Area Forecast Discussion
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FXUS62 KRAH 232227
Area Forecast Discussion
National Weather Service Raleigh NC
627 PM EDT SAT JUL 23 2016
A ridge of warm high pressure aloft will extend across the region
through early next week, bringing a period of hot and humid
conditions to our area.
.Near Term /through tonight/...
As of 320 PM Saturday...
Isolated slow-moving convection over the SW Piedmont and adjacent
Sandhills -- within a zone of weak mass convergence, 8+ C/km low
level lapse rates, and moderate MLCAPE over 2000 J/kg -- will
continue to drift toward the SW. With weak mid level lapse rates,
very weak deep layer bulk shear, and only marginal moisture through
the column, any isolated cells should stay below severe limits,
although locally heavy rain and enhanced wind gusts (feeding on
1100+ J/kg of downdraft CAPE) are certainly possible. The latest
HRRR/HRRRX/RAP runs are a bit overdone spatially but follow the
general pattern of isolated to scattered storms in this area
drifting toward the SW (following the weak 700 mb flow) over the
next few hours. With small adjustments, will maintain the current
pop configuration into the evening. Low level lapse rates will drop
near/after sunset with loss of heating and decoupling, although
models retain some weak instability across the far southern CWA
overnight, with the 925 mb thermal ridge holding over western NC and
lingering moisture near and south of the SC border, so will hold
onto a mention of an isolated shower or storm overnight across the
far south. Lows in the low-mid 70s. -GIH
.SHORT TERM /Sunday through Sunday night/...
As of 225 PM Saturday...
This still looks like our hottest day, and convection chances appear
to be very minimal. Models take the core of the upper ridge overhead
Sun, with continued steady warming aloft evident on forecast
soundings, cutting down considerably on the potential for
destabilization despite surface temps peaking in the upper 90s. CAMs
and models with parameterized convection favor virtually dry weather
tomorrow, with only an isolated cell or two at most. Will keep an
isolated thunder mention in the extreme west and extreme SE, with
the potential for drifting terrain-induced cells and sea-breeze
convection, respectively. Statistical guidance and model thicknesses
support highs in the upper 90s, very close to earlier forecasts.
With dewpoints remaining high but dipping a bit in the afternoon
with mixing, heat index values are likely to reach 100-106, with the
highest values along and east of the Highway 1 corridor. Will go
forward with a heat advisory for these eastern sections. Even if
some spots only reach close to 105 for an hour, given that we will
have been atypically warm for a few days already, and with it being
a Sunday and folks likely spending time outdoors, the risk for heat
illnesses will be elevated. Any isolated convection is apt to
dissipate quickly toward sunset, with fair and muggy conditions Sun
night. Lows in the mid 70s. -GIH
.LONG TERM /Monday through Saturday/...
As of 239 PM Saturday...
With the upper ridge directly overhead and a surface high over the
western Atlantic Monday is shaping up to be a very hot but mostly
dry day to begin the long term. To the north, a low pressure system
over Quebec will spin off to the northeast, dragging a weak cold
front behind it that will approach the Appalachians by Monday night
but get held up by the exiting high. On Tuesday the low pressure
over Canada moves on, leaving the remnants of the cold front just
north of the area. This could leave Tuesday fairly dry as well but
an uptick in afternoon convection is possible with more moisture
filtering into the area and the relaxation of the surface high
replaced by a surface trough over central NC. The frontal zone
slides further south on Wednesday bringing a much better chance for
convection by Wednesday afternoon, particularly across northern
portions of the forecast area. Story remains the same for Thursday
with the added punch of a shortwave disturbance tracking out of the
Mideast and arriving by 00z Friday. Several disturbances will
continue to move through the area through Saturday as a low pressure
system tries to become better organized over the mid-Atlantic states.
No relief to very warm temperatures with mid-90s expected each day
with lows in the mid 70s. Furthermore heat indices will run at
least 100-105 most days with the potential for some >105 readings
possible with Monday and Wednesday afternoons looking like the best
chance for that.
.Aviation /00Z Sunday through Thursday/...
As of 630 PM Saturday...
24-hr TAF Period: High confidence in VFR conditions and
light/variable winds through the TAF period as an upper level ridge
builds over the region from the west.
Looking ahead: High confidence in VFR conditions through the
remainder of the weekend and early next week as an upper level ridge
builds over the region. Isolated convection cannot be entirely ruled
out during the late afternoon/evening hours on Monday/Tuesday,
however, probabilities are too low to warrant mention in the
forecast. Chances for diurnal convection may gradually approach
climatology by mid/late next week. -Vincent
Heat Advisory from noon to 8 PM EDT Sunday for NCZ010-011-