Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
424 PM EST Friday Dec 26 2014

Synopsis...
high pressure over the area tonight will move offshore Saturday. A
weak cold front will cross the region Sunday. A low pressure system
will move northeast along this frontal boundary on Monday. Colder
high pressure will follow for middle week.

&&

Near term /through Saturday/...

Surface analysis shows high pressure over the southeastern U.S. Which has been
responsible for quite a gorgeous boxing day as high temperatures climbed
to 5+ degrees above normal.

Tonight decoupling and clear skies will take temperatures down towards the
freezing mark and to sub-freezing for sheltered vlys/lowlands.
Metropolitan District of Columbia/balt areas should stay west/in the l-m30s range - about
where the current dewpoint readings reside.

The surface high remain parked over the southern Atlantic states into early
Sat...while a deep upper trough digs down over The Rockies and into
the Central Plains. The trough will eventually break off into two
separate features that will affect different parts of the East Coast
in the coming days. Highs tmrw will peak a few degrees higher than
today's values...as a more concentrated/warmer southerly wind flow
develops. Skies will remain generally clear until later in the
afternoon/evening when the cirrus/middle cloud debris from the incoming low
pressure wave arrives from the west.

&&

Short term /Saturday night through Monday/...
hipres ridge will be nudged offshore Sat night as lopres tracks eastward across
southern cnda. A weak cold front extends southwestward from this low...which perhaps will
reach the ptmc Highlands by dawn. The height field aloft packed but
not-quite zonal. Regardless...all signs point to a weak system up to
this stage. Will have isent upglide during the overnight hours...just ahead
of the fnt. Have clouds incrsg through the night...and lowering overnight.
Confined probability of precipitation to where the lower clouds reside...mainly west of blurdg
and across northern Maryland. Enough warm air advection to keep all temperatures above freezing. No ptype
issues. Blended MOS west/ prvs forecast to Iron out any diffs.

Cold front will slip through slowly on Sunday. Meanwhile...weak lopres develops
along fnt in vicinity of Gulf of Mexico CST and heads northeastward. That slug of moisture should
arrive Sun night--a little quicker than prvs forecast cycle. Therefore...probability of precipitation
rise through the day...and have the wettest time frame lt Sun afternoon into
sun evening. Since evolution a pinch quicker...that provides the
opportunity for cold air advection prior to sunrise Monday morning...on the back side of
the low. Dont think there will be that much residual moisture left by that
point /only chance pops/...but its enough to introduce wider covering of
shra/sn...and even some shsn in the Appalachians. Little confidence in actual
seeing measureable snow. Lingering precipitation into Monday as low pulls out and
cold front inches south-southeastward. It/ll be parallel to upper flow...so dont see
rapid improvement occuring.

No big discrepancies in MOS maxt Sunday. However...if frontal passage any sooner
could need to shave off a cpl degf across northern Maryland and the ptmc Highlands.
A bit more wiggle room in the min-T Sun night. Did not go as cold as
some guidance suggesting. Strength and timing of fnt will be discerning
factors. Based on modest cold air advection bhd system...should see a little diurnal
temperature rise...and reflected that in Monday maxt. But it will certainly be
tempered by northerly flow.

&&

Long term /Monday night through Friday/...
the combination of an upslope component to the wind and some upper
level energy from the west will provide a chance of some light rain
or snow in the Potomac Highlands and perhaps the highest terrain of
the central Shenandoah Valley Monday night. Otherwise...high
pressure will build from the west to bring a prolonged period of dry
conditions from Tuesday through Thursday night. Temperatures may
remain on the cool side each period...averaging 3 to 5 degrees below
normal.

Both the European and GFS models are hinting of some upper level
energy accompanying a developing warm front that will move from the
Tennessee Valley to the middle Atlantic region. With some colder air in
place ahead of the warm front and possibly trapped in some
valleys...we have slight chance to chance probability of precipitation of either some light
rain and snow mix or perhaps all snow. Of course...differences in
the timing and movement of the warm front leads to low confidence
for now. Temperatures may try to come up a few degrees Friday and
into Friday night.

&&

Aviation /21z Friday through Wednesday/...
VFR conditions through the current taf period. Same story Sat.

Outlook...
-Sat night...lowering ceilings but should stay VFR.
-Sun-Sun night...MVFR-IFR in low clds/rain. Cold front passage during day. Winds
should stay at or below 10 knots...but will be veering northerly.
-Mon...continued clouds..chc rain showers in vicinity of fnt. Perhaps a few shsn near mrb
toward morning push /low confidence/. Likely MVFR at worst.
-Tue...VFR.

&&

Marine...
light srly winds over the waters will drop off further overnight.
High pressure moving off the Carolina coast Sat will turn the
wind field more southerly and potentially introduce some minor southerly
channeling later in the day but lower than Small Craft Advisory criteria.

Light winds this weekend as passing cold front and low provide stable conds on
the water. Northerly winds could pick up on back side of system Monday. Keeping
it uneventful for now.

&&

Equipment...
klwx 88d will remain out of service until Saturday...when the parts
to repair the radar are expected to arrive.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...none.

&&

$$
Update...Woody!
Prvs...gms/hts/klw

National Weather Service Glossary of Abbreviations