerous heat indices of 105 to 110 f continue today...
The strong mid/upper level anticyclone over the region will begin to
break down late day and tonight, owing to the approach of the
northern stream trough advancing east into the upper MS valley/Great
Lakes region. This subtle weakening however will prove of little
consequence to the ongoing heat, with another day of afternoon temps
in the mid to upper 90s. In fact, without the upper shear axis to
provide a trigger for widely scattered convection and associated
debris cloudiness, the hot temps will be more uniform without the
benefits of rain/outflow cooled air. One factor that may lessen the
impacts of the heat is the better potential to see some mixing of
dewpoints down into the upper 60s this afternoon; enough to keep
heat indices closer to 100-105 f for much of the Piedmont, and 107-
110 f in the coastal plain. Regardless, the cumulative impacts are
still dangerous across central NC. Thus, there are no plans to
change current heat advisory/warning in place across central NC.
Lows in the mid to upper 70s.
Short term /Monday and Monday night/...
as of 400 am Sunday...
Aforementioned northern stream trough will undergo some considerable
amplification as it digs southeast into the TN valley through Monday
night/Tuesday morning. Attendant cold front into the area will be
delayed until Tuesday, which will result in minimal rain chances
across central NC until it's arrival. Instead, isolated to widely
scattered convection Monday afternoon/evening will be focused along
a pre-frontal trough extending across the western portions of the
state and with the inland retreat of the sea-breeze boundary across
the southeastern zones. The delay of the better rain chances also
means one additional day of the heat, especially east of the
Triangle where lingering high dewpoints in the 70s will combine with
mid 90s temps to support heat indices ~105 f. West of the Triangle,
the higher convective rain chances and cooler 800 mb temps will keep
temps down in the lower 90s and heat indices below advisory
criteria. Additionally, breezy southwesterly winds of 25-30 mph will develop
in advance of the front, which should also curb the impacts of the
There remains some minor model differences with the exact timing of
the cold front east into the western Piedmont late Monday
night/Tuesday morning with the GFS faster than the ec in bringing
the front into the area. Will retain highest rain chances across the
western Piedmont Monday night/Tuesday morning with a good
possibility that most of central NC could remain until the arrival
of cold front after 12z Tuesday.
Long term /Monday through Saturday/...
as of 400 am Sunday...
An unseasonably dynamic positively tilted upper-level trough will
begin to protrude southeast out of the Great Lakes region on Tuesday
before nearly stalling overhead before weakening through the
remainder of the period. This will introduce a period of unsettled
weather across the Carolinas on Tuesday with cooler and quieter
surface high pressure settling overhead through the remainder of the
Tuesday: a strong surface cold front will inch east of the
Appalachians early Tuesday morning, working its way northwest to southeast across
portions of central North Carolina Tuesday afternoon and evening.
Global models have come into better agreement with the timing and
progression potential of this system, introducing widespread shower
and storm chances across the northwestern zones as early as daybreak
on Tuesday, with activity spreading southeastward with time during
the afternoon and evening hours. Will need to continue to monitor
frontal passage timing closely, with at least isolated severe thunderstorms
possible across the region. While uncertainty remains high, the
unusual availability of upper-level support hints at the possibility
of sustained updrafts which may form into multicellular type
clusters, capable of producing intermittent damaging wind gusts,
isolated small hail, and possibly localized flooding (especially in
urban type areas). With current progged model timing, the primary
threat area remains across and east of the I-95 corridor, but this
may migrate further westward with time, especially if arrival of the
boundary keeps getting delayed, allowing more time for surface
heating ahead of the primary forcing (which is the current trend).
Rainfall amounts in the 1 to 1.5 inch range will be possible during
this 12 to 18 hour period, with higher amounts possible in areas
that see training or slow moving thunderstorms. A pretty impressive
temperature gradient will be prominent by Tuesday afternoon. Expect
temperatures in the mid to upper 70s across the northwestern zones,
where quickly materializing mid to upper-level cloud cover will
limit heating potential, while a few 90 degree readings will be
possible across the southeastern coastal plain, which should see at
least some daytime heating processes.
Remainder of the period: the front will linger along or slightly
southeast off the mid Atlantic coast through the end of the week,
with little to no pop expected to progress far enough northwest into
our zones through the end of the work-week. The coolest day will
likely be Wednesday, with afternoon temperatures struggling to rise
into the lower 80s under a weakening cold air advection type regime. Dewpoint
temperatures will also remain seasonably low through the end of the
work-week, providing some relief from the constant heat/humidity
headlines witnessed over the last week or so. Afternoon highs on
Wednesday will top out in the lower 80s with a slow climb expected
through the end of the period. Overnight lows will dip into the 60s
before returning to the low 70s over the weekend.
Aviation /06z Sunday through Thursday/...
as of 135 am Sunday...
VFR conditions are expected to prevail through the 24 hour forecast
period ending at 00z/23 Monday. Winds today will be higher than
previous days, with sustain 8-12kt southwesterly winds developing
this afternoon and periodic gusts of 16 to 18 kts.
Outlook: an approaching cold front will bring increasing chances of
showers and storms once again late Monday and Tuesday, with a return
of early morning stratus and fog as well. VFR conditions should
return for the latter half of the week.
record high temperatures and years for the next few days.
Rdu gso Fay
sun 7/21 102/2011 102/1926 105/1937
Mon 7/22 103/2011 101/1926 107/1932
excessive heat warning until 6 am EDT Monday for ncz011-027-028-042-
Heat advisory from 6 am Sunday to 6 am EDT Monday for ncz007>009-
Excessive heat warning until 6 am EDT Sunday for ncz077-085-086.
Excessive heat warning from 6 am Sunday to 6 am EDT Monday for