The edge of a front makes for some fine-line forecasting

The sun finally returned on Wednesday after a couple of really cool, raw and damp days. Now that we are into the second half of the week, it’s time to seriously look at the rest of the week and the weekend forecast.

The start of the weekend’s forecast is a tough call. A front is going to cross the state late today and then slow. The placement of this front and any clouds and rain along it will determine who gets dry, who gets wet and who sees the sun Saturday and Sunday. Since you might be traveling this weekend, it’s important to know there will be very different weather conditions across New England.

With the front nearby today, look for showers this morning and then just mainly cloudy skies. It will feel a bit muggier as well. Tomorrow the front pushes away far enough to yield a nice day.

How Much Sun Saturday?

Southern New England, such as the south coast of Connecticut, Rhode Island and Massachusetts including Cape Cod and the islands, will see the least sun and the greatest chance of showers, but the cloud shield from this storm will likely impact southern and coastal Maine. One model has it cloudy here on Saturday. This is the part of the forecast that could spoil your plans to be lying out enjoying sunshine. A shift of 50 miles either direction will impact sky conditions a lot. Rainfall shouldn’t be an issue here either way – it’s just a question of blue or gray.

The clouds will keep parts of coastal York County in the lower 70s on Saturday, not a great beach day.

Clouds will be thickest over southern New England Saturday.

Across far northern Maine, New Hampshire and Vermont sunshine is most likely along with the warmest temperatures.

Sunday Is The Best Day

Taking into account the latest data. I am leaning toward more clouds on Saturday and more sun on Sunday. A cool northeast wind will keep temperatures from becoming very warm, remaining under their long-term averages for the final days of July.

Saturday will be cooler than average, especially over southernmost Maine.

The Ensemble Forecasting Method

Without overwhelming you with a lot of meteorology, let’s look at one piece of data from the GFS model. I like to share the inner workings of how meteorologists make a forecast as I believe it allows the public to appreciate this science better. What you are seeing below are individual rainfall forecasts of the GFS model. Notice there are 22 squares. Squares e1 through e20 is a forecast tweaked slightly differently. It’s like taking a recipe for cookies and changing how you mix the ingredients. If you get the same result no matter what you do, the recipe becomes more foolproof. If you find the slightest change in the ingredients changes the entire dish, you have less confidence in making it. The final square is the mean eM and the first square is the original without and modifications, the control, eC.

Ensemble forecasting is an important part of meteorological prediction.

By changing small portions of this weather model and still getting the same result we have higher confidence in the forecast. This is called ensemble forecasting and it is a very important part of the forecasting puzzle. Notice how nearly all the squares have the heaviest rain (reds and orange colors) south of Cape Cod. Since there is so much agreement between all these ensemble members there is growing confidence in the forecast. That’s why I believe the rain should not make it this far north.

Could The Forecast Change?

While I think we will see a blend of clouds and sunshine around Portland this weekend, there is still a storm that we need to watch. The trend later today with all of our models will help solidify when any showers might occur and which part of the weekend is the sunniest. You can bet I’ll be watching the ensembles very closely not only from the GFS, but from the European as well. Next time there’s a tough forecast ask a meteorologist what the ensembles are showing; no doubt they will be quite impressed.