Marine Weather and Tide Forecast for Portsmouth, VA

NEAR TERM /UNTIL 6 AM SATURDAY MORNING/
As of 305 PM EDT Friday...

Key Messages:

- A warm front lifts across the forecast area today, with scattered showers and possibly a few thunderstorms mainly west of I-95.

- Showers and isolated storms continuing through tonight.

A diffuse warm front and moisture boundary extends from NE NC up through the VA Piedmont this afternoon. Dew points in the mid-upper 50s are noted across SE VA and on the Eastern Shore and Northern Neck, with low-mid 60s through the I-95 corridor and points W. High pressure also remains offshore, keeping generally light southerly flow across the area. Along the immediate coast, a sea breeze may turn the wind direction E for a time while also keeping it a few degrees cooler. With the front nearby and the higher dew points along and behind the boundary (contributing to modest sfc-based instability), isolated to scattered showers have developed across inland portions of the area. The highest coverage is currently across the SW, in far western Mecklenburg and Lunenburg Counties.
Expect more of the same through the afternoon, with coverage potentially increasing a bit more. PoPs are primarily 30-50% inland and 10-20% closer to the coast. Temperatures this afternoon rise into the upper 70s and/or lower 80s.

The warm front pushes N through the entire area tonight, with dew points inching up into the mid 60s areawide. Gradual height falls will also overspread the area ahead of mid-level troughing over the OH Valley and Appalachians. Additional showers are thus possible through the night, though there is uncertainty regrading coverage given the diffuse nature of the leading shortwave. CAMs indicate several waves of showers (with some embedded thunder), potentially associated with upstream convection currently over the TN/OH Valleys. Showers look to focus through the US-360 corridor and points N and NW and this is where the higher PoPs have been maintained through the night. Still, isolated precip is possible anywhere through tonight with increasing PWATs and height falls.
Overall QPF is on the light side, but locally higher amounts up to 1" are possible in heavier shower activity. Very mild tonight with lows in the low-mid 60s.

SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/
As of 305 PM EDT Friday...

Key Messages:

- Scattered showers and storms are likely on Saturday as a cold front moves across the area. A few storms could be on the strong to severe side.

- Much cooler and drier weather arrives Sunday behind the cold front. Warming up a few degrees for Monday.

On Saturday, a cold front will approach the area from the NW as low pressure moves through the eastern Great Lakes into the New England states. The cold front is expected to cross through our CWA in the late afternoon across the N and in the evening or early parts of Saturday night across the S. Still looking like two rounds of showers and thunderstorms Saturday: one in morning associated with prior-day activity and the leading shortwave trough, and the second with the front itself. There is some uncertainty in how long the morning activity persists, which could have some impact on afternoon destabilization. Additionally, there is also some potential for this initial activity to intensify some if it moves eastward into SE VA during peak heating. This solution is shown in some of the experiment MPAS CAMs.

Attention then turns to likely convective development across northern half of the area as the cold front drops through. This front is also likely to move through during peak heating and guidance indicates moderate instability (MLCAPE ~1000 J/kg)
developing most of the area during the afternoon. A belt of slightly stronger winds aloft will also slide through these areas, creating some higher shear values (around 30 kt) from the Northern Neck onto the MD Eastern Shore. Clusters of thunderstorms are likely to develop and move rather quickly S and SE in the afternoon and evening. The front and shear values should allow for some storm organization and a few strong to severe storms are expected given steep low-level lapse rates and some DCAPE. This would tend to favor a strong wind gust threat.
The hail threat is rather low given weaker deep-layer shear and meager mid-level lapse rates. After collaborating with SPC, the decision was made to hold off on introducing a marginal risk area given potential uncertainties from the aforementioned morning convection. Still, a marginal risk may eventually be introduced on the Day 1 outlook. While locally heavy rainfall is also expected in any storm, a widespread flooding threat is not anticipated given quick storm motions and dry antecedent conditions. For temperatures, warming into the lower 80s for most of VA and NC, with upper 70s on the Eastern Shore.
Overnight lows in the mid 40s N to mid 50s S.

Cooler Sunday with decent cold advection behind the cold front as high pressure builds in from the NW. Highs in the lower 70s are expected for most of the area under a sunny sky. Warming up a few degrees into the mid 70s Monday as the high become centered over the Mid-Atlantic and Carolinas and ridging expands across the eastern CONUS aloft. Lows Sunday night in the mid 40s inland and low- mid 50s at the immediate coast with a persistent northerly wind.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
As of 320 PM EDT Friday...

Key Messages:

- Near normal temperatures Monday, with well above average temperatures Tuesday and Wednesday.

- Scattered (mainly diurnal) showers and storms Wednesday and Thursday, with possibly more organized storms by Friday.

