Update to Weekend Severe Weather

Originally posted on ZoomRadar

As mentioned in my previous blog post, a strong cold front has been predicted to trigger strong to severe thunderstorms as it tracks to the east from the Plains to the Atlantic Coast this weekend. For this reason, the Storm Prediction Center has issued a slight risk for areas in front of this cold front today straight through Sunday. Below are the outlooks issued by the SPC.

Day 1 Outlook - Wind (Today and Tonight)

Day 1 Outlook - Hail (Today and Tonight)

Day 1 Outlook - Tornado (Today and Tonight)

Day 2 Outlook (Saturday and Saturday Night)

Day 3 Outlook (Sunday and Sunday Night)

Now let’s take a look at the specific details of why this threat exists starting with today. Below are images from today’s 12Z NAM model run showing what the scenario may look like come this evening.

Precipitation

Dewpoint Temperatures and Surface Winds

850 mb (Low-Level Jet) Winds

250 mb (Jet Stream) Winds

500 mb Relative Vorticity

CAPE

EHI

Today and tonight thunderstorms are expected to break out in a fairly unstable environment across mainly Nebraska, South Dakota, North Dakota, and Minnesota. Dewpoint temperatures will be generally greater than 55 but as high as the low 70s in some areas which will really aid in creating a moist and unstable environment. 850 mb winds will generally be pretty weak but the storms will get some help from faster winds in the jet stream reaching up to 90 knots in some spots. The trough associated with the surface cold front will still be positively tilted and positive vorticity advection will be somewhat on the low end. Taking a look at CAPE values, some areas may see values reaching above and perhaps beyond 4000 J/kg but most areas will remain between 1000 and 3000 J/kg. The last image shows us that EHI values may become pretty high with values above 6 in some areas. If this turns out to be the case we may see a small tornado threat this afternoon and evening. In fact, today may pose the best chance for tornadoes as this trough pushes across the northern portions of the country. Overall, most storms will pose a damaging wind and perhaps some large hail threat. Today will likely pose the least risk of severe weather this weekend. That being said though, there will definitely still be severe weather today and tonight across the Northen Plains, as depicted by the SPC’s outlook percentages.

Below are images from today’s 12Z NAM model depicting what conditions could be like come Saturday evening.

Precipitation

Dewpoint Temperatures and Surface Winds

850 mb (Low-Level Jet) Winds

250 mb (Jet Stream) Winds

500 mb Relative Vorticity

CAPE

EHI

Saturday I expect the severe weather to start firing up even more. The reasons behind this can be seen in the graphics above. First off, dewpoint temperatures will top out generally higher than the day before with values at and above 65 and perhaps as high as the upper 70s. Surface winds will be about the same magnitude out of the south but winds at the low-level jet level will be stronger with some areas potentially seeing these winds hit 40 knots. Winds in the jet stream will also be stronger, peaking above 100 knots across northwest Wisconsin on Saturday evening. The jet stream will also be aligned in a way now that the right rear quadrant should provide some extra lift for thunderstorms to form and become stronger. The trough will also slowly start becoming more neutral in nature and positive vorticity advection will become stronger, especially across the more northern portion of the nation. We also see that CAPE values will be generally the same as the day before with some areas topping out at and above 4000 J/kg. The last measure, EHI, will once again present some fairly high values mainly across Illinois and Indiana so we may see a slight tornado threat across this area as well as somewhat but to a lesser extent to the north of these regions. Once again, the main threat on Saturday and Saturday night will be damaging winds and some large hail.

Below are images from today’s 12Z NAM model depicting what conditions could be like come Sunday evening.

