SEVERE WEATHER FORECAST SYNOPSIS DAY 1…FORECAST SEVERE WEATHER OUTBREAK PRELIMINARY ASSESSMENT…WIDEST DISSEMINATION REQUESTED…ISSUED 2:25 P.M. EDT…APR. 25, 2016

Disclaimer:  This site is not associated with the National Hurricane Center, Storm Prediction Center, or National Weather Service.  ALL forecasts herein are the result of my analysis, and I am solely responsible for the content.
(T. F. “Storm” Walsh III)

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Good day everyone!

The Storm Prediction Center (SPC) has issued a SLIGHT risk of Severe Thunderstorms over parts of THE MID-MS VLY AND GRT LKS…

There is a MARGINAL risk FROM THE CNTRL PLNS TO OH VLY/LWR GRT LKS and OVER PARTS OF THE CNTRL HI PLNS…

 

…SUMMARY…
SCATTERED MAINLY AFTERNOON AND EVENING STORMS WITH HAIL AND LOCALLY DAMAGING WIND ARE EXPECTED OVER PARTS OF THE GREAT LAKES AND MID-MISSISSIPPI VALLEY. OTHER STRONG TO MARGINALLY SEVERE STORMS MAY OCCUR OVER THE CENTRAL HIGH PLAINS TONIGHT.

SPC DAY 1 CONVECTIVE OUTLOOK
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SPC RISK CATEGORY DEFINITIONS
Outlook-category-descriptions

Based on the SPC outlook, the forecast calls for strong to marginally severe thunderstorms to develop in the slight risk area mainly this afternoon and this evening.

Forecast sounding data from the NAM-WRF and RAP models indicate that supercell development is possible or likely.  Based on my analysis of forecast sounding indices, the information concurs with the SPC percentages in the lookout map.  Tornado activity is listed at a 2% probability.  The hail probability has been increased over a very small area over IL. and WI.  The forecast soundings indicate the most probable area for severe thunderstorms/scattered supercells should occur in the following outlined area:

F5 DATA BEST SEVERE PROBABILITY MAP
f5 nam severe.4-7pmcst

The area with the greatest probability of experiencing isolated tornado activity lies within the following outlined area, based on current forecast soundings:

F5 DATA BEST ISOLATED TORNADO PROBABILITY
f5.nam.tor.4pm

Residents within the risk areas should monitor NOAA Weather Radio and local NWS statements.

The following graphics do not update automatically.  They are linked to their respective sites.  You must mouse over and click the graphics for current, up to date information.

SPC CONVECTIVE WATCH DISPLAY
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SPC MESOSCALE DISCUSSIONS DISPLAY
validmd

INTELLICAST NWS DOPPLER RADAR LOOP DISPLAY
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NWS RIDGE RADAR ACCESS

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COD METEOROLOGY DOPPLER RADAR
(Once you click on the NEXRAD button, and access which radar site you want, scroll over to the far left of the page, and a menu will appear with looping features)
http://weather.cod.edu/satrad/

NCAR DOPPLER RADAR
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NWS HAZARDS AND WARNINGS DISPLAY
US

IF A TORNADO WARNING IS ISSUED…SEEK SHELTER IMMEDIATELY.

The SPC still indicates a SEVERE WEATHER OUTBREAK for tomorrow in their day 2 outlook and indicate a MODERATE risk area.

SPC DAY 2 CONVECTIVE OUTLOOK
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day2probotlk_1730_any
Probability of severe weather within 25 miles of a point.
Hatched Area: 10% or greater probability of significant severe weather within 25 miles of a point.

From the SPC outlook:

…SUMMARY…
SIGNIFICANT SEVERE THUNDERSTORMS WILL BE POSSIBLE ACROSS PARTS OF THE SOUTHERN AND CENTRAL GREAT PLAINS TUESDAY AFTERNOON INTO THE NIGHTTIME HOURS. TORNADOES…SOME STRONG…WILL BE POSSIBLE…IN ADDITION TO VERY LARGE HAIL AND DAMAGING WINDS. ADDITIONAL ISOLATED STRONG STORMS ARE POSSIBLE ACROSS PARTS OF THE OHIO VALLEY TO THE MIDDLE ATLANTIC COAST REGION.

