Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
637 am EDT Tuesday 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/...
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 Ohio/Tennessee 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 Storm Prediction Center 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 northwest 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.
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 Virginia on Wednesday afternoon, helping to increase coverage near
the Virginia/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
Continental U.S.. 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