Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
829 PM EST sun Dec 8 2013
low pressure will move northeast across the middle-Atlantic through
Monday. An upper-level disturbance will pass through the area
Tuesday. Canadian high pressure will build overhead for the second
half of the week.
Near term /until 6 am Monday morning/...
went ahead and extended the Winter Weather Advisory for Calvert/St
Marys until 7am to match the rest. They have a northeast wind that
has no apparent warm up even though it is crossing the Bay with
middle 40s water temperatures.
Winter Storm Warning for balt- wash metropolitan...north to the Mason-
Dixon...west across the Allegheny Front...south to our southern County Warning Area
border...includes shen valley...MD/VA Piedmont. Main wave of
freezing now reaching kcho. Areas of freezing drizzle across the
rest of the region will be overtaken by this swath of light to
moderate freezing rain.
As of 01z...1035mb surface high is over New England. With 1030mb mslp
over balt-wash...a northeast wind has developed...strengthening
The Wedge/cold air damming.
Short term /6 am Monday morning through 6 PM Monday/...
warmer air moves into the region Monday...with freezing rain
changing to rain. In general...expect precipitation to taper off with
temperatures warming into the low to middle 40s. Areas with a snow pack will
not reach the 40s...may struggle to get much above freezing.
Long term /Monday night through Sunday/...
the surface boundary will remain stalled just southeast of County warning forecast area Monday ngt-Tue. The
pttn aloft will be characterized by a broad ridge across the western Atlantic/southeastern
Continental U.S. And a l/WV trough axis from the Great Lakes back toward the desert SW. A
tight 500 mb height pttn prognosticated southeast of the trough...highlighted by a 160+ knots
upper jet. While shortwave energy will cross the Great Lakes headed toward New
England Tuesday...resulting in a more znl flow pttn...County warning forecast area will reside
in rrq of the jetmax. Have been hopeful that the boundary would push far
enough southeast to not be an issue Tuesday when another ripple propagates
along the fnt...but am becoming more concerned that won't be the case.
There/S plenty of upper level lift to support precipitation /even the dry European model (ecmwf)
coming on board/. Thermally...the air mass would be cold enough to support
snow...even though blyr temperatures may be marginal. Subfrzg dewpoints would
support more evap cooling/wet bulb effect...so cannot discount the
potl of more snow. If anything...MOS temperatures may be too warm. Have
kept same flavor in grids for Max/min-T...but placed a little more
emphasis on snowy ptype. Too far out to talk about accums...but severe weather potential statement
already reflects possiblity of addtl snfl...so no further adjustments
Hipres builds eastward from center of Continental U.S....providing a chilly air mass for the
2nd half of the weak. Its also remarkable how quickly subsidence
advcs. Dont believe there will be much opportunity for upslope shsn...
although will be adding a few clouds Wednesday.
Guidance at odds by the end of the forecast. European model (ecmwf) remains dry...but GFS
suggesting lopres tracks across the US/Canadian brdr...dragging a cold front
through and advecting moisture northeastward ahead of it. If that were to occur...
ptypes would again be an issue. Too far out to draw any conclusions
yet...but do have probability of precipitation in the database Sat.
Aviation /01z Monday through Friday/...
periods of freezing drizzle becoming moderate freezing rain
through the late evening. IFR conds prevail through the overnight
hours. Significant ice accumulations possible across the
terminals...particularly at kcho/kmrb/kiad/kbwi. Ceilings and visibility
will remain generally IFR through Monday.
An addtl WV of lopres along the stalled boundary offshore may lead
to more precipitation Tuesday. Cho-dca-BWI will be closer to source...and stands
the better chance at seeing something. Temperatures will be cold enough to
support snow. Even west/o precipitation...flgt restrictions a strong possiblity
due to ceilings...W/ IFR likely in any snow.
VFR expeceted Wednesday-Thursday as hipres builds.
northeasterly flow 10 to 15 knots on the waters tonight as a high pressure
ridge persists over the area.
As the cold front mvs offshore...northerly flow commences around building hipres.
That would support channeling in the chesepeake Bay. Small Craft Advisory possible...primarily
for the Middle Bay. The flow would be interrupted as a wave of lopres mvs
along the surface boundary Tuesday.
quantitative precipitation forecast around an inch into Ely Monday will cause addtl river rises Monday
into Tuesday. However...not most of that quantitative precipitation forecast will fall as freezing
rain...so there/S some uncertainty as to when and how quickly
those rises will occur... or how significant they will be. A Flood Watch may
be warranted also for areas of heavy snow that may experience a
melt on Monday afternoon.
District of Columbia...Winter Storm Warning until 10 am EST Monday for dcz001.
Maryland...Winter Storm Warning until 10 am EST Monday for mdz003>007-
Winter Weather Advisory until 7 am EST Monday for mdz016>018.
Virginia...Winter Storm Warning until 10 am EST Monday for vaz025>031-
Winter Weather Advisory until 7 am EST Monday for vaz055>057.
WV...Winter Storm Warning until 10 am EST Monday for wvz050>053-055-