Today's Text Forecast | Public Forecast Discussion | Technical Discussion | Graphical Forecast

It is raining in the Bronx. That's the bad news. The other bad news is the performance of the models today, which has been atrocious both with the positioning and intensity of precipitation. The NAM continues with it's highly dynamic event, but has shifted a good 50-75 miles southeast of it's previous forecast. In fact, it keeps the highest precipitation confined to the New Jersey Shore/Long Island and the southeastern areas of the metro. The GFS, on the other hand, is well northwest of the guidance envelope (and much warmer aloft). It's interesting to note that the GFS was involved in an awful forecast on last nights 00z model run suite, indicating that heavy QPF would be over the metro area by 12z this morning. Obviously, this hasn't happened. The NAM definitely won the precip-timing battle in that regard, but both models seem to be off with the precipitation falling right now..which is relatively light but is definitely coming down at a decent clip. It's nothing the models usually don't pick up on.

The timing differences from last night's models can be attributed to a few key features, displayed on the image to the right. There's a weakening shortwave, which moved northeast out of the trough base last night, over New England. Meanwhile, the more robust shortwave (which will be responsible for touching off the strong dynamic precipitation tonight and tomorrow) is ready to eject northeast out of the trough in the southeast states. Between these two features, the NAM correctly indicated a brief period of mid level ridging (ridge axis drawn in a pink line). The other two features are circled in pink. The mid level ridging acts to provide subsidence to tamper/inhibit the development of stronger/more steady precipitation. The GFS was incorrectly weak with the initial shortwave, weaker with the ridging/subsidence, and brought precipitation into the area a good 8-10 hours too fast.  This is why the precipitation is currently light/spotty...and it will remain that way until PVA (Positive Vorticity Advection) from the second shortwave can overtake that later tonight as a low pressure area forms off the Mid Atlantic coast.

John