Monday, December9, 2019
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Marine Weather and Tides
Broadlands, VA

Version 3.4
NOTICE
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.
6/2/2019. Many thanks to a user for reporting an error on one of the Edit pages. The switch to PHP 7.2 caused many pages that previously worked to quit working. I fixed many but I still depend on users to report ones I missed. Please report errors HERE or send an email to me at L-36.com. Allen

Sunrise 7:15AMSunset 4:48PM Monday December 9, 2019 11:26 PM EST (04:26 UTC) Moonrise 3:24PMMoonset 4:26AM Illumination 97% Phase: Waxing Gibbous; Moon at 13 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- 938 Pm Est Mon Dec 9 2019
.small craft advisory in effect until 6 am est Tuesday...
Rest of tonight..SW winds 15 kt with gusts to 20 kt. Waves 1 ft. Scattered showers late this evening, then isolated showers.
Tue..W winds 5 to 10 kt. Waves 1 ft. Showers. Patchy fog. Vsby 1 to 3 nm.
Tue night..N winds 5 to 10 kt. Waves 1 ft. Rain and snow. Patchy fog. Vsby 1 to 3 nm.
Wed..NW winds 5 kt. Waves less than 1 ft. Snow likely. Patchy fog.
Wed night..NW winds 5 kt. Waves less than 1 ft.
Thu..NE winds around 5 kt. Waves 1 ft.
Thu night..NE winds around 5 kt. Waves 1 ft.
Fri..E winds around 5 kt. Waves 1 ft. A chance of rain through the day, then showers likely through the night.
Sat..W winds around 5 kt. Waves 1 ft. Showers likely through the day, then a chance of showers through the night.
ANZ500 938 Pm Est Mon Dec 9 2019
Synopsis for the tidal potomac and md portion of the chesapeake bay.. Low pressure will move from the great lakes into southeastern canada overnight, dragging its trailing cold front through the region Tuesday into Wednesday. High pressure will follow Wednesday night through Thursday. Small craft advisories will likely be needed Tuesday night and Wednesday.


7 Day Forecast for Marine Location Near Broadlands, VA
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location: 39.02, -77.52     debug


Area Discussion for - Baltimore, MD/Washington
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FXUS61 KLWX 100226 AFDLWX

Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 926 PM EST Mon Dec 9 2019

SYNOPSIS. Low pressure will move from the Great Lakes into Quebec overnight, dragging its trailing cold front through the region Tuesday. High pressure will build into the region late Tuesday night and remain through Thursday, before shifting offshore of New England as low pressure develops over and approaches from the southeastern United States.

NEAR TERM /THROUGH TUESDAY/. KLWX WSR-88D at 0130Z shows scattered light showers primarily east of Blue Ridge. Short-range HREF and HRRR has these scattered showers becoming more isolated as the overnight continues, with the overwhelming majority of the CWA staying dry between midnight and daybreak. Temperatures are not going to change much overnight, as low level moist advection and southerly flow keep pumping in warmer air. This will result in overnight lows 5-10 deg F above average. Gusty surface winds before midnight as evidenced by numerous surface reports throughout the CWA at 01Z of G15-25KTS, caused by a 60KT H85 jet which was directly overhead the CWA at 10/00Z. This low level jet will eject northeastward towards Cape Cod by midnight, and the winds will slacken after midnight.

SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/. (02Z Update) . Rain showers will develop Tuesday morning, and will be prevalent by Noon across the entire CWA, especially along and east of Interstate 95. The cold front will pass through the area on Tuesday afternoon, which will start to filter in colder air. The 18Z ECMWF continues to be consistent with its prior 4 model runs with measurable snow across much of the CWA Tuesday night. There will be a brief lull in rainfall late tomorrow afternoon and early evening, before the region begins to feel the effects and influence of the right rear quadrant of a 170KT H3 jet which will be optimally positioned late Tuesday night providing jet induced dynamics. By 06Z Wed, the column should be cold enough to support all snow west of a line from Bel Air-Damascus-Sterling-Harrisonburg. Any pcpn that falls after 06Z west of this line will likely be all snow. East of this line, there will be a gradual transition from rain to a mixture to finally all snow by daybreak Wednesday. Accumulations along and east of I-95 will be limited as the race for the cold air to arrive in time before the precipitation departs will be on.

