Thursday, October21, 2021
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Marine Weather and Tides
Poolesville, MD

Version 3.4
NOTICE
3/30/2021 -- ANZ330 has been split into ANZ331 and ANZ332. Click EDIT in Marine Forecast and select your new zone.
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 7:25AMSunset 6:24PM Thursday October 21, 2021 4:40 PM EDT (20:40 UTC) Moonrise 6:07PMMoonset 7:16AM Illumination 99% Phase: Waning Gibbous; Moon at 16 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- 436 Pm Edt Thu Oct 21 2021
Rest of this afternoon..S winds 10 kt. Waves 1 ft.
Tonight..SW winds 5 to 10 kt with gusts to 20 kt. Waves 1 ft.
Fri..NW winds 5 kt. Waves less than 1 ft.
Fri night..NW winds around 5 kt. Waves 1 ft.
Sat..NW winds around 5 kt. Waves 1 ft.
Sat night..NW winds around 5 kt. Waves 1 ft.
Sun..S winds around 5 kt. Waves 1 ft.
Mon..E winds 5 kt. Waves less than 1 ft. A chance of showers through the night.
ANZ500 436 Pm Edt Thu Oct 21 2021
Synopsis for the tidal potomac and md portion of the chesapeake bay.. High pressure will reside offshore through this evening as a cold front approaches from the west. The front is expected to cross the waters by early Friday morning. Then, a second front is slated to cross the waters Friday night. High pressure is slated to build over the area through the weekend.


7 Day Forecast for Marine Location Near Poolesville, MD
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location: 39.18, -77.48     debug


Area Discussion for - Baltimore, MD/Washington
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FXUS61 KLWX 211848 AFDLWX

Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 248 PM EDT Thu Oct 21 2021

SYNOPSIS. High pressure off to our south and east will continue to shift further offshore as a cold front approaches from the west. The front will cross the region overnight into Friday, followed by an additional weaker front on Friday. Dry and seasonable temperatures are slated for the weekend. However our next system may arrive by early next week.

NEAR TERM /THROUGH TONIGHT/. A potent upper low is swinging across the Great Lakes at this time, pushing east. This will slide by to our north tonight as an area of low pressure underneath it drags a cold front through the area. The cold front is currently located over western OH and gradually moving towards western MD. There are 2 distinct lines of convection, with one being along the front and one out ahead of the front. Lots of shear present with this system (~40-50 kts)as it moves in our direction, but not much in the way of instability (<500 J/kg west of the Alleghenies). As this convection moves towards the area, instability may build a little more out ahead of the first line, so could bring down some gusty winds as it approaches western MD. However, do think we are going to run out of daylight, thus limiting any severe threat for our area. If there is a threat, it is Garrett County, MD. Anywhere further east, and there will likely be no instability to work with.

The cold front will push through overnight, and a secondary shortwave from North Carolina could produce a stray shower or two across southern Maryland overnight through Friday morning.

SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/. Closed upper level low over the Great Lakes will continue to retrograde in place Friday. As a result, a second surge of shortwave advection will move eastward across the region. Any precip chances seem minimal on Friday, with the exception of some upslope showers across the Alleghenies. The low will slowly shift northward on Saturday as high pressure returns for the weekend.

Upper trough is still present to our north on Saturday, with shortwave energy exiting the region throughout the day as high pressure builds in at the surface. This should lead to a quiet day with perhaps some high clouds around, especially along the MD/PA border and along/west of the Allegheny Front. Cooler temperatures expected, with highs in the 60s, which is around average for mid-late October.

LONG TERM /SUNDAY THROUGH WEDNESDAY/. The long term period will start off with a large upper low spiraling over Ontario and Quebec. Meanwhile, a potent shortwave will eject from the Rockies toward the Central Plains. At the surface, a warm front will lift northward through the area. Guidance has trended toward most of the area staying dry on Sunday, with the bulk of the warm advection precipitation staying to the north of the front across PA.

Forecast uncertainty increases substantially heading into Monday, as the aforementioned shortwave tracks further east, along with a weak area of low pressure. Meanwhile, high pressure will strengthen well to our north over Canada. The positioning of the aforementioned boundary will depend on the relative strength of these two features, with some solutions crashing the boundary southward as a backdoor cold front, and other solutions keeping us in the warm sector on Monday. As a result, ensemble guidance shows substantial spread, with individual members ranging from high temperatures in the 40s to highs in the upper 70s. There are substantial differences with respect to the timing of precipitation as well, with some solutions producing rain starting late Monday afternoon into Monday Night, and others holding off until Tuesday. Spread in model guidance remains substantial through Wednesday. As a result, the long term forecast is much lower confidence than normal.

