Wednesday, May27, 2020
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Marine Weather and Tides
Ashton-Sandy Spring, MD

Version 3.4
NOTICE
12/16/2019 NOAA is having trouble with requests that include wind gusts. I am posting graphs without wind gusts until it gets fixed.
10/9/2019 Updated the Marine Zones.
9/4/2019 Fixed the weather maps due to NOAA moving them.
7/25/2019 New feature in the Airports section gives a link to 5 minute updates for data reports.

Sunrise 5:44AMSunset 8:26PM Wednesday May 27, 2020 9:34 AM EDT (13:34 UTC) Moonrise 8:58AMMoonset 11:58PM Illumination 29% Phase: Waxing Crescent; Moon at 5 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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ANZ538 Patapsco River Including Baltimore Harbor- 735 Am Edt Wed May 27 2020
Today..SE winds 5 kt. Waves less than 1 ft. Areas of dense fog this morning. A slight chance of showers this afternoon. Vsby 1 nm or less this morning.
Tonight..SE winds 5 to 10 kt. Waves 1 ft. Showers likely. Patchy fog. Vsby 1 to 3 nm.
Thu..SE winds 10 kt with gusts to 20 kt. Waves 1 ft. Showers likely with a chance of tstms. Patchy fog. Vsby 1 to 3 nm.
Thu night..S winds 5 to 10 kt. Waves 1 ft. A chance of showers.
Fri..S winds 10 kt. Waves 1 ft. Showers likely with a chance of tstms.
Fri night..S winds 5 to 10 kt. Waves 1 ft. A chance of showers and tstms.
Sat..NW winds 5 to 10 kt. Waves 1 ft or less. A chance of showers and tstms.
Sun..N winds 5 to 10 kt. Waves 1 ft. Winds and waves higher and visibilities lower in and near tstms.
ANZ500 735 Am Edt Wed May 27 2020
Synopsis for the tidal potomac and md portion of the chesapeake bay.. High pressure will migrate further eastward into the atlantic today. Low pressure will move northward from the southeastern us tonight. A cold front will cross the waters late Friday through Saturday. Small craft advisories may be needed Thursday night and Friday.


7 Day Forecast for Marine Location Near Ashton-Sandy Spring, MD
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location: 39.15, -77     debug


Area Discussion for - Baltimore, MD/Washington
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FXUS61 KLWX 271052 AFDLWX

Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 652 AM EDT Wed May 27 2020

SYNOPSIS. High pressure will remain in the western Atlantic today. A tropical wave near the southeast U.S. coast will move north through the Appalachains by Thursday morning. A cold front will slowly approach through the end of the week and will move through our region from the west early Saturday. High pressure will return early next week.

NEAR TERM /THROUGH TONIGHT/. High pressure is located over the Atlantic this morning, with a closed upper low near the Arklatex, and a disorganized tropical wave near the South Carolina coast. Other than higher clouds preventing fog across the west, stratus/fog pattern is similar to yesterday and have issued a Dense Fog Advisory for portions of central and southern Maryland until 10 AM.

Low clouds will lift by midday, but not expecting completely sunny skies as the atmosphere continues to moisten. Can't rule out a spotty shower as this occurs, but most of the area will be dry through the afternoon. There should be enough insolation for highs to reach the mid 70s to around 80.

The tropical wave will track toward the central Appalachians tonight, then be quickly carried to the north by Thursday morning. This will bring increasing chances of rain, especially across the western half of the area. However, the best forcing may slide just south of the area, so QPF trends have been down a bit. Thus, am not confident there will be enough rain in a short enough period of time (instability will be lacking) for a substantive flood threat, so am not issuing a watch at this time. However, can't rule out a few isolated water issues.

SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/. Closed low will start to be absorbed by a digging northern stream trough on Thursday. However, ridging will still retain some influence locally, and there may be some subsidence behind the departing wave. Would not be surprised if the best shower coverage is in the morning, with breaks of sun by midday. That will help temperatures rise into the 80s, and muggy air with dew points near 70 will be in place. So while there is still some potential for showers/storms in the afternoon, any forcing will be subtle, so have doubts on coverage. Have lowered PoPs some, but they may need to be lowered Thursday.

Better chance for showers and thunderstorms will come Friday as large scale trough approaches and heights fall. Even so, the best forcing and surface cold front will remain to our northwest, so may have to rely on features like the terrain and lee trough to initiate storms. Coverage is still uncertain at this time. However, shear has been trending up, especially western half of the area, and there should be moderate instability in the warm/humid airmass. So a few strong/locally severe storms aren't out of the question. Convection should have a diurnal component, though some showers will remain possible through the night as the cold front approaches.

The overarching theme to address is the heavy rain/flooding potential. While precipitable water values will be high with some potential for slow storm motions or even training, coverage of rainfall remains uncertain, so not expecting more than an isolated threat at this time. More details in the hydro section below.

