Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/25/20
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
600 PM EST Thu Dec 24 2020
Widely scattered light lake effect snow flurry activity will be
replaced with time late this evening into the overnight with a more
general/persistent light deformation snow as a disturbance riding
north into the eastern Great Lakes clips the area. Expect periods of
light snow into Friday with a second enhanced period in the mid
afternoon to early evening as northern through axis pivots east
through the area finally and provides additional forcing. Snow will
be more predominant from KPTK south to the I-94 terminals where IFR
vsbys will become possible at times. Ceilings will range from MVFR
to lower VFR throughout the forecast period.
For DTW...Light snow will eventually pivot north/northwest into the
terminal by the 04z-06z time frame with recent HiRes model trends in
favor a more substantive light snow event overnight thru Friday.
Cigs will be MVFR to lower VFR much of the forecast with IFR/MVFR
vsbys at times with the more persistent periods of light snow
overnight and quite possibly again mid afternoon into early evening.
.DTW THRESHOLD PROBABILITIES...
* High in ceilings at or below 5000 feet for much of the forecast.
* High in p-type as all snow this forecast.
Issued at 348 PM EST Thu Dec 24 2020
The lower tropospheric cold front is now aligned generally east of a
line from Sandusky Ohio northward through Chatham-Kent ON to
Goderich ON. A developing inflection point within the upper level
jet axis over the eastern United States, will cause increasing
phased upper level jet forcing later today. This will lead to
developing surface low pressure wave which will ride along the front
and effectively push the near surface cold to PA and Upstate New
York by 06Z this evening. The 700-500mb extension of the cold front
is much more lagged and will remain over far western Lake Erie and
Lake Huron, invof Southeast Michigan, through tonight.
Deep column dry air pushed into the area post cold front today with
very active subsidence occuring in the 3.5-6.0 kft layer. The
initial round of subsidence appears to be more of a consequence of
the low-mid cold air advection. The advection has already largely
played itself out this afternoon which now essentially locks in
surface based mixed layer and inversion heights at roughly 4.0 kft
agl. The convective depths are good enough for some westerly lake
effect stratocumulus bands/light lake effect snow showers to push
eastward into the cwa at times. However, model soundings are very
dry at the surface which significantly compromises the environment
for substantial lake effect this evening and tonight. Have been
monitoring upstream traffic data and nothing has been concerning. No
reason to deviate from the inherited forecast which calls for
scattered snow showers through this evening.
Tonight...While nothing is certainly gargantuan with regards to the
magnitude of forcing over the 24 hour period from 06Z tonight
through 06Z the 26th, the combination of deep cyclonic flow within
the trough and sneaky secondary height falls occuring in an inverted
fashion back into Southeast Michigan from the east is all good
enough for the development of light accumulating snow. The
aforementioned development of phased upper level jet forcing will
cause an area of low pressure to lift northward through western
Upstate New York. The response upstream is for system relative wind
directions to become easterly tonight here across Southeast
Michigan. As this occurs the main lower to midlevel cold pool is
forecasted to push eastward into Indiana and then lift across far
southwestern Lower Michigan the latter half of tonight. The arrival
of this cold, dense air then results in a steepening of the lagged
baroclinic zone aloft with a compaction of the temperature gradient
right up to the eastern doorstep of the cwa near the Rivers, Lake St
Clair, and the western shoreline of Lake Huron. The easterly system
relative flow will have the opportunity to lead to very weak system
relative isentropic ascent between 06-12Z as well as midlevel thetae
advection. A blend of both ECMWF and GEM is notable with amounts of
0.15-0.20 painted across extreme eastern cwa including Port Huron.
Model soundings show some subtle moistening through 12Z
tomorrow/Christmas morning. This late trend is much more juicy with
the liquid equivalent. The HRRR has also been showing a trend for
more QPF overnight, with the HRRR soundings now resolving a
favorable frontal inversion structure between 700-600mb. Will not
totally buy into these QPF amounts as the QPF gradient is expected
to be very compact. Forecast grids from 06-12Z tonigth will have
snowfall amounts of around 1 inch for Port Huron and far eastern
Macomb county with a few tenths for areas east of U.S. 23 and I 75.
