Yardstickgozinya

   SPC AC 040533

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1233 AM CDT Tue Apr 04 2023

   Valid 051200Z - 061200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS WEDNESDAY
   ACROSS MUCH OF THE LOWER GREAT LAKES REGION AND OHIO VALLEY...

   ...SUMMARY...
   Scattered severe storms posing a risk for strong tornadoes and large
   hail are expected in a corridor across eastern Illinois through
   Lower Michigan Wednesday, with organizing clusters or lines of
   storms accompanied by potentially damaging wind gusts, and perhaps a
   couple of tornadoes, across the Ohio Valley vicinity.

   ...Synopsis...
   Within the more amplified branch of split flow emanating from the
   mid-latitude Pacific, the center of a broad and deep, occluding
   cyclone is forecast to migrate across and northeast of the Lake
   Superior vicinity before beginning to weaken Wednesday through
   Wednesday night.  As this occurs, it appears that mid-level ridging
   centered along an axis across the Yucatan Peninsula into western
   Atlantic will remain a prominent influence across much of the
   Southeast, while short wave ridging also overspreads the Northeast
   and Canadian Maritimes.

   Models indicate a corridor of deepening boundary-layer moisture
   overspreading the Ozark Plateau and middle Mississippi Valley, into
   the Lake Michigan vicinity, by early Wednesday.  This is forecast to
   spread across much of the lower Great Lakes and Ohio Valley, ahead
   of the cold front trailing the cyclone, while the trailing flank of
   the front stalls across the lower Mississippi Valley into
   northwestern Gulf coastal plain, beneath the northwestern periphery
   of the mid-level ridging.

   ...Illinois through lower Michigan...
   Beneath a dry slot overspreading the region, south and east of an
   intensifying cyclonic mid-level jet (in excess of 120 kt around 500
   mb), surface heating and steepening mid-level lapse rates are
   expected to contribute to sufficient destabilization for
   intensifying supercells. This may commence in a pre-frontal corridor
   as early as mid Wednesday morning across parts of central into
   northeastern Illinois, before developing into/across Lower Michigan
   and parts of adjacent northern Indiana and northwestern Ohio through
   late afternoon. 

   It remains unclear what effect the cooler marine layer from Lake
   Michigan has on adjacent coastal areas, particularly into portions
   of western Michigan.  However, Rapid Refresh forecast soundings, in
   particular, indicate a rather potent thermodynamic and kinematic
   environment supportive of strong tornadoes.  This includes sizable
   CAPE, strong deep-layer shear and large clockwise-curved low-level
   hodographs.  It is possible that severe weather probabilities could
   still be increased further in later outlooks for this period.

   ...Ohio Valley...
   To the south of the dry slot (within a plume of seasonably high
   precipitable water, and generally aligned with a belt of 40-70 kt
   west-southwesterly flow in the 850-500 mb layer), models indicate
   the potential for more widespread convection, organizing into
   clusters or lines while overspreading much of the Ohio Valley
   through the day.  While lapse rates may not be particularly steep,
   given the strong flow, with at least modest CAPE and the increased
   potential for heavy precipitation loading and organizing convection,
   the environment probably will become conducive to damaging surface
   gusts, in addition to some risk for tornadoes.

   ...Lower Mississippi Valley...
   South of the Ohio Valley, weakening low-level flow seems likely to
   result in more limited severe weather potential as the cold front
   gradually stalls.  While a corridor of sizable pre-frontal CAPE
   beneath strong deep-layer shear may provide a window for
   strong/severe storm development, this may be limited as convection
   tends to train above congealing outflow and/or the front.

   ..Kerr.. 04/04/2023

   SPC AC 040604

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0104 AM CDT Tue Apr 04 2023

   Valid 041200Z - 051200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS THERE IS A
   MODERATE RISK OF SEVERE THUNDERSTORMS FROM EASTERN IOWA INTO
   NORTHWEST ILLINOIS AND NORTHEAST MISSOURI...AND FROM SOUTHERN
   MISSOURI SOUTHWESTWARD TOWARD THE ARKLATEX...

