Weather Briefing — Atco, NJ 08004

• Updated: Saturday, September 19, 2026 4:00 AM Eastern
• Next update: Saturday, September 19, 2026 8:00 AM Eastern
• Generated: 2026-09-19T08:03:05+00:00
• Type: weather

Headline

A quiet, dry Saturday is in store for Atco as high pressure slides east, but a wet and unsettled stretch begins Saturday night: a warm front and approaching low pressure bring showers and likely thunderstorms Sunday and Sunday night with locally heavy rain possible, followed by lingering shower chances Monday and Tuesday as a series of disturbances and a meandering coastal low keep the region cool and unsettled.

Forecast Area

The official NWS forecast for Atco is issued by the Mount Holly (KPHI) forecast office for forecast zone NJZ018 (Camden), which covers Camden County and vicinity in southern New Jersey. The zone map below shows the area where the official forecast text is valid.

Active Alerts

No active alerts for Atco, NJ 08004. No watches, warnings, or advisories are in effect for the land area (PA, NJ, DE, MD all show none in the KPHI product). Note: a Small Craft Advisory is in effect for New Jersey Atlantic coastal waters north of Great Egg Inlet until 2 PM EDT Saturday — relevant only to marine interests, not Atco itself.

Current Weather

It is a dry, quiet early-morning Saturday across Atco.

• Surface observation: The nearest METAR station is Mount Holly / South Jersey Regional Airport (KVAY), about 12.1 miles from Atco, observed at 06:54 UTC (2:54 AM EDT). This automated station reported a sea-level-equivalent pressure of 30.10 inHg (1019.3 mb), but its temperature, dewpoint, wind, visibility, and cloud sensors were all flagged out of service (PWINO/AO2 auto report with missing fields), so no direct temperature/wind observation is available from KVAY this cycle.
• Regional observations fill the gap: Surrounding stations on the METAR map show a mild, humid early-morning airmass — Philadelphia (KPHL) 68°F/54°F, McGuire AFB (KWRI) 62°F/55°F, Atlantic City (KACY) 64°F/59°F, Millville (KMIV) 66°F/55°F, and Trenton (KTTN) 64°F/54°F. Pressures are uniformly around 1019–1021 mb regionally, consistent with weak high pressure in control.
• Precipitation: MRMS (data time 07:58 UTC) shows no precipitation at Atco and none within a 30 km radius — 0% echo coverage, no surface precipitation anywhere in the 100 km search. The deterministic diagnosis confirms dry conditions with high confidence (0.89).
• Radar: The NEXRAD Level II analysis from KPHL (Philadelphia), 20.3 km away, valid 07:51 UTC, shows mostly clear-air returns with a mean reflectivity of about −4 dBZ and an isolated maximum of 40.5 dBZ — a small, weak echo with no gates at or above 50 dBZ, no organized precipitation, and no storm structure. Beam height over Atco is only ~191 m MSL, so sampling is excellent at the surface.
• Lightning: GOES-19 GLM detected zero flashes within 50 km over the past 10 minutes; no electrical activity and a steady trend.
• Model surface conditions: HRRR guidance (07Z cycle) puts Atco at 19.7°C (67°F) with a dewpoint of 11.5°C (53°F) — a comfortable 8°C dewpoint depression — under 1014.3 mb surface pressure.

Current Synoptic Setup

Per the NWS Mount Holly Area Forecast Discussion (issued 1:49 AM EDT Sat Sep 19):

• Surface pattern: High pressure centered over Ontario is sliding slowly eastward, passing north of the region Saturday before shifting offshore Saturday night. This is the feature keeping Atco dry and tranquil today. A cooler airmass is settling in behind it, with lows near 50 in northern NJ/eastern PA and mid 60s on Delmarva.
• Upper-level pattern: Mid-level ridging over the Gulf Coast is shifting southwestward, and northwesterly flow aloft is increasing across the area tonight through Saturday — a progressive, benign flow regime for now.
• What's coming: Once the high exits to sea Saturday night, low pressure organizes over the Midwest and a warm front lifts north through the Northeast Saturday night into Sunday morning, with showers developing after midnight. As the low approaches, southerly flow pumps deep moisture northward — surface dewpoints rising well into the 60s and low 70s, with PWATs exceeding 2 inches. The low passes through the southern Poconos/Lehigh Valley Sunday afternoon and evening, bringing widespread showers and isolated thunderstorms, then a cold front sags south Sunday night, shifting the heavy-rain axis toward the I-95 corridor and Philadelphia. The front stalls over Delmarva Monday morning.
• Local forcing right now: Essentially none — subsidence under the high, dry low levels (HRRR shows RH dropping to under 10% between 700 and 625 mb), and no instability.