Christmas Day...Composite trough and potential vorticity anomaly
will be in place directly over central Lower Michigan at the start
of the period. Closed heights within this trough axis will cause
slow progression during the early part of the day. As a result,
expecting the midlevel deformation axis to hold position during the
12-18Z time block. The exact position of the western flank of the
deeper midlevel moisture and deformation forcing will be important
as those areas will continue to grind out light snow. Frontal
forcing aloft is not as great with some stabilization in the 700-
500mb layer. Snow amounts should generally remain less than an inch
for 12-18Z. By the afternoon hours, diurnal heating is shown to
result in a surface based mixed/convective layer that tops out at
roughly 5.0 kft agl. Non-trivial as the convective depths push well
into the DGZ at -10 to -20C aloft for the entire cwa. Thefore, the
potential for snow showers will ventually increase for the western
cwa, those areas that miss out on the earlier snow activity.
Differential increase in anticyclonic flow trajectories will be
working against the setup as main absolute vorticity maximum pushes
immediately east of the area. Will need to monitor mesoscale
forcing, more specifically the remnants of the old southern Lake
Michigan lake effect banding/snow and the Lake Superior/Lake
Michigan connected band that was in place near Traverse City. At
minimum, remnant moisture from this lake enhanced moisture plume
will lift/push across the forecast area beginning 21-03Z. Models
show a reinvigoration of UVVS as this moisture/residual convergence
sweeps across the area. Snow accumulations of less than an inch are
expected many areas across Southeast Michiagn 18-00Z with around an
inch possible eastern cwa under the last of the deformation.
Christmas evening/night...Main forcing is expected to be the old
lake effect convergence/lake effect. Most favorable corridor appears
to be I 96-M 59 21-00Z, then north of I 69 including the northern
Thumb between 00-06Z. More than likely a flare up in snow showers
will occur in the northern Thumb/Huron County as favorable northwest
flow trajectories will siphon enhanced moisture off of Saginaw Bay.
Geopotential heights rises rapidly after 06Z which will very
efficiently end precipiation chances.
Summary of 06Z/25 to 06Z/26 event narrative. Snow ratios are
expected to be higher than the common 10:1 to 12:1 given the cold
environment. Peak snow ratios will likely be in the late afternoon
time period Christmas day perhaps pushing 15:1 for a period.
Snowfall amounts of 2 to 3 inches appears likely for far eastern
sections of the cwa/Thumb. Around 1 to 1.5 inches for central cwa
including much of Metro Detroit and less than 1 inch for areas west
of U.S. 23 and I 75. The big talking point is that minimal melting
will occur given very cold temperatures in the teens and 20s.
Roadways are expected to become snow covered and icy. Have forgone
any headline decisions as forecast amounts, for now, are expected to
be below 4 inches for the 24 hour period.
A period of zonal flow is expected to lead to quiet weather for both
Saturday and Sunday. Low pressure is forecasted to gather over the
Mid Mississippi River Valley Sunday which will eventually lead to
developing southwest gradient flow. Rapid moistening will be likely
given low level jet orientation and magnitude. At this time,
precipitation is expected to begin/fall in the form of rain.
Following the passage of this morning`s cold front, west to
northwesterly surface flow will hold through the end of the week
with cold air advection in full effect. This will aid in the
production of some lake effect snow across northern Lake Huron
tonight, with likely lake effect snow chances expanding across all
marine area throughout Christmas Day. Brief reductions in
visibilities will be possible with the stronger lake effect snow.
Otherwise, a relaxed pressure gradient has reduce wind speeds and
gusts this afternoon and has resulted in the end of Gale headlines
for the Saginaw Bay. Lighter winds will persist for the remainder of
the day through tomorrow morning before a second low pressure system
located over PA/NY acts to strengthen the pressure gradient across
the Great Lakes again. As a result, an uptick in gusts between 20 to
25 knots are expected tomorrow afternoon through Sunday morning.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
You can obtain your latest National Weather Service forecasts online
Area Forecast Discussion
National Weather Service Quad Cities IA IL
540 PM CST Thu Dec 24 2020
Issued at 245 PM CST Thu Dec 24 2020
Winter has returned across the area today as the fresh arctic
airmass that moved in behind yesterday`s storm system was firmly
entrenched over the region. Temperatures had climbed only in the
teens as of 2 pm with the help of nearly full sunshine. Brisk
northwest winds from 15 to 25 mph with a few higher gusts were
producing wind chills from around zero to 10 below. Satellite
imagery showed a longwave upper level trough nearly overhead from
the western Great Lakes to lower MS River Valley. The back edge of
the cold air stratus and flurries in the cyclonic flow around the
departing surface low over Hudson Bay was over north central IL.