LONG TERM /SATURDAY THROUGH TUESDAY/. The cold front will continue to push off to the south and east early Saturday. Can't rule out some residual showers/thunderstorms into early Saturday afternoon, particularly in central VA/southern MD, where the front may still linger nearby. Highs on Saturday could reach the low 80s. Now, the one caveat here, is that recent guidance seems to be trending a little faster, pushing the front all the way through the area early Saturday. This would likely keep temps a little cooler, as well as speed up precip. Will continue to monitor in the coming days.

Beyond Saturday though, it looks dry and below average, as surface high pressure builds in out of the northwest. Additionally, the region will be within an upper trough, but remaining within the confluence region, so should stay dry most of the time. High temps Sunday through Tuesday will be in the low to mid 70s, which is well below average for late May/early June.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/. Low clouds taking there time moving westward, but still a decent chance of several hours of IFR this morning in low cigs/reduced visibility. Can't rule out dense fog, but stratus more likely. Cigs/vsbys should gradually improve to VFR levels late in the morning into the afternoon, but isolated showers are possible throughout the day. IFR conditions will return quickly this evening as a wave of low pressure moves west of the area. Rain will be possible as well.

Conditions should improve Thursday afternoon, although a few showers/storms could occur. Showers and thunderstorms will be possible again Friday into Friday night.

VFR conditions expected this weekend for the most part. However, showers/storms may linger into Saturday, which could lead to some restrictions at times. However, likelihood of that seems to be decreasing, as the cold front looks to swing through earlier in the day Saturday in latest model guidance. Winds will be out of the NW, gusting up to 15 knots at the most.

MARINE. Low clouds/locally dense fog will be an issue this morning, but winds will be light through the day. Southeast flow starts increasing tonight, so have issued an SCA for the wider waters of the middle bay, which will continue through Thursday. It's possible some other areas may need an SCA, but confidence is low at this time. A few thunderstorms could occur Thursday afternoon/evening, but coverage is expected to be limited.

Winds may continue to approach SCA levels on Friday in southerly flow. Thunderstorms will be possible over the waters Friday into Friday night, with the highest coverage of storms occurring during the afternoon and evening hours. Gusty winds will be possible in association with any of these thunderstorms.

On Saturday, no marine hazards associated with synoptic winds are expected. However, if the cold front is a little slower exiting the area, some showers/storms are possible over the waters Saturday afternoon, particularly in the lower tidal Potomac and central Bay, bordering southern MD.

No marine hazards are expected to linger into Sunday.

HYDROLOGY. While ingredients will be in place through late week for locally heavy rain (e.g., high moisture content, slow storm motions), coverage and amount of rainfall is still in question. Lowest Flash Flood Guidance is in far southwestern portions of the area. Elsewhere, it may take repeated rounds of rain for flooding, and that remains low confidence at this time. Best chance of heavy rainfall totals will be tonight, roughly near and south of I-64. However, highest totals have shifted south some, and am not sure rates will be there to result in flooding. If flooding were to occur, it would likely be more of a small stream issue, with river flooding less likely.

LWX WATCHES/WARNINGS/ADVISORIES. DC . None. MD . Dense Fog Advisory until 10 AM EDT this morning for MDZ006-011- 013-014-016>018-507-508. VA . None. WV . None. MARINE . Small Craft Advisory from 8 PM this evening to 6 PM EDT Thursday for ANZ534-537-543.

SYNOPSIS . ADS NEAR TERM . ADS SHORT TERM . ADS LONG TERM . CJL AVIATION . ADS/CJL MARINE . ADS/CJL HYDROLOGY . ADS


Weather Reporting Stations
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Stations Dist Age Wind Air TempWater Temp WavesPressureDewPt
WASD2 - 8594900 - Washington, DC 19 mi65 min ESE 1.9 G 5.1 67°F 70°F1023.4 hPa
BLTM2 - 8574680 - Baltimore, MD 24 mi65 min ESE 4.1 G 5.1 64°F 68°F1023.1 hPa
FSKM2 - 8574728 - Francis Scott Key Bridge, MD 25 mi65 min E 2.9 G 4.1 63°F 1023.4 hPa
FSNM2 26 mi65 min ENE 2.9 G 4.1 63°F 1023.3 hPa
APAM2 - 8575512 - Annapolis, MD 30 mi65 min 64°F 1023.1 hPa
BSLM2 - Chesapeake Bay, MD 30 mi125 min SE 2.9 1023 hPa
44063 - Annapolis 32 mi41 min 63°F 65°F1023.4 hPa
CPVM2 34 mi65 min 64°F
TPLM2 - Thomas Point, MD 35 mi35 min Calm G 1 62°F 63°F1024.4 hPa (+0.7)62°F
TCBM2 - 8573364 - Tolchester Beach, MD 40 mi77 min E 4.1 G 5.1 62°F 66°F1023.7 hPa

