Sunday, April18, 2021
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Marine Weather and Tides
Ashburn, VA

Version 3.4
NOTICE
1/26/2021 -- The West Coast Satellite images havd been updated. They now use GEOS-17.
1/1/2021 -- The 7 day forecast are now working well. Thank you NOAA for your support.

Sunrise 6:26AMSunset 7:51PM Sunday April 18, 2021 2:03 AM EDT (06:03 UTC) Moonrise 9:35AMMoonset 12:15AM Illumination 37% Phase: Waxing Crescent; Moon at 6 days in cycle
NOTE: Some of the data on this page has not been verified and should be used with that in mind. It may and occasionally will, be wrong. The tide reports are by xtide and are NOT FOR NAVIGATION.
Marine Forecasts
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ANZ535 Tidal Potomac From Key Bridge To Indian Head- 158 Am Edt Sun Apr 18 2021
Overnight..N winds 5 kt. Waves less than 1 ft. A slight chance of showers.
Sun..W winds around 5 kt. Waves 1 ft.
Sun night..SW winds 5 kt. Waves less than 1 ft. A chance of showers.
Mon..W winds 5 kt. Waves less than 1 ft. A chance of showers.
Mon night..SW winds around 5 kt. Waves 1 ft or less.
Tue..SW winds 5 to 10 kt. Waves 1 ft.
Tue night..S winds 5 to 10 kt. Waves 1 ft.
Wed..W winds 10 to 15 kt. Waves 1 ft. A chance of showers in the morning, then showers likely through the night.
Thu..W winds 10 to 15 kt. Waves 1 ft.
ANZ500 158 Am Edt Sun Apr 18 2021
Synopsis for the tidal potomac and md portion of the chesapeake bay.. A broad area of low pressure will migrate from west to east near or south of the middle atlantic Sunday into Monday. High pressure will develop to the south Tuesday and a strong cold front will pass through Wednesday. A small craft advisory may be needed Tuesday. A gale warning may be needed for portions of the waters Wednesday afternoon into Wednesday night.


7 Day Forecast for Marine Location Near Ashburn, VA
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location: 39.03, -77.47     debug


Area Discussion for - Baltimore, MD/Washington
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FXUS61 KLWX 180052 AFDLWX

Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 852 PM EDT Sat Apr 17 2021

SYNOPSIS. A series of upper-level disturbances will pass through the area tonight through Monday. Low pressure will develop in the Ohio Valley on Tuesday and push a strong cold front across the area Wednesday. High pressure will build in from the west for the latter part of the week..

NEAR TERM /THROUGH SUNDAY/. Vertically stacked low pressure is located off the New England coast this evening. Various shortwave troughs are embedded in broader troughiness that extends back to another upper low near Utah. The surface pressure pattern is fairly weak, with no substantial storm systems expected for the next few days.

Between moisture/stratocumulus embedded in northwest flow, and mid level clouds ahead of a shortwave in the Ohio Valley, skies have clouded up for most areas and will remain that way through this evening. As the trough progresses eastward, some showers/sprinkles have spread across the area this evening south of I-66/US-50. HRRR/RAP have consistently been more generous with QPF, and did bump up PoPs a little, but ultimately it may end up along the lines of "numerous sprinkles with some locations seeing a few hundredths of rain" as the lower part of the atmosphere will remain somewhat dry.

Skies will gradually clear from west to east late tonight with any light showers exiting southern Maryland. Between the clouds and slightly higher dewpoints, don't think frost will be a concern. However, there could be some patchy fog across southern parts of the area, especially anywhere that sees rain. Lows will be in the mid 30s to mid 40s.

SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/. After a mostly sunny start on Sunday, clouds will increase again ahead of the next trough. With someone weak forcing though (more amplified shortwave still well to the west), models are inconsistent on how much precipitation can form. The highest chances appear to be across the Shenandoah Valley into central Virginia, where perhaps a little weak instability can develop. Did allow a slight chance of thunder in this area per NBM probabilities. However, it could just as easily turn out dry in many areas, so limited PoPs to the chance category. Temperatures may be slightly higher, with 60s for most.

For Sunday night into Monday, the shortwave will progress eastward across the area, but with moisture generally limited to the mid levels. Therefore, only a few light showers or sprinkles are expected for most. There is still some potential for an area of low pressure to develop to our south, which could bring better chances of rainfall -- especially southeast of I-95 from late Sunday night into Monday morning. Kept PoPs low for now though since there's not a lot of support for this solution. Skies should be clearing by afternoon though, which could allow some areas to reach into the 70s.

Shortwave ridging will allow dry conditions for Monday night with near to slightly above normal temperatures.

LONG TERM /TUESDAY THROUGH SATURDAY/. Southerly flow will develop ahead of an approaching cold front on Tuesday making it the warmest day of the week. Most of Tuesday is likely dry, but as moisture increases ahead of the cold front, a few rain showers cannot be ruled out late afternoon into the evening mainly west of the Blue Ridge.

The aforementioned surface cold front is currently anticipated to move through the region during the day on Wednesday. The dynamics have trended more favorable with this frontal passage for thunderstorms with the parent upper-level trough becoming more negatively tilted. However, relatively low amounts of instability will be the main limiting factor for thunderstorms Wednesday. That being said, a line of heavier rain with gusty winds is still certainly plausible along the front.

