Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KRAH 261434
Area Forecast Discussion
National Weather Service Raleigh NC
1030 AM EDT TUE JUL 26 2016
-- Changed Discussion --Strong high pressure aloft will extend across the region through
Wednesday, bringing continued hot and humid conditions to central
NC. The chance for afternoon storms will increase toward the end of
the work week.
-- End Changed Discussion --
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --As of 1030 AM Tuesday...
Late today into this evening may bring our best chance for rain in
several days, with good chances for scattered showers and storms
across the northern half of the forecast area. Latest surface
analysis shows the offshore-centered ridge extending across the
Southeast states with weak lee troughing over our west and the
synoptic front to our N/NW along the OH valley. While the mid and
upper level ridge will hold across the region, the axis will shift a
bit southeastward later today as shortwave energy over the lower
Midwest tracks eastward across the OH valley and mid-Atlantic,
nudging the westerlies slightly to the south and inducing sufficient
acceleration aloft to boost deep layer bulk shear to around 20 kts
across northern NC. This, along with a corresponding slight increase
in previously-meager mid level lapse rates along and north of the
NC/VA border, will create an environment that will be more conducive
for convection to initiate and grow upscale. MUCAPE is expected to
peak at 1000-2000 J/kg today, highest near the border and over NE
NC, and this is where the convection-allowing models (CAMs) show the
most long-lived activity today. But the HRRR/HRRRX/RAP, WRF-NMM/ARW,
SSEO, NSSL WRF, and NCAR ensemble neighborhood probabilities all
indicate at least some convection over the remainder of the western
Piedmont as well, warranting at least isolated coverage there, with
warmer/drier air aloft limiting coverage. Scattered coverage is
anticipated over northern NC, and this activity may congeal into
clusters over our NE sections this evening -- fueled by better deep
layer bulk shear and slightly greater instability in this area -
- before gradually diminishing overnight. The only notable changes
to the existing forecast will be to delay convection onset a couple
of hours over all but the NW, raise pops a tad over all of the
western Piedmont, and retain pops in our eastern sections later into
the night as suggested by the NSSL WRF, HRRRX, and others. High-res
guidance still supports highs in the mid-upper 90s, and with a
mixing/lowering of dewpoints with heating likely to follow a pattern
similar to yesterday, we should reach dewpoints from the upper 60s
NW to lower 70s SE this afternoon, equating to heat index values
easily peaking at or above 105 over the advisory area. -GIH
Previous 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.-BSD
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.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
As of 325 AM TUESDAY...
Persistent mid/upper level ridge located just to the south/southeast
of central NC will continue to provide the region with hot and humid
conditions with another day of highs in the mid to upper 90s and
heat index values in the 100-107 degree range (highest east and
south again). Thus, another heat advisory will likely be needed
again on Wednesday afternoon/evening. With a similar pattern to
today, we will again see the best chance of scattered showers and
storms across the northern half of the area, with less across the
south (closer to the center of the ridge). Deep layer shear is a bit
stronger with around 20-25 KTS of 500 MB westerly flow. Thus, think
we could see a few more clusters of storms across northern portions
of the area. In addition a weak cold front will stall across
southern VA on Wednesday afternoon, helping to increase coverage near
the VA/NC border as well.
More of the same is expected on Wednesday night, with warm lows in
the mid to upper 70s and generally dry conditions. However, as will
be the case tonight, we can`t completely rule out isolated
showers/storms associated with possible weak disturbance(s) tracking
across northern portions of the area. Confidence is too low to
include any mention of precip in the forecast at this time though.
.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 /12Z TUESDAY THROUGH SATURDAY/...
As of 635 AM Tuesday...
24-hr TAF Period: VFR conditions are generally expected to continue
outside of isolated to widely scattered showers and storms late this
afternoon into the early evening across northern portions of central
NC (with KGSO/KINT/KRWI standing the best chance, which is where we
have added prob30s for storms and sub VFR conditions). 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 through the period.
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