textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

1. Scattered showers will remain possible across southern parts of the area through much of this afternoon.

2. Showers, possibly some thunderstorms, Wednesday afternoon and Wednesday night, then much warmer air arriving over the weekend.

DISCUSSION

KEY MESSAGE 1...Scattered showers will remain possible across southern parts of the area through much of this afternoon.

As of early this morning, an upper-level low is centered over portions of Ontario and Quebec, with cyclonically curved flow continuing to overspread the region. At the surface, a cold front has moved offshore, and will continue moving southeast away from the region through today and into tonight.

Isolated showers and some drizzle are ongoing roughly from I-95 southeastward. The northern extent of any shower activity will continue to shift southeastward through today, but at least scattered showers could continue to impact portions of the Delmarva and far southern NJ into this afternoon before all precipitation departs. Additional rainfall amounts will be quite light, with only a few hundredths of an inch near I-95 and perhaps up to a tenth of an inch over portions of the Delmarva.

In the wake of the cold front, temperatures will be cooler today, only rising into the upper 50s to mid 60s for most. It will be cool tonight, with lows generally in the low-mid 40s. Across the higher elevations of the Poconos, temperatures are expected to fall into the mid-upper 30s. Some patchy frost can't be ruled out across these areas, but winds may remain elevated enough to prevent this from being much of a concern.

KEY MESSAGE 2...Showers, possibly some thunderstorms, Wednesday afternoon and Wednesday night, then much warmer air arriving over the weekend.

The upper-level pattern is forecast to become rather amplified through this week. A strong upper-level trough axis shifts to our east Tuesday as high pressure will also be shifting offshore. Another upper-level trough then arrives into the East Wednesday into Thursday before lifting out Friday into Saturday. The ECMWF in particular continues to close this trough off across the Mid- Atlantic and Northeast by later Wednesday into Thursday. Other guidance continues with the idea that the trough sharpens but remains open as it crosses our region. Regardless of how this transpires, a round of showers is probable Wednesday afternoon and Wednesday night as a trough and cold front arrives.

As the aforementioned upper-level trough moves into the region Wednesday, low-level warm air advection will increase ahead of it as the low to mid level flow also increases. This will result in an increase in forcing for ascent, and some instability should develop ahead of the main forcing. A warm front should also lift across our area Wednesday with some ascent associated with it. As a result, showers should increase Wednesday from west to east, especially in the afternoon with these peaking Wednesday night as the cold front arrives. The amount of destabilization is more uncertain, however guidance does show some instability which should be enough to support at least a few thunderstorms. The intensity of any thunderstorms however will depend on the magnitude of the instability and shear. If some convection is able to become stronger then locally gusty winds will be possible.

The main forcing should shift to our east and northeast Thursday with the bulk of the showers ending. However, if the closed low scenario ends up happening, then the core of the cold air aloft with this slides overhead and this could result in additional shower development during Thursday and possibly into Friday before the system departs our region. As the trough lifts out and more of a ridge starts to arrive this weekend, a drier and much warmer air mass will overspread our area.

AVIATION /06Z MONDAY THROUGH FRIDAY/

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

Through 12Z...Primarily VFR. A few light showers or BR could lead to brief visibility restrictions for the I-95 terminals, MIV, and ACY. Winds generally north at 5-10 kt. Moderate confidence.

Today...Primarily VFR. A few light showers could lead to brief visibility restrictions for MIV and ACY through 18-20Z before any showers move offshore. Winds generally north-northwest at 5-10 kt, though they may become southeasterly for a time this afternoon at MIV and ACY. Moderate confidence.

Tonight...VFR. Winds generally northwest at 5 kt or less. High confidence.

Outlook...

Tuesday...VFR.

Wednesday...VFR conditions lower to MVFR or IFR later in the afternoon and at night along with showers. A few thunderstorms possible later in the afternoon and evening. Southerly wind gusts up to 25 knots possible during the afternoon.

Thursday...Times of sub-VFR conditions and some showers possible.

Friday...Mostly VFR. A few showers possible.

MARINE

No marine headlines are currently in effect. North winds early this morning will generally be 10-15 kt with gusts around 20 kt. A short window of gusts near 25 kt is possible, but confidence is not high enough to warrant Small Craft Advisory issuance. Winds will decrease further this afternoon. Another uptick in winds is possible tonight, but still below SCA criteria. Seas 2-4 feet this morning, decreasing to 1-3 feet this afternoon through tonight. Scattered showers will be possible for the southern NJ and DE coastal waters through this afternoon.

Outlook...

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

Wednesday...Small Craft Advisory conditions probable.

Thursday and Friday...The conditions are anticipated to be below Small Craft Advisory criteria

PHI WATCHES/WARNINGS/ADVISORIES

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