Cape Henlopen to Fenwick Island DE out 20 nm Marine Forecast
|Overnight...Nw Winds 5 To 10 Kt With Gusts Up To 20 Kt. Seas 2 Ft Or Less. Swell Mainly From The Ne With A Dominant Period Of 5 Seconds.|
|Mon...Ne Winds Around 5 Kt. Seas 2 Ft Or Less. A Chance Of Rain Late. Swell Mainly From The Ne With A Dominant Period Of 5 Seconds.|
|Mon Night...E Winds 5 To 10 Kt, Increasing To 10 To 15 Kt In The Late Evening And Overnight. Gusts Up To 20 Kt. Seas 2 Ft Or Less, Then Around 3 Ft After Midnight. Rain, Snow And Sleet Until Early Morning, Then Rain Late. Vsby 1 To 3 Nm Until Early Morning. Swell Mainly From The Ne With A Dominant Period Of 3 Seconds.|
|Tue...Ne Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 3 To 4 Ft. Rain Until Late Afternoon, Then A Chance Of Rain Late. Swell Mainly From The E With A Dominant Period Of 4 Seconds.|
|Tue Night...N Winds 10 To 15 Kt. Seas 3 To 4 Ft.|
|Wed...N Winds 10 To 15 Kt. Seas 3 To 4 Ft.|
|Wed Night...N Winds 10 To 15 Kt With Gusts Up To 20 Kt, Becoming Ne 20 To 25 Kt With Gusts Up To 30 Kt After Midnight. Seas 3 To 4 Ft, Building To 4 To 6 Ft After Midnight. A Chance Of Rain. Vsby 1 To 3 Nm After Midnight.|
|Thu...N Winds 25 To 30 Kt. Seas 7 To 10 Ft. Rain And Snow Likely. Vsby 1 To 3 Nm.|
|Thu Night...N Winds 25 To 30 Kt. Seas 7 To 10 Ft. A Chance Of Snow In The Evening With Vsby 1 To 3 Nm.|
|Fri...Nw Winds 20 To 25 Kt. Seas 6 To 9 Ft, Subsiding To 5 To 7 Ft In The Afternoon.|
|Fri Night...Nw Winds 15 To 20 Kt. Seas 5 To 7 Ft. A Chance Of Light Freezing Spray After Midnight.|
| Area Forecast Discussion|
National Weather Service Mount Holly NJ
934pm EST Sunday Jan 24 2021
High pressure will migrate slowly eastward offshore through Monday. A surface low in the southern Plains will lift east- northeast to the middle Mississippi Valley on Monday night before weakening as it shifts off the Mid-Atlantic coast Tuesday night and Wednesday. Another surface low will develop in the Southeast Tuesday night and then rapidly intensify as it shifts off the southern Mid-Atlantic coast Wednesday night and Thursday. Strong high pressure will build into the eastern U.S. Friday and Saturday. Another system will likely affect the Northeast by late in the weekend.
Near Term - Through Monday
Tonight...Light radar returns continue to move through the region tonight but with incredibly dry air in place, nothing is making it down to the surface. Instead, we are seeing increasing cloud cover across the area and as a result temperatures are not falling as quickly as previously expected. With more clouds around overnight, it won't be nearly as cold as last night but expect overnight lows to drop down into the teens across the southern Poconos and northwestern New Jersey with 20s across the rest of the region. Possibly a few spots remain near 30 overnight, especially along the immediate coast of southern New Jersey and Delaware and along the eastern shore of Maryland.
Monday...The high will have moved offshore and the next system, which is weakening as it approaches, will be moving into the lower Ohio Valley area. A large area of precipitation will be advancing towards the area, but it will not be that heavy. This precip, mostly rain will begin across Delmarva during the mid/late afternoon, so some chance probability of precipitation are in the forecast for now. Other areas will have increasing clouds and cool conditions. Highs will range from the low/mid 30s for the NW areas to the upper 30s/low 40s for southern NJ and Delmarva.
