Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
950 PM EST Wednesday Mar 4 2015
several waves of low pressure will track northeastward along a cold
frontal boundary tonight and Thursday. This cold frontal boundary
will move offshore Thursday night and will give way to an area of
high pressure moving into the region on Friday. For the weekend
and early next week, we will alternate between areas of high
pressure and cold fronts moving through the region.
Near term /until 6 am Thursday morning/...
945 pm: everything is now posted graphically and i'm comfortable
with our forecast. One to three inches by daybreak from near
kpne to kblm northwestward and amounts increasing steadily
thereafter so that this will have to be a dangerous commute for
eastern PA and much of the northern part of New Jersey. A high confidence
forecast on substantial travel problems developing Thursday morning.
915 pm: checking the new 00z/5 NAM. I think we're close to what
will occur. Amounts with an inch or 2 variation on our new snow
map. We'll continue the dense fog advisory but its marginal and
soon should blow away as cold air advection develops.
835 pm: early estf updated for the dense fog advisory and also
have updated delayed timing of rain changing to snow per reality
and the hrrr. Snow amounts decreased in the 00z-06z/5 time frame
and also decreased on the southern edge near Philadelphia in the
06z- 12z/5 time frame. Increased the snowfall in the 12z-18z time
frame to compensate and balance amounts close to our 330 PM forecast.
Will update the snow map around 945 PM pending a quick check of
the NAM. Temperatures were increased through 14z as were dewpoints
and probability of precipitation too. Reworked the weather grids with delayed change to snow
and added heavy snow to the wording for Thursday morning though
its not a clear cut heavy. Snow water ratios will probably be
closer to 8 to 1 for the first few hours. So the basic message is
the same and the morning rush hour is destined to become hazardous
and difficult, especially Philadelphia northward with many delays
anticipated, if not cancellations.
800pm update...a dense fog advisory has been issued for southern
New Jersey...parts of southeast Pennsylvania and northern Delaware-Maryland-Virginia
including all of Delaware. Numerous stations are reporting
visibility of 1/4 mile or less in fog. Apparently melting snow
evaporated into the lower atmos today and then slight cooling
around Sundown enabled the fog to form. Not sure how long fog will
last but it should begin to dissipate when heavier precipitation arrives
later this evening. Current advisory runs until midnight.
Social media has the updated Wednesday evening briefing package and
request for observations. We will be monitoring mostly our Skywarn
account and phi fb. Thank you very much for all your assistance
including the energy to help US during the night. Safety first.
Short term /6 am Thursday morning through 6 PM Thursday/...
record daily snowfalls possible at kilg and kacy. Please see climate
section for details on the Big Four climate sites.
The warm nose will still be present, and should in fact be a bit
deeper over southern Delaware-Maryland-Virginia as they drop near and below freezing
near sunrise. As such, could see a mix of freezing rain and sleet
before it changes over to all snow no later than middle morning. On
the other side of the region, drier air moving into the Poconos
and northwest New Jersey could erode and end the precipitation for those areas by
Dry air advection will develop over much of the rest of the area
through the afternoon, allowing the precipitation to taper off
almost everywhere by late afternoon except Sussex County
Fgen while decent does not necessarily favor 1/4 to one half Michigan
visibility in MDT to heavy snow. We've put it in there, per wpc quantitative precipitation forecast.
Long term /Thursday night through Wednesday/...
fairly quiet with a general northwest flow pattern of alternating
cold fronts and west-southwesterly flow warm-ups ahead of these
fronts. Slight to low precipitation chances ahead of these fronts,
Thursday night through saturday: a cold Friday morning is on tap
with snowcover in place, clear skies and mainly light winds under 10
miles per hour. Radiational cooling should allow for a quick temperature drop
after clouds clear. Went colder than mav and met guidance sets
closer to the modeled two meter temperatures from the GFS. High
pressure builds into the region keeping this period dry with a
eventual swing from northwest to southwest winds and moderating
temperatures by Saturday. Trended colder than the met and mav at
night due to snowcover and warmer during the day. These guidance
sets have been running with a cold bias in the daytime. Soundings
also yield the potential for some wind gusts around 15 miles per hour
Saturday night and sunday: a cold front will decay into a trough
across New England by Sunday morning providing an increase in
clouds and perhaps a low chance for rain and snow showers across far
northern parts of the region, closer to the front. A few 06z gefs
members have moisture from the Gulf coming north as well, for now
will go with the model consensus away from this idea. Snowcover
should less of a concern with temperatures by Sunday. With more
clouds around the ensemble guidance from wpc is preferred for most
elements. Winds are more in line with the NAM/GFS models though.
Sunday night through wednesday: once again high pressure is in control
in the region with general west winds. This will result in a brief
period of cooler temperatures Sunday night before Spring like days
on Monday through Wednesday. A weak frontal boundary again looks to
focus on New England for Monday, another low chance of
precipitation. Then this will be followed by another high pressure
system. The airmass by Tuesday and Wednesday will be the warmest in
some time across the region. Liked the direction of the ensemble
guidance to trend temperatures several degrees warmer than the
modeled two meter temperatures. The modeled two meter temperatures look
to cool should some southerly component get involved, this looks
like it has a fair chance of occurring by Wednesday. Forecast
high of 56 at phl Wednesday, i'm sure this will be welcome to
many. Low pressure that forms in the Gulf of Mexico Tuesday-Wednesday looks
to stay south of our region at this time.
