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(T. F. “Storm” Walsh)
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Good evening everyone!
Sorry I did not have an update for you last night. Didn’t get out of work until late.
The Storm Prediction Center (SPC), has issued an ENHANCED RISK OF SEVERE THUNDERSTORMS in the current DAY 2 outlook: FROM THE TX PANHANDLE ACROSS WESTERN KS INTO SOUTH-CENTRAL NE…
Severe thunderstorms are expected to develop across parts of the Great Plains into Upper Midwest Friday through Friday night. Supercell thunderstorms capable of all severe hazards, including tornadoes and very large hail, are possible, particularly from the Texas Panhandle into south-central Nebraska.
A strong shortwave trough is forecast to be in place from the western Great Basin through southern CA early Friday morning, while downstream upper ridging extends from the Southeast northwestward through the northern Plains. Expectation is for this shortwave trough to progress quickly eastward/northeastward through the Four Corners/Southwest, reaching the central and southern High Plains by late Friday afternoon.
Deepening lee surface troughing is anticipated ahead of this shortwave across the High Plains, with eventual surface cyclogenesis forecast over northeast CO/NE Panhandle. This low is this expected to move northeastward across central SD while an attendant cold front pushes eastward across the central Plains. By early Saturday, the surface low will likely be centered over central SD with the cold front extending southward across central NE, central KS, and western OK. Interaction between this system (i.e. the shortwave trough and its related surface low) and returning low-level moisture across the Plains is currently expected to result in thunderstorms from the Dakotas/Upper MS Valley southward into the TX Panhandle.
CURRENT SPC DAY 2 OUTLOOK LINK
SPC DAY 2 CONVECTIVE OUTLOOK
Probability of one inch diameter hail or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of two inch diameter hail or larger within 25 miles of a point
DAMAGING THUNDERSTORM WIND PROBABILITY
Based on my analysis of the current DAY 2 outlook from the SPC, and analysis of various severe and tornado indices/parameters, the enhanced risk area should experience discrete supercells tomorrow afternoon into late evening. Based on analysis of forecast CAPE values between 1000 – 3500 j/kg, SWEAT values in the range of 400 – 525, STP values of 4+, moderate to high VGP and EHI values, seem to support the SPC solution of the main threat once again being, strong thunderstorm winds and large to significant hail. These index values should be in place from late afternoon, through late evening. Analysis of the modeling suggests that the strongest indices should occur from 7:00 p. m. CDT, through to 10:00 p. m. CDT. From there, severe and tornado indices begin to slowly diminish. At least this is what the latest model run indicates. Though SPC did not provide any values in the current DAY 2 outlook, given some of the values I analyzed, I cannot rule out an isolated strong and possibly long track tornado sometime after 7:00 p. m. CDT, over the enhanced area of Nebraska. I would not rule out the possibility of and upgrade to a moderate risk over a portion of the enhanced risk outline On severe and tornado indices…the higher the index values, the greater chance of significant and long track tornado activity.
A majority of significant tornadoes (F2 or greater damage) have been associated with STP values greater than 1, while most non-tornadic supercells have been associated with values less than 1 in a large sample of RAP analysis proximity soundings.
A multiple ingredient, composite index that includes effective storm-relative helicity (ESRH, based on Bunkers right supercell motion), most unstable parcel CAPE (muCAPE) and convective inhibition (muCIN), and effective bulk wind difference (EBWD). Each ingredient is normalized to supercell “threshold” values, and larger values of SCP denote greater “overlap” in the three supercell ingredients. Only positive values of SCP are displayed, which correspond to environments favoring right-moving (cyclonic) supercells.
VGP: The VGP (Vorticity Generation Parameter) is meant to estimate the rate of tilting and stretching of horizontal vorticity by a thunderstorm updraft. Values greater than 0.2 m s-2 suggest an increasing possibility of tornadic storms.
The following sites will explain most of these values, and will give you an idea of what to expect:
ENVIRONMENTAL INDICES AND PARAMETERS NWS
THE WEATHER PREDICTION
F5 DATA NAM-WRF, NAM 3km, and SPC SREF models show strongest activity close to
7:00 p. m. CDT, and diminishing after 10:00 p. m. CDT.
Based on this, and my analysis, the following outlines in the F5 DATA maps indicate where the best probability for tornadic activity should occur. This is based on where analyzed indices overlap on the maps.
F5 DATA NAM – WRF 1:00 P. M. CDT
4:00 P. M. CDT
7:00 P. M. CDT
10:00 P. M. CDT
The following NAM 3km animations indicate the locations and strength of the forecast STP (Significant Tornado Parameter) index, and SCP (Supercell Composite Parameter) index.
NAM 3km STP ANIMATION (1:00 P. M. CDT APR 22 – MIDNIGHT CDT APR 23)
NAM 3km SCP ANIMATION
Please use the following maps for all days, which should update automatically, for Mesoscale Discussions and Convective Watches. You may have to refresh your browser, or click on the graphics. I am also providing the SPC homepage link, so you may get the updated information regarding any changes to the outlook:
SPC MESOSCALE DISCUSSIONS (CLICK IMAGE FOR UPDATES)
SPC CONVECTIVE WATCHES (CLICK IMAGE FOR UPDATES)
SPC HOMEPAGE LINK
IF A TORNADO WARNING IS ISSUED FOR YOUR AREA, IMMEDIATELY TAKE STURDY AND SAFE SHELTER
The following NWS Watch / Warning map will provide local NWS information for your area. Click the image, then once it refreshes, click on your area of interest to view any special weather statements, hazards or advisories for your area.
NWS WATCH / WARNING DISPLAY (LINKED…CLICK MAP, THEN YOUR AREA)
WSI DOPPLER RADAR LOOP (LINKED)
RAP RADAR (CLICK IMAGE THEN RADAR SITE)
You may direct any questions by contacting me personally, ANYTIME, at: firstname.lastname@example.org
Have a blessed evening!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
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