Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

000 
FXUS61 KPHI 231315
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
915 AM EDT Sat Mar 23 2019

.SYNOPSIS...
Strong low pressure will gradually work its way across the Canadian 
Maritimes today and tonight. Meanwhile, high pressure will build 
into the Ohio Valley today then just to our south tonight and 
Sunday. A cold front will settle southeastward across our area late 
Sunday night and Monday while a weak area of low pressure tracks 
along it. High pressure builds in Tuesday and Wednesday before 
slowly shifting eastward later Thursday and Friday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

Increased wind gusts just a bit in the far north to account for
observations in that area showing a peak gust of 58 MPH at High
Point NJ (1800 feet ASL) and certainly not respresentative of
the entire area. Vsbl satellite imagery shows cloud cover moving
out with the departing low, and is represented very well by the
current forecast. Temperatures also look on track, so no major
changes to the current forecast package.

...Previous near term discussion below....

Strong low pressure will drift to the northeast across Canada's
Maritime Provinces and the Gulf of Saint Lawrence today. 
Meanwhile, high pressure will build from the western Great Lakes
and the Ohio River Valley toward the Carolinas. The tight 
pressure gradient between the two features will maintain a 
strong west northwest wind in our region. Sustained wind speeds 
should range from 15 to 25 MPH with gusts up to 30 or 40 MPH. 
Wind speeds are forecast to begin slowly diminishing during the 
course of the afternoon.

Clouds are expected to linger through about mid morning, especially 
over parts of eastern Pennsylvania and New Jersey. Very dry air will 
build into our region for this afternoon, with a clear sky 
anticipated at that time.

Maximum temperatures are expected to range from the lower 40s on the 
Pocono Plateau to the middle 50s in southern Delaware.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
The strong low will move farther away to our northeast tonight as 
high pressure settles in the Carolinas and Virginia. We are 
anticipating a clear sky. The west northwest wind is forecast to 
decrease to less than 10 MPH early this evening with the wind 
becoming light and variable overnight.

The ideal radiating conditions should allow temperatures to fall 
into the 20s in much of our region. Readings may not drop below the 
lower 30s in urban locations and in areas near the coast and
bays.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Summary...Mainly some rain later Sunday night and Monday with a cold 
front and wave of weak low pressure; Cooler Tuesday; Warming takes 
place Wednesday through Friday.

Synoptic Overview...A large upper-level trough amplifies across New 
England later Sunday and Monday with a cold front pressing 
southeastward across our region. A trough remains in the East 
through Tuesday, then the flow becomes more zonal for a time. An 
upper-level trough amplifies into the Plains toward late next week, 
building a ridge to the east.

For Sunday and Monday...Surface high pressure is forecast to be 
shifting east of the Carolinas Sunday. An upper-level trough 
amplifies across eastern Canada and eventually into the Northeast, 
with a cold front arriving in our area Sunday night and Monday 
morning. There looks to be limited moisture with the cold front, 
however some showers should occur as it arrives. A short wave 
embedded within the northwesterly flow aloft tracks from the Midwest 
Sunday to the Mid-Atlantic coast by late Monday. This eventually 
looks to get absorbed with the incoming amplifying trough, however a 
weak surface low associated with it tracks along the aforementioned 
surface cold front as it settles southeastward.

While the guidance does vary some with how much shower activity 
accompanies the front, the bulk of the guidance focuses more 
precipitation with the wave of low pressure. The QPF looks to be on 
the lighter side as the system should be moving right along. The 
majority of this is anticipated to be rain, however if enough 
cooling arrives across the north some snow could mix in. Overall 
though it looks like the colder air arrives after the majority of 
the precipitation ends. In addition, much drier air looks to move in 
a bit faster from south to north during Monday and this should also 
help to keep the more organized precipitation becoming more focused 
across the southern areas with time. Prior to the arrival of the 
cold front, a milder flow will occur Sunday allowing temperatures 
away from the coast to get well into the 50s to near 60 degrees, 
then cooling occurs during Monday and especially Monday night when 
it turns colder. 

For Tuesday...As an upper-level trough amplifies across the East, 
some ridging across the Midwest will drive an expansive high 
pressure system eastward into our area during Tuesday. This should 
drive much drier air southward despite a northeast low-level flow. 
As a result, any precipitation lingering across the Delmarva early 
should rapidly end as low pressure moves out to sea. Our sensible 
weather is then dominated by the aformentioned surface high building 
over and to our north and northeast through Tuesday night, and this 
will keep a chilly airmass in place.  

For Wednesday through Friday...Looks like a sliver of tranquil 
weather for our area as surface high pressure becomes entrenched 
across our area and extends to the northeast. This is between an 
eventual trough that ejects out into the Plains toward the end of 
the week, and low pressure east of the Southeast coast. The trough 
out West eventually will send low pressure northeastward from the 
southern Plains, however that will probably not approach until later 
Friday night. In the meantime, a warming trend is expected to take 
place after a chilly to cold start. The warming however may be 
slowed closer to the coast given the surface winds may retain an 
onshore component longer. For now, kept some rather low PoPs 
especially for the western areas by late Friday.

&&

.AVIATION /13Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, 
KILG, KMIV, KACY and surrounding areas.

Today...VFR. Decreasing clouds this morning, clear this afternoon. 
West northwest wind 16 to 22 knots with gusts of 28 to 36 knots.

Tonight...VFR under a clear sky. West northwest wind around 8 to 12 
knots becoming variable 6 knots or less. 

OUTLOOK... 
Sunday...VFR as clouds increase and lower, especially at night. Some 
showers possible toward daybreak Monday. West-southwest winds 10 
knots or less.

Monday...VFR ceilings, which may briefly lower to MVFR with some 
rain especially from the PHL area southward. West-northwest winds 
becoming northerly around 10 knots.

Tuesday and Wednesday...VFR. Northeast winds around 10 knots, 
becoming east to southeast less than 10 knots by later
Wednesday.

&&

.MARINE...
A west northwest wind at 20 to 30 knots is forecast to continue for 
much of the day. Frequent gusts in the 30 to 40 knot range are 
expected. Wind speeds will likely begin to decrease slowly this 
afternoon. We will keep the Gale Warning in place until 6:00 PM for 
the coastal waters of New Jersey and Delaware and for Delaware Bay.

The west northwest wind will continue to diminish tonight, with 
conditions anticipated to fall below Small Craft Advisory levels 
shortly after midnight.

Outlook...
Sunday and Monday...The conditions are anticipated to be below Small 
Craft Advisory, however northeast winds increase later Monday night 
and may gust to around 25 knots.

Tuesday...Small Craft Advisory conditions probable for a time, 
especially for the Atlantic coastal waters where seas will be around 
5 feet. 

Wednesday...The winds are anticipated to be below Small Craft 
Advisory criteria, however seas may linger around 5 feet especially 
in the southern Atlantic coastal waters.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Gale Warning until 6 PM EDT this evening for ANZ430-431-
     450>455.

&&

$$
Synopsis...Gorse

National Weather Service Glossary of Abbreviations