000 
fxus61 kphi 192335 
afdphi 


Area forecast discussion 
National Weather Service Mount Holly New Jersey 
635 PM EST Sat Jan 19 2019 


Synopsis... 
an expansive area of low pressure will approach the region from the 
west tonight and pass over our area overnight Saturday night and 
early Sunday morning bringing a significant winter storm to the 
region. Low pressure moves across southern New England then out to 
sea late Sunday. Strong Arctic high pressure will build quickly into 
the mid-Atlantic through the early part of next week resulting in 
very cold and dry conditions. Another area of low pressure will move 
across the Great Lakes and into southeastern Canada late Tuesday 
into Wednesday pushing a cold front into the region Wednesday. 


&& 


Near term /through Sunday/... 
precip slowly filtering in from the west, mainly in the form of 
snow to the north, and snow, mixing with some sleet, based on 
reports, to the south. For most of the southern portion of the 
forecast area, a quick rain/snow mix should change to all rain 
with minimal snow accumulations. 


Otherwise, will not make any significant changes to previous 
forecast for tonight through Sunday. 


Moisture laden low now over Tennessee is progged to take a 
track northeast and should be centered near southeast PA by 12z Sunday. 
Despite the cold high and ridging over the northeast this will 
result in very strong warm advection on the eastern side of the 
system resulting in a warmer, Rainier system than previously 
forecast with less snow and ice. As a result, winter headlines 
were scaled back and we've now issued a Flood Watch for the I-95 
corridor (see hydrology section below). Remaining details 
below: 


Timing: the bulk of the precip falls tonight through Sunday 
morning with this winding down as the cold front moves through 
during the 15- 19z time frame Sunday. 


Precipitation types and snow/ice amounts: with the track 
farther north and a warmer forecast, mixed snow/rain early this 
evening near the I-95 corridor will quickly change to rain, 
heavy at times, by late this evening. This transition will occur 
south to north. Areas north of here from Berks County into the 
Lehigh Valley North/East into portions of northwest New Jersey along the I-78 
corridor will see wintery precip hang on a bit longer with some 
sleet/freezing rain likely in the transition before a change to 
heavy rain overnight. Even here though, amounts were lowered 
from the previous forecast. Finally, across the far north from 
the southern Poconos into Sussex co. New Jersey expect wintery precip 
with snow/sleet/freezing rain may last well into the night but 
even through much of this region a change to all rain is likely 
by morning. Snow amounts here could still be 4-6 inches with up 
to a couple tenths of an inch of ice so at least for now, we 
keep Winter Storm Warning in effect. 


Winds: late tonight into Sunday morning, a very strong 
southerly low level jet is expected to develop with 925/850 mb 
winds progged to reach 70/90 knots over the area as the warm 
sector moves in. There will be lots of moisture in play with 
rain continuing at this time with some indications a convective 
type line could develop even if it doesn't actually produce 
lightning. Nevertheless, this could potentially bring very 
strong, even damaging winds, down to the surface. Not confident 
in this though and this will need to be handled as a "short- 
fused" type product situation, if needed. Then, following the 
passage of the cold front, expect strong northwest winds to develop 
potentially gusting 30-40+ mph tomorrow afternoon into the 
evening along with rapidly falling temperatures. This could 
result in at least some scattered power outages with more 
significant problems possible in the far north in the areas that 
still may get more snow/ice. 


Flash freeze: as mentioned above, strong cold front moves 
through northwest to southeast late morning into the early afternoon with 
rapidly dropping temps to values well below freezing. This will 
result in quick refreezing of wet/slushy surfaces causing very 
ice conditions. 


&& 


Short term /Sunday night through Tuesday/... 
the beginning of the week will feature deep winter Arctic cold, 
but dry conditions. Temperatures will continue the fall (from 
sunday) and drop into the single digits and low teens across 
most areas. Mercury readings across the southern Poconos may 
reach as low as -5 by dawn Monday. As bad as the cold is, wind 
chills will be brutal with sub-zero readings in most areas and 
readings around -20 to -25 across the Poconos. Proper 
precautions against the cold will be required to be safely 
outdoors Monday. Dry weather is expected Monday and into Tuesday 
as high pressure builds in. Readings Tuesday morning will also 
be very cold, but temperatures will moderate by days end back 
into the low 30s S/east and low/mid 20s N/W. 


&& 


Long term /Tuesday night through Saturday/... 
the midweek period looks unsettled as of now since another 500 mb trough 
will be advancing from the Midwest and low pressure is expected to 
form along it. Another wet/white storm is envisioned with 
confidence on storm track and p-types low at this time. More 
Arctic cold looks to follow this system. 


&& 


Aviation /00z Sunday through Thursday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg, 
kmiv, kacy and surrounding areas. 


Tonight...ceilings quickly lower to MVFR and IFR as 
precipitation overspreads the region from southwest to 
northeast. All rain expected at miv and acy; a snow/rain mix may 
occur at ilg, phl/pne to ttn at the onset then all rain; ridge 
and Abe start as snow then quickly go over to sleet and freezing 
rain then rain overnight. Main snow and ice accumulations occur 
at ridge and Abe. Low confidence on the timing of the 
precipitation type changes. Easterly winds around 10 knots, 
turning southeast or south toward morning (some gusts to 20-25 
knots possible overnight mainly at acy). A low-level southerly 
jet around 2000 feet overnight into early Sunday of 40-50 knots 
results in low-level wind shear. 


