Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
645 am EDT Tuesday Jun 30 2015
low pressure will slide northeast across the eastern Great Lakes
today...with the associated cold front approaching the area from
the northwest late this afternoon into tonight. The front will
stall across the region Wednesday through Saturday...with low
pressure tracking along the front later Thursday afternoon into
Near term /through tonight/...
the current upper air analysis shows a trough over the Great Lakes
region...with a ridge centered over the subtropical western Atlantic.
At the surface...a broad area of low pressure is situated over the
Great Lakes...with a cold front trailing back through the Ohio
Valley. The primary trough axis will lift across the eastern Great
Lakes today...with a shortwave trough approaching from the west by
later this afternoon. Meanwhile...the surface low will lift
through the eastern lakes as well...with the cold front approaching
from the northwest. A pre-frontal trough develops over the region today
with strong diabatic heating...and this will become the Focal
Point for isolated-scattered convection later today into this evening.
Effective shear values are prognosticated to reach 30-40kt by late this
afternoon into this evening coinciding with the approach of the
shortwave trough. Instability is more marginal (mlcape of
1000-1500 j/kg) when compared to the events of Jun 20/25. Overall
storm structure should be less organized than those events...but a
threat of damaging wind gusts still exists based on the strength
of the shear in a region of steep low-level lapse rates and a
The day should begin sunny across the region...before becoming
partly to mostly cloudy late this afternoon into the evening.
Highs are expected to reach the upper 80s to low 90s. Probability of precipitation then
taper off after midnight with partial clear late (especially w).
Lows tonight are forecast to range from the upper 60s to middle 70s.
Short term /Wednesday through Thursday/...
the frontal boundary settles immediately north of the region
Wednesday. Overall...there is little forcing...so only a ~20% pop
is forecast for most of the area...with the exception of ~30%
closer to the coast where low-level moisture will be somewhat
higher. Highs are forecast to once again reach the upper 80s to
low 90s. Partly cloudy conditions are expected Wednesday night
with lows in the upper 60s to low 70s.
The front sags S into the region by Thursday.
Meanwhile...shortwave energy is expected to track into the central
Appalachians by afternoon. The 00z/30 NAM is the quickest...while
the 00/30 GFS/ECMWF/CMC lag the energy to the west until afternoon.
At this time...the later consensus solution has been
favored...with only 20-30% probability of precipitation forecast in the morning...before
bringing 40-50% into western portions by later in the afternoon...with
30-40% farther east. High temperatures are expected to range from the
low/middle 80s north...to around 90 southeast with the front over the region.
Long term /Thursday night through Monday/...
unsettled conditions seen through the period as a frontal boundary
becomes stalled across the region with several S/w's dropping southeast
in the overall northwest flow. Timing of any short wave (or convective complex)
rather problematic at this time...so will carry the probability of precipitation through the 12
hour period versus trying to go with a more diurnal pattern. Some
consensus has developed with respect to a shortwave trough
tracking across the region Thursday night/early Friday. There is a
potential for heavy rainfall with this system. A broad 50% pop is
forecast at this time Thursday night/early Friday...before tapering to
30-40%. Then basically 30-40% for the rest of the period except
Sunday where the latest data is hinting at a somewhat drier day
Temperatures coolest Friday given widespread cloud coverage and precipitation chances.
Highs in the 80s. Boundary location will play a role in temperatures
for the rest of the period...but model trends are for the warm
front to eventually lift north of the forecast area placing region in a
more humid airmass. Thus...highs each day in the m80s-l90s.
Lows Thursday night u60s-l70s. Otherwise...lows in the 70s.
Aviation /12z Tuesday through Saturday/...
VFR through the 12z taf period. Surface hi pressure remains offshore today
with southerly flow developing across the middle Atlantic. Could see some gusts
up to ~20 knots this afternoon with mainly just middle/hi clouds expected.
Rain showers/thunderstorms are possible this afternoon/eveng especially at ric/sby...but
chance is too low to include in the tafs at this time.
Outlook...a frntal systm slowly approaches from the west during the
rest of the week. Mainly VFR conds will prevail. There will be
chances for afternoon/eveng rain showers/thunderstorms each day with the highest
chances on Thursday and Friday with the front in the vicinity.
hi pressure remains offshore today as low pressure traverses the Great Lakes
region. Between these two features...southerly flow will increase through the
day across the middle Atlantic. Marginal Small Craft Advisory remains in effect for the Bay
starting midday as the pressure gradient increases...with winds
staying sub-Small Craft Advisory over the rivers/sound/cstl waters. The Small Craft Advisory ends
tonight...with weaker southerly/southwesterly flow (10-15 kt) expected for Wednesday ahead
of an approaching cold front. The front drops into the area from the northwest
on Thursday...with winds becoming light and vrb Thursday and Friday as the front
stalls over the region. Waves average 1-2 feet and seas average 2-4 feet through
the week. Seas may come close to 5 feet over northern waters at times.
Marine...Small Craft Advisory from 1 PM this afternoon to 4 am EDT
Wednesday for anz630>632-634.