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jhwentworth, on 22 February 2012 - 04:56 PM, said:
Picking up the NWS forecast for Thursday night and later:
A surge of cooler middle-level air behind the surface low will allow middle levels to cool enough in advance of next system...that any precipitation that develops after midnight will start as snow. Most places will not see any precipitation until just before sunrise...but SW zones could see an inch or so by daybreak Friday. The departing low pressure from Thursday deepens and slows down...forcing the Friday system to track more Easterly than northerly. However...the European model (ecmwf) continues to hang significant energy back...that prolongs the storm system for Sat.
Confidence has increased enough for Cat pop in the Friday timeframe...spreading from SW to NE through the day. Rapid secondary cyclogenesis in vicinity of eastern mass will help to slow or stall the advance of warm air aloft. Sounding analysis show warm nose approaching 0c during the height of the precipitation. This would mean an ice pellets mix or poor ratio snfl for a time during the day Friday near the transition zone. Wet bulb temperatures at onset suggest much of the area could start as snow...before usual suspects rise above freezing on a S/southeast wind. This would favor little accumulate S of pwm along the seacoast...and inland to near Concord. However...the latest trends suggest that the foothills and mountains appear likely to remain frozen. 22/15z and 22/09z sref guidance also places high probs for 0.50" of precipitation in 6 hours along the southeasterly upslope zones of the White Mountains this is a favored location for SW flow snow events...and have made sure the quantitative precipitation forecast/snfl grids reflect this feature. Dry slot will quickly move in...so precipitation will have a finite time to accumulate. But a nice 9 hour period of good lift within the snow growth zone could see snfl easily approach warning criteria if upper levels remain cooler. Have leaned closer to the cooler mav guidance for surface temperatures Friday...except across southeastern New Hampshire where temperatures could rise sharply in southeasterly onshore flow.
A surge of cooler middle-level air behind the surface low will allow middle levels to cool enough in advance of next system...that any precipitation that develops after midnight will start as snow. Most places will not see any precipitation until just before sunrise...but SW zones could see an inch or so by daybreak Friday. The departing low pressure from Thursday deepens and slows down...forcing the Friday system to track more Easterly than northerly. However...the European model (ecmwf) continues to hang significant energy back...that prolongs the storm system for Sat.
Confidence has increased enough for Cat pop in the Friday timeframe...spreading from SW to NE through the day. Rapid secondary cyclogenesis in vicinity of eastern mass will help to slow or stall the advance of warm air aloft. Sounding analysis show warm nose approaching 0c during the height of the precipitation. This would mean an ice pellets mix or poor ratio snfl for a time during the day Friday near the transition zone. Wet bulb temperatures at onset suggest much of the area could start as snow...before usual suspects rise above freezing on a S/southeast wind. This would favor little accumulate S of pwm along the seacoast...and inland to near Concord. However...the latest trends suggest that the foothills and mountains appear likely to remain frozen. 22/15z and 22/09z sref guidance also places high probs for 0.50" of precipitation in 6 hours along the southeasterly upslope zones of the White Mountains this is a favored location for SW flow snow events...and have made sure the quantitative precipitation forecast/snfl grids reflect this feature. Dry slot will quickly move in...so precipitation will have a finite time to accumulate. But a nice 9 hour period of good lift within the snow growth zone could see snfl easily approach warning criteria if upper levels remain cooler. Have leaned closer to the cooler mav guidance for surface temperatures Friday...except across southeastern New Hampshire where temperatures could rise sharply in southeasterly onshore flow.
OMG, this post is awesome. I'm going to interpret it as "it's gonna snow like hell". Just watch out for the "cat poop"
