I was hoping, really hoping, that this Thursday would shape up as my first chase day of the year out in Illinois. The NAM sure looked promising for a second, but now, like Dante’s inferno, it has “Abandon all hope, ye who enter here” written over the door.

The GFS was never very positive to begin with, but at this time of year, Great Lakes chasers are optimistic out of sheer desperation, and I guess I wasn’t the only one who was rooting for the NAM with its bullish CAPE of up to 1,500 j/kg and sweet lapse rates.

But it’s gone, all gone. Yesterdays NAM runs weakened the CAPE and shuttled it south and east. A nice cold core setup in southeast Iowa/northwest Illinois materialized long enough to whisper sweet nothings, but nothings are probably all they were. The 500 mb low has since slunk apologetically back west toward Kansas City, with its -25 C temperature minimum well displaced from the surface moisture lobe. The setup could still change, but unless it bumps back east and stacks back up, I’m not going to drive that far to find out.

I will, however, very likely head toward the Michigan border around New Buffalo. Moisture looks to be ample with mid- to upper-50s dewpoints augmented by evaporation, backed surface winds, and precip breaking out by 21Z if this present NAM verifies. If it does, there could be a bit of lightning and thunder, and at least the slim possibility of a brief spin-up; if not, it’ll have been a pleasant break-in drive for chase season 2010.

Here on the last day of February–just one day before meteorological spring begins–temperatures are finally settling into a warming trend here in Michigan. With plenty of snow still on the ground but the promise of better days in sight, and with me feeling my repressed itch for severe weather beginning to surface too insistently not to scratch, I’ve cast a wistful eye on the long-range GFS.

At 180 hours out from today’s 6Z run–in other words, on March 7, early afternoon–things look interesting. Not inspiring, just something to keep an eye on. If you’re a fellow storm chaser, you know the drill, and you know how the models change. With that caveat, while I haven’t been an avid follower of the GFS these days, I seem to recall that it was painting a somewhat similar scenario last week.

Anyway, here are the surface maps for sea level pressure and surface dewpoints at 18Z, March 7. Click on the images to enlarge them. Obviously the moisture could stand improvement, and I wonder whether sea surface temperatures in the Gulf will be warm enough to deliver, but let’s see what happens from here.

Which version of snowfall totals do you prefer–the NAM on the right, or the GFS, shown below? (Click images to enlarge.)

If you live out east, the question is purely academic. I doubt that you much care which forecast model is the more accurate, because either way, you’re going to be sitting under a ton of snow by tomorrow. That much is no secret. While the forecast models shown here are for 00Z Saturday night, the show has already started.

Farther down the page, you can see a level 2 radar grab from Sterling, VA, taken shortly after 10 p.m. It’s much prettier to look at than the picture that is unfolding over the nation’s capitol as I write in the form of heavy snow, freezing fog, mist, freezing rain, blustery winds, blizzard conditions–just about every kind of winter weather you can throw at one area in the space of a few miles as temperatures drift from below to above freezing.

The current Baltimore forecast for tonight and tomorrow reads as follows:

Tonight: Snow and areas of blowing snow. The snow could be heavy at times. Low around 29. Breezy, with a east wind between 16 and 23 mph, with gusts as high as 37 mph. Chance of precipitation is 100%. Total nighttime snow accumulation of 15 to 21 inches possible.

Saturday: Snow and areas of blowing snow. High near 29. Blustery, with a north wind between 18 and 22 mph, with gusts as high as 37 mph. Chance of precipitation is 100%. New snow accumulation of 4 to 8 inches possible.

Ugh! For once I’ll take a Michigan winter forecast over what’s being served up elsewhere. Right now my friend Kathy out there in Greenbelt, MD, is getting her clock cleaned. It’s a good night for her and her boyfriend to eschew the Washington nightlife and hunker down inside. For that matter, I doubt there’s much happening in the way of a Washington nightlife on a night like tonight.

Meanwhile, down in the warm sector, much of eastern North Carolina is under a tornado watch. The radar shows a pretty grungy-looking, non-severe, low-topped squall line that doesn’t show much likelihood of putting out anything tornadic, but it nevertheless adds to the East Coast’s overall weather ambience.

Have fun out there, kiddies, those of you who live out east. As for me, I’m going to pour me a mugful of Bell’s Amber Ale and, for once, enjoy watching the snow not fall outside my window. Gloating over such things is permissible for lifelong natives of the Great Lakes.

Whichever model gives the more accurate picture–the GFS or the WRF-NMM–one thing is sure: we Michiganians can say good-bye to the leaves. This Friday’s weather system promises to be a real October leaf-stripper, with a formidable low-pressure center deepening rapidly as it moves through Ontario.

