Marine Weather and Tide Forecast for St. James, MD

NEAR TERM /THROUGH TONIGHT/
A strong area of Canadian high pressure has slowly begun to pull away from the Atlantic coast. As this occurs, winds around the western periphery of this anticyclone will encourage south- southeasterly flow into the Mid-Atlantic region. This shift in the winds has helped bolster early morning temperatures on the order of 10 to 15 degrees compared to 24 hours ago. As of 07Z/3 AM, there is a quite a range of temperatures across the region.
While most locations sit in the low/mid 50s, areas that have decoupled with calm winds are in the 40s. Those closer to the river/bay influences are close to 60 degrees. Aside from some passing high clouds, skies should generally be clear to start off the day.

Throughout the day, a warm front currently analyzed back near the Indiana/Ohio border is expected to accelerate toward the east in time. Based on the present trajactory of this feature, a warm frontal passage occurs sometime this afternoon. In response, expect winds to shift from southeast to mainly southerly with gusts up to 20 to 25 mph. Further moistening of the boundary layer is expected given Gulf influences to the air mass. Above average heights along the Eastern Seaboard will again help bolster temperatures this afternoon. The current guidance supports widespread low/mid 80s across the region, with even spotty upper 80s over the Allegheny mountain valleys. High clouds do increase by later in the day as anvil cirrus moves in from thunderstorms across the Ohio Valley. Such convective activity will require monitoring given possible evening impacts.

The latest Day 1 Storm Prediction Center outlook paints a Slight risk across Garrett, Allegany, and Mineral counties, as well as portions of Grant County. Extending off to the east 2-3 rows of counties is a Marginal risk for severe thunderstorms. An upstream mesoscale convective system is likely to be approaching the Allegheny Front by around dark. The 00Z high-resolution suite shows some potential for this upstream line of storms to move into areas west of the I-81 corridor. The main threat would be damaging winds gusts, with any taller/stronger cores posing a risk of 1 inch diameter hail. Instability drops off further to the east which casts a doubt of whether this activity survives the Blue Ridge Mountains. Will maintain isolated thunderstorms in the forecast through the overnight hours for locations east of these mountains.

For the overnight hours, a continued warm advection regime favors a very mild night with lows in the low/mid 60s (50s across mountain locales). This is easily 10 to 20 degrees above late April climatology. Winds do gradually shift to southwest to westerly as a cold front slowly pushes through. Aside from some lingering showers along the Alleghenies, most shower activity should abate through the night.

SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/
The mentioned cold front is expected to continue its south and eastward trajectory through the day. This yields a shift to mainly north to northwesterly flow. Although temperatures should remain plenty warm with highs in the upper 70s to low 80s, this does come with a drop in dew points. North of this boundary, dew points may fall into the 40s, while low/mid 60s are more commonplace off to the south in the warm sector. After a mainly dry start to the day, some overrunning showers may impact those south of I-66. Depending on the coverage of this activity, these could inhibit some of the expected warming. Overall skies should consist of a mix of sun and clouds. Any threat for showers is expected to gradually diminish into Wednesday night. Forecast lows will be a bit cooler owing to the drier air mass. Under a light northeast to easterly wind, low temperatures drop into the 50s with a few low 60s possible along I-64.

Thursday brings a return of the frontal zone that had moved to the south the preceding day. Most guidance favor bringing this system poleward as a warm front. This yields a return to mainly south to southeasterly winds, increasing dew points, and more instability to work with. Forecast highs on Thursday are in the upper 70s to low 80s, but with some ensemble spread noted. This is likely due to the timing of upstream showers and thunderstorms that begin to impact the region. Models show a decent shortwave tracking in from the Ohio and Tennessee Valleys during the evening hours. The mid-level flow is a bit stronger as well, generally averaging around 35 to 45 knots.
This carries a non-zero threat for severe thunderstorms, but details remain nebulous at this time. A mild air mass persists into the night ahead of the next cold front. Lows are forecast to be in the low/mid 60s, with mid/upper 50s back over the higher terrain.

