FXUS62 KRAH 191934

Area Forecast Discussion
National Weather Service Raleigh NC
334 PM EDT Thu Jul 19 2018

Weak high pressure will extend across the region today then drift
east on Friday. An area of low pressure will approach central NC
from the west on Friday and stall just to our west this weekend.
This will lead to increasing chances for showers and storms,
beginning late Friday and especially Saturday and Sunday.


As of 340 PM Thursday...

Cool and dry day for July standards this afternoon with
temps in the mid to upper 80s and dewpoints very comfortable in the
mid to upper 50s. With the front well south of the area, the
satellite is mostly clear with some stratocumulus across the area
but otherwise no precipitation is expected. Overnight, some stratus
could roll into southern areas but the bulk of this should be later
in the morning on Friday. Overnight lows in the mid to upper 60s.


As of 340 PM Thursday...

Forecast starts to become more complicated on Friday as
an upper level trough begins to dig into the area from the
northwest. At the surface a low pressure system will move up the
Carolina coast from the south. Meanwhile back across the Midwest a
stacked low pressure system over the Great Lakes will begin to
influence our weather from the west. For the early part of Friday,
central NC will be squeezed in between these features and should
remain fairly dry although cloud cover will begin to increase from
the south as moisture returns to the area, sending our 50s dewpoints
away for maybe the remainder of the summer.

Precipitation chances will begin to increase in response to the
southern low moving up the coast. Therefore expect showers and
thunderstorms to first begin in the southeast. Much of the
convective activity should remain east of US 1 as the afternoon goes
on, but there will be chances for showers in the west as well. The
heaviest rainfall main remain east of I-95. One thing to take into
account is that high resolution models have been very uncertain
about the track of this feature with some of the models taking it to
the east and other right up through central NC.

As far as the timing is concerned we could see showers begin to pop
up around noon but the bulk of the heavier activity should be later
in the afternoon. For now it looks like much of the activity should
be sub-severe and SPC has the area in general thunder for Friday but
cant rule out a severe storm or two as shear begins to increase as
the surface low approaches. Showers and storms will shift to
northeastern areas Friday night as the low continues up the coast.

Temperatures are tricky as with more clouds in the east,
temperatures may end up lower there than in the west. Generally
expect mid 80s across the area. Friday night we will see a
moderation in low temperatures into the upper 60s to near 70 degrees.


As of 340 PM Thursday...

The long term still looks to be characterized by above normal
precipitation and near to slightly below normal temperatures.
This continues to be supported by the GEFS and GEPS illustrating
below normal heights through the weekend.

On Saturday a surface low pressure will be pulling northeast
with most of the region likely initially dry. The very end of
the ARW and NMM runs would tend to indicate this. GFS and ECMWF
PWAT fields also show this with dry air across the Triangle.
Saturday afternoon into evening the vertically stacked upper
level low will drift southeast with DCVA moving overhead.
Forecast soundings do destabilize at this time with 700 MB to
500 MB lapse rates steepening. Sfc to 6 km shear values also
increase to around 40 kts as the upper level jet strengthens
just to our west. As this happens the RRQ will move overhead
with upper level divergence strengthening. Due to the mentioned
above some storms could be strong and with the strengthening low
level jet training of some storms will be possible (as seen by
the corfidi vectors). SPC also has us in a day 3 marginal.

Sunday into Monday the upper level low will head south as a
mid-level ridge over the Atlantic Ocean nudges west. This will
keep precipitation around the area through Tuesday as PWATs
remain near max values. On Wednesday the remnant upper level low
will be pulled southwest around an amplifying mid-level ridge
across the southwest. At the same time an upper level low over
southern Canada will pulling east. Over the last couple of model
runs there has been some hint of drier air possibly moving in
Wednesday and Thursday as the ridge nudges west. Now with the
upper level trough over Canada heading east this doesn't
completely happen. For now confidence remains low here and will
keep PoPs trended towards climo.


As of 150 PM Thursday...

24 Hour TAF Period: VFR conditions will dominate the TAF period with
the exception of the possibility of some MVFR ceilings at KFAY very
late in the period on Friday afternoon as moisture begins to
approach from the south. Winds are mainly east northeasterly at 5-10
kts gusting on occasion to 15 kts. No precipitation is expected.

Long Term: A wetter period will begin Friday night and continue well
into the extended forecast as high pressure off the coast and an
upper level low will combine to keep precipitation over the eastern
seaboard for many days. Adverse conditions are possible beginning
Friday night and through the weekend into next week.




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