AVIATION /18Z THURSDAY THROUGH TUESDAY/. Light S/SSW flow continues through the evening hours with VFR conditions expected. A cold front will swing through the region overnight tonight, resulting in a wind shift out of the NW. Some showers may make it to MRB, but likely not much of significance. Otherwise, remaining dry and VFR at all terminals overnight. Some LLWS possible ahead of the frontal passage at the northern terminals (MRB and MTN), and potentially IAD/BWI/DCA as well.

Prevailing VFR conditions are expected on Saturday and Sunday. Drops to sub-VFR may be possible at times on Monday, but conditions will dependent on both the positioning of showers and a surface front, with sub-VFR conditions more likely to the north of the front.

MARINE. Southerly winds ahead of a cold front that will cross the waters tonight. Winds will uptick with the strongest wind fields clipping the wide waters of the middle portion of the Chesapeake Bay this afternoon. Small Craft Advisory remains in effect for portions of the waters for this uptick in winds.

A second front will approach Friday night, but will be accompanied by a weak pressure gradient. This will continue to support light winds across the waters. Winds should remain below SCA criteria Saturday out of the northwest.

Sub-SCA level winds are expected on Sunday. Winds may approach SCA levels Sunday Night into Monday.

TIDES/COASTAL FLOODING. Anomalies have gradually risen throughout the day today. Most sites have experienced no issues, but Annapolis may reach action stage during this afternoon's high tide cycle. Otherwise, areas should remain below action stage. Winds become more WNW behind a cold front on Friday, allowing anamolies to decrease through the weekend.

LWX WATCHES/WARNINGS/ADVISORIES. DC . None. MD . None. VA . None. WV . None. MARINE . Small Craft Advisory from 6 PM this evening to 4 AM EDT Friday for ANZ531>533-537-539>541. Small Craft Advisory until 6 AM EDT Friday for ANZ534-543.

SYNOPSIS . CJL NEAR TERM . CJL SHORT TERM . CJL/SOUZA LONG TERM . KJP AVIATION . CJL/KJP MARINE . CJL/KJP TIDES/COASTAL FLOODING . CJL


Weather Reporting Stations
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Stations Dist Age Wind Air TempWater Temp WavesPressureDewPt
WASD2 - 8594900 - Washington, DC 32 mi52 min SSW 6G9.9 74°F 67°F1012.3 hPa
BLTM2 - 8574680 - Baltimore, MD 48 mi52 min S 5.1G8 72°F 71°F1012.2 hPa
BSLM2 - Chesapeake Bay, MD 49 mi70 min WSW 5.1 76°F 1013 hPa51°F

Wind History for Washington, DC
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Airport Reports
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AirportDistAgeWind ktVisibilitySky/WeatherTempDewPtHumidityPressure
Leesburg / Godfrey, VA8 mi45 minS 9 G 1510.00 miFair79°F50°F37%1012.9 hPa
Washington/Dulles International Airport, DC, VA15 mi48 minS 710.00 miA Few Clouds76°F49°F39%1012.5 hPa
Gaithersburg - Montgomery County Airport, MD17 mi44 minS 1010.00 miFair75°F50°F42%1014.4 hPa
Frederick Municipal Airport, MD17 mi53 minS 710.00 miFair79°F46°F32%1012.5 hPa

Link to 5 minute data for KJYO

Wind History from JYO (wind in knots)
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Last 24hrW60SW40W300000000000000SE4S5S4S5S12
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Tide / Current Tables for Chain Bridge, D.C.
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Chain Bridge
Click for Map
Thu -- 04:21 AM EDT     0.14 feet Low Tide
Thu -- 07:24 AM EDT     Sunrise
Thu -- 08:14 AM EDT     Moonset
Thu -- 09:57 AM EDT     3.05 feet High Tide
Thu -- 04:21 PM EDT     0.20 feet Low Tide
Thu -- 06:21 PM EDT     Sunset
Thu -- 07:05 PM EDT     Moonrise
Thu -- 10:10 PM EDT     3.35 feet High Tide
Tide / Current data from XTide NOT FOR NAVIGATION
Sorry tide depth graphs only, please select another station.

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Tide / Current Tables for Chain Bridge, one mile below, D.C.
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Chain Bridge
Click for Map
Thu -- 04:16 AM EDT     0.14 feet Low Tide
Thu -- 07:24 AM EDT     Sunrise
Thu -- 08:13 AM EDT     Moonset
Thu -- 09:52 AM EDT     3.05 feet High Tide
Thu -- 04:16 PM EDT     0.20 feet Low Tide
Thu -- 06:21 PM EDT     Sunset
Thu -- 07:05 PM EDT     Moonrise
Thu -- 10:05 PM EDT     3.35 feet High Tide
Tide / Current data from XTide NOT FOR NAVIGATION
Sorry tide depth graphs only, please select another station.

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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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