What's It Look Like on the Lake?

What's It Look Like On the Lake?

Page Edited Last 2022-05-29

Copyright 2021, 2022 David C Brezina

Email Information about Dead or New Links to dbrezina@rcn.com

Same As the VHF Broadcast in Print

  • IF NOT DISPLAYED
    • CLICK HERE,
    • DRAG SCROLL BOX ON SCROLL BAR DOWN TO VIEW ENTIRE FORECAST

    • If the one above does not display, use this one.

    Different URL for NWS Marine Forecasts FZUS53

  • Forecasts

    • Short Term Forecast

    00 Hours 06 Hours 12 Hours 18 Hours
    24 Hours 36 Hours 48 Hours (Two Days) Loop

  • Five Day Forecast

    •
    Day 3 Day 4 Day 5

    Day 6 Day 7 DAYS 3 - 7

    In the old days, forecasts were printed on teletype machines. Essentially, these were "texts", although printed with keys striking ribbons on paper, the paper being automatically fed, responsive to remotely generated signals.

    Date Time

    (Local)

    		Wind

    (MPH)

    		Vis

    (MI)

    		Weather Sky

    Cond

    		Temp

    Air

    		Temp

    Dwpt

    		Temp

    6 Hr

    Max

    		Temp

    6 Hr

    Min

    		Rel

    Humid

    		Wind

    Chill

    		Heat

    Index

    		Pressure

    In Hg

    		Pressure

    (mB)

    		Precip

    1 HR

    (IN)

    		Precip

    3 HR

    (IN)

    		Precip

    6 HR

    (IN)

    ......... ............ ........... ........ ............... .......... ......... ......... .......... .......... ............ ......... .......... ........... ........... ...........

    		........... .

    ..........

    .

    Here it is for O-Hare (ORD) -- Close to Due West from Montrose Harbor

    https://w1.weather.gov/data/obhistory/KORD.html

    IF OBSERVED CONDITIONS NOT DISPLAYED CLICK HERE

    Here it is for Midway (MDW) -- Close to Due West from Jackson Park Harbor

    https://w1.weather.gov/data/obhistory/KMDW.html

    You can make important interpretations yourself from this data of hourly conditions, if you look at the right things.

    a. If I see Pressure falling dramatically over the past, say, four to six hours, I know to consider there may be trouble coming. Remember the old ship's captain looking at the barometer?

    ......... ............

    .....

    		...........

    .....

    		........

    .....

    		............... ..........

    .....

    		.........

    .....

    		.........

    .....

    		..........

    .....

    .....

    		..........

    .....

    .....

    		............

    .....

    		.........

    .....

    		..........

    .....

    		Pressure

    In Hg

    		Pressure

    (mB)

    		...........

    .....

    .....

    		...........

    .....

    .....

    		...........

    .....

    .....

    b. If I see Air Temperature and Dewpoint are really close and high relative humidity I know it’s probably going to be foggy.

    ......... ............

    .....

    		...........

    .....

    		........

    .....

    		............... ..........

    .....

    		Temp

    Air

    		Temp

    Dwpt

    		..........

    .....

    .....

    		..........

    .....

    .....

    		Rel

    Humid

    		.........

    .....

    		..........

    .....

    		..............

    ..........

    		..............

    ..........

    		...........

    .....

    .....

    		...........

    .....

    .....

    		...........

    .....

    .....

    c. If I see wind direction shifting, that’s a good indication of movement of a high or low pressure area (Pressure could help determine which).

    Often comparing interrelated conditions (Direction and Pressure?) can permit interpretation of bigger changes.

    Of course if you're a racing sailor, you've already been watching this, because it often shifts back and forth, locally, as oscillating shifts, or it's a persistent shift.

    29.92 in Hg = 1013.21 mbar

    ......... ............

    .....

    		Wind

    (MPH)

    		........

    .....

    		............... ..........

    .....

    		.........

    .....

    		.........

    .....

    		..........

    .....

    .....

    		..........

    .....

    .....

    		............

    .....

    		.........

    .....

    		..........

    .....

    		Pressure

    In Hg

    		Pressure

    (mB)

    		...........

    .....

    .....

    		...........

    .....

    .....

    		...........

    .....

    .....

    d. Visibility (see foggy, above) is a direct observation and is a basic safety factor in deciding what you can see and avoid.

    It might help you judge if you should be able to see that ATON ("Aid To Navigation"), or not.

    You should have spent some time learning the calculations for distance from an ATON based on its elevation, your height of eye, and curvature of the Earth.

    If you didn't, maybe brush up on navigation.

    But if visibility is not far enough to spot the ATON

    And, of course, it lets you double check your conclusion from Temperature and Dewpoint.

    ......... ............

    .....

    		...........

    .....

    		Vis

    (MI)

    		............... ..........

    .....

    		Temp

    Air

    		Temp

    Dwpt

    		..........

    .....

    .....

    		..........

    .....

    .....

    		Rel

    Humid

    		.........

    .....

    		..........

    .....

    		..............

    ..........

    		..............

    ..........

    		...........

    .....

    .....

    		...........

    .....

    .....

    		...........

    .....

    .....

    e. You might like to see those cute cartoon clouds with raindrops on your phone.

    But if you see Precipitation in Inches over one, three and six hours, and it's going up, down or has stopped, you can make a pretty good extrapolation about what's going to happen. Just not as cute. Like Wind Direction and Pressure, it's Changes that provide great insight.

    ......... ............

    .....

    		...........

    .....

    		......... ............... ..........

    .....

    		......... ......... ..........

    .....

    .....

    		..........

    .....

    .....

    		......... .........

    .....

    		..........

    .....

    		..............

    ..........

    		..............

    ..........

    		Precip

    1 HR

    (IN)

    		Precip

    3 HR

    (IN)

    		Precip

    6 HR

    (IN)

    f. The only confusing thing if you're not an aircraft pilot is that "Pressure - Altimeter" is local air pressure in Inches Mercury, and "Pressure - Sea Level" is local air pressure in millibars.

    The reason to call it "Altimeter" is that an airplane altimeter doesn't measure altitude. You set it to the Inches Mercury at a desired airport, and the altimeter measures pressure where you are located (up in the air it's nearly always lower) but the instrument converts the pressure difference to display "feet" in altitude to make it easy to read. But if pressure has changed at the destination, your indication could be too high or low. Pretty important if you're 200 feet above ground and a radio tower is 190 feet tall.

    Lake Michigan, near Chicago, of course, is about 577 feet above sea level, (Low Water Datum Lake Michigan 9087044 Calumet Harbor, IL = 176.0 m. 577.5 ft.) and the readings are at a station, so O'Hare (ORD Elevation: 680 ft.) or Midway (MDW Elevation: 619.8 ft.) are all measured at a higher location.

    If you're a boater, you pretty much want to stay on the surface, anyway, and its really changes in surface pressure over time that are important for you.

  • Other Links for Water Conditions
  • GLERL Water Temperature

    • Links To NWS Great Lakes Portal

    Select Wave Height at Bottom

    Select Wind Speed at Bottom

    Select Gustsat Bottom

  • Water Level