Lake Effect Tonight and Frost Tomorrow Night

Lake Effect

Lake effect rain and snow showers will likely get started shortly after sunset tonight and will continue throughout the overnight.  At this point it looks like if you are inland of Lake Ontario that the atmosphere should be cold enough in the low levels for a complete changeover to snow by midnight.  This activity will start across the northern half of Jefferson and Lewis Counties and sink south to around southern Jefferson and central Lewis Counties around midnight.  By sunrise the lake effect rain and snow will centered across the Tug Hill area.  As temperatures warm with sunrise, the lake effect snow will begin to change back to all rain by late morning and the band itself will continue to sink south slowly, perhaps reaching a few areas just south of the Tug Hill region.  By early afternoon if any lake effect rain is around it should begin to break up quickly as 850 mb temperatures warm and create a less favorable environment for lake effect.  The band may also move slightly north before dissipating.  To the right is what I expect for snowfall totals tonight and early tomorrow morning.  The gray area will have snowflakes possible tonight, the light blue area will have snowflakes likely with a dusting of snow possible, and the darker blue area will probably see a dusting a snow and perhaps up to an inch or so in some areas.

The Frost

Tomorrow night we transition to colder temperatures than tonight even.  Without the lake effect clouds and the stronger winds helping keep the temperature a bit warmer at the surface, temperatures will plummet.  A widespread frost can be expected for all areas in the north country with the exception of a few areas near the lake shore that will be protected by the warmer lake waters.  While most areas will see temperatures fall to between 27 and 32, a few areas could see mid 20s for low temperatures.  Regardless, everyone should take measures to protect their plants tomorrow night (and tonight also).  Fruit trees that have blossomed should only receive minimal damage to their blossoms but if temperatures do fall into the mid 20s, preventive measures to save the yield of the trees will be needed.  To the right are the predicted lows from the National Weather Service for tomorrow night.

Stay warm everyone, warmer weather is on the way!

Lake Effect Snow Sunday Night!?

Please tell me this is a joke!

I wish I could...  It may be mid-May but unusually cold air associated with a deep upper trough will affect Upstate New York and other areas of the upper Midwest and Northeast one more time (this should be the last frost for northern New York until fall).  Lows Sunday night will drop into the low 30s, resulting in frost in some areas of northern New York.  By Monday night, temperatures will likely drop into the upper 20s for regions away from Lake Ontario.  This will result in a widespread frost for many areas of northern New York.  As if this was not enough shock for everyone who has been waiting to kick Old Man Winter for good this year, some residents to the east of Lake Ontario may witness a certain white precipitation on Sunday night into early Monday morning.  I am talking of course about snow.

The Technical Stuff

Sunday night surface air temperatures will drop into the low 30s, as mentioned previously.  Meanwhile 850 mb temperatures are forecast to drop at least to the low 20s and perhaps the upper teens.  This magnitude of cold air aloft will be enough to create instability across Lake Ontario, as the current water temperature of the lake is 44.  Typically, at least a 13 degree Celsius temperature difference between the 850 mb temperature and the lake temperature is needed to be favorable for lake effect snow development.  Sunday night this temperature difference will exist from shortly after sunset into Monday morning.  The temperature profile will also be conducive to any precipitation that does form to fall in the form of snow away from the lake shore area.  Other parameters that are needed for lake effect snow development that will be in place Sunday night include less than a 30 degree wind shift between the surface and the 850 mb level, with most of the night having less than a 15 degree shift, and abundant moisture for the majority of the night in the boundary layer.  Additionally, the lake equilibrium level will be right around 10,000 feet the entire night, which is also favorable for lake effect snow development.

Where might this occur?

Taking all of this into consideration, it appears likely that at least a band of lake effect snow showers will set up on Sunday night to the east of Lake Ontario.  The band appears at this time that it will form over central Jefferson and north/central Lewis Counties and shift southward throughout the overnight.  The snow band will likely fall apart around sunrise Monday morning over the Tug Hill region.

Do I need to break out my shovel and snowbrush again?

Probably not.  While snowflakes will be in the air across the region, accumulations are probably not likely at this point.  Due to recent warm weather, ground temperatures have warmed significantly and the snow will probably not become heavy enough or last long enough in any one area for accumulations to occur.  However, minor accumulations under a half inch are not impossible if the band happened to become heavier or sits in one place for a few hours.  Minor accumulations are most likely on elevated surfaces, such as your car or hand railings.

Optimistic Closing Remarks (for those of you I just severely depressed...)

Now that I have you dreading Sunday night and contemplating your choice of living in northern New York, I will tell you that after this cold snap the weather will turn nice again.  Next week temperatures will slowly climb back to normal and next weekend we may even see slightly above normal temperatures again!  And there are some indications that more summer like weather may start to set in by late May into early June.

