SUNDAY THROUGH TUESDAY...
CLOUDS WILL BEGIN TO INCREASE AHEAD OF AN APPROACHING STORM SYSTEM
SUNDAY. A COLD START AND POOR MIXING SHOULD LIMIT HIGHS TO THE
UPPER 20S TO NEAR 30 ACROSS THE INTERIOR...TO THE LOW TO MID 30S
ELSEWHERE. MODEL CONSENSUS IS FOR PRECIP TO ARRIVE INTO SOUTHERN
NEW ENGLAND EITHER LATE IN THE DAY OR AT NIGHT SUNDAY. MODEL
CONSENSUS ALSO POINTS TO LOW PRESSURE AND ANY SECONDARY DEVELOPMENT
TRACKING OVER OR WEST OF NEW ENGLAND. THIS IS IN RESPONSE TO MID
LEVEL CIRCULATION MOVING ACROSS THE ST. LAWRENCE RIVER VALLEY.
THEREFORE...DEEP LAYER COLD AIR WILL ERODE AND LIKELY YIELD PTYPE OF
SNOW TO SLEET/FREEZING RAIN TO PLAIN RAIN. BEFORE THE CHANGEOVER A
FEW INCHES OF SNOW ARE POSSIBLE FOR MUCH OF THE REGION GIVEN THE
MAGNITUDE OF WARM AIR ADVECTION.
ANOTHER SCENARIO WE WILL HAVE TO MONITOR WILL BE IF SECONDARY LOW
PRES DEVELOPS AND TRACKS ALONG THE COASTAL PLAIN. THIS WILL DELAY
THE ARRIVAL OF WARMER SURFACE AIR AND RESULT IN LONGER DURATION OF
FREEZING RAIN AND SLEET INLAND SUN NIGHT INTO MON.
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MODEL DIAGNOSTIC DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1215 AM EST WED NOV 28 2007
VALID NOV 28/0000 UTC THRU DEC 01/1200 UTC
MODEL INITIALIZATION...
...SEE NOUS42 KWNO ADMNFD FOR STATUS OF UPPER AIR INGEST...
ANY INITIALIZATION ERRORS WITH THE NAM AND GFS DO NOT APPEAR TO
SIGNIFICANTLY IMPACT THEIR FORECASTS.
MODEL TRENDS...
...TROUGH CROSSING THE PLAINS EARLY DAY 1...
THE NAM HAS TRENDED SLOWER AND MORE AMPLIFIED WITH THIS SYSTEM.
THE GFS HAS ALSO TRENDED SLOWER WITH THE TROUGH.
...SHORT WAVE SLIDING INTO THE PACIFIC NORTHWEST DAY 1...
THE NAM HAS TRENDED FASTER WITH THIS IMPULSE. THE GFS SHOWS
REASONABLE CONTINUITY.
...ARCTIC SHORT WAVE SWINGING THROUGH ONTARIO DAY 3...
THE NAM HAS TRENDED BROADER AND MORE PROGRESSIVE WITH THIS
IMPULSE. THE GFS SHOWS REASONABLE CONTINUITY.
...TROUGH CARVING OVER THE WEST DAY 3...
THE NAM AND GFS HAVE TRENDED SLIGHTLY DEEPER WITH THIS SYSTEM.
MODEL DIFFERENCES AND PREFERENCES...
...TROUGH CROSSING THE PLAINS EARLY DAY 1...
THE NAM AND THE GFS HANDLE THIS SYSTEM COMPARABLY...BOTH ALOFT AND
AT THE SURFACE.
...SHORT WAVE SLIDING INTO THE PACIFIC NORTHWEST DAY 1...
THE NAM IS SLIGHTLY MORE AMPLIFIED THAN THE GFS WITH THIS IMPULSE.
WITH THE SUPPORT OF THE 12Z ECMWF AND THE 00Z GEM REGIONAL AND
UKMET...WILL RECOMMEND A SOLUTION CLOSER TO THE NAM WITH THE SHORT
WAVE.
...ARCTIC SHORT WAVE SWINGING THROUGH ONTARIO DAY 3...
THE GFS IS FASTER THAN THE NAM WITH THIS IMPULSE...INDICATING LESS
OF A POSITIVE TILT. WITH THE SUPPORT OF THE 12Z ECMWF AND THE 00Z
GEM GLOBAL AND UKMET...WILL RECOMMEND A SOLUTION CLOSER TO THE GFS
WITH THE SHORT WAVE.
...TROUGH CARVING OVER THE WEST DAY 3...
THE GFS KICKS THE ENTIRETY OF THE LARGE VORTEX CURRENTLY WEST OF
BAJA NORTHEASTWARD AHEAD OF THIS TROUGH...WHILE THE NAM LEAVES
THESE SYSTEMS SEPARATE. AS A RESULT OF THE PHASING...THE GFS
SPINS UP A DEEP LOW OVER COLORADO BY THE END OF THE PERIOD. THE
GFS IS A PHASED...DEEP OUTLIER WITH THIS SYSTEM...WITH THE 12Z
ECMWF AND THE 00Z GEM GLOBAL AND UKMET SLOWER TO EJECT THE PACIFIC
VORTEX INLAND. THERE LOOKS TO BE ENOUGH MID LEVEL FLOW ACROSS
COLORADO TO PRODUCE AT LEAST A MODEST LEE SURFACE LOW...ALONG THE
LINES OF THE 00Z GEM GLOBAL.
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The stronger low pressure progged by the GFS and ECMWF and trending that way in the NAM is the signficant problem when coming to storm track and precipitation type. The stronger low forces a stronger southeast ridge downstream. This first of all prevents CAD from getting further south and east and forces the low as it heads east towards the north. Right now, there is a reasonable consensus for low pressure traveling toward the Great Lakes region, and deepening before transfering energy eastward to over or just east of New England. A couple of issues associated with the track of the initial low is the aforementioned phasing/deepening of SW low, the resulting SE ridge, and lack of a static high pressure in SE Canada. Right now, it is still questionable whether the robust phasing in the west will take place, as well as if the low would be able to punch through the arctic air mass in the north central states and southern Canada. With 5 to 6 days remaining, there is enough time for notable model flipping to take place. One thing that can be monitored in the short term is the clipper that will bring a rain/snow mix to the region tomorrow. The stronger and further south the low travels, the deeper the cold air mass will be and the resulting track of the day 5 low would be further south. (On top of which, we would get more snow from the storm tomorrow). So that can be something to watch model verification on.
Whatever the track is (assuming it is also still west of the region), the next major point to monitor is how quickly the energy of the low is transfered (and where it is transfered too). The faster low pressure can develop east of the initial storm, the quicker cold air can flow into the region and precipitation flip to snow. For instance, the latest run of UKMET track low pressure into western NY state but transfers energy to the coast late Sunday Night and bombs low pressure down to 970mb. This would be a major wind and snow storm for New England.
Many factors to consider, and many questions will be answered by Friday morning: Clipper track will be realized, and low pressure will be inland over the SW.
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