Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 160242
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
942 PM EST Fri Feb 15 2019

.SYNOPSIS...
A surface low will track east along a cold front that
will settle south through the area tonight through early Saturday.
A series of upper levels disturbances and fronts tracking
through the region will result in very wet and unsettled conditions
Sunday through the upcoming week.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 945 PM Monday...

Main update to the forecast this evening was to slow down the
onset of precipitation. Surface cold front is currently in
western North Carolina with virga moving across the area. At 250
MB a strong sub-tropical jet extends from western California all
the way east to Nashville. At 500 MB a shortwave was analyzed
around Kansas/ Missouri. Comparing current 500 MB heights shows
the ECMWF and GFS are slightly underdone with the amplification
of the wave. Looking at observations in Tennessee it took
sometime for measurable precipitation to occur. This makes sense
as the main DCVA and 500 mb height falls are holding slightly
back (and low level WAA). The better chance of precipitation
looks to hold off until around 6-9z as the surface cold front
sags south. With winds turning from the north isentropic upglide
will commence. Just after sunrise Saturday morning surface low
pressure will be located near Georgia/ South Carolina with the
250 MB jet streak axis centered to our southwest. This will
place the CWA in a LFQ (favoring upper level divergence). As
mentioned above, lift looks impressive thanks to multiple
sources (the DCVA, surface cold front, and LFQ). Saturday
morning the surface front will pull east across northern South
Carolina with widespread precipitation over central North
Carolina. Across the northern zones high temperatures will
likely occur in the morning as the cold front sags south with
temperatures falling through the day. Given the slightly
stronger analyzed wave have gone with a correspondingly faster
frontal passage as well. Saturday afternoon the surface low will
move off the coast with dry mid- level air working in behind.
Weak omega still remains on the backside and with only the low
levels remaining saturated (helping to limit warm rain
processes) light rain/ drizzle will be possible.


Prev Discussion -->
Overview: A shortwave trough/compact upper low crossing the Great
Lakes into southern New England will drive a sfc cold front(currently
moving into the central and southern Appalachians) into central NC
late this evening and through the overnight hours.  A series of
shortwave perturbations embedded within the quasi-zonal flow aloft
across the southern CONUS, the most significant of which will cross
through the area between 12 to 18z Saturday; will consequently induce
a surface wave along the front as it settles south across the area.

Initially this evening and through the early overnight hours, precip
will be light and patchy. However, strengthening low-level moisture
convergence INVOF the eastward tracking surface low, in-tandem with
increasing forcing divergence in the left exit region of a 140-150
kt jet spreading east across the Carolinas, will cause precip to fill
in with a period of moderate rain spreading east across the area
between 09 to 15z. Shortly thereafter, as the surface low and cold
front pass east and south of the area, drying aloft will
result in precip tapering off from west to east, though there is
the potential for some lingering drizzle well into the afternoon,
given low-level saturation. Expect rainfall amounts to average a
solid 0.50" to 1.0" across the area.

Temperatures overnight are expected to remain mild south of the
front, primarily south of highway 64. Across the north, cooler air
will begin to advance southward prior to daybreak. Lows tonight
ranging from lower to mid 40s north to mid 50s south. Expect nearly
steady temperatures until the low and front passes through the
area, with temperatures slightly falling thereafter.

&&

.SHORT TERM /SATURDAY NIGHT/...
As of 245 PM Friday...

Anticipate variably cloudy skies with some clearing possible across
the far north-northeast underneath a low-level dry air ridge wedging
south into the area. Weak overrunning may cause some patchy
light rain or drizzle occur across the southern Piedmont overnight.
Low level cold air advection will continue, sending temperatures
down into the lower 30s across the north, and mid-upper
30s across the south.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
As of 200 PM Friday...

A persistent, generally wet and unsettled pattern is in store for
most of the long term period.  The main features of this pattern
include an upper ridge centered over or just east of the Bahamas, a
moist WSW mid and upper flow around this ridge and over the
Carolinas, and a CAD ridge anchored over the Piedmont which will be
occasionally and briefly interrupted by the passage of a series of
cold fronts.  In general, this pattern will favor high-chance and
even likely PoPs during much of the long term period, with QPF
estimates of 1-3 inches of rain from Sun through Fri. The best
chance for any pause in this wet pattern may be late Monday into
early Tuesday as we briefly see some drying in the wake of early
Monday`s cold fropa. Otherwise, temps should be warm enough this
entire period to preclude any P-type concerns other than rain,
except for a "very brief" period Tuesday night when forecast
soundings over our western Piedmont counties suggest it may be
barely cold enough for a "very brief" period of wintry mix with the
rain. Of course we`ll be evaluating that potential during the coming
days, but for now, expecting most if not all rain as p-type during
this time.

Temps during the long term period will be largely dependent on where
you are in relation to the CAD and timing and positioning of the
cold front and rain episodes.  Generally speaking though...look for
the coolest readings across the Triad during CAD and wet times, and
warmest across our SE zones when the warm front or the wedge front
will be positioned north/west of those zones.

&&

.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
As of 730 PM Friday...

A cold front analyzed at 00Z from wrn VA swwd through ern TN will
settle ssewd into cntl NC tonight, with following nly to nely
surface winds that will increase into the 10-15 kt range, with gusts
up to 20-25 kts, through Sat afternoon. Meanwhile, an area of low
pressure centered over the ArkLaTex this evening will track enewd
along the foregoing front, and across the Carolinas on Sat. The
approach of that low pressure will cause a shield of rain and IFR-
MVFR ceilings and visibility restrictions to spread newd across cntl
NC late tonight through early Sat afternoon, heaviest between 11Z-
17Z.

Outlook: Drier air will then spread swd from VA behind the area of
low pressure by Sat night, at which time ceilings may lift to MVFR
or even low VFR, particularly from Piedmont sites ewd to RWI.
However, another wave of low pressure will track across the
Carolinas and result in the redevelopment of rain and IFR-MVFR
conditions across cntl NC late Sun and Sun night, followed by VFR
conditions Mon through early Tue. Yet another wave of low pressure
will cross the Carolinas with another round of rain and sub-VFR
conditions late Tue and Tue night.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...CBL
NEAR TERM...Haines/ CBL
SHORT TERM...CBL/WSS
LONG TERM...NP
AVIATION...MWS


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