Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
857 PM EST Thursday Dec 18 2014
a weak upper-level trough will continue to pass through the
region tonight. High pressure will build overhead through Friday
night...then persist through Sunday. Low pressure will track
up the southeast coast Sunday night through Monday night...with
a stronger low crossing the middle-Atlantic Wednesday.
Near term /through tonight/...
as of 01z...994mb surface low over Canadian Maritimes and a 1030mb surface
high just west of Lake Superior (boundary waters). A weak upper
shortwave low is moving east from West Virginia. Light echoes have
spread east with some light snow reported in the Harrisonburg
area. Added some flurries to the forecast for all elevations above
500 feet. Will need to monitor possible expansion of flurry mention
for entire Baltimore metropolitan (where echoes are above about 1200 feet
mean sea level at 0148z).
Otherwise...thick middle-level clouds persist through tonight. Min
temperatures middle to upper 20s with dewpoints remaining in the low 20s.
Short term /Friday through Saturday night/...
high pressure will be in control for Friday and Friday
night...leading to tranquil weather and less gusty winds. Perhaps
some passing clouds but even overnight with the more suppressed
southern stream system...most of the County Warning Area may only see cirrus. Not
much temperature advection...highs perhaps a tick warmer but still
in the 40s...with overnight lows below freezing.
Surface high pressure will build over New England and the ridge axis
will extend south into the middle-Atlantic Saturday through Saturday
night. This will allow for seasonably chilly conditions during this
A couple shortwaves...one in the northern stream of the jet and one
in the southern stream of the jet will pass through our region
Saturday afternoon and night. These systems will not phase so the
northern stream shortwave will remain to our north and the southern
stream shortwave will remain to our south. Most of the moisture will
remain to our south with the southern stream system as well.
Therefore...most areas are expected to remain dry during this time.
However...light precipitation may brush portions of the Potomac
Highlands and central Virginia Saturday into Saturday night. There
will be enough cold air for snow if precipitation occurs...but
little or no snow accumulation is expected with most of the moisture
remaining to the south.
Maximum temperatures Saturday will range from the 30s in the mountains to the
lower and middle 40s across most other locations. Min temperatures Saturday
night will be in the middle to upper 20s across most locations...but
lower and middle 30s in downtown Washington and Baltimore.
Long term /Sunday through Thursday/...
upper level cut-off low centered over the upper Mississippi Valley
Sunday will slowly drift to the east and fill by Wednesday night.
A shortwave moving through the pattern will support development of a
surface low over eastern North Carolina and Virginia Wednesday.
Surface low will move on to New England by Wednesday night.
Moisture will increase over middle Atlantic region will increase on
southwest winds during early half of period. Marginal 1000-500 mb
thickness values and air temperatures around freezing may support
snow...or wintry mix. More moisture will follow at middle week ahead of
low approaching from the middle west. Temperatures should stay high
enough that precipitation should be rain.
Aviation /01z Friday through Tuesday/...
VFR middle level ceilings overnight...VFR conditions expected through
the taf period. Northwest flow 5-10 knots tonight...10 to 15 knots Friday.
VFR conditions are expected across most of the terminals Saturday
through Saturday night. A period of light snow or rain may impact
kcho. Subvfr conditions are possible if any precipitation develops.
High pressure will build over the terminals Sunday...but low
pressure may impact the area Tuesday and Wednesday with
precipitation and subvfr conditions.
high pressure builds over the waters through Friday night.
Small Craft Advisory returns for all but western tributaries Friday morning into
the afternoon as the gradient remains high enough to warrant 18 knots
High pressure will remain over the waters Saturday through
Sunday. Dual low pressure will impact the waters early and middle
of next week.
District of Columbia...none.
Marine...Small Craft Advisory from 6 am to 3 PM EST Friday for