Author Topic: SPC Moderate Risk, 7/20; KY, TN, MS, AL, IN, IL  (Read 1964 times)

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Offline WeatherHost

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SPC Moderate Risk, 7/20; KY, TN, MS, AL, IN, IL
« on: July 19, 2018, 03:37:23 PM »



Day 2 Convective Outlook 
   NWS Storm Prediction Center Norman OK
   1236 PM CDT Thu Jul 19 2018

   Valid 201200Z - 211200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR SOUTHERN
   IL/IN...CENTRAL/WESTERN KY...MIDDLE/WESTERN TN...NORTHERN MS/AL...

   ...SUMMARY...
   Scattered severe thunderstorms associated with large hail, wind
   damage and a tornado threat will be possible Friday afternoon and
   evening across parts of the MIssissippi, Ohio and Tennessee Valleys.
« Last Edit: July 20, 2018, 09:47:00 AM by WeatherHost »

Offline snowlover2

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Re: SPC Enhanced Risk, 7/20; KY, TN, MS, AL, IN, IL
« Reply #1 on: July 20, 2018, 01:49:27 AM »
Moderate risk area now and enhanced expanded.

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DAY 1 CONVECTIVE OUTLOOK   
NWS STORM PREDICTION CENTER NORMAN OK 
1234 AM CDT FRI JUL 20 2018 
 
VALID 201200Z - 211200Z 
 
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM WESTERN TN 
TO SOUTHERN IN... 
 
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM LOWER MI TO 
MS AND AL... 
   
..SUMMARY 
 
SEVERE THUNDERSTORMS WILL DEVELOP ACROSS THE OHIO AND TENNESSEE 
VALLEY REGION INTO THE MID-SOUTH FRIDAY. VERY LARGE HAIL, DAMAGING 
WINDS, AND A FEW TORNADOES CAN BE EXPECTED. ISOLATED SEVERE STORMS 
ARE POSSIBLE ACROSS THE CENTRAL HIGH PLAINS. 
   
..OH/TN VALLEYS INTO THE MID-SOUTH 
 
STRONG MID-LEVEL JET, IN EXCESS OF 60KT AT 500MB, IS FORECAST TO DIG 
SOUTHEAST ACROSS THE MID-MS VALLEY REGION FRIDAY AS PRIMARY 
MID-LEVEL CIRCULATION SETTLES INTO THE SOUTHERN LAKE MI AREA DURING 
THE LATTER HALF OF THE PERIOD. WITH 500MB HIGH CENTERED OVER THE 
SOUTHERN HIGH PLAINS, PRONOUNCED MID-LEVEL DIFFLUENCE WILL EXTEND 
ACROSS A GOOD PORTION OF THE OH VALLEY INTO THE CENTRAL GULF STATES. 
THIS LARGE-SCALE REGIME WILL PROVE FAVORABLE FOR ROBUST CONVECTION 
ALONG THE EASTERN PLUME OF SOUTHERN PLAINS HEAT DOME. 
 
EARLY THIS MORNING A SUBSTANTIAL RESERVOIR OF INSTABILITY EXISTS 
FROM THE CENTRAL PLAINS INTO THE LOWER MS VALLEY. SEVERAL POCKETS OF 
STRONG/SEVERE THUNDERSTORMS HAVE EVOLVED WITHIN A WARM ADVECTION 
CORRIDOR ACROSS SOUTHERN KS/NORTHERN OK AND AHEAD OF THE LARGER 
TROUGH OVER WI/IL. THIS ACTIVITY IS NOT CURRENTLY EXPECTED TO GROW 
UPSCALE PRIOR TO DAYBREAK. AS A RESULT, EXTREME BUOYANCY IS EXPECTED 
TO DEVELOP ACROSS THE MID-SOUTH INTO SOUTHERN IN WITHIN 
SOUTHWESTERLY LOW-LEVEL FLOW WHERE SURFACE TEMPERATURES ARE EXPECTED 
TO WARM RAPIDLY AHEAD OF SYNOPTIC FRONT. THE AFOREMENTIONED 
MID-LEVEL JET WILL DIG INTO THIS REGION DURING THE DAY ENHANCING 
SHEAR PROFILES AND VENTING ALOFT FOR ROBUST UPDRAFTS. 
 