Precipitation

Dewpoint Temperatures and Surface Winds

850 mb (Low-Level Jet) Winds

250 mb (Jet Stream) Winds

500 mb Relative Vorticity

CAPE

EHI

Sunday and Sunday night will likely present the largest threat for severe weather out of the three days. Once again we will see high dewpoint temperatures from the mid 60s to as high as the mid 70s with nice southerly surface winds, helping to increase the moisture content of the air even more. Winds at 850 mb will be the strongest out of any of the three days with some areas just north of New York in Canada, seeing these winds peak at above 60 knots. The jet stream winds will once again be strong, topping out at above 100 knots, and placing that right rear quadrant right across a portion of the threat region. Our trough by now will likely have tilted negative which will help enhance that threat of severe weather as it makes this tilt towards negative on Sunday. 500 mb positive vorticity advection will likely remain fairly strong, especially across the northern portions of the threat area. CAPE values may be lower on Sunday but it is the current thought that the strengthening of upper air processes will outweigh this. Still, CAPE values will generally be above 1000 J/kg which will be enough instability for these storms to maintain themselves. EHI values will generally remain below 2 with some pockets being a little higher so the tornado threat should be pretty low. However, this does not mean that an isolated tornado risk cannot be ruled out. Once again though, the main threats will be damaging winds and some large hail.

This weekend will surely lead to multiple severe weather reports, including some large hail, perhaps a couple tornadoes, and what will likely be some widespread damaging wind reports. Please remain aware this weekend across the northern portions of the Plains, Midwest and Northeast.

Another Round of Storms for the Midwest and Northeast

Originally posted on ZoomRadar

Last week at this time, parts of the Plains and Midwest straight into the Northeast were gearing up for what would be two days of back to back severe weather with the main event occurring last Thursday. Below are the storm reports from those two days, showing the progression of the cold front which allowed storms to fire up in advance of this feature. The threat started across the Midwest and Plains and progressed eastward, affecting areas of the Northeast before pushing out to sea. While most of the damage occurred due to severe straight-line winds, Thursday did result in a handful of tornadoes, mainly along the New York and Pennsylvania state border.

Another round of strong to severe storms appears to be in the making for many of these same areas as we head into this weekend. A cold front extending from a Low centered just north of Minnesota will drape back across the Plains on Saturday morning, shown below. The advancement of this front will result in the triggering for strong to severe storms as it enters unstable and moist air ahead of this system.

The image above shows where this front will be on about Sunday morning and the below image then shows about where it will be come Monday morning.

The 12Z NAM model shows what the precipitation may look like come Friday evening as this front begins its push across the northern Plains.

CAPE values in advance of the front will be above 1000 J/kg with pockets above 3000 J/kg.

EHI values will also be quite nice with many areas in Minnesota recording values at or above 3. This is the result of good low level turning of the winds with height which means if supercells can form, there may be some tornado threat on Friday.

For these reasons, the SPC has highlighted a region across the eastern Dakotas and most of Minnesota in their Day 3 Outlook as being at a slight risk for severe storms. The main threat at this time appears to be some large hail but mainly damaging wind gusts. If supercells can get going out in front of the cold front however, we may see a few tornadoes.

On Saturday, the front will continue pushing east and even though the SPC has not highlighted an area for severe weather risk at this time, they do mention that a risk will likely be present across portion of the Midwest and Great Lakes. Below the 12Z NAM model shows what the precipitation may look like come Saturday evening with storms stretching from Michigan into Illinois and back across the Plains.

CAPE values and EHI values will once again be fairly high, with CAPE values looking much like Friday’s CAPE values but EHI values being somewhat less spread out but potentially packing areas of higher values above 6. This once again would result in a mainly damaging wind threat but a few tornadoes may not be out of the question in the areas with stronger EHI values.

Check out what hodographs may look like across central Indiana come Saturday evening. If this ends up being the case, a few tornadoes would definitely not be out of the question.

The risk of severe weather in general will also probably be worse on Saturday than it was on Friday due to the strengthening of winds aloft and better moisture across these areas. Below are images from the 12Z NAM model showing the winds at 250 mb, 850 mb, and dewpoints with surface winds. A 100 knot plus jet streak will likely be centered across the Wisconsin and Minnesota border with an 850 mb low-level jet with winds approaching 50 knots from Illinois into Michigan.

