Scientific Forecaster Discussion
fxus62 krah 210202
Area forecast discussion
National Weather Service Raleigh NC
1002 PM EDT Tue Aug 20 2019
a mid and upper level disturbance will drift northeastward across
central NC through early Wednesday. Central NC will otherwise remain
situated between an appalachian-Lee trough and high pressure
centered east of Bermuda through Friday.
Near term /ttonight/...
as of 1000 PM Tuesday...
WV satellite and 00z upr air data depict a positively-tilted mid-upr
lvl trough axis extending from the middle Atlantic swwd across the
sern US. Within that trough, a vort Max has been apparent in both
satellite and regional vwp data over the upstate of SC today; and
this feature is forecast to drift newd across cntl NC through early
At the surface, high pressure centered several hundred miles east of
Bermuda will continue to extend wwd into the Carolinas tonight. On
the wrn/nwrn periphery of the high, synoptic features remain well-
removed from cntl NC, with a primary synoptic front analyzed at 02z
from the nrn middle Atlantic coast nwwd across W-cntl PA to a 1012
mb low over nrn Michigan. A myriad of outflow boundaries were analyzed to
the south of that front, including a couple closest to home over the
srn NC Piedmont and nrn coastal plain, respectively.
Rain chances have been reconfigured and increased to reflect a
likely probability of showers and storms over most of Piedmont
overnight, where convection will be apt to redevelop in association
with the aforementioned relatively strong mid-upr lvl vort Max. Some
wind gusts up to 40-45 mph will be possible with relatively deeper
convection on the nern edge of the foregoing outflow (and
approximate swrn bound of surface-based convection) now over the srn
Piedmont. Heavy rain and a risk of localized flooding will otherwise
prove the primary hazard owing to training/backbuilding potential,
as parcels are drawn isentropically up and in toward the center of
the mid-upr vort Max and atop the outflow/surface-based cold pool,
supported by forecast corfidi vectors over the Piedmont.
Areas of stratus will also likely develop through Wed morning,
particularly in the rain-cooled air behind the leading arc of
surface-based convection. Some fog may accompany the stratus in the
vicinity of the Yadkin River, as the extensive multi-layered overcast
accompanying the vort Max edge ewd/newd. It will be muggy and mild
otherwise, with lows generally in the lwr-mid 70s.
Short term /Wednesday through Wednesday night/...
as of 235 PM Tuesday...
Energy associated with a complex currently moving through Indiana
and Illinois will make its way southeastward over the next 24 hours
and will reach our northwestern extent by 15z on Wednesday. This
will be pushed through by an upper level trough that will cross the
area during peak heating helping a more progressive linear feature
to form as picked up by the cams. As it does the trough aloft will
be flattening out and thus this activity should weaken as it comes
across the area. As such the Storm Prediction Center has the marginal risk for severe
weather just off to our northwest but maintains general thunder over
our County Warning Area. Highs in the low 90s. Lows in the low 70s.
Long term /Friday through Tuesday/...
as of 245 PM Tuesday...
Weak ridging aloft will quickly give way to an amplifying upper-
trough across the eastern Continental U.S. As we head into the weekend. At the
surface, anticyclonic surface flow via the western periphery of the
weakening Bermuda high will continue to stream moisture into central
NC ahead of a cold front, set to slide southeast through the mid
Atlantic over the weekend before stalling nearby. High pressure will
attempt to settle in across the Lee side of the Appalachians into
early next week, keeping central NC in the "battle zone" of two
Thursday will likely be the warmest day of the period as
southwesterly flow continues to stream warm moist air across the
region. There are some hints that a lull in shower and thunderstorm
activity may be present as weak subsidence persists between
strengthening upper trough across the Great Lakes and the broad
scale surface troughing to our south. Can't completely rule out some
isolated, especially late day, thunderstorm development as the
leeside/pre-frontal trough begins to sharpen though. Severe threat
should remain localized, with isolated downburst potential likely to
remain the primary culprit of any near-severe level surface wind
gusts from tstorms. Afternoon highs will remain in the low to mid
90s, with overnight lows settling in the lower 70s with patchy
fog/stratus formation possible.
Shower and storm chances will become enhanced beginning Friday as
the cold front approaches the region from the northwest. Timing of
frontal passage is still a bit uncertain, with the GFS sliding the front just
about all the way through the County Warning Area roughly 12 hours faster than most
other models, who now tend to stall it across central NC into early
next week. Thus, have trended pops higher for longer, keeping at
least chance pops in the forecast through Tuesday. Still can't rule
out portions of the northwest Piedmont emerging in the cooler
north/northeasterly flow behind the front for a brief period of
time, but the likelihood of a complete frontal passage seems to be
diminishing with each model run. High temperatures should remain
near normal on Friday before dropping considerably the remainder of
the period thanks to a plethora of cloud cover and the presence of
ongoing showers/storms. Expect afternoon temperatures to meander
within the low to mid 80s, with lows dipping into the low to middle
60s during the overnight hours. Some hints at a temperature increase
as the front attempts to return north early next week, plausibly
allowing central NC to return back into the warm sector.
Aviation /00z Wednesday through Monday/...
as of 745 PM Tuesday...
24 hour taf period: scattered showers and thunderstorms will
continue to move through central NC from the southwest this evening
into the early overnight hours. The usual sub-VFR cigs and visbys
will accompany heavy storms if they move over a terminal. Given the
much smaller spatial extent of the rainfall this afternoon compared
to yesterday and the lack of any sub-VFR conditions anywhere but
krwi until after daybreak today, will hold off on including reduced
visbys in this issuance. However, low stratus could develop
overnight, generally in the MVFR range. Otherwise, VFR conditions
with light and variable winds will prevail through the taf period.
Showers and thunderstorms will be possible again Wednesday aft/eve,
primarily moving in from the west toward the end of the taf period.
These storms will again result in the usual adverse aviation
conditions where they occur. -Kc
Looking ahead: more unstable weather over the next several days as a
frontal system moves in from the north brining chances for adverse
aviation conditions each day this week with fog/low stratus possible
each morning. -Ellis
equipment issues at the upper air site in Greensboro will prevent
upper air flights from occurring through 12z Wednesday. If repairs
are successful, expect upper air flights on a regular schedule (00z
and 12z) through at least 12z Friday.