688 
FXUS62 KRAH 031708
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1208 PM EST Sun Mar 3 2019

.SYNOPSIS...
An area of low pressure will move across central North Carolina
this evening bringing the threat of heavy rain as well as an
isolated severe storm towards the southern Coastal Plain. Much cooler
and drier weather will prevail for early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1155 AM Sunday...

Just some minor adjustments made to hourly temperatures and 
dewpoints, and resultant slightly cooler high temperatures across 
cntl NC, amidst a widespread, lowering overcast and expansion 
of initially patchy light/stratiform rain today. Otherwise, two 
notable forecast concerns will result from the track of a primary 
surface cyclone from e-cntl MS at 17Z, enewd across cntl Al and GA 
this afternoon and cntl SC and e-cntl NC this evening and early 
tonight: 1) a small spatio-temporal risk of damaging wind gusts 
and/or an isolated tornado over the far srn Sandhills and srn 
Coastal Plain, along and south of the track of the foregoing 
cyclone, and 2) a moderate to high probability of a stripe of one to 
one and a half inches of rain focused over the sern half of cntl NC, 
in the deformation axis immediately north of cyclone - both of which 
have been described in detail below.


Previous discussion as of 430 AM Sunday...

A stalled surface front remains across central South Carolina
this morning with weak isentropic upglide occurring over central
North Carolina. On water vapor the next upper level disturbance
to affect the area can be seen over Kansas. This morning the 
wave will eject east through Missouri with surface cyclogenesis 
occurring across Mississippi/ Alabama in response to the DCVA 
and corresponding 500 MB height falls. As the surface low is 
forming this morning the stalled boundary, currently across 
central South Carolina, will begin to move north as a warm 
front. Latest runs of the GFS/ ARW/ NMM all show pretty good 
coverage of weak rain in the warm air advection wing, but dry 
air continues to be advertised in the forecast soundings. High 
res models are also indicating pretty good coverage right now of
light rain, but this has not materialized. Overall thinking is 
that the initial morning precipitation as advertised by the high
res models is overdone. 

By the early afternoon hours embedded pockets of PV in the 
southwest flow, will traverse the region which will likely help 
to get slightly better coverage. The NAM shows this occurring 
earlier (late morning). This afternoon the wave will be moving 
into Tennessee with the surface low deepening across Georgia/ 
South Carolina. The current suite of global models has the warm 
front making it into central North Carolina before stalling. 
The NAM Nest, ARW, NMM have the warm front stalling across the 
Sandhills and Coastal Plain. This appears to be the most likely 
scenario given the track of the wave. The surface low will then 
track northeast along the stalled baroclinic zone. North of the 
stalled front, elevated instability does exist for isolated 
thunder with the main threat being heavy rainfall. The upper 
level support with this feature is impressive. The jet streak is
forecast to strengthen over central PA to near 150 kts with 
central NC in a RRQ. Widespread DCVA and 500 MB height falls 
will also be occurring at this time. PWATs at this time are 
forecast to be around 1.40" or at max values. Along and just 
northwest of the surface low track global models are advertising
a swath of QPF in the 1 to 1.50" range. Given the strong 
forcing mentioned above and ample moisture these totals make 
sense. The latest GEFS and EPS means are slightly on the lower 
end of the totals mentioned above. With area creeks and streams 
already running high, this may produce additional river flooding
across the area. 

The other concern here will be the potential for severe storms.
The main threat at this time appears to be well south of the
region. Forecast soundings do advertise a brief window were an
isolated storm or two could become severe across our far
southeastern counties. SFC to 1 KM bulk shear values are near 50
kts at this time as LLJ quickly strengthens. SB CAPE is limited
here though. Temporally the window is also small with only a
brief overlap in shear and instability. SPC has brought the
marginal risk across our far southeastern counties given the
forecast track of the warm front. Due to the forecast shear, 
instability, and track of the surface low there is a marginal
risk for severe weather across the far southeast. Have included
a mention in the HWO for this. 

Late Sunday night, the surface low will quickly pull northeast
with a surface cold front sweeping through the counties.

&&

.SHORT TERM /MONDAY/...
As of 430 AM Sunday...

