A Look at the Weekend

THU 4/24: A somewhat tricky weekend forecast is unfolding as a battle between persistence forecasting and statistical/numerical forecasting is at hand. One argues for a continuation of dry (even pleasant) weather, the other suggests some wet weather may be in store for Saturday night and Sunday. Whatever happens this weekend, rains seem far more certain for early next week and cooler temperatures on the way.

As for the weekend forecast, it hinges upon just how long high pressure holds in to our Northeast - the longer it does so, the less likely we are to see any precipitation until Monday or Tuesday. The persistence forecasting idea is simply to argue that the recent upper level and surface weather pattern has favored drier than normal conditions. For instance, looking back 7 to 10 days ago, it appeared as though a moisture loaded storm wanted to move into Southern New England this past weekend and ruin a nice stretch of weather. However, strong high pressure ended up being the winner, forcing the storm well south of us and allowing nice, mild conditions to persist (now going 2 weeks strong). It's been tough to squeeze out moisture of late with such dominant high pressure, and with the fair weather center not moving too far east this weekend, why would that change?

Most model guidance wants to drive a band of rain across New England Saturday and Sunday as moist air lifts north and eastward ahead of a deepening trough well to our west. While this may very well come to fruition, it may never make it to the Cape - despite what appears to be a moist onshore flow.

If we combine the persistence forecast with the numerical guidance, we should see high pressure holding firm in the Canadian Maritimes, feeding *relatively* dry air westward into the coastal plain of New England (Cape Cod). This dry air will act to fight and eat away at the advancing shield of clouds and showers. Given this and the fact that the band of moisture will be running away from its source, I believe it bodes well for dry air to hold on stronger. So...the weekend could end up quite wet over western New England, but overall, rather dry here on the Cape. A good bet would be to expect a decent - though somewhat cool - Saturday followed by more clouds than sun Sunday and just a few scattered showers or sprinkles. That's what I've got in the Extended Forecast for now.

Early next week a far more formidable weather system will spin eastward into our part of the country, bringing a much higher likelihood for clouds and rain. This storm will be driven by an active jet stream and a rather potent clash of air masses - unusually cold air digging south from Northern Canada and warm spring time air over the southern and eastern parts of the U.S. As the system approaches, look for thickening clouds on Monday with a band of rain, perhaps heavy, developing sometime Monday Night or Tuesday.

Not only does this system set us up for our first chance of widespread soaking rain since early / mid April, but it will also mean a return to at or below average temperatures. After the initial round of rain Monday night or Tuesday, we will be stuck under a pocket of cold upper level air through mid-week next week. Minimally, this will mean more clouds than sun and temperatures in the 50s Tuesday and Wednesday. But with a bit of energy and daytime heating, such a chilly air mass aloft could lead to some pop-up showers and thunderstorms later Tuesday and/or Wednesday.