Sunday, January19, 2020
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Marine Weather and Tides
Round Hill, VA

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 7:24AMSunset 5:17PM Sunday January 19, 2020 8:52 AM EST (13:52 UTC) Moonrise 2:27AMMoonset 1:05PM Illumination 31% Phase: Waning Crescent; Moon at 24 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- 643 Am Est Sun Jan 19 2020
.small craft advisory in effect through this evening...
Today..NW winds 10 to 15 kt with gusts to 25 kt. Waves 1 ft.
Tonight..NW winds 10 to 15 kt. Gusts up to 25 kt in the evening. Waves 1 ft.
Mon..NW winds 10 to 15 kt with gusts to 20 kt. Waves 1 ft.
Mon night..NW winds 5 to 10 kt. Waves 1 ft.
Tue..NW winds 5 to 10 kt. Waves 1 ft.
Tue night..NW winds 5 kt. Waves less than 1 ft.
Wed..SW winds around 5 kt. Waves 1 ft or less.
Thu..Light winds. Waves 1 ft or less.
ANZ500 643 Am Est Sun Jan 19 2020
Synopsis for the tidal potomac and md portion of the chesapeake bay.. High pressure will build eastward from the northern plains during the first half of the week, then move offshore during the second half of the week. Small craft advisories will likely be needed Monday, and may be needed for portions of the waters Monday night and Tuesday.


7 Day Forecast for Marine Location Near Round Hill, VA
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location: 39.12, -77.77     debug


Area Discussion for - Baltimore, MD/Washington
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FXUS61 KLWX 191127 AFDLWX

Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 627 AM EST Sun Jan 19 2020

SYNOPSIS. After a cold front pushes to the east this morning, an expansive area of high pressure will translate eastward from the northern Plains, becoming centered overhead by Wednesday. High pressure will move offshore during the second half of the week, then low pressure will approach from the central United States.

NEAR TERM /THROUGH TONIGHT/. Low pressure will move eastward today exiting northern New England by this afternoon. A cold front arcing to its southwest will cross the region this morning, ushering in drier air on gusty northwest flow. Wind gusts to around 30 MPH seem likely today, breezy but well shy of Wind Advisory criteria (which is frequent gusts of 46 to 57 MPH for 2 or more hours).

Daytime highs today will be warmer than yesterday despite cold air advection aloft due to more sunshine and downsloping effects. Highs in the upper 30s to mid 40s are expected east of the mountains, with 20s and 30s for the higher terrain. Given the low-level wind trajectories and a ribbon of vorticity aloft, scattered snow showers are likely over the Allegheny at times, particularly this afternoon. A few flurries could hop east of the mountains into the I-81 corridor this afternoon as inversion heights briefly rise above the ridge line, but a lack of stronger upper forcing or very steep lapse rates in the low levels should preclude any more substantial snow shower activity east of the higher terrain today.

A secondary push of cold, dry air will make its way into the Mid-Atlantic tonight. A few flurries or snow showers are possible near the higher terrain, but drier air will overwhelm the column, so accumulations should be minimal. Low temperatures are expected to drop into the teens and lower 20s tonight as the colder air mass pushes in, and with the steady northwest wind, wind chills likely bottom out in the single digits and teens late tonight into early Monday morning. The higher terrain along the Allegheny Front (generally above 3000 feet elevation) will see lower wind chills dipping as low as -10 F or even a pinch lower, but the brevity and localized nature of the threat precluded the issuance of a Wind Chill Advisory on this shift.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/. Breezy and cold conditions continue Monday with highs only in the lower to perhaps briefly middle 30s expected for much of the area (colder in the higher elevations). The good news is that while winds will not be calm by any means, they will become relatively lighter, especially late Monday into Tuesday, taking a bit of a bite out of the wind chills.

Dry air and subsidence associated with building high pressure will lead to nil precipitation chances and very little cloud cover Monday through Tuesday.

LONG TERM /WEDNESDAY THROUGH SATURDAY/. Nearly vertically stacked ridging will move overhead Wednesday and edge east Thursday, so dry weather can be expected. Daytime temperatures will begin moderating back above normal, although overnight lows will remain chilly (teens/20s) due to favorable radiational cooling.

Low pressure will be developing in the central Plains Friday ahead of a digging upper level trough. There's a small chance some precipitation in the warm advection ahead of this system could sneak in late Friday, but the more likely scenario at this time is a Friday night-Saturday period for most of the precipitation as the surface low moves toward the Great Lakes. There is a low probability some of the western valleys could see some wintry precipitation at the onset, but a warming column and lack of classic cold air damming signature greatly deter these chances. Guidance does seem to be trending more toward a closed low solution that could pass overhead later Saturday. This could lead to greater chances of snow in the Appalachians depending on the system evolution, although confidence is very low given the Day-7 timeframe.

AVIATION /12Z SUNDAY THROUGH THURSDAY/. CIGs have lifted to VFR for all terminals except DCA, where they should lift momentarily. NW flow will increase today, 15G25kts, though a few gusts in excess of 30 kts are possible 1) immediately behind a departing cold front this morning right as diurnal mixing increases, generally through 16Z, then again later this afternoon 20-22Z during peak diurnal mixing and as the gradient increases a bit ahead of a secondary cold front approaching from the eastern Great Lakes. Otherwise, VFR SCT- BKN FL050 today into tonight. A flurry can't be ruled out near MRB this afternoon, but no restrictions are anticipated.

