Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 231909
Area Forecast Discussion
National Weather Service Raleigh NC
305 PM EDT Mon May 23 2016
.SYNOPSIS...An upper level low will move across the area today,
before tracking along the East Coast and away from the region on
Tuesday. A strong upper level ridge will build over the Southeast
through the remainder of the week.
.NEAR TERM /through tonight/...
As of 1125 AM Monday...
Minor tweaks made to the near term forecast. Have adjusted PoPs up
over the northeast third of the CWA to account for patchy light rain
through mid day/early afternoon. Otherwise expect scattered showers
and a thunderstorm or two across the region from mid afternoon
Pesky upper level low has begun push to the east-northeast and on
track to exit our region by late in the day and well offshore
tonight. Spokes of vorticity will continue to pivot around this
feature with one axis currently working its way across our northern
counties. This feature will continue to progress south-southeast,
possibly triggering additional shower development across the
southern counties by mid afternoon.
While a thunderstorm possible, parameters are not quite there for
the potential for severe storms. The shear is too weak and
instability even weaker.
Temperatures this afternoon highly dependent upon extent of cloud
coverage and showers. Where clouds are thickest/more prominent and
potential for rain highest (ne third), temperatures in the 60s will
be the rule. Where peeks of sunshine occur, temperatures should warm
into the 70-75 degree range. Expect the warmest temperatures in the
far south and southwest where mixture of sun/clouds expected. -WSS
Height rise aloft and high pressure building in from the west will
rapidly diminish precip coverage this evening, while skies slowly
clear behind the departing upper trough. Lows in the low/mid 50s. -22
.SHORT TERM /Tuesday and Tuesday Night/...
As of 340 AM Monday...
While the center of the mid/upper-level low will be in the process
of lifting up the coast of the northern Middle Atlantic and
Northeast...a couple of low amplitude impulses are forecast to wrap,
in NW flow on the WSW periphery of the departing low, across eastern
VA/NC through early-mid afternoon Tue. Residually steep mid-level
lapse rates /6 to 6.5 C/KM/ over the NE Piedmont and Coastal Plain,
and diurnal heating into the lower 80s, will contribute to perhaps a
couple of hundred J/KG of MLCAPE there, where an isolated
shower/sprinkle (POP of only 10-15 %) may occur before following
strong height rises aloft and an associated subsidence inversion
overspread the region.
One more night in the 50s, to around 60 degrees, is expected in
continued height rises in NW flow aloft Tue night.
.LONG TERM /Wednesday through Monday/...
-- Changed Discussion --As of 305 PM Monday...
Wed-Fri: Warm and mainly dry. The mid level pattern will feature
longwave troughing over the western CONUS with ridging in the east,
albeit with a weakness aloft which will extend from a weak low over
the central Bahamas northwestward across SW NC. At the surface,
Bermuda-centered high pressure will ridge narrowly westward across
the Southeast, yielding a light low level flow with minimal moisture
influx. The above normal heights aloft and resulting subsidence,
along with the absence of lift mechanisms and the lack of a good
moisture source, will help suppress deep convection over central NC.
While the aforementioned weakness in heights aloft to our SW may
lead to scattered afternoon storms over the higher terrain, the
steering flow pattern does not favor movement of any such convection
into our area. Thickness will be well above normal, supporting highs
each day in the mid 80s to around 90 (Thu appears likely to be the
warmest of these days) with lows in the lower to mid 60s.
Sat-Mon: Lots of uncertainty in the details, although guidance
continues to favor temps staying slight above normal through the
upcoming holiday weekend, but with an increasing chance of
showers/storms by Sun/Mon. The western end of the surface ridge axis
will pivot northward (following the strengthening of the Atlantic
mid level ridge extending into the mid Atlantic region), and this
will allow a long-fetch southeasterly flow to stream increasing
amounts of moisture into the Southeast. Meanwhile, the Bahamas mid
level low begins to drift to the NW into the height weakness toward
the Southeast states, and model solutions are converging toward some
similarity at the surface, showing either an inverted trough or low
tracking northwesterly toward the Southeast coast. It is far too
early to say whether or not this feature might have tropical or
subtropical characteristics, but regardless, we are still likely to
see an increase in clouds and precip chances as mid level heights
fall and moisture increases and deepens through the low levels.
Thicknesses support temps slightly above normal, tempered by
the increase in clouds. -GIH
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.AVIATION /18Z Monday through Saturday/...
As of 125 PM Monday...
Ceilings varying between MVFR across the northeast piedmont and the
coastal plain to low end VFR across the western and southern
piedmont will persist through sunset as energy rotating around an
upper level low over far northeast NC. As the atmosphere heats
up, scattered showers and isolated thunderstorms will blossom over
the region. The greatest coverage will occur between 20Z-00Z.
After 00Z, shower coverage will decrease. Later tonight, as
the low pulls farther away, skies will gradual clear, clearing
first over the western/southern piedmont and sandhills, and last in
the vicinity of KRWI.
Pockets of MVFR fog may occur early Tuesday morning. Otherwise,
high pressure will begin to exert its influence on our weather.
A prolonged period of VFR conditions is anticipated across central NC
Tuesday through Saturday.