Palm Sunday 2013 Significant Winter Storm -- First Call

First accumulation map rides on most recent model trends and accounts for model majority. Current thinking is a major snowstorm will erupt from the Rockies and produce major accumulating snow across much of the Plains, Midwest and Ohio Valley. Latest model trends support amounts over one foot in some isolated areas, and it is these areas that are in the lowest confidence zones.

For my first forecast, I am predicting a light accumulation zone of 1-3 inches in the Lower Great Lakes and far northern Central Plains states like northern Nebraska and northern Iowa. Recent model trends have been showing these amounts, and in accordance with what seems to be the final track, I agree with model guidance on those amounts. General 4-8 inches is predicted from the Front Range in Colorado across the midsection of the Plains, through the southern Midwest and into the Ohio Valley. I'm liking the higher end of that scale for portions of central Nebraska, north central Kansas and towards I-80 in Illinois and south of Gary, Indiana. Darker blue depicts 8-12 inch forecasts. I expect these amounts to be most prevalent from northeast CO into border counties of Nebraska and Kansas. Keep in mind that this zone is uncertain, and will likely take another ~12 hours to determine where (and if) that higher accumulation zone sets up. A west to east line continues with the 8-12 inch predictions, cutting through northern Missouri and Central IL/IN into Ohio. Isolated spots in central Illinois, central Indiana and central Ohio could see 12 to 16 inches out of this event, more likely in the lower end of that spectrum.

Andrew

Palm Sunday 2013 Significant Winter Storm (Updated 3/21)

Model guidance has come into line with its first consensus for the storm. The model choice is for the storm system to drop well into the Plains before skirting to the east-northeast/northeast up the southern Midwest region and into the Ohio Valley. This track would blanket portions of Illinois, Indiana, Ohio and more Plains states out west with snow that could reach beyond one foot, especially in the Midwest. Shown above are four model guidance members, with the Canadian model in the top left, the American model in the top right, the European model in the bottom left and the United Kingdom's model in the bottom right. Due to timing issues, this is the best depiction I could get of the storm at tis timeframe, which is 96 hours away (4 days away). The colors shown are 500 millibar heights, while the mean sea level pressure values are shown in black contour lines. The Canadian and European models are sticking to a solution that has the storm in the Midwest/Ohio Valley at this timeframe, while the American and United Kingdom models favor the system being offshore by the time Hour 96 rolls around. This shows how there remains considerable uncertainty in the track even though we are only a few days away.

Notes on model guidance... Slight trend north has been observed with most recent forecasting guidance, will have to watch this as models tend to bring the storm to the north after dropping south, like we saw the models do with this storm. Model uncertainty remains too great to pick any particular forecast.

Analysis of multi-model snowfall forecasts above shows a clear consensus on where the heaviest snow should fall. Portions of Illinois, Indiana and Ohio are likely to receive the brunt of this storm system, with accumulating snow continuing out to the Plains and possibly into the Northeast. Short range American NAM model takes the storm's snowfall a bit further to the south than other model guidance, bringing snows just over 1 foot into Ohio and a portion of Indiana. Nebraska and Kansas are also hit hard. American GFS model hits the same areas with heavy snow, but is slightly weaker in Illinois and Indiana. European model blows up the snow in IL/IN/OH, with formidable snows back out to the west. Canadian model is in its own world, I have no desire to take its solution seriously.

NOTE: Nebraska SHOULD be included in this graphic, time constraints would not allow me to go back and put NE in.

Current thoughts are shown above, with a wide stripe of accumulating snow potential from Kansas and Nebraska (even though NE is not marked, it is in the stripe) into the southern Midwest and Ohio Valley, continuing through the Northeast. I am feeling confident of NE/KS/MO getting in on an accumulating snow event, however confidence drops when we reach the Midwest and Ohio Valley. The storm track is not set in stone just yet, and we could very well see a shift further north in the next 24 hours. I did put the Northeast in this graphic in the chance that some snow does hit that area. Again, even though model forecasts aren't too supportive, there is lots of time for change. I will put in amounts when models clear up further, probably in tomorrow afternoon's update.

Andrew

Palm Sunday 2013 Potential Significant Winter Storm

Model guidance remains disorganized as far as where this storm will go. The past 24 hours have seen model guidance stage a southward shift, now bringing the storm through the southern Midwest and into the Ohio Valley. This track would bring the heaviest snow more into the southern Midwest, Plains and portions of the Ohio Valley. Models shown above are the Canadian model (GEM), American model (GFS), European model (ECMWF), and the United Kingdom's model (UKMET). The forecast period is for Hour 96, which is 4 days away from today, and is forecasting 500 millibar heights in colors and pressure values in the black contour lines. Canadian, European and United Kingdom model guidance prefers a southern track, which would take this system through the southern Plains into the far southern Midwest and northern Gulf Coast states, before moving offshore and possibly instigating a disturbance out there, although model guidance is too great to divulge anything further than that for the Northeast. European model has definitely been more consistent than other guidance, with a solid track of having the storm go through the southern route. Other model guidance has been catching on as of late, with all but the American model pulling for a southern track.

