Saturday, December14, 2019
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Marine Weather and Tides
Mercersburg, PA

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 7:22AMSunset 4:48PM Saturday December 14, 2019 7:39 AM EST (12:39 UTC) Moonrise 7:21PMMoonset 9:39AM Illumination 92% Phase: Waning Gibbous; Moon at 17 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- 637 Am Est Sat Dec 14 2019
.small craft advisory in effect from 4 pm est this afternoon through Sunday afternoon...
Today..E winds 5 kt...becoming sw 10 to 15 kt with gusts to 20 kt this afternoon. Waves 1 ft or less. Areas of fog this morning. A chance of rain this morning, then rain likely this afternoon. Vsby 1 to 3 nm this morning.
Tonight..W winds 10 to 15 kt with gusts to 25 kt. Waves 1 to 2 ft.
Sun..W winds 10 to 15 kt with gusts to 20 kt. Waves 1 ft.
Sun night..NW winds 5 to 10 kt. Waves 1 ft.
Mon..E winds 5 kt. Waves less than 1 ft. A chance of rain and snow or sleet.
Mon night..S winds 5 to 10 kt. Waves 1 ft. A chance of rain.
Tue..NW winds 5 to 10 kt. Waves 1 ft. Showers likely through the day.
Wed..NW winds 10 to 15 kt. Waves 1 to 2 ft.
ANZ500 637 Am Est Sat Dec 14 2019
Synopsis for the tidal potomac and md portion of the chesapeake bay.. Low pressure will move northeast of the region today. High pressure will briefly build overhead for Sunday before low pressure impacts the area Monday. The cold front associated with this low will pass through Tuesday. Small craft advisories may be needed again on Tuesday.


7 Day Forecast for Marine Location Near Mercersburg , PA
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location: 39.79, -77.93     debug


Area Discussion for - State College, PA
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FXUS61 KCTP 141230 AFDCTP

Area Forecast Discussion National Weather Service State College PA 730 AM EST Sat Dec 14 2019

SYNOPSIS. A potent shortwave will lift northeast across Pennsylvania today, as the associated surface low tracks northward across upstate New York. An area of low pressure originating over the southern plains will track northeast into the Mid Atlantic region late Monday and early Tuesday.

NEAR TERM /THROUGH TONIGHT/. Dry slot has worked into eastern Pa this morning with little more than patchy drizzle falling across much of the forecast area at 10Z. However, potent shortwave lifting northeast from the Ohio Valley will spread rain back into the region later today.

Model soundings become cold enough for a transition from rain to snow over the Allegheny Plateau this afternoon. Latest HREFV2 indicates a brief period of heavy snow is possible over the northwest mountains between 19Z-21Z in association with strong forcing ahead of upper trough axis. Will have to monitor this area for a possible short-fused advisory. However, marginal surface temperatures will likely limit accumulations, especially in valley locations. NBM data suggests spotty advisory level snow accumulations are likely on the ridgetops of Warren/Mckean/Potter counties. However, countywide averages are likely to remain below advisory criteria.

As shortwave lifts north of the region this evening, expect snow to diminish this evening over the Allegheny Plateau, and rain showers to taper off elsewhere. A tightening gradient in wake of intensifying low over upstate NY will result in increasingly gusty west winds across the entire forecast area tonight. Bufkit soundings indicate there will be frequent gusts to near 30kts.

Downsloping subsidence should bring partial clearing tonight east of the mountains. Over the Allegheny Plateau, orographic forcing will keep clouds and scattered snow showers in the forecast. Additional snow accumulations tonight should be generally be an inch or less.

SHORT TERM /SUNDAY/. Sunday should be a blustery day, as region will remain under the influence of intense storm system lifting into Quebec. Model soundings support gusts around 30kts through much of the day.

Approach of high pressure and lowering inversion heights should cause lake enhanced, orographic snow showers/flurries over the western mountains to gradually diminish Sunday. Any additional accumulation will be less than an inch. Subsidence to the lee of the Appalachians should result in a decent amount of sunshine Sunday across the eastern half of the state.

Mixing down model 850 temps between -10C and -5C yields expected max temps from around 30F over the high terrain of western Pa, to the low 40s across the Susq Valley.

LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/. The bulk of medium range guidance tracks surface low associated with southern stream wave along the Mason Dixon Line late Monday into early Tuesday. NBM thermal profiles support an initial period of snow, followed by a change to rain over much of the area. However, temperatures may remain cold enough for a wintry mix along the northern tier even as waa ramps up Monday night. Although the surface low is not progged to be very deep, this system will be drawing copious Gulf of Mexico moisture northward. All guidance currently supports potential precip totals of around 1 inch across southern Pa, the bulk of which should fall as rain.

