Area Forecast Discussion

WHAT HAS CHANGED

Forecast trends of unsettled and potentially impactful weather along the coast continue for much of next week.

KEY MESSAGES

1) Generally quiet conditions this weekend ahead of the next cold front.

2) Persistent onshore flow and a potential strengthening coastal low will create a wetter, cooler, and breezier forecast next week.

DISCUSSION

As of 330 PM EDT Saturday...

KEY MESSAGE 1...Generally quiet conditions this weekend ahead of the next cold front.

A cold front moved through the area this morning and is now well south of the area and is draped across the Carolinas. A brief surge of drier, cooler air moved in the wake of the front as high pressure built in, but winds have already shifted to the east, so it will only be short-lived. Temperatures are currently in the upper 70s to lower 80s and dew points are in mid 60s, making for a comfortable mid-September afternoon. Satellite imagery has been depicting mostly cloudy skies for much of the morning, but cloud cover has finally started to scatter out some this afternoon.

The high will quickly move offshore tomorrow as the next front moves into the Ohio River Valley, and winds will shift to the southeast to south. This will invite the warmer, slightly more humid conditions to the area, with highs creeping back up into the mid to upper 80s (lower 80s for the Eastern Shore). Expect to see more breaks of sunshine, especially across southern counties. The front will nudge closer to our northern/western CWA border by late Sunday potentially bringing some showers along with it. Sunday night low temperatures will be a smidge milder in the mid to upper 60s as cloud cover and scattered rain chances return.

KEY MESSAGE 2...Persistent onshore flow and a potential strengthening coastal low will create a wetter, cooler, and breezier forecast next week.

A big shift in the weather pattern is on tap for next week as another front approaches the area, bringing unsettled weather to the local area. The cold front will slowly drop through the area late Monday through Tuesday as an expansive ridge sets up from the Great Lakes through the Hudson Bay area. The slow progression of the front will allow for rain/storm chances to linger through the day on Monday. WPC currently has a Marginal risk for excessive rainfall as some showers/storms could produce areas of localized flooding. SPC has included a Marginal risk (level 1/5) for the far SW piedmont counties, as this is where the warmer temperatures and slightly better environment will be. Due to the slow movement of the front, there will likely be a sharp temperature gradient across the forecast area, with upper 70s possible across the northern half of the area and 85F to near 90F across the southern half of the area. Global models have an area of low pressure developing along the frontal boundary as it moves through the area. The ridge will shift a bit eastward on Tuesday, which will move this low offshore of the Mid-Atlantic region. Guidance has the low strengthening as it lifts northeast, however, there are discrepancies between models in the exact details. Ensemble guidance has a wide range of possible strength and various tracks, so there is uncertainty regarding exact impacts to our area. This low is forecast to slowly lift northeastward, and the gradient between this low and the aforementioned high to the north will tighten, bringing increasing NE winds to the area starting Monday night. The duration of the elevated flow, the proximity of the low to the coast, and the strength of the low will all play an important role in how several coastal hazards pan out, so stay tuned to the forecast for next week as this system develops.

While the coast is potentially seeing impacts from the low, the broad high will build down to the west of the low and put most of the area in a CAD set-up. This will keep temperatures likely well below normal through most of the week, especially in the piedmont. With the forecast NE flow, coastal areas will still be modified by the warmer water temperatures, but are still forecast to be below normal mid-late week.

AVIATION /19Z SATURDAY THROUGH THURSDAY/

As of 133 PM EDT Saturday...

Generally VFR conditions will prevail through tomorrow, though a few brief intermittent MVFR CIGs are possible this afternoon due to persistent low level clouds across the area. Winds will be from the northeast-east at 7-12 kts through this evening before shifting to the east then southeast and diminishing to 4-8 kts overnight through tomorrow.

Outlook: Another cold front slowly crosses the region Monday into Tuesday bringing a more unsettled pattern with degraded flight conditions through at least mid-week. Coastal terminals may also have elevated northeasterly winds for an extended period.

MARINE

As of 330 PM EDT Saturday...

Key Messages:

- Mainly sub-SCA conditions are forecast through the weekend. Elevated NE to E winds prevail later through tonight.

- Decent model consensus that strong high pressure becomes locked in place across eastern Canada/northern New England next week, bringing several days of onshore flow and the increasing potential for Gales. SCA level winds are forecast by Monday night/Tuesday, with the highest winds likely occurring between late Tuesday night and Thursday night.

Strong high pressure over eastern Canada allows for mainly sub-SCA conditions this weekend, keeping E-NE winds around 10-15 kt across the local waters. A push of CAA today behind the cold front yesterday has allowed for winds to reach ~15 kt with gusts up to 20 kt this afternoon and evening, with winds relaxing back to 10-15 kt overnight. With the E-NE flow, a brief period of near 5 foot seas is possible tonight for coastal waters off NE NC, but confidence is not high enough to issue a Small Craft Advisory. Winds will then shift out of the SE by Sunday night and veering to the SW by Monday morning, remaining below the SCA threshold at 10-15 kt.

While there is some uncertainty with respect to timing, a stronger front is progged to cross at least the northern half, possibly more, of the marine area by late Monday/Mon night. The latest models show the front moving through all local waters by Tuesday morning, shifting the winds back out of the NE, but exact timing make change with future forecasts. Regardless, the strongest CAA doesn't look to make it to the area until Wednesday or Thursday, as a low pressure system deeps off the Atlantic coast. Significant to potentially dangerous marine conditions are possible from late Tuesday night through Thursday as NE winds increase in response to the tightening pressure gradient between the strong high to our north and deepening sfc low offshore. Confidence in a period of northeasterly gale force gusts (35-40+ kt) is increasing, with the most likely timeframe being from Wednesday-Thursday. Local wind probs show a 60-80% chc of gusts to 34 kt across the coastal waters and a 30-60% across the Ches. Bay. Seas likely build to 9-13+ ft by Wed/Thu due to the prolonged onshore flow. Solid SCA level winds will likely continue through the end of next week as the low potentially lingers offshore. Of course, this is still several days away, so the timing and placement of the synoptic scale systems are not locked in place yet, but there continues to be quite a strong consensus amongst the Euro, GFS, and Canadian ensembles in the general pattern. We will continue to monitor the trends as this gets closer in time.

There is a moderate rip current risk for all beaches Sunday and Monday from onshore flow. Dangerous surfing conditions are likely by the middle of next week with the prolonged onshore flow. Localized beach erosion is possible from mid to late next week as well depending on how things evolve.

AKQ WATCHES / WARNINGS / ADVISORIES

MD...None. NC...None. VA...None. MARINE...None.