Rather than just stare at the models and see what we can get out of them, let's look at the projected atmospheric set-up and see what the atmosphere is most likely to do with this system. This is the forecasted 500 millibar height anomaly from the American ensembles (also supported by at least one other ensemble system), where cold colors indicate low pressure and warm colors depict high pressure. This forecast is valid as the storm is moving towards the Midwest and Ohio Valley. We'll start off with the monumental high pressure system over northern Canada and Greenland. This type of set-up is one that typically allows storms to be suppressed to the south. In that vision, the European model's idea of the storm taking the southern route is not that far-fetched. However, there is an obstacle that must be overcome for this storm to be pushed far enough south to validate the European model's idea.

When the storm falls down into the Plains to begin its trek either east or northeast, it will naturally provoke high pressure in the Eastern Seaboard. This can be anticipated by the general idea that the low pressure system pushing down will force high pressure to form and push up to equal out the stress inflicted on the atmosphere. Because of this high pressure in the Eastern Seaboard, the storm could very well want to take the northern route and bring heavy snow to the Lower Great Lakes and northern regions of the Midwest, like I showed yesterday. Previous model forecasts enticed the idea of that ridge acting on the storm system and sending it north, but more recent guidance has the ridge being overwhelmed by the low pressure system, which is also very possible.

Here is my top analog for the upcoming Palm Sunday 2013 winter storm. I analyzed multiple analogs from the St. Louis University website, and chose the one with the highest correlation with the latest GFS forecast at the 300 millibar level and 500 millibar levels. These two levels are the most crucial in analog forecasting, as they project the jet stream pattern and high/low pressure alignment, both of which are key in this storm system in particular.

Considering how model guidance has tended to bring storms to the north just a day or two before the event happens, I'm not willing to discount either solution right now. I think both the northern solution and southern solution have valid reasoning and solid evidence as to why each could happen. The next 48 hours will be crucial to see incoming model forecasts as the storm edges closer to shore.

Andrew

Palm Sunday 2013 Potential Winter Storm

There is indeed potential for a winter storm from March 23rd to March 25th.

We will do a model overview today. All models are forecasting Hour 144 (6 days away), and are showing 500 millibar heights in colors with sea level pressure in contour lines. To start, we will analyze the American GFS model. This model takes the storm into the southern tip of Lake Michigan at a minimum pressure of 992 millibars, considered pretty strong for an onshore storm system. Typically, storms will easily exceed that strength offshore in the Pacific or Atlantic, but close to 990 millibars onshore, while not infrequent, is relatively uncommon. Regardless, the storm system is taken through the Great Lakes, allowing significant snow to bury the Midwest and Great Lakes, upwards of one foot in many states west of Lake Michigan and into the Plains.

The general synopsis that is probable to happen is a storm system dropping from the northwest into the Plains, and then moving either east or northeast to bring winter weather to people in the north and severe weather to people in the south. The models are having trouble with grasping how far south the storm will end up dropping into the Plains and what direction the storm will head after encountering the high pressure in the Southeast and East US when the system is in the Plains.

We're going to move onto the foreign models now, and we start that part of this post with the Canadian model. Before I get into this model, know that it is notorious for being unreliable with storms and should not be trusted easily, no matter how amazing the solution is. The Canadian model has this storm system moving through south-central Illinois, dropping over half a foot in cities like Chicago, Gary, maybe even into Iowa (I haven't had an opportunity to see precipitation charts, just a few meteograms). The Canadian model drops this storm to 998 millibars, suprisingly weaker than the American model. The reason it is so surprising is because its usually the Canadian model over-exaggerating a storm's strength and not the other way around. Something to watch for the future? You bet.

We now go onto the United Kingdom's model. Because the phrase United Kingdom is too long to type every time I mention the model, I will refer to this forecasting system as the UKMET, its official model name. The UKMET sees this system weakly progressing in a track from Alabama to Ohio that would bring severe weather to the Southeast and snow to the southern Midwest. This is the weakest model yet of the three we have seen thus far, and its track is the third option of the three models. As you can already tell, the chances of figuring out a track for this system today are quite low.

