Scientific Forecaster Discussion
fxus61 kphi 172214
Area forecast discussion
National Weather Service Mount Holly New Jersey
614 PM EDT Tue Sep 17 2019
high pressure across eastern Canada will build southward into
the mid-Atlantic through Thursday and then shift south of the
area on Friday. The high will then push offshore this weekend
as Canadian low pressure and an associated cold front approach
the area on Monday.
Near term /through Wednesday/...
630 PM update: adjusted wind vectors to favor a northerly
direction in the Philadelphia Metro area and increased gusts
just a bit, all to conform to current observations. The
prevailing wind direction is still expected to favor the NE
after sunset and through the overnight hours. Otherwise current
forecast still on track.
High pressure centered in Quebec will continue to
bring dry weather conditions to our region for tonight. We are
anticipating a mainly clear sky. However, some clouds
approaching from the northeast may begin to drift overhead
toward daybreak. Initially, the clouds may affect only parts of
central and southern New Jersey.
A northeast wind around 5 to 10 miles per hour is expected in our region from
the Interstate 95 corridor to the coast. The wind should be light
and variable in areas to the northwest. The light wind and the
mostly clear sky may allow for the development of some River Valley
fog in eastern Pennsylvania and northern New Jersey late tonight.
Low temperatures are forecast to favor the 50s.
Short term /Wednesday night through 6 am Wednesday/...
the high to our northeast should continue to influence our weather
for Wednesday. We are expecting another rain-free day. However,
there should be more cloud cover than we observed today.
A short wave trough is expected to drop southward in the mid level
flow on Wednesday. Also, the moisture associated with today's cloud
cover over much of New England is forecast to be over our region at
that time. As a result, the sky cover should vary from partly to
mostly cloudy especially over the coastal plain.
Temperatures on Wednesday are anticipated to be cooler than those of
today. Highs should be mostly in the upper 60s and the lower 70s
with a northeast wind around 8 to 14 miles per hour.
Long term /Wednesday through Tuesday/...
Mid-lvl ridging will reside upstream of the area at the start of
the period before shifting overhead and then finally cresting
the area in the Saturday/Sunday timeframe. At the surface
Canadian high pressure will build into the area on Thursday
before shifting south of the area Friday, and then eventually
moving offshore over the weekend. A trough will approach the
area Monday, with the primary surface low tracking well north of
the area through eastern Canada. The attendant cold front and
surface trough will cross the area in the Monday-Tuesday
timeframe, resulting in the only real shot at any precipitation
during the period.
Thursday... it will be quite dry Thursday as the surface high
shifts overhead (pwat values are forecast to be only around 0.3
inches!). given onshore flow for most of the day temperatures
will remain seasonable with highs generally in the low 70s.
Friday-Sunday... as the high shifts south of the area, flow
will transition more westerly and then southwesterly by Sunday.
Temperatures will warm through this period, and highs
Saturday/Sunday should make it into the mid or potentially even
the upper 80s.
Monday... we will likely see warm temperatures again (similar to
sunday) in prefrontal southwesterly flow on, however, these
temps could be tempered somewhat if the front and/or associated
mid- lvl clouds arrive early enough in the day (as the
(generally too fast) GFS indicates). Precipitation chances near
or just ahead of the boundary increase in the afternoon,
although this far out the setup does not look overly impressive
from a convective standpoint. Consequently at this point left
any mention of thunder out of the forecast.
Aviation /22z Tuesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Tonight...VFR under a mostly clear sky. Northeast wind 8 knots or
Wednesday...VFR ceilings developing. Northeast wind 6 to 12
Thursday...some sub-VFR am stratus potential primarily near the
coast, otherwise VFR with east-northeast winds 5-10kts.
Friday-Sunday... VFR prevailing with generally light winds
favoring the western half of the Compass.
Hurricane Humberto will remain well to the southeast of Delaware and
New Jersey. However, high pressure to our northeast will maintain a
northeast wind on our coastal waters for tonight and Wednesday. Wave
heights will build gradually to 5 to 8 feet on our ocean waters. As
a result, a Small Craft Advisory is in place from Little Egg Inlet,
New Jersey to Fenwick Island, Delaware. A Small Craft Advisory
begins for our coastal waters from Little Egg Inlet to Sandy Hook,
New Jersey at midnight.
Thursday through Saturday morning...Humberto swells will likely
keep seas above Small Craft Advisory criteria (in the 6-8 ft range) through the
period. Fair weather with northeasterly winds gusting 20-25
kts. Early Thursday and then decreasing Friday/Saturday.
Saturday through Sunday... seas should subside below Small Craft Advisory
criteria sometime on Saturday and remain low on Sunday.
Generally fair weather with relatively light winds (around 10
A northeast wind into tonight will continue to result in a moderate
risk for the development of dangerous rip currents along the coasts
of Delaware and New Jersey.
We are anticipating a high rip current risk for Wednesday. Breaking
waves are forecast to build to 4 or 5 feet with a stiff northeast
wind at 20 to 25 miles per hour. Also, a long period (around 12 seconds) swell
emanating from Hurricane Humberto will affect our coast at that
Marine...Small Craft Advisory until 6 PM EDT Thursday for anz452>455.
Small Craft Advisory from midnight tonight to 6 PM EDT
Thursday for anz450-451.