Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
345 am EST Sat Dec 20 2014
weak low pressure will track from the Gulf of Mexico eastward and
off the southeast coast through tonight. High pressure will be over
the area again during Sunday. Another low pressure area moves
northeast out of the Gulf of Mexico and up along the Carolina coast
late Sunday night through Monday night.
Near term /through tonight/...
surface high pressure over the middle-Atlantic today keeps deeper
moisture from the Gulf shunted to our south as middle level flow
remains fairly zonal. Latest radar mosaic not showing much in the
way of precipitation making it any farther north than the NC/SC border
early this morning...and latest surface observation confirm that.
Therefore...will keep forecast dry through 12z. 00z suite of models
try to bring some light precipitation into far southern portions of our County Warning Area
later this morning into the afternoon. However...models have
continued to trend drier since yesterday...and will limit probability of precipitation to
no more than 30% across NE NC this afternoon. Generally expecting dry
weather north of Highway 58 in Virginia. With temperatures at or below freezing
across the Piedmont this morning...an precipitation that falls near the NC
border prior to 15z could be in the form of a snow shower or sleet
pellets with no accumulation. Cloudy to mostly cloudy today with
highs in the upper 30s northwest to middle 40s southeast.
Surface high pressure rebounds tonight with decreasing clouds. Lows in
the middle 20s north to the low 30s south.
Short term /Sunday through Monday/...
high pressure remains entrenched over the middle-Atlantic Sunday with
a mix of sun and clouds. Seasonable highs of 45-50.
Next system...this one more amplified will affect the area on
Monday...with likely to categorical probability of precipitation all zones Monday am/Monday afternoon.
Looks like all rain aside from a brief mix possible at onset in
far northwest counties. At this point...it does not appear enough frozen
precipitation would occur to cause any concerns. Lows Sunday night from
around 30 northwest to around 40 Virginia Beach. Highs Monday only around 40 northwest
to the middle 50s far southeast in cad setup.
Long term /Monday night through Friday/...
low pressure lifts to the NE Monday night with probability of precipitation slowly diminishing
from SW-NE overnight. Middle-level ridging briefly builds into the
region Tuesday. However...moist southerly flow originating from
the Gulf Stream will prevail so low chance (30%) probability of precipitation will be
maintained. A very dynamic system lifts north-northeast west of the
Appalachians Tuesday night with the attendant cold front crossing
the middle-Atlantic Wednesday. The first potential of rain arrives
Tuesday night associated with moist warm air advection. The second potential will
be Wednesday ahead of the cold front. There is a potential for
thunder Wednesday as surface dewpoints potentially exceed 60f
(especially over the coastal plain). The pattern does support the
possibility of a dynamically forced line of convection containing
strong wind gusts as current forecast guidance suggests a
925-700mb wind field averaging 40-50kt. This would be a
climatologically rarity this time of year...so confidence is on
the low-side given that this is 5-6 days out. Temperatures will be
very mild ahead of the front Tuesday and Wednesday...with highs
averaging from the middle 50s northwest...to middle/upper 60s southeast. Dry and
breezy conditions will likely prevail by Christmas day...with high
temperatures of 50-55. The flow becomes more SW by Friday with
current forecast highs of 55-60...but 60-65 is possible based on
low-level thickness fields.
Aviation /08z Saturday through Wednesday/...
VFR conds in place across the region this morning, with
predominately VFR conds to persist through the taf period. High
pressure will continue to ridge south across the region from the
eastern Great Lakes/northeast through the taf period, as an upper
level disturbance moves across the southeast toward the Carolinas
today, while associated weak surface low moves across the southeast
today and tonight. East flow will allow for lowering ceilings through
the morning, with overcast at 5-8 kft above ground level expected through afternoon.
Forcing will be enough for some spotty light rain shras, mainly in
far southern portions of the area. Periodic MVFR ceilings will be possible
across phf/orf/ecg after 18z. However, rain should be light enough
to preclude any visibility restrictions.
Outlook...any precipitation comes to an end early Saturday evening and
conditions will gradually improve from west to east through the rest
of Sat night. High pressure builds to the north of the area Sunday.
A series of low pressure systems and complex frontal boundaries will
bring chances for rain and periods of low ceilings and visibilities
latest observation high pressure spreads east across New England through
tonight, ridging south into the area today. Meanwhile, weak surface low
pressure will pass south of the region later today and tonight. This
will maintain light northerly flow ~10 knots over the marine area
today. High pressure moves farther east Sunday and Sunday night, as low
pressure develops off the southeast coast Sunday night before
tracking NE off the Lower Middle Atlantic coast later Monday and Monday
night. The resultant tightening surface pressure gradient will allow
onshore (east) flow to gradually increase Monday aftn, gradually
building seas Monday night and early Tuesday. 15-20kt easterly flow
over the ocean and Lower Bay could produce a period of Small Craft Advisory
conditions especially over the southern ocean zones (mainly for seas) and
Lower Bay/mouth of James. There is no cold air advection in the wake of this
low...so sub-Small Craft Advisory conditions should prevail behind the system later
Monday night into Tuesday.
A strong low pressure system looks to develop across the Ohio
Valley, tracking west of the mountains Tuesday night. However, this
system will push a strong cold front across the middle Atlantic coast
later Wednesday. Small Craft Advisory conditions are likely Wednesday night into
Christmas day as high pressure builds in from the west-northwest.