Short Term - Monday Night Through Tuesday Night
A long duration but mostly low impact weather system is expected for Monday night through Tuesday night. Low pressure tracking out of the southern Plains will steadily fill in and occlude as upper level support diminishes, while a weak secondary coastal wave develops south of Delmarva. The result will be an increasingly elongated but poorly organized field of precipitation over the eastern half of the country, which will bring some unsettled weather to our area.
Limiting factors with this system are plentiful. Dynamically, most of our precipitation Monday night into Tuesday will be warm advection driven as the primary low tracks to our west. However, this lift source will be weakening as the system becomes more elongated and fractured. The mid level shortwave trailing the surface low will be deamplifying as it runs into ridging in place over the East. This ridging will also prevent the developing coastal wave from achieving any kind of coherent organization even as the primary low weakens. The result is a strung out mess both at the surface and aloft. In addition to weakening upper support, low level dry air will be plentiful at the onset with Canadian high pressure in place well to the north. This will erode the leading edge of the precipitation shield, and lead to a very slow northeastward advance of precipitation Monday night.
Precipitation Monday night should begin mainly as snow, though may be warm enough for rain across southern Delaware and parts of the Eastern Shore of Maryland. It should eventually make it at least close to the Philadelphia metro area during the overnight, but probably not much further, and it will be light in intensity. Sleet and freezing rain should start to mix in over Delmarva and southern NJ later in the night as warmer air filters in aloft. By Tuesday, light precipitation will overspread most of the area. Thermal profiles become more marginal on Tuesday, with a steady transition to rain or freezing rain/drizzle expected from south to north, though should stay all snow across the north. Light mixed precipitation may continue through much of Tuesday night, but Quantitative Precipitation Forecast for the entire event is only around 0.25 inches in most of the area, which indicates how light the precipitation rates are expected to be.
In terms of snowfall amounts, it is generally a coating to 2 inches across the entire CWA, and would not be surprised if some areas fail to see any measurable snow due to the combination of dry air at the onset and increasingly marginal temps later in the event. Accumulations across Delmarva and southern NJ will be contingent on what happens Monday night, and whether precipitation is able to overcome the dry air while it's still cold enough for snow. The 24.12z NAM for instance shows more snow than forecast, even indicating the potential for a few inches. However, it is an outlier and several other models indicate little to no precipitation at all during the overnight. Further north, confidence is higher in some light but non-zero accums mainly during the day on Tuesday. It does still appear that a sizable zone of light freezing rain or drizzle could develop late Monday night through much of Tuesday, which combined with the little bit of snow preceding it could make for areas of hazardous travel on Tuesday. We will also have to watch temperatures Tuesday night. It won't be a very cold night with the lingering clouds and light precipitation, but some areas will probably go from above to below freezing. Not exactly a flash freeze, but with light winds and high RH values, standing water will probably freeze up as opposed to dry out in areas that do drop below freezing, so black ice may be a concern Wednesday morning.
Long Term - Wednesday Through Sunday
Main concern this period remains the influence of a rapidly intensifying surface cyclone off the southern Mid-Atlantic coast Wednesday night and Thursday.
The large-scale pattern Wednesday through the end of the week remains consistent in the deterministic guidance. Three vigorous midlevel vorticity maxima will dominate the weather in the eastern U.S. through this period. The first will be a northern- stream vort max moving eastward and then southeastward through south-central and southeast Canada. The second will shift southward in the far eastern Canadian Maritimes and vicinity. The third (a southern-stream perturbation) will race from the southern Plains Wednesday morning to the East Coast by Thursday morning. As expected, models have not trended northward with the developing surface low attendant to the southern-stream vort max, as the northern-stream blocking flow (via a high-amplitude ridge between the two aforementioned vorticity maxima) will prevent much northward progression of the southern-stream system. If anything, models have trended southward today as the cyclone rapidly intensifies near the Carolina coast. As such, think the primary impacts from the storm will be seen in the far southern CWA, and these will likely be muted compared to portions of Virginia and North Carolina.
