Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
351 PM EST Friday Mar 7 2014
a coastal low pressure system will continue to pull away from the
region late tonight. A cold front will then cross the area from the
northwest late on Saturday into Sunday morning allowing for a return
of high pressure for the start of the new work week. The high will
depart to our south on Tuesday while a clipper like system nears
from the west-northwest. This is followed by the potential for
another coastal low pressure system to cross the region late
Wednesday and Thursday.
Near term /until 6 PM this evening/...
as of middle afternoon...a high pressure ridge over New England continues to
weaken whil low pressure is deepening off the NC coast. Hi level clouds
and moisture ahead of the associated upper low over NC/SC cover the forecast
area while low clouds have spread over eastern/southern parts of the area on
low-level northeasterly flow. Surface temperatures are in the middle to upper 30s from the
Poconos to northern delmava. Northeasterly winds are noted across the area
and are relatively light northwest but stronger southeast towards the Atlantic
coast. Radar shows some very light rain over southern Delaware.
For tonight...the surface low is forecast to continue a gradual deepening as
it moves northeastward past cape hat and then out to sea. The pressure gradient
around the low will maintain a good northeasterly flow this evening over southern
New Jersey and Delaware...then winds will back to the north and diminish some as the
low pressure moves away from the middle-Atlantic coast. Associated precipitation
should stay well S and east of phl...with southern Delaware and extreme southeast New Jersey
being the only places likely to see any measurable rain...and even
those amounts should be only a few hundreths. At least partial
clearing of the skies is expected overnight which should allow temperatures
to fall into the 20s in most areas.
Short term /6 PM this evening through 6 am Saturday/...
Saturday looks like a pretty good day with temperatures close to normal and
considerable sunshine especially in the morning. Winds should be
relatively light west to northwest. Winds at 850mb are up to 40kt or so but
there appears to be an inversion above 950mb that will limit
downward mixing during the day. Clouds will increase during the afternoon
as a cold front moves southeastward into northern New Jersey and adjacent PA. There is not
much moisure with the front but we have put in just a slight chance for
-shra/-shsn over the Poconos for late in the afternoon.
Long term /Saturday through Friday/...
5-wave model guidance is showing weak troughing, pseudo-zonal flow,
across the region at the start of the period. By the middle of next
week we start to see a return to a rather familiar, and frankly
unable-welcome pattern, ridging in the west, troughing in the east. The
few blissful days of at or above average temperatures comes to halt
and winter once again takes grasp of the region. The Silver-lining
in all of this, at least we gain an extra hour of daylight on the
clocks in the evening...we actually only gain a few minutes of
actual daylight astronomically.
Generally speaking the latest 12z initialization looks pretty good
off the GFS/NAM/ggem though there are minor differences in the
thermal fields this morning...the 12z ec was slightly better than
the three above. For the most part the guidance seems to be too cold
across the Upper Middle-west and the northern plains and not fast
enough with the next cold front entering into the upper plains. This
will cause issues for the temperature forecasts through the first
half of the longterm period as a parade of clipper like systems
should traverse close to our region before the more established
troughing takes over.
The first such system will track well to the north of the region and
push through a weakening cold front later on Saturday into Sunday
morning. Guidance is showing the low-level temperatures crashing
with the advancement of the front which would allow for more of a
rain/snow mixture. The issue with this system will be the amount or
no associated ice within the clouds. There is very limited, nearly
none, moisture being that the split flow in the middle-levels continues
and with the little forcing its not likely to be a cold enough cloud
producer. That being said decided to add in some freezing drizzle
across our northern most zones with a rain/snow mix elsewhere.
Sunday will be a colder day with a stiff northwest wind as
temperatures falling below average behind the front. The good news
is there should be plenty of sunshine around to make it not feel as
bad. Did side more with the warmer mavmos in this case given the
above information, though it must be noted that the 2m temperatures
off the GFS have been underperforming the past couple of weeks...at
Monday we will restart our warming trend with ridging slide to our
south and a nice return flow developing. Low-level temperatures jump
back up above freezing and will remain that way through at least the
later half of Tuesday, ahead of the next northern stream system.
Both Monday and Tuesday will feature dry conditions and above
We then turn our attention to later on Tuesday as we watch how
fast/slow another frontal boundary will shift through the region.
Given the current speed of the northern stream would have to err on
the side of a faster movement of the cold front thus dropping it
through our region on Tuesday evening. The next big issue becomes
how the middle-level troughing progresses through the middle-west and into
the eastern U.S. By mid-week.
There is relatively good consensus from the Middle-Range model package
through about Tuesday, and then we start to see the GFS/ggem/ec part
ways with the speed and deepening of the trough. To put it simply,
we are will be in middle-March with split flow still aloft and we need
a deep thermal trough to change that with phasing of northern and
southern stream systems. We then need to robust wave to develop
along the frontal boundary that just moved through to drag in enough
cold air and then sling the southern stream moisture overhead. Much
like the last event, March 2-3, there are a lot of moving parts that
need to fall in-line for more snow.
What does have somewhat higher confidence is the occurrence of a low
pressure moving by/through the region Wednesday into Thursday
producing precipitation. That being said went with a wpc approach
for probability of precipitation and rain/snow mixture for the time being.
Aviation /20z Friday through Wednesday/...
the main limiting factor for aviation today is the ceilings. Abe/ridge are
VFR while the lower del valley has some ceilings broken 020-025 and miv/Acy
have ceilings 015-020. Thus conds deteriorate somewhat from northwest to southeast and
the northeasterly winds also increse in the same pattern. These general conds
should continue for the rest of the afternoon and into middle evening. These weather
issues are caused by low pressure off the NC coast...and so as the low
moves off the coast starting late this evening...conditions should begin
to improve and become VFR at all locs overnight. Miv and Acy may
see some light rain and fog at times this evening and they will
likely be the last to improve overnight.
Saturday night - Sunday...mostly VFR. Light rain/snow showers
possible early Sunday morning north of ridge...maybe some patchy
freezing drizzle late Saturday night.
Monday - Tuesday...VFR.
Tuesday night - Thursday...MVFR or lower in scattered showers.
Increasing chances for more rain/snow Wednesday into Thursday with
sub-VFR conditions likely.
a surface low off the NC coast is forecast to continue gradually deepening
as it moves northeastward past cape hat this evening and then out to sea
overnight. The surface pressure gradient and associated winds will be strongest
over the coastal waters of southern New Jersey and Delaware...and so a Gale Warning
remains in effect for that area. The strongest gusts should occure
this evening...then winds will diminish overnight and will back from
NE to north to northwest by Sat morning. Elsewhere a Small Craft Advisory remains in effect except
for upper del Bay.
The sustained NE flow has caused seas to build to 10 feet at buoy
44009 and some further increase is possible this evening. Highest
seas during the evening should begin to subside overnight...but will
remain elevated through the day on Saturday. A Small Craft Advisory will likely need
to continue for coastal waters...even after winds diminish
Sunday - Tuesday...sub-sca conditions are expected at this time.
Winds become more northwesterly behind a cold front on Sunday.
Tuesday night - Thursday...increasing chances for a coastal low
pressure to near later on Wednesday. Seas and winds will increase
with this low. Small Craft Advisory conditions looks very possible.
Marine...Small Craft Advisory until 7 PM EST Saturday for anz450>452.
Gale Warning until midnight EST tonight for anz453>455.
Small Craft Advisory until 6 am EST Saturday for anz431.