ENHANCED SEVERE WEATHER THREAT/ SPECIAL TROPICAL WEATHER STATEMENT/DEVELOPING NOR’EASTER FORECAST SYNOPSIS…ISSUED APR. 17, 2022…4:40 P. M. EDT7 min read
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(T. F. “Storm” Walsh)
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Good evening everyone!
Ok gang, a lot going on today, so I had to make each section short.
The Storm Prediction Center (SPC), has issued an ENHANCED RISK OF SEVERE THUNDERSTORMS in the current DAY 2 outlook: FROM NORTHERN LOUISIANA INTO SOUTHWEST MISSISSIPPI…
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SOUTHERN TEXAS…
Large to very large hail, damaging wind gusts, and a few tornadoes, are possible over parts of the lower Mississippi Valley/central Gulf Coast region today into this evening. Severe/damaging hail will be the main threat with thunderstorms over parts of south Texas.
A low-amplitude trough is noted in mid-morning water vapor imagery translating eastward across the Plains. An embedded vorticity maxima/shortwave is noted within this trough moving across KS with a broad swath of subsidence overspreading the southern High Plains. Ascent associated with this feature is already overspreading the southern Plains/lower MS valley this morning with scattered showers and isolated thunderstorms noted across southeast OK in the vicinity of a diffuse surface low and ahead of a modest cold front. This activity is expected to increase in coverage and intensity through the afternoon as it propagates along a surface warm front draped to the east/southeast into the lower MS river valley. The surface cold front will continue to push into southern/southeast TX and will be the impetus for isolated thunderstorms this afternoon.
SPC DAY 1 CONVECTIVE OUTLOOK LINK
SPC DAY 1 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 analysis of both the SPC outlook, and severe/tornado indices, with MLCAPE values forecast at 2000-2500j/kg, SBCAPE values of 2000-3000 j/kg, lifted indices of -4 to -8, and effective bulk shear of 40+ kts, there is plenty of energy and lift in the atmosphere over the risk areas to support large and/or significant hail. Given lower ESRH values of 100-150 m2/s2, and low to moderate end EHI and STP values, tornadoes are possible in the risk areas, however significant EF2+ tornadoes are currently a low probability. However, I want to point out, tornadoes can, and have developed outside the outlined risk areas. In addition, stronger than forecast tornadoes HAVE occurred in the lesser probability risk areas. This is not because we in the meteorology world have no idea what we are doing, but the fact that conditions can change at any time from the time let’s say, in a morning analysis, conditions can definitely change between “soundings”, in when we get update information.
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.
Based on these analyses this early afternoon, the following outlined F5 DATA maps indicate where the strongest tornado and severe indices where shown, and represent the best probability for the strongest severe weather and probability for tornado development. All times are in CDT.
F5 DATA NAM – WRF 4:00 P. M. CDT BEST TORNADO PROB
7:00 P. M. CDT
The severe threat may carryover into the overnight hours, however the F5 DATA NAM-WRF was very dispersed on indices at that time. The NAM 3km model also indicated the severe threat decreasing after 7:00 p. m. CDT, becoming minimal by 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 (4:00 P. M. CDT APR 17 – 10:00 P. M. CDT APR 17)
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)
Elsewhere, the mid level low over the Bahamas has become less discernible on satellite imagery.
GOES 16 IR, VISIBLE AND WATER VAPOR LOOP IMAGERY
Analysis of the TAFB Surface analysis map, NHC Tropical Weather Discussion, and vorticity maps from CIMSS, indicates a surface trof has developed near the coast of Cuba, and the mid level feature closer to the Bahamas. Wind shear is still a factor, however shear has reduced over the past 24 hours in between Cuba and Hispaniola. Analysis of the ECMWF forecast shear map does indicate wind shear to relax during the next 24 -30 hours, with a diffluent pattern aloft, shear is forecast to increase by 36 hours in the period from 12Z this morning. The relaxing of the shear could allow for the area to build convection, and possibly organize slightly, causing shower and thunderstorm activity to increase SEWD over Hispaniola. The area is forecast to remain stationary over the next couple of days, and this will allow for flooding rains over portions of Cuba, southern Bahamas, and Hispaniola.
Based on the premise of the increase of shear, and although upper divergence is supposed to remain decent, I do not believe this area will develop. IF anything did come to fruition, based on the analysis of stronger shear, and the area being within a trof axis, it would be more of a baroclinic feature.
I will however continue to monitor this area for any significant changes.
CIMSS CURRENT SHEAR
ECMWF WIND SHEAR FORECAST
The ECMWF and GFS global models indicate an area of low pressure to move offshore near the Carolinas during the next 24-30 hours, and moving along the eastern Seaboard. The low will strengthen once over the water, and eventually affect the DELMARVA and Cape Cod regions as a Nor’easter.
ECMWF MSLP ANOMALIES FORECAST
Both the ECMWF and GFS indicate surface winds to reach tropical storm force offshore, east of the low center. This will most likely generate some minor coastal flooding and beach erosion for those receiving an onshore flow with the easterly fetch. This system will also generate high wave heights close to the coastal areas and well offshore. Small craft should remain inport, and commercial shipping should take action to avoid the area.
ECMWF AND GFS FORECAST SURFACE WINDS
WAVEWATCH 3 AND ECMWF FORECAST WAVE HEIGHTS AND DIRECTION
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Have a blessed evening!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
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