A really quick update today, because I think the discussions this week and especially from yesterday have a fairly good handle on the situation.
Bottom line here is that the weakening anticylcone over Northern Maine is keeping just enough dry air in play to erode the northern edge of the rain, but it will advance as the mid-level warm and moist advection described yesterday looks to be verifying, and has actually been producing some really impressive cold cloud tops evident on IR imagery, even if the rain hasn't been penetrating the dry 10-15000 feet of atmosphere we have near the ground. You can track the rain through the radar links at right, but remember that some of it is virga - evaporating before hitting the ground - so check out the surface observations, too - I like the "Java" map that is located in the pull down menu of Current Conditions to the right of this discussion. Of course, that column will moisten, but it's interesting to see the guidance in great agreement on very low QPF in Eastern and especially Northeastern MA through about 10 PM or so, and we've certainly seen this happen in similar circumstances before, where the easterly wind can actually hold the surface dry air in place even though it has to bleed across the ocean first. I don't think it can successfully stop the rain from advancing, but I do think it may keep the intensity light from Boston to Portsmouth and inside the north end of route 495. Heaviest burst of rain comes tonight as the storm strengthens. .50" to .75" looks good for Southern and Eastern New England, with some local variation.
I'll just outline any changes or addition of detail for the rest of the forecast....
The one feature that should stand out about Saturday's forecast in addition to the upper low and cold pool and the myriad of surface troughs and a cold front racing east across NY State is the overall speed of the flow. As the storm - surface and aloft - cranks over Eastern Canada, the wind flow becomes quite fast from west to east through most of the atmosphere. This propels a surface trough/cold front quickly east, and with surface cold advection slow under the belly of the storm, low level and mid level lapse rates should really be steepening. This allows for the expected convection to develop after sunshine boosts temps to either side of 70, but the convection (thunderstorms) could be somewhat nasty in a few spots, especially Western New England. Given the unidirectional, fast flow, severe wind gusts (excess of 58 mph) are possible in the healthier storms, and the situation actually is marginally favorable for a squall line to develop. Given the rapidly cooling air aloft, hail is another possibility. As mentioned yesterday, convection may last longer than normal after sunset.
Sunday's convection still comes with cold air just off the ground, so I still like the idea of hail, graupel and high terrain snowflakes. Additional trough on Monday means keep the chance of scattered, mostly diurnally fueled showers, especially in Northern New England, and though shortwave ridging comes in Tuesday, we're ahead of the next system over the Ohio Valley, so clouds increase late with a chance of rain by evening and night.
Enjoy your weekend!
Matt
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