Wednesday, January 27, 2010

Winter Stormcast Zone:
Jan-Feb 2010
Collaborating forecasters:
Brisko, Winterman, Dakota, PasadenaMatt, Ryan K., Mr. Foot

12:30 PM Friday 1-29-10: SNOW THREAT UPDATE
 Lead Stormcaster Ryan K.,
Sparrows Point High School ~ Edgemere, Maryland
---As we expected, the latest models (12z Suite) have gone quite a bit to the north and have led us to believe a 2-4'' snowfall is expected Tonight into Tomorrow. 
---The NWS will likely issue advisories for the Metro areas this afternoon as they are likely waiting for confirmation of the north trend.
---The storm is already producing virga in the area, which makes things 12 hours ahead of schedule (obviously something that was not expected to occur.)
---There is a potential for a more significant event if the trends continue and observations show a continued northerly component in movement.

CURRENT THOUGHTS Despite the raging snow/ice storm in the southern plains, the waiting game continues in central Maryland to see what happens with our previously expected snow event. Things went away, but the trends definitely point to one thing: this is coming back north. Precip is back into the area, and if this occurs, say only 50-75 miles more north which is definitely possible, we could get a decent hit. At this point, the amount of snow only looks to be 1-2 inches, but as I said in last nights e-mail things could change (and that has already begun to occur.) All of the afternoon models so far have pointed to that farther north solution, leaving DC in a good area for snow and our area on the northern fringe.

MODEL ANALYSES The most aggressive model at this point is the Canadian model which at its latest run gave the area 4-6” of snow. This model has led the models on their trek northward, and in the 12-19/20 blizzard, this model led the way. Also, the ECMWF (European model) which has been the best model according to statistics, trended north last night. In my opinion, if this trend is one that continues this afternoon with the 1PM run, then we will have a legitimate risk for a nice snow event.

INDICATOR OF THREAT This map (12z GFS snow output) shows how close we are to notable snow, the 1-2 is here now, but the slightest shift, 25-50 miles puts us in 3-4’’ with any more than that giving us a 6’’ snowstorm. The chance is definitely there, so stay alert to our latest updates.

THE MAIN ISSUE: It appears the Polar Vortex (PV) centered over northeast Canada is being modeled too far south and stronger. In actuality, the trend this winter that the PV has been often over-projected like that, only to trend weaker and north. It is likely that this occurs once again and is factored into the forecast. With some models trending from heavy snows to southeren suppression toward eastern Virginia, we need to question which outcome will rule.

TRACKING THE POLAR VORTEX. This section includes links to the NCEP site on the 4 daily model runs that provide a sense of where the polar vortex is located. We believe monitoring this closely the next 48 hours will be our canary in the coalmine.
00Z GFS (7pm) | 06Z GFS (1am) | 12Z GFS (7am) | 18Z GFS (1pm)
00Z NAM (7pm) | 06Z NAM (1am) | 12Z NAM (7am) | 18Z NAM (1pm)

MY PROJECTION:  Strength of the high pressure system will play a big role. The high was been modeled weaker over the last few days and that will help allow the storm to jump a bit to the north. The NAO setup is something to be watched closely because the index could easily rise as the PV lifts north 50-100 miles, thus negating any suppression potential. The result would be another December 19, 2009 type storm with 12-18" coming well north of current public forecasts.

---a "50/50 low" in place in the Canadian maritimes
---Artic air to invade the Mid-Atlantic Friday morning.

---The temperatures will allow snow ratios to be quite high, near 17:1 for some.
---The NAO rising by Friday may negate suppression

---South of DC including Charlottesville,VA : Potential for 12" or more extending into the Piedmont areas of VA/NC.
---Delay of arrival has moved storm timing back to Saturday/Sunday due to the blocking

BUST POTENTIAL? Right now the storm is modeled south of the area, with the models putting no snow north of DC. However, NWS forecast offices remain vigilant with this storm. Model trends as of Tuesday night were promising, with the 7pm NAM showing an apparent northward drift in eventual track of the southern low.

MY NEXT UPDATE: Wednesday afternoon 1/27 with a preliminary map by evening.

The forecast team has increased confidence a major winter storm will impact the Tennessee Valley, Mid-Atlantic and possibily the coastal areas of the Northeast Friday 1/29 to Sunday 2/1. Our analyses indicate precipitation amounts will likely be between a half inch to an inch which would lead to snowfall amounts that could exceed 6 to 12 inches across this area by Saturday night.  Read more by clicking the link below.

Arrival Thursday night: Tennessee,west VA, southwest VA.
Friday afternoon: Central MD and the I-95 corridor
Impact Afternoon bus routes, evening commute, weekend travel.

Liquid Equivalent GFS projection for BWI is already near 1.0"
Temperatures By 7 am Sat, 2 meter temps ~ 20 F across I-95 corridor
5000 foot temps by 7 AM Sat  -8 to -10 C range to maximize snow growth. However, were temperatures to trend even colder, this could reduce efficiacy of crystal production.

Ratios Temperatures that low may permit ratios of 15:1 to 20:1 across the Mid-Atlantic, promoting a potential snowfall that could easily exceed 12 inches by midnight Saturday.
Snowfall  These data suggest 6 - 12" is possible for the Mid-Atlantic.

VA: Charlottesville | Richmond | Washington, DC | Martinsburg, WV 
Akron, OH | Pittsburgh, PA | Lancaster, PA | Baltimore, MD

HPC Prelim Extended | HPC Heavy Snow/Ice | Sterling, VA 

1. Predict the high, predict the storm: A "banana high" type orientation may occur between a 1026 mb Atlantic ridge fueling moisture, a 1026 mb high progged to setup in southeast Ontario, and a 1038 mb high in the upper plains. This would slow the storms's forward movement and keep air ahead of the system cold for high ratios.

2. It's all about the O - as in NAO: North Atlantic Oscillation projections for late this week are showing an IDENTICAL pattern to that seen just prior to both the 12/19/2009 stsorm and the February 2003 blizzard. The negative trend has reintroduced cold air as evidenced by the second front sweeping east today. A slight easing of the NAO Friday and Saturday would permit the surface highs to drift that extra 50 or so miles north. This is the canary in the coalmine some TV forecasters overlook in their long range projections.

3. If it's snowing in Memphis... Winter Storm Watches abound across the
south central states already. HPC shows a classic low-rider track of a southern surface low bringing oogobs of El-Nino juiced moisture with it from the Pacific. Hey if it's going to snow in Memphis, there'll be snow in Baltimore.

4. The secret lies with Charlotte. Mid-level indicators such as the GFS current 850 mb temp/height/vorticity map as compared to the projected map for 7 AM Friday 1/29 reveal the secret to our forecast. All those sub-polar temps and heights in northern Canada reform a new center right
over top of Charlotte, North Carolina. That means all the associated energy can easily tap Atlantic moisture and synthesize it with Canadian cold.

THE NEXT UPDATE APPROXIMATELY 9 PM THIS EVENING. The following are focal statements regarding mission of the Winter Stormcast Zone.

OUR MONTHLY FOCUS: A collaborative investigation of climate data and weather trends across the Northern Hemisphere which can be used to signal time periods when significant winter weather is likely to develop in the eastern United States. Contributors include our student climate research teams, the winter stormcasters and professional meteorologists.

OUR BI-WEEKLY FOCUS: Synthesizing specific data indicators regarding the atmosphere, ocean and polar regions. Evaluating those results against a set of criteria in order to determine likely scenarios which will result in significant winter storms.

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