The last of our foreign models is the European model. While it is typically regarded as the top forecasting model in the world as far as accuracy goes, I have been seeing a recent drop-off in its accuracy, and you may want to note that when taking this forecast into account. The European model doesn't show the system anywhere near the Midwest. If you look closely, you will see it off the coast of the Mid-Atlantic. It has cut across the South and prohibited any major snow event from occurring in the Midwest or Ohio Valley. While it is the fourth different solution from the four models we have seen, the European has been rather consistent with its idea of a storm system offshore the Carolinas for at least two runs. In the other models defense, the American GFS' idea of a major snow event in the Midwest, Great Lakes and Plains has been trending as well. Looks like the traditional American vs European model battle is setting up here, with the other foreign models just doing their own thing.

I did take a look at a few ensemble sets. Two ensemble sets, the American ensembles and another set called the North American Ensemble Forecasting System (NAEFS) are showing solutions that are very nearly identical. Because the NAEFS does not provide precipitation graphics on the website I used to evaluate these ensembles, I looked at the American ensembles for precipitation. The American ensembles predict a major snowstorm from the east central Plains into the Midwest and Great Lakes. Cities like St. Louis, Chicago, Milwaukee, Detroit and Gary would all be affected, many of them by pure snow. It is also worth noting that the Canadian ensembles and European ensembles keep the storm system further to the south. While the European ensembles cancel out a Midwest snowstorm altogether, the Canadian ensembles still throw a swath of accumulating snow at all of the aforementioned cities. Precipitation charts are not available on the European ensembles.

My current thoughts on this system are solid enough for me to show a swath of significant snow potential and a swath of severe weather potential. I am leaning towards the very weak model consensus that there will be the aforementioned types of weather in their respective regions. The red L's show where current model forecasts have this system, and as you can see, the consensus is loose at best.

Stay tuned to The Weather Centre for daily updates on this potential winter storm.

Tornado Warning - Atlanta, GA Metro Area

ULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
600 PM EDT MON MAR 18 2013

THE NATIONAL WEATHER SERVICE IN PEACHTREE CITY HAS ISSUED A

* TORNADO WARNING FOR...
SOUTHERN CHEROKEE COUNTY IN NORTH CENTRAL GEORGIA
NORTHERN COBB COUNTY IN NORTH CENTRAL GEORGIA
NORTHWESTERN DEKALB COUNTY IN NORTH CENTRAL GEORGIA
FORSYTH COUNTY IN NORTH CENTRAL GEORGIA
NORTHEASTERN FULTON COUNTY IN NORTH CENTRAL GEORGIA
NORTHWESTERN GWINNETT COUNTY IN NORTH CENTRAL GEORGIA
SOUTHERN BARTOW COUNTY IN NORTHWEST GEORGIA
NORTHERN PAULDING COUNTY IN NORTHWEST GEORGIA
NORTHEASTERN POLK COUNTY IN NORTHWEST GEORGIA

* UNTIL 645 PM EDT

* AT 557 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
LINE OF SEVERE THUNDERSTORMA CAPABLE OF PRODUCING A TORNADO NEAR TAYLORSVILLE...
MOVING EAST AT 60 MPH. THERE IS ANOTHER AREA OF ROTATION CAPABLE OF PRODUCING
A TORNADO SOUTHEAST OF BRASWELL.

* OTHER LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO
EMERSON...ACWORTH...KENNESAW...MARIETTA...WOODSTOCK...HOLLY
SPRINGS...CANTON...MOUNTAIN PARK...SANDY SPRINGS...BUFFINGTON...
ROSWELL...DUNWOODY...ALPHARETTA...MILTON...FREE HOME...NORCROSS...
BERKELEY LAKE...JOHNS CREEK...DULUTH...CUMMING AND SUWANEE.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

HEAVY RAINFALL MAY OBSCURE THIS TORNADO. TAKE COVER NOW! IF YOU WAIT
TO SEE OR HEAR IT COMING...IT WILL BE TOO LATE TO GET TO A SAFE
PLACE.

IF YOU SEE WIND DAMAGE...HAIL OR FLOODING...WAIT UNTIL THE STORM HAS
PASSED...AND THEN CALL THE NATIONAL WEATHER SERVICE TOLL FREE AT 1 8
6 6 7 6 3 4 4 6 6. YOU CAN ALSO TWEET YOUR REPORT USING HASHTAG GAWX.

A TORNADO WATCH REMAINS IN EFFECT UNTIL 1000 PM EDT MONDAY EVENING
FOR NORTHWESTERN GEORGIA. A SEVERE THUNDERSTORM WATCH ALSO REMAINS IN
EFFECT UNTIL 1000 PM EDT MONDAY EVENING FOR NORTHWEST GEORGIA.