…SYNOPSIS…
DEEP UPPER TROUGH CURRENTLY EXTENDING FROM THE PACIFIC NW INTO THE WRN GREAT BASIN WILL CONTINUE EWD THROUGH THE GREAT BASIN TODAY BEFORE CONTINUING THROUGH THE FOUR CORNERS AND INTO THE CNTRL PLAINS ON TUESDAY. SHORTWAVE TROUGH CURRENTLY ROUNDING THE BASE OF THE UPPER TROUGH WILL EJECT NEWD INTO THE CNTRL HIGH PLAINS TONIGHT…LEADING TO SURFACE CYCLOGENESIS THIS AFTERNOON AND EVENING ACROSS THE HIGH PLAINS. ASSOCIATED STRONG NLY LOW-LEVEL FLOW IS EXPECTED TO PERSIST OVERNIGHT…CONTINUING THE POLEWARD TRANSPORT OF LOW-LEVEL MOISTURE OVERNIGHT AND INTO TUESDAY. SECOND SHORTWAVE TROUGH NOW MOVING THROUGH NRN CA WILL FOLLOW A PATH SIMILAR /BUT SLIGHTLY MORE SLY/ TO THE LEAD SHORTWAVE…MOVING THROUGH THE SRN/CNTRL HIGH PLAINS TOMORROW AFTERNOON.

SURFACE CYCLOGENESIS RELATED TO THIS SECOND SHORTWAVE TROUGH IS EXPECTED TO RESULT IN A SURFACE LOW ACROSS THE CNTRL HIGH PLAINS BY EARLY TUESDAY AFTERNOON.

SOME UNCERTAINTY EXISTS ON THE EXACT LOCATION OF THIS LOW BUT CURRENT THINKING IS THAT AT 18Z IT WILL BE CENTERED OVER NE CO WITH A DRYLINE ARCING FROM THE LOW EWD TO CLOSE TO HYS AND THEN SWD TO SPS AND A WARM FRONT EXTENDING EWD FROM THE LOW N OF THE KS/NEB THROUGH CNTRL IL.

PROGRESSION OF THE PREVIOUSLY MENTIONED SHORTWAVE TROUGHS AND THE SURFACE FEATURES WILL LIKELY RESULT IN TWO SEPARATE AREAS OF NUMEROUS TSTM WITH THE POTENTIAL FOR A RELATIVE MIN IN COVERAGE /BUT NOT INTENSITY/ IN BETWEEN /DISCUSSED IN MORE DETAIL BELOW/.

…CENTRAL PLAINS…
THERMODYNAMIC ENVIRONMENT AHEAD OF THE DRYLINE OVER THE CNTRL PLAINS WILL LIKELY BE CHARACTERIZED BY TEMPERATURES IN THE UPPER 70S/LOW 80S…DEWPOINTS IN THE MID 60S…MID-LEVEL LAPSE RATES GREATER THAN 8 DEG C PER KM…AND VERY STRONG INSTABILITY /MLCAPE OVER 3000 J PER KG/. AS SUCH…THE THERMODYNAMIC ENVIRONMENT WILL BE MORE THAN SUPPORTIVE FOR SEVERE TSTMS. THE KINEMATIC ENVIRONMENT IS EXPECTED TO BE CHARACTERIZED BY 0-6 KM BULK SHEAR AROUND 40-50 KT. STRENGTH OF THE LOW-LEVEL FLOW WILL NOT BE PARTICULARLY STRONG WITH SURFACE WIND SPEEDS GENERALLY ANTICIPATED TO BE AROUND 15-20 KT…WITH SLIGHTLY STRONGER 850 MB WINDS. THE STRENGTH OF THE LOW-LEVEL WINDS IS THE PRIMARY FACTOR ANTICIPATED TO LIMIT HIGHER-END SEVERE POTENTIAL — I.E. NUMEROUS LONG-TRACK TORNADOES — PRECLUDING THE NEED FOR AN UPGRADE TO HIGH RISK WITH THIS FORECAST. THAT BEING SAID…NUMEROUS SEVERE TSTMS ARE STILL ANTICIPATED WITH ALL SEVERE THREATS POSSIBLE…INCLUDING VERY LARGE HAIL AND A STRONG TORNADO OR TWO.