April 17-18 Severe Weather Update

Severe weather is underway from portions of northern Texas all the way into Indiana.  This system will continue to create severe weather over these regions this evening before beginning to shift eastward tonight.  The Storm Prediction Center has issued a moderate risk of severe weather for both today and tonight as well as tomorrow and tomorrow night.  The threat for today from the Storm Prediction Center is shown to the right, where the moderate risk exists across extreme portions of northern Texas, central Oklahoma, southeastern Kansas, and a section of Missouri.  The threats come in all forms today and tonight.

Tomorrow and tomorrow night, all threats will once again exist but the risk of tornadoes should be lower than today's threat.  To the right our the risk maps from the Storm Prediction Center depicting an area of moderate risk from northwestern Mississippi and southeastern Arkansas northward through extreme western Tennessee and Kentucky as well as the Missouri Bootheel and finally into eastern Illinois and western Indiana as well as a small portion of southwestern Michigan.

The rest of this blog post will attempt to put together what I believe will happen tonight and into tomorrow.  I expect thunderstorms to continue to increase in coverage this evening, eventually forming into a line of storms tonight which will continue into tomorrow morning.  The main concern here will be with the early discrete cells as well as with any cells that can form in front of the main squall line as the environment is set up well for rotating updrafts to lead to tornadoes within some of these storms.  Outside of these discrete cells, the squall line's main threat will be wind damage but some large hail as well as a few tornadoes will also be possible.  To the right is my threat area, with the red shaded area depicting the area with the greatest risk for severe weather, including tornadoes.

Tomorrow the squall line will continue to push eastward bringing about likely widespread wind damage reports in areas.  Once again, if discrete cells can get going in front of the main squall line, the tornado threat could be higher.  This is possible across the southern portions of the threat area.  However, there will likely be a tornado threat associated with the squall line itself as well, as a highly sheared environment with high helicity values will exist.  My threat area for tomorrow and tomorrow night is shown to the right, with the best threat for wind damage and a few tornadoes shown in red.


If you live in any of these areas please remain alert to the weather conditions over the next 36 hours.  Be sure you know what to do in case severe weather.

Lastly, I will leave you with two target cities where I would head to if I were storm chasing tonight or tomorrow.  For tonight, given where storms have already fired and where I believe they will continue into the overnight, I would say the best chance of seeing severe weather, including tornadoes, would be starting in Ardmore, OK and heading west throughout the night towards Fort Smith, AR.  For tomorrow, I would start in the afternoon around El Dorado, AR and continue towards the northwest heading into the evening toward Oxford, MS.  Now these are just my initial thoughts and obviously with storm chasing initial preparation should be altered as the most current information and conditions arise.

Stay safe everyone!

Severe Weather Poised to Strike Again

Last week's severe weather outbreak was largely a bust despite the system producing nearly 400 damaging wind reports, over 350 severe hail reports, and 40 tornado reports in six days.  Eight of these tornado reports were associated with an EF3 tornado that touched down in eastern Mississippi and traveled just over 68 miles into western Alabama, leaving one dead and nine injured.  However, most weather models overpredicted the amount of moisture that was present in front of this system, which led to a threat in reality that was less concerning than was once predicted.  If a more unstable air mass had been present, this system would have likely produced many more severe weather reports, including more long tracked, violent tornadoes.  The Storm Prediction Center noted this issue when describing their somewhat busted forecasts and stated that this tends to be a concern for the first early severe weather season system.

Well, here we go again, as another system approaches many of the same areas as last week's system.  This time the concern that the models will overpredict the amount of moisture present should be significantly lower.  This is due to the amount of moisture left behind by the last system as well as continued return flow from the Gulf of Mexico across most of the threat regions.  A dry line and stationary front today and tomorrow will remain nearly stationary until Wednesday when it begins to push east, reaching the east coast by Friday.


The largest threat at this point is expected to occur on Wednesday and Wednesday night.  The Storm Prediction Center has issued a Day 3 moderate risk for portions of central Oklahoma, southeast Kansas, and extreme southwest Missouri.  This is only the twelfth time the Storm Prediction Center has issued a Day 3 moderate risk since the first one was issued for a June 10, 2005 event.  Of the 12 events, four events resulted in the issuance of a Day 1 high risk.  These events resulted in varying reports of severe weather but all resulted in some reports.  The June 10, 2005 event recorded the least amount of severe weather but this also comes at a time when severe weather reports were not reported as frequently as today.  In this event, only 4 tornado reports resulted along with 55 wind damage reports and 59 severe hail reports. However, some events that prompted Day 3 moderate risks that were later upgraded to Day 1 high risks resulted in much more historic events, such as April 27, 2011 and April 14, 2012.

