Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
635 am EST Thursday Nov 27 2014
Synopsis...an upper level disturbance and associated low pressure
system will track east across the region early this morning. High
pressure will build into the region from the west this afternoon and
tonight then settle over the Carolinas on Friday and Saturday.
Near term /through tonight/...
as of 305 am Thursday...
Today...a pair of short wave...a well-defined feature crossing the smokey
mountains at 07z...and the other less defined feature over the lower
Ohio Valley...will bring a period of unsettled weather to central NC
this morning with gradually improving conditions anticipated this
The lead short wave will bring an area of showers to mainly the northern
Piedmont early this morning (through 12z-13z) though a stray shower
or two may track across the southern Piedmont-sandhills by daybreak.
The second short wave will follow quickly on the heels of the initial short wave
and cross the Piedmont middle day-early afternoon. Subsidence behind
the lead short wave may dry out the atmosphere enough to cause a decrease
in shower activity with the second short wave. Thus plan to have solid
chance/low end likely probability of precipitation early this morning across the far
northern pop...trending to slight chance over the southern Piedmont.
After 18z...will confine probability of precipitation to the far north-NE with the second
short wave...trending probability of precipitation to less than 15 percent by 21z as this feature
exits the region.
Low level flow will become west-northwest this afternoon in the wake of the
departing S/ws. Due to presence of fairly steep lapse rates aloft
caused by The Pocket of cold air associated with the middle level S/ws
(-30 degree c at Nashville at 00z...and -32 at central il)...expect
blustery conditions to develop around late morning in the south..and
this afternoon across the north. Wind gusts in the 25-30 miles per hour will be
common. Maximum temperatures middle-upper 40s across the far north where showers
and clouds will be more prevalent...to the middle 50s across the far
Tonight...skies will clear off fairly quickly west-to east late this
afternoon early evening as drier air overspreads the region. Cold
air advection will keep the near surface atmosphere well mixed until
just prior to daybreak. The cold air advection will send temperatures into the middle-upper
20s by early Friday.
Short term /Friday and Friday night/...
as of 305 am Thursday...
Friday...chilly high pressure will build into and settles overhead.
Low level thicknesses average 45m below normal...suggestive of maximum
temperatures 10-14 degrees below normal. This yields maximum temperatures in the low-
middle 40s. Skies will remain mostly clear aside from a few passing
cirrus in the afternoon. -Wss
Friday night: surface high pressure will settle over the region on
Friday night. Meanwhile... middle level flow will remain out of the west-northwest
with the potential for a few weak disturbances to move across the
middle Atlantic region. However... we will remain dry with only an
increase in some high clouds on Saturday morning. Still think the
clouds will be thin enough not to have a significant impact on low
temperatures. Given this... think we should see temperatures plummet into the 20s
across the entire area... with lows in the middle to upper 20s (maybe
even a few lower 20s in the usual rural cold spots depending on the
cloud cover). -Bsd
Long term /Saturday through Wednesday/...
as of 310 am Thursday...
High pressure will shift to the south and east of central NC this
weekend allowing for a warming trend. High temperatures are expected to be
in the lower to middle 50s for Saturday and lower to middle 60s for
Sunday. Middle level ridging is forecast to build northward during this
time frame and nudge into our area. However... as a northern steam
trough is forecast to track near the U.S./Canadian (east coast that
is) border during this time frame a trailing cold front will drop
southward and into central NC early next week. Model guidance has
trended towards the surface front moving into the area on Monday
night into early Tuesday morning... pushed by a 1035-1040 mb surface
high to the north/northwest. This should allow for one last warm day
on Monday... with highs in the 60s to lower 70s south.
Given the last several days medium range models have trended wetter
with the aforementioned front and the potential for at least some
hybrid cold air damming for Monday night into Tuesday. However...
wpc still prefers to keep probability of precipitation low with the arrival of the front
given the apparent spread in guidance/ensembles guidance over the past
few days and differences with the operational models vs their
ensembles. Thus... for now prefer to keep probability of precipitation at slight chance for
Monday night into Tuesday and trend temperatures downward. For Wednesday...
we may have some form of lingering cad across the area. However...
the parent surface high should be well off the northeast U.S. Coast
by this time. The next system will quickly approach from the
northwest. However... there is a large spread among the guidance in
timing of the front. Wpc holds the front to our north during this
time frame... going with a less amplified pattern. Given the lower
confidence will keep temperatures within a couple categories of normal at
worst... given the large possible spread in temperatures. This yields highs
on Tuesday in the upper 40s to 50s... with highs on Wednesday in the
50s to some 60s... and lows in the 30s and 40s.
Aviation /12z Thursday through Monday/...
as of 635 am Thursday...
A strong upper level disturbance crossing central NC early this
morning will exit our region by early this afternoon. This system is
triggering patches of light rain across the northern Piedmont and
northern coastal plain along with varying ceilings...resulting in
pockets of LIFR conditions. Ceilings are expected to lift and
dissipate from the SW later this morning...leading to improving
After 14z...west to northwest surface winds will be blustery with gusts 18-23
kts likely. The gusts will become less likely after 22z...though a
steady northwest wind around 10kts expected well into tonight.
High pressure will build into central NC tonight and settle overhead
Friday through Saturday...providing a period of VFR conditions with
surface winds less than 10kts.
The high will shift offshore Sunday. The resulting south-southwest
low level flow will advect moisture into our region by late Sunday-
Sunday night leading to the potential for areas of MVFR fog or IFR
ceilings in stratus by early Monday.