SOME THREAT EXISTS FOR A CONVECTIVE CLUSTER TO DEVELOP ALONG AND NORTH OF THE WARM FRONT DURING THE AFTERNOON AND EVENING AND THEN TRACK EWD/SEWD ALONG THE WARM FRONT TOWARDS THE LWR MO RIVER VALLEY OVERNIGHT. MARGINAL RISK WAS EXPANDED EWD TO ACCOUNT FOR THIS SCENARIO.

…SOUTHERN PLAINS…
ANTICIPATED CONVECTIVE COVERAGE IS A BIT MORE UNCERTAIN ACROSS THIS REGION THAN AREAS FARTHER N. SECOND SHORTWAVE IS EXPECTED TO EJECT OUT OVER THIS REGION DURING THE AFTERNOON. HOWEVER…THE SHORT WAVELENGTH BETWEEN THE LEAD SHORTWAVE MOVING THROUGH THE CNTRL PLAINS AND THE ONE EJECTING OUT OVER THIS REGION IS LEADING TO MORE BACKED — I.E. SOUTHERLY — MID-LEVEL FLOW…CREATING WIND PROFILES THAT APPEAR MORE FAVORABLE FOR LESS DISCRETE SUPERCELLS AND MORE QUICK TRANSITIONS TOWARDS A LINEAR MODE. ADDITIONALLY…LIKE AREAS FARTHER N…LOW-LEVEL FLOW IS NOT CURRENTLY ANTICIPATED TO BE PARTICULARLY STRONG. AS SUCH…THE POTENTIAL FOR HIGH SIGNIFICANT SEVERE COVERAGE IS INSUFFICIENT TO UPGRADE ANY AREAS TO HIGH RISK. IN FACT…SOME OF THIS REGION MAY ONLY SEE ISOLATED TO SCATTERED SVR COVERAGE. HOWEVER…GIVEN THE OVERALL THERMODYNAMIC AND KINEMATIC ENVIRONMENT…SUPERCELLS CAPABLE OF ALL SEVERE HAZARDS INCLUDING VERY LARGE HAIL AND STRONG TORNADOES REMAIN POSSIBLE.

THE MODERATE RISK WAS EXTENDED SWD TO THE RED RIVER TO ACCOUNT FOR HIGH CONFIDENCE IN WIDESPREAD SEVERE THUNDERSTORM COVERAGE. THIS AREA IS EXPECTED TO EXPERIENCE THE GREATEST OVERLAP IN ANTICIPATED STORM COVERAGE…INSTABILITY…AND LOW-LEVEL SHEAR…PARTICULARLY AROUND 00Z AS THE LOW-LEVEL JET INCREASES. SOME ADDITIONAL SWD EXTENSION INTO TX MAY BE NEEDED AS DETAILS BECOME MORE CLEAR IN SUBSEQUENT OUTLOOKS.

Based on all of the information provided, SPC suggests a HIGH risk issuance is not warranted at this time.

Based on my analysis of current forecast sounding indices and parameters from both the GFS and NAM-WRF models, via F5 DATA Severe Weather forecast software, the outlined area will have the highest probability of experiencing the large/giant hail, strong/long track tornadoes, and damaging wind gusts as in the aforementioned summary from SPC.  I have all of the analyzed indices overlapped on each other to save time and space on the site. You can basically get the idea of where the “worst” conditions should occur, based on the current model runs.  Pretty much, the higher the indices value, and deeper the colors indicate the higher probability.  Based on this, though I may rescind it tomorrow, depending on what the forecast soundings show in the morning, and what SPC has issued in their outlook, this office is issuing a PDS (Particularly Dangerous Situation) statement regarding this proposed severe weather outbreak.

F5 DATA FORECAST SOUNDING INDICES
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Since indices values are overlapped, I will list what the current forecast values are.

SBCAPE (Surface Based CAPE): 3000-4000
MLCAPE (Mixed Layer CAPE): 2500-4000

CAPE (from Wikipedia): In meteorology, convective available potential energy (CAPE),[1] sometimes, simply, available potential energy (APE), is the amount of energy a parcel of air would have if lifted a certain distance vertically through the atmosphere. CAPE is effectively the positive buoyancy of an air parcel and is an indicator of atmospheric instability, which makes it very valuable in predicting severe weather. It is a form of fluid instability found in thermally stratified atmospheres in which a colder fluid overlies a warmer one.

