May 15, 2021

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SPC DAY 2 CONVECTIVE OUTLOOK…SLIGHT RISK OF SEVERE THUNDERSTORMS SYNOPSIS…ISSUED APR. 26, 2021…7:56 P.M. EDT

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(T. F. “Storm” Walsh)

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Greetings to everyone!
Please be aware, even though I do not post every night, rest assured I am continuously monitoring various areas for any significant weather.  I will be taking Sundays off (family time), unless we have active systems that may be posing a threat (i.e. Tropical, Winter Weather, Coastal Storms, etc.).

Good evening,
In credit to the SPC, I will post portions of the outlook text as deemed necessary with the understanding I am in no way posting the SPC information and claiming it as “my” forecast, but to hopefully provide a better understanding to the synopsis.

The Storm Prediction Center (SPC) has issued a SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF THE SOUTHERN PLAINS…

…SPC SUMMARY…
Severe thunderstorms are possible Tuesday afternoon through Tuesday night, primarily across a portion of the Southern Plains.
SPC DAY 2 CONVECTIVE OUTLOOK

SPC DAY 2 TORNADO OUTLOOK

SPC DAY 2 HAIL 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
SPC DAY 2 WIND OUTLOOK

Based on information contained in the current DAY 2 Outlook, and my analysis of the current run of the NAM-WRF model via F5 DATA software, it IS possible for some isolated severe weather to occur over the Central High Plains, and Upper Midwest.  However, the greater probability for severe weather, including large hail and isolated tornadoes appears to be mainly over the Southern Plains region.  The following is an excerpt from the outlook regarding the Southern Plains region:

A broad fetch of southwesterly winds aloft will become established over the Southern Plains Tuesday downstream from an upper trough that will amplify over the Southwest States. A warm elevated mixed later (EML) will advect through much of the warm sector resulting in a strong cap to surface based storms during the day over much of this region. Low-level dewpoints in the low to mid 60s will advect as far as northwest TX into western OK during the afternoon beneath the EML resulting in a corridor of moderate surface-based instability with 1500-2000 J/kg MLCAPE possible east of the dryline. An early round of scattered showers and thunderstorms still appears likely from late morning into the afternoon across parts of central and northern Texas into OK in association with ascent attending a leading shortwave trough. However, this activity will likely be elevated above the CAP, but could pose a risk for marginally severe hail.

Upstream of the early activity, a corridor of surface heating will likely occur from western TX into far western OK, and surface based storms will likely initiate in vicinity of the eastward-mixing dryline by late afternoon. Effective bulk shear from 45-55 kt will support supercells as the initial storm mode and this activity will pose a risk for large to very large hail. A relatively small window will exist for isolated tornadoes as the low-level jet increases during the early evening and before the boundary layer decouples. Some upscale growth may occur, and activity may continue east through parts of northwest and north central TX into OK during the overnight with a continued threat for large hail and damaging wind. An upgrade to ENH risk for large hail may be introduced from a portion of western TX into southwest OK on the day 1 updates.

A couple of supercells might also develop over the higher terrain of northern Mexico and spread into south central TX with very large hail and a tornado or two the main threats during the evening.

Based on the forecast MLCAPE values, significant moisture, and effective bulk shear, initial storm formation may be in the form of supercells.  Given the CAPE, and the analysis of fairly moderate lifted indices, and the shear, hail could become large to very large.  At the current time, based on the analysis of the severe and tornado indices, the severity does not appear to be to the extent we’ve seen over the past 2 events.  The onset of the severe weather appears to be approximately 4:00 p.m. CDT.  Indices at the moment appear to start out moderate to low at that time, and increase as time goes on, and become moderate by around the 10:00 p.m. to 1:00 a.m. CDT 4/27 – 4/28.  The following maps are from the NAM-WRF model 18Z run, utilizing F5 DATA Severe Weather software.  The outlined areas indciate where the most significant severe weather and tornadic activity could occur tomorrow.  ALL times are in Central Daylight Time.  As a reminder, these areas could change given any risk upgrade from the SPC, and any new information from the next 2 model runs.  As of current, the following outlines pretty much line up with the current STP parameters from the SPC SREF model.  Please refer to the SPC Home page link below the watches graphic for further updates regarding tomorrow’s severe weather, which will be the DAY 1 Outlook.  You’ll note the dryline with the first 2 graphics.  I did not include it further, as the dryline usually retreats west during the late evening.
F5 DATA NAM-WRF 4:00 P.M. CDT



DRYLINE

F5 DATA NAM-WRF 7:00 P.M. CDT


DRYLINE

F5 DATA NAM-WRF 10:00 P.M. CDT

F5 DATA NAM-WRF 1:00 A.M. CDT


SPC MESOSCALE DISCUSSIONS (CLICK IMAGE FOR UPDATES)

SPC CONVECTIVE WATCHES (CLICK IMAGE FOR UPDATES)


SPC HOME PAGE LINK
https://www.spc.noaa.gov/classic.html
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.
IF A TORNADO WARNING IS ISSUED FOR YOUR AREA, IMMEDIATELY TAKE STURDY AND SAFE SHELTER

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: twalsh22000@yahoo.com

Have a blessed evening!

T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS

palmharborforecastcenter

2021-04-26 23:57:48

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