Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 230111

Area Forecast Discussion
National Weather Service Raleigh NC
911 PM EDT Tue May 22 2018

A lee trough will linger over the srn middle Atlantic states ahead
of a cold front that will settle southeastward into the area late
Wednesday and early Wednesday night. Following high pressure will
ridge south across the region on Thursday.


As of 900 PM Tuesday...

A mid/upper level trough will approach from the west tonight,
allowing for a weakening band of showers and isolated thunderstorms
to move into western/northern portions of the area late this
evening/early Wednesday morning. However, the latest HRRR has
trended towards very little of this activity making it into central
NC. Given nocturnal stabilization and PW`s noticeably lower tonight,
with the KGSO sounding showing PW`s of only 1.21 inches this
evening, will lower pops some and only keep a low end chance across
the far west and north late this evening into early Wednesday
morning with a slight chance elsewhere. Low temps temps will remain
warm though for this time of year, generally 65-70 degrees.


As of 345 PM Tuesday...

At the base of a mid-upr low migrating ewd across Hudson Bay and
Quebec, a series of minor perturbations will sweep across the
Northeast and middle Atlantic Wed, then offshore by Wed night. Mid-
upr lvl flow will consequently strengthen slightly and veer to nwly
over cntl NC, with effective bulk shear values likely to increase
into the 25-30 kt range.

At the surface, a cold front will settle swd, in backdoor fashion,
across VA during the day, then into the nrn NC Piedmont very late
Wed afternoon and evening, where it will overtake a preceding, quasi-
stationary lee trough over w-cntl NC. The front, modulated by
convective outflow, will settle swd through cntl NC overnight. A
somewhat drier/lee humid/cooler air mass will follow, as post-
frontal high pressure ridges swd across the middle Atlantic region.

Initially scattered showers and storms are likely to focus along
remnant outflow from convection from the previous day/night; and
also along the lee trough. This activity is expected to become
numerous by late afternoon and early evening, as convergence/lift
increase with the arrival of the surface front. Storms are likely to
become semi-organized in a multi-cellular storm mode along common
outflow, with an associated strong to isolated damaging wind threat
as storm clusters propagate sewd, with the relative greatest
potential where the aforementioned bulk shear should be maximized
over the nrn Piedmont and nrn Coastal Plain.

The chance of showers and storms will linger overnight, particularly
over the srn half of the CWFA, as the (effective) frontal zone
settles swd. Any earlier severe threat will have diminished owing to
both nocturnal cooling and prior convective overturning.

Generally persistence temperatures in the mid-upr 80s are expected
on average, though modulated and shortened by convection/clouds,
with lows in the mid 60s to around 70 degrees.


As of 235 PM Tuesday...

Progressive high pressure over the Great Lakes will make a stab at
drying us out, pushing a front south of the area early on Thursday.
With the front along or south of the area, will have only small
chance PoPs along the southern tier counties Thursday into Thursday
night. Highs will be only mildly influenced by the front due to
strong insolation and should reach mostly mid 80s.

The high moves off the New England coast, with return flow beginning
to spread into the west Friday into Saturday. As such, chance
category PoPs in the west Friday taper off eastward, with all areas
in the low chance category on Saturday as we sit beneath an upper
ridge conducive to airmass thunderstorms in the resulting unstable,
but weakly forced environment. Highs both days will mostly reach mid
80s after mild morning lows in the mid and upper 60s.

The moisture transport from the south returns once again for the
late weekend aided by the Bermuda high and a developing low pressure
system in the Gulf of Mexico. The moisture return will increase
precip coverage Sunday and into early next week, and while there is
a lot of uncertainty as to the timing of forcing mechanisms driving
heavier convection, it will be diurnally influenced, and will
maintain high chance to likely PoPs Sunday through Tuesday. Highs
will show little variation from previous days, mostly mid 80s, with
morning mins in the soupier airmass closer to 70 each morning.


As of 720 PM Tuesday...

Showers and storms, other than a few extremely localized downpours,
have cleared central North Carolina by late evening Monday. Additional
showers may be possible near to slightly after dark at INT and GSO,
primarily related to the approach of a mid level trough and band of
upstream convection now over the central Appalachians. Storm
coverage is otherwise expected to remain isolated and/or of limited
with decreasing coverage as the night continues. Similar to Tue
morning, IFR-MVFR ceilings will be possible in the several hours
centered around 12Z, with rising CIGs and eventually shower and
thunderstorm development by Wednesday afternoon/evening.

Outlook: Otherwise, another round of sub-VFR ceilings will probably
result late Wed night-early Thu, owing to low level moisture
convergence along and ahead of the aforementioned frontal zone.
After relatively dry/VFR conditions Thu-Sat, moisture will increase
by Sun-Mon, with resultant increasing probabilities of convection
and morning stratus and/or fog during that time.





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