CURRENT THINKING IS STRONGER FORCED REGIONS OF IN/LOWER MI WILL 
EASILY CONVECT BY EARLY AFTERNOON AND A POSSIBLE SQUALL LINE COULD 
EVOLVE AFTER 18Z WHERE MID-LEVEL BACKING AND HEIGHT FALLS ARE MORE 
EVIDENT. HOWEVER, MORE INTENSE THUNDERSTORMS ARE EXPECTED TO DEVELOP 
TOWARD 21Z FARTHER SOUTH ACROSS WESTERN KY, THEN INTO WESTERN TN BY 
LATE AFTERNOON. FORECAST SOUNDINGS ACROSS THE MDT RISK REGION ARE 
QUITE IMPRESSIVE REGARDING BUOYANCY WITH SBCAPE ON THE ORDER OF 
5000-6000 J/KG AND SFC-6KM SHEAR APPROACHING 60KT. ENVIRONMENTAL 
PARAMETERS STRONGLY FAVOR SUPERCELLS ACROSS THIS REGION AND VERY 
LARGE HAIL COULD ACCOMPANY THIS ACTIVITY. IN ADDITION, TORNADO 
THREAT WILL BE GREATEST WITH THESE DISCRETE STORMS THAT WILL 
PROPAGATE STRONGLY SOUTHEAST AROUND 25KT. IF THIS REGION IS NOT 
CONVECTIVELY CONTAMINATED PRIOR TO MID AFTERNOON THERE IS SOME 
CONCERN THAT A HIGHER TORNADO THREAT MAY BE EMBEDDED IN THIS REGION. 
WILL MONITOR MESOSCALE DETAILS AND ADDRESS THIS CONCERN IN LATER 
OUTLOOKS. OTHERWISE, MULTIPLE SEVERE THUNDERSTORM CLUSTERS SHOULD 
EVOLVE ACROSS THE MID-SOUTH DURING THE EVENING WHICH SHOULD 
PROPAGATE ACROSS NORTHERN MS/AL WITH AN ATTENDANT THREAT FOR LARGE 
HAIL/DAMAGING WINDS.

Offline ak9971

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Re: SPC Enhanced Risk, 7/20; KY, TN, MS, AL, IN, IL
« Reply #2 on: July 20, 2018, 09:34:06 AM »
They've expanded the moderate risk to now include portions of SW Ohio. Looks like all severe types are in play with an expansion in the tornado risk. Wondering if the morning convection moving through quicker than modeled the past few days has something to do with that?




 
Quote
Forecast Discussion
   SPC AC 201255

   Day 1 Convective Outlook 
   NWS Storm Prediction Center Norman OK
   0755 AM CDT Fri Jul 20 2018

   Valid 201300Z - 211200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   NORTHERN/WESTERN TENNESSEE...WESTERN/NORTHERN
   KENTUCKY...SOUTHERN/EASTERN INDIANA...AND SOUTHWESTERN OHIO....

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SEPARATELY LOCATED
   OVER PARTS OF THE CENTRAL HIGH PLAINS...

   ...SUMMARY...
   The greatest threat for severe thunderstorms will develop across the
   Ohio and Tennessee Valley regions into the Mid-South today into
   early tonight, with damaging gusts, large hail and tornadoes
   possible.

   ...Synopsis...
   In mid/upper levels, a strong high is forecast to shift eastward
   across the southern Rockies to the TX/OK Panhandles region through
   the forecast period, with ridging westward to southern CA and
   southeastward across LA to the north-central Gulf.  To its
   northeast, the main upper-air feature for this forecast will be a
   strong shortwave trough -- now evident in moisture-channel imagery
   from the Upper Mississippi Valley to KY, with am embedded low near
   LSE.  By 00Z, the center of the expanding 500-mb cyclone should
   reach southern Lake Michigan, with trough extending to the southern
   Appalachians, loosely phased with a broad/weak southern-stream
   perturbation over the Carolinas.  By 12Z, the cyclone should cover
   much of the Great Lakes and Ohio Valley region, with 500-mb low near
   the MI/IN border.

   At the surface, a low was analyzed at 11Z over
   south-central/southwestern WI, with two cold frontal segments:
   leading one across central/southwestern MO and the KS/OK border
   area, trailing/reinforcing one over portions of IA and southern NE.
   By 00Z, the low should be over or very near southern Lake Michigan,
   essentially stacked with respect to the mid/upper vortex.  The
   blended cold front should extend from an occlusion triple point over
   southwestern Lower MI across southwestern IN, north-central AR and
   northeastern OK, stalling west-northwestward across northern OK to a
   secondary low over the southwestern KS/southeastern CO/central OK
   Panhandle region.  By the end of the period, the cold front should
   reach the IN/OH border region, western TN and west-central AR, while
   remaining quasistationary from there to the OK Panhandle.

   ...Lower MI to Mid-South and TN Valley...
   Scattered to locally numerous thunderstorms should develop in this
   corridor, perhaps evolving into multiple clusters or bands at
   different times from midday through at least late evening.  The
   environment across the enhanced and moderate risk areas will be the
   most favorable for supercells, bow echoes and organized convective
   clusters, with tornadoes, damaging winds and large/damaging hail all
   possible.