The risk on Wednesday does appear that it could result in all forms of severe weather, including the potential for strong tornadoes.  To the right is my threat outlines for Wednesday and Wednesday night defined by an area that has the potential for CAPE values above 1000 J/kg within the area outlined by the orange line, potential for convective type precipitation within the area outlined by the green line, bulk shear values greater than 40 knots within the area outlined by the brown line, 0-3 km helicity values greater than 300 meters squared per seconds squared within the area outlined by the red line, and 0-3 km EHI values greater than about 3 within the area outlined by the pink line.  All of this information was used for me to come up with my threat area to the right.

This threat area is very similar looking to the current Day 3 threat issued by the Storm Prediction Center, with a slight risk being portrayed in yellow and the moderate risk where tornadoes would be more likely being shown in red.  The Storm Prediction Center also has a threat area on Day 4 and this is shown below.  I have put together a tentative map of my threat area for this day as well, which will be Thursday and Thursday night.  This day should have fewer severe storms than the previous day due to lower CAPE values and weaker shear values.  However, the threat for an intense squall line to develop is one that could bring widespread damaging wind reports.  The threat for tornadoes will exist but Wednesday and Wednesday night should have a better chance of these.

Once again my threat looks similar to the current Day 4 threat where the Storm Prediction Center has outlined the 30% area of severe weather within 25 miles of a point.  I do not think they will introduce another Day 3 moderate risk tomorrow for Thursday and Thursday night, but I think the area I outlined in red will include a 30% probabilistic at this point.  If as the event gets closer the wind damage threat becomes more apparent or a greater threat of tornadoes appears to evolve than a moderate risk will likely be warranted at that time.

Stay tuned for further updates on this weeks developing severe storms situation!

Update: Early April Severe Weather Outbreak

Severe weather is currently underway across portions of eastern Colorado, western Kansas, and western Nebraska.  The Storm Prediction Center's latest Day 1 Convective Outlook to the right shows how the convection will spread to the east overnight, affecting areas of northern Kansas and southern Nebraska.  The severe weather threat tonight will include all hazards, with some large hail, damaging winds, and a few tornadoes.

The threat will ramp up more tomorrow as a slightly positively tilted trough continues its push eastward.  The warm sector in front of the associated dry line and cold front will be the main focus for severe weather during this period, which is reflected in the Day 2 Convective Outlook from the SPC to the right.  Once again, all severe weather threats will be possible with large hail, damaging winds, and perhaps a greater tornado threat.



By Wednesday, the trough will remain positively tilted but will continue moving eastward, refocusing the severe weather threat a little further to the east.  The Day 3 Convective Outlook from the SPC is seen to the right.  All severe weather threats will again be possible though the main threat on this day will likely be damaging winds as a large line of thunderstorms should develop.



The animation below shows the 00Z NAM model run depicting composite reflectivity from tomorrow afternoon through Wednesday morning.  I circled areas of severe thunderstorm risk in orange and circled areas with an enhanced risk of tornadoes in red.  Below this is the same thing but for the period running from Wednesday morning to Thursday morning.

A limiting factor to the overall tornado threat during these periods will be a relatively weak low-level jet in most areas.  Additionally, helicity values should remain relatively low in most areas as well.  If these values had been higher the tornado threat could have been much more substantial.  Nevertheless, a strong line of storms will likely produce widespread wind damage reports starting tomorrow evening and continuing into Thursday morning.  Below are my overall threats for tomorrow and Wednesday with the orange area showing where severe thunderstorms could occur and the red area depicting the best threat for tornadoes during each day.

This may end up being the largest severe weather outbreak so far this season, though that is not saying too much given the fairly inactive season so far.  People within these threat regions should pay close attention to their local weather sources and make sure you have a plan in place in case of severe weather, especially tornadoes.

Early April Severe Weather Outbreak

A potentially major outbreak of severe weather could be in store from portions of the Plains into the Deep South early next week.  This probably could have been predicted months ago when I elected to leave Mississippi during severe weather season to present at the Association of American Geographers Annual Meeting in Los Angeles during this same time frame.  Nevertheless, here are some of my early thoughts on the developing situation.

A low pressure system and associated cold front forming in the lee of the Rockies on Sunday will begin to progress eastward Monday.  As this system progresses toward the east it will become the focus for severe weather for at least the early portions of the week.  Major model differences do exist right now with the most notable difference existing between the timing of the system between the GFS and ECMWF models, which are nearly a day apart on the timing of the front now.  The animation to the right shows the GFS model's progression of the 250 mb winds during its past four model runs.  The GFS has moved the trough further east over the past 24 hours and

tilted it more neutrally.  The ECMWF has the trough further to the west with more of a positive tilt in its two past runs, both shown to the right with the 00Z run from last night on top and the 12Z run from this morning on the bottom.  The timing differences here between the two models are rather vast and mean the difference between severe weather on Tuesday or Wednesday for some.  However, the GFS has a bias in pushing these systems through too quickly and thus it is the ECMWF model that should be given more weight.

