2013 Chasing Days

Want to know when your best chance to go storm chasing will be?  In a new segment on my blog, I will post periodic updates informing you of when your best chance of tracking down that big storm could be.

Based on the latest model guidance, these are the days I consider their to be a chance of severe weather in the short to medium range.

February 9th

The latest Day 2 Outlook from the SPC shows a slight risk of storms across portions of northern Texas and southwest Oklahoma.  The main threats here will be wind along with the potential for a tornado or two and some small hail.  These storms will occur along and just in front of a sharp cold front pushing east through the region.  Limited moisture and instability will keep this threat relatively low.

February 10th

The latest Day 3 Outlook from the SPC depicts a slight risk of severe thunderstorms across eastern Texas, most of Louisiana, and western Mississippi.  These storms will be associated with the same warm sector and advancing cold front as the previous day's storms.  Once again, limited moisture and instability will preclude a more significant threat.  Nevertheless, damaging winds will be the main threat along with some potential for marginally severe hail and a couple tornadoes.

February 11th and 12th

Thunderstorms may continue in some limited instability and moisture along areas of the Gulf Coast and across southern Georgia and northern Florida.  Once again this should be a limited threat with only a few damaging wind reports or hail reports.  Shear values support a weak tornado or two.





February 13th

Thunderstorms will exist across portions of central Florida during this period.  Moisture will be fairly good but instability will be limited still.  The main threats should be damaging winds and some marginally severe hail though a tornado or two cannot be ruled out, especially in the northern sections of the threat area.



In this section, I will give some estimates on severe weather dates in the long term.  These dates are not based solely off of model guidance but rather based on information from teleconnections and other knowledge.  It is important to remember that these dates are far from set in stone and the farther away they are, the more likely they are to change.  But I figured hey, let's have some fun and see how close I can come on some of these springtime events.  Below is what I am thinking for events through about Mid-April.

February 19th - Southern Texas
February 20th - Gulf Coast
February 21st - Florida
February 24th - Southern Plains
February 25th - Mississippi Valley
March 6th - Mississippi Valley
March 7th - Deep South
March 21st - South/Central Plains
March 22nd - Deep South
March 23rd - Southeast
March 25th - Mississippi Valley
March 26th - Southeast
March 30th - Southern Plains
April 2nd - Southeast/Midwest
April 4th - South Plains/Mississippi Valley
April 5th - Southeast
April 10th - South Plains/Mississippi Valley
April 11th - Southeast

Be on the lookout for my next update in a few days!

Update: February 7-9 Northeast Winter Storm

Surface chart as of late this afternoon

A major winter storm is set to begin tonight and continue through Saturday night in some areas of the Northeast.  A low pressure system, currently located around northern Illinois, will move east tonight into northern Ohio by morning.  Meanwhile, another low pressure system, currently located along the Georgia and Florida border, will push up the east coast tonight reaching the North Carolina coast by morning.  By Friday evening, the coastal low will be located off the coast of New Jersey and Delaware, where it will merge with the energy from the Midwest low pressure.  As this happens, the coastal low will deepen dramatically reaching sub 980 mb readings according to the 18Z runs of the NAM and GFS.  The peak strength of this low will be overnight Friday off the coast of New England.  This will be when the heaviest snow falls and when the gustiest winds occur then.  By Saturday morning, the low will start to weaken and move slowly to the east throughout the day.  Only a few lingering snow showers will likely remain across portions of New England, especially near the coast, by the time Saturday night comes around.

So when can you expect the precipitation to begin in your area?

To the right is a map I made depicting the onset of the precipitation from either of the lows.  The earliest onset of precipitation is occurring right now across areas near Lake Ontario as snow slowly begins to cover this area.  By tomorrow morning, snow will be covering many areas across Upstate New York, Vermont, and the western portion of New Hampshire, Massachusetts, and Connecticut.  Most of this will be in the form of snow associated with the low originating from the Midwest.  Precipitation will also be occurring across Ohio from this low.  Meanwhile, the coastal low will be responsible for rain, snow, and sleet starting by tomorrow morning across eastern Pennsylvania, New Jersey, and the lower portion of New York and Connecticut.  By midday precipitation will encompass most of the Northeast.  Northern Maine will be the last are to see the onset of snow, occurring either tomorrow afternoon or tomorrow night.  It should be noted that this denotes only when the precipitation will begin for an area and not when the heaviest snow will be.

So when will the heaviest snow fall in your area?

To the right is a map I made showing when the heaviest snow will likely fall in each area.  Keep in mind that this is the heaviest snow with respect to each area.  This means that some areas will receive heavier snow than others but this map does not take that into account.  In general, the areas receiving the heaviest snowfall will begin in the west and move toward the north and east as the time period progresses.

So how much snow can you expect?

