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ANZ530 Chesapeake Bay North Of Pooles Island- 333 Pm Est Sun Dec 10 2023
.small craft advisory in effect until 6 pm est this evening...
.gale warning in effect through Monday afternoon...
Rest of this afternoon..S winds 15 kt with gusts to 20 kt. Waves 2 ft. Rain with a slight chance of tstms. Vsby 1 to 3 nm.
Tonight..NW winds 15 to 20 kt. Gusts up to 25 kt... Increasing to 35 kt after midnight. Waves 2 ft. Rain. Vsby 1 to 3 nm.
Mon..NW winds 15 to 20 kt with gusts to 35 kt. Waves 2 ft. Rain. Vsby 1 to 3 nm.
Mon night..W winds 10 to 15 kt with gusts to 20 kt. Waves 1 to 2 ft.
Tue..SW winds 5 to 10 kt. Waves 1 ft.
Tue night..SW winds 5 to 10 kt. Waves 1 ft.
Wed..NW winds 10 to 15 kt. Waves 1 ft.
Thu..NW winds 5 to 10 kt. Waves 1 ft.
winds and waves higher and visibilities lower in and near tstms.

ANZ500 333 Pm Est Sun Dec 10 2023
Synopsis for the tidal potomac and md portion of the chesapeake bay..
a strong frontal system will impact the waters through Monday. High pressure will return Tuesday through Thursday. A small craft advisory will likely be needed Monday night into early Tuesday morning.

FXUS61 KLWX 101953 AFDLWX

Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 253 PM EST Sun Dec 10 2023

SYNOPSIS
A strong cold front will cross the region this evening bringing heavy rain, mountain snow, and gusty winds. The front pushes east of the area Monday morning with high pressure set to return Monday afternoon and Monday night. Dry weather and moderating temperatures are expected Tuesday through Saturday as high pressure sits nearby.

NEAR TERM /THROUGH TONIGHT/
A potent upper-level trough with northern and southern stream energy will continue to slowly pass through the Ohio Valley while surface high pressure remains offshore over the Atlantic.
The cold front associated with the trough axis will slowly approach from the west this evening. This is a potent system and this can be seen by the strong meridional component to the upper-level trough axis. Therefore, warm advection and moisture advection will be strong ahead of the cold front. Also, the thermal gradient will be quite strong with subtropical air being pulled into the area ahead of the cold front and a Canadian airmass on the other side of the boundary. A strong low-level jet will also aid in moisture advection as well with PWATs most likely around 3 to 4 standard deviations above climo.

Therefore, widespread rain is expected across the area into tonight. There is elevated instability progged in much of the latest guidance, suggesting an embedded thunderstorm is possible with the convection. A line of heavier showers and perhaps a thunderstorm will also accompany the frontal passage later this afternoon into this evening. Given the strong winds aloft, this has the potential to mix down gusty to perhaps even locally damaging wind gusts. One mitigating factor will be the lack of instability that is progged to be rooted within the boundary layer. Therefore, certainty for damaging wind gusts is low at this time (with the best chance for strong to damaging wind gusts near and east of the Blue Ridge Mountains where SPC has a marginal risk). A soaking rain is expected given the dynamics and moisture associated with this system (more info in the hydrology section below).

Colder air will move in quickly behind the front, first this evening in the mountains, and then later tonight from northwest to southeast across the valleys and metro areas. With the upper- level trough axis lagging behind the frontal passage by a few hours or so, this suggests that there will be some anafrontal characteristics to the boundary. Therefore, moderate precipitation is expected for a few hours or so behind the cold front before drier air eventually works its way in toward Monday morning. There will be enough cold air for rain to change to snow in some areas. A brief period of favorable upper jet dynamics could enhance lift and lead to heavier snow rates for a few hours where this sets up. Latest guidance continues to laterally translate this from west to east. As of now, it appears that the heaviest snow will be in the areas of higher terrain. Winter headlines are in effect. For locations along and west of the Allegheny Front, an upslope component to the low- level flow will cause additional snow showers to last longer behind the cold front, enhancing accumulations. The snow squall parameter is also highlighting a favorable environment for heavy snow showers/squalls late tonight into Monday morning across the Alleghenies. Snows ratio will improve in the Alleghenies through the overnight, though the best moisture is trapped below the inversion/DGZ which may limit snow crystal growth.

There remains uncertainty with this event. At this time, a slushy coating to an inch of snow will make it into some of the valleys, and a slushy coating may approach the metro areas.
However, the most likely scenario is for the boundary layer to remain above freezing, so impacts should be minimized.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/
The cold front will continue to push offshore Monday morning with brisk and blustery northwest flow kicking in. Upslope snow showers will continue to fly over the Allegheny Front with perhaps a bit of spillover to the Blue Ridge and Catoctins given high FROUDE numbers and even the potential for a few squalls over northern portions of the Allegheny Mountains. Further east, any residual anafrontal mixed precipitation will come to an end by mid-morning as dry air rushes in. Winter weather headlines remain in place through early Monday afternoon for the Allegheny Mountain locales.