The main question will be how far north the precipitation shield reaches relative to the surface low, and this will be primarily controlled by two factors: the ultimate track of the low and the timing of its rapid intensification. The models continue to disagree on the timing of the intensification, though the CMC has trended faster with this (and also much slower with the progress of the low). The ECMWF (European Centre for Medium-Range Weather Forecasts) remains most suppressed and progressive, with the GFS the strongest in the fastest amount of time, though noticeably more progressive than the CMC. Think typical model biases are now dominating the signal in the model variance. As such, a model blend was again incorporated today, though I leaned a little toward the stronger/slower guidance given the favorable synoptic-scale setup.
Main changes to the forecast as a result of the above: (1) PoPs were lowered slightly across the CWA but remain mentionable everywhere Wednesday night and Thursday morning. Think the most likely outcome now is little or no precipitation north of I-78, with the best chances south of the I-76 corridor. Quantitative Precipitation Forecast may be high enough to come with some impacts in Delmarva and far southern New Jersey, but amounts should trail off quickly to the north of these areas. Precipitation type will largely be snow, especially if the timing favors the overnight hours into Thursday morning (and have made changes to the weather grids to key in on this). Given the fast progress of the storm and questions regarding our proximity, think snow amounts will not be particularly noteworthy in our southern CWA. There is still quite a bit of time to fine-tune this aspect of the forecast, however. (2) Trended temperatures downward Thursday onward, as models continue to look much too warm within and north of the precipitation shield given the overall pattern (and typically observed model biases in these regimes). (3) Trended winds/gusts slightly upward again Thursday through Friday, particularly given model soundings depicting 40-kt flow at 900 mb (with mixing to this level quite likely). Wind gusts of 30-40+ mph seem probable during this period of time.
A relatively high-confidence aspect of the forecast is the cold air arriving Thursday night through Saturday. With winds likely quite elevated through Friday, wind chills will likely be in the teens or colder for much of this period (and below zero for the Poconos). Bumped highs and lows Friday through Saturday down several degrees given model trends, the strength of the approaching surface high, and typical model biases in these regimes. Lows Friday night may be in the teens or lower in most locations.
After transient ridging Saturday into Saturday night, quick recovery should begin as return flow sets up. Max and min temperatures will likely warm around ten degrees Saturday night and Sunday.
Another system will approach the eastern U.S. by late in the weekend, as the Canadian perturbation separates/weakens by this time. Precipitation will likely move in by Saturday night or Sunday (with wintry weather probable), but the surface low track appears to be well west of the region. Thus, precipitation type issues will likely be a feature with this one.
The remaining SCA (Small Craft Advisory) flag will continue on the waters thru 6 PM. Overnight fair weather is expected with decreasing NW winds. On Monday, conditions will remain sub-SCA (Small Craft Advisory) as high pressure pushes offshore. Seas on the ocean 3 to 5 ft early then 2 to 3 ft overnight and Monday.
Outlook... Monday night... Sub-SCA (Small Craft Advisory) conditions expected. Northeast wind 10 to 20 kt. Seas 2 to 3 ft. Light rain or snow possible especially late.
Tuesday-Tuesday night... On Delaware Bay, sub-SCA (Small Craft Advisory) conditions are expected. On the Atlantic coastal waters, conditions may approach SCA (Small Craft Advisory) levels late in the day Tuesday and into overnight as northeast winds gust to near 25 kt and seas build to 3 to 5 ft. Winds shifting more northerly overnight and decreasing. Light rain expected, mixing with snow to the north.
Wednesday...Sub-advisory conditions expected.
Wednesday night and Thursday...Northeast winds will rapidly increase and likely reach gale force by daybreak Thursday. Winds will slowly become northerly on Thursday. Seas on the Atlantic waters may build to around 10 feet by Thursday afternoon. A chance of snow or a wintry mix, especially late Wednesday night into early Thursday afternoon, with visibility restrictions possible.
Thursday night...Northwest gales likely, with seas remaining well above 5 feet. Freezing spray possible.
Friday...At least advisory-level northwest winds continuing, but seas slowly diminishing with time. Freezing spray possible, particularly Friday night.
NOAA Mount Holly NJ Office: Watches - Warnings - Advisories
PA...None. NJ...None. DE...None. MD...None. MARINE...None.