Area Forecast Discussion
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FXUS62 KRAH 220143
Area Forecast Discussion
National Weather Service Raleigh NC
940 PM EDT SAT MAY 21 2016
.SYNOPSIS...Surface low pressure and an upper level disturbance
over the region will move northeastward tonight. A strong upper-
level low pressure area will settle over the area Sunday through
Monday, producing unsettled weather. Warmer and drier weather will
follow from Tuesday through late week as the upper low moves
offshore and high pressure builds across the area.
.NEAR TERM /through tonight/...
As of 940 PM Saturday...
Primary forecast change with this update was to adjust toward
reality, raising short term pops across the southern CWA, and
reducing them across the north. Latest surface map shows the strong
low off Delmarva and weaker low over the southern Piedmont,
connected by a frontal zone that is slowly sliding to our SE. Storms
were only able to achieve marginal severity late today into this
evening given poor mid level lapse rates which hindered updraft
growth, although the current scattered storms over the south will
continue to feed on marginal instability and a favorable deep layer
shear environment in place as they track toward the SE over the next
few hours. Otherwise, the loss of heating and subsequent
stabilization behind this band of convection should limit coverage
and upscale growth of any subsequent showers or storms. However,
there remains a fairly potent vorticity maximum diving ESE into the
southern Appalachians, and this feature acting on lingering low
level moisture (the result of weak low level flow) could spawn
additional isolated showers and perhaps another storm or two into
the overnight hours, diminishing late as the southern Piedmont low
sinks to our south and southeast and the DPVA departs. Low level
moisture will deepen further over the northern and eastern CWA as it
advects in from eastern VA on the back side of the offshore low, so
will maintain cloudy skies there through daybreak, while areas in
the southwest and western CWA should see a trend to partly cloudy
skies overnight. Lows 55-61, with dewpoints dropping a bit across
the south as cooler air spills in. -GIH
.SHORT TERM /Sunday and Sunday Night/...
As of 330 PM Saturday...
Unsettled weather will continue on Sunday as a deep upper low, 2 to
3 SD below normal, becomes centered over northeastern NC by Sunday
night. DCVA and steepening mid-level lapse rates coincident with
peak but tempered daytime heating will support scattered showers.
Expect highest POPS invof of the upper level core and deepest
moisture across the NE coastal plain/piedmont.
Temperatures will continue to run below normal underneath the
anomalous negative height anomalies. Highs ranging from upper
60s/near 70 northeast to mid 70s southwest.
.LONG TERM /Monday through Saturday/...
As of 230 PM Saturday...
Monday and Monday night: To start the day off on Monday, a closed
upper low is progged to be over northeast NC and it will make its
way eastward/northeastward throughout the day. As such, shower
chances will continue, but will likely stay confined to the
northeast half of the forecast area. Any precip is expected to come
to an end Monday night as the upper low slowly pulls away from the
region. Temps will remain below normal given the proximity of the
upper low and associated cloud cover/precip, with highs expected to
be in the lower 70s across the northeast and the mid/upper 70s
further to the southwest. Overnight lows should fall into the mid
Tuesday through Saturday: Conditions should dry out by Tuesday as
the upper low pulls further away and shortwave ridging builds over
the region. However, one model is now showing one last piece of
energy rounding the backside of the departing upper low and
triggering some precip across the northeast. Given the lack of other
model support, have kept the forecast dry for now but will keep a
close eye on it. Otherwise, the ridge that will build in, will keep
the main storm track to our north, resulting in mostly dry
conditions through the end of the week. There are indications that
the ridge may weaken some towards the end of the forecast period,
allowing an uptick in mostly diurnal type convection. However, there
is some disagreement among the models with regard to this and
therefore, will just show an increase in clouds and bring in a
slight chance of precip. Temps will gradually moderate through this
time frame, from mostly lower 80s on Tuesday to mid/upper 80s by for
the remainder of the period.
.AVIATION /00Z Sunday through Thursday/...
As of 715 PM Saturday...
24 hour TAF period: A cluster of showers and thunderstorms will move
east through the area between 00z-06z, resulting in local IFR
conditions. Model guidance suggests the re-development of low
clouds/stratus and possibly some fog between 06 to 12z, especially
across central and eastern terminals(KRDU,KFAY,KRWI). Drier air
advecting into the area behind the a surface front is expected to
preclude stratus development at KINT and KGSO.
The low ceilings/stratus across central and eastern areas will be
slow to lift through the day on Sunday morning, with the potential
for MVFR ceilings to persist at eastern/northeastern NC(KRDU and
KRWI)until late in the afternoon. Meanwhile...western and southern
most terminals could see VFR conditions return by mid morning. A
deep upper low moving over the region will bring scattered showers
across the area on Sunday, with greatest coverage expected across
the east/northeast invof of the upper low.
Beyond 00z Monday: The risk for sub-VFR conditions with scattered
showers will continue through at least mid-day Monday as a closed
low gradually moves south across eastern NC. VFR conditions expected
to return by Tuesday and remain for the mid-week period as the
closed low moves east and short wave ridging moves over our region.