Mar 27, 2014: Rainy Weekend Ahead

Forecast Highlights:

gfs_namer_060_850_temp_mslp_precipThe anomalously cold air mass over the last few days has left the region, giving way to more spring-like conditions as high temperatures peaked in the 40s today and will continue to rise into the 50s on Friday. The warm up will come with additional precipitation, however, as a series of low pressure systems will approach the region beginning on Friday, with occasional periods of rain expected especially on Saturday and Sunday with 1-2 inches of rain possible.




Tonight – Sunday: Warming Up, Widespread Rain Returns


Posted above from left to right are the latest available surface analysis and radar composite from WPC, and the NAM initialized 500 millibar heights and vorticity from NCEP MAG; both are valid at 0z (8pm). The strong mid-latitude cyclone which explosively deepened off the northeast US yesterday has since departed the region, tracking into the Davis Strait, removing the cold air mass along with it. Meanwhile, a more zonal flow is developing over the US as a shortwave trough over Iowa races ENE, having set up a southwesterly flow over the region with a warmer air mass being advected in. Temperatures today accordingly warmed up into the low to mid 40s; Central Park reached a high of 43 degrees, which is somewhat warmer than yesterday but still 11 degrees below average.

The trough over Iowa is associated with a surface low pressure near the same region, producing heavy thunderstorms to its south and snow to its north. The low will follow the southwesterly flow and track into Canada, bringing warmer temperatures into the region for Friday peaking in the mid to upper 50s. Areas of moderate to locally heavy rain are expected to reach Pennsylvania and New York in the late morning to early afternoon hours, but will weaken prior to reaching the area, with scattered showers generally expected amounting to less than 1/4 inch for most locations, locally higher west of NYC. Windy conditions are expected ahead of the cold front, with a SSW wind at 10-25 mph.

Attention then turns to another weak shortwave trough currently near Idaho; this will continue to track east towards the Ohio Valley and support the formation of a surface low pressure near Tennessee, which then tracks towards New Jersey and south of New England. The system will pull widespread moisture into the region, which along with a relatively slow progression as it becomes cut off from the main flow will support occasional periods of rain from Saturday morning through Sunday evening; rain is generally expected to be light to occasionally moderate in this time period, with the highest likelihood of heavy rain currently forecast between the late evening and mid overnight hours on Saturday with strong upward vertical motion expected around this time frame. Forecast rain totals are at least 1 to 2 inches, locally up to 2.5 inches near and south/east of NYC, but with the rain forecast subject to some changes. As the back end of the precipitation shield comes through around Sunday evening, colder air aloft will gradually filter into the surface, but with light precipitation rates and only marginally cool temperatures in the low-mid levels likely to continue supporting rain as the precipitation type.

Next Week: Temperatures Stay In 40s And 50s

For the first time in a while, there does not appear to be a major cold outbreak on the way for the next 7-10 day range. The cutoff low from the weekend will only slowly progress to the east once offshore, preventing a significant warm up over the area and especially over New England, but with a slight warming of temperatures nonetheless likely, especially over western parts of the area where highs in the mid to upper 50s are likely. Another low pressure is forecast to track into southeast Canada on Tuesday night into Wednesday, bringing a cold front through with a slight cool down likely for Wednesday into Thursday, although this cold front does not appear to be a major rain producer at this time. Looking towards late next week, the model guidance is in general agreement regarding another low pressure approaching the region by late Thursday into Friday, but as should be expected for an event a week away are struggling to maintain run-to-run continuity. This time frame will continue to be monitored for the potential of rain over the region.

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