North American warmth

[Stephen Davenport]

It's getting abnormally warm across the eastern 2/3 of the U.S. Here's our back yard at 13:30 EST today, Friday 17th:

There's some strength in the sun now so it feels marvelous.

Saturday and Sunday will get into the high teens C, maybe close to 20C Sunday, and then 20-21C Monday.

Here's why:

Here are the forecast T2m anomalies per GFS. Little doubt that there'll be date records in places east of the Rockies across the Ohio and Tennessee Valleys to Appalachia.

Tuesday will have showers on a warm front. Temperatures stay in the upper teens here until a proper break down around Friday - chances of heavy showers and thunderstorms ahead of a cold front that will usher in much colder air as an upper trough edges eastwards: expecting a high of around 3C in Indianapolis Saturday 25th.

Stephen

Indianapolis IN

[Stephen Davenport]

The weather has unfolded similar to expectations this week. The temperature reached 22-25 C across Indiana today and we had 23.1C here at my weather station with DP of 13C. Date records fell all over the place but not the monthly record (at the airport this is 24.5 C). It's the eight day in a row with the temperature above a nominal 18 C, and all but one of those was above 19 C. Meanwhile Boston MA easily broke its February high temperature record (145 years of records), reaching 23C today. It was also their second-highest temperature ever for the winter months, DJF.
   

A line of relatively weak thunderstorms went through between 1430 and 1500 EST ahead of a cold front approaching from the west on the forward side of a deep upper trough over the Central Plains. There's ~1000J/kg of MLCAPE along and south of a warm front straddling Michigan and lake Erie west-east, with decent vertical shear and steep lapse rates, so that's going to be favourable for severe storm / isolated tornado risks as the second wave develops and comes through Indianapolis 1700-1900 EST. There's a greater threat to the east and northeast of the city but damaging straight line winds and hail are likely on the squall line.

It'll be much colder after the front with a few flurries - looking at highs of just 1-2 C for Saturday, a drop of 21-22 degrees.

Midwest weather is rarely boring. There's virtually four seasons in one system with storms and heavy rain here + severe storm risks, deep snow for the central Plains and the Upper Midwest, freezing rain for the eastern Great Lakes and parts of central-southern Ontario, record or near-record high temperatures ahead of it and below-seasonal cold behind.

I made a few screen grabs at midnight last night as this all started - radar (green-orange rain, blue snow, pink freezing rain / ice pellets just beginning). There was thundersnow, too, in Wisconsin. 

Stephen

Indianapolis IN

[Richard Dixon]

Cheers Stephen. Very interesting. Never a dull winter in America, it would seem..

[Julian Mayes]

Yes, thanks Stephen, a very useful overview as usual (it is nice to see the synoptic context for the specific events - we hear a lot of the individual weather extremes and other events in North America via the media without explanatory context).

Cheers    Julian    

 

[John Hall]

I noticed in my newspaper this morning that New York had reached 21C and Washington 24C yesterday (the 24th).

[Stephen Davenport]

========

 

Thanks. It's certainly extraordinarily warm for mid-late February, along with most areas of the eastern half of the U.S. during the past couple of days. 

The following, among  others, set all-time February records on Friday 24th: Boston MA (73 F, which was 3 F above the previous record), Allentown, PA (a remarkable 77 F), Binghamton, NY (70 F), Akron OH, Dayton OH, Cincinnati OH and Columbus OH. On Thursday 23rd, Albany NY hit 74 F, its highest temperature for any winter day, Dec-Jan-Feb. Burlington VT beat its February record on Thursday 23rd (hitting 63F) and again on Saturday 25th with 66F.  

According to the NCEI, 336 monthly record highs have been set or tied for February, with 203 records set or equalled for the highest overnight minimum temperature (through February 23rd). In the same period there was not one monthly low temperature record set or tied.

On Wednesday 22nd Milwaukee (71F), Madison (68F) and Green Bay WI all had record highs for not just February but for any month during meteorological winter. Meanwhile, Ottumwa IA had a high of 79 F - another monthly record. 

Although warm south-westerly winds were at root responsible, the lack of snow cover due to previous warm periods during the winter meant that they stayed even warmer than they would ordinarily have been. Only 19% of the lower 48 is currently snow-covered; and aside from New England and near the Canada border, most of that is over the Rockies, Sierra Nevadas and Cascades.

