textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Highest rainfall amounts have shifted a bit north for the Wednesday- Wednesday Night system. Rainfall amounts from a quarter to half an inch expected near and north of I-78, with diminishing amounts south. Confidence increasing in this system being an all-rain event.

High confidence in above normal temperatures this week, with moderate confidence in above normal temperatures continuing through the weekend. Snow forecast remains on tap for tonight with the highest totals north of the I-195 and PA Turnpike corridors.

KEY MESSAGES

1. High pressure develops over the area today. A weak low passes north of the area tonight.

2..Above normal temperatures are expected for most of this week and should continue into next weekend.

3...An unsettled pattern takes hold for this week with multiple chances for rain, and potentially some mixed precipitation in the higher elevations of our northern areas.

DISCUSSION

KEY MESSAGE 1...High pressure develops over the area today. A weak low passes north of the area tonight.

High pressure develops over the area today, but a prolonged onshore flow will keep skies cloudy throughout the day. A pressure gradient between the developing high and the low pressure offshore will lead to winds around 10-15 mph this morning, with gusts up to 20-30 mph possible along the coast. Winds diminish this afternoon and evening as the high strengthens overhead. Highs will mostly be in the upper 30s to low 40s, which are still several degrees below normal.

A weak low passes to our north tonight as a weak shortwave dives in from the northwest and moves through the Northeast. This system may be able to result in some light mixed precipitation in our northern areas. An area of slight chance (20%) PoPs have been maintained to show the potential for light precipitation. When mentioning this as light mixed precipitation, it has the potential to include snow, freezing rain/drizzle, and plain rain. Due to the mixed precipitation potential, the timeframe bears watching. Overall though, the light precipitation looks relatively unimpactful given the limited coverage of it.

KEY MESSAGE 2..Above normal temperatures are expected for most of this week and should continue into next weekend.

High pressure that is moving offshore Tuesday leads to a southwest wind with its return flow and remains offshore into Wednesday. This leads to warm air advection and temperatures trending above normal for this timeframe. Beyond this, multiple systems move through the region allowing for more opportunities for warm air advection keeping above normal temperatures going into next weekend.

For the specifics on temperatures, highs range from the mid 40s to low 50s for much of the area Tuesday through Saturday. Highs on Wednesday through Friday get into the mid to upper 50s with some spots potentially getting to 60 in the southern portion of Delmarva.

In terms of overnight lows, after tonight, most locations will stay above freezing. Lows range from the mid to upper 30s to low 40s for most locations Tuesday Night through Friday Night. Temperatures could get back below freezing on Saturday Night and especially Sunday Night.

Temperatures look to regress near normal levels perhaps by Sunday, but more likely next week.

After over two weeks now with snow on the ground, these warmer temperatures will allow the snowpack to melt quicker and most spots likely will be rid of snow by this weekend.

KEY MESSAGE 3...An unsettled pattern takes hold for this week with multiple chances for rain, and potentially some mixed precipitation in the higher elevations of our northern areas.

During this week and into next weekend, there will be multiple areas of low pressure moving through the region. This will lead to multiple rounds of precipitation mainly in the form of rain but some wintry precipitation is possible in the higher elevations of our northern areas at times.

Wednesday into Wednesday Night, a shortwave moves through. At the surface, there will be a low pressure system near the Midwest that drags a warm front northward on Wednesday which will result in some rain for the area Wednesday afternoon into Wednesday Night. Model guidance has trended more in the direction of this being an all rain event for our area. Guidance has also trended a bit north with QPF amounts, with the highest rain totals north of I-78. However, QPF amounts across the board look rather light with the shift in higher rainfall amounts north. NBM Probability over 1 inch is less than 5%. Probability of rainfall amounts over half an inch are around 15-30% north of I-78 with less than 10% south. Our area could certainly use some rain and this could be the first measurable rain for some in almost a month or more (given how cold it has been, precipitation type has been all snow). We then stay in the warm sector Thursday into Thursday night with the potential for some isolated rain showers to pass through the area during this timeframe.

