textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Aviation section updated for 06Z TAFs.

A Small Craft Advisory is now in effect from 10 am to 4 pm for Delaware Bay and the coastal ocean waters around the mouth of Delaware Bay.

Timing moved up slightly with midweek rain and a reduction in the threat for severe weather (though it was already low to begin with).

KEY MESSAGES

1. Freezing temperatures for the southern Poconos early this morning. Patchy frost for northern New Jersey, the Lehigh Valley, and the far northwestern suburbs of Philadelphia.

2. Potential for fire weather conditions today.

3. A series of systems on Wednesday and Thursday likely brings the next widespread rainfall.

DISCUSSION

KEY MESSAGE 1...Freezing temperatures for the southern Poconos early this morning. Patchy frost for northern New Jersey, the Lehigh Valley, and the far northwestern suburbs of Philadelphia.

Cold air advection will be underway due to a northwest flow. Lows tonight will drop into the lower 30s across the southern Poconos, and a Freeze Warning remains in effect for Carbon and Monroe counties until 9 am.

For portions of the Lehigh Valley, northern New Jersey, and the far northwest suburbs of Philadelphia, the Frost Advisory remains in effect until 9 am, but confidence is much lower that frost will develop due to cloud cover, marginal temperatures in the mid and upper 30s, and winds being elevated enough to keep widespread frost from developing.

KEY MESSAGE 2...Potential for fire weather conditions today.

A tight pressure gradient will form between low pressure moving into the Gulf of Maine and high pressure centered over the Gulf Coast states. Northwest winds will increase to 15 to 20 mph with 25 to 30 mph gusts late this morning and early this afternoon. Temperatures will be warming into the low to mid 60s. With deep mixing up to around 775 mb, dew points will mix down from the low 30s this morning to the low to mid 20s. and this will result in Min RH values 25 to 30 percent.

Based on collaboration with state fire weather partners though, fuel moistures remain damp with the rainfall over the last few days along with the green up across most of the region. Therefore, no statements will be issued at this time.

KEY MESSAGE 3...A series of systems on Wednesday and Thursday likely brings the next widespread rainfall.

As high pressure shifts further away on Tuesday, a low passing well to the north may bring a few showers late Tuesday into Tuesday night for areas northwest of the I-95 corridor. A cold front then approaches from the west on Wednesday and will stall out over the area. A potentially more dynamic area of low pressure develops over the southeast and moves up through our area (guidance has shifted a bit east in the track with the latest runs). This will result in widespread rainfall over those two days.

Precipitation likely will come in multiple waves Tuesday Night through Thursday. The first wave will be with the incoming cold front mainly late Tuesday into Wednesday. The second wave would come more towards Wednesday Night and Thursday as the area of low pressure slides through.

Timing of the peak activity and the front will play key roles in the potential for any strong to severe thunderstorms. If the peak of the rainfall comes Wednesday morning and Thursday morning, that may inhibit the ability for the low-levels of the atmosphere to become unstable enough for stronger storms in the afternoon. This appears to be the case with the 00z guidance. Would expect the track and timing of both the cold front and area of low pressure to fluctuate over the next few runs. However, the most likely outcome at this point is another beneficial rain with a limited to zero severe threat.

The NBM Probability of total rainfall from those two systems is about 40-70% for 1 inch or more from Philadelphia on north and about 30-40% south of Philadelphia. With how dry we have been, flooding concerns appear to be minimal, again pointing to that these systems should largely be beneficial rainfall for the area.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

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

Early this morning...VFR. NW winds 5 to 10 kt. High confidence.

Today...VFR. NW winds 10 to 15 kt with 20 to 25 kt gusts this morning, increasing to 15 to 20 kt with 25 to 30 kt gusts around midday. Winds diminish to 10 to 15 kt by 00Z. High confidence.

Tonight...VFR. W winds 5 to 10 kt, becoming SW around 5 kt after 06Z. High confidence.

Outlook...

Monday...VFR. South/southwest winds with gusts up to 20 kt.

Monday Night...VFR. No significant weather.

Tuesday...VFR. South/southwest wind gusts around 20-25 kt.

Tuesday Night through Thursday...Restrictions expected through most of this period as periods of rain with a slight chance (15%) of thunder at times move through. Outside of showers, low clouds and patchy fog expected which likely will drop conditions down to IFR. Wind gusts out of the south/southwest on Tuesday Night through Wednesday around 15-25 kt, diminishing by Wednesday Night.

MARINE

A tight northwest pressure gradient will develop on the waters later this morning and winds increase to 15 to 20 kt. However, on Delaware Bay and the southern New Jersey and Delaware ocean waters around the mouth of the Bay, northwest winds will increase to 15 to 20 kt with gusts up to 25 kt. Will hoist a Small Craft Advisory for Delaware Bay and ocean waters zones ANZ453-455 from 10 am to 4 pm. Sub-SCA conds elsewhere.

Winds diminish tonight. Sub-SCA conditions expected.

Outlook...

Monday...SCA conditions possible (30-40% chance) as seas begin to build near 5 feet with wind gusts around 20-25 knots.

Monday Night through Thursday...SCA conditions expected (100% confidence). Will let current SCA for today ride before issuing one for the week. Wind gusts out of the south around 20-30 kt. Gale conditions possible (25-35% chance) on Tuesday Night. Seas of 4 to 7 feet anticipated.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Frost Advisory until 9 AM EDT this morning for PAZ060>062-101- 103-105. Freeze Warning until 9 AM EDT this morning for PAZ054-055. NJ...Frost Advisory until 9 AM EDT this morning for NJZ001-007>009. DE...None.90-100% MD...None. MARINE...Small Craft Advisory from 10 AM this morning to 4 PM EDT this afternoon for ANZ430-431-453>455.