Meteorology

We spent the night in Scotts Bluff and joined Chuck and Vickie Doswell near Imperial, Nebraska, near the Colorado border in southwest Nebraska. The morning pattern featured a changing 500 mb pattern, with the trough that gave California inclement weather over the Four Corners region and changing the flow to southwesterly over Colorado, spreading eastward during the day. The Denver sounding showed the top two-thirds of the proverbial "loaded gun sounding" with an Elevated Mixed Layer surmounted by Pacific air.

Further east, relatively moist surface air could be found in southeasterly flow over Kansas heading towards southwest Nebraska. There, a trough axis separated that from drier air over Colorado, and the pattern was complicated by a couple of outflow boundaries in Kansas. We figured if the moisture made it to sw Nebraska at the same time that the incoming mid-tropospheric trough changed the shear profile, we'd have a chance to see a couple of supercells.

The RUC forecast exactly that, with favorable buoyancy showing up in the forecast CAPE field east of the trough axis, surmounted by 45 knots of 500 mb flow. SPC had outlooked the area for a slight risk, with a 5% tornado risk in the area.

What eventually occurred is that the rich dew point air over Kansas "mixed out" as it marched towards Nebraska. In addition, very strong surface souteasterlies (20-30 mph) underran 700 mb southerlies that were actually weaker, and then the progged 500 mb southwesterlies did verify. Unfortunately, that wind profile produced a backing wind shear vector with height, favoring left moving storms.

Pictures (and less Meteorology)

Here are Chuck, Vickie and Thom, as we waited in a graveyard near Imperial, Nebraska for storm initiation. The first storm developed in Yuma County, CO adjacent to the Nebraska border. It was a left mover with the inflow area on the north side of the storm. Here's a shot of the anvil flaring eastward. The radar showed the reflectivity gradient on the north side of the echo, and the storm shot due northward across the prevailing westerly or west-southwesterly flow. Later, new storms developed to the north and south of the first. Finally, in this shot you can see the effects of the messed up shear in the anvil of the storm to our due west. The updraft has shifted north, relative to the northeastward flaring anvil, and left it behind as a trail, extending southeasward, apparently (because the anvil producing updraft propagates northward, leaving the older anvil material in its wake.)

Meteorology

The chaser caravan today featured Chuck and Vickie Doswell (here's a picture of Chuck and me) chasing with Thom and me. We were joined by Scott Landolt (who will be joining me when Thom leaves on Sunday) who came out on a spot chase with his co-worker Seth. The day opened with a bit of promise as started from the York, Nebraska library.

We were debating a northeast Nebraska target and a target from Hebron to Belleville. These two target areas werenortheast of the incoming midtropospheric trough: (a) the further north one went, the surface wind field was more backed (with better low level shear), but progged mid and upper tropospheric winds were nearly parallel to the surface winds....we felt that storms there would be developing in unidirectional shear; (b) further south, the low level shear was not nearly as great, but the 0-6 km shear vector was southwesterly and about 6 X 10-3 s-1 progged for the afternoon. We were also very uneasy about the CAPE "hole", which ended up verifying. That was evident in a number of the morning soundings in the area, which showed a very shallow moist layer.

SPC had a slight risk for the area, with a 5-10% tornado within 25 miles of a point probabilistic forecast for the area.

The storms that developed in the Grand Island area were clustered together with competing outflows. However, the southern most of those tended to be discrete, and there was a persistent development area near Kearney, a couple of times having a "hookish" look to it. Storms roared northeastward (35 to 45 mph), and were high-based. A check of the dew points showed why the latter was the case...the originally mid 60 dew points had mixed into the high 50s, just as the RUC had forseen.

Pictures (and less Meteorology)

Eventually, ThreatNet was showing wheels of fortune and shear markers. We figured many of those were outflow shear signatures, but several were embedded in deformed areas of the radar reflectivity. One of those was visually linked to a lowered base, northwest of Capital City. For a brief time, this base appeared to be a blocky lowering, but was wrapped in rain from both its own forward flank, and the forward flank of the next storm upshear. We saw a number of gustnadoes, or whirls underneath inflow/outflow fingers/features, but nothing we would classify as tornadic.

Meteorology

We began the day in North Platte, Nebraska. The model data suggested that the high plains of eastern Colorado and southwestern Nebraska into northwest Kansas would have a number of factors that would contribute to a favorable enviornment for supercells, and, possibly, tornadoes. First, ahead of incoming trough at 500 mb, which would provide at least marginal deep layer shear in the area, the model suggested the development of a mesolow in eastern Colorado. North of that low would be accelerated easterly flow upslope into the area. That, in fact, verified, with strongly backed flow in northwestern KS into ne Colorado. But, the additional focusing features was a synoptic boundary, probably a warm front, extending east from this low, and an outflow boundary from pre-existing convection just east.

