519 
FXUS62 KILM 062321
AFDILM

Area Forecast Discussion
National Weather Service Wilmington NC
621 PM EST Sat Jan 6 2018

.SYNOPSIS...
Arctic high pressure over Illinois will build into the Carolinas  
Sunday. The frigid air of Arctic origin, will move offshore 
Monday, with temperatures rebounding up to normal levels. A 
weak cold front will move through Monday night, with high 
pressure building down behind it through mid week. Rain chances
will increase late Thursday and Friday, as a warm front lifts 
north, followed by a cold front into next weekend.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 621 PM Saturday...GOES-E simple water vapor RGB channel 
illustrates nicely the frigid cold pool/trough, dippings its 
wintry toes into the heart of the Gulf coast states presently, 
with progress of the upper trough being made to the S and the E.
Areas of snow-pack coupled with clear sky and current readings 
in the 20s at 6 pm, will bring a deep cold overnight of single 
digits and teens. No noteworthy changes to the frigid forecast. 
With minimum air temperatures like these, not a great deal of 
wind will be needed to reach wind chill advisory criteria, and 
this product remains posted for early Sunday.

As of 300 PM Saturday...This extraordinary cold wave is breaking 
water pipes and breaking climate records stretching back 100 years. 
Lake Waccamaw is freezing over, along with our tidal creeks and 
salt marshes. Tundra Swans were spotted a few days ago in the 
Cape Fear River behind Carolina Beach, and local populations of 
pelicans and egrets are experiencing high winter mortality. 
We're approaching the end of our famed Southern Hospitality for 
this visiting arctic airmass and can't wait to see it leave the 
area on Monday.

Until then, another extremely cold night is in store for the eastern 
Carolinas. The center of the arctic high will move from Indiana into 
Virginia by daybreak Sunday. Excellent radiational cooling over a 
few inches of persistent snowpack should allow temperatures to fall 
to 6 to 12 degrees tonight. It wouldn't surprise me if a few of our 
normally cold spots in Robeson or Pender counties approached zero. 
Areas of devoid of significant snow cover from Elizabethtown and 
Whiteville south into the Myrtle Beach/Pawley's Island area should 
run several degrees warmer with 12-17 degrees forecast for this 
stripe. My forecast for Wilmington of 9 degrees, should it verify, 
would be the coldest reading since the Christmas snowstorm of 1989 
over 28 years ago.

Aside from a few cirrus streaming in during the afternoon, sunny 
skies again on Sunday will only have limited success melting the 
snow as temperatures struggle into the 32-37 range.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
As of 300 PM Saturday...One last cold night forecast for Sunday 
night as this seemingly never-ending arctic blast finally retreats. 
Surface high pressure will be centered across the eastern Carolinas 
early Sunday night before slowly lifting eastward into Monday 
morning. This may be forecasted to occur too quickly, as the E NC 
snow pack (how weird is that to write) reinforces the cold high 
pressure and likely causes it to linger longer than guidance 
suggests. This will create a very weak gradient and strong 
radiational cooling will begin after dark. However, WAA just above 
the surface, which is actually beneficial to radiational cooling, 
will causing increasing moisture trapped within the near-surface 
inversion, and stratus may develop overnight. Even if cloud cover is 
delayed, increasing moisture within this layer will inhibit ideal 
cooling in a "dirty IR window" type setup. Additionally, increasing 
cirrus is expected from west to east, so although mins will be cold, 
they will be warmer than the past several nights. Expect lows 
falling into the upper teens across NC and inland SC, just above 20 
elsewhere.

Monday is a tricky forecast as the guidance suggests highs rising to 
near normal for the first time in 2018. However, the trend in MOS 
has been notably colder the last few days, and the with the guidance 
likely too fast in developing return flow as the high shifts 
offshore, cool north winds and increasing stratus will keep highs 
cool once again Monday, although our string of days without reaching 
40 will come to an end with highs in the mid to upper 40s forecast. 
A cold front will drop into the area Monday night driven by a weak 
vorticity streamer moving through the mean trough. However, cold 
advection is weak and lagging with this feature, so temperatures 
into Tuesday morning are forecast to be near seasonable norms as 
cloud cover and wind inhibit much cooling. GFS profiles and time 
heights show enough moisture in the lower half of the column to 
produce some light showers with this feature, however the NAM/ECM 
and WPC suggest a dry FROPA. Inherited forecast is SCHC for late 
Monday night, and will leave this unchanged as it is D3, but expect 
most of the area will stay dry Monday night. if any light rain does 
fall will be of the liquid variety, no mixed ptype issues this time 
around.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 300 PM Saturday...High pressure will build down behind a
weak cold front on Tues while a ridge tries to nose up into the
Southeast over the top of a cutoff low over the Gulf. A very 
shallow moist layer and a steep inversion early Tues may keep
some low clouds to start the day, but as warming and mixing
occurs, should see increasing sunshine and warming on Tues into
Wed. Temps should reach well into the 50s Tues and into the 60s
by Wed. There will be westerly downslope flow aloft through mid
week and the h5 heights and 850 temps will continue to rise 
through the week. Therefore expect a warming trend as the 850 
temps reach up to 6c by Tues aftn. 