The 00Z NAEFS supports below average temperatures and generally dry weather the second half of the week, as upper trough swings through the northeast conus.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/. A potent shortwave will lift northeast across Pennsylvania today, as the associated surface low tracks northward across upstate New York.

IFR to LIFR conditions ongoing at sunrise. A dry slot has worked into eastern Pa with little more than patchy drizzle falling across much of the forecast area. However, rain will again overspread the area from the SW through the mid/late morning as the shortwave moves throughm reinforcing low cigs/vsbys.

Rain transitions to snow over the Allegheny Plateau this afternoon as colder air arrives. Snow will diminish this evening, but a tightening gradient in wake of intensifying low over upstate NY will result in increasingly gusty west winds to near 30 mph across the entire forecast area late this afternoon and tonight.

Downsloping subsidence should bring partial clearing tonight east of the mountains, with a return to MVFR over the central mountains and VFR for the SE. Over the Allegheny Plateau, orographic forcing will keep ceiling restrictions and scattered snow showers in the forecast.

Outlook.

Sun . Gusty west wind. AM low cigs/snow showers possible W Mtns.

Mon . PM low cigs/wintry mix possible.

Tue . Low cigs NW, improving conditions elsewhere.

Wed . Restrictions likely north/west with snow showers.

CTP WATCHES/WARNINGS/ADVISORIES. None.

SYNOPSIS . Fitzgerald NEAR TERM . Fitzgerald SHORT TERM . Fitzgerald LONG TERM . Fitzgerald/Gartner AVIATION . RXR


Weather Reporting Stations
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Stations Dist Age Wind Air TempWater Temp WavesPressureDewPt
BLTM2 - 8574680 - Baltimore, MD 80 mi57 min N 1.9 G 6 46°F 46°F998.4 hPa
WASD2 - 8594900 - Washington, DC 80 mi51 min WNW 2.9 G 4.1 42°F 43°F999.5 hPa
FSKM2 - 8574728 - Francis Scott Key Bridge, MD 84 mi51 min NNW 6 G 7 45°F 998.6 hPa

Wind History for Washington, DC
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Airport Reports
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AirportDistAgeWind ktVisibilitySky/WeatherTempDewPtHumidityPressure
Hagerstown, Washington County Regional Airport, MD12 mi46 minSE 30.25 miFog35°F33°F93%1001.3 hPa

Link to 5 minute data for KHGR

Wind History from HGR (wind in knots)
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Last 24hrCalmCalmN4N3N5NE4N6N7N4N5N4N8N7N4N4NE4CalmW4CalmW4S6S5SE6SE3
1 day agoCalmCalmCalmCalm35S5S6S7S7SE6SE4S6SE8SE6SE8SE7S9SE6S4S4CalmCalmCalm
2 days agoW4W14W10W8NW7W8W12W15
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Tide / Current Tables for Chain Bridge, D.C.
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Chain Bridge
Click for Map
Sat -- 04:31 AM EST     -0.15 feet Low Tide
Sat -- 07:19 AM EST     Sunrise
Sat -- 09:32 AM EST     Moonset
Sat -- 09:48 AM EST     2.56 feet High Tide
Sat -- 04:18 PM EST     -0.10 feet Low Tide
Sat -- 04:46 PM EST     Sunset
Sat -- 07:19 PM EST     Moonrise
Sat -- 09:55 PM EST     3.08 feet High Tide
Tide / Current data from XTide NOT FOR NAVIGATION
Sorry tide depth graphs only, please select another station.

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1.81.20.60.2-0.1-0.10.31.222.52.62.31.71.10.50.1-0.1-00.41.32.32.93.12.8

Tide / Current Tables for Chain Bridge, one mile below, D.C.
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Chain Bridge
Click for Map
Sat -- 04:26 AM EST     -0.15 feet Low Tide
Sat -- 07:18 AM EST     Sunrise
Sat -- 09:32 AM EST     Moonset
Sat -- 09:43 AM EST     2.56 feet High Tide
Sat -- 04:13 PM EST     -0.10 feet Low Tide
Sat -- 04:46 PM EST     Sunset
Sat -- 07:19 PM EST     Moonrise
Sat -- 09:50 PM EST     3.08 feet High Tide
Tide / Current data from XTide NOT FOR NAVIGATION
Sorry tide depth graphs only, please select another station.

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1.71.10.60.2-0.1-0.10.41.222.52.52.31.71.10.50.1-0.1-00.51.42.32.93.12.8

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 State College, PA (7,2,3,4)
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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 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.