Marine Weather and Tide Forecast for Annapolis, MD

NEAR TERM /THROUGH TONIGHT/
No major changes to the near term. Rather quiescent through daybreak with mid to high level clouds overspreading the area overnight. Any rainfall chances hold off until the following day. Expected low temperatures will be in the 50s, accompanied by some spotty upper 40s across the higher terrain.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/
Monday will act as a day of transition ahead of a wet pattern setting up through around mid-week. The mentioned upper low swirling across the Deep South is part of a larger scale blocking regime (Rex Block). As a deep upper trough swings into the western U.S., this will help nudge the stalled downstream upper low. As this feature gains latitude in time, so will its immense moisture pool, strong jet forcing, and overall shift in sensible weather. Its slow poleward movement will carry some risk of flooding, particularly where upslope trajectories come into play (i.e., the eastern slopes of the Blue Ridge Mountains). Although the local area is in continued drought conditions, forecast rainfall amounts are high enough to cause some flooding concerns late Monday through at least Tuesday night.

The latest forecast package calls for rain to arrive into the Potomac Highlands and central Shenandoah Valley by Monday morning. Amounts should initially be light, particularly in light of initial dry boundary layer conditions which may cause some evaporation to occur. However, eventual moistening of the column is expected which will gradually increase overall precipitation efficiency. The swath of showers is expected to track northeastward in time before reaching the I-95 metros by around the evening rush hour. Despite all of the increased cloud cover, high temperatures should still reach the low/mid 70s, with 60s more likely across the central Shenandoah Valley back into the Alleghenies.

Conditions continue to deteriorate into the night with southeasterly moist advection further increasing. This moisture plume appears tied all the way down through the southern Gulf of America into the western Caribbean. Characterized by precipitable waters around 1.50 to 1.60 inches, this is easily 1.5 to 2 standard deviations above average for mid-May. Not surprisingly, forecast rainfall amounts are quite high, but are also variable due to uncertainties in the upper low track.

By Tuesday morning, the main upper low is expected to lift across the Mid-South toward the southern Appalachians. The surface reflection of this system weakens as the upper low slowly begins to fill, but the quality of moisture remains intact. Tuesday will offer plenty of rainfall with 6-hour totals in the 0.25 to 0.50 inch range, locally higher toward the Blue Ridge. Given how spread out this event occurs over, much of this rain could prove to be beneficial in nature. However, this will less likely be the case along and east of the Blue Ridge where storm totals could be double the rest of the area. Current forecast storm totals are around 1.50 to 2.00 inches, but with 2.50 to 4.00 inches in the mentioned mountainous locations.
While Flood Watches are not out yet, these will likely be considered during subsequent shifts.

Conditions remain unsettled into Tuesday night as the upper low should be just off to the west across eastern Kentucky/southern West Virginia. Based on the position of this low center, there will likely be some dry slot that moves through the area. It remains to be seen where this sets up. Outside of this mentioned dry slot, there will continue to be decent rain producing storms that track through the region. Overall skies through the period remain overcast with low diurnal temperature ranges. After Tuesday's highs rise into the upper 60s to low 70s, low temperatures should only be in the upper 50s to mid 60s.

LONG TERM /WEDNESDAY THROUGH SUNDAY/
The upper low that will impact the region over the next few days will start to shear out into an open wave as it lifts northeastward from the Mid-Atlantic on Wednesday toward the Northeastern states by Thursday. As this occurs, we should start to see a few more breaks in the cloud cover, and as a result, should heat a little better during the day. High temperatures are expected to reach into the 70s on Wednesday, and then upper 70s to lower 80s on Thursday. Showers and thunderstorms appear possible either afternoon, with the highest coverage expected Wednesday afternoon beneath the upper low.
Model soundings show mostly saturated profiles, along with some limited instability (around 500-1500 J/kg) and relatively weak flow through the depth of the troposphere. As a result, slow moving, heavy rain producing thunderstorms appear possible. While there likely won't be any synoptic scale boundaries to focus regeneration of storms in any one given location, the slow storm motions and heavy rainfall rates may be enough to cause localized instances of flooding on the heels of heavy rains on Monday and Tuesday. Areal coverage of storms should be a bit lower, and storm motions should be a bit faster on Thursday. When coupled with slightly drier vertical profiles, this should lead to a lesser threat for flooding on Thursday.

As we move toward the end of the week, a deep upper low and attendant strong surface low will slowly track eastward into the Upper Great Lakes. As this occurs, rich low-level moisture will be drawn north and east from the Gulf into the Ohio Valley and Mid- Atlantic. Simultaneously, a strong belt of mid-level flow (35-50 knots in the 700-500 hPa layer) will spread overtop that rich low- level moisture, advecting a remnant elevated mixed layer plume eastward as it does so. Rich low-level moisture, steeper than climatology mid-level lapse rates, and strong mid-level flow will result in an environment on Friday, and potentially even Saturday as well, characterized by both strong instability and strong deep layer shear. The EPS and GEPS ensemble means have 2000-3000 J/kg CAPE along with 35-50 knots of 0-6 km bulk shear. The GEFS show lesser instability and similar shear values, but have a well-know low bias when it comes to instability. This type of parameter space raises concerns for severe thunderstorms. While the parameter space being advertised at the moment by models is toward the higher end of what we typically see in this part of the country, we're still at day 6 and 7, and there is plenty of time for things to change, especially when an upper level low is involved (which models notoriously struggle with in the long range). With an elevated mixed layer involved, there are also signs of stronger capping than we typically see, so that could complicate things as well. For now, the end of the week is a period to monitor for potential severe thunderstorms, with the expectation that forecast can and will change this far out.

AVIATION /01Z MONDAY THROUGH FRIDAY/
Quiet weather is expected through tonight as a weak cold front shears apart today. Minimal gradients support a light and variable wind field. Rain does not arrive until Monday as a closed low slowly approaches from the Deep South. Sub-VFR conditions track in from southwest to northeast, with restrictions likely in place from Monday evening through Tuesday night. For Tuesday, the continued rainfall will maintain IFR conditions along with a southeasterly wind that gusts to around 15 to 20 knots.

IFR ceilings are expected to start the day Wednesday, but improvement to MVFR, or even VFR, may be possible by the end of the day. Showers and thunderstorms may also be possible, especially during the afternoon and evening. Ceilings may drop back down to sub- VFR for a time Wednesday night, before prevailing conditions become VFR again during the day Thursday. Thunderstorms may be possible again Thursday afternoon. Winds will generally be out of the southeast on Wednesday and out of the south on Thursday.

MARINE
Light gradients remain over the waters which will keep wind gusts at 10 knots or less through the first half of Monday. As a broad upper low lifts northward from the Deep South, southeasterly flow will pick up in strength into Monday night and Tuesday. As this occurs, Small Craft Advisories will likely be needed as gusts rise to 20 knots or so. A soaking rain accompanies this system which may come with a few thunderstorms, particularly during the second half of Tuesday.

Sub-SCA level winds are expected within southeasterly flow on Wednesday and southerly flow on Thursday. Afternoon thunderstorms may be possible on both Wednesday and Thursday afternoon.

TIDES/COASTAL FLOODING
As a low pressure system slowly approaches through mid week, continued onshore flow will gradually build anomalies. Sensitive shoreline could approach minor tidal flood levels by Tuesday and Wednesday.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.