Scientific Forecaster Discussion
fxus62 krah 202356
Area forecast discussion
National Weather Service Raleigh NC
655 PM EST Sat Jan 20 2018
high pressure will drift across the southeastern United States
through tonight, then offshore on Sunday. A cold front will approach
from the west Monday, and cross central NC on Tuesday.
Near term /through Sunday/...
as of 330 PM Saturday...
Current stretch of tranquil weather conditions will continue during
the near term. An area of sfc high pressure located over southern
Georgia will continue to slowly weaken as it drifts eastward tonight
and Sunday. Meanwhile, a compact upper level low pressure system
over the north central Gulf early this afternoon will weaken as it
slowly lifts east-NE tonight and Sunday. This weather system will
spread patchy mid-high level clouds over central NC very late
tonight and more notable on Sunday.
The moistening of the atmosphere may allow for the development of
patchy fog overnight into early Sunday morning, primarily over the
Piedmont as warmer air traverses over the cooler ground in the wake
of the recent snowpack. Not all models are showing this signal so
there is the potential that no fog or low clouds will develop. For
now, will advertise visibility no worse than a mile or two at this
time. Min temps near 30 to the lower 30s. Expect enough sunshine
Sunday afternoon along with a steady swly low level flow to push
temperatures into the low-mid 60s.
Short term /Sunday night through Tuesday/...
as of 330 PM Saturday...
May see a better potential for areas of fog late Sunday night into
early Monday morning, primarily across the Piedmont, though
increasing high cloudiness may inhibit fog development in vicinity
of the Yadkin/Pee Dee River valley. Min temps mostly in the mid 30s.
Monday, a deep cyclone over Central Plains will slowly lift into and
across the Great Lakes Monday night and Tuesday. Swly low level flow
will continue to pull warm air into the Carolinas. This warm air
coupled with ample sunshine will push temperatures well into the 60s
along and east of Highway 1. Thickening cloud coverage over the west
will inhibit sunshine to result in cooler temps, holding the NW
Piedmont in the upper 50s to around 60. At this time, expect bulk of
the showers to hold off until after sunset, though a stray shower or
two cannot be ruled out in vicinity of Winston-Salem by late
The trailing sfc cold front associated with the deep cyclone will
approach from the west Monday evening, and cross our region early
Tuesday. Thickening clouds and steady sly flow will likely maintain
mild conditions Monday night with some places likely not dropping
much below 55 degrees. Better support aloft over the northwest Piedmont
suggest better shower coverage in this region, with support waning
farther to the south and east. Currently not expecting abundant
rainfall with this system as forcing not overly impressive. Rainfall
totals will likely vary from less than a half inch northwest to under a
quarter of an inch southeast. Morning clouds and scattered showers Tuesday
morning will giveway to increasingly sunny skies. 850mb front does
not cross region until the afternoon, so we should have time to warm
before low level cold air advection commences late in the day. This
required an adjustment up in high temperatures Tuesday. Currently
expect Max temps Tuesday to be in the 60-65 degree range.
Long term /Tuesday night through Saturday/...
as of 212 PM Saturday...
Tuesday night and beyond: quiet weather with near to above
seasonal temperatures are expected into early Saturday. The
upper air pattern Tuesday night features a departing short wave
trough aloft and cold front. A period of short- lived strong
cold advection Tuesday night results in clearing skies and
temperatures that fall to near normal in the upper 20s to lower
30s. Weak short-wave ridging develops on Wednesday and
temperatures reach he mid to possibly upper 50s. A short-wave
trough and an associated cold front with very little moisture
swings across the region late Wednesday/early Thursday. Skies
will remain mainly clear with limited sensible weather impacts.
Ridging aloft with increasing heights build into the area for
Thursday into early Saturday. Skies will remain generally clear
with moderating temperatures. Highs on Thursday will range in
the lower to mid 50s, in the mid to upper 50s on Friday and in
the mid 50s to lower 60s on Saturday.
A higher amplitude trough that moves onto the Pacific coast on
Thursday reaches the Central Plains by Saturday night. Deep
layer southerly flow transports moisture northward from the Gulf
and Pacific as a surface wave develops in the mid-Mississippi
Valley. Both the 12z operational GFS and ec have trended slower
with the precipitation arrival in our region, especially with the
precipitation spreading northward across Georgia and the Carolinas
as the surface high is slower to depart. Will keep pops confined
to the Saturday night period for now. -Blaes
Aviation /00z Sunday through Thursday/...
as of 700 PM Saturday...
24 hour taf period: a lot of discrepancy in the short term models
over the extend of fog during the early morning hours on Sunday
morning. The fog in the models appears to be related to the left
over snow pack over The Triad and as far east as rdu. Models are
split on the effects of the leftover snow on visibility and the sref
points to a fairly extensive fog event where as other short term
models such as the hrrr are keeping visibilities at VFR levels. Have
decided to go with IFR visibilities after 6z in The Triad and after
9z at krdu. Any fog will rebound to VFR after sunrise. Some mid
level clouds can be expected on Sunday especially later in the day
as relative humidity cross sections point to a lot of moisture in the 4-6 kft
range. No precipitation is expected and winds should remain light
and variable as surface high pressure remains in control of the
Long term: after another bout of possible fog early Monday morning,
VFR conditions are expected through Monday night before a weak
frontal system approaches the area by Tuesday morning. Sub-VFR
conditions can be expected through Tuesday evening before a return
to VFR on Wednesday.