Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Baltimore Maryland/Washington District of Columbia
842 PM EST Friday Nov 27 2015
high pressure will sink southward tonight and Saturday. A cold
front will push south across the area Saturday night. A weak wave
of low pressure will pass south of the area Sunday. High pressure
will try to build in from the northeast Monday before another
storm pushes a cold front across the area Wednesday.
Near term /through Saturday/...
high clouds will thicken overnight keeping temperatures mild. Curr
dewpoints suggest overnight lows will only dip a degree or two below
50f. We'll see clouds thicken further on Sat. Despite widespread
thick clouds...it still appears it will be mild although not as
warm as today was with highs expected in the middle 60s. Showers
will start working into western Maryland Sat morning and eventually work its
way southward as front enters the forecast area. It should stay dry
south of U.S. Highway 29 and 211.
Short term /Saturday night through Sunday night/...
front crosses the area Sat night with rain likely in the northern
half of the forecast area as weak wave of low pressure moves along the
front. Rainfall amounts of a tenth to a quarter of an inch will be
common north of the front Sat night.
Cold front should be near the southern border of the County Warning Area Sunday
morning...making only slow progress during the day. Warm/moist air
aloft will overrun the front...allowing for cold rain on the north
side of the boundary. Models do show a trend of the dry air slowly
filtering in from the north...but the GFS is sort of out on its
own in showing Sunday totally dry. There is enough support from
ensembles to justify retention of the current 40 pop on
Sunday...and actually increasing it to 50-plus over the west/SW
portion of the forecast area where the dry air will take the
longest to reach.
Sunday night is low confidence with simulation solutions all over
the place. The one common theme seems to be development of a wedge
as the strong surface high centers itself in the perfect place over
southern Quebec. What is not clear are precipitation chances. Again the op GFS
is dry as a Bone while the European model (ecmwf)...many gefs ensemble
members...and the overall consensus hint at continued rain
chances. While I did leave far northestern Maryland dry...a small chance of
rain was introduced for the Baltimore metropolitan...increasing as you go
further south and west.
Long term /Monday through Friday/...
stalled frontal boundary remains to the south through midday
Monday...keeping highs generally in the 40s...with onshore flow
and chances for overrunning showers. Boundary lifts north through
the area as a warm front late Monday...while an area of low
pressure ejects northeastward from the Central Plains toward the
Great Lakes. Passage of warm front will lead to an increase in
return flow and subsequent low-/mid-level moisture and allow
temperatures to return to the M/u50s Tuesday and Wednesday.
Cold front...associated with aforementioned low pressure over
Great Lakes...approaches our western border late Tuesday and moves
through the area Wednesday...bringing the highest chances for
precipitation during the long term. Cold air could filter in fast
enough to allow for some changeover to light snow showers across
our far west.
While there are a few noticeable outliers among the different
ensemble guidance...general consensus moves precipitation out by
late Wednesday. Cooler and drier air filters into the region
behind the front...with high pressure building over the area
through the end of the workweek.
Aviation /02z Saturday through Wednesday/...
VFR tonight with increasing probs of MVFR conditions starting late
Sat as front enters the area and light rain begins to fall. MVFR
conditions likely Sat night.
Potential for MVFR ceilings/visibility in rain Sunday and Sunday night. IFR
ceilings possible during that time.
Stationary boundary to our south Monday will allow for some
overrunning showers over mainly the southern half of the
area...with sub-VFR conditions possible in these areas. Periods of
sub-VFR spread across all terminals by late Monday into Tuesday as
warm front lifts over the area and then through Wednesday as cold
front passes through.
sub-Small Craft Advisory conditions expected through Sunday with increasing risk of
Small Craft Advisory conditions starting Sun night.
Cold front settles just south of the lower Maryland waters by Sunday.
Gradient winds pick up with mixing...yielding potential for 15
knot gusts Sunday night. Capped just below Small Craft Advisory criteria at this
time due to uncertainty of the strength of The Wedge/pressure
Mainly sub-Small Craft Advisory conditions expected Monday through
Tuesday...though pressure gradient may keep winds near Small Craft Advisory early
Monday...before it relaxes and winds subside.
Cold front will pass through the waters Wednesday...with a
potential for Small Craft Advisory conditions.
District of Columbia...none.