The two forecast models continue to differ in timing, with the GFS moving the cold front rapidly through the state’s mid-section by 18Z, while the NAM plays it more conservatively and backs the surface winds considerably more. The NAM is also much more aggressive with 850 mb winds, with the 12Z run calling for 75 knots (!!!), while the GFS dribbles out a paltry 55-knot LLJ.

I have a hunch that the GFS is closer to the truth, though of course, time will tell.

Both models agree that instability will be non-existent. Not much there to gladden the heart of a storm chaser. But by golly, we’ll be seeing some wind. Bye-bye leaves!

For the sake of comparison, I took a sampler of 6Z model soundings for both the GFS and the NAM for Jackson, Michigan–a nice, central location that should offer a good compromise between both models. The differences are striking. Click on the images to enlarge them. For 21Z, I’ve shown only the NAM; by that time, the GFS has the winds lined out.

Forecast hours for Friday, October 30

15Z

GFS

NAM

18Z

GFS

NAM

21Z

NAM

Given the unreliability of long-range forecast models, there’s a lot of justifiable skepticism in the storm chasing community when someone (like me, for instance) talks about an event that’s 120 or more hours out. Beyond maybe three days, trying to forecast weather events becomes increasingly like reading tea leaves. We watch the ECMWF and GFS for signs of agreement and consistency, and if they start showing up, we cross our fingers, knowing that a lot can happen between now and payday.

So I’m not sure what to think when the revered Farmers’ Alamanac gazes into its crystal ball and issues with serene confidence the following prognostication for the Great Lakes region:

November 2009
1st-3rd. Sunny, with increasing clouds. 4th-7th. Rain spreads in from the west. Turning clear and frosty. 8th-11th. Rapid temperature changes. Storm moves east, with heavy rain or wet snow. Frigid cold air follows. 12th-15th. New storm moves into Great Lakes. Heavy rain and/or wet snow. Then clearing and very cold. 16th-19th. Storm sweeps across the area, followed by very cold air. Fast-moving storm, reaching the region by the 19th. Heavy snow, followed by colder air. 20th-23rd. Cold Canadian front brings rain and thunderstorms for the Great Lakes region. 24th-27th. A wet Thanksgiving.  28th-30th. Few rain or wet snow showers. Turning colder.

December 2009
1st-3rd. Rain and wet snow shift into the Great Lakes, south to Kentucky, followed by clear and cold weather. 4th-7th. Storm Ohio River Basin deposits heavy rain and wet snow. Very cold air follows. 8th-11th. A “winterlude” for Great Lakes and the Ohio River Basin. Temperatures still well below seasonal norms. 12th-15th. Scattered snow showers and flurries. 16th-19th. Considerable cloudiness over most areas, but little precipitation. Nights are seasonably cold, days are mild. 20th-23rd. Rain and/or snow.

Not being a climatologist, I’m unaware of what sophisticated meteorological resources the Farmers’ Almanac may be tapping into. Possibly they’ve been consulting woolly bear caterpillars. According to folklore, you can tell how severe the winter will be by the ratio of brown to black banding on the woolly bears. Plenty of brown means a mild winter; wide black bands with little brown points to a nasty snow season. A few weeks ago, I found an all-black woolly bear. I knew that couldn’t be good.

If only we could get the woolly bears to cooperate when storm chasing season is underway. But the little critters have other things on their minds by then, namely, pupating and becoming Isabella tiger moths. So I guess we’re stuck with the Euro and the GFS. Or sacrificing chickens, though the research supporting the link between chicken sacrifice and improved storm intercepts is slim.

No doubt the government is covering up the information, just like they do everything that’s related to severe weather. They want us to remain ignorant, unsuspecting guinea pigs while the weather gods at Norman conduct their insidious experiments, using their array of antennas and radars to generate monster tornadoes 400 miles away and then guide them unerringly through populated areas. Take the May 13 Kirksville, Missouri, tornado, for instance. That one had Government Issue written all over it. The lack of a single shred of substantiating evidence just goes to show how expert Big Brother is at keeping the truth hidden.*

That’s why you’ll find no NOAA papers correlating tornado outbreaks and chicken sacrifice. Same with woolly bears and long, hard winters–though the Farmers’ Alamanac folks, bless their hearts, have obviously made the connection, and hence, they have the weather for November and December pretty well locked in. I call that kind of forecasting ability reassuring.

As for the rest of us, well, we’ve got the ECMWF, the GFS, and tea leaves. How do you like your tea?

