Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 191030
Area Forecast Discussion
National Weather Service Raleigh NC
700 AM EDT Thu May 19 2016
.SYNOPSIS...An upper level disturbance will push across the region
today. A weak and cool surface high pressure will continue to extend
into central North Carolina through Friday. A much stronger storm
system is expected to move into the region late Friday into early
.NEAR TERM /through tonight/...
As of 122 AM Thursday...
The main issues to deal with today will be the rain chances
associated with the upper disturbance, and the expected persistent
chilly NE low level supply of cool stable air and overcast
associated with the hybrid CAD, resulting in temperatures again 20-
25 degrees below normal for highs.
The predominate NE flow continued along the Appalachians and east
coast states this morning, courtesy of the low pressure exiting into
the western Atlantic and the surface high pressure located over the
lower Great Lakes states. This flow is one that continues to advect
cool and some marginally drier air into the state from central VA.
The NE-E flow extended all the way into central SC and northeast GA
where a weak low pressure was noted. Some drier air was trying to
work down the coast from the north with some partial clearing of the
low clouds noted east of I-95. There was a weakness in the pressure
pattern noted over the Appalachians associated with the current weak
hybrid CAD high pressure over NC/VA and the stronger high located
over the lower Great Lakes states. Radar indicated scattered showers
and thunderstorms developing over upstate SC spreading NE into
western NC to near Hickory and Statesville. This is area was
associated with the approaching upper level disturbance and the mass
convergence near the surface wave and front stalled over upstate SC.
For the chances of rain today, the latest Hi-Res convection allowing
models support the current radar trends in bringing an area of
showers and general rain (north in the cool stable air) across the
Piedmont this morning. This occurs as the low level flow remains NE
bringing a continuous supply of cool stable air into the Piedmont
Damming region. This scenario above is favored by the conventional
GFS/NAM as well. MOS guidance finally caught up with the much cooler
stable temperatures yesterday associated with the NE flow and
damming; therefore, we will not have to adjust guidance down as much
today as we did yesterday. Bottom line today, expect a good chance
of showers in the SE Coastal Plain with occasional rain over the
Piedmont. Most of the rain should be light with QPF of around 0.25
expected in the Piedmont, lesser amounts over the Coastal Plain.
Temperatures should only go up 3-5 degrees or so as the low overcast
develops/persists through the day. Highs only in the 50s NW and N
Piedmont ranging into the upper 60s SE.
Significant rain chances lower tonight in the rear of the upper
disturbance departing to the NE. However, the low overcast
conditions should continue tonight enhanced by the low level NNE
flow. In fact, the main chilly surface high pressure is forecast to
move east to PA later tonight. The high is of sufficient strength
and in a proper position to deliver additional cool stable air into
the region to allow for the persistence of the CAD, then enhancement
of the CAD Friday into Friday night as the next storm approaches
from the SW (see discussion below). Lows tonight 50s except lower
.SHORT TERM /Friday through Saturday/...
As of 258 aM Thursday...
...Hybrid CAD and Miller B storm system to affect the region into
Issues ahead for Friday through Saturday will be mainly with the
rainfall forecasts and the continued very cool temperatures for
daily highs through at least Saturday.
Any severe threat associated with the approaching storm system late
Friday and Friday night have essentially been erased by the
agreement of the models with hybrid CAD over our region and by the
forecast of the storm track to be up along or east of I-95 late
Friday night and early Saturday. This storm track is more of a
Miller B with one low lifting NE through the TN and OH valley as
another develops along the SC/NC coastal area late Friday night,
then tracks up the coast Saturday. This pattern has a cool stable
and almost "wintry" look to it.
To begin Friday, a very cool surface high pressure is forecast to be
centered over PA. The strength is expected to be around 1025 MB. The
location and strength are both sufficient to deliver additional
cool stable air into central NC from the north Friday. This occurs
as the initial low pressure is forecast to track NE into the TN
valley region by late Friday. All of our region is expected to be
dominated by the cool stable low level high to the north. As such,
temperatures Friday will be hard pressed to get out of the 60s
anywhere in the region. Some upper 50s may again linger around the
Triad to Roxboro in the continued hybrid CAD resume. The CAD will be
strengthen as the day goes on as a cool stable NE flow pumps into
the damming region of the Piedmont. Models suggest that some areas
of light rain may develop/overspread portions of the Piedmont during
the afternoon before widespread rain arrives Friday night.
Even though the parent surface high will move offshore of New
England Friday, the cool stable dome will have already been enhanced
and firmly established. The coastal front is forecast to be pinned
at the immediate coast. As one storm lifts NE toward the central
Appalachians, another one will develop and take over near the
boundary along the SC coast Friday night. This low will then lift NE
along the coast early Saturday. There will be very little chance in
this scenario of the coastal front being pulled inland, thus
eliminating the severe risk over our region. However, a few elevated
thunderstorms are expected to be embedded in the large rain area
that overspreads the region Friday night, then ends from the
southwest Saturday morning. The storm will then lift away from the
region Saturday afternoon with dramatically lowering POP. However...
the northerly flow behind the system along with lingering moisture
in the low levels should keep any partial clearing confined to the
SW Piedmont Saturday afternoon. Highs will be held down again by the
residual CAD and then the persistent northerly flow as the storm
pulls away. Expect readings to be warmest where any breaks occur in
the SW Piedmont (possibly near 70). Most areas will stay in the
lower to mid 60s (which is a good 20 degrees below normal).
QPF will continue to be a tough call given the complexity of the
evolving storm and the hybrid CAD over inland areas. Not to mention
the deep south/Gulf coast convection potential. Even though models
continue to be generous with 1 to locally 1.5 inches, this may be
overdone in some areas. Flash flooding is not anticipated with the
lack of strong convection and with the FFG values running rather
high in the 3+ inch range in 6 hours. This is not expected to be
threatened. But 1 to 1.5 inches in 6 hours may result in some minor
flooding in urban and flood prone areas.
.LONG TERM /Saturday night through Wednesday/...
As of 3 AM Thursday...
Additional energy is expected to dive southward out of Canada
helping to close off into a mid/upper level low along the mid
atlantic coast late weekend into early next week, which will result
in continue chances for showers and possibly some storms depending
on the placement of the mid/upper low for Sunday and Monday (chance
of convection everywhere for Sunday and limited to just eastern
portions of the area my Monday). However, the best chance for precip
will be during the afternoon into the evening/more diurnally driven
convection. Highs Sunday and Monday are expected to remaining below
normal in the 70s. Highs Tuesday and Wednesday will return to more
seasonable values as the mid/upper low is expected to lift off to
the northeast and surface high pressure is expected to shift
offshore finally. Lows temps are expected to be near to slightly
below normal for the medium range.
.AVIATION /12Z Thursday through Monday/...
-- Changed Discussion --As of 700 AM Thursday...
Low ceilings and occasionally low visibilities as well will persist
today and tonight. Occasional rain and drizzle can be expected in
the region along with persistent MVFR becoming IFR CIGS at or below
1K feet today. Abundant moisture will continue the low ceilings
through tonight and into Friday. However, surface visibilities
should improve somewhat Friday before falling again to IFR with rain
and fog late Friday into Saturday morning. This occurs as a low
level NE flow strengthens out ahead of an approaching storm system
from the SW Friday night. This storm is expected to lift N of the
region Saturday afternoon.
The outlook for Saturday late through Sunday is for improving
aviation conditions as the widespread rain/fog move north of the
region between 12z-18z Saturday.
VFR conditions are expected Sunday into early next week.
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