Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
638 PM EST sun Feb 7 2016
Synopsis... a strong coastal low off the South Carolina coast will
move away tonight and Monday. An upper level disturbance and cold
front will cross the region late Monday...followed by and extended
period of below normal temperatures through the work week.
Near term /through tonight/...
as of 515 PM Sunday...
Msas shows a sub-1000mb (~994mb) surface low east of Myrtle Beach
this afternoon...with further deepening to near 980mb east of the
obx forecast tonight as an upper low over the Savannah River basin
begins to lift northeast. Precipitation rates...a period mix of
rain...snow and sleet (at times all sleet)...have begun to
decrease...with most locations in the coastal lain now reporting
light rain. While a very brief burst of sleet is still possible over
eastern Wayne and eastern Wilson counties...threat/bulk of wintry
mix precipitation has ended. No additional accumulation expected...in
addition to the quarter to half inch reports on some areas that is.
So will cancel the Winter Weather Advisory before the 6 PM expiration.
We'll see fairly rapid clearing of the cirrus shield after
midnight...with overnight lows expected to drop into the upper 30s
and lower 30s under shortwave ridging aloft and light surface winds.
There may be some black ice in the coastal plain if roads do not dry
out prior to the clearing...and this is something that will be
monitored this evening.
Short term /Monday through Monday night/...
as of 330 PM Sunday...
There shortwave ridge aloft between the departing upper wave and its
kicker wave approaching from the west will quickly give wave to a
strong shot of DCVA Monday afternoon and evening. A southerly
wind...gusting to 20-25kt by Monday afternoon...will provide a brief
period of warming and moisten...yielding steep lower tropospheric
loose rates and the potential for a band of showers during the
afternoon. Forecast highs in the upper 40s and lower 50s will keep
this all liquid despite the lapse rates and a pattern that often
favors snow showers. However...a secondary band of rain that
changes to snow is still possible late Monday evening and overnight
as an Arctic front surges across the area and a wave of low pressure
develops somewhere over southeast Virginia (per a loose model consensus).
The 12z NAM and GFS are drier than in previous runs...so confidence
in this second band is low and probability of precipitation will be limited to just slight
or low end chance values from the Triangle northeast. Lows Monday
night will be in the upper 20s and lower 30s and cold advection
starts to kick in behind the aforementioned front.
Long term /Tuesday through Sunday/...
as of 400 PM Sunday...
Cold and mainly dry northwest flow...in a highly amplified pattern
characterized by a strong western noam ridge and eastern noam
trough...will prevail through the upcoming week...though an east
Pacific trough will briefly flatten the ridge next weekend.
Although mainly a dry pattern...there still appears to be a couple
of opportunities for light precipitation over portions of central NC
during the period...on Tuesday and late Friday-Friday night.
The first opportunity will occur as the eastern noam trough reaches
maximum amplitude down the East Coast on Tuesday...owing to the
amplification of a shortwave trough axis accompanying a circulation
(now over the upper great lakes) into the trough base/across the
Middle Atlantic States. With associated weak height falls aloft and
amidst steep lapse rates as the cold upepr trough pivots east...
enhanced instability cloudiness --and a chance of sprinkles/
flurries...or worst case a brief rain/snow shower across the
northern Piedmont-- will result on Tuesday.
Of potentially greater consequence...but still with low forecast
confidence given larger than average model spread...the eastern noam
trough will briefly relax and allow a brief episode of low-middle level
warm air advection accompanying a clipper-type wave to spread from the Central
Plains Thursday eastward to the Carolinas by late Friday-Friday night. This may
result in a brief period of light rain or snow across our southern
counties centered around Friday evening.
Otherwise...guidance has trended colder throughout the period...with
highs in the 30s-40s and lows in the teens and 20s...coldest Wednesday-Thursday
and again on sun.
Aviation /00z Monday through Friday/...
as of 638 PM Sunday...
For the 24 hour taf period: precipitation has moved east of I-95...and the
eastward exit of the precipitation will continue tonight as the low moves
away. As such...look for improving ceilings the rest of this evening. In
fact...as of 23z...VFR conditions were found across all of central
NC including all of our 5 taf sites. The only other lingering issue
this evening is the gusty north winds that are occurring mostly east of a
line from kmeb-khnz...where gusts at or above 18kt remain. Look for these
winds to gradually diminish to 10kt or less by 08/07z. Otherwise
west of the aforementioned line...winds are already below 12kt and
expected to remain so overnight.
VFR conditions will continue Monday morning...but as the next
disturbance approaches from the northwest...look for SW winds to increase
again during the afternoon...along with the risk for rain showers
increasing during the middle-late afternoon.
Outlook...after the disturbance on Monday passes by...the remainder
of the week should be mostly VFR...with gusty northwest winds each