_______

* The following disclaimer is intended only for those who take me seriously: I’M JUST KIDDING! Sad that I’ve even got to say it, but the truth is, some folks out there do in fact believe some damn crazy things about the government’s ability to manipulate the weather. I’m not one of them, and I wouldn’t want to be mistaken for such.

That being said, I would love to see the SPC’s research on chicken sacrifice and tornadogenesis.

If I were to pick a chase target for tomorrow, it would be Rolla, Missouri. That’s based on a sampling of the 6Z model soundings of the GFS, NCEP’s present model preference.

Frankly, though, I can’t get too excited about this system. True, it seems to be shifting the activity to within striking distance, where I could conceivably go chasing and still make it back Friday morning in time to make an appointment that I absolutely can’t miss. But instability isn’t all that great, and besides, who wants to go chasing in Missouri hill country?

If the NAM verifies, things will shift north a bit. But I don’t see that making a practical difference. It’s a marginal setup at this point, and unless things improve, I don’t think I’ll feel short-changed sitting this round out. Maybe the next trough will be an improvement.

ADDENDUM: Ouch! Just looked at the SPC’s afternoon update. If they’re right, then only the desperate and the insane will be chasing tomorrow. They’ve pulled the 30 percent risk down mostly into Arkansas, tapping on southeast Oklahoma, northeast Texas, and extreme southern Missouri down around Branson. Anyone for a chase through the Ozarks?

Yesterday’s trough passed through pretty much as expected, without a whole lot of fanfare and certainly not with anything tornadic. So the question is, what lies ahead? Anything?

Maybe.

At least we’re not locking in under another ridge. Today is the first day of autumn, the weather patterns are changing, and the GFS and ECMWF seem to agree on a 500 mb trough affecting the Midwest over the next several days. And yeah, yeah, I know it’s just reading tea leaves, but here are a couple 132-hour GFS maps for next Sunday at 00Z. At the risk of stating the obvious, click on the images to enlarge them. The first shows sea level pressure (shaded), surface wind barbs, and 500 mb height contours.

The second map shows 500 mb winds (shaded) with wind barbs, and 300 mb wind contours.

The big question mark may be moisture. But this far out, it’ll be nice if that even matters by the time Sunday arrives. This time of year, living in the Great Lakes, the best one can do is hope. But there’s nothing wrong with hoping.

Out of idle curiosity, I ran the latest GFS and came up with the image below. The colored shading is 500 mb winds, and the contours are CAPE. Not shown: H7 temps of 4 C throughout Michigan, 50-60 kt bulk shear, and dewpoints in the mid-60s.

GFS for 00Z Friday evening, July 24.

CAPE stinks, but I’ve got to love that jet streak parked right over Grand Rapids. Without decent convective energy, this setup is hard to get too hopped up about, but it’s certainly worth keeping an eye on. Probably a pipe dream in July, but in this part of the country you just never know.

A significant weather event appears to be shaping up for the northern plains and cornbelt this coming Tuesday. For all you weather buffs and storm chasers, here are a few maps from the 18Z NAM-WRF run for 7 p.m. CT Tuesday night (technically, 00Z Wednesday), courtesy of F5 Data.

A couple items of note:

* The NAM-WRF is much less aggressive with capping than the GFS.  The dark green 700mb isotherm that stretches diagonally through central Minnesota marks the 6 C contour, and the yellow line to its south is the 8 C isotherm.

* The F5 Data proprietary APRWX Tornado Index shows a bullseye of 50, which is quite high (“Armageddon,” as F5 software creator Andy Revering puts it). The Significant Tornado Parameter is also pretty high, showing a  tiny bullseye of 8 in extreme northwest Iowa by the Missouri River.

Obviously, all this will change from run to run. For now, it’s enough to say that there may be a chase opportunity shaping up for Tuesday.

As for Wednesday, well, we’ll see. The 12Z GFS earlier today showed good CAPE moving into the southern Great Lakes, but the surface winds were from the west, suggesting the usual linear junk we’re so used to. We’ve still got a few days, though, and anything can happen in that time.

SBCAPE in excess of 3,000 j/kg with nicely backed surface winds throughout much of region.

500mb winds with wind barbs.

MLCINH (shaded) and 700mb temperatures (contours).

APRWX Tornado Index (shaded) and STP (contours). Note the exceedingly high APRWX bullseye.

Some months back, I wrote a review of F5 Data, a powerful weather forecasting tool that aggregates a remarkably exhaustive array of atmospheric data–including over 160 different maps and a number of proprietary indices–for both professional and non-professional use. Designed by storm chaser and meteorologist Andrew Revering, F5 Data truly is a Swiss Army Knife for storm chasers, and thanks to Andy’s dedication to his product, it just keeps getting better and better.

