The Lakes Region of New Hampshire has come on-board with spring - welcome! Ice Out was declared on Lake Winnipesaukee and the full article can be found on the homepage.
As expected, conditions are ripe for fire growth and expansion today with very dry air that has settled in behind last night's/early AM cold frontal passage. Northwest wind is the key to that fire forecast, though, contributing some 10-20 mph of ventilation with gusts to 25 mph, and this is the real concern for transport of embers over dry fuel. Tremendous mixing has driven the Haines Index up a bit - low to moderate for most of New England, which helps to define vertical ventilation of a fire once it develops. Fire danger will decrease a bit on Friday owing to lighter winds.
Of course, flooding continues thanks to snowmelt, with rivers in Northern and Western New England continuing to exhibit minor flooding as the wealth of snow in the mountains melts and runs into the waterways. I shudder to think of what would have happened if we'd seen heavy spring rains, but that situation was thankfully disarmed in exactly the method we needed.
In the short term, my biggest question for the forecast is the area of clouds I've been unwilling to let go of from the forecast for coastal areas for Friday morning. As has been discussed since Monday (old discussions below and in the archives), I see very clearly that the guidance has not supported carrying a cloud deck in as high pressure builds over Eastern Maine, but I just have trouble believing it! Nonetheless, it's important not to make a mountain out of a mole hill. The fact is that the surface anticyclone over PA will still have definition and therefore will bring a northwest wind to New England lightly overnight Thu night, continuing for interior New England on Friday. The weakening anticyclone moving over Maine will become a surface ridge axis over the Gulf of Maine, and this will induce an onshore flow. We may end up seeing pockets of low clouds and fog along the coastal plain of ME overnight tonight (especially as low level mositure evident on visible satellite imagery advects slowly south, then southwest), and perhaps expanding in patches to extreme eastern NH or MA tomorrow morning, but while I think the moisture in coastal locales only increases in the low levels on Friday, the initiation of thermals and diurnal convective processes will probably mean a scattered, then broken deck of cumulus results in these coastal communities with a gorgeous day otherwise...most certainly just inland where the northwest wind prevails.
I'm sticking to my guns for the weekend - holding the ridge axis firm on Saturday and keeping raindrops out until Saturday night. On Sunday, the swath of warm and moist advection moves directly overhead, but is fighting not only the stubborn middle and upper level ridge, but also the dry boundary layer air. All of this should result in lots of clouds, but limited rain drops as only scattered or isolated light rain showers. Temperatures were a real struggle. After the wide range I shared with you yesterday, there's been some agreement among the Ensemble MOS members, but it's been in the opposite direction than I expected - cooler than climatology. Now, some of this is due to a still too-wet forecast (in my opinion) by the guidance, keeping the numbers down, but I felt it was necessary to at least shave a couple of degrees off my forecasted highs.
Yesterday I mentioned that Monday looked to bring a more significant chance of rain as new upper level shortwaves dig into the longwave trough and nudge it east. I also don't think we should underestimate the power of this ridge and its stubbornness - after all, it's performed so well thus far, that if we see signals of holding the ridge, it makes sense to hold it. One such signal is the slowing showing up in most of the guidance products of slowing the upper low over the Great Lakes. With this slowing, that means that getting substantial rain in during the day on Monday may even be difficult! The surface cyclone would wind up to our west, under the area of greatest upper level diffluence over Eastern New York, and drop its heaviest rain under that jet streak, though Western New England would stand a good chance of getting in steadier and heavier rain by late Monday or more likely Monday night. Eventually, of course, this thing has to swing through New England. What's really interesting, though, is the way in which it will swing through! That is, what holds up the passage of the upper low just as much as the ridge ahead of it is the intense Canadian energy dropping into the trough on the backside, coming due south out of Northern Canada, and tapping vorticity from the North Pole on its way south. This implies a great deal of energy and a substantial cold pool aloft that will enter the mix as it rounds the base of the trough, gets wrapped into the upper low, and serves to kick the upper low east for a passage over New England on Tuesday. By this point, though, the surface cyclone has wound up enough that warmth and moisture has spread north, and while New England seems likely to get a round of very intense dynamic lift associated with the passage of the vorticity maximum on Tuesday, the potential is there for not just heavy rain but severe thunderstorms, too! Not saying that's going to happen for sure, just that this type of energy, cold pool aloft, substantial lift focused along a narrow but sharp line of cyclonic vorticity advection, all supports the potential for this scenario. There seems to be pretty good agreement among the guidance that this upper low is in no big hurry to move out through the middle of next week, meaning the cold pool remains overhead. With a boundary layer northwest flow, this promotes downsloping in Central, Southern and Eastern areas, but the instability in the middle layers should be enough for lots of Cu with convective showers in especially the orographically favored areas.
I'd like to promise warmer air for the end of the week next week, and while that's possible given a forecasted 850 mb temperature rebound to near or slighty above normal, I think we'd best make no promises on that, given a confluent flow at 500 mb to Eastern ME, and the propensity to hold high pressure at the surface, thanks to the subsidence below this confluent flow. The result very well may be a period of northeast wind Thu/Fri if that verifies. For now, just another thing in the line of stuff to keep an eye on.
Matt