Temperature anomaly Feb 1st-25th:

Snow cover on Feb 22nd:

For interest, Europe temperature anomaly February 1st-25th:

Stephen

[Stephen Davenport]

On Saturday, February 25, 2017 at 5:49:15 AM UTC-5, Julian Mayes wrote:

Yes, thanks Stephen, a very useful overview as usual (it is nice to see the synoptic context for the specific events - we hear a lot of the individual weather extremes and other events in North America via the media without explanatory context).

Cheers    Julian    

========

Thanks, Julian. 

Actually, I could have illustrated better. Here are three charts, 12 UTC Friday Feb 24th: 1. 500 hPa showing the upper trough over the Plains and the strong eastern / north-eastern ridging; 2. surface pressure with the broad Colorado Low getting steered north-eastwards; and 3.dew points.   

As suspected most of the severe action was to the east and northeast but even more so than I thought. The second band of storms on the cold front did not amount to much over Indianapolis but got severe-warned for the Ohio border and into SW Ontario, and eastwards across Ohio Friday night then into Pennsylvania Saturday. In fact there was a tornado in Pennsylvania:

http://paweatheraction.com/raw-video-a-tornado-on-the-ground-near-scranton-pa

...and another suspected in Maryland (warning - video starts automatically):

http://www.wusa9.com/weather/tornado-warning-for-parts-of-maryland/414664663

The temperature here in Indy got to just 0 deg C Saturday, 23 degrees lower than Friday, with on-and-off flurries leaving just a trace covering.

Stephen

Indianapolis IN

[Stephen Davenport]

On Friday, February 24, 2017 at 4:49:28 PM UTC-5, Richard Dixon wrote:

Cheers Stephen. Very interesting. Never a dull winter in America, it would seem..

========

Even in a 'mild' winter it's all relative. For the northern states and Canada that's still going to mean snow and it just makes forecasting more difficult in many ways: seasonal temperatures would mean just snow, with the main challenge being forecasting accumulations; but the mildness means more marginal conditions with fine margins between rain, snow, freezing rain and ice pellets. It's been tricky at times this winter for Ontario forecasts, for example. Always interesting, though, as you say. It's been a roller-coaster of temperatures this winter and it's often similar in spring. Currently you'd think it WAS spring given the extremes of the upswings.

Stephen

Indianapolis IN

[Stephen Davenport]

Here's a lovely if ominous shelf cloud near Mercersburg, Pennsylvania, on Saturday 25th February.

Photo and video credit: Laura Bernardo.

https://www.youtube.com/watch?v=XT7GAtFApPI

Stephen.

[John Hall]

I see that British Columbia has very much missed out on the February mildness, seeming to have been the one part of North America that's been notably cold.

[Richard Dixon]

I saw that video elsewhere Stephen - it's an absolute stunner. Also early in the video you'd be forgiven from thinking there was a funnel on the left of the shot as she pans left right at the start:

[Trevor Harley]

I am looking to a bit of time back home in San Francisco from this weekend, where it has been stormy and wet. But things look to be turning a bit more settled - just a bit more mild than Dundee.

[John Hall]

On Tuesday, 28 February 2017 09:10:04 UTC, Trevor Harley wrote:

I am looking to a bit of time back home in San Francisco from this weekend, where it has been stormy and wet. But things look to be turning a bit more settled - just a bit more mild than Dundee.

San Francisco is home for you? I confess to being surprised.

 

[Stephen Davenport]

On Tuesday, February 28, 2017 at 4:10:04 AM UTC-5, Trevor Harley wrote:

I am looking to a bit of time back home in San Francisco from this weekend, where it has been stormy and wet. But things look to be turning a bit more settled - just a bit more mild than Dundee.

========

Yes, the hemispheric pattern is edging eastwards with western ridge building. 

Both CFSv2 and ECMWF month-ahead ensembles have been impressively consistent with this outlook for 2-3 weeks now and look like verifying. There will still be some cool flows initially as it becomes drier but it'll warm by the end of the first week of March onwards.

Meanwhile there'll be severe storms and tornadoes developing later today from the Ozarks to the Ohio Valley; I'll make another post about that. 

Stephen.

