I am posting a new post as opposed to replying to Justin’s most recent post about the upcoming possible HSLC environment because I can’t seem to find a way to include images in a comment of an existing post (if anyone has insight on how to do this please let me know).

I just wanted to post a few SREF images which provide some additional confidence in a possible HSLC environment this coming Tuesday afternoon into Wednesday morning. As Justin noted in his post, the models seem to be converging on a solution that show the possibility of a squall line/QLCS scenario within an HSLC environment.

28 Nov 2010 03z SREF forecast valid 21z 30 Nov depicting the probability of CAPE greater than or equal to 250 J/kg

28 Nov 2010 03z SREF forecast valid 21z 30 Nov depicting the probability of CAPE greater than or equal to 500 J/kg

In the above images you will see that the SREF forecast has a high probability of CAPE values greater than 250 J/kg across much of South Carolina, but lower probabilities of CAPE exceeding 500 J/kg. Shown in the images below, there is a very high probability of 0-3km helicity meeting or exceeding 200 m2/s2 and the effective shear meeting or exceeding 30 knots.

28 Nov 2010 03z SREF forecast valid 21z 30 Nov depicting the probability of 0-3km Helicity greater than or equal to 200 m2/s2

28 Nov 2010 03z SREF forecast valid 21z 30 Nov depicting the probability of effective shear greater than or equal to 30 knots

Another interesting aspect of this scenario is the amount of moisture that will be available for this system to work with. Below is the SREF mean precipitable water image which shows PW values pushing up to or exceeding 1.5 inches just ahead of the frontal boundary, which is significantly higher than normal.

28 Nov 2010 03z SREF forecast valid 00z 01 Dec depicting the mean precipitable water value

This should be an interesting event to monitor as it unfolds.

Hunter Coleman

WFO CAE

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I think ensemble forcasts of CAPE and shear are a great way to approach this problem. I will be interested to see d(prog)/dt for the SREF. Deterministic runs seem to have a hard time differentiating low CAPE from CAPE=0.0.

The CIPS Analog webpage now shows severe weather reports in addition winter weather reports (Coop Snowfall), and for this event there are several good matches for the overall wave pattern.

http://www.eas.slu.edu/CIPS/ANALOG/thumbnails.php?reg=CENT&model=GFS212&fhr=072&flg=old&map=500HGHT&sort=FINAL

The events with severe weather reported are about half and half, a few cases with widespread reports and a few with no reports.

http://www.eas.slu.edu/CIPS/ANALOG/thumbnails.php?reg=CENT&model=GFS212&fhr=072&flg=old&map=SVR&sort=FINAL

Great posts from the SREF output and the CIPS analog page – these are both very helpful operational tools. Matt mentioned seeing the SREF dProg/dt; the SREF combined probability of measurable precip, over 30 kts of deep layer shear, and at least 500 J/kg of MUCAPE has shown a slowing and increasing trend in the last few runs:

http://www.spc.noaa.gov/exper/sref/sref_matrix_hover.php?fhr=f069&startdate=2010112815&field=SREF_prob_combined_0.01_30_500__

-Gail

I notice that the SREF only provides probabilities for CAPE > 250 J/kg, which might be about the median value for HSLC events. Interestingly, one can instead look at the probabilities of LI 250) goes to zero over NC in last night’s SREF, the prob(LI<0) is around 50% all the way north into the Triangle. This could be a more meaningful metric in some scenarios (provided the EL is not below 500 mb), although testing and calibration for these probabilities would ultimately be needed.

Wow, my browser butchered that somehow. Reposting:

I notice that the SREF only provides probabilities for CAPE > 250 J/kg, which might be about the median value for HSLC events. Interestingly, one can instead look at the probabilities of LI 250) goes to zero over NC in last night’s SREF, whereas the prob(LI<0) is around 50% all the way north into the Triangle. This could be a more meaningful metric in some scenarios (provided the EL is not below 500 mb), although testing and calibration for these probabilities would ultimately be needed.

Grr… somehow I am using a combination of characters that is being interpreted as a comment by the blog software (or my browser). Last try…

I notice that the SREF only provides probabilities for CAPE greater than 250 J/kg, which might be about the median value for HSLC events. Interestingly, one can instead look at the probabilities of LI less than 0. So, for example, the probability of CAPE greater than 250 goes to zero over NC in last night’s SREF, whereas the probability of LI less than 0 is up around 50% all the way north into the Triangle. This could be a more meaningful metric in some scenarios (provided the EL is not below 500 mb), although testing and calibration for these probabilities would ultimately be needed.

Please work this time!

Thanks to Justin and Hunter for posting the “heads-up” for the upcoming event. (Well, I guess at this point it was yesterday’s event). When I left on Friday afternoon, the models were still suggesting that CAPE would be non-existant, although shear was very high. Evidently, the situation changed considerably.

It would be nice if we could get the CAPE threshold of 250 J/kg for the SREF probabilities in the Volume Browser on AWIPS. Depending on what we come up with for HSLC severe environments, this will be another positive outcome of the project. That is to say, making sure we have the ability to view important parameters and thresholds through the Volume Browser on AWIPS instead of having to go to an external web site to get this information.

-pat

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