Aviation /03z Thursday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Rest of tonight...MVFR conds in rain/fog variable LIFR in patchy
dense fog this evening. Then as the colder northwest wind
increases, the change from rain to sleet/freezing rain for 1-2
hours and then IFR snow occurs. Please see the tafs for details.
Confidence in MDT 1/2 mile snow is below average for Thursday.
However, I am confident that widespread plowing and extensive
delays will develop by sunrise Thursday from Philadelphia north
and then spread southward during the morning after 12z. North wind
gusts to 18 knots by 11z Thursday.
Thursday...IFR snow in the morning with temperatures falling into
the 20s at all taf sites by 15z. North wind gusting to 20 knots.
Conditions should improve to VFR from north to south during the
afternoon. Plowing operations and extensive delays are anticipated
with widespread event totals of 4 to 8 inches.
Thursday night: improving to VFR by mid-evening. Northwest wind
around 10 knots.
Friday and Friday night: VFR, northwest wind 10 knots or less.
Saturday through Sunday night: VFR, west to southwest wind around 10
knots, gusts around 15 knots Saturday afternoon. Middle-level clouds
Saturday night and Sunday morning, passing rain/snow shower can not
be ruled out for Abe.
Monday and Monday night: VFR, middle-level clouds.
waves along the coastal waters will continue to remain near 4-5
feet. After midnight, winds increase with gusts above 25 knots possible.
Therefore the Small Craft Advisory continues through Thursday
evening along the coastal waters. On the Bay, a few gusts near
20kt are possible, but conditions should generally remain below
Small Craft Advisory criteria.
Seas look to remain below five feet throughout the entire outlook
period, with seas near five feet early Thursday night. The forecast
is about a foot higher than wavewatch. Northwest wind gusts around
20 knots may occur Thursday evening. Otherwise wind gusts should
stay under 20 knots. Some freezing spray may occur Thursday night
and early Friday in ice free waters. Confidence is not high for any
moderate freezing spray in terms of duration and likelihood, may
just last a few hours if it occurs. With some moderate freezing
spray in the grids, did include mention in the severe weather potential statement.
models continue to show a decent amount of quantitative precipitation forecast across the area
tonight into Thursday. In general and breaking the County Warning Area into
thirds, a changeover to sleet or snow is expected across the
northern third by around midnight, the middle third by daybreak,
and the southern third by middle-morning tomorrow.
With the ground being frozen everywhere, any runoff will be very
efficient before the changeover.
Morning models continue to produce between 0.50 to 1.00 inch of quantitative precipitation forecast
before the changeover. With this amount, we feel nuisance poor
drainage and low lying flooding will be the most likely outcome.
With more snow or sleet expected across the northern half of the
cwa, we're less concerned about flooding there.
Modeled solutions suggest we would need between 1.50 to 2.00 inches
of liquid (over a 6 to 12 hour period), either in the form of all
rain or rain and melting snow to have our southern creeks and
streams leave their banks. None of our river forecast points are
forecast to hit flood stage or even caution stage.
The short term good news is that rain will change over to snow
quicker across places that have a snowpack and where more rain is
expected, there is less snow pack.
The longer term bad news is that we're potentially kicking the can
down the line and just adding to our snowpack for a future melt.
With the rainfall, the flow on area creeks and streams will
increase. This could start to move ice, and in a worst case
scenario, create restrictions or jams. The good news is we've
seen some recession/melt the last few days.
climate: with a snowcover in place and another modified Arctic
airmass settling into the region and radiational cooling occurring,
we have another chance for more record lows across the region.
Acy 10 1888
phl 10 1978
ilg 11 1926
Abe 7 1960
ttn 7 1872
Ged 10 1978
ridge 7 1978
mpo -5 1909
The current forecast currently has most locations breaking there
record low on Friday morning. The one exception would be Mount
Acy 10 1890
phl 9 1960
ilg 11 1960
Abe 1 1960
ttn 7 1890
Ged 3 1960
ridge 10 1989
mpo -18 1911
Most locations are forecasted to be several degrees warmer than the
record lows for Saturday morning.
Record daily snowfall for Thursday March 5
Kacy 0.3 - 1960
kilg 3.7 - 1981
kabe 7.0 - 1917
kphl 8.8 - 1981
PA...Winter Weather Advisory until 7 PM EST Thursday for paz054-055-
Winter Storm Warning until 7 PM EST Thursday for paz060-
Dense fog advisory until midnight EST tonight for paz070-071-
Winter Storm Warning until 7 PM EST Thursday for paz070-071.
New Jersey...Winter Weather Advisory until 7 PM EST Thursday for njz001-007-
Winter Storm Warning until 7 PM EST Thursday for njz009-010-
Dense fog advisory until midnight EST tonight for njz015>027.
Winter Storm Warning until 7 PM EST Thursday for njz013-014-
Delaware...dense fog advisory until midnight EST tonight for dez001>004.
Winter Storm Warning until 7 PM EST Thursday for dez001-002.
Winter Storm Warning from 3 am to 7 PM EST Thursday for dez003-
Maryland...dense fog advisory until midnight EST tonight for mdz008-012-
Winter Storm Warning until 7 PM EST Thursday for mdz008-012-
Marine...Small Craft Advisory until 7 PM EST Thursday for anz450>455.
near term...amc/drag 951
short term...drag 951