textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Temperatures have trended colder for Thursday.

KEY MESSAGES

1. Near-record warmth today and Wednesday will be ended by a cold front sliding into the region by Wednesday night, accompanied by showers and thunderstorms.

2. A fairly strong front will be located near the region Thursday into Friday leading to the potential for a large temperature gradient across the area and along with continuing chances for some showers.

3. Temperatures increase into the weekend. A few showers or storms will be possible Saturday with more widespread showers and storms expected for Sunday.

DISCUSSION

KEY MESSAGE 1...Near-record warmth today and Wednesday will be ended by a cold front sliding into the region by Wednesday night, accompanied by showers and thunderstorms.

High pressure remains situated off the east coast this afternoon while low pressure is moving through the lower Great Lakes. This set up is keeping the area in a continuing warm SW flow with temperatures as of 2 PM generally in the upper 70s to around 80 (except cooler right near the coast and over the higher terrain of the Poconos and NW NJ). Many areas will likely gain another degree or two before reaching their high thus bringing these numbers to near or above record values for this date (see the climate section below. Otherwise, with the warm front to our north, this is where showers and storms are at this hour. There's a small chance some of these could eventually get into our NW zones (Leigh Valley, southern Poconos into NW NJ) late this afternoon into this evening but POPs are only around 20 to 30 percent. If some storms do eventually make it in, can't rule out a strong to severe storm but again, chances of all this coming together are pretty low. Main threat would be damaging winds.

Going into the overnight hours of tonight, the front to our north will draw a bit closer so this will keep the chances for some showers and storms in the forecast for our N/W areas despite the loss of daytime heating. Otherwise, with the area squarely in the warm sector with continuing sW flow this will result in a very mild night for this time of year with lows only getting down into the 60s.

For Wednesday, the cold front to our north starts advancing into our area...reaching N/W zones around late morning (10am - noon), the I- 95 corridor around late afternoon, and then moving through Delmarva through the course of the evening. Where the front is not expected to clear the area until very late day or in the evening, expect highs getting back into the upper 70s to mid 80s. This essentially includes most areas near and south of the I-95 corridor (except right along the coast where it will be cooler). Heading farther north though it will be cooler with the Poconos and NW NJ likely seeing highs only seeing highs in the 60s to around 70. The cold front along with daytime heating will bring an increasing chances (POPs 60 to 80 percent) for showers and thunderstorms during the afternoon into the evening hours. ML CAPE values over SE PA into southern NJ and Delmarva could top out around 1000 j/kg along with modest mid level flow and shear values (winds in the 700-500 mb layer around 35 to 40 knots). A limiting factor though is that the advancing front may tend to undercut the developing showers/storms resulting in them becoming more widespread on the cooler side of the boundary. This all said, the Storm Prediction Center has expanded the MARGINAL risk for severe storms for Wednesday into Wednesday evening over SE PA, roughly the southern half of NJ, and Delmarva. This means isolated severe storms will be possible within this area. The main threat will be damaging winds. It's also worth noting that PWAT values will be increasing to around 1.25 to 1.5 inches and there will also may be a tendency for storms to train a bit during the late afternoon into the evening. For this reason, can't rule out some localized flooding issues...especially if heavier storms occur over the urban corridor.

KEY MESSAGE 2...A fairly strong front will be located near the region Thursday into Friday leading to the potential for a large temperature gradient across the area and along with continuing chances for some showers.

Our cold front from Wednesday looks to stall over southern Delmarva for Thursday keeping the area on the cool side of it along with mainly cloudy skies and east winds. There could be some light showers around or even some patchy drizzle but it will be too stable for any thunderstorms. with confidence increasing in the front being farther south, our temperature forecast for Thursday has trended colder. in fact portions of NE PA into northern NJ that are forecast to get down into the 40s for Wednesday night may remain stuck in the 40s for Thursday. Farther south, generally expect highs in the 50s over SE PA into southern NJ but even these temperatures could be a bit optimistic as there's some guidance that's even cooler. Closer to the front over our Delmarva zones, it looks to generally get into the 60s with these areas also having the best chances for seeing some sunshine.

The front doesn't look to make much progress north for Thursday night so many areas should see lows in the 40s except some low/mid 50s over portions of Delmarva. Some spotty light showers will be possible but otherwise not expecting much in the way of precip. The front should finally lift back northward on Friday but it's progress may be a bit slower than previous thinking. Nevertheless, expect that by afternoon we'll be back into the S/SW flow as the front lifts north with highs generally in the 70s. With a bit more of a southerly component to the wind it will be cooler near the coast and potentially extending a bit farther inland compared to today and Wednesday. Highs for these coastal areas may only reach the low/mid 60s. Can't rule out a few shower or storms for Friday but overall it looks to be dry.

