Scientific Forecaster Discussion
fxus61 kphi 222142
Area forecast discussion
National Weather Service Mount Holly New Jersey
442 PM EST Mon Jan 22 2018
low pressure located in Iowa this afternoon will progress to the
northeast and it should reach the Saint Lawrence River valley and
northern New England late on Tuesday. The low is forecast to pull a
cold front through eastern Pennsylvania, northeastern Maryland,
Delaware and New Jersey on Tuesday afternoon. High pressure is
expected to build into our region from the west during the balance
of the work week. The high is anticipated to move out to sea on
Saturday with a cold front following in its wake on Sunday.
Near term /until 6 am Tuesday morning/...
345 PM...low pressure currently situated near Iowa with a warm
front extending east across the area. As a result, quite a
spread in temperatures with temps currently in the 60s over much
of the Delmarva but only around 40 across the southern Poconos
where there are currently a few showers north of the front.
Heading into tonight, the aformentioned low heads north and
east toward the Great Lakes with mild temps persisting as the
area will be in the warm sector. Any showers across the north
lift out of the area this evening but areas of mist and fog will
be possible across the Poconos tonight in association with the
warm front. Elsewhere, breaks in the cloud cover persist
farther south through this evening with dry conditions. However
overnight, clouds thicken up as showers in association with the
low approach from the west and also expect coastal fog to
develop due to the warm, moist air flowing north over the
relatively colder ocean waters. Expect these showers to arrive
west to east beginning in the predawn hours with even a few
rumbles of thunder possible as there will be elevated
Short term /6 am Tuesday morning through 6 PM Tuesday/...
low pressure will track well to our north and west through the
day Tuesday moving from Michigan across Ontario into Quebec by
late day. This will drag a cold front with associated showers
across the area. To begin the day, the low will be around
Michigan with showers ahead of the system's cold front quickly
overspreading the area by 12z. These showers persist through the
morning and concern is that forecast models, especially the
NAM, are depicting several hundred j/kg of elevated cape so at
least a few thunderstorms look like a good bet. Also, Worth
noting, mid level lapse rates will be fairly steep (near 7 c/km)
with a very strong low level jet ahead of the cold front...around 60
knots at 925 mb. For these reasons, we have concerns that any
thunderstorms or heavier showers could mix locally damaging
winds down to the surface...especially over southeast PA, southern NJ,
and the Delmarva where the instability will be the greatest. In
fact the Storm Prediction Center has placed these areas in a
marginal risk for severe storms. The limiting factor will be
that the low levels will be fairly stable so confidence of
severe weather is not high. The most likely window for this
occur looks to be mid morning through early afternoon after
which time the cold front will clear the area with showers
ending. Also, Worth noting, pwats will be 1.0 to 1.25 inches so
heavy rain and local poor drainage flooding may also be a
concern. Highs Tuesday range from near 50 across the southern
Poconos to the upper 50s to mid 60s across southeast PA, southern NJ,
and the Delmarva.
Long term /Tuesday night through Monday/...
surface low pressure is forecast to be located in Maine on Tuesday
evening. The system is expected to strengthen as it moves across
Atlantic Canada on Tuesday night and Wednesday. The gradient between
the departing low and high pressure building into our region from
the west should result in brisk conditions developing for Wednesday.
A west northwest wind around 10 to 20 miles per hour is anticipated at that
Surface high pressure should move from the south central states on
Wednesday to the Carolinas and Virginia late on Thursday. The center
of the high is anticipated to slide over the western North Atlantic
on Friday and Saturday. The air mass is forecast to bring dry
weather conditions for the period from Wednesday into Saturday.
Temperatures are expected to be seasonable on Wednesday and Thursday
with a warming trend as we head toward and into the weekend.
Low pressure and a cold front are forecast to approach from the west
over the weekend. There is a spread in the guidance solutions
regarding the timing of the arrival of the cold front in our region.
We will carry a chance of showers for Sunday and Monday.
Aviation /22z Monday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Tonight...conditions will deteriorate during this period on
multiple fronts. Low-level (southwesterly) wind shear is a
concern after 00z as a strong low-level jet develops. Cigs will
lower through the evening hours, becoming MVFR at most terminals
between 09z and 10z and IFR shortly thereafter. Vsbys may also
become sub- VFR with fog development possible, at least locally.
Finally, showers will move in from the west after 06z, likely
affecting the philly terminals around/after 09z. Lightning
cannot be completely ruled out, though confidence in this is too
low for taf mention at this point. Overall confidence is
Tuesday...IFR or lower in rain and isolated thunderstorms and rain. Locally heavy
rain possible. Strong, gusty winds possible in heavier showers
and isolated thunderstorms and rain. Showers taper off from west to east Tuesday
afternoon as cold front moves through the region. South winds
15-20 knots with gusts up to 25 knots Tuesday morning become west-northwest in
the afternoon. VFR conditions likely in the afternoon. Low level wind shear will
be an issue to start the day but diminishes by afternoon.
Tuesday night through Saturday...mainly VFR.
for tonight, south winds should begin to increase, especially
after midnight, with speeds reaching Small-Craft Advisory
criteria a couple of hours before daybreak. Also, areas of fog
likely to develop over the waters overnight with showers
arriving west to east near morning.
Tuesday...strong Small Craft Advisory conditions over the waters
with a few gusts to gale force possible around
midday...especially in any heavier showers. Since this looks to
be brief, we opted for sca, not Gale Warning. Marine weather
statements and possibly a special marine warning may be needed
for these locally stronger winds. Small Craft Advisory conditions expected for
Delaware Bay Tuesday. South winds in the morning shift to the west in
the afternoon behind the passage of a cold front.
Tuesday night...a Small Craft Advisory is in effect on our ocean
waters for westerly wind gusts around 25 knots.
Wednesday through Thursday...a west northwest wind could gust around
25 knots and the Small Craft Advisory may be extended in time.
Thursday night through Saturday...no marine headlines are
one temperature record was set today (jan 22):
Ged- the high was 68 degrees (occurred at 153 PM est) which
ties the previous daily high temperature record from 1959.
Marine...Small Craft Advisory from 4 am Tuesday to 6 am EST Wednesday
Small Craft Advisory from 4 am to 6 PM EST Tuesday for anz430-