There will likely be a sweet spot in this colder region north and west of the Balt/Wash metro areas where 2-3 inches could accumulate on grassy surfaces, i.e., near the Catoctins, northern portions of Carroll, Baltimore, and Harford Counties, and along the Blue Ridge. Impact-wise, I am concerned about I-70 from eastern Frederick County to Hagerstown, and the confluence of other high-speed roads around Frederick MD, including the I-270 corridor from Frederick to Rockville. Motorists on the roads in these areas between midnight and daybreak will be prone to slick roads and low visibilities. The one thing that is working in favor of lesser accumulations on roadways is that temps will max out at least mid-50s CWA-wide today, and along and east of I-95 will be hovering in the lower 60s. I do think that snowfall early Wednesday morning will make its way to the Chesapeake, although the surface temps will still be AOA freezing, thus very unlikely to stick on roadways. I have updated the snow graphics reflecting grassy accumulations to the Bay, and slightly increased snowfall totals north and west of the major metro areas Reminder. official NWS snowfall forecasts are for accumulations on whiteboards/grassy areas, and not on road surfaces./End 02Z update/

The latest model guidance has honed in on the 10:00AM to 4:00PM window for greatest coverage of shower activity Tuesday, as low level convergence increases along an eastward advancing cold front and PVA associated with another mid level shortwave pivot across. Showers will probably become a bit less widespread for a time during the late afternoon and evening following the frontal passage, but coverage is expected to increase again by late evening into the overnight in concert with RRQ jet dynamics associated with a very strong upper jet.

Since the low level front will have passed by Tuesday night, temperatures will begin to cool. As such, rain is expected to change to snow. There is still uncertainty in the timing of temperatures becoming cold enough for snow, especially east of the Blue Ridge where downsloping and compressional warming effects tend to be most notable. Even when precipitation changes to snow, surface temperatures will likely be near or above freezing, so snow may have trouble sticking in the lower elevations. Overall, the setup remains largely unchanged, with typical run to run and model to model variability noted. The highest confidence in snowfall accumulations will be over the higher terrain (above about 1000 feet), with the higher elevations of north-central/northwestern Virginia likely to see the highest totals.

Even though boundary layer temperatures are expected to be marginal in the lower elevations and especially in the I-95 corridor, the timing of wintry precipitation lines up with the Wednesday morning commute, and the powerful mid/upper jet dynamics may result in localized heavier bands of precipitation, beneath which snowfall rates could overcome surface temps and result in accumulation even on paved surfaces.

Precipitation should come to an end by midday Wednesday, with gusty northwest winds ushering in an Arctic airmass in its wake.

LONG TERM /THURSDAY THROUGH MONDAY/. Guidance overall is in good agreement with the synoptic pattern concerning the long term. A strong area of high pressure moves eastward out of the Great Lakes region and extends down the majority of the Eastern Seaboard. The resultant is dry yet chilly conditions expected for Thursday. At the same time, low pressure develops over the Gulf of Mexico and will begin to lift northeastward late Thursday night into Friday.

While guidance is in better agreement about the timing of precip, there is still some spread in regards to timing, track and temperatures. The GFS/GEFS bring precipitation into the CWA by Friday morning, while the ECMWF/EPS delay precip onset by about 6 hours. Interesting to note that today's 12Z ECMWF suite advanced the precip by about 6 hours, compared to the 12 hour difference (from the GFS) it showed yesterday. Therefore, there is better confidence that precip onset will occur by Friday afternoon. With the chilly air mass in place, some wintry precipitation (freezing rain), will be possible at the onset, mainly near and west of the Blue Ridge. Elsewhere, mainly plain rain is most likely.

The low will exit the region by early Saturday morning with some partial clearing expected for the afternoon. Dry weather persists through Monday as temperatures remain slightly on the cooler side of normal.

AVIATION /02Z TUESDAY THROUGH SATURDAY/. IFR CIGS will prevail through 05Z/midnight then improve to LIFR and remain through daybreak. Winds should start to relax too after 05Z as the H85 ejects northeastward.

Latest guidance pegs the 15-21Z window Tuesday for most likely showers and sub-VFR CIGs/VSBYs. A brief respite is anticipated Tuesday evening, before precipitation re-develops and changes to snow after midnight. The most likely terminal to see accumulation is MRB, least likely at CHO/DCA, though there could be a quick coating even on paved surfaces at any terminal if a localized heavier band of snow moves overhead, overcoming marginal surface temperatures.