   Tornado and significant/damaging-hail probabilities for now are
   maximized across parts of the lower Ohio Valley and Mid-South
   regions where seasonably steep lapse rates (7-8 deg C/km), very
   strong to extreme instability (MLCAPE 4000-6000 J/kg), rich moisture
   (70s F surface dew points, mean mixing ratios 17-20 g/kg), and
   strong deep shear 50-65 kt northwesterly effective shear vectors)
   are expected to juxtapose.  Tornado probabilities also have been
   increased/expanded in two directions:
   1.  Northward across the eastern IN/western OH corridor along and
   near an eastward-moving warm front, where thunderstorms developing
   in the warm sector or along the cold front may have time to evolve
   into mature supercells before interacting with the warm frontal
   zone's vorticity-rich, low-LCL environment.
   2.  Westward across the Mid-South and northeastern AR, where some
   discrete supercell modes are possible in a high-CAPE,
   adequate-shear, high-PW environment before upscale evolution occurs
   to more of a clustered mode and wind threat.  In that regard, some
   potential also exists for activity developing near either cold front
   in KS or southwestern MO to grow upscale near an already-observed
   moist axis, evolving into a southeastward-moving MCS with damaging
   wind over parts of the Ozarks region, and perhaps reaching parts of
   the lower Mississippi Valley.

Offline WeatherHost

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Re: SPC Moderate Risk, 7/20; KY, TN, MS, AL, IN, IL
« Reply #3 on: July 20, 2018, 10:10:37 AM »
Not feeling good ....

Offline Bruiser

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Re: SPC Moderate Risk, 7/20; KY, TN, MS, AL, IN, IL
« Reply #4 on: July 20, 2018, 10:15:00 AM »
The first round of heavy (though non-severe) rains dropped a quick .71 inches of rain IMBY this morning.  It was definitely needed!

Offline ak9971

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Re: SPC Moderate Risk, 7/20; KY, TN, MS, AL, IN, IL
« Reply #5 on: July 20, 2018, 10:16:07 AM »
The first round of heavy (though non-severe) rains dropped a quick .71 inches of rain IMBY this morning.  It was definitely needed!

I'll agree with that, haven't had any appreciable rains in weeks.

Offline snowlover2

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Re: SPC Moderate Risk, 7/20; KY, TN, MS, AL, IN, IL
« Reply #6 on: July 20, 2018, 01:45:33 PM »
Tornado watch up until 9pm.
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URGENT - IMMEDIATE BROADCAST REQUESTED
   Tornado Watch Number 289
   NWS Storm Prediction Center Norman OK
   135 PM EDT Fri Jul 20 2018

   The NWS Storm Prediction Center has issued a

   * Tornado Watch for portions of
     Southern Indiana
     Central Kentucky
     Southwest Ohio

   * Effective this Friday afternoon and evening from 135 PM until
     900 PM EDT.

   * Primary threats include...
     A few tornadoes likely
     Widespread large hail and scattered very large hail events to
       2.5 inches in diameter likely
     Widespread damaging wind gusts to 70 mph likely

   SUMMARY...Multiple rounds of strong/severe thunderstorms are
   expected to affect the watch area this afternoon and evening, posing
   a risk of large hail, damaging winds, and isolated tornadoes.

   The tornado watch area is approximately along and 70 statute miles
   east and west of a line from 55 miles north northwest of Cincinnati
   OH to 30 miles southeast of Bowling Green KY. For a complete
   depiction of the watch see the associated watch outline update
   (WOUS64 KWNS WOU9).

   PRECAUTIONARY/PREPAREDNESS ACTIONS...

   REMEMBER...A Tornado Watch means conditions are favorable for
   tornadoes and severe thunderstorms in and close to the watch
   area. Persons in these areas should be on the lookout for
   threatening weather conditions and listen for later statements
   and possible warnings.

   &&

   AVIATION...Tornadoes and a few severe thunderstorms with hail
   surface and aloft to 2.5 inches. Extreme turbulence and surface wind
   gusts to 60 knots. A few cumulonimbi with maximum tops to 500. Mean
   storm motion vector 28030.

   ...Hart

Offline WeatherHost

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Re: SPC Moderate Risk, 7/20; KY, TN, MS, AL, IN, IL
« Reply #7 on: July 21, 2018, 03:06:34 AM »
Near total Bust for me.  Other areas got hit, but I got a few passing clouds and the pavement sprinkled.

Good thing.  Too many storms recently for my tastes.

Offline ocala

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Re: SPC Moderate Risk, 7/20; KY, TN, MS, AL, IN, IL
« Reply #8 on: July 21, 2018, 06:09:00 AM »
Slight risk close to my area in Florida for Sunday.
That's a rare event for Florida in the summer where pretty much all the convection is initiated by seas breezes.
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