Thursday, December12, 2019
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Marine Weather and Tides
Ashburn, 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 7:17AMSunset 4:49PM Thursday December 12, 2019 12:38 AM EST (05:38 UTC) Moonrise 5:24PMMoonset 7:36AM Illumination 100% Phase: Full Moon; Moon at 15 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- 937 Pm Est Wed Dec 11 2019
Rest of tonight..NW winds 5 kt. Waves less than 1 ft.
Thu..E winds 5 kt. Waves less than 1 ft.
Thu night..N winds around 5 kt. Waves 1 ft or less.
Fri..NE winds around 5 kt. Waves 1 ft or less. Rain likely.
Fri night..N winds around 5 kt. Waves 1 ft. Rain.
Sat..W winds 5 kt. Waves less than 1 ft. Rain likely.
Sat night..W winds 5 to 10 kt. Waves 1 ft. A chance of showers.
Sun..NW winds 5 to 10 kt. Waves 1 ft.
Mon..E winds around 5 kt. Waves 1 ft. A chance of rain through the day, then rain likely through the night.
ANZ500 937 Pm Est Wed Dec 11 2019
Synopsis for the tidal potomac and md portion of the chesapeake bay.. High pressure will build across the region today through Thursday. Low pressure system developing over the northern gulf of mexico will move northeastward toward the region Friday into Saturday. Small craft advisories may be needed Saturday through Sunday morning


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 120241 AFDLWX

Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 941 PM EST Wed Dec 11 2019

SYNOPSIS. A strong area of high pressure, originating from Canada, will build overhead tonight before shifting to our northeast tomorrow. Meanwhile, an area of low pressure will develop over the Gulf of Mexico Friday and track north across the eastern United States as high pressure departs offshore. Low pressure will then move across the area Saturday, with another area of low pressure approaching Monday into Tuesday.

NEAR TERM /THROUGH THURSDAY/. Strong high pressure will build overhead tonight. With the high originating from Canada, the air mass is quite chilly, with temperatures generally 10 degrees below normal or so. Low temperatures overnight will dip down into the 20s, with the normal colder spots getting into the teens.

With high pressure shifting to our northeast tomorrow, temperatures will remain cool, with highs in the mid 30s to low 40s. No precipitation to speak of though, and winds will be light, so wind chills won't be an issue. Overall, a dry and chilly day across the area.

SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/. High pressure will slide offshore Thursday night, as low pressure develops along the Gulf Coast and heads north toward the region. A wedge of cold air will remain through much of Friday morning, especially in the valleys west of the Blue Ridge. This could create some problems with freezing rain at the onset of the event Friday morning, when warm advection precipitation is likely to begin across the area. The most significant risk of freezing rain appears to be along the I-81 and I-64 corridors, where the precipitation arrives earlier and the cold air lingers the longest. Farther north and east of these areas, thinking that surface temperatures should warm just quick enough to avoid any major issues, but certainly can't rule out some light accumulations north and east of I-64. Right now, generally thinking this will be a light event, with less than a tenth of an inch along the I-81 and I-64 corridors, and perhaps a couple hundredths farther north and east, if conditions line up just right.

Outside of the freezing rain threat comes a soaking rain event areawide starting Friday night, as low pressure moves over the area. Temperatures may actually rise overnight in some spots, but most locations should stay in the 30s and 40s.

LONG TERM /SATURDAY THROUGH WEDNESDAY/. Low pressure overhead Saturday will move off to the north later Saturday morning and afternoon. A soaking rain will be around to start, but a dry slot will work its way into the area during this time, and this may cause a lull in the precipitation. Confidence in timing the lull of precipitation remains low at this time. A second round of precipitation will be possible Saturday evening into early Sunday morning due to forcing by the upper level low passing over our area and the surface low's associated cold front. Some upslope wintry precipitation can be ruled out over and along the higher elevations.

High pressure will build back into our region Sunday through early Monday morning. Clear skies along with cooler temperatures in the mid 40s during the day and the 20s and 30s overnight. A warm front is forecast to lift through our region Monday morning. Overruning precipitation will be possible as this frontal boundary moves through our region. As high pressure is in place over the Northeast US, models have been hinting at a cold air damming situation. As the warm front lifts through our area, this precipitation could potentially fall as wintry precipitation. We will need to continue to track the model trend. Models have the damming setup breaking early Tuesday as the main cold front moves through our area. A brief warm up into the 40s will lead to rain Tuesday afternoon. It looks like the cold front is forecast to fully move through our area by Tuesday evening with cooler temps building back into our area Tuesday overnight into Wednesday.

AVIATION /02Z THURSDAY THROUGH MONDAY/. VFR conditions will continue overnight tonight, with a light wind out of the WNW. VFR conditions will persist tomorrow, with mostly sunny skies and light winds.