We were hoping that the upper 50 to low 60 dew points that had overspread the area overnight would not mix out (this was not to be). Thus, the warm front might serve as a source of lift for the east southeasterlies, and the outflow boundary could either serve as a source of parcel lift or a source of vorticity for storms that might form west of the area on the Palmer Divide. As it happened, the intiation occurred near the intersection of the outflow boundary and the warm front, but the moisture was very shallow, and the storms were high based. Ultimately, we observed beautiful supercells, but with high LCLs, no rotating wall clouds. To emphasize this, I measured a temperature of 99F and a dew point of 57F in the inflow area of these storms. Hardly conducive for tornadogenesis.

Here are a few of the Threatnet radar plots that show the storm initially splitting south of Hoxnie, and utlimately having significant rotation, and hook echoes/shear signatures.

Pictures (and less Meteorology)

Here's a picture of the initial storm development as it moved across Interstate 70. The picture is shot looking northwest. You can see the flanking line towers building into the updraft area (see corresponding radar) with the base of a horseshoe updraft visible in the middle of the picture.

Later the storm progagated and had new developments on its right flank. This is a picture of the strongest mesocyclone cloud signature. Note the beautiful striations, and the rain curtains wrapping around the updraft area. The corresponding radar showed a shear signature of 103 mph across the hook echo (on the west part of the radar image). Here's a shot of Thom taking pictures of this impressive feature.

North of us was another mesocyclone. Here's a shot of Thom, Chuck and Vickie Doswell, with the cloud features in the background. And, a spectacular shot of the multiple midlevel cloud bands (cigars) that were being pulled into the various rotation centers.

East of us, was another mesocyclone. Note the low level inflow band and the spectacular mammatus overarching it in the anvil.

Towards sunset, we had a wonderful view of the backlit cloud features with the major mesocyclone. And, as a final treat, that area had a downburst crash through the circulation...with a vibrantly colored cloud band to its east.

All in all, this was a spectacular day for storm chasing. No tornadoes, but a very photogenic and classically structured supercell.

Meteorology

The pattern on this day favored supercells perhaps in the northern poriton of South Dakota, but, more likely, in North Dakota. Since Thom's flgiht was tomorrow, we decided not to chase and drove into Denver.

Meteorology

The meteorological theme for this trip seems to be a misphasing of any low level buoyancy (deep moisture) with adequate shear. To explain, there has been, usually, more than adequate shear on each day of this trip, and there has been steep lapse rates and deep moisture, somewhere in the Plains, but these three ingredients have not been phased properly. May 28 was another such day.

On the morning surface map, steep lapse rates in an elevated mixed layer had overspread all of the Central Plains. But the deep moisture (generally in the green shaded area bounding the 60F+ dew points) was well east of the best (or any) deep layer shear (generally within 150 km of the arrow. SPC had outlooked a bit of the area for tornadic storms.

Scott Landolt had joined me, and we headed toward the northern Nebraska Panhandle, an area in which the RUC suggested a mesolow would circulate easterly flow not evident on the morning analysis back west into an upslope area of eastern Wyoming and western Nebraska, an area in which the prognosis had 500 mb flow more than adequate for rotating storms by the late afternoon...though the buoyancy, due to lack of deep low level moisture, would be meager.

Storms did develop, first in isolated fashion, and then more numerous. The early storms had signs of rotation, but by the afternoon, the area of western Wyoming had erupted with many storms, some with transient mesocyclones, that eventually coalesced into a derecho/MCS. In this radar image you can see the bowed segments, and the shear signatures of either mesocyclones or the surging gust front. We ducked into Chadron for the night as the bow echo came slamming through with frequent cloud to ground lightning, 3/4" hail, heavy rain, and winds gusting to 65 mph. There may have been some forward flank mesocyclones and weak tornadoes with the line as well.

Pictures (and less Meteorology)

Near Ellsworth Nebraska (in the panhandle) we spotted a cumulus field. Here's a shot of a horeshoe vortex left behind as a cumulus dissipated. Later on, north of Ellsworth, a small storm developed but quickly dissipated. Here's a picture of the growing cumulus with crepescular rays behind its top.

In Chadron, the bow echo caught up to us. Looking to the west, we could see the tiered forward flank, with the suggestion of some rotation, just ahead of heavy precipitation, and dust being kicked up by the 60 mph outflow winds. Out to the west, we could see cloud features on the forward flank that had vortices. That shelf was roiled as it passed directly over us and showed curling cloud features consistent with the Threatnet Wagonwheels seen on the radar.

Meteorology

This was a down day. There were multicellular storms that evolved into a squall line in northwestern Oklahoma on this day. But the risk of supercells was slight. So we dropped down to Garden City to be in position for what we expected to be an interesting day on May 30.

Meteorology

The day dawned with a complicated pattern. Scott and I awoke to lightning at around 5:45 as a thunderstorm rolled into Garden City. Later, while I was on a run, an outflow boundary from yet another thunderstorm chased me in to the motel. All of these coalesced into a large MCS, hopefully, not to ruin the pattern further west and south.The surface analysis showed the outflow boundary associated with this large area of convection. Further west, the mesolow, forecast by the RUC and NAM to turn the winds in southeastern Colorado to southeasterly, was in the process of formation. All of this would occur on the "cold air" side of the cold front that had sagged southward into the Panhandle.