GFS Guidance

GFS cycle: 2026-09-19 00Z (pgrb2.0p25), with lead hours 24, 48, and 72 tied to that single cycle. All values are model guidance, not observations.

Day 1 — F24, valid Sat 8 PM EDT (00Z Sun): - Point guidance: 2 m temperature 18.9°C (66°F), dewpoint 13.4°C (56°F), MSLP 1020.5 mb, 10 m wind 6.7 kt, no precipitation. - Surface chart shows the high sliding offshore with the next system still west of the Appalachians. 500 mb heights ~585 dam with modest vorticity (6.8×10⁻⁵ s⁻¹) and 32.5 kt flow — flat NW flow. 850 mb RH is already 82% with light flow (3.8 kt), signaling moisture beginning to return aloft. 300 mb winds ~44 kt.

Day 2 — F48, valid Sun 8 PM EDT (00Z Mon): - Point guidance: temperature 22.0°C (72°F), dewpoint 17.7°C (64°F), MSLP falls to 1012.7 mb, 850 mb RH 95.7% with a brisk 22.2 kt 850 mb flow — the warm conveyor belt is overhead. No instantaneous precip at the exact point, but the environment is primed. - The surface chart shows the Midwest low and its warm front lifting into the Northeast with the low approaching the Poconos/Lehigh Valley — exactly the setup the AFD describes for Sunday evening showers and thunderstorms. 500 mb heights lower slightly (582.9 dam).

Day 3 — F72, valid Mon 8 PM EDT (00Z Tue): - Point guidance: temperature 17.5°C (64°F), dewpoint 15.9°C (61°F), MSLP rebounds to 1019.3 mb, light 10 m wind (6 kt), and a light precipitation rate of 0.27 mm/hr — consistent with lingering showers behind the stalled front. - 850 mb RH is near saturation (98.5%), and 500 mb absolute vorticity jumps to 11.3×10⁻⁵ s⁻¹ — a vorticity maximum passing overhead, matching the AFD's "several more disturbances Monday and Tuesday." 300 mb winds ~35 kt.

HRRR Analysis

All HRRR data below are model guidance from the 2026-09-19 07Z cycle, valid 07:00 UTC (3 AM EDT) at the HRRR grid point 0.36 km from Atco — not an observed balloon sounding.

• Surface thermodynamics: 19.7°C (67°F) / dewpoint 11.5°C (53°F), surface pressure 1014.3 mb. The 8.1°C dewpoint depression indicates a relatively dry boundary layer for now.
• Precipitation type: HRRR categorical guidance is "none" — no rain, snow, freezing rain, or ice pellets. Freezing level is high at 4,901 m MSL (~16,080 ft), so any precipitation would be all-liquid; no winter weather concerns whatsoever.
• Instability: Surface-based, mixed-layer, and most-unstable CAPE are all 0 J/kg with 0 J/kg CIN — a completely stable profile. DCAPE is 620 J/kg (potential downdraft energy if rain-cooled air develops later, but with no convection ongoing this is just environmental context). No LFC or EL exists because there is no instability; the LCL sits at ~1,085 m MSL.
• Moisture: Precipitable water is 23.4 mm (0.92 in) — modest now, but GFS/AFD indicate PWATs will climb past 2 inches by Sunday, a dramatic moisture surge.
• Lapse rates: 4.0°C/km surface-to-3 km and 4.9°C/km in the 700–500 mb layer — both well below the dry-adiabatic threshold; no steep midlevel lapse rates.
• Wind/shear: Winds veer from NE at 925 mb (16.5 kt) to W at 500 mb (30.8 kt) and WNW at 300 mb (48.1 kt). Bulk shear is 11 kt (0–1 km), 12 kt (0–3 km), and 32 kt (0–6 km) — decent deep-layer shear exists, but with zero CAPE it is moot for organized convection today. K index is −5.1 and Total Totals 31.1, both indicating a convectively inert airmass.
• Vertical structure: A very dry layer between roughly 775 and 550 mb (RH as low as 4–7%) sits above a moist 850–875 mb layer (82–84% RH) — classic anticyclonic subsidence aloft with residual low-level moisture.