A tall ridge aloft builds across the East Coast into Tuesday before a shortwave trough moves across the Great Lakes and Canada by midweek. At the surface, high pressure remains over the area Monday before sliding SE offshore Tuesday. This will allow for a significant warmup into the mid 80s Tuesday. The warmest day is expected Wednesday with temps well into the mid- upper 80s, with a few areas possibly touching 90-91F. A cold front approaches the area from the N Wednesday and Wednesday night allowing for cooler temps with highs in the low- mid 70s NE to mid 80s SW Thursday. Will also need to watch if an earlier passage of this front could keep Wednesday a tad cooler than forecast (as suggested by the 25/04 ECMWF). Additionally, scattered (mainly diurnal showers and storms) are possible Wednesday and Thursday afternoon and evening. Overnight lows generally fall into the 60s.

By the end of the week, another cold front looks to push through the region. Model guidance depicts strengthening 500 mb flow aloft and increasing deep-layer shear, in addition to sufficient instability. If the frontal timing is favorable during the afternoon and evening Friday, some threat of organized strong- severe storms could materialize. This potential is indicated across various machine learning aids. However, confidence is low at this time range and much can change. Stay tuned.

AVIATION /00Z SATURDAY THROUGH WEDNESDAY/
As of 755 PM EDT Friday...

High pressure is centered offshore as of 00z with a warm front lifting through the region. Scattered showers are occurring in vicinity of the warm front but are presently not impacting any of the terminals. Otherwise, VFR under BKN mid and high level clouds with a SE wind of 8-12kt. The warm front will slowly lift through the area overnight into Saturday morning with the wind veering to SSW and remaining 8-12kt. Isolated to scattered showers will linger across the area overnight into Saturday morning, but confidence in any direct impact to a given TAF site is low. MVFR cigs are expected to develop after 10z and should lift to VFR by ~16z. Showers and a few embedded tstms are expected to develop by Saturday aftn in advance of a cold front.
Confidence in timing is low, but any showers/tstms have the potential to produce brief flight restrictions. Additionally, A SW wind will become gusty ahead of the cold front with gusts to 20-25kt.

Scattered showers and a few tstms could linger into Saturday evening, especially near the coast. Otherwise, becoming dry and VFR later Saturday night through Tuesday as high pressure builds into the region. Another cold front potentially drops into the area by the middle of next week.

MARINE
As of 230 PM EDT Friday...

Key Messages:

- Winds increase ahead of a cold front tonight into Saturday with low-end Small Craft conditions expected. High end Small Craft Advisory are likely Saturday night into early Sunday behind that cold front.

- SCAs are in effect for all marine zones starting either tonight or Saturday night and continuing through Sunday.

- Calmer conditions return Sunday night into the first half of next week.

This afternoon, winds are generally out of the E to SE and ~10 kt.
Winds gradually increase this afternoon into this evening (highest across the southern Chesapeake Bay), becoming southerly tonight. A cold front approaches from the NW later this evening-tonight as low pressure tracks well N/NW of the area. With the pressure gradient tightening, winds increase to 15-20 kt (with gusts of 20-25 kt).
Also, seas are expected to build to 4-5 ft N/3-4 ft S by late tonight. SCAs start at 08z/4 AM tonight for the bay, James River, and coastal waters N of Parramore Island. SCAs run through Sunday and continue for the remainder of the waters for the post-frontal winds starting Saturday night. Still expect a brief lull in the winds Saturday afternoon before the cold front crosses the waters Saturday night. Tstms are possible late Saturday afternoon through Saturday evening along and just ahead of the front, which could necessitate SMWs.

The front (with decent CAA for late April with 925mb temps dropping to 3-6C) is progged to cross the waters during the first part of Saturday night. While the 12z/25 guidance continues to back off by a couple of knots with respect to winds, still expecting solid SCA conditions for 6-12 hours following the FROPA. NNW winds will average 25 kt with gusts of 30-35 kt between midnight and 10 AM Sunday morning. While occasional low-end gale gusts are possible (especially on the bay at elevated terminals), not expecting these to be frequent enough (or persist long enough) to warrant any Gale headlines. Will note that the stronger (~35-40 kt)
900-925mb winds remain just to our north Sunday AM as per the NAM/GFS. Local wind probabilities for >34 kt gusts have decreased a bit, and are 20-30% north and around 10% S of Windmill Pt/Parramore Island. Small Craft Advisory winds continue through most of Sunday, followed by much lighter winds Sunday night into the first half of next week. SCAs potentially return early Wednesday in elevated SW flow, though uncertainty is high at this time range.

Waves in the Chesapeake Bay of 1-2 ft and seas of 2-3 ft persist today. Seas build to 4-5 ft across the northern coastal waters by late tonight/Saturday with 3-4 ft seas farther south. Seas build further to 4-6 ft Sunday morning behind the front, with 3-5 ft waves on the bay.

AKQ WATCHES/WARNINGS/ADVISORIES
MD...None.
NC...None.
VA...None.
MARINE...Small Craft Advisory from 4 AM Saturday to 4 PM EDT Sunday for ANZ630>632-634-637-638-650-652.
Small Craft Advisory from 1 AM to 4 PM EDT Sunday for ANZ633.
Small Craft Advisory from 10 PM Saturday to 4 PM EDT Sunday for ANZ635-636-654-656-658.