Visible satellite imagery also revealed relatively narrow streaks of
fresh snow deposited from overnight snow showers curving from
central Iowa into southeast Iowa. Otherwise, most of the forecast
area appeared to have escaped the departing system with only a
dusting of snow.
.SHORT TERM...(This Evening through Friday)
ISSUED AT 245 PM CST Thu Dec 24 2020
Bitter cold temperatures and wind chills will be the weather story
for Christmas Eve into Christmas Day.
Tonight, the crisp cold and dry air should win out, keeping skies
mainly clear as surface high pressure over the eastern Dakotas
builds southeastward. In the upper levels, the trough axis and
embedded circulation nearly overhead will shift eastward with
weaker impulses continuing to rotate over the area in the cyclonic
flow through morning. However, with very dry as evident by
12Z area soundings that had pw values of.10 or less, this should
lead to only thin high level cloud cover at best. Low level
moisture fields and associated cloud cover that many models try to
generate and move back into the area tonight appears overdone.
Latest satellite images show mainly diurnal and lake enhanced
cloud cover over IL and WI, with clear skies across MN and the
eastern Dakotas. This all points to a clear and cold night with a
sufficiently strong pressure gradient to keep winds around 10 mph
or greater through the night, preventing would could otherwise be an
all out temperature plunge in this arctic airmass. Forecast lows
are kept around zero in the far NW and single digits elsewhere.
Even with decreasing winds, this results in overnight wind chill
values as low as 5 below to 15 below zero.
Christmas Day looks sunny and bright. Temperatures will continue to
be below normal, but warm in comparison to today. The sunshine and
low level flow backing from the northwest, to west, then southwest
by evening should allow temperatures to recover into at least the
20s by afternoon.
.LONG TERM...(Friday Night through Thursday)
ISSUED AT 245 PM CST Thu Dec 24 2020
1. Warmer temperatures this weekend, with a slight chance of very
2. Strong and possibly significant storm system will impact the
central Plains and Midwest Tuesday-Wednesday night. Confidence
remains low on many of the finer details of this system.
This Weekend...upper air pattern transitions from northwest flow to
more zonal, allowing for warmer air to move into the Midwest. RAP
850mb temps rise above 0C on Saturday morning and with mostly sunny
skies/little snow cover left, will help boost high temps back above
normal and into the upper 30s-mid 40s. An upper level wave will
track across the central Rockies on Sunday, with a surface low
developing over Iowa during the day. Latest models continue to
struggle with saturation and the NBM blend continues to show dry
condtions. However, enough 12z GEFS members and the 12z NAM/ECMWF
show saturation will be sufficient enough Sunday afternoon to
generate some pcpn, albeit light. Added some slight chance PoPs
in the northern third of the CWA to account for this. Assessing
thermal profiles, any precip that occurs would likely fall as
light rain/sprinkles, before changing over to snow by the evening
over northern IL. Some light snow/flurries may linger over the
northeast portions of the CWA Sunday night.
Monday-Monday night...quiet and more seasonable temperatures are
forecast, as a large 1033mb surface high drifts over the Midwest.
Highs will be in the mid-upper 20s and lows dropping into the teens.
Tuesday-Thursday...a deep upper level trough will bring another
strong and possibly significant storm to the central Plains and the
Midwest. Clouds will be on the increase on Tuesday, with winds
increasing out of the east southeast. The latest 12z models continue
to show a wide range of possible solutions with this system and I
anticipate better continuity to occur by this weekend. For now, it
appears that this system will be strong as noted by the latest
NAEFS/ENS output of standardized anomalies of -2 or greater at
850mb/700mb and it will have a strong Gulf moisture feed as
evident by +2 standard deviations of PWs per NAEFS/ENS ensemble
situational awareness table. At this time, thermal profiles
suggest precipitation to start out as snow Tuesday night, then
transition to rain/snow mix on Wednesday, before switching back to
snow Wednesday night, with the longer duration of snow and
possible accumulation expected for the northwest third of the CWA.
The exact track of the surface/850mb low will be a big factor as
to who receives what precip type with this event. Strong
northwest winds and snow showers will occur behind this low on
Thursday. Additional details will be ironed out in future
.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
ISSUED AT 540 PM CST Thu Dec 24 2020
MVFR cloud streets have formed across the area as slightly warmer
air aloft moves over the snow pack from the north of the area.