   ...SUMMARY...
   A large area of severe potential will develop today into tonight,
   from eastern portions of the Plains into the Missouri and mid/upper
   Mississippi Valleys. Strong, potentially long track tornadoes are
   possible, in addition to large hail and damaging winds. Both
   afternoon and overnight potential is expected across various
   regions, including the risk of dangerous nighttime tornadoes.

   ...Synopsis...
   A deep upper trough will move from the Intermountain West/Rockies
   toward the Great Plains today. Within the large-scale trough, an
   upper cyclone will deepen as it moves northeastward toward the
   Dakotas. An 80-100 kt midlevel jet will overspread the central
   Plains during the afternoon/evening, while a secondary jet maximum
   intensifies through the day from the southern Plains into parts of
   the Midwest. At the surface, a broad cyclone will gradually
   consolidate and deepen as it propagates from the central High Plains
   toward western IA by early evening. A warm front will move northward
   into central/northern IA and northern IL by late afternoon, and into
   parts of WI/lower MI late tonight. A dryline will extend southward
   across eastern portions of the central/southern Plains, with a cold
   front expected to sweep through the Plains/Midwest this evening into
   the overnight. 

   ...Iowa into parts of the Great Lakes states...
   Short-term guidance continues to vary greatly regarding the extent
   of mixing across the warm sector over parts of the Midwest later
   today. The typically overmixed RAP/HRRR drop surface dewpoints to
   near 60F south of the warm front as temperatures warm to near 90F,
   while the generally undermixed NAM maintains cooler temperatures and
   upper 60s F dewpoints across the warm sector, and is slower to
   advance the warm front northward. The current expectation is for the
   magnitude of mixing to be somewhere between these two extremes, with
   dewpoints remaining in the mid 60s in closer proximity to the warm
   front, with somewhat stronger mixing possible farther south. 

   Considerable spread remains regarding convective evolution among
   regional/global guidance and CAMs. However, two areas of possible
   storm initiation this afternoon are evident. The first is near the
   MO/IA/IL border region, where substantial warming/moistening beneath
   steep midlevel lapse rates will result in rapid destabilization
   near/south of the warm front. Any supercell that develops in this
   region during the afternoon will pose a threat of very large to
   giant hail. Very favorable low-level and deep-layer shear will
   support a threat of strong tornadoes as well for as long as any
   supercell traverses the warm sector along/south of the warm front. 

   The second area of potential initiation will be farther west across
   west-central IA, closer to the surface low. Some uncertainty remains
   regarding the moisture quality this far west, but moderate buoyancy
   and very favorable wind profiles will support a threat of supercells
   capable of all severe hazards, including the potential for a strong
   tornado or two with any cell that can persist in the warm sector.

   Additional convection may develop later tonight in association with
   the cold front and move into the region, posing a threat of hail and
   damaging gusts. A conditional tornado threat will also persist
   overnight with any sustained supercells. 

   Finally, storms capable of hail will be possible north of the warm
   front, where MUCAPE in excess of 1000 J/kg, steep midlevel lapse
   rates, and sufficient deep-layer shear will support elevated
   supercell potential, despite rather cold surface temperatures.

   ...Southern Plains into the Ozark Plateau...
   A very favorable severe thunderstorm environment will also reside
   across the southern Plains into the Ozark Plateau, beginning this
   afternoon and persisting overnight east of the dryline/cold front.
   Diurnal storm development along the dryline is expected to be
   isolated at best, with large-scale ascent remaining weak for much of
   the day. However, convection is expected to increase this evening
   and especially overnight from northeast TX into AR and southern MO,
   within a persistent low-level moist plume associated with a strong
   low-level jet. 

   Moderate buoyancy and very favorable wind profiles will support
   supercells, both with diurnal storms (if any develop) and nocturnal
   convection. Some nocturnal storms may be somewhat elevated (at least
   initially) and the mode may be a mix of discrete cells and clusters,
   but weak MLCINH will not prohibit surface-based convection, and the
   current expectation is for supercell potential to increase
   overnight. Any nocturnal supercells will be capable of all severe
   hazards, and the concern remains regarding the potential for
   nocturnal strong tornadoes from near the ArkLaTex region into parts
   of southern MO.

   ..Dean/Thornton.. 04/04/2023