Dewpoints will also be high from the mid 60s into the low 70s across these areas. Surface winds will be mainly out of the south in front of the cold front which will aid in bringing this moist air in and help the inflow into these thunderstorms as winds could be as strong as 20 knots at the surface Saturday evening.

Storms will continue throughout Saturday night before we get to what will likely be the main event from this cold front on Sunday across the Northeast. While this event is still five days out, the SPC has highlighted an area on their Day 4 to 8 Outlook meaning that they expect a 30% chance or greater of severe weather within 25 miles of a point on Sunday and Sunday night.

The 12Z GFS model depicts this event probably a bit differently than the NAM will depict it come this time tomorrow when the NAM begins to send predictions for an event this far out. This is based on the fact that the GFS depicts the Friday and Saturday events slightly different, mainly with not as much moisture being pushed north as the NAM thinks it will. Despite this, here is what the CAPE may look like come Sunday evening and below that are images depicting 250 mb winds, 850 mb winds, and surface winds and dewpoints.

CAPE values will be above 1000 J/kg and a 100 knot jet streak will be in place north of the threat area with the right rear quadrant being placed over the threat area. Additionally, an 850 mb low-level jet will become quite strong with areas of 50 knot plus wind and widespread dewpoints at and above 70. All of these conditions along with what should be some good positive vorticity advection, will result in what should be a pretty substantial severe weather threat come Sunday. The main threat will likely be damaging winds.

This cold front will definitely be something we should all keep an eye on this weekend as it sparks strong and severe thunderstorms. This is still an evolving situation so the exact locations which may come under a threat due to these storms is still somewhat unknown. Below is my threat map depicting where I think the threats may be come Friday (shaded in brown), Saturday (shaded in yellow), and Sunday (shaded in red).

Severe Weather Outbreak for the Northeast and Midwest

Originally posted on ZoomRadar

A severe weather outbreak will begin today and continue through tomorrow night across many parts of the Midwest and the Northeast. While some of the details as far as exact locations and timing go are still somewhat unknown, it is clear that by Friday morning, many will likely be cleaning up from storm damage over the past two days. This is because of unstable air which will be in place behind a warm front but in front of a cold front which will push through these portions of the country over the next two days.

First let’s concentrate on what is going on right now and into tonight. Below is the current Day 1 Outlook from the SPC showing a large area highlighted under a slight risk of severe thunderstorms across the upper Midwest and into parts of western New York. The main threat will be damaging winds from these storms but some large hail and a couple of isolated tornadoes cannot be ruled out.

Here is the Day 1 SPC Outlook showing the wind damage probabilities for this evening and tonight. A 30% chance of severe wind within 25 miles of a point is expected to occur from areas in southeastern Wisconsin east toward central Michigan. In fact, most of this area is also under a 10% or greater probability of seeing significant wind gusts in excess of 65 knots.

The threat for damaging winds will mainly occur due to straight-line winds associated with lines of thunderstorms. This is the scenario that the current 18Z NAM model run depicts as well. This line or lines of storms should fire up this evening and continue into the overnight hours. Below is the 18Z NAM run showing what the reflectivity may look like this evening around sunset.

A line of storms may be most intense right across and around that 30% area the SPC highlighted for wind damage this evening and tonight. Taking a look at the modeled CAPE and EHI values, we also see that the storms will have plenty of instability to work with.

Storms are expected to continue through the overnight hours and into tomorrow morning, weakening some in the early morning hours. However, a line or lines of storms will refire up tomorrow most likely around midday and continue to track off to the east. Here is a look at what the 18Z NAM model is thinking right now as far as what the reflectivity may look like. The top image shows the reflectivity around midday into the early afternoon whereas the bottom image shows how it may appear in the late afternoon.

Once again, these storms will have plenty of instability with CAPE values approaching and exceeding 3000 J/kg according to the 18Z NAM model.

