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Forecast Outlook Monday, November 3, 2008, snow, rain, snow, and rain? =)

My forecast from last Thursday is holding true as areas of snow and rain will begin increasing through the Pacific Northwest, Rocky Mountains, and into the Great Plains over the next few days. Conditions in the upper atmosphere initially favor a split-flow scenario along the Aleutians and into the Pacific Northwest, with a southerly track speeding towards the desert southwest. Following the initial development, at least three more systems will follow enhancing flow into Rockies with the final system developing an enclosed circulation enhancing the favored prediction of snowfall in the Northern Great Plains by midweek. The greatest uncertainty is the exact degree and direction of the large scale flow for the week.

Current thinking of NAM shows very respectable snowfall accumulations over the next few days (note below).

NAM 84 Hour Forecast Snowdepth Animation (3 hr intervals)

As you watch the animation above (click for full size), note the slowly increasing accumulations in upper elevations of the Cascades, Sierra Nevadas, and Rocky Mountain ranges. This animation is valid through 00z Friday, and just prior to the last three hour interval significant accumulations are visible in the Northern Great Plains. Please see the following post for more information on the product.

GFS is in ‘general’ agreement with location and intensity of projected precipitation for the period (note below).

GFS 180 Hour Forecast Snowdepth Animation (6 hr intervals)

However the interesting part is the projected position in area of highest snowfalls for the great plains. Notice that after the loop passes the 00z Friday interval, GFS feels the area of greatest snowfall is further east into North Dakota than NAM predicts. Another interesting segment of this scenario is that is also the general area that GFS was forecasting last week. It will definitely be an interesting few days!

On the liquid side of things, an area of lower pressure is becoming better organized and will trail up the eastern coastline for the next few days (note below).

GFS 180 Hour Liquid Precipitation Animation (6 hr intervals)

The exact forecast track is a little indeterminate at the moment, with models hedging bets as to how long she will hug the shore before heading completely out to sea. Above is what GFS is thinking at the moment.

Another interesting portion of the above animation is the potential for tornadoes that I mentioned last week. Depending upon the degree to which the enclosed system deepens over the next few days, plus a myriad of other factors, will determine the intensity to which tornadoes will form on Wednesday and Thursday. I can say from my preliminary evaluation, that the probability for tornadoes is above normal, especially in the east-central Great Plains.

On the tropical front, as I forecast last week, tropical development has occurred in the form of Invest 93L. I am not overly excited at the moment, but some development is possible with this system, as well as the line that I previously defined through the Bahamas and up to Bermuda. If something of significance develops I will let you know.

As always stay tuned to your favorite weather outlet, stay informed, and stay safe.



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