Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Baltimore Maryland/Washington District of Columbia
1045 am EST Sat Dec 27 2014
high pressure will remain across the middle-Atlantic today...before
moving east of Cape Hatteras tonight. A cold front will stall
across the region early Sunday...then low pressure will move along
the stalled front Sunday afternoon and evening. Another low
pressure system will move across the Carolinas Monday and Monday
night...followed by high pressure building into the region on
Tuesday...and remaining through the remainder of the work week.
Near term /until 6 PM this evening/...
skies clearing out again behind the weak upper shortwave passage.
This feature brought some middle cloud decks earlier this morning
that are now dissipating over southern Maryland/Virginia Piedmont. A few more hours
of sun into the afternoon...then the beginnings of yet another multi-
day rain event for the mid-Atlc. Cirrus and middle cloud debris from
the incoming low pressure system won't arrive until later this
aftn/eve. Temperatures at this time still fairly moderated but expecting highs
today to still approach 60f in the lower shen valley/northern Virginia Piedmont
west/ M-u50s elsewhere but still a few degree below guidance.
Short term /6 PM this evening through 6 PM Sunday/...
an area of low pressure will be tracking from the Great Lakes into
Quebec tonight. The trailing cold front will be approaching the
Appalachians but begin to lose steam as it runs into the upper
level ridge and becomes parallel to the upper flow. Forcing and
moisture will be limited...with a chance of showers reaching the
western ridges after midnight. With cloud cover...warm air advection and increasing
low level moisture...temperatures should hold above freezing and
thus eliminate any ptype issues.
A wave of low pressure originating from the Gulf Coast will track
along the front and bring the highest probability of rain to the
entire area on Sunday. Timing may be a hair quicker than the
previous forecast...but the highest probability of precipitation still reside in the
afternoon. Despite precipitable waters increasing to around an inch...forcing is
rather scant...and it appears most areas will receive less than a
quarter inch of rainfall. Temperatures during this stage of the
front will undergo more influence aloft than at the surface...with
highs Sunday expected in the upper 40s to lower 50s...possibly a
little cooler in the northwest depending on timing of frontal passage.
Long term /Sunday night through Friday/...
models look very coincident on Sunday night having high
probability of precipitation...however the GFS has substantially more quantitative precipitation forecast. Both models
drop the quantitative precipitation forecast south through the County Warning Area on Monday...with decreasing
probability of precipitation during the daylight hours Monday.
However...Monday night the 00z European model (ecmwf) and the 00z GFS diverge on
their quantitative precipitation forecast...with the GFS having more quantitative precipitation forecast. Both models have low
pressure moving from the southeast U.S across the Carolinas...but the GFS
throws the precipitation shield all the way back west of the Blue Ridge
into the cold air. I am discounting this solution and will go with
the European model (ecmwf) quantitative precipitation forecast which paints the heaviest quantitative precipitation forecast across southern
Probability of precipitation below climatology will commence Tuesday night and continue through the
end of the work week...with the period Tuesday night through
Wednesday night being below climatology for min temperatures and maximum temperatures on
Wednesday. Otherwise looks like a fairly seasonable late December week
for both temperatures and precipitation...with new years evening a few degrees colder
than normal but dry...and New Years Day remaining dry with near
normal daytime maximum temperatures.
Aviation /14z Saturday through Wednesday/...
high pressure will slide offshore today. VFR expected through
tonight...with middle/high level ceilings lowering late tonight. Winds
light/vrb...becoming more pronounced out of the south by this
afternoon/evening but remaining less than 10 knots.
Sunday...MVFR/IFR at times with low clouds and rain. Cold front
passes...veering winds to the north.
Sunday night and Monday the terminals will see continued MVFR
conditions due to low ceilings and visibilities...improving on Tuesday.
high pressure will bring continued light winds across the waters
today. As the high moves offshore tonight...winds will become
southerly but should remain less than Small Craft Advisory levels. Low pressure and
a cold front will bring rain on Sunday...but stable conditions
will keep winds light.
Winds may approach Small Craft Advisory conditions during daylight hours Wednesday and
klwx WSR-88D will remain out of service until at least later today as
repair parts and technicians are expected to arrive later this
District of Columbia...none.