These are the same thoughts the Storm Prediction Center has also abide by in issuing there latest Day 4-8 Convective Outlook, seen below and to the right.  An enhanced severe threat would be possible over a small portion of western Kansas on Monday, to the northeast of the surface low.  A larger threat area would exist on Tuesday over eastern Kansas, eastern Oklahoma, northeast Texas, western Arkansas, and western Missouri.  Wednesday the threat would move into portions of northern Louisiana, western

Mississippi, eastern Arkansas, southwest Missouri, western Tennessee, western Kentucky, and southern Illinois.  The threats over these three days will include all forms of severe weather with some large tornadoes possible, especially on Tuesday and Wednesday.  Unfortunately, until the GFS comes around toward a solution that is similar to that of the ECMWF, most of the products I am able to look at do not depict an event I believe will actually occur.  Therefore, I have created my own map showing where I believe the threats will be on Tuesday and Wednesday based on limited ECMWF guidance.  The orange outlined area is the area I believe could see CAPE values in excess of 1000 J/kg.  Meanwhile the green line represents the area that according to the ECMWF is at risk of precipitation during this time period.  As of right now, without knowing much more than this, the threat area could really be just about anywhere within this region, which I show in red shading.  However based on some other analysis, I have also tried to outline an area of where I think a greater likelihood of severe weather could occur, which I shaded in pink.  This is my preliminary outlook, I will update this sometime this weekend, especially if the GFS and ECMWF begin to converge on a more similar scenario.

Spring and Severe Weather Season are Here

After a very warm start to spring last year, this year's below average temperatures that plagued much of the nation have left many wondering whether spring will ever arrive.  To the right is an image from NOAA depicting the temperature anomalies across the northern hemisphere during March.  Many parts of the eastern two-thirds of the nation saw temperature anomalies anywhere from one to as much as five degrees Celsius below average.  However, areas in the southwestern United States actually experienced above normal temperatures.

The reason for this can be seen in the two images at left, with the top image showing the Arctic Oscillation (AO) and the bottom image the North Atlantic Oscillation (NAO).  During much of the month of March the AO was negative.  It even reached record negative levels during the later part of the month.  When the AO is negative, the frigid air that is normally confined to the polar regions is blocked and forced to sink into the mid-latitudes.  During this time, if the NAO is also negative then the cold air tends to flow into the eastern half of the United States.  This was also the case for much of the month, especially the mid to late portion.

The red lines in the figures above depict the model forecast for these indexes over the next half month.  As can be seen, after one last cold shot of air this week, the AO is forecasted to spike well into the positive numbers.  During this same time, the NAO is forecasted to continue to trend towards neutral to perhaps even slightly positive.  This is a signal that spring is here!  The latest temperature outlook from NOAA also depicts this, forecasting above normal temperatures across most of the country for the month of April, as seen in the image on the right.  Now that spring has arrived however, severe weather will begin to get rolling with it.  The slow start to severe weather season this year was due entirely to the slow onset of spring and now that spring is here, severe weather will arrive with it.

Over the past four days, there has already been 242 severe hail reports, 119 reports of damaging wind, and 6 tornado reports.  While the preliminary count of tornado reports thus far this year remains very low, it is important to remember that this year really is not that far from average in terms of tornado reports up until this point.  In fact, 2011 had only 15 more tornado reports to date.  Last year the severe weather season got off to a very quick start due to the early spring.  However, the early spring led to an early summer and thus an early end to the severe weather season.  This year our spring has started much later but the risk of the onset of summer leading to an early end of severe weather season exists yet again.  This is because if the AO and NAO go positive and stay positive, cold air will be cut off from the United States.  Additionally, a neutral SOI tends to be correlated with lesser amounts of severe weather across much of the nation.  Lastly, if we take a look at the current sea surface temperature anomalies on the left, we see that sea surface temperatures are below average for most of the Gulf of Mexico and Atlantic seaboard.  Taking all of this into account, while there will definitely be severe weather this spring, especially during the month of April, I do not expect this to be an above normal year for severe weather.  However, it probably will not end up being as quiet as last year was overall.  Therefore, the next couple months will likely become active.

That being said, it appears that a severe weather outbreak will be possible next week though the exact placement of the event is still unknown.  Warm air and moisture from the Gulf will begin to surge northward starting later this week and this will ripen the atmosphere for severe weather.  Areas that should keep a close eye on this involving situation range from the southern and central Plains to the Southeast and Midwest.