Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 231840

Area Forecast Discussion
National Weather Service Raleigh NC
240 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 1045 AM Saturday...

See no reason to depart significantly from the earlier forecast. The
current surface analysis shows a diffuse MSL pressure pattern with
weak lee troughing holding in place and a soggy air mass with
dewpoints in the 70s areawide. We should see some dip in dewpoints
with mixing this afternoon, down into the upper 60s to lower 70s,
however given that observed thicknesses this morning are nearly 10 m
higher than yesterday, heat index values are still expected to reach
the upper 90s to around 100. The weak shear/moisture axis aloft
along which last night`s convection developed is slowly pushing
through southern NC, and the latest CAM runs suggest this feature
serving as a focus for deeper moisture resulting in organized
convection formation this afternoon. Will retain the greater rain
chances across the southern CWA, in line with the RAP/HRRR/SSEO
output, although we`ll need to monitor development trends as a bump-
up to scattered coverage may be warranted. We should see highs in
the mid 90s, factoring in high-res temp guidance, current trends,
and expectations of more diurnal cloudiness in the south this
afternoon. -GIH

Previous discussion as of 315 AM: An expansive area of high pressure
aloft centered over the central/southern plains will shunt the main
band of westerlies near or north of the Canadian border. This
pattern will result in a weak flow aloft over central NC. Thus, any
convection that develops later today will be focused on outflow
boundaries from Friday`s convection, or move into our region from
the higher terrain to our west-nw.  Expect the highest chance for
isolated convection south of highway 64 where better low level
moisture expected to reside. if later meso analysis depicts
sufficient low level convergence, a bump up in PoPs to chance may be
warranted. Strong low level lapse rates suggest strong gusty winds
probable in vicinity of any convection.

Afternoon low level thicknesses projected to be 7-10m warmer than
Friday. This is supportive of max temps solidly in the mid 90s. Heat
indices will be in the upper 90s northwest to 100-104 degrees

Tonight, any isolated convection will quickly dissipate with loss of
heating. Overnight temps will lower into the mid 70s. -WSS


.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 /18Z Saturday through Thursday/...
As of 100 PM Saturday...

High confidence in VFR conditions prevailing through mid afternoon
Sunday. A weak disturbance aloft will reside over southern NC today
into early tonight, and with a moist and hot air mass in place at
the surface, a few showers and storms are expected this afternoon
into tonight, with the best coverage (still just scattered) across
the south (including FAY) and only isolated cells elsewhere
(including INT/GSO/RDU/RWI). The chance that a storm will impact any
particular TAF site is quite low, so will not include thunder as a
prevailing or tempo condition at this time, but will monitor. As
always, lightning along with erratic/gusty winds are possible in and
near any storms. Otherwise, clouds today will follow a typical
diurnal cycle with maximum cloud coverage in the late afternoon,
decreasing slowly this evening/tonight. Any clouds will be based
above 3 kft. Later tonight, isolated patches of MVFR fog are
possible, but chances are too low of this affecting a TAF site to
include in the forecast. High pressure in the mid and upper levels
of the atmosphere will continue to build atop the region through
Sun, resulting in drying and warming aloft and a reduced chance of
showers and storms Sunday.

Looking beyond 18z Sunday: VFR conditions will be dominant through
this period, with no significant, large-scale sub-VFR conditions on
the horizon, although shower/storm chances will start to rise during
the mid week (Tue night into Thu). There will, however, be improving
chances for late night / early morning sub-VFR fog as we head into
next week. -GIH





NEAR TERM...Hartfield/WSS
SHORT TERM...Hartfield
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