It looks like there is a chance for a deck associated with these
clouds for the next few hours. As such, have gone with a tempo.
Will need to monitor to see if they actually do break up as
confidence in what is going to occur is low.
Area Forecast Discussion
National Weather Service Grand Rapids MI
931 PM EST Thu Dec 24 2020
Issued at 255 PM EST Thu Dec 24 2020
- Higher impacts likely along the lakeshore tonight due to lake
- Rain and snow Sunday night leading to reinforcing shot of colder
air early next week
- More active weather to end the calendar year Wednesday and Thursday
Issued at 931 PM EST Thu Dec 24 2020
Snow has shifted towards the lakeshore as expected with an
increasingly sharp eastern edge that indicates subsidence. This
coincides with a ribbon of upper subsidence indicated by water vapor
imagery - but there likely is at least some near surface fgen that
is contributing the most.
Recent HRRR runs show increasing chances that the most intense lake
effect snow will remain west of even Van Buren County overnight. Not
going to jump on this yet, but will mention it as a possible
scenario in the WSW update, which we will try to have out before 10
PM ET. Have also slashed PoPs northeast of a Muskegon to Battle
Creek line to reflect expectations.
.DISCUSSION...(This evening through next Thursday)
Issued at 255 PM EST Thu Dec 24 2020
-- Higher impacts likely along the lakeshore tonight due to lake
We will be upgrading Van Buren and Allegan counties to a Winter
Storm Warning for tonight and for a good deal of Friday/Christmas
Lake effect has been causing slick roads and some travel issues this
morning, even with amounts not that high as expected through this
point. The ground having been somewhat warm from yesterday, melted
some of the snow initially, only to have it refreeze with temps
around 20 degrees this afternoon. This has been handled well with
the ongoing advisory.
There are indications this afternoon that the flow is shifting as
expected. Radar indicates SW to NE oriented bands south of a more
organized convergent band that runs from near Holland to GR. North
of this band, the bands are starting to take on a NW orientation. We
expect the winds to continue to shift to more NNW flow by midnight,
and hold nearly steady into Friday morning before shifting more
westerly again. This will shift the snow showers from much of the
area this afternoon, to hugging the lakeshore tonight.
There are many favorable ingredients to make this band fairly strong
tonight and Friday morning. We will have improving upper support and
rising inversion heights tonight as short wave energy rotates
through the area. Right now, inversion heights are around 6-7k ft.
These are forecast to increase to almost 10k. This may be
conservative as the flow down most of Lake Michigan there, and
plenty of pre-conditioning from Lake Superior will help the cause.
This will also help to enhance the low level convergence/forcing for
far western Allegan and much of Van Buren counties. The signal of
convergence/forcing is not nearly as strong or persistent for the
remainder of the lakeshore, but still enough to justify the
advisory. Inland areas will see snow diminish greatly, if not even
come to an end. The advisory may even be allowed to be canceled
early for inland counties.
We are expecting 1-2" of snow/hour to drop under this dominant band.
If it sits in one place for a long enough period (which is likely),
snow will accumulate quickly. Also, under these convective bands,
blowing and drifting is likely to be a problem. We expect that we
could mix down 25 to 30 mph of wind under these. That would blow the
fluffy snow fairly easy. This will cause significant travel impacts
on a holiday.
We expect this to continue to be ongoing through Friday morning,
before the wind shifts to a more westerly flow, and becomes less
intense. This will spread the snow showers inland once again. The
snow showers will become less intense also as the upper low move
east, and inversion heights fall with the coldest air aloft moving
-- Rain and snow Sunday night leading to reinforcing shot of colder
air early next week --
We will see a break in the weather then Friday night through much of
Sunday, before the next weather maker moves in. High pressure will
be responsible for that. Then a SW flow will push the cold air out,
and bring back more seasonable weather for a bit.
We will see a short wave and associated sfc low lift out of the
Central Plains later in the day on Sunday. It will take until almost
dark or even after for precipitation to start falling over the area.
This system does not have much moisture with it initially as the
Gulf is not open for moisture return until late in the day and
When precipitation does start, there is some uncertainty as to what
type it is. The rain and snow line will likely run through the area.
