Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 260708
Area Forecast Discussion
National Weather Service Raleigh NC
307 AM EDT TUE JUL 26 2016
Strong high pressure aloft will extend across the region through
Wednesday, bringing a period of hot and humid conditions to central
NC. The chances for afternoon storms will increase toward the end of
the work week.
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --As of 305 AM Tuesday...
Today: Mid/upper level ridging continues over the area this morning
with the mid level high centered across the Carolinas. Weak
disturbances aloft continue to track around the mid/upper level
ridge to the west and north of central NC. The center of the
mid/upper level ridge is forecast to shift slightly to the southeast
today, which will allow for a better chance of weak disturbances
tracking around the ridge to affect northern portions of central NC
this afternoon/evening. Once such disturbance is helping to support
and area of showers drifting northward across northern GA/AL. This
weak energy coupled with another weak disturbance located over the
lower OH/TN valley region this morning will combine along with a
weak surface trough across the area to produce isolated to widely
scattered showers and storms this afternoon/evening (with better
coverage likely to the north of our area). Given strong heating
during the morning into the early afternoon hours we will likely see
at least 2000 to 2500 J/KG of MLCAPE across the area today. Deep
shear however looks fairly weak, with maybe 15 to 20 kts of westerly
flow at 500 MB. This environment will be supportive of wet
downbursts, with perhaps a few clusters of storms possible. Thus,
the latest day one convective outlook from SPC has our far northern
counties in a marginal risk for severe storms with possibly a few
damaging wet downbursts.
The main story today though will again be the relentless heat, with
high temps expected to again range from the mid to upper 90s and
heat index values ranging from near 100 NW to 104-107 elsewhere.
Thus, will continue the heat advisory today from noon to 8 PM for
all but the far Western Piedmont.
Tonight: Most convection will generally die off by late evening with
another warm night expected. Expect lows temps tonight to generally
be in the mid to upper 70s. Can`t completely rule out additional
weak disturbance tracking across northern portions of the area
overnight, possibly sparking a shower or storm, though think any
activity will be quite isolated as we should still be under the
general influence from the nearby mid/upper level ridge.
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.SHORT TERM /Tuesday and Tuesday night/...
As of 325 PM Monday...
Shortwave energy over the central part of the country will push
eastward into the OH valley toward the mid-Atlantic/Northeast
through Tue night. While the primary bound of mid level westerlies
will stay well to our north, this wave will help push both the
surface frontal zone and the slightly deeper moisture (as noted on
water vapor imagery) to the SSE toward NC, not quite reaching the
NC/VA border but making enough southward progress to bring a
scattered showers and storms to northern NC. Mid level lapse rates
should be a bit better than today, in the 5.7-6.0 C/km range,
although deep layer shear will remain minuscule as the mid-upper
level ridge axis will continue to extend across the region. Model
forecast CAPE values are expected to remain muted with the continued
warmth aloft, particularly across the southern two-thirds of NC,
closest to the ridge axis. Will bring in late-day low chance pops
across the northern sections of the CWA Tue into early Tue evening,
before coverage drops off through the evening with loss of heating.
See little reason to depart from persistence regarding temps, with
thicknesses remaining well above normal, topped by anomalously high
temps and heights through the column, and high surface dewpoints
holding at or above the low-mid 70s for a good portion of the day.
Will retain highs in the mid-upper 90s, as statistical guidance
supports, with lows again in the mid 70s. These temps again equate
to heat indices near or above 105 over the south and east, so will
go with another heat advisory for Tue for the same areas. These
successive days of hot temps and high humidity without much recovery
at night will exacerbate the risk of heat illnesses heading into mid
.LONG TERM /Thursday through Monday/...
As of 300 AM Tuesday...
Persistent upper level high over the Southeast U.S. will maintain
hot conditions over central NC Thursday and Friday. Heating of the
moist and moderately unstable air mass will support the development
of isolated-scattered late afternoon-evening convection, mainly
north of highway 64 where subtle height falls and presence of
surface trough will occur. Low level thicknesses Thu still support
max temps in the mid/upper 90s, and with sfc dewpoints in the
low/mid 70s, potential for the continuation of heat advisory very
possible. Thicknesses Fri lower 15-18m as the upper high begins to
weaken, though this may be too aggressive as history suggest that
the thicknesses may only lower 5-8m. Thus expect highs Friday back
into the mid/upper 90s.
Potential for more appreciable change in the weather pattern
expected by Saturday-Monday as center of upper ridge shifts
southward. This will allow weak upper disturbances to skirt across
our area, especially across the north. This should lead to an uptick
in the coverage of afternoon-evening convection. In addition, with
more clouds/convection, should see max temps lower a few degrees
with max temps generally in the 90-95 degree range. Presence of the
surface trough and available moisture and instability will support
additional convective development early next week.
.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
As of 150 AM Tuesday...
24-hr TAF Period: VFR conditions are generally expected to continue
outside of some patchy morning sub-VFR fog/stratus (best chance at
KRWI) and isolated to widely scattered showers and storms late this
afternoon into the early evening (again best chance at KRWI).
Otherwise, a mid/upper level area of high pressure over the region
will help steer the main track of convection to the north and west
of central NC, yielding VFR conditions with south to southwesterly
winds at around 6 to 10 KTS.
Looking ahead: VFR conditions will generally prevail through mid-
week as an upper level ridge remains in place over the southern
CONUS. Diurnal convection will become increasingly possible as the
ridge weakens /week progresses/, with chances near climatology by
late week into the weekend.
Heat Advisory from noon today to 8 PM EDT this evening for