Sunday...MVFR/IFR conditions to start, then rapidly improving by 
late morning or afternoon as the precipitation ends. An abrupt wind 
shift to the northwest occurs by midday with winds increasing to 15- 
25 knots with gusts to around 35 knots (highest during the 
afternoon/evening). Low confidence on timing for improvement to 
VFR. 


Outlook... 
Sunday night and Monday...VFR. Northwest winds 15-20 
knots with gusts to around 30 knots, diminishing Monday night. 


Tuesday...VFR. Northwest winds 10-20 knots, diminishing by late 
afternoon. 


Wednesday and Thursday...sub-VFR conditions possible with the chance 
for some snow to a rain/snow mix. 


&& 


Marine... 
east to southeast winds tonight will increase to advisory 
levels, then become more southerly early Sunday morning. The 
passage of low pressure and a strong cold front will result in 
an abrupt wind shift to northwesterly during Sunday with a rapid 
increase in the winds as bitterly cold air pours in across the 
region. The gales may not fully take hold until the afternoon or 
evening, however will maintain the Gale Warning as is although 
did extend the end time to 23z/6pm Monday. 


Outlook... 
Sunday night and Monday...Gale Warning through 23z/7pm 
Monday due to a bitterly cold airmass and deep mixing. The warning 
may need to be extended into a portion of Monday night. Due to the 
bitterly cold air and strong winds, freezing spray is expected 
especially later Sunday night through Monday. As of now, looks like 
moderate ice accretion rates will be achieved and therefore issued a 
freezing spray advisory. 


Tuesday...the conditions (winds) are anticipated to be dropping 
below Small Craft Advisory early. 


Wednesday and Thursday...winds may increase to Small Craft Advisory 
criteria Wednesday then decrease through Thursday. Seas could remain 
at 5 feet or higher on the ocean waters. 


&& 


Hydrology... 
with the trend toward warmer solutions, models indicate that 
the threat for heavy rain along the I-95 corridor has increased. 
Consensus of operational model solutions suggests a swath of 
1-2+ inches in this general area. These totals have been 
observed to generate localized flooding on several occasions 
during the past few months. 


Additionally, there are indications that some of the rainfall 
may result from convection, especially late tonight into early 
Sunday morning. Should rainfall rates approach/exceed half an 
inch per hour, urban and small stream flooding is likely to 
occur, especially in the quickly responding basins within and 
surrounding the Philadelphia Metro. 


River flooding is possible, but appears to be more likely if 
quantitative precipitation forecast exceeds the current forecast (i.E., Widespread totals of 2+ 
inches). 


&& 


Tides/coastal flooding... 
onshore continues across the region, and will increase tonight 
and into Sunday morning. With the approaching full moon, the 
threat of coastal flooding will increase by Sunday morning's 
high tide. However, winds are expected to become more southerly 
late tonight, which should mitigate a more substantial coastal 
flooding event. To this point, guidance continues to advertise 
mainly minor flooding, though models do tend to exhibit a low 
bias in these sorts of events. Notably, the Stevens Institute 
ensemble guidance does suggest potential for spotty moderate 
flooding, especially on the northern New Jersey coast. Also 
noteworthy is the potential for heavy rainfall tonight and 
Sunday morning, which may exacerbate coastal flooding owing to 
contributions from freshwater runoff. At this point, however, 
think widespread minor flooding is more likely on the New Jersey 
and Delaware Atlantic coasts, along Delaware Bay, and the tidal 
Delaware River, for Sunday morning's high tide. Some locally 
moderate coastal flooding remains possible. 


As a result, we have issued a coastal flood advisory for the 
above-mentioned areas. As flow will become strongly offshore by 
Sunday afternoon, coastal flooding is not expected with high 
tides following Sunday morning's. 


At this time, coastal flooding is not expected for the Eastern 
Shores of Chesapeake Bay. 


&& 


Phi watches/warnings/advisories... 
PA...Winter Weather Advisory until 1 PM EST Sunday for paz060>062- 
103-105. 
Flood Watch through Sunday afternoon for paz070-071-101-102- 
104-106. 
Coastal flood advisory from 10 am to 3 PM EST Sunday for 
paz070-071-106. 
Winter Storm Warning until 1 PM EST Sunday for paz054-055. 
New Jersey...Winter Weather Advisory until 1 PM EST Sunday for njz007>010. 
Coastal flood advisory from 5 am to 11 am EST Sunday for 
njz012>014-020>027. 
Flood Watch through Sunday afternoon for njz012>019. 
Coastal flood advisory from 8 am to noon EST Sunday for njz016. 
Coastal flood advisory from 10 am to 3 PM EST Sunday for 
njz015-017>019. 
Winter Storm Warning until 1 PM EST Sunday for njz001. 
Delaware...coastal flood advisory from 5 am to 11 am EST Sunday for 
dez002>004. 
Flood Watch through Sunday afternoon for dez001. 
Coastal flood advisory from 8 am to noon EST Sunday for dez001. 
Maryland...Flood Watch through Sunday afternoon for mdz008. 
Marine...freezing spray advisory from 1 am to 6 PM EST Monday for 
anz430-431-450>455. 
Gale Warning from 8 am Sunday to 6 PM EST Monday for anz430- 
431-450>455. 


&& 


$$ 
Synopsis...staarmann 
near term...fitzsimmons/Johnson/mps 
short term...fitzsimmons/Johnson 



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