Drier and cooler weather is in store for Monday as the upper
level trough axis will swing east of central North Carolina.
Strong CAA will take hold Monday morning with 850 MB
temperatures falling towards 5 degrees C below zero. NAM
forecast soundings are showing some mid-level moisture remaining
across the region Monday afternoon while the GFS has mostly
clear skies. For now have raised sky cover a bit, but thinking
is that skies will remain more clear than not. Given the above,
the thinking is for high temperatures to be near 50 degrees with
mid 50s towards the Sandhills. This would be about 5 to 10
degrees below normal for this time of year.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
As of 400 AM Sunday...

Monday night: DCVA resulting from a series of low-amplitude 
disturbances rotating east through the base of the mean upper trough 
Monday night and into Tuesday will result in renewed lift that will 
lead to clouds re-developing across the area Monday night and 
Tuesday. The GFS has backed off considerably with precip across the 
area Monday night/early Tuesday, with the model consensus now 
keeping the bulk of measurable precip south/southeast of the area, 
in proximity to weak surface low development across SC. Added a 
slight chance pop across the far SE zones(Sampson and Cumberland 
counties)  around daybreak Tuesday; and with sfc wet-bulbs right 
around freezing and the absence of any warm air aloft, could see a 
brief period of very light snow or flurries with no expected 
impacts. Lows ranging from near 30 north to mid 30s south. 

Tuesday through Wednesday night: An expansive surface high from 
Canada will advect significantly colder air into the region during 
this period. H8 temps are forecast to bottom out between -10 to -15 
C on Wednesday, which is a good 1 to 2 S.D. below normal. 
Temperatures during this period will average a good 10 to 20 degrees 
below normal, with highs Wednesday, despite abundant sunshine, 
struggling to make it into the upper 30s to lower 40s. Overnight 
lows well down into the 20s, with some teens possible in the 
typically colder spots Tuesday night and again Wednesday night. 

Thursday through Saturday: Eastern US trough lifts out of the region 
on Thursday with a transition to a more zonal and progressive flow 
pattern to end the week. Temperatures will begin to moderate, but 
will stay remain below normal on Thursday as the parent high across 
the area begins to break down.

Significant model differences arise Friday and into the weekend-in 
the handling of a pair of Pacific shortwave troughs ejecting east 
across the CONUS.  The EC is significantly more sheared/weaker with 
the lead shortwave trough into the eastern US on Friday, delaying 
the better rain chances until late Friday and into Saturday. 
Meanwhile, the GFS brings precip chances into the area as early as 
Thursday night and Friday. Given antecedent cP airmass in place, wet-
bulb cooling and favorable nocturnal timing of precip could support 
a brief period of frozen or freezing precip at onset across northern 
portions late Thursday night/early Friday morning, before changing 
over to all rain. Given all of the uncertainty will maintain low 
chance pops Fri through Saturday with temperatures moderating to 
near or above normal by the weekend as southerly return flow becomes 
established.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
As of 700 AM Sunday...

24 hour TAF period: MVFR conditions are slowly progressing in
from the southwest this morning as isentropic upglide commences.
Most of the morning hours will likely remain dry as forecast
soundings take sometime to moisten up. This afternoon a boundary
that is currently stalled across central South Carolina will
drift north as a warm front with ceilings continuing to lower
across the TAF sites. Latest high res guidance has the warm 
front making it to just around KFAY before stalling. South of 
the warm front, thunder will be likely with an isolated threat 
just north of the boundary where some elevated instability 
exists. 

A surface low is then forecast to move across the Sandhills/ 
Coastal Plain this evening along with heavy precipitation. The
surface low looks to be far enough north to require the mention
of thunder in KFAY with the potential for some gusty winds as
well with the convection. There will also be a brief window here
with the strengthening LLJ to allow for low level wind shear to
be present. In fact, at 2 kft AGL the NAM is showing winds
approaching 60 kts. As the surface low exits the region to the
northeast a surface cold front will sweep through the TAF sites.
The 925 MB front is slightly lagging behind which might delay
clearing a bit, but an overall recovery to VFR early Monday
morning is expected. Behind the cold front winds will pick up
with gusts of 20 to 25 kts possible.

Looking ahead: Mostly VFR conditions are expected through the
week, though some transitory MVFR will be possible Tuesday 
morning.

&&

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

&&

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