Areas that see all snow could see some additional accumulations,
where southern areas might see mostly rain on the front side of the
Once the system moves by, we will see some colder air filter back
over the area. There looks to be a relatively small window of
opportunity for some lake effect. The initial upper wave moves by,
and a northern stream upper trough clips the area on Monday. How far
south this dives will dictate how far south the lake effect threat
-- More active weather to end the calendar year Wednesday and
We will see another short lived break on Tuesday with residual cold
surface air hanging in. The break will be so short, that the lake
effect clouds will hang on until the upper level moisture arrives
from the next system in December-like fashion.
The next system will be a bit more energetic and pack more of a
punch that the Sunday night system. This will be energy supporting a
long wave trough out west that will lift up into the area. There may
be a little snow on the leading edge of the system on Wednesday. It
is looking more and more likely that the low will lift to our NW,
and a warm surge of air will help to change precipitation over the
rain. By New Year`s Eve day, the associated front would move
through, and bring more cold air back over the area. This is a ways
out yet, and adjustments in the track, timing, and p-types are
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 647 PM EST Thu Dec 24 2020
Still expecting an end to snow at inland TAF locations as winds
veer to the northwest and keep lake effect snow pinned near the
lakeshore. KMKG is going to be tricky because a north to south
oriented snow band will set up near or just west of the KMKG
terminal. One possible scenario is that this terminal stays MVFR
and borderline VFR with the band just to the west until around
10-12Z when this north to south oriented band pushes eastward,
giving KMKG and other terminals downstream very brief IFR
Issued at 255 PM EST Thu Dec 24 2020
Small Craft Advisory will be allowed to continue as is through
Friday night. Strong winds from yesterday and this morning are
coming down gradually this afternoon. This lull will be short lived,
as another core of wind will start to come up this evening, peaking
toward daybreak on Christmas morning. Winds will try to approach
gales, but should come up just short. Winds will hold up in the 20-
30 knot range through early Friday night before coming down enough.
MI...Winter Storm Warning until 7 PM EST Friday for MIZ064-071.
Winter Weather Advisory until 7 PM EST Friday for MIZ037-038-043-
LM...Small Craft Advisory until 7 AM EST Saturday for LMZ844>849.
Area Forecast Discussion
National Weather Service Mount Holly NJ
1049 PM EST Thu Dec 24 2020
A strong and complex storm will affect the region tonight and
into Friday. This storm will weaken and move away over the weekend
as high pressure builds over the area. Another low will cross
north of the area Monday causing a cold front to cross our region.
More high pressure is expected for the middle of next week.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Winds continue to escalate quickly. We`ve gotten reports from
Cumberland (NJ) and Kent (DE) County that are just below high
wind warning criteria. With another 2 to 3 hours of peak winds,
decided to include those two counties within the high wind
warning. Otherwise, no significant changes.
Center of the 500 mb closed low is over IL now, with the trough
axis extending all the way down to the Gulf. There are two
surface lows, one centered over Quebec, the secondary low
has lifted all the way into western MD/PA from the Carolinas
just over the past few hours. The cold front currently over
western PA is expected to rapidly sweep east as we go through
Southerly flow should increase through the evening. As mentioned
above though, it is slightly behind schedule. Dew points are
already in the 50s, and could get close to 60 F just ahead of
the front. This will yield PWATs between 1.3-1.5 inches, which
is over 300% of normal for this time of the year. Heavier rain
will move into the western zones by early this evening, and then
several rounds of heavy rain will affect the region into the
Storm total QPF forecast remains about what the forecast had previously
had, which is generally 1-2 inches throughout, and the highest amounts
will be in the Lehigh Valley, southeast Pennsylvania, and northern
New Jersey. For the southern Poconos, storm total rainfall will
average 3-4 inches. Up to 2 inches is possible for the New Jersey
coast. For more on the flooding potential, please see the Hydrology
Winds between 925 mb-850 mb will average 70-90 kt tonight, and
with heavy rain and a tight pressure gradient, a good deal of
those winds will mix down, especially along the coastal areas.
Even back towards southeast Pennsylvania, the LLJ will average
50-70 kt winds. The High Wind Warnings and Wind Advisories
remain in effect for most of the areas, but will make one
change. Currently expecting 60-70 mph winds along the barrier
island of New Jersey and into coastal portions of mainland New
Jersey, as well into Sussex county, Delaware. Will upgrade from
Wind Advisory to a High Wind Warning there. For the rest of the
region, maximum wind gusts will range from 45-55 mph.
