Key messages
- 1. A warm front moves north through the region this morning,
What Has Changed
Key Message 1 updated.
Aviation section updated for the 06Z TAFs.
Key Messages
followed by a strong cold front this afternoon and evening.
2. Widespread frost and freeze conditions are increasingly likely Saturday night.
Discussion
KEY MESSAGE 1...A warm front moves north through the region this morning, followed by a strong cold front this afternoon and evening.
Low pressure over the Great Lakes lifts northeast into the Province of Ontario by daybreak, then into the Province of Quebec as the day progresses. A warm front south of the area lifts north through the region this morning, then low pressure passing north of northern New England will drag a cold front through the region this afternoon and evening.
Some light showers will impact the area through daybreak or so, possibly into the late morning with the passage of that warm front. Clouds over the area will lift and dissipate somewhat this afternoon, and then it will warm up quite nicely with highs in the upper 70s to low 80s. With clouds breaking up and sunshine developing, gusty southwest winds will usher a more humid airmass into the area with surface dew points in the mid and upper 60s.
While instability values will be relatively low, generally SBCAPE values and MLCAPE values around 500 J/kg, but 06-km Bulk Shear will be upwards of 55-60 kt. SPC has the region in a Slight Risk (level 2 out of 5) for severe weather this afternoon and evening. Timing looks to be around 4pm to 6pm for the southern Poconos, far northwest New Jersey, and the Lehigh Valley, 5pm to 7pm along the I-95 corridor, and from 6pm to 8 pm over Delmarva and southern New Jersey. After sunset, with loss of diurnal heating, the risk for severe weather will diminish.
A tight pressure gradient then develops over the area tonight through Saturday as broad high pressure centered over the Southern Plains begins to build east. Gusty north to northwest winds will develop tonight and will continue through Saturday, with winds ranging from 15 to 25 mph with 25 to 35 mph gusts. Much cooler and drier on Saturday with highs in the 50s and surface dew points in the 30s.
KEY MESSAGE 2...Widespread frost and freeze conditions are increasingly likely Saturday night.
The primary trough axis looks to pass over the region by Saturday evening, with subtle height falls through Saturday night and into Sunday. Guidance is coming into better agreement that a portion of the trough will close off and linger offshore in the vicinity of the Carolinas, but high pressure will be settling into the region from the northwest. The end result should be mostly clear skies and diminishing winds through Saturday night.
With the coldest airmass so far this season settling into the region, the primary question remaining for Saturday night's temperatures is how quickly winds diminish. Current indications are that it could remain a bit breezy through much of the evening, shortening the window of good radiational cooling conditions. Nevertheless, by dawn Sunday winds should be fairly light at least across the Poconos, Lehigh Valley, and adjacent northern NJ. Given this, the current forecast calls for temperatures at or below freezing across these areas. For southeastern PA and central and southern portions of inland NJ, temperatures will likely still fall into the mid 30s. Upper 30s to low 40s are expected across much of Delmarva and coastal NJ.
Regarding frost, the airmass that will be infiltrating the area will also be fairly dry, so good radiational cooling will be needed to get widespread frost. Given this, the potential for widespread frost appears limited at this time to the Poconos and far northern NJ, with patchy frost still possible across the remainder of our eastern PA counties and inland NJ, especially the Pine Barrens. Frost and/or freeze headlines are still very likely to be needed for at least parts of the area Saturday night.
Temperatures will begin slowly moderating Sunday into the early part of next week.
Aviation /06Z Friday Through Tuesday/
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas.
Early this morning...CIGs lower to IFR. Some VSBY restrictions, as low as MVFR, in SHRA possible. S-SE winds 5 to 10 kt. Moderate confidence.
Today...IFR CIGs in the morning, gradually lifting to VFR from 16Z to 20Z. A line of SHRA and TSRA will move fairly quickly across the terminals generally from 18Z to 21Z at KRDG/KABE, 19Z to 22Z at KTTN/KPNE/KPHL/KILG, and from 20Z to 23Z at KMIV/KACY. SW winds 10 to 15 kt with gusts up to 20 kt. Moderate confidence.
Tonight...SHRA/TSRA taper off by 02Z, then VFR. NW winds 10 to 15 kt with 20 to 25 kt. High confidence.
Saturday...VFR. NW winds 15 to 25 kt with 25 to 35 kt gusts. High confidence.
Outlook...
Saturday night through Sunday...VFR. No significant weather.
Sunday night through Monday night...Primarily VFR. There is a slight chance for a few rain showers for the near-coast terminals.
Tuesday...VFR. No significant weather.
Marine
Southwest winds increase to 15 to 20 kt with gusts up to 25 kt by this afternoon. A Small Craft Advisory remains in effect for the ocean waters. for later today.
A line of showers and thunderstorms capable of damaging wind gusts will move across the waters early this evening with the passage of a strong cold front.
Winds turn north-northwest tonight and increase to 15 to 20 kt with 25 to 30 kt gusts that will last through Saturday. 30 to 35 kt gusts are possible Saturday morning. Will leave the Gale Watch up for all waters tonight through Saturday.
Outlook...
Saturday night...Advisory conditions likely with gales possible for the outer marine zones. North winds 20-25 kt with gusts 30-35 kt. Seas 4-7 feet.
Sunday...Advisory conditions may linger for much of the day with north-northeast winds 15-25 kt and gusts to around 30 kt. Winds should begin to subside later in the day. Seas 4-7 feet, diminishing to 3-5 feet late.
Sunday night through Tuesday...There is low confidence due to the potential influence of a possible developing surface low to the south of the region. Advisory conditions may re-develop and could potentially continue at times through Tuesday with elevated north-northeast winds and increasing seas.
Phi Watches/Warnings/Advisories
PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 2 AM to 6 AM EDT Saturday for ANZ430- 431. Gale Watch from Saturday morning through Saturday afternoon for ANZ430-431-450>455. Small Craft Advisory from 3 PM this afternoon to 6 AM EDT Saturday for ANZ450>455. Gale Watch from Saturday morning through Sunday morning for ANZ480>483-485.
DISCUSSION...Cooper/MPS AVIATION...Cooper/MPS MARINE...Cooper/MPS