Falling temperatures and gusty northwest winds will be the primary concerns for the short term period. A very tight pressure gradient will set up overhead as low pressure phases to the northeast over New England and high pressure builds from the southwest over the Tennessee River Valley. Expect consistent gusts between 30-45 mph out of the northwest throughout Monday morning into Monday afternoon. Wind Advisory criteria may be met for a period of time over the mountains Monday morning into Monday afternoon where gusts could exceed 50 mph along the western facing slopes. Gale conditions are expected across the waters. Winds will gradually decrease Monday night into Tuesday as high pressure builds over the region.

With the gusty northwest winds in place, expect wind chills in the 20s and 30s (teens in the mountains) Monday afternoon and evening. Actual air temperatures Monday will struggle to get out of the low to mid 40s, with 20s and 30s over the mountains. The cold air continues into Monday night as high pressure builds overhead. Winds will lighten a bit allowing lows to fall into the teens and low to mid 20s.

High pressure takes full control Tuesday with less wind and dry conditions. Highs Tuesday will push back into the mid to upper 40s, with lows in the mid to upper 20s and low 30s.

LONG TERM /WEDNESDAY THROUGH SUNDAY/
Overall, looking at a fairly zonal flow heading into midweek.
Surface high pressure will build in from the south with a weak upper-level trough/front passing through late Wednesday. No precipitation is expected with this system due to ample dry air in place. Some extra clouds may be noted late Wednesday afternoon into Wednesday evening along with a reinforcing shot of chilly air. Highs Wednesday will range from the 30s over the mountains to low 40s over northern and central MD/northern VA.
Slightly warmer conditions are expected south of I-66/US-50.

Dry weather and moderating temperatures will continue for Thursday and Friday due to strong surface high pressure nearby. The models have remained consistent with the overall pattern throughout the workweek, but that consistency breaks down on Saturday as guidance struggles to discern southern stream low pressure developing along the Gulf Coast states.

Some of the latest deterministic/ensemble solutions keep this low pressure south of the region while others lift it northeast toward the coast. With very low confidence in place, have decided to introduce low end precipitation chances late Saturday night into Sunday.

Temperatures will remain at or slightly below average through Thursday before warming into the upper 40s and low to mid 50s Friday through the weekend.

AVIATION /19Z SUNDAY THROUGH FRIDAY/
IFR to MVFR with sporadic periods of LIFR conditions will continue to impact the terminals through tonight. Rainfall continues to vary in intensity from terminals west of the Blue Ridge to those in the urban corridor. Periods of moderate to heavy rain look to continue through this evening with even a few more embedded thunderstorms at terminals east of a line that extends from KFDK to KCHO/KLYH.
Highest chances for thunderstorms appears to be between 3-7pm at KIAD/KBWI/KDCA/KCHO. Strong winds may accompany these storms at the aforementioned terminals above. Confidence in this remains low based upon limited instability within the boundary layer. Winds will remain out of the south and southeast today at 5 to 15 kts with gusts of 15 to 20 kts later this afternoon.

Winds will continue to increase tonight as a strong cold front crosses the region. Southeasterly winds will increase to 10 to 20 kts before shifting to the northwest early Monday morning in the wake of the frontal passage. Gusts of 25 to 35 kts can be expected at all terminals late tonight into Monday. Outside of the wind, rain looks to continue with a change to snow at terminals west of KMRB and KSHD Sunday night into Monday morning. Snow accumulations will remain between a slushy coating to an inch at KMRB and KSHD with accumulations greater than 2 inches toward KEKN/K2G4. Corridor terminals may see a brief period of snow during the early Monday morning timeframe between 4-9am. A slushy coating is possible on grassy and elevated surfaces with little to no impact on the pavement. Worst case snow scenario for the metros paints amounts around an inch or two. MVFR to IFR conditions will linger through mid-morning for eastern terminals with improvement to VFR by the afternoon. MVFR to IFR conditions with upslope snow showers will remain over the Alleghenies.

Conditions will improve areawide Monday night into Tuesday as high pressure builds back into the region. Winds will gradually decrease with gusts upwards of 15 kts. VFR conditions are expected Wednesday through Friday. A dry cold front is expected to pass through on Wednesday afternoon with gusts initially out of the west shifting to northwest at 15-20 kts. Clouds during the day clear out Wednesday night. Winds diminish and shift to the west/southwest Thursday and Friday.

MARINE
Southerly flow is increasing across the waters south of the warm front. An SCA remains in effect. A line of heavier showers and embedded thunderstorms will pass through the waters this evening. This line may produce strong winds and lightning.

