INTERPRETATION
DISCUSSION
|
Regional and Mesoscale Meteorology Team Cooperative Institute for Research in the Atmosphere (CIRA) Colorado State University Fort Collins, Colorado |
May 6, 2003
|
|
On 29 April 2003, a stationary front extended across east-central Colorado,
with southerly winds and relatively dry air south of the front, and moist
easterly winds north of the front (see the 1800 UTC surface map below).
By mid-afternoon, dew point values near 50 (deg F) were in place north
of the boundary in eastern Colorado. Due to the expectation of severe weather,
GOES-10 rapid scan operation (RSO) was called.
Topography and Surface Obs (click to enlarge) |
The GOES-10 Visible Loop shows a northwest/southeast oriented cloud boundary around 1840 UTC along the northern edge of the Palmer Lake Divide (a higher terrain feature which extends eastward into the Colorado plains - see the image above). Around 2000 UTC, towering cumulus clouds were evident along this boundary, and by 2030 UTC a storm anvil is visible. Shortly thereafter, the storm appears to split. As the right-mover intensifies, notice the cumulus clouds feeding in from the southeast. By 2200 UTC, the storm has taken on definite supercellular characteristics: a super-crisp edge on the south and west sides of the anvil, vertical cloud wall on the west side of the storm (extremely bright due to reflected sunlight), and a nice flanking line extending from beneath the southern portion of the anvil. The storm continues to progress eastward (to the right of the wind shear vector), and eventually dies around 0030 UTC. Note that before it begins to dissipate, around 2245 UTC an arc-shaped line of cumulus clouds is moving southwestward into Eastern Colorado from Kansas. This boundary separated unstable air to the west from more stable air to the east. The stable air mass originated from a cloudy region in northwest Kansas. The storm dissipates shortly after intersecting this boundary and ingesting the cooler, more stable air.
Visible imagery |
Click on images to start loops.
The KFTG radar loop (Denver's NEXRAD radar) shows storm initiation near Limon, Colorado, which is about 55 miles from KFTG (for Limon's location, see the first map above - Limon is LIC). It quickly split, and the right mover became the dominant storm (verifying what we observed on satellite). At 2200 UTC, the visible satellite indicated an impressive-looking supercell; the radar signature is more marginal, with maximum reflectivities near 45 dBZ. At this time, the storm is 60 miles from KFTG, so at 0.5 degree tilt, we're looking at 4700 ft AGL. In other words, the radar does not give us a good idea how intense this storm actually is.
The second radar loop is from the Goodland,
Kansas, NEXRAD (KGLD), approximately 90 miles east of the storm's location
at 2230 UTC. By 2245 UTC, the radar signature is much more impressive,
with a 60 dBZ core and a nice inflow notch. We can also see the southward
moving boundary noted in satellite which intersects the storm around 0015
UTC, shortly before the storm's rapid dissipation.
KFTG Radar Loop 0.5 degree tilt |
KGLD Radar Loop 0.5 degree tilt |
The two photos below were shot near Seibert, Colorado, around 2315 UTC. This is a perfect example of an LP supercell, with a bell-shaped updraft base and relatively little precipitation visible. The storm also produced 2.25 inch diameter hail during this portion of its life.
This example shows a case in which radar signatures were not impressive
early in the storm's life, but visible satellite imagery indicated an intense
supercell. Severe thunderstorm warnings accompanied the storm throughout
most of its lifecycle, and a few tornado warnings were issued due to strong
mid-level rotation evident on radar (not shown).
photo by Brian McNoldy |
photo by John Haynes and Chris Rozoff |