KEY MESSAGE 3...Temperatures increase into the weekend. A few showers or storms will be possible Saturday with more widespread showers and storms expected for Sunday.

We should remain largely in the warm sector for Saturday as one low will be pulling away as it moves into the Canadian Maritimes while a stronger low advances into the Great Lakes region. This should help keep us in the S/SW flow with highs Saturday likely a bit warmer than Friday...generally in the 70s to low 80s. However the front may waver near our northern zones or even make it slightly into our area at times so this will once again keep the chance for some shower/storms in the forecast. This will be mainly for areas N/W of the urban corridor though with POPs still only around 20 to 30 percent.

The better coverage of rain showers arrives Sunday (POPs 60-70 percent) with a strong cold front moving through. Ahead of the cold front, highs are in the 70s for many spots with 60s in the Poconos and along the coast. Behind the cold front, lows are in the mid 30s to mid 40s. On Monday highs reach the upper 40s to mid 50s.

AVIATION /19Z TUESDAY THROUGH SUNDAY/

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

Rest of today... VFR expected. A couple showers or a TSTM may occur north of the KRDG/KABE terminals into the early evening but not expected to affect KRDG or KABE attm. Southwest winds 10 to 15 kts with gusts to 25 kts into the evening. Medium/high confid.

Tonight... VFR most of the time. A few showers KABE/KRDG possible but not certain with the VCSH used. LLWS (low-end) most terminals as sfc winds decrease but winds at 020 remain around 40-45 kts. Medium confid.

Wednesday... Mostly VFR with W to SW winds increasing again 10 to 15 kts with gusts around 25 kts developing. Scattered showers may bring lower CIGS/VSBYs with VCSH in the present terminals. More coverage expected after 18Z as a front approaches. Winds will turn to N behind the front as shown in the 30hr KPHL TAF. Medium confid.

Outlook...

Wednesday night and Thursday...Sub-VFR conditions likely with widespread showers and scattered thunderstorms moving through.

Thursday night through Sunday...Primarily VFR, but sub-VFR possible in any rain showers.

MARINE

A Small Craft Advisory remains in effect for all Atlantic Coastal waters until 6 PM Wednesday. For the Delaware Bay, a Small Craft Advisory is in effect until 8 PM this evening.

South-southwest winds around 10-20 kt are expected to continue into tonight with occasional gusts around 25 kt. Seas will largely range between 5-7 feet. Spotty showers possible tonight but otherwise generally fair weather outside of SCA conditions. Winds relax a bit Wednesday but seas remain elevated, and the risk of showers/t-storms will increase later in the day.

Outlook...

Wednesday night through Friday night...Seas will be lingering around 4 to 5 feet for much of this period. Generally sub SCA winds except a period of stronger east winds likely later Wednesday night into Thursday morning off the coast of Monmouth and Ocean Counties.

Saturday...Conditions are expected to be below Small Craft Advisory criteria.

Sunday...Small Craft Advisory level winds probable.

CLIMATE

The warmth is forecast to surge into our area during the first half of this week. Given the current forecast, some inland areas could challenge their record high temperatures on Tuesday (March 31) and Wednesday (April 1).

Location Record High 3/31 -------- --------------- ACY Atlantic City, NJ 85/1979 PHL Philadelphia, PA 82/2025 ILG Wilmington, DE 82/1998 ABE Allentown, PA 86/1998 TTN Trenton, NJ 84/1910 RDG Reading, PA 86/1998 GED Georgetown, DE 82/1998 MPO Mount Pocono, PA 81/1998 55N AC Marina, NJ 73/1936

Location Record Warmest Low 3/31 -------- --------------- ACY Atlantic City, NJ 58/1998 PHL Philadelphia, PA 61/1998 ILG Wilmington, DE 57/1979 ABE Allentown, PA 52/1981 TTN Trenton, NJ 60/1998 RDG Reading, PA 57/1998 GED Georgetown, DE 64/1998 MPO Mount Pocono, PA 51/1998 55N AC Marina, NJ 56/1998

Location Record High 4/1 -------- --------------- ACY Atlantic City, NJ 80/1978 PHL Philadelphia, PA 81/1978 ILG Wilmington, DE 81/1978 ABE Allentown, PA 84/1978 TTN Trenton, NJ 81/1986 RDG Reading, PA 82/1917 GED Georgetown, DE 80/1979 MPO Mount Pocono, PA 81/1998 55N AC Marina, NJ 72/1955

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ430- 431. Small Craft Advisory until 6 PM EDT Wednesday for ANZ450>455.