Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
312 PM EDT Thursday Oct 8 2015
Synopsis... high pressure will shift south of the area overnight in
advance of a cold front moving into the region Friday evening
through Saturday morning. Cool high pressure will build in from the
northwest Saturday night through Sunday.
Near term /tonight/...
as of 255 PM Thursday...
Zonal flow aloft will develop over the region today through
Friday...downstream of a broad positive tilted trough advancing
southeastward into the Great Lakes into the Central Plains. At the
surface...weak high pressure will shift south of the area overnight.
Very weak-low amplitude shortwaves embedded in the quasi-zonal flow
aloft will result in scattered cirrus clouds through the remainder
of the afternoon through tonight. These clouds could slightly impede
radiational cooling overnight...especially in the west. The
combination of these high clouds and light southerly return flow
will support slightly milder overnight lows in the upper 50s to
Short term /Friday and Friday night/...
as of 255 PM Thursday...
Positive-tilted trough extending from the Great Lakes to Central
Plains/middle MS valley will split on Friday...with a progressive
northern stream trough tracking through the northeast and into New
England...while a southern stream wave amplifies over the lower MS
valley and Tennessee Valley...moving into the southern Appalachians by
Rain chances Friday should generally hold off until after sunset
Friday...with rain chances increasing from west to east Friday
evening-Friday night with a broken band of showers expected to
accompany a cold frontal passage into the area between 00z Saturday
in the west to 09 to 12z in the east. The better rain chances and
higher quantitative precipitation forecast will be with a secondary area of Ana-frontal precipitation that
is forecast to Blossom over the area...in response to the amplifying
wave moving into the southern Appalachians. Took out any mention of
thunder as instability look too limited(~mucape 200 j/kg)given late
With rain holding off until after sunset...expect highs once again
in the upper 70s to lower 80s...perhaps a degree or two cooler in
the far northwest where cloud cover will be more opaque. Lows Friday night
ranging from upper 50s/near 60 northwest to middle 60s southeast.
Long term /Saturday through Friday/...
as of 300 PM Thursday...
Saturday and Saturday night: shortwave energy digging southeast through the
upper Midwest this afternoon will amplify as it digs through the
central MS river valey (fri) into the Tennessee Valley/deep south (fri
night). The wave will further amplify and close off into an upper
low over the southeast states (ga/SC/nc) on Saturday...then linger
along the southeast coast Sat night. Meanwhile...a cold front
associated/west a surface low attendant shortwave energy progressing from the
Great Lakes (fri) to the Canadian Maritimes (fri night) will become
increasingly west-southwest-east-northeast oriented as it approaches the Carolinas Friday
night...then track south/southeast through central NC early Saturday. The
latest 12z GFS/European model (ecmwf) have trended toward a wetter solution...showing
widespread precipitation Sat into Sat night as the upper low
interacts with the front expected to stall in vicinity of the
Carolina coast. With increased confidence on the evolution of the
synoptic pattern...have increased precipitation chances to categorical over
the bulk of central NC...lowest near the Virginia border and highest near
the SC border...with precipitation amounts ranging from 0.25-0.50". Given
northerly flow...overcast cloud cover...and precipitation /evap cooling/...
expect highs to occur early Sat morning...with temperatures falling into
the middle/upper 50s during the day. Expect lows Sat night ranging from
the upper 40s north/northwest to low/middle 50s southeast coastal plain.
Sunday and monday: the upper level low is expected to stall in
vicinity of the southeast coast sun/Mon. Lingering rain will be possible in
south/southeast portions of central NC on sun...though uncertainty is above
normal. Precipitation chances should increasingly become confined to the
south in SC or to the east along the Carolina coast.
Tuesday-friday: expect another upper level trough passage on
Tuesday...though guidance remains largely dry. Otherwise expect
continued dry conditions through the week. -Vincent
Aviation /18z Thursday through Tuesday/...
as of 145 PM Thursday...
Underneath scattered to occasional broken cirrus clouds...there is
high confidence that VFR conditions will prevail through this
evening. Overnight...light southerly winds will allow an increase in
low-level moisture...supporting areas of MVFR fog between 06 to 13z
Friday. Any fog will quickly lift to VFR at or above 14z with southwesterly winds
strengthening to 10 to 15kts in advance of a cold front moving into
the area from the west.
Looking beyond 18z Friday...in the wake of a cold front moving through
the area Friday night...an amplifying middle/upper level trough moving
into the region will result in widespread IFR conditions in
rain/showers Friday night and through the day on Saturday. VFR
conditions are likely to late from west to east late Saturday
through early Sunday as cool high pressure builds into the area.