Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
1214 am EST Friday Dec 19 2014
high pressure builds into the area from the northwest through
Friday. Low pressure will track from the Gulf of Mexico eastward
and off the southeast coast late Friday night into Saturday night.
High pressure will be over the area again during Sunday. Another
low pressure area will move northeast out of the Gulf of Mexico
and up along the coast late Sunday night into Monday night.
Near term /until 6 am this morning/...
latest regional radar mosaic depicts light echoes over the northern
local area and northern Virginia this evening. However...latest kwal sounding
depicts a narrow band of moisture from 12-16k feet above ground level. The dry air
below that level will prevent any precipitation from reaching the ground.
This in response to a shearing...low amplitude wave crossing the
region. Based on bufr soundings and latest infrared satellite
trends...expect cloud cover to stick around through late tonight.
Wave pushes offshore late tonight into Friday morning...with skies
clearing through the morning. Surface high pressure will continue to
extend into the region...resulting in calm-light northerly winds. Bumped
temperatures down a degree or two...even with cloud cover...in the upper 20s
to low 30s.
Short term /6 am this morning through Sunday/...
models (gfs/NAM/ecmwf) continue to trend farther S with precipitation and
weak low late Friday night into Sat night...due to northern stream upper trough
swinging ewrd from the upper Midwest through the Great Lakes. NAM is the
farthest S and thus the driest model. Hi pressure stretching from
scntrl/southeast Canada south-southeast into the middle Atlantic will maintain dry weather Friday
into Friday night. Partly to mostly sunny on Friday with highs ranging from
the middle 40s to around 50. Mostly clear or partly cloudy Friday
night...with increasing cloudiness spreading in from the south-southwest. Cold
again with lows ranging from the middle 20s to lower 30s.
For Sat into Sat night...will go with a blend of the GFS/European model (ecmwf) with
low pressure tracking from the Gulf of Mexico ewrd and off the southeast CST.
Will go with no higher than 30-40% probability of precipitation for extreme southern Virginia and NE NC
mainly Sat afternoon into early Sat night. Just have slight chance (20%) or no
precipitation (14%) across northern half of County Warning Area at this time. Any precipitation at the
onset over western/northwest Piedmont counties could be very light sleet or
snow. Otherwise...precipitation will be just a cold light rain...and mainly
over extreme southern Virginia and NE NC. Could be a few flurries mixed in at
the end early Sat night. Hi temperatures on Sat only in the lower to middle 40s.
The weak low will be well off the southeast CST late Sat night...with a mostly
cloudy or partly cloudy sky. Lows Sat night ranging from the upper 20s
to middle 30s. Hi pressure will be over the area again during sun. Partly
or mostly sunny with highs in the middle to upper 40s.
Long term /Sunday night through Thursday/...
low pressure is expected to develop off off the southeast coast and
track NE off the middle Atlantic coast Monday into Monday night. Timing
differences continue amongst 18/12z numerical guidance...and given
this probability of precipitation will remain capped in the chance category. Probability of precipitation increase to
20-30% Sunday night...with 40-50% probability of precipitation across the area Monday and
Monday night. Precipitation type should generally be rain...although there
could be a brief period of sleet at the onset over the northwest Piedmont
late Sunday night and early Monday morning. Highs Monday should
range from the low 40s northwest...to middle 50s southeast...after morning lows in
the low 30s northwest...to around 40 southeast. Middle-level ridging briefly builds
into the region Tuesday (bringing milder conditions with highs in
the low 50s northwest to near 60 se)...before low pressure and a strong
cold front impact the region Tuesday night into Wednesday. Spatial
and timing differences continue with the 18/12z GFS tracking the
surface low west of the mountains...and the 18/12z European model (ecmwf) tracking the
surface low up the coastal plain. This will have impact on
temperatures and whether the rain is more stratiform or showery. If
the farther west 18/12z GFS were to verify there could be a potential
for thunder. However...even with this solution...surface dewpoints
at or above 60f remain offshore. Dry and breezy conditions will likely
prevail by Christmas day.
Aviation /06z Friday through Tuesday/...
broken middle level cloud deck between 9-12k feet will continue to move east across
through the ovrnight hours as trough of low prs moves east. These clouds
prognosticated to thin out aftr 12z as high prs builds into the area from
the west. North winds a0b 10 kts.
Outlook...low pressure tracks well to our south Sat/Sat night. This
may bring a period of broken/overcast conditions but ceilings are expected to
remain 4-5 k feet or higher. High pressure builds to the north of
the area Sunday. A series of low pressure systems and complex
frontal boundaries will bring chances for rain and periods of low
ceilings and visibilities beginning Monday.
high pressure continues to build in from the northwest tonight into
Friday. A secondary north-northwest surge arrives late tonight into early
Friday. Wind speeds over the Bay could briefly reach 20kt...but at
this time the duration is not expected to be long enough to warrant
an Small Craft Advisory. High pressure builds north of the region Friday night through
Sunday...with weak low pressure tracking off the southeast coast
Saturday. This should result in north-NE flow at or below 15kt through
Sunday...with 2-3ft seas. Another low pressure system develops off
the southeast coast Sunday night...and tracks NE off the middle
Atlantic coast Monday and Monday night. There is little to no cold air advection in
the wake of this low...so conditions should remain sub-Small Craft Advisory with a
wind becoming westerly by Tuesday. A potentially stronger low tracks
west of the mountains Tuesday night...with a strong cold front crossing
the middle Atlantic coast Wednesday.