With the warm and humid air spreading into the region, surface
instability parameters remain fairly low, but MUCAPE values are
projected to be from 100-200 J/kg, but as much as 500 J/kg in
portions of southern New Jersey. 0-6 km Bulk Shear will range
from 70-80 kt. SPC Day 1 outlook has the southern half of the
forecast area in a Marginal risk for severe weather, and several
stronger cells, or even broken line segments may form and that
would mix down the damaging wind gusts mentioned above. NAM-3km
showing a squall line developing, and this is reflected in the
HRRR as well. Will go ahead and add a chance for thunder to the
southern half of the forecast area. That could mix down
damaging winds that are stronger than forecast in the Wind
Advisory and High Wind Warning areas.
The heaviest of the rain should be just offshore by the time this
period ends. Temps this evening and into most of the night
will remain warm, generally in the 50s and low 60s.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
The bulk of the rain ends fairly abruptly Friday morning, and models
continue to indicate a dry slot sliding up the coast. CAA will be
underway in the morning as low pressure departs and a cold front
works its way through the region. Temps drop off even further during
the day as a stronger cold front passes through in the afternoon. As
the cold air surges east, temps will drop during the day, but
probably not below freezing until towards the evening. With the
passage of the front, as well as with the strong shortwave energy
approaching from the west, cannot rule out scattered rain and/or
snow showers into the afternoon hours. The high temperature for the
day will likely occur between midnight-2am.
.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
The upper pattern continues to remain fairly amplified and
progressive during the long term part of the forecast.
The system from the near/short term parts of the forecast will
continue to exit off to the northeast Fri night/Sat leaving only
some scattered snow showers across the higher elevations of the
Southern Poconos and northwest NJ for the evening Friday. The
coldest of the airmass will be settling across the area, so below
normal temps and a chilly wind will be over the region. Lows Fri
night will be in the teens/low 20s over the northern areas and
mostly low/mid 20s for Delmarva, srn NJ and metro Philadelphia. Wind
chills will take about ten degrees off these air temperature values.
Saturday and Sunday both looks dry at this point with high pressure
settling across the region. Temperatures will be cold Saturday but
moderate back close to normal by Sunday.
Another low and upper air feature will pass north of the region
Monday with high pressure building in again Tuesday. While
widespread precipitation is not expected with the system Monday, a
couple scattered rain/snow showers will accompany the trailing
fronts. Temperatures will reach the 40s regionwide Monday, but then
drop back below normal (mostly 30s) Tuesday following a cold front.
After a fair weather day Wednesday, most forecast models are showing
another potent low developing across the middle part of the country
and tracking towards the Great Lakes later Wed/Thu. This
patters kinda looks like the present system, perhaps weaker with
a maturing cyclone and strong cold front to cross the MIddle
Atlantic perhaps later Thu into Friday. Too early for specifics,
but it could get very warm preceding the system and this is
reflected in out high temps for Thu being in the 50s for many
areas. We will go along with the NBM guidance for now with chc
pops for Wed night/Thu/Thu night.
.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Through tonight... Conditions will continue to deteriorate from west
to east through this evening, due both to lower ceilings and
visibility restrictions in rain. For most of the overnight
hours, mainly IFR or low end MVFR is expected with rain, which
could be heavy at times. Rain may begin to diminish by late in
the night from west to east. South- southeast winds will
continue to increase overnight, with speeds of 20 to 25 kt and
gusts of 35 to 45 kt expected in most areas, a little higher
near MIV and ACY. LLWS will continue although the increasing
surface winds will mitigate it somewhat, especially near and
west of PHL where winds aloft will not be as strong. Surface
winds should turn more southerly with time and become more
southwest during the predawn hours, with speeds also beginning
to decrease during the predawn hours. Moderate confidence on the
overall pattern, but low confidence on the timing.
Friday... Mainly MVFR to begin the day with ceilings of 1000 to
2000 ft lingering even after the rain pulls away, which should
occur from west to east between 12z and 15z. MVFR should
continue for most of the morning and likely into the early
afternoon. Low clouds may begin to lift and/or scatter out by
mid to late afternoon, which could allow VFR conditions to
develop. Winds will be southwest shifting to west-southwest at
10 to 15 kt with gusts to 20 kt, except a little stronger near
the coast. Moderate confidence.
Fri night thru Sun night...VFR expected. Gusty winds Fri night
Mon/Mon night...Mostly VFR. Scattered showers mostly N/W.