[Stephen Davenport]

On Monday, February 27, 2017 at 4:17:04 PM UTC-5, Richard Dixon wrote:

I saw that video elsewhere Stephen - it's an absolute stunner. Also early in the video you'd be forgiven from thinking there was a funnel on the left of the shot as she pans left right at the start:

========

It's one of the best I've seen.

One could certainly be fooled by the look of that feature. Wrong spot, though.

Stephen.

 

[Trevor Harley]

I think of it as my spiritual home. I try and spend as much time in the SW as possible (which isn't a lot).

[Stephen Davenport]

The Storm Prediction Center (SPC) has raised the severe storm risk to moderate for a large area from the central Mississippi Valley / Ozarks across Illinois and the Ohio Valley this evening and tonight. In Indiana the threat starts developing after 7pm but the main risk is going to be after 9-10pm. All threats are in play, from strong straight line winds (gusts 60-80mph possible) to large hail and tornadoes. Given that this is coming overnight it's a particularly dangerous situation, potentially, and could be one of those where it's wise to sleep in the basement.

Public Severe Weather Outlook (PWO)

ZCZC SPCPWOSPC ALL WOUS40 KWNS 281650 ARZ000-ILZ000-INZ000-KYZ000-MOZ000-OHZ000-TNZ000-010200- PUBLIC SEVERE WEATHER OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1050 AM CST TUE FEB 28 2017 ...Severe thunderstorms expected over parts of the Ozarks region to the Ohio Valley late this afternoon into tonight... * LOCATIONS... Indiana Western and northern Kentucky Southern and eastern Missouri Illinois Northern Arkansas Northwest Tennessee Far western Ohio * HAZARDS... Several tornadoes, a few intense Widespread large hail, some baseball size Scattered damaging winds * SUMMARY... Severe thunderstorms are expected to develop from portions of the lower Mississippi Valley to the Ohio Valley through tonight. Strong tornadoes will be possible, especially across portions of the lower and middle Ohio Valley. Otherwise, large hail and damaging winds are expected. Preparedness actions... Review your severe weather safety procedures for the possibility of dangerous weather today. Stay tuned to NOAA Weather Radio, weather.gov, or other media for watches and warnings. A tornado watch means that conditions are favorable for tornadoes to form during the next several hours. If a tornado warning is issued for your area, move to a place of safety, ideally in a basement or interior room on the lowest floor of a sturdy building. Stephen Indianapolis IN

[Stephen Davenport]

Here's a scary-looking forecast sounding (NAM) for 0300 UTC (2200 ET / 2100 CT) 

Stephen.

[Richard Dixon]

Parcels buoyant aaaaall the way up to the top! CAPE values not to be sniffed at...

On an entirely different note - this interested me - something else from Twitter - sorry for enormous size - it's this or too small to read. Interesting to see how the snowiest month varies spacially in America. Would be interested to see similar for Europe (or even the UK...)

Richard

Richard

[Stephen Davenport]

Enormous CAPE. 

Large hail and tornadoes are already being reported in Missouri and Illinois. Here's the most recent at 19:08 ET, a tornado NNE of Pontiac and SSW of Chicago IL (Super-Res reflectivity left, Super-Res velocity right).

 

Stephen

Indianapolis IN

[Jack Frost]

The thunderstorm warnings issued looked like they might miss out Chicago, but thankfully not! Had one storm after another between about 6pm and 11pm. I filmed this video from the balcony of my apartment during a period of continuous thunder and lightning. The sound doesn't really pick it up, but there was non-stop thunder the whole time. Apologies for the poor quality! I only moved to Chicago from the UK 3 weeks ago. I hope weather like this is common! :-D

https://www.youtube.com/watch?v=Kv-AiFj_nbw

Liam
Chicago

[Stephen Davenport]

Richard,

Thanks for the map, by the way. It is interesting, and I've squirreled that away. I don't know of similar for the UK. 

On another different note, there were 24 tornadoes (so far) recorded across Missouri, Illinois, Iowa, Indiana and Ohio yesterday afternoon, evening and overnight into Wednesday, and some large hail. Here is a particularly startling hailstone found in Aurora, Indiana (50 km west of Cincinnati OH across the Ohio River).

Stephen

Indianapolis IN

[Stephen Davenport]

========

Welcome to the Midwest, Liam.