Another system arrives towards the end of the week for the Friday into Saturday timeframe. This is another low pressure system originating from the Midwest and moving towards our area. Just like the midweek system, this should mainly be an all rain event for most, if not all of the region given the track of the low. However, if more precipitation comes during the overnight hours, higher elevation areas in the southern Poconos and far northern NJ could see some snow or freezing rain. NBM Probability of QPF over 1 inch is still on the lower side at around 15-25%. The details will be ironed out over the next couple days, especially once the timing comes more into focus.

Beyond this, there is the potential for yet another system towards the end of the weekend but there remains uncertainty with the details of this system as it is at the end of the long term period. Guidance remains all over the place, ranging from an all rain event to a storm with measurable snowfall. Too early to speculate though on what exactly precipitation type and impacts would be.

Overall, these systems will bring primarily rain to most of the area, with the potential for mixed precipitation in far northern New Jersey and the southern Poconos depending on timing. One key note with these systems, we are not currently expecting moderate or major impacts. In fact, for most of the region, it will be more of a beneficial rain.

AVIATION /12Z MONDAY THROUGH FRIDAY/

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

Today...IFR CIGs in the morning, slowly lifting to MVFR in the afternoon. High uncertainty about how quickly it lifts, especially to VFR towards the evening. NE winds around 10 kt, with gusts up to around 20 kts possible at KMIV/KACY, becoming LGT/VRB late. Moderate confidence, overall, low confidence in details.

Tonight...MVFR to IFR conditions likely redeveloping with low stratus. Highest likelihood for IFR conditions are at KABE and KRDG. KACY and KMIV may remain VFR. SSW winds around 5 knots or less. Moderate confidence, overall, low confidence in details. Outlook...

Tuesday...MVFR/IFR conditions expected with low CIGs likely hanging around through most of the day.

Tuesday Night through Wednesday Morning...VFR. No significant weather.

Wednesday Afternoon through Wednesday Night...MVFR/IFR conditions expected with low clouds and light to moderate rain moving through. Worst conditions will be near KRDG/KABE.

Thursday through Friday...Restrictions likely (60-70%) with periods of showers and low clouds hanging around.

MARINE

Small Craft Advisory in effect for Atlantic Ocean coastal waters. Northeast winds increase to 15 to 20 kt with gusts in excess of 25 kt. Seas build to around 5 feet. Though winds diminish late this morning as low pressure departs, seas on the ocean remain elevated through tonight, around 5-7 feet. Sub-SCA conditions on the Delaware Bay though winds may briefly gust around 20-25 knots this morning.

VSBY restrictions in fog, potentially continuing through late this morning.

Regarding the river/bay ice...Ice cover continues across many area bay waters and inland estuaries. This includes, but is not limited to the Delaware estuary. On rivers, the ice thickness is enough to cause some restrictions in the flow. Per satellite imagery and ice analysis data, the Delaware River is mostly ice covered from the Delaware Memorial Bridge upstream, to at least Washington Crossing, though we are seeing improvement with warmer temperatures that will only get better with warmer days ahead.

According to latest analysis from the National Ice Center, Delaware Bay is actually mainly ice-free with less than 10% coverage of ice.

The most common ways river ice can break up is either through a thermal or mechanical means. We would like to see temperatures rise into the 40s for a few days, which parts of the region are forecast to continue to get to this week with some areas getting into the 50s early this week. Significant rainfall, producing river rises, can also break up ice but that is not in the forecast this week.

As a result, ice cover will gradually decline over the next week or so and we are already seeing major improvement in Delaware Bay.

Outlook...

Tuesday...A Small Craft Advisory is in effect for all ocean zones through Tuesday evening. Winds will be well below SCA levels but seas of 4 to 7 feet expected. Sub-SCA conditions on Delaware Bay.

Tuesday Night...Lingering 5 foot seas possible (40-50%) could result in an extension to the Small Craft Advisory on the ocean. Sub-SCA conditions expected on Delaware Bay.

Wednesday through Wednesday Night...SCA conditions possible (50%) as seas could get near 5 feet and wind gusts near 25 kt.

Thursday through Friday...No marine headlines expected.

EQUIPMENT

KDIX will remain out of service through at least Monday and possibly Tuesday.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EST Tuesday for ANZ450>455.