Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 181909

Area Forecast Discussion
National Weather Service Raleigh NC
309 PM EDT Fri Aug 18 2017

A weak surface trough will extend from the western Piedmont of
Virginia south into the Piedmont of the western Carolinas. A
cold front will move across the southern Appalachians this
evening and into the Piedmont of the Carolinas and Virginia
overnight. The front will slow across the Coastal Plain on
Saturday before pushing off the coast on Sunday.

As of 235 PM Friday...

The latest surface analysis shows a surface trough extending
from the western Piedmont of Virginia south into the Piedmont
of the western Carolinas. A cold front extends from western PA
southward into WV and eastern KY and TN at 18Z. A tongue of
extremely high dew points in the upper 70s to lower 80s extends
from the coastal region into the Coastal Plain, Sandhills and
eastern Piedmont. Dew points at 2pm include 80 at Goldsboro and
79 at Halifax which combined with temperatures of 90 to 95
result in heat index values from 100 to 109 supporting the
current heat advisory.

Visible satellite from GOES 16 shows deep convection across the
coastal region of NC, some enhanced cumulus in the northern
Piedmont and Coastal Plain and scattered convection across the
mountains. The air mass across the region is moderately to
strongly unstable with MLCAPE values ranging from 1500 to 3000
J/Kg with modest mid-level lapse rates of 5.5 to 6.0 deg C/km.
Central NC is in a region of weak forcing for ascent despite the
loaded airmass. The closest forcing mechanisms include an
eastward advancing shear axis with attendant cold front
approaching the mountains with another short wave trough over
AL/GA which slips southeastward. Still expect there will be only
isolated convection across central NC into the late afternoon
hours with limited forcing. A broken lines of showers and storms
moving across the NC mountains will slip east and probably
intensify as it experiences a relative increase in instability
late this afternoon and evening. This area of convection will
likely reach the Triad between 5 and 8pm. Signals are that the
convection will tend to very slowly weaken as it moves into the
eastern Piedmont and Coastal Plain. The best forcing will be
across the northern half of the CWA with decreased coverage and
intensity in the south. As the shear axis and front move slowly
east overnight the threat of convection will wane and shift
eastward. Portions of the area are in a marginal risk for severe
weather, primarily from downburst winds. Don`t think there will
be much cold advection so lows tonight will once again be in
the lower to mid 70s. -Blaes

As of 300 PM Friday...

The cold front reaches the Coastal Plain Saturday morning and
slowly slips east and moves off the coast by daybreak Sunday.
An upper level trough approaches the region from the OH Valley
on Saturday afternoon with the trough axis moving across central
NC toward daybreak Sunday. A much drier air mass moves into the
region with precipitable water values dropping into the 1.1
(west) to 1.6 (east) range by Saturday afternoon. While a small
threat for a shower or storm lingers across the Coastal Plain
and Sandhills near the cold front, generally dry conditions are
expected elsewhere. The air mass cools slightly with highs
ranging between 88 to 94 degrees Saturday afternoon. Drier air
moves into the area from the northwest Saturday night, and dew
points fall into the mid to upper 60s across the Piedmont and
the lower 70s in the Coastal Plain. This will support much more
comfortable lows in the upper 60s in the Piedmont and lower 70s
in the Coastal Plain. -Blaes &&

As of 244 PM Friday...

Dry weather is expected on Sunday across all of central NC with a
dissipating front now progged well to our south and rather inactive
westerly flow aloft.  Given the steady-state airmass combined with
ample sunshine, we should easily see highs into the low 90s.

On Monday we`ll see heights rise as the ridge off the SE coast
builds northward.  The sfc pattern will be fairly typical for this
time of year with the sfc high over the western Atlantic promoting a
southerly low level flow over our area.  Forecast soundings show a
notable inversion around H7 with dry air in the mid-levels, and in
some cases (particularly across our southern and eastern counties) a
fair amount of moisture above H4.  Thus with heating, the forecast
soundings suggest a decent amount of shallow cu may form below the
inversion across much of central NC as the afternoon progresses.  To
make matters worse, the soundings also suggest a veil of cirrus, esp
the farther south you go.  If there is any good news, these
soundings do not support rain or deep convection, so will keep PoPs
well below climo for Monday.  So in summary for the eclipse weather,
neither clear nor completely overcast, but rather partly cloudy with
cu briefly obscuring the sun at times, along with some high clouds.
Keep in mind that if you spend any substantial time outside, be
ready for highs in the low-mid 90s with heat index values in the
upper 90s.

Tuesday should be mostly dry as the ridge slowly moves east, but
then rain chances will increase on Wednesday as the next northern
stream short wave moves south and east and pushes a cold front
across our area.  The longwave trough will continue to deepen over
the East, so look for cooler temps by late next week, and perhaps
even a brief break from the high humidity for next weekend.


As of 230 PM Friday...

VFR conditions across central NC this afternoon will give way
to scattered showers and thunderstorms this evening. The
convection will largely be associated with an eastward
advancing cold front. Look for the greatest chances of adverse
aviation conditions in the Triad (KINT and KGSO terminals) from
21 to 02Z, in the Triangle (KRDU terminal) from 23 to 03Z and
in the east and southeast (KRWI and KFAY terminals). An isolated
shower or storm is possible across the Piedmont and especially
the Coastal Plain overnight. Don`t expect much in the way of
late night or early morning low-level stratus although a BKN
layer of clouds is expected overnight at around 6kft. Generally
fair weather with SCT-BKN cumulus with bases around 4kft is
expected on Saturday, with some scattered afternoon storms
across the Coastal Plain and Sandhills impacting the KFAY
terminal. Southwest winds at 5 to 10kts this afternoon will
become light west overnight behind the front and light
northwesterly on Saturday.

Looking beyond 18Z Saturday....generally VFR conditions are
expected on Saturday and Sunday with just a few showers or
storms across the Coastal Plain on Saturday and dry weather
on Sunday. The threat late-day storms and some early-morning
fog and stratus increases on Monday into tuesday. -Blaes

Heat Advisory until 6 PM EDT this evening for NCZ025>028-


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