The boundary northwest or southeast along the KS-se CO border south to the western OK Panhandle, it could act as a focus for subsequent convection. Both the RUC and the NAM 12 UTC runs have 30 knot or greater southwest flow at 500 mb from the extreme western OK Panhandle and north to Palmer Divide and east to about the GCK longitude. I overlaid that on top of the surface southeasterlies and the CAPE field (slightly different for the NAM and the RUC, though) and got a box that covers se CO to the western OK Panhandle. In that box the progged surface flow for each model shows either easterlies in the OK Panhandle (or southeasterlies from the NAM) and southeasterlies in eastern CO. That gives an effective shear of 40 knots or greater, particularly in the OK Panhandle.

Soundings in the area showed the usual...a steep lapse rate in the elevated mixed layer (for Denver and OKC) surmounting a very shallow mixed layer (for OKC). As usual, we're concerned about the quality of the moisture that will make it back underneath the strengthening flow at 500 mb by the afternoon. SPC had outlooked our area for a slight risk, with a 5% probabilistic forecast for tornadoes.

Storms fired on the Raton Mesa and eventually one became a supercell...subsequently to become outflow dominated and a part of yet another MCS. We targeted the storm near the border, and, eventually, got a shot of a wall cloud (see below).

Pictures (and less Meteorology)

The storm that came out of the Raton Mesa had supercellular characteristics. We could see a distant flanking line building into the main updraft, a rain-free base on its southwest flank, inflow stingers at midlevels. Several strong "rain feet" developed in the forward flank, and each of those was associated with a surge of scud that pushed out underneath the rain free base. One of these pushes was associated with the development of a wall cloud.

Shortly after that, a new storm developed on the south flank of the first (you can see it in the first radar above), and our storm became outflow dominated, with a shelf that connected south to the southern storm. Here's another view of the shelf from a vantage point to the south looking back to the rain core which had overwhelmed our storm. The southern storm had a rotating base and looked good briefly visually and on radar.

We dropped south to get a better view, but the storm kept on getting undercut by outflow, although each outflow push had a lowering on its southern side, that looked briefly interesting in each instance. Further east, othet storms were developing and splitting, with rain cores punching through updraft areas. Here's a spectacular example.

As the southern storm merged with the line it still retained decent structure. Here's a shot of it with a roll cloud on the leading edge of the undercutting outflow.

Meteorology

Seems like a broken record. Yet another day of weak deep layer shear and marginal buoyancy. Yet, the pattern, which featured a forecast of strong southeasterlies into southeast Colorado, under 30 knot 500 mb flow, dew points near 55F and CAPE near 1500 J/kg, held great promise. SPC seemed to concur, with a forecast of 5% risk of tornadoes within 25 miles of any point. However, the morning surface pattern was diffuse, and never seemed to deliver the promised southeasterly flow of richer moisture. At best, we had easterly flow, with near 50F dewpoints.

Thunderstorms erupted west of Denver, and one storm moved out onto the Palmer Divide, seemingly on a boundary which might make it a classic supercell, with a tornado. Although it briefly looked good, the storm quickly became outflow dominated and merged with the other cells in the area to form yet another MCS.

Pictures (and less Meteorology)

Despite the disappointing evolution summarized above, the cloud features that developed were nonetheless spectacular. Here's a shot, looking northwest, of the merger of a storm south of the original supercell. This storm briefly rotated (as you can tell by the wrapping rain curtains around its west flank). There may have been a small funnel on the lowering.

This is a shot looking north on the now outflow dominated main storm, with its shelf ominously extending southward. The purples, greens and blues were striking. The storm eventually propagated southward and had a mesocyclone out to our east, although it was outflow dominated. The shelf had downbursts of precipitation very evident.

The storms visible on radar to the west had brief lowerings and rain-free bases. Finally, we were treated to a spectacular sunset.

The pattern would not cooperate this year. Not only did we see no tornadic supercells, we figure that we only saw two storms that were briefly supercellular. And, this year, this was not attributable to bad decisions, either meteorological or navigational. There simply were no storms.

In fact, the survey of the couple of tornado reports that occurred during that time (off the Cheyenne Mesa on the Wyoming/Colorado border) indicated that what had been reported as tornadoes were, in fact, gustnadoes, as we saw on May 23. (These are shear-induced whirlwinds that have nothing to do with cloud layer rotaitonal processes...hence, are not tornadoes, and have more in kin to dust devils). Such as it is.

We made one more attempt on June 2 in a somewhat favorable pattern in eastern Colorado, but even that "threat" evaporated quickly during the day. Chuck and Vickie went home, and Scott and I drifted north into the southern portions of the Nebraska Panhandle, on the chance that pattern forecast by the models for June 3 would firm up. But with each successive run of the models, the threat of supercells, let alone tornadic supercells, seemed more and more remote.

That was it. Scott and I decided to "...call it a chase..." I got an early flight out of Denver on Saturday, June 3.

Good luck to all my colleagues who are still in the Plains hoping to wrest some science knowledge of tornadic supercells out of this unfavorable weather pattern. Thom and I, along with Scott (and Chuck and Vickie) will be back next year. Till then, all the best.

John Monteverdi
June 3, 2006