Area Forecast Discussion
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FXUS62 KRAH 291402
Area Forecast Discussion
National Weather Service Raleigh NC
1000 AM EDT FRI JUL 29 2016
A weak upper-level trough will become centered over the eastern
U.S.today through Saturday, bringing increased chances for showers
andstorms late Saturday through Monday, along with a trend toward
.NEAR TERM /THROUGH TONIGHT/...
As of 1000 AM Friday...
Little change needed to ongoing forecast. The latest surface map
shows low pressure off the Northeast coast with troughing extending
down through central NC, aligned closely with the 850 mb trough. The
low level flow from the WNW is likely to hold down temps and
dewpoints enough to limit convection, although there may still be a
sufficient combination of low level mass convergence (along and east
of a weak lee low that is expected to form over the western
Sandhills) and higher temps/dewpoints along and east of the trough
for scattered storms this afternoon into early evening. The SSEO, 3
km NAMRR, and the NCAR ensemble output all suggest a weak
shower/storm cluster traversing the southern third of the forecast
area late today, fitting with this scenario, and will place chance
pops here with just isolated elsewhere. Despite the decent deep
layer bulk shear, CAPE values should be small today, at or under
1000 J/kg of MUCAPE, limiting storm intensity. Thicknesses this
morning are markedly lower than previous mornings, suggesting highs
around a category below yesterday`s highs, and in fact current temps
are already running 1-4 degrees below yesterday`s pace. Expect highs
in the lower-mid 90s, except upper 90s SE. Will keep the heat
advisory in place in the east, although a few spots may come up
short, especially if dewpoints mix out more than expected in the
eastern CWA. -GIH
Previous discussion as of 230 AM Friday: Mostly sunny skies today
with just slightly lowering heights/thicknesses will only yield
subtle changes to the heat. Highs will still reach 95-100 from
Fayetteville to Rocky Mount eastward to Goldsboro and Clinton. Heat
indices will still reach 105 or 106 in many areas this afternoon.
This will be another day to take precautions to prevent heat related
issues or illnesses.
Central NC will be on the back or subsidence side of the departing
mid/upper trough over VA this morning. Skies were clear this
morning over much of the region with partly cloudy skies near
the VA border. The mean flow is a bit more westerly into the
mountains and western Piedmont on the backside of the
departing trough. The SW-W low level flow has aided in some dry
advection from upstate SC into western NC, allowing dew points to
fall into the 60s. In the east, dew points remained very oppressive,
in the 70s. This lowering of dew points will eliminate the heat
advisory from the Piedmont today. Heat indices will be in the 95-100
range during the mid to late afternoon in the Piedmont. However,
highs will still reach the mid to upper 90s. Even though a heat
advisory will not be needed, this subtle lowering of the heat
indices from 105 to 95 to 100 will essentially not be that
noticeable; therefore, it will be good idea to treat today just as
the last few when advisories were in effect in the Piedmont.
Convection is expected to be at a minimum again today with the
subsidence this morning and more of a westerly flow. There will be
slight chance of thunderstorms this afternoon and early evening as
the surface trough develops and the low level flow begins to back to
the SW then S by evening. The best chances should be in the
Coastal Plain this afternoon. Dew points will again rise this
evening, back into the 70s in the Piedmont and remain high in the
east as the surface trough backs westward. An isolated storm is
possible, but the chances remain slim without a trigger aloft. Lows
generally in the 70s again.
.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
As of 225 AM Friday...
Yet another heat advisory appears likely in the south and east on
Saturday as strong heating and high humidity values will occur
again. There will be more clouds over the Piedmont and northern
areas, closer to the approaching mid/upper trough. This will bring
some cooling, even if the showers do not become widespread. Highs
should range from around 90 NW into the upper 90s in the Coastal
Plain. Heat indices should reach 105 again SE, but will be in the
As the trough aloft digs into Tennessee Valley and over the central
Appalachians, a surface trough will tighten over central NC.
However, the main focus for convection appears that it will be in
the northern and eastern section of NC, and especially over VA due
to the best lift... low level convergence... and moisture pooling to
our NE. We will continue to show 40-50 POP in the NE with only 20-30
POP to the SW. This chance of showers and thunderstorms will be
mainly during the afternoon and evening. Partly cloudy skies
otherwise, lows Saturday night in the 70s.
.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 200 AM Friday...
Broad troughing aloft over the central MS river valley will progress
eastward over the Carolinas and Mid-Atlantic through early next
week, followed by a period of NW flow aloft mid-week as an upper
level ridge re-strengthens over the lower MS river valley and Deep
South, followed by a ridging aloft late next week as the
aforementioned ridge builds E/NE over the Carolinas and Mid-Atlantic.
With the above in mind, expect a cooling trend late the weekend
through early next week with temperatures becoming near normal,
followed by an increase in temperatures by late week as ridging
aloft returns to the region. With broad troughing aloft, expect
above-normal chances for convection Sunday and early next week, with
chances somewhat more ambiguous in NW flow aloft by mid-week,
followed by below normal chances for convection late-week. With
central NC situated on the southern periphery of the westerlies and
eventually a period of NW flow aloft, an above normal potential for
severe weather will exist if small amplitude waves and/or upstream
convection /MCVs/ progress into/across the region, particularly in
vicinity of peak heating. -Vincent
.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
As of 650 AM Friday...
VFR conditions are expected today and tonight. The chance of a
thunderstorm will increase Saturday afternoon.
Outlook: Scattered showers and thunderstorms are expected each
afternoon/evening Sunday and Monday. Otherwise, expect
predominately VFR conditions.
Heat Advisory from noon today to 8 PM EDT this evening for