I think you'll find that severe weather is frequent enough here to keep you interested, and of a different stamp and kidney to storms in the UK (as you will have noticed). It looks like the long-wave pattern could be such that you could get your fill with quite an active spring into early summer (at least). Last year was a bit too much with rounds of strong or severe storms right through summer and into the autumn.


Stephen

Indianapolis IN .

[Richard Dixon]

That large hail pic is interesting - I realise large hail is agglomeration of smaller hailstones, but this seems like an agglomeration of moderate-sized conical-shaped hailstones.

Richard

[Trevor Harley]

So what is the cause of this exciting weather?

I see on the 9.55 News 24 last night they were saying this USA weather was going to "energise" the jet stream, although when I think about it, I don't understand how.

There is still so much I don't really know about the weather.

[Jack Frost]

Thanks for the welcome Stephen!

It's the first time I've ever been in a storm with constant thunder and lightning. It was quite something. I hear there was quite a bit of destruction southwest of Chicago due to a tornado. When I moved here at the start of February I was expecting snow, but I read yesterday that this is the first time since 1884 that Chicago has not had snow lying on the ground for a whole day in January or February. I've brought my snow shield with me it seems. :(

Liam

Chicago

[Stephen Davenport]

You'll get used to such storms. They never cease to be impressive; or at least I have yet to tire of them. I'd advise a weather radio if you don't have one yet, and identify a safe place in case of tornadoes. A basement if you have one. But I might be teaching you suck eggs there! Anyway, it looks like it could be a pretty active spring and early summer for the Plains and Midwest if the expected pattern works out. This week's early severe outbreak is not unprecedented but its rare to be so far north in late February / early March. 

http://www.spc.noaa.gov/exper/archive/event.php?date=20170228

There was one extraordinary supercell that traveled nearly 600 miles across five states. There wasn't a tornado all that way, of course, but that's an extraordinarily long-lived cell. Some of these beasts were moving at a really fast clip, 80 to 90 mph, or even one estimated at 105 mph.

It's certainly been a warm winter in the Midwest (and the warmth and deep moisture certainly assisted this severe outbreak). Correct about the lack of snow. Lying snow is logged just at 6am ET but even so only traces were measured a couple of times later in the day, on January 30th and February 25th. It's a remarkable record. You could get some flurries tonight and into Saturday but not much, and there's another relatively mild week coming up. Wet on Monday. Chillier after that positive single digit highs but likely above-average temperatures on the whole through the middle of March. 

You won't need me to tell you that Chicago is a great city. Enjoy!

Stephen

Indianapolis IN

[Stephen Davenport]

========

Here's the 500 hPa height and anomaly chart at 0600 UTC 01 March:

 

This produced warm and deeply moist flows across the eastern U.S. with cold air aloft, so there were steep lapse rates + strong vertical wind shear. The usual ingredients, therefore (buoyant, moist air with wind shear) just much earlier in the year than usual. Grabbing the 700 hPa temperatures you can see a strong south-north temperature gradient, favoring a veer from surface S'lies to upper westerlies.

 

A couple of triggers were the warm front across the Midwest-Great Lakes-Ohio Valley and the approaching strong cold front... plus a dryline to the south.

Regarding News 24's comments about "energizing" the jet stream, they probably were referring to the strong baroclinic zone exiting the Northeast into the Atlantic. There was certainly a strong temperature gradient across the cold front:

Stephen

Indianapolis IN

 

[Stephen Davenport]

On Wednesday, March 1, 2017 at 5:52:06 PM UTC-5, Richard Dixon wrote:

That large hail pic is interesting - I realise large hail is agglomeration of smaller hailstones, but this seems like an agglomeration of moderate-sized conical-shaped hailstones.

Richard

========

Indeed. There are often arguments about whether this sort of thing is one hailstone or a bit of a cheat with many stuck together. Ultimately it makes little difference if your roof, car or head is underneath it!

Stephen. 

[Richard Dixon]

On Friday, 3 March 2017 19:13:06 UTC, Stephen Davenport wrote:

Indeed. There are often arguments about whether this sort of thing is one hailstone or a bit of a cheat with many stuck together. Ultimately it makes little difference if your roof, car or head is underneath it!

Stephen. 

I guess both mechanisms (ice accretion to one blob, or multiple hailstones joining up) are both an indicator of updraught strength and storm severity !

Richard