textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

A Winter Weather Advisory has been issued for Monroe County for Freezing Rain tonight. Increasing confidence in widespread fog this evening around the Philly Metro and areas farther north. Expect a gradual warming trend through the rest of the week.

KEY MESSAGES

- Freezing rain will create hazardous road conditions tonight for Portions of the Poconos.

- Widespread fog will make travel challenging this evening for areas north of the Philly Metro Area.

- A pattern change is expected with seasonably warmer temperatures and multiple shower chances in the longer term.

DISCUSSION

KEY MESSAGE 1... - Freezing rain will create hazardous road conditions tonight for Portions of the Poconos.

Low pressure along with an associated upper level trough will move eastward from near Michigan this afternoon through the lower Great Lakes and then on into upstate NY tonight. An associated area of precipitation from this system will affect the area through the evening and overnight period as it moves through west to east. With the track of the low to our north, the heavier and steadier precipitation will stay mainly to our north. However at least some light precip will affect our northern zones especially near and north of the I-78 corridor through the I-80 corridor. It will be warm enough that this will be mostly light rain however over the higher elevation areas of the Poconos into NW NJ (areas roughly near and above 1200 ft) it will likely be cold enough for frozen precipitation. Surface temperatures have warmed above freezing here this afternoon but in these higher elevation areas should get back down to near or below freezing as precip moves in this evening due to wet bulb cooling effects. And due to a warm layer aloft with a shallow cold layer this will result in freezing rain. The period of greatest concern will be from around 7 PM this evening until 2 AM overnight. A Winter Weather Advisory is in effect for Monroe County in PA. Main impacts will be slippery and hazardous road conditions as accretion should be limited to at most a few hundredths of an inch. So this won't be enough for tree damage or power outages. After 2 AM or so temperatures should be above freezing everywhere as a warm front lifts through changing any precip to just rain. Precipitation will also be winding down through the predawn hours.

KEY MESSAGE 2... - Widespread fog will make travel challenging this evening for areas north of the Philly Metro Area.

A warm front will slowly lift northward through the area through the evening and overnight period. As this occurs low level winds from the east and southeast will continue to advect in moisture in the lower levels. This will result in saturation occuring by later this evening causing fairly widespread fog to develop which could be quite dense. Most of the fog will be for areas near and north of the warm front as it's moving through so this should limit the fog potential over Delmarva, extreme SE PA, and southern NJ where the front lifts through earlier. North of here fog should become quite widespread through the mid to late evening and may be dense in spots with visibility potentially down to a quarter of a mile or less. A Dense Fog Advisory may end up being needed so this will need to be monitored closely by future shifts. The main impacts of the fog will of course be poor visibility leading to hazardous travel especially for areas along and north of the PA Turnpike through the I-195 corridor in NJ. The fog should diminish with time from south to north through the predawn hours into Wednesday morning as the front lifts through. In terms of impacts the morning commute, fog by this time should be mainly confined to portions of NE PA and NW NJ (areas mainly near and north of the I-78 corridor) but even here will diminish through the first half of the morning.

KEY MESSAGE 3... - A pattern change is expected with seasonably warmer temperatures and multiple shower chances in the longer term.

With the passage of a cold front Wednesday morning into early afternoon, breezy northwest winds are expected. Gusts 20-30 mph are anticipated, with winds diminishing during the evening hours.

In the wake of the cold front, high pressure will quickly shift into the region for Thursday, and then to the east of the region by Friday morning. This will set the stage for southerly return flow, and warming temperatures are expected into the weekend. As of right now, Friday into Saturday look like the warmest days, with temperatures generally 10-15 degrees above average for this time of year.

A potent upper-trough will shift eastward towards the region beginning on Friday. A warm front will lift through the region Friday night. Scattered showers will likely develop ahead of the warm front during the day on Friday, and continue into the evening hours. A brief lull in precipitation may occur Friday night while our region is in the warm sector, but more widespread showers are anticipated on Saturday as a cold front approaches. Wind fields aloft are expected to be quite strong, so it is not out of the question that these showers could mix down isolated instances of damaging gusts, but very meager instability suggests overall severe potential should be quite limited. Overall, appreciable rainfall amounts are expected for most of the area, but there are no major concerns at this time. After the cold front passes through Saturday evening, high pressure looks to build back in with temperatures returning to near normal.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

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

Tonight...MVFR ceilings currently will continue to rapidly deteriorate this evening with CIGs dropping to IFR and LIFR with VSBYs likely following soon after. At minimum expect IFR at all terminals, with LIFR to VLIFR likely, esp northern terminals. Occasional drizzle and light rain possible. The extent of fog development is less confident, however suspect that most terminals will see a period of dense fog at some point overnight. Winds light/variable early, gradually settling out of the west-southwest around 5-10 kt overnight. Low-level wind shear of 35-40 kt also likely. Low-moderate confidence overall, especially with regard to timing and fog development.

Wednesday...Lingering IFR/MVFR ceilings may continue through about 12-15Z, before skies gradually begin to scatter and lift to VFR. Residual MVFR ceilings may linger for much of the day at KRDG and KABE. Increasing west-northwest winds around 10-15 kt with gusts up to 20-25 kt. Winds decrease in the evening.

Outlook...

Wednesday night through Thursday night...VFR. No significant weather.

Friday through Sunday...Sub-VFR periods are expected in low clouds and widespread showers.

MARINE

Winds and seas expected to stay below Small Craft criteria through tonight. Winds SSE 5-10 kt today, increasing to 10-15 kt tonight. Seas 1-2 feet today, increasing to 3-4 feet tonight. Patchy dense marine fog possible tonight especially north of Atlantic City.

For Wednesday, a Small Craft Advisory has been issued for all of the Atlantic coastal waters for seas of 4-6 feet and wind gusts of 25 kt.

Outlook...

Wednesday night...SCA conditions may linger into the overnight hours. West-northwest winds 10-20 kt with gusts approaching 25 kt decreasing to around 10 kt late. Seas 3-5 feet decreasing to 2-4 feet late.

Thursday through Thursday night...No marine headlines are anticipated with winds below 25 kt and seas below 5 feet.

Friday through Sunday...SCA conditions are expected with south winds 15-20 kt with gusts around 25 kt, shifting to west- southwest Sunday at 20-25 kt with gusts near 30 kt. Seas 3-5 feet.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Winter Weather Advisory until 3 AM EST Wednesday for PAZ055. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 6 AM to 10 PM EST Wednesday for ANZ450>452. Small Craft Advisory from 6 AM to 7 PM EST Wednesday for ANZ453>455.