textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Snow chances have increased for tonight, mainly north of I-78. No significant accumulations expected though.

Model guidance continues to trend towards the consensus of a more southerly track for the Sunday-Monday system, resulting in less impacts for our region.

There is another chance for rain with a system Wednesday into Thursday.

KEY MESSAGES

1...One last day of below normal temperatures for today and tonight. Milder temperatures closer to normal expected this weekend, then temperatures likely get above normal next week.

2. Snow showers are possible late Friday Night into early Saturday Morning, mainly for areas north of I-195 in New Jersey and north of I-78 in Pennsylvania

3. Another round of precipitation, primarily for the coastal plains, is likely Sunday into Monday with a low pressure system sliding south of our region.

4. The next chance of precipitation, primarily for areas north of the PA Turnpike/195 corridor, comes Wednesday into Thursday.

DISCUSSION

KEY MESSAGE 1...One last day of below normal temperatures for today and tonight. Milder temperatures closer to normal expected this weekend, then temperatures likely get above normal next week.

After a very long stretch of temperatures below normal, change is on the horizon. However, one last chilly day of temperatures below normal are expected for today. While skies will be mainly sunny for today, highs only top out in the low to mid 30s. Clouds increase ahead of a weak system moving through tonight, though lows will drop into the mid to upper teens and low 20s, which is about 2 to 5 degrees below normal depending on the location.

The airmass over the area moderates this weekend as high pressure slowly shifts off to the east. High temperatures both Saturday and Sunday generally range from the upper 30s north to the mid/upper 40s south. Overnight lows, at least for Saturday night, will be below freezing (in the 20s). The overall moderating trend looks to continue into next week, although low pressure sliding by to our south later Sunday into Monday could result in some cooling on Sunday (see Key Message 3 below). Regardless of what happens with the storm, it will have departed by next Tuesday and Wednesday with highs by then looking to be well into the 40s for most areas with even some 50s over parts of the coastal plain. Dewpoints will also begin rising above freezing next week, which is anticipated to result in more substantial melting of the stubborn snowpack across the region.

KEY MESSAGE 2... Snow showers are possible late tonight into early tomorrow morning, mainly for areas north of I-195 in New Jersey and north of I-78 in Pennsylvania.

A fast moving mid level short wave trough will spark some snow showers which could progress as far southeast as northern New Jersey very late tonight into early tomorrow morning. Initially dry air in the boundary layer could result in mostly virga. However, some model soundings depict that dry air will erode and snow will begin to reach the surface. The 00z runs overall were more robust with snowfall, so PoPS were increased to around 30-50% for areas north of I-78 in Pennsylvania and north of I-195 in New Jersey. That being said, it is a fast moving system, so the window for accumulating snow from these showers is quite brief, and as mentioned above, some dry air will initially make it tough for snow to make it to the surface. Thus, any snow accumulations are likely to be a few tenths of an inch at most.

Overall, this is unlikely to produce widespread impacts, but with temperatures in the 20s and teens as the snow is falling, if there are any light accumulations then untreated surfaces could be slippery. By the time the sun comes up on Saturday, precipitation should be out of the area.

KEY MESSAGE 3...Another round of precipitation, primarily for the coastal plains, is likely Sunday into Monday with a low pressure system sliding south of our region.

There were minor changes in model depictions of the Sunday/Monday system with a continued move towards the consensus for a more southerly track that does not phase with the northern stream trough (at least while it is near our region) resulting in less impacts for our region. These solutions favor a warmer, faster system, with precipitation primarily confined to the coastal plains. This solution would result in little, if any, snow accumulations. The precipitation type, especially if it is confined only to the coastal plains would be primarily rain, but could start off as a rain snow mix. Further working against snow accumulations is the fact that the air mass in place ahead of this system is milder than what we have seen with the last few systems. Overall, with the models continuing to coalesce, confidence is increasing in precipitation across the coastal plain, so PoPs were increased in this area.

That being said, there are still a few models that depict the stronger and further north solution, most notably the AI-ECMWF. Additionally, if the precipitation extends outside of the coastal plains, then precipitation in those areas is more likely to be snow for longer. Therefore, stayed with the blend of guidance for the forecast.

KEY MESSAGE 4...The next chance of precipitation, primarily for areas north of the PA Turnpike/195 corridor, comes Wednesday into Thursday.

The next system we are watching is a low pressure system which could be crossing the northeastern U.S. Wednesday into Thursday of next week. Unlike the late weekend system, the center of this low is currently depicted crossing north of our region. This would favor precipitation north of the PA turnpike/195 corridor. That being said, our region would be in the warm sector with this track, which would favor mostly, if not all, rain.

The latest trends do bring the low a bit further south than previous runs, which could potentially allow for some mixing at the higher elevations in the southern Poconos and northwest New Jersey. Additionally, a more southerly track would potentially bring rain into the southern portions of the region as well.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

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

Today...VFR. West/northwest winds around 10 kt. High confidence.

Tonight...Primarily VFR. West/southwest winds around 5 kt or less. 15-20% chance of snow showers at KTTN/KABE which could result in brief restrictions down to MVFR. Moderate confidence.

Saturday...VFR. West/northwest winds around 10 kt. High confidence.

Outlook...

Sunday and Monday...Periods of MVFR or even IFR are possible with rain and snow. KMIV and KACY have the highest risk of sub- VFR conditions.

Tuesday...VFR expected.

MARINE

Sub-SCA conditions expected through Saturday with west/northwest winds around 8-15 kt and seas 1 to 3 feet.

Regarding the river/bay ice...Significant 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 entrance to Delaware Bay northward, or upstream, to at least Washington Crossing. Delaware Bay has quite a bit of ice cover, however satellite imagery the last few days has shown icing flowing out of Delaware Bay into the Atlantic Ocean.

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 get to once again over the weekend with some areas getting into the 50s early next 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 continue. There may be a pause in the ice growth during the daylight hours as temperatures rise to and above freezing, however temperatures at night will continue to support some ice expansion.

Outlook...

Saturday night...The conditions are anticipated to be below Small Craft Advisory criteria.

Sunday through Tuesday...Winds and seas should stay below SCA criteria. However this will depend on the track and strength of low pressure sliding by to our south.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...None.