Outlook

Synthesizing the KPHI Area Forecast Discussion for Atco:

• What changed: Increased concern for MVFR ceilings developing as early as 03Z (11 PM EDT) Saturday night for aviation interests — the first signal of the approaching wet pattern.
• Key message 1 (today): Tranquil conditions through Saturday daytime as the Ontario high slides east. Dry, partly sunny, and notably cooler with highs in the low-to-mid 70s.
• Key message 2 (the main story): A series of cold fronts and low pressure systems keeps unsettled weather over the area from Saturday night through Thursday. Heavy rain is possible Sunday and Sunday night. WPC has a Slight Risk (2/4) for Excessive Rainfall Sunday and Sunday night along the I-95 corridor and points north and west, with a Marginal Risk for areas south and east of I-95 (which includes Atco) and another Marginal Risk for the entire region Monday. Locally heavy rain may develop at times Sunday afternoon/evening as the low passes, with the heavy-rain axis shifting toward the Philadelphia area Sunday night.
• Monday–Tuesday: Several more disturbances keep rain chances going, with PoPs limited to 30–50% given timing/coverage uncertainty. A low develops off the Mid-Atlantic coast and meanders in the western Atlantic between the Jersey Shore and south of Long Island midweek, keeping onshore flow and below-normal temperatures.
• Hazards: Flash-flooding potential Sunday/Sunday night (Marginal Risk locally, Slight Risk just to the north/west); isolated thunderstorms Sunday afternoon and night; patchy fog Saturday night and again Sunday night into Monday morning. Marine interests face building seas and possible gale-force winds Tuesday, but no land-based headlines for NJ.
• Confidence: High confidence in the dry Saturday and the unsettled Sunday; moderate confidence in the exact timing/coverage of Monday–Tuesday showers (hence the capped PoPs).

Forecast for Next 3 Days

Today — Saturday, September 19

• Overnight (early AM): Mostly cloudy, low around 61°F, NE wind ~5 mph, 0% PoP.
• Daytime: Partly sunny, high near 74°F. East wind 5–10 mph. Precipitation chance only 2% — a genuinely dry, pleasant day. Hourly rows show temperatures climbing from 62°F at 7 AM to the low-to-mid 70s between 1 and 3 PM, with RH falling to ~55% midday and dewpoints in the mid 50s.
• Saturday night: Patchy fog developing after 9 PM as RH climbs to 93–97% with dewpoints rising to 61°F. Mostly cloudy, low around 62°F, east wind ~5 mph, PoP 7%. MVFR ceilings may build in from the west/east after 11 PM for aviation interests.

Sunday, September 20 — the wet day

• Morning: Patchy fog before 8 AM, then a chance of rain showers 8 AM–5 PM. Cloudy, high near 77°F, SE wind 5–10 mph. Hourly PoPs climb steadily: 10–15% early morning, 26% late morning, 38% mid-afternoon.
• Afternoon/evening: Showers and thunderstorms likely from about 5 PM onward (PoP jumps to 63%), as the low passes through the Poconos/Lehigh Valley and dewpoints surge to 68–69°F. New rainfall less than a tenth of an inch during the day.
• Sunday night: Showers and thunderstorms before 11 PM, then patchy fog with more showers and storms. Low around 63°F, wind shifting W 5–10 mph, PoP 81%. Rainfall of a quarter to half an inch possible — this is where the locally heavy rain and Marginal/Slight excessive-rainfall risk focus. Isolated thunderstorms are possible; no severe weather is currently forecast.

Monday, September 21

• Overnight into morning: Patchy fog and lingering showers early (PoP 52% around dawn), then a chance of rain showers all day as the stalled front and passing disturbances affect the area. Mostly cloudy, high near 70°F, NE wind 5–10 mph, PoP ~50% daytime with another quarter to half inch of rain possible.
• Afternoon: Temperatures hold in the mid-to-upper 60s with RH 81–90%; PoPs ease to ~32% by late afternoon.
• Monday night: Continued chance of showers (PoP ~31%), mostly cloudy, low around 58°F, NE wind 5–10 mph.

Tuesday, September 22 (early look)

• A chance of rain showers continues (PoP ~37–40%), mostly cloudy, high only near 65°F with a NE wind around 10 mph — well below seasonal normals as the coastal low meanders offshore and onshore flow persists. Overnight lows fall into the upper 50s.

Bottom Line

Enjoy Saturday: dry, partly sunny, and cooler with a high near 74°F and no meaningful rain chance. The pattern turns active Saturday night as fog forms and the first showers arrive after midnight ahead of a warm front. Sunday is the day to plan around — showers and likely thunderstorms from late afternoon through the night, with a quarter to half inch of rain possible, locally heavy at times, and a Marginal excessive-rainfall risk for the Atco area (Slight Risk just north/west along I-95). Unsettled, showery, and cool weather lingers Monday and Tuesday (highs 65–70°F) as disturbances pass and a coastal low meanders offshore, so keep rain gear handy through at least midweek. No severe weather or land-based alerts are in effect, and no winter concerns exist with freezing levels near 16,000 ft.