LONG TERM /FRIDAY THROUGH MONDAY/
Low pressure will track northeastward into the St. Lawrence Valley on Friday, while upper troughing and a surface cold front lag off to our west over the Ohio Valley/Great Lakes. Pre-frontal southerly flow will lead to another warm day, with temperatures likely climbing into the low-mid 80s for most. With a very warm and seasonably humid airmass in place at the surface and heights falling aloft, instability should be able to develop, with showers and thunderstorms possible during the afternoon. Some of these storms may potentially be strong, given ample surface based instability and around 30-40 knots of effective bulk shear present.

Guidance has trended slower with the eastward progression of the trailing upper trough and surface cold front, with some solutions (namely the 12z Euro) showing showers and thunderstorms again on Saturday, with a cold frontal passage later in the day Saturday.

Most solutions favor dry conditions on Sunday as the cold front clears the area. However, model guidance diverges substantially by Monday, resulting in significant forecast uncertainty early next week. Some solutions have surface high pressure and upper level ridging build in, which would lead to sunny skies and seasonable temperatures. Other solutions have Friday/Saturday's upper trough cutting off to our east, and then retrograding westward back toward the Mid-Atlantic as an upper low, which would result in rainy and cooler conditions.

AVIATION /07Z TUESDAY THROUGH SATURDAY/
VFR conditions are likely through sundown today, although some upstream convection approaches the area from the west after dark. During the daytime, southerly winds will increase as a warm front pushes through. Afternoon gusts up to 20 to 25 knots are expected all terminals. Regarding the thunderstorms that arrive late, the best chance to see impacts would be at KMRB in the 02-04Z timeframe. It is much less certain whether these storms reach the D.C. terminals. However, have added a PROB30 group around the 03-06Z time period, so will continue to monitor.

A cold front moves through later tonight which yields a gradual shift to southwest to westerly winds. VFR conditions are expected on Wednesday as this boundary continues to sink southward. Winds should be mainly northerly through the day before shifting to a light northeast to easterly by Wednesday night. Some showers are possible south of I-66 (i.e., near KCHO)
which could warrant a few brief restrictions. Eventually this frontal zone returns northward as a warm front on Thursday which brings back southerly flow and thunderstorm chances.

Prevailing VFR conditions are expected for Friday and Saturday, although brief drops to sub-VFR conditions may be possible in showers or thunderstorms either day. Winds are expected to be out of the south on Friday, and then west to northwest on Saturday.

MARINE
As Canadian high pressure continues to pull away from the Atlantic coast, a southeasterly flow should further increase in strength through the morning. Small Craft Advisories eventually go into effect at all marine locations today. Winds begin to turn more southerly through the day with gusts up to 20 to 25 knots. Some upstream thunderstorms arrive later tonight which may warrant a Special Marine Warning or two. However, this is dependent on how far east these storms remain potent.

A cold front moves through later tonight before sagging off to the south on Wednesday yielding a shift to northerly winds. This boundary again returns northward as a warm front on Thursday which yields a shift to southerly flow and more thunderstorm chances. In response, winds increase on Thursday which may warrant a return to small craft conditions.

SCA conditions appear possible in southerly flow on Friday.
Thunderstorms may also be possible during the afternoon and evening hours. Sub-SCA west to northwest winds are expected on Saturday.

TIDES/COASTAL FLOODING
Given a modest uptick in southerly flow, some of the typically higher guidance (SFAS, CBOFS) approaches minor flood stage at vulnerable sites like Annapolis during the astronomically higher morning tides through Wednesday. However, given the brevity of the southerly flow and its relatively low magnitude, feel that flooding seems unlikely at this time.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...Small Craft Advisory until midnight EDT tonight for MDZ008.
VA...None.
WV...None.
MARINE...Small Craft Advisory until midnight EDT tonight for ANZ530>532- 538>540-542.
Small Craft Advisory until 6 AM EDT Wednesday for ANZ533-534- 537-541-543.
Small Craft Advisory from 9 AM this morning to midnight EDT tonight for ANZ535-536.