Wind History for Washington, DC
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Airport Reports
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AirportDistAgeWind ktVisibilitySky/WeatherTempDewPtHumidityPressure
Gaithersburg - Montgomery County Airport, MD9 mi39 minESE 510.00 miOvercast68°F64°F90%1024.8 hPa
Baltimore, Baltimore-Washington International Airport, MD18 mi41 minE 53.00 miFog/Mist66°F64°F93%1023 hPa
Washington/Reagan National Airport, DC, VA20 mi43 minN 010.00 miOvercast68°F63°F84%1023.3 hPa
Baltimore, Inner Harbor, MD23 mi41 minno data mi67°F63°F87%1023.5 hPa
Camp Springs / Andrews Air Force Base, MD23 mi39 minESE 410.00 miOvercast65°F64°F100%1023.9 hPa

Link to 5 minute data for KGAI

Wind History from GAI (wind in knots)
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Last 24hr3SE7E33SE7SE9SE6E5SE9SE8SE8SE5E3CalmSE3SE3SE3E3CalmCalmE3Calm4SE5
1 day agoE3CalmCalm3CalmS7SE5E4NE4SE4SE5SE5SE5CalmSE4CalmCalmE3CalmCalmCalmCalmCalmCalm
2 days ago3E54CalmE443SE7SE5SE73SE9S3SE3CalmCalmSE4CalmCalmCalmSE3CalmCalmCalm

Tide / Current Tables for Chain Bridge, D.C.
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Chain Bridge
Click for Map
Wed -- 12:12 AM EDT     Moonset
Wed -- 12:21 AM EDT     2.92 feet High Tide
Wed -- 05:46 AM EDT     Sunrise
Wed -- 06:45 AM EDT     0.58 feet Low Tide
Wed -- 09:58 AM EDT     Moonrise
Wed -- 12:22 PM EDT     3.41 feet High Tide
Wed -- 07:45 PM EDT     0.42 feet Low Tide
Wed -- 08:24 PM EDT     Sunset
Tide / Current data from XTide NOT FOR NAVIGATION
Sorry tide depth graphs only, please select another station.

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2.92.92.521.410.70.60.81.32.233.43.32.92.41.71.20.80.50.40.71.32.1

Tide / Current Tables for Benning Bridge, D.C.
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Benning Bridge
Click for Map
Wed -- 12:11 AM EDT     Moonset
Wed -- 12:17 AM EDT     3.04 feet High Tide
Wed -- 05:46 AM EDT     Sunrise
Wed -- 06:39 AM EDT     0.62 feet Low Tide
Wed -- 09:58 AM EDT     Moonrise
Wed -- 12:18 PM EDT     3.54 feet High Tide
Wed -- 07:39 PM EDT     0.44 feet Low Tide
Wed -- 08:24 PM EDT     Sunset
Tide / Current data from XTide NOT FOR NAVIGATION
Sorry tide depth graphs only, please select another station.

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32.92.621.410.70.60.91.52.43.23.53.432.41.81.20.80.50.50.81.52.3

Weather Map
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wmap_A
GEOS Local Image of    EDIT
NOTE: East coast views moved to GEOS-16. They are experimental and not well supported by NOAA so they may not be correct so be warned. This change required redoing a large amount of the GOES code. If the image you are expecting is not showing, please let me know. You may need to use the EDIT function to update your location.
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Wind Forecast for Baltimore, MD/Washington (9,2,3,4)
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Ground Weather Radar Station Sterling, VA
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The information on this web site has not been checked for accuracy. It is for entertainment purposes only and should be independently verified before using for any other reason. There are five sources. 1) Documents and manuals from a variety of sources. These have not been checked for accuracy and in many cases have not even been read by anyone associated with L-36.com. I have no idea of they are useful or accurate, I leave that to the reader. 2) Articles others have written and submitted. If you have questions on these, please contact the author. 3) Articles that represent my personal opinions. These are intended to promote thought and for entertainment. These are not intended to be fact, they are my opinions. 4) Small programs that generate result presented on a web page. Like any computer program, these may and in some cases do have errors. Almost all of these also make simplifying assumptions so they are not totally accurate even if there are no errors. Please verify all results. 5) Weather information is from numerous of sources and is presented automatically. It is not checked for accuracy either by anyone at L-36.com or by the source which is typically the US Government. See the NOAA web site for their disclaimer. Finally, tide and current data on this site is from 2007 and 2008 data bases, which may contain even older data. Changes in harbors due to building or dredging change tides and currents and for that reason many of the locations presented are no longer supported by newer data bases. For example, there is very little tidal current data in newer data bases so current data is likely wrong to some extent. This data is NOT FOR NAVIGATION. See the XTide disclaimer for details. In addition, tide and current are influenced by storms, river flow, and other factors beyond the ability of any predictive program.