2 April 2015 severe thunderstorm event

On 2 April 2015, severe thunderstorms were forecast by the SPC as summarized in their Day 1 convective outlook graphic:

20150402 1300 UTC Day 1 Outlook Graphic

We will focus on the western edge of the enhanced outlook area which is roughly southeast Kansas, northwest Oklahoma, southwest Missouri and northwest Arkansas.

One of the key ingredients for this severe weather setup was an upper-level jet.  The GOES water vapor imagery overlaid with the RAP 250 mb isotachs for the late afternoon / early evening hours depicts this upper-level jet:


The core of the jet is across southern Colorado, and quickly moves eastward across Kansas towards the threat area in southeast Kansas / northeast Oklahoma.  There appears to be a good correlation between the arrival of the upper-level jet streak and the timing of convective initiation in southeast Kansas.

GOES visible imagery along with RAP 250 mb isotachs:


Shows considerable cirrus at the leading edge of the jet streak across Kansas and in fact convective initiation occurs along a low-level convergence boundary around that time.  The low-level convergence boundary can be seen in southeast Kansas extending eastwards into southwest Missouri where convection occurred earlier and moved off to the east.

A closer inspection of the visible imagery at 20:15 UTC:

vis2015shows the different boundaries and air-masses.  Unstable cloud streets can be seen along and south of the segment where convective initiation occurs.  Stable cloud streets exist further north and northeast of the boundary where cooler temperatures exist.  The thunderstorms developed at the northern edge of the lid associated with an elevated mixed layer profile.


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Typhoon Hagupit

By Kate Musgrave

Typhoon Hagupit in the northern West Pacific basin underwent intensification until reaching a peak intensity of 155 kt at 0000 UTC on 4 Dec 2014 (intensities obtained from Joint Typhoon Warning Center (JTWC)). This was a 65 kt increase over the intensity 24 hours previous (90 kt at 0000 UTC on 3 Dec 2014) and marked Typhoon Hagupit as a supertyphoon. VIIRS overpasses were available both during the intensification and at peak intensity in Typhoon Hagupit (all images provided by Dan Lindsey, NOAA/NESDIS). Below is shown the VIIRS visible image from Typhoon Hagupit at 0440 UTC on 4 Dec 2014, at peak intensity.


Zooming in further, displayed below is the infrared from the same VIIRS overpass. The eye is clear down to the ocean surface and both the eye and eyewall display highly symmetric features.


Previously, a VIIRS overpass occurred at 1555 UTC on 3 Dec, during the period when Typhoon Hagupit was rapidly intensifying (the intensity at 1200 UTC on 3 Dec was 100 kt). Shown below is the infrared from that earlier VIIRS overpass:


Notably, the features in the eye and eyewall at this time are more asymmetric, with the interface between the eye and eyewall appearing more ragged and less circular than at peak intensity. The eye has also not yet cleared out to the ocean surface. The overall shape of the coldest cloud tops at this time bears a particularly strong resemblance to the common symbol used for representing tropical cyclones, as illustrated in the bottom right corner of the figure.

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