Hawaii Extended Forecast Discussion NWS Weather Prediction Center College Park MD 712 AM EST Wed Nov 19 2014 Valid 00Z Thu Nov 20 2014 - 00Z Thu Nov 27 2014 For Hawai'i, the 19/00Z guidance maintained good continuity with the migration of a mid-latitude upper-level trough and attendant cold front across Hawai'i---24/12Z to 26/12Z. The 19/00Z deterministic ECMWF, GFS-Parallel and Canadian attempt to close off a 500mb low just north of the state around the 25/00Z-25/12Z, then migrate the system slowly northeastward during the latter portion of the medium range forecast period---days 6-7. The 19/00Z and 19/06Z GFS are more progressive with the front and delay the formation of the cutoff feature until it is downstream of the Islands. The presence of a 500mb cutoff---or lack thereof---will likely make for a challenging precipitation forecast between Monday and Tuesday. At this point, the deterministic guidance is unsure when--and actually where--this cutoff will develop---with its formation, depth and forward momentum directly tied to an Aleutian Low's progression across the Gulf of Alaska. Using a blend of the 19/00Z ECENS/GEFS will preserve and maintain height falls and support the timing of the surface front (with upper-level support) from Sunday into Tuesday afternoon. In the coming days, the forecast may then require some alterations---with the possible cutoff generating some additional 'shear-line' clouds and showers in the wake of the surface frontal passage. But at this point in time---and 6-7 days out---the depth and overall size of the cutoff is far from clear---with respect to the sensible weather impacts it may generate upon Hawai'i. Vojtesak