A low pressure system will track near our area Friday through Saturday. Showers are expected on Friday, and could lead to sub-VFR conditions. Rain should become steadier Friday Night through early Saturday morning and will likely cause sub-VFR conditions. Rain should dissipate late Saturday into early Sunday. Some showers can't be ruled out with brief restrictions on Sunday, but prevailing VFR conditions expected on Sunday at this time.

MARINE. Small Craft Advisory remains in effect for much of the Bay and the lower Tidal Potomac. Winds will gradually subside overnight, so will keep with the previous Small Craft Advisory for the central Bay and lower Tidal Potomac into Thursday morning.

As coastal low passes near our area, winds will likely reach Small Craft Advisory levels Saturday and Sunday. Small Craft Advisories will likely be needed this weekend.

LWX WATCHES/WARNINGS/ADVISORIES. DC . None. MD . None. VA . None. WV . None. MARINE . Small Craft Advisory until midnight EST tonight for ANZ531>533- 538>541. Small Craft Advisory until noon EST Thursday for ANZ534-537- 543.

SYNOPSIS . CJL/KJP NEAR TERM . CJL/KJP SHORT TERM . CJL/KJP LONG TERM . BJL/JMG AVIATION . CJL/KJP/JMG MARINE . CJL/KJP/JMG


Weather Reporting Stations
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Stations Dist Age Wind Air TempWater Temp WavesPressureDewPt
WASD2 - 8594900 - Washington, DC 26 mi69 min WNW 5.1 G 9.9 35°F 44°F1035.9 hPa
BSLM2 - Chesapeake Bay, MD 44 mi129 min NW 1.9 33°F 1034 hPa19°F
BLTM2 - 8574680 - Baltimore, MD 50 mi69 min NW 2.9 G 6 34°F 46°F1034.9 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 mi47 minW 410.00 miMostly Cloudy31°F16°F54%1035.9 hPa
Leesburg / Godfrey, VA6 mi44 minNW 610.00 miMostly Cloudy30°F21°F69%1035.9 hPa
Gaithersburg - Montgomery County Airport, MD19 mi43 minNW 510.00 miFair29°F17°F61%1037.4 hPa
Manassas, Manassas Regional Airport/Harry P. Davis Field, VA22 mi43 minWNW 310.00 miA Few Clouds30°F19°F66%1037.1 hPa

Link to 5 minute data for KIAD

Wind History from IAD (wind in knots)
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Last 24hrNW12N8NW9NW5NW8W5NW11NW11NW12NW13
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1 day agoS14S13
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S13S13S10S10S10S13SW9S9W5S3NW5W3NW7NW7NW10NW14
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2 days agoCalmCalmSE3CalmCalmCalmSE3CalmS5S5S7S9S10S9S8S10
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Tide / Current Tables for Chain Bridge, D.C.
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Chain Bridge
Click for Map
Thu -- 12:14 AM EST     Full Moon
Thu -- 03:00 AM EST     -0.10 feet Low Tide
Thu -- 07:17 AM EST     Sunrise
Thu -- 07:34 AM EST     Moonset
Thu -- 08:26 AM EST     2.53 feet High Tide
Thu -- 02:44 PM EST     -0.09 feet Low Tide
Thu -- 04:46 PM EST     Sunset
Thu -- 05:22 PM EST     Moonrise
Thu -- 08:28 PM EST     3.04 feet High Tide
Tide / Current data from XTide NOT FOR NAVIGATION
Sorry tide depth graphs only, please select another station.

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0.90.40.1-0.10.10.81.62.22.52.52.11.40.80.3-0-0.10.20.91.82.6332.62

Tide / Current Tables for Chain Bridge, one mile below, D.C.
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Chain Bridge
Click for Map
Thu -- 12:14 AM EST     Full Moon
Thu -- 02:55 AM EST     -0.10 feet Low Tide
Thu -- 07:17 AM EST     Sunrise
Thu -- 07:33 AM EST     Moonset
Thu -- 08:21 AM EST     2.53 feet High Tide
Thu -- 02:39 PM EST     -0.09 feet Low Tide
Thu -- 04:46 PM EST     Sunset
Thu -- 05:22 PM EST     Moonrise
Thu -- 08:23 PM EST     3.04 feet High Tide
Tide / Current data from XTide NOT FOR NAVIGATION
Sorry tide depth graphs only, please select another station.

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0.90.40-0.10.10.81.72.22.52.421.40.80.3-0-0.10.211.92.7332.61.9

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.
Link to Loop

Other links: Northern Pacific     Contential US     Full GOES-East
Wind Forecast for Baltimore, MD/Washington (0,6,7,8)
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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.