Snowfall totals are still in question for some areas as the exact track of the lows, especially the coastal low, could result in drastic changes in snowfall.  For instance, in the 18Z run of the NAM and GFS models, the NAM runs the coastal low a little closer to the coast.  This means the difference between 18" plus of snowfall for New York City with the NAM track and 5" to 10" for the GFS track.  With that in mind, to the right is my prediction for snowfall totals starting this evening through Saturday night from this system.  This will be the first major winter storm for many of these areas in nearly two years.  The heaviest snowfall

totals appear as though they will span from near New York City northeastward into southern Maine.  One thing to consider is that especially along the coast, strong winds will also accompany this snowfall resulting in blowing and drifting snow.  To the right is what I expect for wind gusts during the event.  For most areas wind gusts will only cause minor drifting and blowing.  However for coastal Maine, southeast New Hampshire, eastern Massachusetts, Rhode Island, Connecticut, and Long Island, winds could cause major drifting of any accumulated snow and result in some isolated power outages from falling limbs and perhaps a few trees.  People in these areas should be prepared for the worst case scenario that they could be without power during the winter.  Temperatures Saturday night after the storm will be quite cold too with most areas getting down to 20 or lower.  Some areas will even see temperatures at or below zero.

Bottom line, if you do not need to travel during this storm, don't!  Stay safe everyone.

February 7-9 Northeast Winter Storm

A winter storm will impact portions of the Northeast beginning Friday and continuing through Saturday Night.  While confidence is high that this winter storm will form, differences in model tracks and timing have left some questions.  Below are the 12Z and 18Z GFS and NAM model runs depicting snowfall through Saturday evening.

The main difference here is the GFS starts the formation of the low pressure off the coast of the Carolinas about 6 hours sooner than the NAM model does.  This time difference results in the precipitation shield reaching the Northeast sooner and more of the precipitation falling overnight.  The nighttime temperatures will be more conducive for snow or sleet to occur at the surface and thus accumulations could occur.

The other difference is in the track and strength of the low pressure.  The 18Z GFS model is depicted to the right and the 18Z NAM model is depicted below that.  The NAM model takes longer to mature the low and keeps it farther off the coast than the GFS model.  The result is a more impressive look to the GFS but the NAM is still able to achieve similar snowfall amounts in most areas due to its higher QPF (Quantitative Precipitation Forecast) totals.  This is likely due to its better understanding of processes related to the deformation zone as well as stronger PVA (Positive Vorticity Advection).

Another major difference has to do with the phasing of the energy between the shortwave cutting through Michigan and Upstate New York and the Coastal Low.  The NAM model appears to hold off on phasing these energies until after the Coastal Low is north of New York City.  Meanwhile, the GFS phases the energies much sooner, in the vicinity of New York City, about at the point when the low begins to push more east, rather than north.  This earlier phasing helps to strengthen the low and produce heavier precipitation amounts across the New York City area instead of out to sea and along coastal Maine as the NAM does.

Keeping in mind these model differences, a major snowstorm will impact portions of the Northeast beginning Thursday night.  Given what the current American models are thinking, I would lean closer to the GFS solution as it seems to have a slightly better handle on how the energy will evolve.  Additionally, it has been the more accurate model thus far for this event, predicting better what would happen today over Texas with a portion of the energy that will help create this Coastal Low.  The Arctic Oscillation is also forecast to be slightly negative, which could be further evidence for favoring the GFS solution.  Another way to verify this thinking is to consult the ECMWF model.

The ECMWF model has a track of the low that is very similar to the GFS model.  One reason for the similarities in these models is they are both global models, which means they are able to take into account information from the whole globe and produce an output for the globe.  The NAM model on the other hand only takes into account information from around North America and therefore only has an output in that same area.  One major similarity between the ECMWF and GFS then is that they both forecast a strong area of high pressure (ridging) that results in the stalling of the Coastal Low off the coast of New England (as shown in the image with the black line showing the blocking ridge).  This results in a longer period of precipitation as the low slowly moves and may have been why the GFS phased the energies better as previously mentioned.  The NAM model does not depict as strong of a high pressure due to its limited domain.  Therefore, it continues the Coastal Low on a northern track instead of stalling it.  Now it is likely that as the event draws nearer that the NAM model will understand the effects of the high pressure more, but for now this is a major influencer of the Coastal Low track that the NAM is missing.  The GFS and ECMWF both forecast the ridge to begin breaking down over the Atlantic Ocean late Saturday night.  This would allow the Coastal Low to begin moving out to sea as opposed to northward as the NAM model has depicted.  This will result in major snowfall forecast differences in the northern portions of Maine, New Hampishere, and Vermont.

So what am I thinking in the way of snowfall amounts then?

Well, given the overall better solution of the track via the GFS and ECMWF but better feedback via the deformation zone by the NAM and ECMWF, I will go with a blend of the best qualities of all of these models.  Below is my snowfall totals for the event across the Northeast.  This is subject to change but as of right now this is my best estimate.

The snow will be combined with strong, gusty winds in many areas, especially along the coast too.  This will result in blowing and drifting snow, making travel almost impossible at times Friday and Saturday.  Stay tuned to this evolving situation.