News & Events for Chesapeake Bay

Weather App Shootout – Round 3 – Across the Potomac

Date Posted: 2018-06-20
Source: Robert Sherer, contributor

Editor’s Note: Predicting weather and interpreting data from the numerous computer models used by meteorologists is tricky business. Added to that is the way in which various weather apps present information along with the timing of their updates. In this review of five weather apps - PocketGrib, PredictWind, Ventusky, Windy and Windfinder Pro  - Contributing Editor Bob Sherer conducted a simple evaluation based on his experience on a particularly windy day.



When we first started cruising down the ICW, everyone told us to watch out for crossing the Potomac River. The currents run north and south in the Chesapeake but the currents in the Potomac flow east and west (not exactly but close enough). That creates interesting situations for a crossing, especially when there’s some wind involved.

Depending on the details of the currents (including eddies), you can easily find yourself in a wind against current situation. We know of people that cross over to the other side of the Chesapeake just to avoid getting too close to the mouth of the Potomac River. For us, we’ve been okay for the most part and that’s due to just picking days to travel on the Chesapeake with little wind or with wind at our backs. It also helps being retired and not having a schedule.

With that preamble, we were in the Mill Creek Anchorage inside Ingram Bay at the southern end of the Great Wicomico River at Reedville, VA and were anxious to get across the Potomac without incident. The previous night’s weather reports were for winds of 10 kts or less and we were eager to see the morning’s reports.

Let’s take a look first at the pleasant NOAA forecast.  This looks pretty good! No sweat.

I looked at PocketGrib out of respect for fond memories of past usage and it predicted 7.9 kts at the mouth.


Next up was Windy for 7:00 am, which was a little more disconcerting with winds of 12 kts. Still okay, I told myself but let’s check the other apps.

Ventusky was bordering on us being careful. It was showing 14 to 15 kts at 7:00 AM; about the time we would be crossing the mouth.

PredictWind was forecasting 18 kts! How can PocketGrid say 8 kts and PredictWind say 18 kts? That’s a lot more than even Windy.

Windfinder Pro showed 11 kts, whom to believe?

With such stark contrasts between apps, I started looking around for a weather buoy near the mouth of the Potomac that would give me current conditions there.

I found a weather buoy on the north shore of the mouth. The report was 15 to 16 kts with gusts to 21 kts. And the buoy is not in the middle of the Potomac where it’s likely to be even windier. What to do? I really didn’t want to do a 10-mile crossing with gusts of 20 kts or greater ahead of the beam.

All the forecasts except PredictWind showed the wind decreasing during the day. With that and a coin toss, we decided to wait a couple of hours to give the wind a chance to die down. We waited until 9:30 to haul anchor and started out. Leaving Mill Creek was directly into the NE wind and it was the roughest part of the passage. As we started crossing the mouth, the wind was on the beam at 12 kts or so, not too bad. Once past the mouth, the wind died off as the rest of the apps promised, but PredictWind was still showing low teens.

How to judge? Clearly, PocketGrib is at the bottom once again with its prediction of 8 kts. It was not 8 kts, as evidenced by the buoy record. The rest of the apps were grouped in the middle, but it was PredictWind that alerted me to the high winds at the mouth. However, it fell down in not predicting the decreasing wind later in the afternoon. When the winds died off to around 5 to 7 kts once past the mouth, PredictWind was still saying 12 kts. So it’s a plus and minus situation for the best app.


At the bottom are PocketGrib and NOAA. Both predicted winds of less than 10 kts at the mouth. Everyone else is in the second group but PredictWind gets some credit for correctly predicting the high winds in the morning when no other app agreed. However, it did miss the decreasing winds in the afternoon. So I would say two levels of apps in this round, PocketGrib and NOAA at the bottom and everyone else up a notch higher.

The next review will be on Delaware Bay, always a fun place to test out your prognostication skills, albeit with some help from modern electronics. Then there’s always that coin toss to help level out the analysis.

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