textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

A major winter storm is underway across the region, and will continue impacting the area through Monday. Very heavy snowfall and areas of blizzard conditions are already occurring. Snowfall rates of 1-2+ inches per hour have been observed.

Coastal Flood Warnings and Advisories remain in effect for the Atlantic coast and Delaware Bay for tonight's high tide cycle.

KEY MESSAGES

1. A major winter storm is impacting the region with very heavy snowfall and areas of blizzard conditions, which will continue through Monday.

2. Widespread coastal flooding will occur with tonight's high tide cycle. Moderate coastal flooding is likely for many ocean- front and back-bay communities along the Atlantic coast with major flooding possible. Further tidal flooding will linger into Monday and potentially into Tuesday as well.

3...An unsettled pattern continues through this week with some light snow expected on Tuesday Night and then another system likely bringing some rain and snow Thursday into Thursday Night.

DISCUSSION

KEY MESSAGE 1...A major winter storm is impacting the region with very heavy snowfall and areas of blizzard conditions, which will continue through Monday.

10 PM Update: Widespread snowfall totals of 3-6" have been reported so far, with localized amounts as high as 9". Snowfall rates of 1-2 inches per hour have been observed. Blizzard conditions are developing along the Atlantic coast. Additional snowfall amounts between 6-16" are forecast area wide. Blizzard Warnings and Winter Storm Warnings remain in effect for the entire forecast area through Monday. Previous discussion follows...

A potent upper trough currently centered over portions of the Appalachians will continue to shift eastward towards the region this afternoon and evening. A 140 kt jet streak is rounding the base of the trough, with significant height falls and associated ascent overspreading the region. At the surface, a rapidly deepening low is located off the NC and VA coasts. As the low tracks northeastward towards our region, it is expected to continue deepening rapidly, particularly through tonight. The low will track northeastward away from the region on Monday.

Model guidance has shifted slightly eastward across the board as of this afternoon, but there remains good consensus that the surface low will track close enough to the coast to bring significant impacts to most, if not all, of the area. The GFS and NAM have both shifted east, but still feature a deep cyclone in the neighborhood of 970 mb tracking fairly close to the coast, leading to significant snowfall accumulations across most of the region. The ECM has also stopped in its northwestward trend, but still features warning level snow across most of the region. Other deterministic guidance remains in general consensus with this evolution. Significant impacts from snow, winds, and coastal flooding are still expected across much of the area.

In addition to the surface cyclone off the coast, an inverted trough is noted on Objective Analysis extending northwestward across portions of central and eastern PA. These features tend to increase snowfall amounts and rates where they set up, even when these totals are not well-depicted by model guidance. While this does lend confidence in significant snowfall occurring across eastern PA, the highest amounts are expected to be near the NJ and DE coasts. There is slightly lower confidence on exact snowfall amounts on our western fringe, but regardless, warning level snow is still expected everywhere.

Precipitation continues to overspread the region this afternoon, with rates gradually increasing. As the surface low continues its approach from the southwest, precipitation rates should continue to increase. While most of the region is seeing mixed precipitation currently, a changeover to all snow is expected through this afternoon as colder air begins to infiltrate the area in concert with the heaviest precipitation rates. Snowfall rates could exceed 2 inches per hour where the heaviest accumulations are forecast, primarily along and east of I-95. The heaviest snowfall is anticipated to occur beginning late this evening and continuing through tonight. Snow is expected to gradually begin to taper off Monday morning, and come to an end from west to east sometime Monday afternoon.

In terms of snowfall totals, most of eastern PA and Delmarva are expected to receive a widespread 10 to 18 inches, though it is possible that some western areas receive under 10 inches. The heaviest snowfall should remain focused on New Jersey, with the greatest potential for localized amounts near or exceeding 24 inches around Monmouth, Ocean, and southeastern Burlington Counties where coastal convergence is maximized and heaviest snowfall rates should occur. Farther inland, there will likely be some topographic effects on snowfall, with locally higher amounts possible on windward (north) sides of mountains and ridges.

In addition to the heavy snowfall, as the low deepens tonight into Monday, winds will begin to ramp up. Northeast winds sustained 20-35 mph will gradually shift north then northwest, with gusts 35-45 mph for inland areas, and up to 60 mph possible along the coast. The snow will be heavy, wet, and sticky until later in the event. However, blowing and drifting of snow is certainly a concern, especially closer toward the coast where winds will be strongest.

