Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
FXUS62 KRAH 251330
Area Forecast Discussion
National Weather Service Raleigh NC
930 AM EDT MON JUL 25 2016
Strong high pressure aloft will extend across the region through
much of the work week, bringing continued hot and humid conditions
to central NC. The chances for afternoon storms will increase by mid
.Near Term /through Tonight/...
As of 930 AM Monday...
...Dangerously hot conditions continue today across much of central
Little change needed to existing forecast. Hot/humid weather will
persist, with warm and dry mid levels resulting in low CAPE this
afternoon despite highs in the mid-upper 90s, and very weak deep
layer shear as deep high pressure ridging stays parked overhead.
Latest CAM runs including the 3km NAMRR, SPC SSEO, HRRRX, and WRF-
NMM/ARW suggest that isolated convection will occur over central NC
late today, mainly over the southeast CWA in late afternoon and in
the NW CWA early in the evening, a reflection of sea breeze activity
and convection easing off the higher terrain, respectively. Given
the dry air in place noted on water vapor imagery and 12Z RAOBs,
though, I would expect any coverage to be under 10%, and will keep a
pop-free forecast for the rest of the day. High confidence in highs
in the mid-upper 90s, agreed upon by high-res guidance, but heat
index forecasts will still be tricky as they will depend greatly on
dewpoints. A delay in the mixing-out of these dewpoints by even a
couple of hours will make a big difference in HI. Will lean toward
yesterday`s dewpoint trends, with readings slipping into the upper
60s to around 70 in the NW CWA this afternoon, while in the east
readings will hold in the mid 70s for several more hours before
dropping into the lower 70s late. Today`s slightly higher surface
winds from the SW should facilitate a bit earlier mixing-out than we
saw yesterday. Nevertheless, with these temps and dewpoints, HI
values should peak in the 100-106 range across the heat advisory
area. Considering the successive days of hot/humid weather with
little recovery at night, exacerbating the risk of heat illnesses,
will keep the heat advisory as is. -GIH
Previous discussion from 305 AM: An area of high pressure centered
aloft over the Carolinas will maintain the hot and dry conditions
today. Low level thicknesses around 1440m Sunday are projected to
inch upward to 1443/44m this afternoon, supportive of max temps in
the mid-upper 90s. Surface dewpoints mixed out quite a bit in the
northwest Piedmont Sunday afternoon with mid-late afternoon
dewpoints in the mid 60s. While expect sfc dewpoints to mix out
again, do not think that they will go as low as Sunday afternoon.
Thus, should see heat index values around 105 degrees over most of
central NC, excluding the nw Piedmont. Thus, little change required
to the current heat advisory.
Cannot rule out the potential for an isolated t-storm, mainly across
the far south. However, considering the pocket of warm air aloft(as
per 00Z GSO sounding), convective inhibition will be high.
Thus,will refrain from mentioning an isolated t-storm for now.
Tonight, very warm and muggy conditions will persist with most
places not dropping below 80 degrees until after midnight.
Min temps generally in the mid 70s.
.SHORT TERM /Tuesday and Tuesday night/...
As of 305 AM Monday...
Tuesday, a minor s/w approaching from the west will weaken the upper
high overhead. This lowering of heights, the approach of the
slightly cooler air aloft associated with the s/w, and a sfc tough
over the Piedmont may be enough to allow for the development of
isolated-scattered afternoon convection, mainly north of the I-40/85
corridor late Tuesday afternoon-evening. Elsewhere, presence of the
upper ridge should inhibit convective development south of highway
Low level thicknesses projected to be just as warm Tuesday as today.
Thus, will forecast max temps comparable to today in the mid to
upper 90s. Another heat advisory may be warranted for most of the
Any convection occurring early Tuesday evening across the north
should quickly dissipate after sunset. Continued warm and muggy with
overnight temps only cooling into the mid-upper 70s.
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 3 AM Monday...
Wednesday through Wednesday night: The remnants of a weak cold front
will settle southward into northern portions of the area on
Wednesday into Wednesday night eventually merging with a surface
trough over the area. Meanwhile, the strong mid level ridge
currently over the area will be located off the Southwest U.S. Coast
by Wednesday. This will leave central NC on the southern fridges of
the better westerlies for Wednesday. Given the the weak boundary
will reside across northern portions of the area and potential for
weak impulses to move across the area in the westerly mid level
flow, expect we will see scattered to locally numerous showers and
storms Wednesday afternoon/evening.
Locations across the north will stand the best chance of seeing
convection (closer to the actual boundary where better coverage is
expected). With central NC on the southern fringe of the better
westerly mid level flow (maybe around 20-25 kts at 500 mb across the
north) we may see some multi-cell clusters of storms. Given this and
expected mlcape values of around 1500 J/KG or higher during the
afternoon into the evening and expected frontal zone placement we
may see a better chance for severe storms on Wednesday than past
days (especially across the northern half of the area). Though hard
to time disturbances/mcv`s from upstream convection can and will
have and impact on the eventual convective chances and placement.
High temps on Wednesday are again expected to be above normal
despite increasing chances for storms. Expect high temps to range
from the lower to mid 90s north/northwest to the mid to upper 90s
elsewhere, with heat index values from around 100 north to around
103-105 degrees southeast. Lows Wednesday night are expected to
generally be in the mid 70s.
Thursday through Sunday: Isolated to widely scattered showers and
storms are expected each afternoon/evening through Saturday as the
mid level ridge to our south/southeast is expected to bulge
northward a bit late week into the first half of the weekend. This
should result in high temps continuing to run in the mid to upper
90s for highs, with perhaps a few sites touching 100 by late week.
This combined with a continued moist low level air mass (especially
to the east of the lee side trough expected over the area) will
allow for heat index values of around 100+ across the
southern/southeastern half of the area which may result in
additional heat advisories even if we dont reach heat index values
of 105 degrees, thanks to the prolonged stretch of heat and humidity.
The mid/upper level ridge is expected to shift eastward as s/w
energy is expected to track across the Great Lakes into the
Northeastern U.S next weekend. This should result in another weak
frontal zone approaching central NC from the north by Sunday,
yielding and increasing chance of mainly afternoon/evening
convection. High temps by Sunday are expected to generally be in the
lower to mid 90s. Low temps for the period are expected to generally
be in the mid to upper 70s.
.Aviation /12Z Monday through Friday/...
As of 750 AM Monday...
There is a high probability that VFR conditions will persist across
central NC through Tuesday as an area of high pressure aloft remains
There is a good probability that VFR conditions will persist through
much of the remainder of the work week. Chances for afternoon-
evening scattered convection will increase the later half of the
week, along with the possibility of early morning fog and low clouds.
Heat Advisory from noon today to 8 PM EDT this evening for