Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
841 PM EST Thursday Nov 26 2015
high pressure will dominate the weather through Friday night. A
cold front will slide southeast into the area Saturday and then
slowly dissipate Sunday. High pressure will briefly dominate
Monday before a cold front pushes across the area Tuesday.
Near term /through Friday/...
no changes to the synoptic pttn this evening...strong surface hipres remains
centered southeast of Nova Scotia with surface ridge extending
southwest across the middle Atlantic. Ridging is building aloft too...from
h8-5. Next cold front is pushing eastward across the western Great Lakes
and middle- Mississippi River valley. Through Friday...the high will
stretch out over our area and split in two as the front approaches
from the northwest and a low develops near Bermuda. This high will
be centered near US Friday morning...but will sink southward as
the front continues to approach from the northwest during the
Sensible-weather wise...expect mild weather to continue through
Friday. In fact...the mild temperatures today should end up even
milder tomorrow as the ridge aloft builds a bit...allowing even
warmer air to push north into our area. 850 temperatures right now are
around 5c will rise up to near 9c by about 24 hours from now. We
are getting slightly better mixing than expected and thus guidance
has generally been running below temperatures. If there were nothing
stopping US Friday 70 would be in reach...and it might be. For
that reason...especially given the recent cool bias...have opted to
raise maxt Friday by a degf over what the dayshift forecasted.
However...the southeast flow off the Bay and ocean have raised dew
points into the 40s. With the southwestern lobe of the high expected to
sit over US late tonight and Friday morning...winds should end up
near calm. Problem is...there is a veil of high clouds over County warning forecast area
at this time. Would need them to part first...and dont have a good feel how
quickly that will hppn. That said...latest lamp/hrrr/sref/narre guidance
all suggest strong fog potl east of the blurdg. A few of these guidance
sets even suggesting dense fog potl. However...overdoing dense fog
tends to be a model bias...leading to relatively lower confidence in
light of satpix. Will keep fog in forecast but limited it toward dawn. The
setup is too good to discount it outright.
Short term /Friday night through Sunday night/...
approaching cold front continues to slow down on guidance with
only a slight chance of any showers later Friday night northwest
of I-95. This results in an increased risk of patchy fog though
there may be enough wind to prevent it. Nevertheless...have some
patchy fog in grids.
Light precipitation possible over the western half of the County Warning Area Sat morning with
frontal boundary extending from New England south across the Ohio
River valley. 12z model suite showing the weakening of the
boundary as it moves into the middle-Atlantic with surface high pressure
holding strong just to the south...and flow aloft weakens to a
more zonal flow. Despite the weakening...the boundary holds
together enough to act as a triggering place for showers Sat into
sun...with the most likely location being the southwestern corner
of the County Warning Area closer to the boundary as well as the placement for a
passing shortwave. Will keep chance wording in for the remainder of
the County Warning Area through Sun night until confidence increases to where/when
the precipitation will occur.
Temperatures ahead of the front on Sat will still reach the middle 50s to
lower 60s. By sun...cold air advection behind the front will keep highs in the
middle 40s to low 50s and overnight lows both Sat and sun in the middle
30s to lower 40s.
Long term /Monday through Thursday/...
active first half of next week with the stalled boundary just to
the south Monday...eventually lifting north into the eastern gl
region Tuesday...with the associated cold front then passing
through midweek. Ely to northeasterly flow persistent Monday...and with SW-west
flow aloft...expecting a cloudy...cooler day on Monday. Have chance
-ra in the forecast at this time...but could very well end up more -dz in
nature...with periods of dry weather throughout the day. By Monday
night...warm front lifts north...though potentially over the
western half of the County Warning Area...resulting in Ely flow continuing for the
eastern half. Whatever the wind flow at the surface...see the
potential for incrsg coverage in -ra with incrsg moisture
Timing of the cold frontal passage on the 12z model guidance generally
showing sometime Tuesday night/early Wednesday morning. With the
uncertainty...keeping chance wording in for this time period...with
drying conditions by Wednesday night as westerly flow injects in
drier...cooler air. Snow possible in the wake of the front on the
Allegany front during this time frame as well.
Aviation /01z Friday through Tuesday/...
expect VFR through at least 6z at all terminals with some mainly middle
and high clouds passing through. Winds light with an overall
Low level moisture has advected into the region today and with
light winds under high pressure expected overnight...the stage
appears set for fog. Exact timing...density and location is still
somewhat uncertain...since we need to get rid of high clouds across
the terminals first. If that hppns late the fog potl will be
reduced. Kept MVFR all terminals except mrb/dca late tonight and
early Friday. IFR and perhaps even LIFR remains possible but far
from certain at this point.
Conditions should improve to VFR by afternoon Friday with light
southerly winds. Patchy fog again possible later Friday night.
Generally VFR conditions on Sat...with sub-VFR conditions becoming
likely Sat night into sun with incrsg chance of -ra. VFR conditions
return Sun night...with yet another chance of sub-VFR conditions Monday
night into Wednesday with the next round of precipitation.
light...generally southerly winds 10 kts or less through Friday
night. Patchy fog possible later tonight and Friday morning...and
then again later Friday night.
Sub-Small Craft Advisory conditions through the weekend into Monday. Possible Small Craft Advisory
gusts Tuesday-Tuesday night ahead of the cold front.
today was the warmest Thanksgiving since 2007...when highs were in
the 70s. In addition...the 63 degree high at iad tied for the 7th
warmest Thanksgiving on record. However...the period of record at
iad is shorter than at dca/BWI...where today doesn't even rank in
the top 10.
District of Columbia...none.