Here are the snowfall, freezing rain and ice pellet projections from the NAM-4KM WRF-NMM 06Z model run.
Freezing rain will be a big problem across Northern Arkansas and the data also suggest that Western NC may experience some buildup of ice. An experimental product we are working on in the Wright-Weather labs is a freezing rain accretion product. This is the 60 hour, pretty much direct model output, graphic from the NAM 4KM WRF-NMM. Keep in mind that actual ice accretion amounts will be less than the totals on this graphic. This is due to drip loss, that is freezing rain that drips off surface before freezing. Drip loss is highest when the temperature is closest to freezing and the precipitation rate is high.
Here is the NAM 4km Nest WRF-NMM model’s Snowfall using a 10:1 ratio.
A new winter storm with blizzard conditions will affect the Northern Plains this Weekend. Here is a snowfall accumulation map from the NAM-4km.
A powerful winter storm will bring heavy snow and strong winds to the Northeastern U.S. on Friday. The models are in good agreement. The NAM-WRF 4KM is producing snowfall totals in excess of 3 feet. In fact, the latest 00Z run tonight is producing amounts of 41.5″ using a 10:1 snowfall ratio.
The model animation from the WRF-NMM shows how strong the storm will become
as it moves up the east coast. Blizzard warnings are in effect for parts of the New England coast.
Latest 18Z track model guidance continues to remain tightly clustered around a landfall location in New Jersey. The 12Z ECMWF is very consistent with its previous runs and the GFS. Below is the spread and the mean (consensus) forecast tracks from the 12Z dynamic models / 18Z statistical models.
The mesoscale models are in good agreement of a low level wind max from 900-800 millibars around 100-110 knts that will move inland as Sandy approaches the coast. The NAM 4km nest is forecasting surface gusts in the 80 knot range over open water which seems reasonable. Generally a 90% reduction is used in warm core eyewall from 850 millibars, to estimate surface wind speeds (10 meters). But since this system will not have very much deep convection, that will likely be too generous. My feeling is that much of the wind at 900mb will remain aloft due to the lack of deep convection, but occasional gusts will make it to the surface in some of the heavier showers that will rotate around the center of the cyclone. If the models verify with the 850mb wind forecasts then it seems almost certain that surface wind speeds will exceed 70 mph in gusts. Also, based on the NAM 4km it appears very strong gusts may occur much further north, near Boston. On the order of 60-70 mph near the coast.
Below are two images. The first is the latest track forecast. The second is the 4km WRF Wind Gust Forecast. Note the fetch of 70+ wind gust from Nantucket to the New Jersey Coast.
Click this link for the 36 hour animation of the surface wind gust forecast
Added 925 Mb winds to the NAM, NAM CONUS Nest & HWRF Models. They are in the drop down menus. Should be available with the 10-28-12 12Z runs.
Below is the forecast 925mb winds (just above the surface) as Sandy makes landfall. Winds of 95 knots are forecast by the HWRF near Long Island. Mixing of these winds near surface by heavy rain showers will likely transport gust to 70 knots at times as the strong gradient north of the center rotates through.
The GFS 850mb vorticity was added this past weekend to the GFS Tropical menus. The 850mb vorticity can be a potential early indicator of tropical cyclone genesis.
The 850mb vorticity parameter has already been part of the ECMWF model guidance for a number of years.
Fixed the 88D image map for Witchita, KS.
The Hurricane WRF (HWRF) Model received a physics upgrade today. More information is available from the NWS TIN. The model graphics at Wright-Weather.com will incorporate these changes.