Tonight...Winds this evening will quickly ramp up to Storm Force on
all waters, and will expand the Storm Warning to include upper DE
Bay. Sustained winds of 35-45 kts are expected with gusts of 50-60
kt are expected with the passage of low pressure. Visibility
restrictions likely in heavy rain and fog. Seas across the ocean
waters will build to 10-20 feet.
Friday...Winds abruptly shift to the west early, and decease to 20-
30 kt with 30-40 kt gusts. Going into midday, conditions lower to
SCA levels and should remain at SCA levels through the
Fri night thru Saturday...SCA conditions continuing on the
waters diminishing late. Fair weather.
Sat night thru Sunday night...sub-SCA expected. Fair.
Monday thru Tue...SCA expected. Scattered showers Mon mostly north.
Tue night into Wed...sub-SCA expected. Fair.
A widespread 1-3" of rain will fall with 2-4" in the southern
Poconos. There is about an inch of liquid equivalent in the snowpack
across interior portions of southeast Pennsylvania and northern New
Jersey. This snowpack should rapidly melt into tonight due to the
combination of the warm temps and heavy rain. Flooding will develop
on the smaller smaller streams and creeks, and there will be rises
on the mainstem rivers. In addition, urban and poor drainage
flooding is likely to develop. A Flood Watch remains in effect for
all of southeast Pennsylvania and northern New Jersey.
After the rain ends Friday morning, is is likely that rises on area
rivers and streams will continue into Friday afternoon and Friday
night. Several forecast points, including along the Macopin,
Raritan, Passaic, and Schuylkill Rivers will approach and may go
over minor flood stage, and the Millstone River at Blackwell Mills
is expected to crest at moderate flood stage.
Update: a coastal flood advisory has been issued for Kent County
MD as Tolchester is now expected to be above advisory levels
with the high tide overnight.
A strong southerly wind is expected for tonight. As a result, the
most susceptible locations in our region for any tidal flooding will
be our counties on the eastern shore of Chesapeake Bay, areas around
Barnegat Bay in New Jersey, and areas around Little Assawoman Bay in
The strong southerly flow is forecast to continue until about 3:00
to 5:00 AM on Chesapeake Bay. As of mid afternoon, the surge had
built to about 1 foot on parts of the lower bay. The astronomical
high tides will be running particularly low as we move away from the
first quarter moon phase. As a result, it will take a surge of 2.5
to 3.0 feet to cause even spotty minor tidal flooding in the
counties of Talbot, Caroline, and Queen Anne`s. We will
forecast that scenario for now, and we will continue to monitor
trends on Chesapeake Bay. The high tide works its way northward
through our counties on the eastern shore between about midnight
and 5:00 AM, so we still have a little time in case we find
that we need to issue an advisory.
The southerly flow is anticipated to persist until around daybreak
of the oceanfront. The usual situation in this type of pattern is
that water becomes trapped in Little Assawoman Bay in southeastern
Delaware, and in Barnegat Bay in New Jersey. It seems likely that we
will eventually need a Coastal Flood Statement for those areas at
some point from late tonight into Friday.
Our remaining tidal areas in New Jersey and Delaware, and those
along Delaware Bay and the tidal Delaware River should experience no
more than some spotty minor tidal flooding. The more significant
flood potential will come from the heavy rainfall.
Data quality errors at the KDOX radar site are making the
reflectivity and radar estimated precipitation look worse than
it actually is. Technicians are aware of the issue and working
to resolve it.
PA...Flood Watch through Friday morning for PAZ054-055-060>062-070-
Wind Advisory until 7 AM EST Friday for PAZ054-055-060>062-070-
NJ...Flood Watch through Friday morning for NJZ001-007>010-012-015.
Wind Advisory until 7 AM EST Friday for NJZ001-007>010-012-
High Wind Warning until 7 AM EST Friday for NJZ013-014-020>027.
DE...Flood Watch through Friday morning for DEZ001.
Wind Advisory until 7 AM EST Friday for DEZ001.
High Wind Warning until 7 AM EST Friday for DEZ002>004.
MD...Wind Advisory until 7 AM EST Friday for MDZ012-015-019-020.
Coastal Flood Advisory from 2 AM to 6 AM EST Friday for MDZ012.
MARINE...Storm Warning until 7 AM EST Friday for ANZ430-431-450>455.
Tides/Coastal Flooding...WFO PHI