Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Baltimore Maryland/Washington District of Columbia
1018 am EST Monday Dec 29 2014
weak disturbances will ride along a cold front...mainly to our
south...today through Tuesday. High pressure will build into the
eastern half of the country for the second half of the week. Low
pressure is expected to affect the middle Atlantic region this
Near term /through Tuesday/...
an airmass influenced by high pressure is not normally associated
west/ strong intensity...but the one over western Canada that is pushing
down into the northern half of the Continental U.S. Is. Analyzed a 1056mb ob in
western British Columbia...W/ global models forecasting over 1060mb in
the coming hours over this area. The high is so large that it is
dragging the cold air from much of northern Canada all the way down
past the US border and pushing the freezing line all the way to
the southern US border. Only the deep south and into the middle-Atlantic still
holding out. Overhead...a locally dense band of clouds and precipitation
from a relatively warmer southwesterly upper flow riding along a
The southern fringe of our County Warning Area is on the northern fringe of the current
precipitation shield...while colder air continues to filter down from the
north - and effect of the intense surface high thousands of miles to
the east. Skies across the Mason-Dixon line even showing
breaks...a sign the cold/dry air is eating away at the edge of the
incoming cloud decks.
From previous disc...
Ely component will promote precipitation development for central Virginia Blue
Ridge and areas farther west. Colder air there will allow some
snow above about 2500 feet today...lowering below 1000 feet tonight.
Expanded chance probability of precipitation farther northeast toward the balt-wash metropolitan
area per 06z NAM/GFS. Looks like some ageostrophic forcing along a
baroclinic zone will aid forcing in spite of mslp approaching
1030mb. Added some light snow amounts across the north-central Virginia
Piedmont. Snow probs updated as well which highlights the threat
for banded snow which could accumulate one to two inches fairly
quickly...should they set up. Cloudy across the County Warning Area with min temperatures
upper 20s to low 30s (mid 30s for near shore).
Precipitation shifts south Tuesday as high pressure continues to move
into the County Warning Area from the west. Expect light northerly flow and maximum temperatures
upper 30s to low 40s under clearing skies.
Short term /Tuesday night through Thursday night/...
high pressure expeceted to build into the area for new yrs evening...so weather will
not be a problem Wednesday night or the 1st day of 2015. The high should
remain in control of middle Atlantic weather through the end of the weak. This will
allow temperatures to moderate - Thursday morning lows will mainly be in the
l20s...by Sat morning about ten degrees warmer. The same will be true west/
high temperatures - Thursday around 40...a50 Sat.
Long term /Friday through Sunday/...
low pressure will be influencing the eastern U.S. Over the weekend. There is
difference in the models as to the trajectory of the system - Euro
has it on a southern track while the GFS takes it into the eastern Great Lakes
alng west/ a cold fnt pushing onto the east CST. Obviously this will need
to resolved in the coming days. At this moment p-type looks to be
liquid. If temperatures are able to drop below freezing then freezing rain will need to be
considered but that is a long way away.
Looking at the hemispheric 500 mb pattern of both the GFS and
ecm...the coldest air looks to remain locked over Hudson Bay into next
weak. Jan 5-8 2014 saw extremely cold air in the County Warning Area and the issuance of
multiple wind chill advisories and warnings (actual wind chill of -11
at dca....blo -40 in the highlands). No repeat in 2015.
Aviation /15z Monday through Friday/...
VFR conds continue to prevail as cold front and associated rain
continues to move south.
VFR conds expeceted Tuesday night through Friday.
light southwesterly flow veers northwesterly today as a cold front crosses the waters
this afternoon and evening. Could be a northerly surge with gusts around
18 knots late tonight. Did not raise an Small Craft Advisory due to uncertainty...but
one out of Sandy Point is possible into Monday.
No probs expeceted Tuesday night through Friday on the waters.
District of Columbia...none.