Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 291831

Area Forecast Discussion
National Weather Service Raleigh NC
230 PM EDT Mon May 29 2017

An unsettled pattern associated with cyclonic flow aloft will
persist through mid-week.


As of 115 PM EDT Monday...

A plume of enhanced 925-850 mb moisture advecting into central NC
from the W/SW amidst strong insolation and modest mid-level lapse
rates (~6.0C/km) is expected to yield 1000-1500 J/kg MLCAPE with no
CINH by peak heating this afternoon. W/regard to forcing, numerous
perturbations were noted in WSW flow aloft upstream of the Carolinas
at 17Z. A series of the aforementioned disturbances are progged to
track ENE across the Carolinas this aft/eve into tonight. In the
lower levels, a developing thermal trough over the NC Piedmont this
afternoon should help serve as a focus for development once CINH has
eroded, particularly if a weak/broad low forms over central SC/NC as
some of the latest 12Z guidance suggests.

With the above in mind, expect convection to develop across the W/SW
Piedmont by late afternoon. Given an environment characterized by
steep low-level lapse rates (0-3km ~8c/km) and moderate DCAPE (~1000
J/kg) in a westerly flow regime, it seems likely that convection
will grow upscale along outflow and propagate east across central NC
by late evening (~03Z), with the relative best chance along/south of
Hwy 64. Additional convection is progged to develop over southwest
NC/upstate SC (upstream of the initial activity) this evening as
additional disturbances in WSW flow aloft track across a moist
/conditionally unstable/ airmass in place over the region. As a
result, it is possible that convection could persist past midnight
into the 06-09Z time-frame, primarily along/south of Hwy 64. Deep
layer shear and moderate destabilization will be sufficient for
supercellular organization with initial activity that develops this
aft/eve, with a primary threat of damaging winds and severe hail
(the latter of which may be tempered by modest mid-level lapse
rates). With steep low-level lapse rates and moderate DCAPE expected
this afternoon, activity is likely to grow upscale along outflow
with time. This suggests the primary severe threat will transition
to damaging winds late this afternoon and early evening.

Expect highs ranging from the mid 80s far NW Piedmont to lower 90s
Sandhills and SE Coastal Plain. Lows tonight in the 60s, coolest
N/NW and warmest S/SE. -Vincent


As of 230 PM Monday...

Tuesday and Tuesday night: Upper low over Ontario will move very
little over the next couple of days, with a gradual NEWD wobble over
James Bay region by Tuesday night. The evolution of this
evening/tonight`s convection may leave behind a surface
trough/thermal-moisture boundary across eastern/southeastern NC,
while also serving to modulate buoyancy due to convective
overturning. So will have to wait and see how that plays out as
models show weak to to moderate instability developing Tuesday
afternoon in response to strong insolation/steep low-level lapse
rates. While insolation alone could allow for some isolated
convection to develop across central NC, the primary convective
trigger Tuesday afternoon/evening will be with any shortwave
impulse(s) or MCV(s) ejecting NEWD from the MCS blob currently over
the western GOM. POPS/rain chances look to range from slight to
small chance across the NW to good/high chance across the east.

While, deep layer shear won`t be as favorable as in previous days,
30-35 kts will still be sufficient to support a few strong to severe
multicell clusters during peak heating.

Highs ranging from lower to mid 80s north to mid/upper south, high
dependent on convective evolution. Lows in the lower 60s NW to upper
60s/near 70 south.

Wednesday and Wednesday night: The closed low over Ontario/James Bay
will get reinforced by another closed cyclone diving SE out of
central Canada. Shortwave energy rotating through the base of the
mean  trough will push a cold front into the region from the
northwest Wednesday evening/night, which will allow for a continued
threat of scattered showers and storms area-wide Wednesday. Pre-
storm environment in place across central NC on Wednesday will be
very similar to Tuesday, thus a few strong to severe storm clusters
are possible, especially across the NW Piedmont where arrival of low-
level frontal zone will better coincide with more favorable diurnal
timing. Highs in the mid to upper 80s. Lows slightly cooler below
the front. Lows around 60 NW to mid 60s SE.


As of 230 PM EDT Monday...

Weak high pressure building into the area in the wake of the cold
frontal passage Wednesday night, will advect drier more stable air
advecting in from the WNW, potentially keeping central NC convection
free on Thursday. However, these dry conditions look to be short-
lived with the return of moist low-level SWLY and potential
shortwave disturbances ejecting east from the Southwest US. Rain
chances look to increase even further through the weekend, in
response to height falls aloft and under the increasing influence of
cyclonic flow aloft as the the upper trough amplifies across the NE
US, sending a cold front southward into the region late Saturday and
into Sunday. Temperatures should hover around normal, falling to
below normal on Monday as high pressure builds into the region from
the northwest.


As of 115 PM EDT Monday...

24-HR TAF Period: VFR conditions will prevail through mid to late
afternoon at all terminals. Sub-VFR conditions associated with
scattered convection are expected late this afternoon and evening,
primarily at southern/eastern terminals (FAY/RDU/RWI) with the
relative best potential at the FAY terminal. Convection could
persist past midnight (into the 06-09Z time frame), though once
again it would appear that southern/eastern terminals are more
likely to be affected. In areas that experience rain, a short period
of IFR/LIFR ceilings or fog could develop prior to sunrise if skies
clear, though whether or not this will occur remains difficult to
ascertain at this time.

Looking Ahead: Aside from a potential for isolated to scattered
afternoon and evening convection associated with cyclonic flow aloft
over the region, expect VFR conditions to generally prevail through
mid to late week. -Vincent





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