The winds increase Wednesday night into Thursday as temperatures plummet behind the front. Sustained winds out of the northwest of 20- 25 mph with gusts upwards of 30-40 mph seem increasingly likely as the upper-level low sits nearby and a tight pressure gradient exists. Late season upslope snow showers are possible Wednesday night across the favored higher terrain of the Allegheny Front and could produce accumulations along the highest ridges.

After below normal temperatures Thursday due to the lingering upper- level trough, temperatures should rebound closer to average for highs Friday as high pressure builds.

AVIATION /01Z SUNDAY THROUGH THURSDAY/. VFR ceilings in stratocumulus likely continue through part of tonight with light northwest winds. Some guidance shows fog potential at CHO tonight as skies clear, but am not sure that will happen unless it rains.

Additional disturbances will cross the area Sunday through Monday morning. Any light rain showers or sprinkles would likely have little impact. A few sources of guidance hint at fog or low clouds, especially for CHO, Sunday night, but this is far from certain. VFR conditions with light winds are expected Monday night.

VFR conditions much of Tuesday under a southerly flow. Showers possible Wednesday as a cold front moves through. Strong northwest winds behind the cold front Wednesday night into much of the day on Thursday.

MARINE. Weak surface pressure pattern is expected through Monday. Winds will largely be out of the northwest or west, but could shift to the south at times as weak troughs cross the area. Am not expecting any Small Craft Advisories at this time.

SCA conditions become possible Tuesday as southerly winds develop ahead of a cold front.

The winds will quickly shift from the south to the northwest Wednesday as the cold front passes. This time frame will need to be monitored for potential Special Marine Warnings for gusty showers along the front. The winds remain strong out of the northwest Wednesday night before relaxing some on Thursday. A Gale Warning is possible for portions of the waters Wednesday afternoon into Wednesday night with a Small Craft Advisory likely being extended into Thursday.

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

SYNOPSIS . ADS NEAR TERM . ADS/RCM SHORT TERM . ADS LONG TERM . CPB AVIATION . ADS/CPB/RCM MARINE . ADS/CPB/RCM


Weather Reporting Stations
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Stations Dist Age Wind Air TempWater Temp WavesPressureDewPt
WASD2 - 8594900 - Washington, DC 26 mi46 min WNW 1.9 G 2.9 54°F 60°F1011.8 hPa
BLTM2 - 8574680 - Baltimore, MD 50 mi46 min NNW 1.9 G 4.1 51°F 52°F1010.9 hPa

Wind History for Washington, DC
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Airport Reports
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AirportDistAgeWind ktVisibilitySky/WeatherTempDewPtHumidityPressure
Washington/Dulles International Airport, DC, VA5 mi72 minN 010.00 miMostly Cloudy48°F40°F74%1011.9 hPa
Leesburg / Godfrey, VA6 mi69 minW 310.00 miPartly Cloudy43°F41°F93%1012.5 hPa
Gaithersburg - Montgomery County Airport, MD19 mi68 minN 010.00 miA Few Clouds45°F38°F77%1013.5 hPa
Manassas, Manassas Regional Airport/Harry P. Davis Field, VA22 mi68 minN 010.00 miOvercast52°F40°F64%1012.5 hPa

Link to 5 minute data for KIAD

Wind History from IAD (wind in knots)
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2 days ago54CalmCalmW5NW9NW11NW12
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Tide / Current Tables for Chain Bridge, D.C.
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Chain Bridge
Click for Map
Sun -- 01:13 AM EDT     Moonset
Sun -- 01:32 AM EDT     2.78 feet High Tide
Sun -- 06:27 AM EDT     Sunrise
Sun -- 07:30 AM EDT     0.60 feet Low Tide
Sun -- 10:33 AM EDT     Moonrise
Sun -- 01:22 PM EDT     3.16 feet High Tide
Sun -- 07:48 PM EDT     Sunset
Sun -- 08:31 PM EDT     0.59 feet Low Tide
Tide / Current data from XTide NOT FOR NAVIGATION
Sorry tide depth graphs only, please select another station.

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2.52.72.82.521.40.90.60.60.91.42.22.83.13.12.82.31.71.20.80.60.60.81.4

Tide / Current Tables for Chain Bridge, one mile below, D.C.
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Chain Bridge
Click for Map
Sun -- 01:13 AM EDT     Moonset
Sun -- 01:27 AM EDT     2.78 feet High Tide
Sun -- 06:27 AM EDT     Sunrise
Sun -- 07:25 AM EDT     0.60 feet Low Tide
Sun -- 10:33 AM EDT     Moonrise
Sun -- 01:17 PM EDT     3.16 feet High Tide
Sun -- 07:48 PM EDT     Sunset
Sun -- 08:26 PM EDT     0.59 feet Low Tide
Tide / Current data from XTide NOT FOR NAVIGATION
Sorry tide depth graphs only, please select another station.

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2.52.82.72.51.91.40.90.60.60.91.42.22.93.13.12.82.21.71.20.80.60.60.91.5

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NOTE: This section has been updated as of 1/26/2021. If the image you are expecting is not showing, please let me know. You may use the EDIT function to update your location.
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