My own effectiveness in using this potent tool continues to grow in tandem with my development as an amateur forecaster. Today I encountered a phenomenon that has puzzled me before, and this time I decided to ask Andy about it on his Convective Development forum. His insights were so helpful that, with his permission, I thought I’d share the thread with those of you who are fellow storm chasers. If you, like me, have struggled with the whole issue of CINH and of figuring out whether and where capping is likely to be a problem, then I hope you’ll find this material as informative as I did.

With that little introduction, here is the thread from Andy’s forum, beginning with…

My Question

SBCINH vs MLCINH

I’m looking at the latest GFS run (6Z) for Saturday at 21Z and see a number of parameters suggesting a hot spot around and west of Topeka. But when I factor in convective inhibition, I get either a highly capped environment or an uncapped environment depending on whether I go by MLCINH or SBCINH. I note that the model sounding for that hour and for 0Z shows minimal capping, which seems to favor the surface-based parameter.

From what I’ve seen, SBCINH often paints a much more conservative picture of inhibition, while MLCINH will show major capping in the same general area. How can I get the best use out of these two options when they often paint a very different picture?

Andy’s Answer

This is a great question, and very well worded… I guess I should expect that from a wordsmith!

SB *anything* is calculated using a surface-based parcel. ML *anything* is calculated using a mixed layer parcel. It is done by mixing the lowest 100mb temperature and lowest 100mb dew points and using those values as if those values were the surface conditions, and then raising from those values.

This is why when you look at a sounding it looks to favor the SB CIN because the parcel trace on those soundings is always raised from the surface. If you were to ‘average’ or mix the lowest 100mb temperatures by simply finding the section of the temperature line that is 100mb thick at the bottom of the sounding, and find the middle of that line (average value) and see what that temperature is, and then go to the surface and find where that temperature would be on the sounding at the surface, and raise the parcel from there (after doing the same thing with the dewpoint temperature) then you will have the ML Parcel trace and would then have MLCIN and MLCAPE to look at in the sounding.

A drastic difference in capping from SBCIN to MLCIN indicates that there is a drastic difference in values just above the surface that are causing this inconsistency. So when the parcel is mixed it washes out the uncapped air you get from the surface value.

We have different ways of looking at these values with different parcel traces because quite frankly, we never know where this parcel is going to be raised from. The same idea is why we have Lifted Index and Showalter Index. ITs the same index, but Showalter uses the values at 850mb and pretends thats the surface, while Lifted Index uses the surface as the surface.

We just never know where the parcel is going to raise from.

It seems to be consensus that ML-anything is typically the favored parcel trace. This means smaller CAPE and bigger CIN usually.

I have stuck strictly to my APRWX CAP index for years now because it considers both of these, as well as the temperature at 850mb, 700mb, and temperatures at heights from the surface up to 3000m, cap strength/lid strength index, as well as some other things when looking at capping. It seems to perform very well.

To summarize though… capping is a bear. If anything is out of line, you’ll easily get capped. So what I do is look at every capping parameter I can, and if *anything* is suggesting it being capped, then plan for it to be capped during that time period.

Now to confuse the situation even more, keep in mind that capping only means that you won’t get a storm to take in parcels from the suggested parcel trace location… IE.. from the surface. You can be well capped and have elevated storms above the cap. However for them to be severe you tend to need ‘other’ parameters in place, such as very moist air at 850mb (say 12c dew), some strong winds at that level, etc. to feed the storm.

Another map that is neat to look at for capping is the LFC-LCL depth. You may be capped, but want to be in position where the cap is ‘weakest’ and may have the best chances at breaking… with this map you get into your area of interest and then look at this map and find where the LFC-LCL depth is ‘smallest’.

For a capped severe situation, this usually means high values with a donut hole of smaller values in the middle. This is a great indication that the cap would break most easily in the middle of that donut.

This map (in a different, but similar form) can be seen on the SPC Mesoanalysis web site as LFC-LCL Relative Humidity. Its the same idea, but on their map you want high humidity values for weakening cap indication.

——————

So there you have it–Andy’s manifesto on capping. It’s a gnarly subject but an important one, the difference between explosive convection and a blue-sky bust. There’s a lot more to it than looking at a single parameter on the SPC’s Mesoanalysis Graphics site. If nothing else, this discussion has brought me a step or two closer to knowing how to use the ever-increasing kinds of forecasting tools that are available.