VFR returns by midday Wednesday with gusty NW winds. Another round of rain seems definite Friday afternoon into Saturday as coastal low pressure develops to the southwest and lifts northeast. Expect IFR conditions in moderate rain Fri night and Saturday. Mixed pcpn possible mainly near MRB.

MARINE. Winds will continue to blow SCA overnight as the H85 jet impacts continue. There will likely be a lull in the winds Tuesday, so the headline drops to just the lower most Maryland portion of the Chesapeake Bay and lower tidal Potomac. Winds likely increase in NW flow behind a cold front Tuesday night and especially Wednesday.

Winds lighten Wednesday night through Thursday night as high pressure builds overhead.

SCA conditions possible Friday into Saturday as pressure gradient tightens in advance of a coastal low pressure lifting northeast.

LWX WATCHES/WARNINGS/ADVISORIES. DC . None. MD . None. VA . None. WV . None. MARINE . Small Craft Advisory until 10 AM EST Tuesday for ANZ531>533- 538>542. Small Craft Advisory until 6 PM EST Tuesday for ANZ534-537-543. Small Craft Advisory until 6 AM EST Tuesday for ANZ530. Small Craft Advisory until 6 AM EST Tuesday for ANZ535-536.

SYNOPSIS . Lee NEAR TERM . Lee SHORT TERM . Lee(update)/DHOF LONG TERM . MSS AVIATION . LFR/DHOF MARINE . LFR/DHOF


Weather Reporting Stations
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Stations Dist Age Wind Air TempWater Temp WavesPressureDewPt
WASD2 - 8594900 - Washington, DC 28 mi56 min SSW 11 G 14 51°F 44°F1010.1 hPa
BSLM2 - Chesapeake Bay, MD 46 mi116 min SSW 9.9 55°F 1009 hPa53°F
BLTM2 - 8574680 - Baltimore, MD 53 mi62 min W 8.9 G 18 53°F 45°F1008.5 hPa

Wind History for Washington, DC
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Airport Reports
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AirportDistAgeWind ktVisibilitySky/WeatherTempDewPtHumidityPressure
Leesburg / Godfrey, VA5 mi31 minSSW 9 G 1410.00 miPartly Cloudy45°F44°F100%1009.5 hPa
Washington/Dulles International Airport, DC, VA6 mi34 minSSW 18 G 2510.00 miOvercast and Breezy52°F48°F86%1009.1 hPa
Manassas, Manassas Regional Airport/Harry P. Davis Field, VA21 mi30 minSSW 910.00 miOvercast53°F48°F86%1010.4 hPa
Gaithersburg - Montgomery County Airport, MD21 mi30 minSSW 10 G 1610.00 miOvercast51°F48°F92%1010.7 hPa

Link to 5 minute data for KJYO

Wind History from JYO (wind in knots)
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Tide / Current Tables for Chain Bridge, D.C.
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Chain Bridge
Click for Map
Mon -- 12:37 AM EST     0.09 feet Low Tide
Mon -- 04:24 AM EST     Moonset
Mon -- 06:21 AM EST     2.50 feet High Tide
Mon -- 07:15 AM EST     Sunrise
Mon -- 12:29 PM EST     -0.02 feet Low Tide
Mon -- 03:21 PM EST     Moonrise
Mon -- 04:46 PM EST     Sunset
Mon -- 06:34 PM EST     2.85 feet High Tide
Tide / Current data from XTide NOT FOR NAVIGATION
Sorry tide depth graphs only, please select another station.

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0.20.10.51.11.82.22.52.421.30.70.3000.41.11.92.52.82.82.51.91.30.7

Tide / Current Tables for Chain Bridge, one mile below, D.C.
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Chain Bridge
Click for Map
Mon -- 12:32 AM EST     0.09 feet Low Tide
Mon -- 04:24 AM EST     Moonset
Mon -- 06:16 AM EST     2.50 feet High Tide
Mon -- 07:15 AM EST     Sunrise
Mon -- 12:24 PM EST     -0.02 feet Low Tide
Mon -- 03:21 PM EST     Moonrise
Mon -- 04:46 PM EST     Sunset
Mon -- 06:29 PM EST     2.85 feet High Tide
Tide / Current data from XTide NOT FOR NAVIGATION
Sorry tide depth graphs only, please select another station.

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0.10.10.51.21.82.32.52.41.91.30.70.2000.41.222.52.82.82.41.81.20.7

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 (23,6,7,8)
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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 numerious 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.