General Weather/Earth Sciences Topics > Severe Weather
SPC Moderate Risk, 7/20; KY, TN, MS, AL, IN, IL
WeatherHost:
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.
snowlover2:
Moderate risk area now and enhanced expanded.
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--- Quote ---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.
--- End quote ---
ak9971:
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.
--- End quote ---
WeatherHost:
Not feeling good ....
Bruiser:
The first round of heavy (though non-severe) rains dropped a quick .71 inches of rain IMBY this morning. It was definitely needed!
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