Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 290013

Area Forecast Discussion
National Weather Service Raleigh NC
815 PM EDT THU JUL 28 2016

An upper level disturbance will track just to the north of the
region today and tonight around the hot high pressure over the
Southeasten US. A surface trough of low pressure will stall across
the area through the weekend.


As of 320 pm Thursday...

...Have upgraded the Heat Advisory to an Excessive Heat Warning for
areas along and east of I-95...

...Heat Advisory continues for all of the Piedmont counties...

The Subtropical ridge in place over the SE U.S. will continue to
produce very warm and humid conditions across Central NC today.
A mid-level shortwave trough, currently over the TN Valley, will
skirt the NW periphery of the subtropical high in place over the
region and will track newd across the southern and central
Appalachians this evening, shearing along the way before reaching
the Northern Mid-Atlantic States by Friday morning. In response to
the approaching trough, the persistent lee side surface trough in
place east of the Appalachians will sharpen with a weak surface
wave expected to develop invof of Virginia/DC later this evening.

Dangerously high dew points in the mid 70s to upper 70s has and will
continue to pool on the east side of the sharpening surface trough.
As of 10 am, heat indices along and east of the I-95 corridor are
already in the 100 to 105 range. When combined with afternoon
temperatures in the upper 90s to 100 F range, heat indices of 110 to
115 F are expected and thus have upgraded the heat advisory to a
heat warning for areas along and east of the I-95 corridor.
Elsewhere across the western and central piedmont will leave heat
advisory in place with heat indices expected to range between 103 to
109 F.

As far as rain/convective chances:
Regional mosaic radar shows a band of showers and storms across
eastern KY/TN that has developed along ahead of the approaching
trough. While the bulk of the convection is expected to affect
TN/KY/WVA/VA, associated outflow boundaries may set off new
convection, at least on a scattered basis, over much of the northern
tier into the mid-evening hours. While the stronger mid-level flow
is expected to be just north of the region, 20 to 25 kts of deep
layer shear bordering the northern counties combined with moderate
to strong instability of 2500 to 3000 J/KG of mlcape will yield a
threat for one or two severe clusters to develop, with damaging wind
the main threat.

The threat will diminish rapidly this evening as is typically the
case with strongly diurnally driven storms. We will carry 30 to 40
POP across the N, with only 10 to 15 POP SE.

Lows tonight 70-76.


As of 320 PM Thursday...

Low-level thicknesses and heights aloft fall slightly on Friday as
the subtropical high shifts just east of the area and broad troughiness
begins to settle into the area from the west. However of more significance,
is the potential for dewpoints to mix out into the upper 60s and lower 70s
Friday afternoon owing to the low-level westerly flow that
develops in the wake of the surface low exiting off the Mid-Atlantic
Coast. So despite similar afternoon temperatures in the lower 90s NW to upper
90s SE, the drier air will suppress heat indices with current forecast
grids showing only the far SE zones close to advisory criteria.
Confidence is too low at this time to warrant the issuance of an
advisory with this package so will let midnight shift re-evaluate.

Expect the westerly low-level flow east of the mountains to also suppress
convection Friday afternoon, maintaining isolated/slight chance of diurnally
driven convection.

Lows Friday night in the lower to mid 70s.


As of 250 PM Thursday...

The pattern for the long term period will feature a low amplitude
but broad trough across much of the eastern third of the country.
With our area on the eastern side of the trough axis during the
weekend, look for above normal temps to continue (low-mid 90s)
during that time, but daily diurnal rain chances should be at or
above normal (30-40% each day) given more abundant deep layer
moisture and a series of passing short waves embedded in the sw
flow. Perhaps the increased rain chances and assoc cloud coverage
may help mitigate the oppressive heat somewhat compared to what
we`ve seen the past few days.

For the early part of next week, the aforementioned trough axis is
progged to cross the eastern seaboard.  The assoc sfc cold front may
attempt to move across our area, setting up increased rain chances
for Monday.  Assuming the front does indeed push south of our area,
we may see at least a brief return to normal temps (highs in the
upper 80s and lows in the upper 60s) during the mid-week period with
lower humidity and at or below climo pops.


As of 815 PM Thursday...

VFR conditions are expected with some patchy early morning ground
fog possible late tonight. Scattered to isolated storms are possible
again tomorrow afternoon, but chances of a storm occurring at a TAF
site are too low to include.

Outlook: Outside of isolated to scattered storms each
afternoon/evening and some patchy early morning fog, expect
predominately VFR conditions through Friday. Rain chances are
expected to increase by the weekend and into early next week.


Excessive Heat Warning until 8 PM EDT this evening for NCZ011-027-
Heat Advisory until 8 PM EDT this evening for NCZ007>010-021>026-



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