Thursday, December 3, 2009

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Dec 5 Game Is On

Reader photo from the Houston Chronicle, Friday 12/4/2009

10:00 PM UPDATE Friday, 12-4-09  [revised from 12/3] Synopsis of forecast ideas for the Saturday 12/5 event: Marginal but improving boundary layer temperatures tonight and Saturday across the Mid-Atlantic will permit snow to fall on the fabled date of 12/5. Text of the current NWS Winter Weather Advisory for the Baltimore region spells out the timing in good detail. My official storm grade call for this will be 2.4" at BWI airport. Acccumulations east of I-95 between Richmond and Philadelphia will be enough for a pretty picture, but west of the cities there is increasing potential for amounts closer to the original call of 4" or more. The good news is that cool-to-seasonally cool temperatures follow the storm, not the "much below normal" regime originally forecasted.

NOWCASTING THE 12/5 KICKOFF STORM: For a precip timeline at BWI, check projections by the GFS and the NAM computer models. For the surface perspective, monitor 3 hour plots for the southeast and northeast, as well as 3-hour pressure falls and temperatures. A more comprehensive view of factors influencing this system can be observed from the water vapor loop, and by tracking upper level short-waves on the 850 mb / 700 mb / 500 mb charts. (note:  click save instead of open, and rotate the images) It would also be interesting to check our old friend the North Atlantic Oscillation. Any "westward trend" in the model projections may also appear right about now as a slight rise in the index, even if currently negative.

ACCOUNTABILITY NOTE: Outcome of this event will be graded according to criteria developed that scores accuracy of the original first call made on November 1, 2009, with followup analysis on 11/11/09 and 11/24/09.

LOOKING AHEAD: Next Wednesday and Thursday features a powerful cross-country storm producing mostly rain across the I-95 corridor and eastern Mid-Atlantic. Timing of this system will need close monitoring. Early indications are that surface temperatures from the western I-95 suburbs into central Pennsylvania between 3AM - 7AM on Wednesday may be low enough to spawn a short period of light freezing rain.

TEXT OF ORIGINAL 12-3-09 POST (left for comparison to updated forecast ideas)

WHY ONLY A INCH OR SO? DON'T WE DESERVE MORE? Good points were made about this in the comments by a meteorologist with the handle "TQ" whom operates his own valuable analysis site, and administers the longest-running snowfall forecast contest on the web. TQ's point is that even though 5,000 foot level temps may be <32 F, 2 meter temps around 35 F in Maryland and Virginia will keep the snow-to-liquid ratio quite low: 6- or 8-to-1. Running the conversion of .30" potential moisture, results in a maximum 2.4" falling under best case conditions, but much less reaches the ground, and those boundary layer temps prevent most of that from accumulating. Remember, students at Mt. Saint Joseph's School in Baltimore City early this week also saw that problem coming.

HOUSTON, WE HAVE A PROBLEM (with you!) Seriously, if you want a guaranteed good December snowfall, don't hold out for Baltimore: head to Houston, Texas - which may received 2 to 6 inches on Friday 12/4. The best we might muster in Charm City.. an inch. Which means all this storm analysis is really just ego cover for snow-starved Mid-Atlantic powderhounds. We have to compensate in some way for the jealousy of reading about WINTER STORM WARNINGS for the Houston/Galveston area. Yes, you read that correctly-- areas known more for hurricane impacts than snowstorms will receive snow before Baltimore the SECOND year in a row. They sure didn't miss a chance to enjoy it all.

Reader photo from the Houston Chronicle, Friday 12/4/2009.

Still, if snow falls across our region this weekend, it only reinforces the legendary prowess of the date itself: on the fifth day of December, the Baltimore area has been one of many that will have seen snow the sixth time in eight years on the same date. Details of what happened on previously "fabled fifths" of December can be found in Mr. Frank Roylance's recent report on his Baltimore Sun weather blog.