High pressure will shift off shore and a warm front will lift 
north Thursday. May see some enhanced lift as cutoff to the 
south gets caught up in deep southerly flow on front end of 
digging mid to upper level trough later in the day on Thurs. 
Therefore expect increased clouds and chc of rain on Thurs. 
Once this warm front moves north of the local area by late 
Thurs, we will see an increasing southerly return flow into Fri.
The 850 temps will reach up to 10c Thurs and with continued WAA
through Fri, they will increase up above 12c. This should bring
temps a good 15 degrees above normal, into the 70s, by Fri 
aftn, especially if we get enough sunshine. The digging mid to 
upper trough will push a cold front east late Fri into Sat with 
increasing chc of pcp once again. Expect the best chc to come 
Fri night into Sat. Should be interesting to see if we get areas
of sea fog Thurs and Fri as warm and moist air flows over the 
cool waters. Overall expect drier weather Tues through early 
Thurs and wetter weather late Thurs into the first part of the 
weekend with warming temps through the week.

&&

.AVIATION /23Z SATURDAY THROUGH THURSDAY/...
As of 00Z...Arctic high pressure will settle over the region
through  the valid TAF period. Winds will diminish overnight, 
going calm at times with near record cold temperatures. Sunday, 
scattered cirrus with a predominately northerly wind, mainly 
less than 10 kts.

Extended Outlook...MVFR/SHRA Monday through Tue morning, Otherwise 
VFR.

&&

.MARINE...
NEAR TERM /THROUGH SUNDAY/... 
As of 621 PM Saturday...Seas 2-4 ft, in mixed wave periods from
the ENE, accompanied by a moderate NNW chop prevails, and this 
regime should hold overnight, possibly up to 5 feet near Frying 
Pan Shoals overnight. A SCEC is not out of the question later if
winds clock in stronger than model guidance is laying forth. 

As of 300 PM Saturday...Arctic high pressure over Indiana this 
afternoon will slide southeastward into Virginia by daybreak Sunday. 
Very cold air continuing to pour into the region from the north will 
create wind chills from 5-15 degrees across the coastal waters late 
tonight and into Sunday morning. Northerly winds of 15-20 knots will 
continue into Sunday morning while veering a little more 
northeasterly, then diminishing to 10-15 kt Sunday afternoon. Seas 
currently 2-4 feet could build toward 5 feet at 20 miles' distance 
from shore overnight into Sunday morning.

SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... 
As of 300 PM Saturday...High pressure centered near the Outer Banks 
will drift slowly eastward this period while maintaining a ridge 
back into the Carolinas. This leaves a weak gradient across the 
waters with NE winds Sunday night and Monday around 5-10 kts, 
veering slowly to become Southerly late Monday night. At the very 
end of the period, a weak cold front will push offshore turning 
winds to the NW at still light speeds by Tuesday morning. A general 
10-sec SE swell will exist in the wave spectrum through early next 
week, and with the light winds will noticeable to mariners. 
Otherwise expect a 1-2 ft NE wind wave becoming S late, and 
significant seas will be around 2 ft.

LONG TERM /TUESDAY THROUGH THURSDAY/... 
As of 300 PM Saturday...High pressure will build down behind
weak cold front through Tues with light northerly flow. This
will maintain lower seas of 3 ft or less. High pressure will 
shift farther off shore Wed into Thurs and winds will veer 
around becoming more on shore and eventually southerly as a warm
front lifts north late Thursday into early Fri. The winds will
gradually increase late Thurs as gradient begins to tighten 
ahead of next cold front approaching the Carolinas from the 
west. Expect winds to increase up to 10 to 15 kts out of the 
south by Thurs night. This on shore, then southerly flow will 
push seas up to 3 to 5 ft by late Thurs and possible into SCA 
thresholds by end of the period, heading into Fri morning.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...Wind Chill Advisory from 4 AM to 10 AM EST Sunday for SCZ017-
     023-024-032-033-039-054>056-058-059.
NC...Wind Chill Advisory from 4 AM to 10 AM EST Sunday for NCZ087-
     096-099-105>110.
MARINE...None.

&&

$$

NEAR TERM...TRA/MJC
SHORT TERM...JDW
LONG TERM...RGZ
AVIATION...43