Area Forecast Discussion
Issued by NWS Mt. Holly, NJ-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KPHI 262327
Area Forecast Discussion
National Weather Service Mount Holly NJ
627 PM EST Sun Feb 26 2017
High pressure will move off shore tomorrow. Low pressure approaching
from the west will lift a warm front through the region on Tuesday.
That low will track from the Great Lakes region into eastern Canada
on Wednesday. The associated cold front will move through the East
Coast by Thursday morning. An upper trough builds into the Northeast
for the end of the week.
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Water vapor imagery depicts the strong vort max affecting our region
yesterday moving into the Canadian Maritimes with the trailing end
becoming elongated zonally by the upper-level jet streak
encompassing much of the eastern half of the U.S. Cold air advection
is waning as a surface high approaches the East Coast. Stratocumulus
deck is eroding from southeast to northwest as northwest flow
weakens. As the surface high reaches the coast this evening,
surface winds will begin to decrease. With the clearing skies and
light winds, should see a fairly decent drop in temperatures this
evening. However, low-level isentropic ascent will commence by late
tonight as return flow on the upstream side of the surface high
moves in. Clouds will begin to increase late tonight, especially in
the southern CWA, which may curb more substantial cooling in this
area. As a result, I stuck close to guidance given the competing
factors in place -- but it is possible the places most susceptible
to radiational cooling could be cooler than what is forecast. These
trends will be monitored this evening to see if temperatures need to
be lowered a little bit.
.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
As the surface high moves farther east into the Atlantic, southwest
surface winds will become established across the area on Monday.
Substantial near-surface warm air advection will contribute to a
much warmer day Monday, with temperatures returning to well above
average values. A perturbation in the west-southwesterly upper-level
flow will approach the Mid-Atlantic by 00Z Tuesday, with cloud cover
continuing to increase. However, residual dry air in the low levels
and generally weak large-scale ascent should prevent much if any
precipitation from occurring before sunset. Notably, model guidance
has been all over the place in the handling of this system for days,
rendering confidence much below average in the details -- even for a
12-24 hour forecast.
There are at least some indications lift may become sufficient to
produce light precipitation to the west of the area (generally the
Appalachians westward in southern PA and adjacent MD/VA/WV) by late
morning or early afternoon. However, the aforementioned limiting
factors seem too much to overcome for generating precipitation in
the CWA by the end of the short term period. Thus, reduced PoPs on
Monday to non-mentionable levels.
Guidance has struggled mightily with temperatures in warm air
advection patterns this past month. Went slightly above guidance
for highs based on the expected cloud cover present -- otherwise, I
would have gone well above guidance. However, would not be at all
surprised to see highs several degrees warmer than forecast,
especially if the models are overdoing the moist air advection in
the 900-700 mb layer.
.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
A very active pattern continues through the long term.
Monday night through Tuesday night...warm front will lift north
through the region. Some weak lift is expected with the front
followed closely by a local vorticity maxima associated with the low
lifting into the Great Lakes Region. It isn`t exactly an
impressive set up for widespread precip, but models continue to
depict QPF across the region through this period. It looks like
the best chance through this period would be Tuesday afternoon
and evening, when we still have a slight onshore component to
the low level flow.
Wednesday and Wednesday night...This is the period of greatest focus
as it looks like our region will once again be solidly in the warm
sector as a pre-frontal trough slides offshore and the cold front
approaches from the west. With continued southwesterly flow, should
see temperatures once again well above normal, approaching record
highs (see climate section below). The combination of the very warm
boundary layer (resulting in a relatively unstable profile with
modest CAPE values) and a mid and upper level southwesterly jet
(resulting in bulk shear values above 50kt) means there is once
again a risk for strong or severe storms. The biggest source of
uncertainty right now is the timing, primarily of the cold front.
There are considerable differences with the GFS showing the most
progressive solution, bringing the cold front through Wednesday
evening, while most of the rest of the guidance shows a cold frontal
passage late Wednesday night. The GFS solution would be the highest
risk as the warmest conditions would be coincident with the best
lift. Even with the slower solutions, there remains some risk for
severe storms, it would just be a more limited period.
As for the hazards, it looks like the primary hazard would be strong
winds. Current model soundings show limited instability in the hail
growth region, limiting the threat of large hail. If there is
widespread rain on Tuesday leading in to the event, then the risk
for poor drainage flooding could increase for Wednesday.
Thursday and Friday...strong cold air advection with breezy
northwesterly winds. At this point, it looks like we will have at
least 2 consecutive days of below normal temperatures. A fast moving
low may dig across the region, though there remains considerable
uncertainty with the track.
Saturday and Sunday...High builds south, keeping us in the cold air
for a few more days, although there may be a modest warming trend by
Sunday as winds shift more westerly.
.AVIATION /00Z MONDAY THROUGH FRIDAY/...
-- Changed Discussion --The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
VFR through Monday afternoon, with only a FEW/SCT stratocumulus
deck around 5,000-6,000 feet dissipating through this evening.
Northwest winds will continue diminish through this evening,
becoming mostly light westerly or even variable by late evening.
After a period of mostly clear skies through about 09Z, clouds
will increase with CIGs of 8-15 kft expected after 12Z.
Southwest winds will develop tomorrow, sustained winds should
generally remain below 10 kts, with some gusts around 15-18
knots for a few hours during the afternoon.
Tuesday...Should begin as VFR, but ceilings could lower to MVFR
later in the day as rain begins to move in.
Wednesday and Wednesday night...Thunderstorms are likely, primarily
Wednesday afternoon or Wednesday night. With any storms or showers,
MVFR or even IFR conditions are expected. There will be an abrupt
shift to breezy northwesterly winds with the cold front which should
arrive Wednesday night.
Thursday and Friday...Mostly VFR conditions. There is a small chance
of lower conditions with rain and snow showers Thursday night into
Friday. Very breezy northwesterly winds are possible both days.
-- End Changed Discussion --
-- Changed Discussion --Winds have lowered below advisory levels for the Delaware Bay
and southern New Jersey and Delaware Atlantic coastal waters.
Therefore we`ve let the Small Craft Advisory expire for these
areas. The Small Craft Advisory remains in place from Little Egg
northward as winds continue to gust around 25 knots. But Small
Craft Advisory conditions should end later this evening. Sub-
advisory conditions are forecast thereafter through Monday
Tuesday through Wednesday...southwesterly winds at or above 25 kt
likely, especially on the coastal waters. Periods of showers and
thunderstorms possible, especially on Wednesday.
Wednesday night...Thunderstorms and showers possible. An abrupt
shift to northwesterly winds is expected with a cold front either
late Wednesday night or Thursday morning.
Thursday and Friday...Northwesterly winds gusting above 25 kt are
likely through out the period. There is also a chance for gale force
gusts, primarily Friday afternoon and Friday night.
-- End Changed Discussion --
Record max temps for Wednesday March 1.
1972 was the year for most except GED
-- Changed Discussion --PA...None.
MARINE...Small Craft Advisory until 9 PM EST this evening for ANZ450-
-- End Changed Discussion --