National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 230309
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1009 PM EST Tue Jan 22 2019

.SYNOPSIS...
Arctic high pressure over the region will drift offshore through
this evening, allowing a slightly warmer and more moist air mass to
overspread the region. An approaching storm system will bring
unsettled weather to central NC Wednesday into Thursday. Drier and
colder weather will arrive for the end of the week.

&&

.NEAR TERM /TONIGHT/...
As of 1000 PM Tuesday...

The Winter Weather Advisory has been extended in time, through
16Z/noon for the nw Piedmont, where the highest probability of
measurable freezing rain and/or drizzle of up to several hundredths
of an inch are expected, and where a developing in-situ cold air
damming regime will likely cause temperatures to remain colder and
and supportive of light glazing longer. There remains the potential
for spotty light glazing to the east of those areas, from Stanly Co.
newd across Randolph, Alamance, Chatham, Orange, and Person Co.,
where we will highlight that patchy and lower confidence risk with a
Special Weather Statement (SPS). Observational trends will need to be
monitored overnight for consideration of a short-fused expansion of
the Advisory in those counties.

1038 mb Arctic surface high pressure centered about 60 miles off the
sern VA coast this evening will continue to extend wwd into NC
through early Wed, while drifting toward and just north of Bermuda.
A developing and strengthening WAA regime on the wrn periphery of,
and rising isentropically-atop, that dry air ridge characterized by
02Z surface dewpoints in the single digits to teens in cntl NC, has
caused an area of 1000-4000 ft ceilings to develop from ern GA and
SC nwd into w-cntl NC during the past several hours. It will be that
developing and deepening low level saturation that will likely
produce an axis of light precipitation into the srn and wrn NC
Piedmont late tonight-early Wed - a process that will take some time
and probably not materialize until after 09Z owing to the preceding
Arctic dry. Indeed, some light radar returns have been recently
noted from near GSP to AVL, though none has yet been reported at
nearby AWOS/ASOS.

Opposing physical processes will be at work as those clouds and
precipitation expand newd. Initially, downward IR from the expanding
low clouds, and some light ssely surface stirring, will cause
temperatures to rise as the clouds move overhead tonight, as has
been observed already as far east as HFF, SOP, and SCR in the past
couple of hours, where earlier upr 20s have been replaced by 32
degree readings. The aforementioned development of light
precipitation should then cause surface temperatures to diabatically
cool as they trend toward the wet bulb temperatures in the upr 20s
to near freezing. As was noted earlier, the highest probability of
overlap of sub-freezing surface wet bulb temperatures and light
precipitation will exist over the wrn Piedmont, near the Yadkin
River. And should that measurable precipitation indeed materialize
as expected, the colder NAM/NAM Nest/HiRes NMM/HiRes ARW
simulations, for temperatures holding in the 30s over the nw
Piedmont for most of Wed, will likely prove most realistic.

What could go wrong: If the precipitation is too light and/or
spotty, then incomplete wet-bulbing would result in surface
temperatures hovering aoa freezing, even in the Advisory area. That
is considered a lower probability, but next most likely solution
versus the official forecast discussed above. That alternate
scenario is more likely to the east of the Advisory area (in the SPS
counties), where the expected patchier and lighter nature of the
precipitation there was the primary reason we elected to not expand
the Advisory ewd.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
As of 345 PM Tuesday...

The icing threat will persist in the far NW sections until just past
daybreak, although models indicate temps rising above freezing in
these areas soon thereafter, not unreasonable given that the parent
high will be pushing offshore and in an unfavorable location to
provide a replenishing of cold dry air into our area, rendering it
vulnerable to the strengthening and deepening warm surge aloft. Pops
through much of the day will patchy and light as we await stronger
forcing for ascent with the potent but dampening mid level shortwave
trough moving in from the WSW. Expect widespread showers to move
into the W CWA by early Wed evening, with coverage peaking overnight
in tandem with passage of vigorous upper divergence, and waning by
lunchtime Thu as the trough axis and surface cold front move
through. One to two inches of rain is possible, given the strong
focused lift late Wed night into Thu morning, and a few urban
flooding problems are possible. Expect very gradual clearing W to E
late Thu with downslope low level flow and drying aloft. Highs Wed
will range from the mid 40s NW to the mid 60s SW, followed by a
minimal drop or steady/rising temps Wed night within strong warm air
advection. Highs from the low 50s to mid 60s Thu should occur early,
with steady or slowly falling temps during the afternoon. -GIH

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 230 PM Tuesday...

Quiet weather shaping up for much of the long term forecast. Rain
will move out of the area Thursday night which will lead to a period
of dry and cold weather with below featuring below normal
temperatures through the end of the work week and into the weekend.
Synoptically, a long wave upper trough will remain over the eastern
CONUS with a continental surface high over the Midwest that will
promote cold air advection through the weekend. High temperatures
during this time frame will be generally in the 40s with lows in the
20s. Wind chills are not expected to be much of a factor as they
winds will be light and variable during the overnight hours.

Looking past the weekend, models are trending towards taking a
coastal low pressure system further offshore and likely have no
impact on central NC weather on Monday but perhaps a rain shower or
two on Tuesday in the extreme east as it moves up the coast and
eventually further out to sea. A little warmer on Monday with highs
in the upper 40s to low 50s.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
As of 750 PM Tuesday...

Surface high pressure remains centered just east of the VA
coastline this evening with cloudy skies just moving over INT
and GSO. This evening surface high pressure is forecast to pull
east with isentropic upglide commencing. This can actually
already be seen in South Carolina with widespread MVFR to VFR
conditions. Wednesday morning, VFR ceilings will slowly lower to
MVFR then IFR as upglide continues. Also at this time, light
returns will likely appear on the radar across INT/ GSO and
temperatures will likely be below freezing (meaning freezing
rain). Temperatures will likely remain just below freezing
possibly into mid-morning before rising above.

The other concern here will also be the increasing low level
flow. The NAM strengthens the low level jet across the northwest
with 2 kft AGL wind actually above 50 kts at times Wednesday
morning. The wind is then weaker further to the south and east.
Late Wednesday morning into afternoon the wedge front will lift
northwest allowing a rise in ceilings towards KFAY and KRWI.
Northwest of the wedge front widespread LIFR ceilings and
visibilities will be likely. For now have just trended the
forecast this direction. By the end of the TAF issuance the
wedge front will likely only be just northwest of RDU.

Looking beyond 00z Thur: The wedge front will likely stall
between KINT and KGSO as another strong system approaches the
terminals. Widespread rain and sub-VFR conditions will continue
with winds turning from the northwest behind the front. Drier air
will arrive with high pressure behind the front, and VFR
conditions are likely from late Thu through Sun.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from midnight tonight to 12 PM EST Wednesday
for NCZ021-022-038.

&&

$$
SYNOPSIS...Hartfield
NEAR TERM...MWS
SHORT TERM...Hartfield
LONG TERM...Ellis
AVIATION...Haines