January 18, 2001
Quite an active few days upon us beginning Thursday and perhaps ending as late as Sunday night. Computer guidance has changed course several times this week, but may finally have trended upon a reasonable solution with the forecast through at least Saturday. First, we will have to deal with a wave of precipitation arriving Thursday which will start out as snow and change over to rain for the majority. Behind that, we have a wave of low pressure (the main low) which will pull out of the Western Gulf of Mexico on Friday and head Northeast. And believe it or not, if ingredients in the upper levels come together just right, we may have yet a third area of low pressure to deal with during the day on Sunday.
Thursday will start off cloudy. Light snow will break out early in the afternoon in response to a wave of precip well in advance of the main low in the Western Gulf. This preic is not really the 'main' system however. The main system is still sitting in the Western Gulf waiting for a piece of energy from the Northen jet to 'phase' with it, which will occur late Friday and allow the system to move Northeastward. Light snow *may* continue through a portion of the afternoon and then will turn to plain rain as warmer air gets entrained into the system. Little or no accumulation is expected as warmer air should win out rather quickly. Regardless, whatever snow falls will be washed out during the night on Thursday. Highs in the upper 30s.
Light rain, drizzle, and fog will continue through the night on Thursday with temperatures rising to near 40. Rain and fog will continue during the day on Friday. Rain may become heavy at times. Highs Friday in the lower 40s.
Two pieces of energy, one in the northern branch and one in the southern branch, will phase late on Friday and into early Saturday morning. The main low in response will be moving into Central North Carolina during the night Friday. Once again, another batch of heavier precip will be moving into our region later Friday night and early on Saturday. Lows Friday in the upper 30s.
Guidance differs slightly again come Saturday, but the trend has clearly been colder and farther South and East with the low each run. Rain will likely change to snow at some point Saturday. It's still early to say exactly when a changeover will occur, but the trend is to force colder air South and East across PA early Saturday night. Most guidance transfers energy from the system offshore, leaving the 'brunt' of the precip to the East. However, it's important to note (although it *should* change by 12Z Thursday) that the ETA family keeps heavy precip over our area during the day Saturday and implies a decent snowstorm. It's also important to note that the ETA hasn't quite 'been with the program' thus far this season. The AVN/GGEM/EC imply a moderate event. Will go with rain changing to snow during the day on Saturday. Temperatures gradually dropping into the mid 30s during the day. Another important note, if the models continue to trend farther South and East too much, the system will pass out to sea to our South and do nothing more than graze our area.
By late Saturday into Sunday, the main low, or whatever is left from the energy transfer, is off the VA coast oriented SW->NE. Light to moderate snow is still being shown for our area by guidance. This of course depends on whether or not high pressure wins out and pushes the system out to sea. Meanwhile, another piece of energy is diving into the backside of the trough trying to phase with the low off the coast. That scenario would imply bombogenesis, or rapid deepening of a low in the area of weakness which was left by the storm. If this were to occur quickly enough, our area would see another round of moderate to perhaps heavy snow on Sunday. However, most guidance has this happening just too far east, and with the tilt of the trough already negative, would likely keep the system off the coast. Just another scenario that needed to be thrown into the mix that is not out of the realm of possibilities. Will go with light snow Sunday morning tapering to flurries by midday. Highs in the mid 30s. Again, it high pressure wins out and guidance continues South and East, any precip will have likely ended on Saturday.
Things should clear out late Sunday into Monday. Monday will be partly cloudy with highs in the mid 30s.
So, quite an active period we are in through the weekend. Nothing is etched in stone, but confidence is average with the forecast through Saturday. Expect a brief period of snow Thursday changing to all rain. Rain and fog will continue on Friday. Rain will change to snow at some point Saturday. Too early to call for specifics, i.e., accumulations, duration, and intensity at this time. Sunday *may* begin with light snow if high pressure fails to win out. Any remaining precip will taper to flurries by midday. Another *brief* update around noon Thursday. Will keep this posted and just add an addendum. Take care.
