Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
935 am EST Tue Dec 6 2016
cool and wet conditions are expected today, ahead of a Miller b low
pressure system and associated cold air damming. An Arctic cold
front will approach the area Wednesday night and cross the Carolinas
Near term /through tonight/...
as of 935 am Tuesday...
Spotty light rain continues this morning ahead of a slowly shearing
upper wave lifting out of the lower Mississippi Valley and a Miller
b low transitioning across the locked in cad airmass. Radar returns
are still pretty unimpressive and have really fallen off over
upstate SC as the dry slot is surging north. Expect this trend of
spotty rain diminishing from southwest to northeast to generally
continue this morning. There is an area of convective elements to
watch upstream over northern GA, where dry air aloft looks to create
a little potential instability (100-200 j/kg mucape) between 800mb
and 600mb, per rap soundings, which may be enough to enhance or
fill in precipitation as the upper lifts across the area through
early afternoon. Any instability will remain elevated above the
strong cold dome, with guidance keeping the warm sector well
southeast near the NC/SC coastal areas.
Changes to the forecast have been relatively minor; mainly tweaks to
pops in the next few hours and reductions in qpf, with a focus of
best rain rates in the 15z to 21z period. Temps will hold
relatively steady in the 40s areawide, possibly rising a few degrees
in the southeast as the surface low passes by this afternoon. -Bs
Low-level moisture could be slow to mix out tonight. However, in
areas that do clear out, wet soils could result in some areas of
fog, potentially dense in spots. Lows in the upper 30s to lower 40s.
Short term /Wednesday through Thursday night/...
as of 220 am Tuesday...
Minimal drying will occur on Wed (in the wake of the low pressure
system progged to track offshore the Carolina coast tonight) as low-
level flow quickly backs to the south/southwest (giving rise to weak
warm advection) in response to upstream height falls as potent
shortwave energy ejects east/east-northeast from The Rockies toward the central
Appalachians and the leading edge of an Arctic cold front progresses
eastward through the Tennessee/Ohio Valley to the western slopes of the
southern Appalachians by 12z Thu. Low-level frontogenesis, glancing
DPVA, strengthening cyclonic flow aloft and lingering low-level
moisture are expected to result in the development of light
rain/sprinkles /anafrontal precipitation/ along and behind the
Arctic cold front as it progresses through central NC during the day
Thu. 00z European model (ecmwf) guidance has trended wetter compared to yesterday and
is in relatively good agreement with the 00z GFS now, indicating
that a few hundredths of an inch of rain will be possible between 12-
18z Thu, with the relative best chance of measurable precip in the
northern Piedmont and NE coastal plain. Expect highs in the 50s on
Wed and lows in the lower 40s Wed night. Highs on Thu will depend on
fropa timing, timing/amount of precipitation and cloud cover. At
this time, will continue to indicate highs ranging from the upper
40s/lower 50s far northwest to mid /upper 50s far S/se. Lows Thu night will
highly depend on fropa timing and ensuing cold advection. Anticipate
lows ranging from the mid/upper 20s northwest to lower 30s southeast. -Vincent
Long term /Friday through Monday/...
as of 220 am Tuesday...
Expect cold/brisk conditions on Friday with highs in the mid/upper
30s to lower 40s and a northwest breeze assoc/W strong cold advection as
1040 mb Arctic high pressure builds eastward from the Central Plains
toward the Appalachians in the wake of the cold frontal passage
Thu/Thu night. Expect cold lows in the upper teens to lower 20s Sat
morning as the Arctic high settles over the Carolinas late Friday
night. Highs on Sat will be similar to Friday (albeit a few degrees
warmer). Forecast confidence decreases at the end of the weekend and
early next week as guidance diverges with regard to the onset of
southerly return flow /warm advection/ as the next cold front
approaches the mountains from the west and modified Arctic high
pressure shifts offshore the Carolina coast. -Vincent
Aviation /12z Tuesday through Friday/...
as of 650 am Tuesday...
24-hour taf period: conditions will deteriorate to IFR to LIFR by 12
to 15z and should remain that way through the taf period as rain
overspreads the area ahead of Miller b low pressure system and
associated cad. The low pressure system will lift northeast away
from the area during the late afternoon, allowing precip to taper
off from SW to NE across the area between 21 to 00z. However, IFR to
LIFR conditions in low clouds and possibly fog could persist well
into the overnight hours Tuesday night.
Finally, concerning llws, given little variation in directional wind
component between 1000-925mb along with recent guidance showing
sustained winds of 10 to 12 kts at krdu, kfay, and krwi, will
not include low level wind shear in 12z taf package.
Looking ahead: VFR conditions will return on Wednesday. However, sub-
VFR ceilings could return Wednesday night and linger into the day on
Thursday ahead of an Arctic cold front moving through the area. &&