textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Slight downward adjustment in temperatures for this weekend and next week. Still very warm though.

Small Craft Advisories extended until 2AM EDT Thursday.

KEY MESSAGES

1. Low pressure passing through the region will bring showers and isolated thunderstorms later today through Thursday.

2. Above normal temperatures take over beginning this weekend, with temperatures potentially climbing towards the 90s next week.

DISCUSSION

KEY MESSAGE 1...Low pressure passing through the region will bring showers and isolated thunderstorms later today through Thursday.

An upper trough extending from a closed H5 low over Ontario will move through the eastern Great Lakes and into the Ohio Valley tonight. The primary surface low pressure associated with this low will stay well north of the area, but the closed low will sag down into the Northeast by Thursday. Behind the departure of the surface low, a cold front slides through the region. Unsettled weather on tap during this period.

Getting into the details, the cold front associated with the aformentioned low was located over western PA as of early this afternoon and there are showers and storms that have developed just ahead of it. Farther east, there's another area of some showers getting into eastern PA but this is weaker with much less in the way of any lightning. As we go through the rest of the afternoon into this evening, this first area of showers could bring some showers or sprinkles into our eastern PA zones through mid to late this afternoon but really not expecting much if any lightning to occur. The stronger line farther west will continue to move eastward as well and likely get into our CWA around the early to mid evening timeframe. There's actually a fair amount of shear and strong dynamics with this system but the limiting factor will be instability as CAPE values will be diminishing as we get into the evening. Thus while the chance of severe weather is not zero, it is low with the Storm Prediction Center continuing to keep the MARGINAL risk of severe storms just to our west. In other words, the line of showers/storms should be weakening as it enters our forecast area. Main period of concern looks to be the evening into the first part of the overnight with precip generally diminishing west to east after this time.

For Thursday, there may be some lingering showers early in the day near the coast with some additional scattered showers developing in the afternoon over portions of NE PA and northern NJ due to the upper level low. Otherwise, it will be cooler with considerable clouds around and highs generally in the 60s.

Total precipitation amounts through the course of the next 24 hours continue to not look very impressive, generally speaking. Amounts should mostly be a tenth to a quarter inch with some locally higher amounts possible in storms.

KEY MESSAGE 2...Above normal temperatures take over beginning this weekend, with temperatures potentially climbing towards the 90s next week.

An upper level ridge builds into the Eastern US this weekend and into next week, bringing a period of above normal and summer-like temperatures. At the surface, high pressure over the western Atlantic anchors off the coast of the Mid Atlantic. This will result in a warm southerly flow for several days and gradually warming temperatures from Saturday through Tuesday or Wednesday. Given the NBM has been running a bit warm lately, temperatures were lowered slightly Sunday through Tuesday as most of the deterministic guidance has highs a few degrees lower than what the newest NBM had.

Regardless, it will be quite warm in the extended to borderline hot. Saturday will feature upper 70s to low 80s, with Sunday getting into the low to mid 80s. Temperatures continue to climb for Monday with mid to upper 80s and an outside shot at 90. Tuesday looks to be the warmest day of the stretch with upper 80s and low 90s currently anticipated. Tuesday could flirt with Heat Advisory criteria for the I-95 corridor and adjacent counties, where the current threshold through June is a heat index of 96 degrees F or higher. The heat looks to break down after Tuesday though another warm day could come on Wednesday. It will depend on when a cold front comes in sometime midweek.

Overall this stretch looks mostly dry. Guidance is now trying to hint at some diurnally driven showers/thunderstorms though, mainly on Sunday as a shortwave passes by to the north. Don't have more than 15-20% PoPs in though as forcing looks weak but we will have a better idea once we get into range of the CAMs.

As mentioned earlier, sometime mid-week next week a cold front will approach and likely bring an end to the stretch of above normal temperatures. Precipitation will likely accompany that front but too early to speculate on specific impacts or hazards.

AVIATION /01Z THURSDAY THROUGH MONDAY/

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

Tonight...Lowering ceilings then visibilities as showers and storms overspread TAF sites west to east this evening. MVFR expected, but IFR possible by late evening. Good chance for storms affecting RDG and ABE with lower confidence farther S/E. S/SW winds 10-15 knots, becoming shifting to NW late with the passage of a cold front. Low confidence.

Thursday...Lingering MVFR cigs likely early in the day at MIV and ACY but otherwise generally VFR. Northwest winds 10 to 15 with some gusts up to 20 knots possible. Moderate confidence.

Outlook...

Thursday Night through Monday...VFR conditions with no significant weather expected.

MARINE

Extended SCA for all waters until 2AM EDT Thursday.

Southerly winds 20 to 25 gusting up to 30 knots continue into this evening along with seas around 5 feet. These conditions abate by later in the evening but there will also be some showers with the chance of isolated thunderstorms reaching the waters late this evening into the overnight. Any storms could produce locally gusty winds.

Sub Small Craft Advisory conditions for Thursday with west winds 10 to 15 knots and seas around 3 to 4 feet.

Outlook...

Thursday Night...Sub-SCA conditions expected.

Friday...Chance (20-30%) of SCA conditions on the ocean waters as seas could near 5 feet.

Friday Night through Monday...Sub-SCA conditions expected.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 2 AM EDT Thursday for ANZ430-431- 450>455.