Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
944 PM EDT Monday Oct 20 2014
low pressure moves into the region tonight and Tuesday...locating
off the northeast coast for much of the middle to late week period.
Near term /until 6 am Tuesday morning/...
surface high pressure was centered well off the coast this evening
allowing for a relaxing pressure gradient along the coast and inland with
southerly winds 10 knots or less. Meanwhile...an upper level trough digs
into the Great Lakes/northeast tonight...with a surface cold front
reaching The Spine of the Appalachians around 12z Tuesday.
Shortwave energy rounding the base of the trough has been
providing weak lift supporting a thin band of isolated showers on
radar over the western County Warning Area...however due to the dry air in place
in the lower levels most of the radar are resulting in virga. Bufr
soundings show overall dry airmass in place tonight (pw's at or below
0... it will be hard to get much of precipitation to reach the
ground. The hrrr ties to develop a thin band of showers east of
I-95 around 06z...but this appears to be overdone. That said
cannot rule out a few brief sprinkles overnight. Overall dry
conditions are expected through tonight with some increasing cloud
cover. The cloud cover and light SW flow could keep some areas
from reaching forecast lows keeping conditions milder. Lows
generally in the upper west to middle 50s at the coast.
Short term /6 am Tuesday morning through Thursday/...
flow amplifies during the short term as a blocking pattern develops
over eastern Canada. Additional energy dives south over the Great
Lakes/Ohio Valley Tuesday thanks to a ~100 knots jet streak diving southward
from Canada. As a result...upper low prognosticated to develop over the
middle-Atlantic into the NE states late Tuesday. The upper low will
progress slowly eastward Tuesday night into Wednesday...locating off the
Delaware-Maryland-Virginia coast late Wednesday. With the upper low pivoting across the
local area Tuesday/Tuesday night...will see a better chance for showers
develop especially north/NE where best upward motion is
anticipated. Have chance (pops 25-40%) along and NE of a line from
lku-ofp-mfv on Tuesday...then best chance (30-50%) mainly along the
Virginia coast and onto the Eastern Shore Tuesday night. Elsewhere...will
carry no higher then 20% probability of precipitation. Highs Tuesday in the upper 60s northwest to
middle 70s southeast. Lows Tuesday night in the middle 40s to middle 50s. Mostly
cloudy north to partly cloudy south during thie time.
Deep upper trough/closed low slowly moves east and offshore Wednesday.
Forecast soundings fairly dry aloft over inland sections as the
trough/surface reflection swing offshore. Will therefore keep chance probability of precipitation
limited to areas along and NE of the I-64 corridor Wednesday...with
emphasis on the Northern Neck and Eastern Shore (30-50% pops).
Could end up being dry over far SW zones. Cooler Wednesday with highs
The closed low moves farther NE Wednesday night into Thursday...locating off
the New England coast by 00z Friday. Any leftover shower chances
by then will be limited to the Eastern Shore (20%). Decreasing
clouds are also expected across interior Virginia. Lows Wednesday night in the
low 40s to low 50s. Cool again Thursday with highs 60-65.
Long term /Thursday night through Monday/...
low pressure lifts to the NE Thursday night through Saturday as
upper ridging expands eastward from the central US. A weak trough
clips the northern middle-Atlantic Saturday night and quickly moves off the
coast Sunday. Middle/upper level ridging builds over the eastern US early
next week. Overall...dry conditions should prevail through the
medium range period. High temperatures should average in the middle 60s
to around 70 Friday and Saturday...and trend upward into the upper
60s to low 70s Sunday...and potentially 70-75 by Monday. Lows should
range from the low/middle 40s northwest...to the low/middle 50s for southeast coastal
Aviation /02z Tuesday through Saturday/...
VFR weather is forecast through 00z taf period. Expecting periods of middle
level cloudiness (cigs mainly 10-15kft) tonight west/ scattered-broken cloudiness (mainly 10-12
kft) early Tuesday morning lowering to 5-6k feet Tuesday afternoon. No precipitation is expected
overnight with low levels too dry but there is a chance for showers
mainly at sby by Tuesday afternoon (not in taf). Light S winds become west
near 10 knots toward midday Tuesday as a weak cold front moves
Outlook...low pressure off the middle Atlantic coast deepens and
lingers off the New Jersey coast through middle week. There will be a
chance for showers and MVFR ceilings (especially eastern portions) Tuesday night
and Wednesday ending Wednesday night. MVFR ceilings may linger into early Thursday
but no significant IFR is indicated. The low pressure system moves
away from the coast and high pressure builds in from the north
Thursday through Saturday with dry and VFR conds.
surface high pressure slides offshore tonight...allowing the wind to
remain S/SW. Expect sub-Small Craft Advisory conditions to prevail with wind speeds
averaging up to 15-20 knots across northern coastal waters...and
generally 10-15 knots elsewhere. The next cold front will slowly cross
the coast late Tuesday afternoon/evening...followed by eventual Small Craft Advisory
conditions later Wednesday into Wednesday evening as surface low
pressure then deepens off the coast. This system is expected to
stall offshore Thursday through the end of the week bringing a
prolonged period of Small Craft Advisory conditions. With flow being offshore from
the northwest...seas would tend to stay capped at 5-6 feet and tidal flooding
is not expected. North/northwest flow is expected to continue into next weekend
with speeds diminishing to 10-15kt and seas subsiding.