No changes have been made to the Blizzard or Winter Storm Warnings. It is important to note that regardless of whether blizzard criteria is met for any given location, the combination of strong winds and heavy snow will lead to nearly impossible travel conditions, as well as the potential for scattered power outages.

Confidence remains very high in major to extreme impacts to our region from this unfolding winter storm.

KEY MESSAGE 2...Widespread coastal flooding will occur with tonight's high tide cycle. Moderate coastal flooding is likely for many ocean-front and back-bay communities along the Atlantic coast with major flooding possible. Further tidal flooding will linger into Monday and potentially into Tuesday as well.

Strong onshore flow ramps up due to bombing out low pressure off the Mid-Atlantic coast over the next 24 hours. This will have direct impacts on tidal levels which are expected to rapidly rise, especially for tonight's high tide cycle. The onshore flow will continue to pile water toward the coast coinciding with the time of high tide. Fortunately, we will be in between the full/new moon phase cycle which will lead to lower astronomical tide contributions.

Confidence remains high that most of the ocean-front communities and back bays of New Jersey and Delaware will rise well into Moderate flood stage due to the strong background wind field and proximity of the deepening low off the coast. There still remains potential for some areas to reach Major flood stage if the right ingredients all come together. The most likely locations of Major flood stage will be from Ocean County NJ southward to Sussex County DE, especially in the back bays where water piling will be enhanced.

Coastal Flood Warnings remain in place for tonight's high tide cycle for Middlesex, Monmouth, Ocean, Southeastern Burlington, Atlantic, and Cape May Counties in NJ, as well as Kent and Sussex Counties in DE where moderate to potentially major tidal flooding will occur. Coastal Flood Advisories have been expanded to include New Castle County in DE and Salem County in NJ for minor tidal flooding with tonight's high tide cycle in addition to Cumberland County in NJ.

On Monday, winds will gradually turn to a more offshore component, however, the deepening offshore low will continue to keep ocean swells onshore through the day. As a result, it is becoming more likely that another round of widespread coastal flooding will occur with the Monday afternoon high tide within the area currently in a Coastal Flood Warning. Some of these areas may again reach well into moderate flood stage, particularly in the back bays from Ocean County NJ on south. Still some uncertainty whether widespread minor or moderate will occur, along the ocean-front, so have opted to not extend warnings out in time for now. However, further extensions will likely be needed at some point. By Monday night, conditions begin to improve, though another round of tidal flooding may occur with the high tide late Monday night into Tuesday morning.

For the tidal Delaware River and tidal Maryland Eastern Shore, no tidal flooding is expected.

KEY MESSAGE 3...An unsettled pattern continues through this week with some light snow expected on Tuesday Night and then another system likely bringing some rain and snow Thursday into Thursday Night.

Our next system arrives Tuesday night into Wednesday morning. Low pressure moving through the Great Lakes and into New England will drag a front through the region as the clipper system grazes the area. This will produce light snowfall of around 1-3" from Philadelphia on north, with potentially higher amounts up to 4" possible over the Poconos and NW NJ. South of Philadelphia, precipitation will start as snow but could change to rain, with snow accumulations likely under an inch. This system will be relatively minor, though cannot rule some Winter Weather Advisories being needed north of I-78. Precipitation should generally taper off after daybreak Wednesday morning.

The next system looks potentially stronger, but the track supports more of a rain event for the duration of the event. Low pressure looks to track through the Ohio River Valley up into the Great Lakes and through New England. Inland cutters usually result in our area being in the warm sector, and the case is no different here. However, ahead of the warm front moving through on Thursday evening/Thursday night, there could be some wintry precip. Would focus most of the attention in the Poconos as this setup could be conducive to some freezing rain, but currently not expecting significant snow accumulations anywhere. While there could be some flakes at onset, this mainly should be a rain event.

The pattern should settle down for the weekend as high pressure moves in.

AVIATION /03Z MONDAY THROUGH FRIDAY/

The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas.