 Based on current standing values, CAPE indices of 2500+ indicate EXTREME CAPE, indicating the atmosphere to be very unstable and very buoyant.

LI (Lifted Index): -12 to -14

L.I. (from Wikipedia):

The lifted index (LI) is the temperature difference between an air parcel lifted adiabatically Tp(p) and the environment Te(p) at a given pressure height in the troposphere (lowest layer where most weather occurs) of the atmosphere, usually 500 hPa (mb). When the value is positive, the atmosphere (at the respective height) is stable and when the value is negative, the atmosphere is unstable.

The lifted index can be used in thunderstorm forecasting, however, convective available potential energy (CAPE) is considered by most as a superior measurement of instability and is preferred by many meteorologists for convection forecasting.[1] However, LI is easier and faster to determine without using a computer, as determining CAPE requires integration from one level to another.

LI is generally scaled as follows:

  • LI 6 or Greater, Very Stable Conditions
  • LI Between 1 and 6 : Stable Conditions, Thunderstorms Not Likely
  • LI Between 0 and -2 : Slightly Unstable, Thunderstorms Possible, With Lifting Mechanism (i.e., cold front, daytime heating, …)
  • LI Between -2 and -6 : Unstable, Thunderstorms Likely, Some Severe With Lifting Mechanism
  • LI Less Than -6: Very Unstable, Severe Thunderstorms Likely With Lifting MechanismEHI (Energy Helicity Index): 2 to 7EHI or Energy Helicity Index:From Haby Hints:  The Energy Helicity Index (EHI) is a combination of two indexes. By itself, it is the best index available for tornado prediction since it combines both CAPE and Helicity. The CAPE is the amount of pure instability present from a parcel of air that rises from the lower PBL. Helicity is the product of low level shearing (known as streamwise vorticity) and storm inflow directly into the streamwise vorticity. The Helicity is storm relative which means the Helicity is calculated from the storm’s frame of reference.  EHI in the areas of 4 or greater, indicate the likelihood of strong/long track tornadoes is very high.CRAVEN BROOKS: 50,000-90,000

    The Craven Brooks Index is another parameter which indicates pretty much the type of severe weather an area may experience.  As you can see, values in the risk area are from 50,000-90,000.  Based on the scale, values of 45,000 or greater indicates widespread severe weather is likely.  Multiple significant hail, wind, and/or tornado events may also occur.

    STP (Significant Tornado Parameter): 1 to 6

    STP or Significant Tornado Parameter is just that.  It pretty much indicates where significant tornado activity may occur.  The values in the map, for the most part are averaging 2 t0 6.  Values of 1 or greater indicates the potential for significant tornadoes (EF2-EF5) increase dramatically.

    Provided nothing comes up for me tomorrow, I intend to have a detailed update on this situation.

    Have a blessed day!

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

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About palmharborforecastcenter

I am a Tropical Forecast meteorologist, providing hurricane forecasts during the Atlantic Hurricane Season. I retired from the U.S. Coast Guard in July of 2001. Meteorology became my passion in high school, and I have continued my educational background in meteorology since 1996, when I undertook the study of Tropical Meteorology. While working toward my degree, I had to unexpectedly withdraw from college due to my oldest sons medical reasons. I do however, meet the educational criteria of the AMS to be recognized as a meteorologist. Studies include, but are not limited to the Navy Aerographers Mate course, Naval METOC meteorology course, Meteorology 2010 Sophomore level course while attending St. Petersburg College, Clearwater, FL., Basic Forecasting course for operational meteorologists from Rapid WX, meteorology institute, a four month meteorological internship, and extensive research on numerous meteorological topics such as the MJO, NAO, satellite imagery interpretation, etc. I have been forecasting Tropical Weather (Tropical Storms and Hurricanes) since 1996, with my main client being three different Coast Guard Commands.
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2 Responses to SEVERE WEATHER FORECAST SYNOPSIS DAY 1…FORECAST SEVERE WEATHER OUTBREAK PRELIMINARY ASSESSMENT…WIDEST DISSEMINATION REQUESTED…ISSUED 2:25 P.M. EDT…APR. 25, 2016

  1. Dellamon says:

    Thank you storm. Prayers to all in the path of potentially dangerous conditions. Southeast Louisiana is still recovering from our latest.

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