textproduct: Wakefield

WHAT HAS CHANGED

Updated aviation discussion for 00z/13 TAFs.

Chances have increased for SCA conditions on Monday after a stronger frontal passage.

KEY MESSAGES

1) Unsettled and humid through Sunday as a frontal boundary lifts north later today, followed by a cold frontal passage late Sunday. Numerous showers, thunderstorms, and localized heavy rain today- tonight, with scattered showers/storms Sunday.

2) Mainly dry with seasonable temperatures and significantly lower humidity Monday-Wednesday. Temperatures warm back above normal late in the week an upper ridge builds back into the region.

DISCUSSION

As of 315 PM EDT Saturday...

KEY MESSAGE 1...Unsettled and humid through Sunday as a frontal boundary lifts north later today, followed by a cold frontal passage late Sunday. Numerous showers, thunderstorms, and localized heavy rain today-tonight, with scattered showers/storms Sunday.

Scattered showers and isolated thunderstorms have started to develop across the area, with the most robust convection developing closer to the coast in NE NC thanks to the influence of the sea breeze. Though the storms are moving slow, they have been moving just enough to keep from causing any hydro concerns just yet, however, it is still early. The main focal point is a formerly stalled boundary starting to lift back northward as a warm front. Current SPC mesoanalysis is highlighting PW values of over 2" across SE VA and NE NC where the best showers and thunderstorms currently are located. Satellite imagery does show some clearing across the southern half of the forecast area, so temperatures have been able to climb into the mid-upper 80s. Across the northern half of the area, temperatures have been generally capped in the lower 80s due to the cloud cover, though clouds are starting to clear some, so these areas could see temperatures climb a few degrees if this trend continues.

While there is decent instability across the region, the best height falls will be later tonight as a shortwave slides through the area. With the instability and better support aloft not occuring at the same time, the severe threat remains low today, though a few gusty showers cannot be ruled out. With high precipitable water values, modest instability (skinny CAPE profile), and weak steering flow, the environment is favorable for efficient warm rainfall processes and localized hydro concerns (supported by an area-wide WPC ERO Marginal Risk and a localized upgrade to Slight for portions of the I-95 corridor, including metro RIC. Though there is good confidence in hydro concerns somewhere across the area, the main question is where. This hinges on the movement of the front. Though the event is already starting, confidence is too low in any specific location to put out a Flood Watch for this afternoon/tonight. Heading into tonight, though the best instability does wane overnight, the aforementioned shortwave will help provide an additional cold air pool aloft that should be sufficient to keep high chc to likely PoPs through tomorrow morning. The boundary washes out Sunday, leading to noticeably lower convective coverage for the NW 1/2 of the area, but high chc to likely PoPs remain in the forecast for the SE and some late day storms are still possible in the NW as well.

KEY MESSAGE 2...Mainly dry with seasonable temperatures and significantly lower humidity Monday-Wednesday. Temperatures warm back above normal late in the week an upper ridge builds back into the region.

The upper level flow becomes NW on Monday as a strong upper level trough dives SE from the Great Lakes and pushes off the NE and mid- Atlantic coast Monday night, with an upper level ridge slowly expanding NE from the lower MS Valley. This looks strong enough to drive the sfc cold front well south of the CWA Monday, and bring significantly lower dew points that are more typical of September. The models have trended a little farther south and slower with the shortwave on Monday, so do expect to see a 3-6 hr window where clouds increase and even a few isolated showers develop on Monday before the much drier air surges in from the NNW during the afternoon (with slight chance PoPs lingering through the afternoon across the southern areas).

As high pressure builds in behind the front Monday night, a pleasant night is expected Monday night/Tue AM with lows mostly in the upper 50s to lower 60s (low-mid 50s are likely in many locations to the NW of Richmond). The models have trended a bit slower with the return flow of moisture so that now dew points look to remain comfortable through at least Wednesday as strong sfc high pressure (nearly 1030 mb), sets up from off the New England coast SW into the Carolina coastal plain through midweek. Highs will stay mostly in the low-mid 80s through Wed with lows in the 50s to lower 60s (locally warmer at the immediate coast). The upper level ridge is forecast to expand E- NE to the TN Valley and central Appalachians Thu-Fri. Temperatures climb back to above normal for mid- September, with highs generally in the mid-upper 80s. Low end diurnal rain chances return Thu- Fri.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

As of 730 PM EDT Saturday...

Scattered showers with locally heavy rainfall and isolated lightning are observed across the area this evening. Degraded flight conditions are reported across most terminals from lowered MVFR CIGs or VSBY. Showers are expected to last until 05- 08z/13, with chances for lightning decreasing over the next 3 or so hours. Behind the showers, lowered VSBY and CIGs are likely, especially for RIC and terminals to the west which could see IFR VSBY/CIGs. For the remaining terminals, MVFR VSBY/CIGs are likely before sunrise. Winds are generally light out of the southwest.

Outlook: Remaining unsettled Sunday, though with a lower coverage of showers/storms than today, with the highest probs across SE VA/NE NC. Becoming dry and mainly VFR by Monday with NE winds, then staying dry Tue-Wed with light winds expect locally breezy SE VA and NE NC along the coast.

MARINE

As of 315 PM EDT Saturday...

Key Messages:

- Generally benign marine conditions are favored this weekend through Sunday night.

- Low-end Small Craft Advisories are possible with increased NE winds behind a front late Monday morning through Monday evening.

Early this afternoon, a nearly stationary frontal boundary was draped over the far southern coastal waters, extending back into the eastern Ohio Valley. This front will slowly lift north this evening into Sunday as it weakens. Locally, winds are SSE ~10-15 kt south of the front, and mainly E around 10 kt north of it. Onshore flow and E-NE wind waves have allowed seas to build to ~3 ft this afternoon, with waves 1-2 ft, highest in the far southern portions of the Ches Bay.

Winds shift to the E-SE this evening as the front lifts north, then veer to S-SW by late this evening/early Sunday. With minimal WAA, expect winds to remain ~10 kt overnight, with occasional gusts to 15 kt. Winds remain SSW 5-10 kt Sunday as the front lifts farther north of the local area. Winds do eventually increase ~10-15 kt Sunday night ahead of the next frontal passage.

Guidance continues to trend stronger with that front for Monday, with better post-frontal CAA on NNE winds Monday afternoon and night. Latest local wind probabilities show an uptick for potential sustained winds => 18kt in the Ches Bay, with probabilities now in the 60 to 90% range late Monday morning into early evening. For nearshore coastal waters, high-res guidance shows a 30-50% chance of 25 kt gusts during that same period. Probabilities and the first look at high-res CAM guidance also indicate a brief secondary surge is possible Monday night into Tuesday morning, especially in the lower Bay and lower James River. WaveWatch and Euro wave guidance are a bit more aggressive, which aligns well with the quick ramp-up of NE flow late Monday into Monday night. 5-6 ft seas remain possible for the southern coastal waters during this timeframe, with those 5-6 ft seas potentially lingering in the 20-60 nm offshore zones from Monday night into mid-week.

A low risk of rip currents is expected Sunday and Monday.

AKQ WATCHES/WARNINGS/ADVISORIES

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