Gusty northwest winds are expected behind the cold front overnight through Monday. A Gale Warning is in effect for the waters. Winds will gradually diminish Monday night, but an SCA will likely be needed. High pressure will be nearby for Tuesday and Tuesday night.

Winds over the waters Wednesday increase out of the W/NW with a passing dry cold front and may hover around SCA criteria most of the day. As of now, the best chance for SCAs looks to be in the late afternoon through the overnight in our southern waters, but marginal SCA conditions may warrant issuance earlier in the day. Winds diminish and shift out of the W/SW Thursday afternoon.

HYDROLOGY
Widespread rainfall is expected through tonight as a strong cold front and multiple waves of low pressure pass through the region. A strengthening low-level jet combined with increased warm air advection/isentropic upglide will yield efficient heavy rainfall over a 3 to 6 hour period this evening into tonight. Rain has been fairly stratiform and heavy this morning, but looks to turn toward more of a convective element with a strengthening low- level jet ahead of the front by this evening. A few thunderstorms may also enhance totals east of the Blue Ridge with SBCAPE/MLCAPE values running less than 500 J/kg and 0-6km shear hovering at 70-90 kts.

PWATS ahead of the boundary per the 12z HRRR will surge into the 1.2 to 1.6" range along and east of the Blue Ridge. This aligns with the NAEFS/EPS guidance which suggest PWATS running 3 to 4 standard deviations above climo for this time of year which is fairly significant.

Storm total rainfall will range between 1.25 to 2.50 inches along and east of the Alleghenies. Localized amounts up to 3 inches remain possible across southern MD/the northern neck of VA, and favored upslope zones of the northern/central Blue Ridge due to increased southeast flow.

For that reason, a Flood Watch continues for both the Washington DC and Baltimore metros as well as urban areas of northern VA. The watch extends from this afternoon into late evening to encompass the heaviest rainfall. Urban flooding due to runoff looks to be the main concern here, although smaller streams and creeks could see rises due to the amount of rain coming in a short period.
Antecedent drought concerns should help limit any widespread flooding across the region.

TIDES/COASTAL FLOODING
Tidal anomalies will continue to increase into this evening under increased south-southeasterly flow. Some vulnerable locations may approach minor tidal flooding during high tide heading into tonight. Current guidance illustrates most locations holding at caution stages as the front quickly pushes through.

Strong offshore northwesterly flow returns tonight into Monday in the wake of a strong cold frontal boundary. This will allow anomalies to drop, eliminating any residual coastal flooding concerns.

LWX WATCHES/WARNINGS/ADVISORIES
DC...Flood Watch until 1 AM EST Monday for DCZ001.
MD...Flood Watch until 1 AM EST Monday for MDZ008-011-013-014-016- 503>506-508.
Winter Weather Advisory from 7 PM this evening to noon EST Monday for MDZ001.
VA...Flood Watch until 1 AM EST Monday for VAZ053>055-502-506-526- 527.
Winter Weather Advisory from 7 PM this evening to noon EST Monday for VAZ503.
Winter Weather Advisory from 7 PM this evening to 6 AM EST Monday for VAZ025>027-029-504.
Winter Storm Warning from 8 PM this evening to 6 AM EST Monday for VAZ507-508.
WV...Winter Weather Advisory from 7 PM this evening to 6 AM EST Monday for WVZ055-506.
Winter Storm Warning from 6 PM this evening to noon EST Monday for WVZ501-505.
MARINE...Small Craft Advisory until 6 PM EST this evening for ANZ530>543.
Gale Warning from 6 PM this evening to 1 PM EST Monday for ANZ530>543.

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Pond Point
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Sun -- 12:48 AM EST     0.35 feet Low Tide
Sun -- 04:45 AM EST     Moonrise
Sun -- 05:20 AM EST     0.97 feet High Tide
Sun -- 07:13 AM EST     Sunrise
Sun -- 11:40 AM EST     -0.26 feet Low Tide
Sun -- 02:49 PM EST     Moonset
Sun -- 04:41 PM EST     Sunset
Sun -- 06:30 PM EST     1.72 feet High Tide
Tide / Current data from XTide NOT FOR NAVIGATION

Pond Point, Susquehanna River, Maryland, Tide feet

Battery Point
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Sun -- 12:16 AM EST     0.29 feet Low Tide
Sun -- 04:46 AM EST     Moonrise
Sun -- 04:47 AM EST     0.82 feet High Tide
Sun -- 07:14 AM EST     Sunrise
Sun -- 11:08 AM EST     -0.22 feet Low Tide
Sun -- 02:50 PM EST     Moonset
Sun -- 04:41 PM EST     Sunset
Sun -- 05:57 PM EST     1.46 feet High Tide
Tide / Current data from XTide NOT FOR NAVIGATION

Battery Point, Gunpowder River, Maryland, Tide feet

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