Area Forecast Discussion
Issued by NWS Wilmington, NC

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FXUS62 KILM 211938

Area Forecast Discussion
National Weather Service Wilmington NC
338 PM EDT Fri Jul 21 2017

Hot and humid conditions will prevail today through the weekend
with only isolated rain chances. Storms will increase next week
as a series of weak fronts approach the coast, with near normal
temperatures for late July.


As of 300 PM Friday...Steep low level lapse rates have combined
with just enough low level moisture to pop some cu throughout
the forecast area, especially along the sea breeze boundary
where moisture advecting in off the ocean provides a little more
fuel. However, it is very dry above 850 mb so still looks like
the remainder of today will be a dry one with only the odd spot
shower or thunderstorm possible. Best chances for anything look
to be well inland in closest vicinity to the persistent thermal
trough. As this is all diurnally-driven, expect overnight to be
clear and dry with lows in the mid 70s.

Similar story for Saturday, with diurnally-driven slight chance POPs
at best during the afternoon and early evening. It is possible that
a heat advisory may be required for heat index values of 105F or
higher, but confidence is not high enough at this time for issuance.
A consensus of guidance has actual temperatures for Saturday much
the same as today, with highs from around 90 near the coast to the
mid 90s inland.


As of 330 PM Friday...Overall expect hot and humid weather with
heat advisory conditions over most of area on Saturday. A Broad
trough in the mid to upper levels extends just far enough south
into Carolinas as to prevent strong ridging to build in from
west or east to push temps high enough for any record heat, but
enough to produce temps a good 3 to 7 degrees above normal.
Temps should reach into the mid 90s over most of the area. Temps
overnight will remain well into the 70s most places. SW sfc
winds around Bermuda High will become quite gusty Sun aftn into
Sun eve as sea breeze and trough inland become more pronounced,
and should see winds increase further Sun night as trough pushes
east and tightens pressure gradient.

Both the Atlantic ridge and strong ridge over central CONUS
seem to exert enough influence with enough dry air and
subsidence to keep area mostly rain free, but with with
troughing inland and decent sea breeze on Sunday, can not rule
out an isolated shower Sat night into Sunday. By Sun night, the
mid to upper trough begins to dig a bit more south and a
shortwave rides by as well as a disturbance moving up the coast
from the south. This will all lead to better chc of shwrs/tstms
late Sun into Mon.


As of 300 PM Friday...A shortwave trough moving through New England
on Monday night, and a large upper low developing across southern
Quebec late in the week will help put a dent in the heat. Falling
upper level heights associated with these systems will shift the
core of the upper ridge (and its associated heat) farther west into
Texas and New Mexico. Don`t expect a cleansing frontal passage by
stretch, (06Z GFS ensemble 850 mb temps don`t fall below climatology
next week) but at least we should lose the 100+ heat indices for a
few days.

Both the GFS and ECMWF show a cold front moving into northern North
Carolina on Tuesday. The GFS then sinks the boundary a little
farther south by Wednesday morning. There are enough GFS ensemble
members showing the front making it into South Carolina that I`m
leaning toward the GFS in this case. This front should enhance the
coverage of t-storms Tuesday night and Wednesday, and I`ve placed my
highest forecast PoPs (50-60 percent) of the extended period during
this period.

With a progressive upper level pattern to our north, surface high
pressure will push off New England and out into the western Atlantic
Thursday and Friday, probably with enough southerly wind developing
over the Carolinas to lift the front or its remnants back to the


As of 18Z...High confidence in VFR for all terminals through the
TAF valid period. Very dry air aloft makes precipitation of any
sort very unlikely through the period.

Extended Outlook...VFR through Sunday. Brief MVFR/IFR possible
in scattered showers and tstorms Mon and Tue due to a slowly
approaching cold front from the NW.


As of 300 PM Friday...Circulation around high pressure over the
western Atlantic will keep winds from the SW, generally in the
10 to 15 kt range, through the period. Seas will likewise show
little variation, running right around 3 ft through Saturday.

As of 330 PM Friday...Precautionary headlines may be needed Sun
into early Mon as winds increase to 15 to 20 KT winds and seas
reach 4 feet offshore and possibly up to 5 ft. The afternoon sea
breeze circulation will keep winds gusty and seas choppy near
shore Sun afternoon to early evening. Very little TSTM activity
is expected until Sun night into early Mon when activity will
increase across the waters as trough shifts farther east toward
the coast.

As of 300 PM Friday...Bermuda High Pressure well offshore will lose
its influence on our weather by the middle of next week as low
pressure in the Canadian maritime provinces pushes a cold front down
the U.S. East Coast. This front is shown by the latest GFS and ECMWF
models to make it down to near Hatteras on Tuesday. Models diverge
slightly on Wednesday as the ECMWF keeps the front stalled to our
north and the GFS brings it down to the Myrtle Beach vicinity
Wednesday morning. Regardless of which solution is correct, the
frisky southwest winds of the weekend should diminish by Tuesday
within the weaker pressure gradient near the front. Unfortunately
thunderstorm potential should also increase as the front approaches.





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