Gusts likely subside a bit and become more occasional overnight, before the aforementioned secondary front drops through after 09Z. Winds may take on a bit more of a northerly component Monday morning as they increase in the wake of the front and as diurnal mixing increases. Gusts in excess of 25 kts are possible Monday into Tuesday, but with VFR conditions expected.

VFR conditions and light winds are then expected with high pressure Wednesday into Thursday.

MARINE. Upstream observations indicate a brief surge of 20 to 30 kt gusts moving across northern Virginia into central Maryland. These may reach the middle and upper Potomac and Patapsco/Baltimore Harbor prior to the valid start time of the Small Craft Advisory (14Z/9 AM), but should be brief in nature. Therefore, have covered with a Marine Weather Statement.

Gusty northwest winds in the wake of low pressure departing the northeastern U.S. will persist right through Tuesday. A Small Craft Advisory includes all waters through midnight tonight before the more sheltered tidal Potomac River north of Cobb Island and Baltimore Harbor drop out of the advisory. There will be a secondary push of gusty winds toward daybreak, but for now believed mixing would subside just enough to leave some of these more sheltered waters out of the advisory during the bulk of the overnight.

Gusts in excess of 20 knots will likely linger Monday into Tuesday before high pressure builds overhead causing winds to become lighter. Light winds are expected Wednesday and Thursday as high pressure continues to build overhead.

TIDES/COASTAL FLOODING. South-southwest winds have piled up water in the northern half of the Chesapeake Bay with anomalies exceeding 2 feet from Annapolis northward. A cold front will shift winds this morning, but they will be westerly until veering some tonight. Thus would not expect a sharp drop in water levels, and places like Straits Point and Annapolis could hit at least caution stage again with the upcoming high tide.

LWX WATCHES/WARNINGS/ADVISORIES. DC . None. MD . None. VA . None. WV . None. MARINE . Small Craft Advisory until 6 AM EST Monday for ANZ530>534-537- 539>543. Small Craft Advisory until midnight EST tonight for ANZ535-536- 538.

SYNOPSIS . DHOF NEAR TERM . DHOF SHORT TERM . DHOF LONG TERM . ADS AVIATION . ADS/DHOF MARINE . ADS/DHOF TIDES/COASTAL FLOODING . ADS


Weather Reporting Stations
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Stations Dist Age Wind Air TempWater Temp WavesPressureDewPt
WASD2 - 8594900 - Washington, DC 43 mi52 min 42°F 43°F1009.6 hPa (+1.8)
BSLM2 - Chesapeake Bay, MD 61 mi142 min NNW 1.9 -39°F 1008 hPa
BLTM2 - 8574680 - Baltimore, MD 64 mi58 min 43°F 42°F1008 hPa

Wind History for Washington, DC
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Airport Reports
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AirportDistAgeWind ktVisibilitySky/WeatherTempDewPtHumidityPressure
Leesburg / Godfrey, VA11 mi77 minNW 1510.00 miPartly Cloudy37°F32°F81%1009.8 hPa
Winchester Regional, VA20 mi57 minWNW 15 G 1810.00 miOvercast36°F26°F70%1009.8 hPa
Washington/Dulles International Airport, DC, VA20 mi60 minNW 1410.00 miPartly Cloudy38°F30°F73%1009.6 hPa
Eastern WV Regional Airport/Shepherd Field, WV23 mi59 minW 12 G 1710.00 miOvercast38°F25°F60%1010.8 hPa

Link to 5 minute data for KJYO

Wind History from JYO (wind in knots)
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N7NW10N7N8N5N3NE4NE3CalmCalmCalmCalmCalmCalmCalmCalmS7S11S6S8
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Tide / Current Tables for Chain Bridge, D.C.
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Chain Bridge
Click for Map
Sun -- 02:24 AM EST     Moonrise
Sun -- 03:30 AM EST     2.49 feet High Tide
Sun -- 07:24 AM EST     Sunrise
Sun -- 10:01 AM EST     -0.23 feet Low Tide
Sun -- 01:02 PM EST     Moonset
Sun -- 03:55 PM EST     2.87 feet High Tide
Sun -- 05:14 PM EST     Sunset
Sun -- 11:00 PM EST     -0.20 feet Low Tide
Tide / Current data from XTide NOT FOR NAVIGATION
Sorry tide depth graphs only, please select another station.

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0.71.52.12.42.421.40.80.3-0.1-0.2-00.61.52.32.72.92.62.11.50.90.50-0.2

Tide / Current Tables for Chain Bridge, one mile below, D.C.
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Chain Bridge
Click for Map
Sun -- 02:24 AM EST     Moonrise
Sun -- 03:25 AM EST     2.49 feet High Tide
Sun -- 07:24 AM EST     Sunrise
Sun -- 09:56 AM EST     -0.23 feet Low Tide
Sun -- 01:02 PM EST     Moonset
Sun -- 03:50 PM EST     2.87 feet High Tide
Sun -- 05:14 PM EST     Sunset
Sun -- 10:55 PM EST     -0.20 feet Low Tide
Tide / Current data from XTide NOT FOR NAVIGATION
Sorry tide depth graphs only, please select another station.

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0.81.62.22.52.421.40.80.2-0.1-0.200.71.62.32.82.92.62.11.50.90.4-0-0.2

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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Other links: Northern Pacific     Contential US     Full GOES-East
Wind Forecast for Baltimore, MD/Washington (8,2,3,4)
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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.