EHI values will also be good in some areas meaning that if any supercells can form out in front of the main line of storms, there could be a chance for a couple tornadoes.

For these reasons as well as the great upper air support that these storms will be dealing with, the SPC has issued a moderate risk for some areas in their Day 2 Outlook. These areas are the areas highlighted in purple, indicating a 45% chance of severe weather within 25 miles of a point, as well as a 10% or greater probability of significant severe weather within 25 miles of a point.

A large area is looking at a slight chance of severe weather tomorrow but the areas at the greatest risk will be from southern Illinois into Indiana, Ohio, Pennsylvania, New Jersey, New York, southern Vermont and New Hampshire, Massachusetts, Rhode Island, and Connecticut. Residents of these areas should prepare for the potential of straight-line wind damage, as this will be the main threat tomorrow and tomorrow night. If the line of storms becomes strong enough, and this is the current thinking, we could be looking at a long lived derecho which could produce damage similar to the one that affected areas of the Midwest and Mid-Atlantic on June 29th of this year.

The threat could be very extreme in some areas tomorrow so stay alert to the latest weather conditions and remember to seek shelter in advance of these storms.

Historic Heat and Drought

Originally posted on ZoomRadar

If you could ask people throughout the contiguous United States what two words they would use to describe the weather conditions this spring and so far this summer, I would imagine the answers would run along the lines of hot and dry. This has been the case for most areas in the lower 48 states so far this year, though it is important to note that this is not true for everywhere in the lower 48. In fact, some areas have seen above normal precipitation so far this year, including areas of central Texas, most of Maine, as well as many areas of the Pacific Northwest, northern Rockies, and northern Plains.

The graphic below shows how temperatures compared to the 1981 to 2010 average across the lower 48 last month. Despite the month officially rating as the fourth warmest June on record globally, with records dating back to 1880, some areas of the U.S. saw below normal temperatures during this time period, denoted in blues below.



But like I stated previously, most of the nation has been experiencing heat and little rainfall. June marked the 328th continuous month with temperatures above the 20th century average according to NOAA. The United States seems to be taking the brunt of the heat as well. Temperatures globally in June were nearly two degrees Fahrenheit above average on the world’s landmasses and have been 1.57 degrees above average so far this year. But in the U.S., temperatures have been averaging 4.5 degrees above normal so far this year, now that is some heat!

And as if the heat was not enough to worry about, drought conditions have continued to worsen across a vast portion of the lower 48 states. Drought conditions are depicted in the map below as of July 10th and have likely continued to worse across many portions.

In terms of the area affected by this drought, this is now officially the worse drought since the 1950s. About 61% of the continental U.S. currently qualifies as being in some level of a drought according to the U.S. Drought Monitor. The Palmer Drought Index, an older and less detailed index, reports that 56% of the United States is currently under drought conditions. The last time drought covered more area in the lower 48 states was in December 1956.

This current drought does not compare to past droughts in duration yet, but with no major relief in the near future, conditions may continue for some time. Below is the NAM model depicting how much precipitation may fall over the next 84 hours. While some relief may fall over this time period, it will not affect all areas and will not be enough to eliminate the precipitation deficit, though any help will be very welcomed in these areas.

Below is the precipitation across the United States over the past 60 days when compared to normal, showing many areas suffering from precipitation deficits.

All of this heat and lack of precipitation has unfortunately led to many issues across the nation and will continue to do so. Heat related deaths have occurred in many states and many more have likely suffered from heat related illnesses. Additionally, dry conditions have wreaked havoc on the nation’s corn crop, with the U.S. Department of Agriculture now reporting that 38% of the crop is in poor or very poor condition. Problems have also arisen in the form of wildfires due to the dry conditions. Below is a map showing the current large wildfires across the United States.

The summer will likely continue with more hot and dry conditions so it is important to take precautions to protect your life and property. Be sure to stay hydrated, take breaks from the sun, monitor any fires you start closely, and of course stay up to date on the latest weather information.