Scientific Forecaster Discussion
fxus62 krah 101557
Area forecast discussion
National Weather Service Raleigh NC
1055 am EST Tue Dec 10 2019
a retreating wedge front will be overtaken by a cold front that will
push east across central NC this evening. High pressure will build
across the mid-Atlantic states Wednesday and Thursday, before a
coastal low pressure system tracks up the eastern Seaboard this
Near term /today and tonight/...
as of 1055 am Tuesday...
14z surface analysis showed the linger wedge front still in The
Triad, with temps in the mid/upper 50s to the west and mid 60s to
the east. The synoptic cold front stretched from SW PA through
central Alabama. Vis satellite shows some thinning of stratus east of US
1 and some clearing near and southeast of Fay. 15-25kt sswrly gusts will
become more regular through the afternoon hours, and guidance still
support mid to some upper 70s in the far se, with upper 60s and
lower 70s in the Piedmont, and perhaps 60 in The Triad.
The cold front will move east into the western Piedmont by 18z and
overtake The Wedge airmass, then push east through the County Warning Area by 00z.
As the associated upper trough over the Midwest moves toward the Ohio
Valley region this evening, the 180kt jet analyzed at 250mb will
pivot east and cause increasingly anafrontal rain to spread across
the area in the right front entrance region of the jet...a trend
already evident in radar imagery across the mid-MS valley
region...and possibly intensify a bit in the Piedmont and fgen
Cranks up after 03z. The Post-frontal, rain cooled air will cause
temps to crash into the 40s and upper 30s by Wednesday morning. Area
average rainfall totals will be in the 0.25-0.5" range. The back
edge of the rain should be near the coastal plain by 12z, with some
lingering showers after daybreak.
Short term /Wednesday through Wednesday night/...
as of 3350 am Tuesday...
Ana-frontal showers will continue across just about the entire
forecast area beginning the day Wednesday, with a gradual decrease
in pops expected as a mid-level shortwave slides west to east during
the mid to late afternoon. Additional rainfall up to 0.10" will be
possible with locally higher amounts. The cold air advection regime will remain
constant during this time period, teaming up with the enhanced cloud
cover to limit overall high temperature potential. Even with a few
degrees of warming possible during the day, expect afternoon highs
to top out in the middle 40s. Clearing behind the front and
continued cold air advection will allow lows to dip into the middle 20s with a few
teen readings possible in the usual cold spots along and west of US-
Long term /Thursday through Monday/...
as of 400 am Tuesday...
A strong 1040 mb Canadian surface high centered over the mid-
Atlantic region to start the day on Thursday will eventually shift
off the NE and southern New England Thursday night. Meanwhile to our
south, a sheared southern stream trough ejecting NE across the southeast US
and mid-Atlantic state will support low pressure development over
the gom early Friday, that will then track up the East Coast through
The onset timing of precip into the area remains the chief source of
forecast uncertainty. If moisture/precip from this southern stream
storm system can make it to our area early enough Friday morning,
wet-bulb cooling within the antecedent cp airmass in place
(dewpoints in the upper teens to lower 20s across the NC piedmont)
will help set the stage for a very brief period of freezing rain
Friday morning, mainly along and north of the I-85 corridor. Otherwise,
if precip is delayed until late morning/midday, it will be all rain.
With that said, even if the more progressive/faster solutions
verify, with the parent high too far removed to supply any
additionally low-level caa, warm air processes rooted in a h9 warm
nose of 5 to 10 c), will overwhelm the freezing sfc temps, resulting
in a quick change-over to rain between 12 to 15z, with temps
eventually warming through the 30s to lower 40s by the afternoon.
Thus, any impacts are expected to be limited and very short-lived
with any ice accrual confined to elevated surfaces such as trees,
power-lines and car roof tops.
The remainder of the area will see all rain, with temps slowly
warming into upper 40s/near 50 across the central Piedmont to
lower/mid 50s across the coastal plain and sandhills. The other
story here is that this system will be a good rain producer for the
state, with rainfall amounts expected to average a 0.5 to 1.0"
across the area. While he bulk of rain from this system will taper
off from west to east during the day on Saturday, additional spotty
rain showers could re-develop across the area Saturday evening/night
as a trailing upper disturbance traverses the area.
Thereafter, dry weather should prevail for Sunday into Monday. A
vigorous shortwave trough approaching from the west Monday night and
into Tuesday has the potential to bring another widespread soaking
to the Carolinas on Tuesday. Although it appears we will have yet
another cad event, p-type with this event doesn't look to be an
Aviation /12z Tuesday through Saturday/...
as of 630 am Tuesday...
Poor aviation weather conditions continue across much of the area,
primarily in the form of IFR/MVFR cigs. The dense fog that we've
been battling all night at kint/kgso has diminished thanks to The
Retreat of The Wedge front and should no longer be a concern in
those areas. Expect low cigs to continue being an issue, at least
until the anafrontal rain showers push in from the west during the
mid-morning hours. During this time-period, the forecast is likely
to showcase predominantly bouncing IFR/MVFR cigs/vsbys highly
dependent on the intensity and duration of ongoing scattered to
widespread shower activity throughout the day.
Further east, cigs will likely see some continued MVFR range cigs,
but IFR/LIFR conditions are not likely. Primary impacts at
krdu/kfay/krwi will be MVFR cigs through sunrise, gusty
southwesterly winds once mixing is allowed mid morning (which may
also allow a brief return to VFR along and east of the coastal
front, primarily at kfay), and cigs/visibility drops in association with
cold frontal passage and shower arrival late morning through the
remainder of the period.
Significant improvements in aviation weather conditions not likely
through 12z/7am Wednesday.
Outlook: lingering rain showers, low cigs, and dropping vsbys will
decay after dawn Wednesday morning as drier northerly flow takes
control across the region. A coastal storm will result in another
high probability of rain and sub-VFR conditions Fri-Fri night,
including a short-lived period of a potential light icing event at
int/gso at precipitation onset Fri morning.