Tonight...Overall, IFR and LIFR conds, with VLIFR VSBYs in 1/4SM +SN and BLSN. CIGs may hover in the IFR/low end MVFR range. Snowfall rates as high as 4 inches per hour in the heaviest bands. N winds, backing to the NW at 15 to 25 kt with 30 to 45 kt gusts. Strongest winds at KMIV/KACY, and winds lighter at KRDG/KABE. Low confidence on timing details.

Monday...IFR in the morning. Conds lift to MVFR by midday along and west of the I-95 corridor terminals, then conds will not lift to MVFR until late in the day at KMIV/KACY. After SN ends, BLSN may result in VSBY restrictions through the day. NW winds 15 to 20 kt with 25 to 35 kt gusts, diminishing late. Moderate confidence overall, low confidence on timing.

Outlook...

Monday night...VFR. West-northwest wind gusts up to 25 knots.

Tuesday...VFR, then sub-VFR conditions possible at night with a period of snow. Gusty northwest winds possible during the day.

Wednesday and Thursday...Periods of sub-VFR conditions possible with some rain/snow.

Friday...Conditions may improve to VFR.

MARINE

A powerful coastal storm will develop across the coastal waters through tonight. North winds 35-50 kts with gusts up to 60 kts tonight. Winds will shift eventually northwestward on Monday, before beginning to decrease by Monday afternoon and evening. Seas building to 12-18 feet tonight into Monday morning before beginning to decrease.

The Storm Warning for NJ and DE Atlantic coastal waters, as well as the lower Delaware Bay remains in effect until 6 PM Monday. The Gale Warning for the upper Delaware Bay also remains in effect until 6 PM Monday. The highest winds and seas will occur overnight tonight, with gale force winds likely lingering into Monday afternoon. Heavy snow could lead to near zero visibility at times Sunday night through Monday morning.

Small Craft Advisory conditions Monday night, with northwest wind gusts up to 30 kts.

Regarding the river/marine ice, Delaware Bay continues to be mainly ice free outside of shallow near-shore areas. Ice coverage remains around 10-30% from the the Delaware Memorial Bridge up to the Commodore Barry Bridge. North of that up through Philadelphia, ice coverage is around 30-70%.

Outlook...

Monday Night through Tuesday...SCA conditions expected. Wind gusts near 25 kt, especially on Monday Night. Seas over 5 feet will persist through Tuesday.

Tuesday Night...A brief lull in SCA conditions possible.

Wednesday through Wednesday Night...SCA conditions expected. Winds increase out of the south/southwest around 25-30 kt and seas 4 to 6 feet.

Thursday...No marine headlines expected.

CLIMATE

The daily snowfall records for February 22 and 23 from our climate sites listed below:

February 22 Site Record/Year Allentown (ABE) 8.6"/1948 AC Airport (ACY) 8.0"/2001 Philadelphia (PHL) 7.0"/2001 Reading (RDG) 6.5"/1948 Trenton (TTN) 6.3"/2001 Wilmington (ILG) 5.0"/1935

February 23 Site Record/Year Allentown (ABE) 6.5"/1987 AC Airport (ACY) 6.5"/1987 Philadelphia (PHL) 6.5"/1987 Reading (RDG) 6.5"/1994 Trenton (TTN) 11.4"/1987 Wilmington (ILG) 12.4"/1987

PHI WATCHES/WARNINGS/ADVISORIES

PA...Blizzard Warning until 6 PM EST Monday for PAZ054-055-070-071- 104>106. Winter Storm Warning until 6 PM EST Monday for PAZ060>062- 101>103. NJ...Blizzard Warning until 6 PM EST Monday for NJZ001-007>010- 012>027. Coastal Flood Advisory until 4 AM EST Monday for NJZ016. Coastal Flood Warning until 5 AM EST Monday for NJZ012>014-020- 022>027. Coastal Flood Advisory until 4 AM EST Monday for NJZ021. DE...Blizzard Warning until 6 PM EST Monday for DEZ001>004. Coastal Flood Advisory until 4 AM EST Monday for DEZ001. Coastal Flood Warning until 5 AM EST Monday for DEZ002>004. MD...Blizzard Warning until 6 PM EST Monday for MDZ015-019-020. Winter Storm Warning until 6 PM EST Monday for MDZ012. MARINE...Gale Warning until 6 PM EST Monday for ANZ430. Storm Warning until 6 PM EST Monday for ANZ431-450>455.