Thursday, March 11, 2010

Flood City?


2:10PM THURSDAY 3.11.2010 Today will be the final day of a string of pleasant weather. Tonight rain will move in from the south up to PA, and remain light to moderate till afternoon Tomorrow. Rainfall amounts will be around .25-.5" and up to .75" by noon tomorrow for the mid-atlantic. Rain will move into areas north of PA by Tomorrow evening. A break will move into the mid-atlantic before the real action begins late Tomorrow into Saturday afternoon where another 2"+ can fall from south to north. Some area may see up to 4" by the end of this storm. The Middle Atlantic River Forecast Center now has all of the area from Central VA up to Southern NY in a significant river flooding possible with parts of MD, PA, DE, NJ, VA, and WV in significant river flooding likely. This situation will have to be watched very closely from VA up into the NE.

5:00 AM TUESDAY 3.9.2010  Abundant sunshine and mild temperatures dominate parts of the eastern U.S. into Wednesday. As indicated in NOAA's Day 4-5 Quantitative Precipitation Forecast map above, we also must get ready for some "red rain." This Pacific and Gulf-juiced system, which produced the season's first tornado in Oklahoma, is sending a squall line through the southern plains. Details in the Severe Storm Zone. Like many of its recent predecessors, this developing system will drench many states east of the Mississippi with copious rainfall between Wednesday and Sunday. The larger problem for the Mid-Atlantic may be downstream runoff from heavy wet snows in the Northeast.

Any snowcover in central and eastern New York not melted by Thursday will begin melting much more rapidly and wash into streams within the Chesapeake Bay watershed. This upcoming rainfall pattern combined with excessive snowmelt may have a considerable impact on the Susquehanna River and water quality in the Bay itself.

Thankfully the upper air pattern does not support any snowfall from this (1 PM GFS model map  for Friday). Otherwise, we would all be headed to group therapy if the projected 4.9" of liquid over New York City by Sunday had to be calculated using previous snow ratios of 15:1 observed this winter.

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