Warning: file(http://www.wunderground.com/climate/extremes.asp): failed to open stream: HTTP request failed! HTTP/1.0 500 Internal Server Error in /homepages/6/d330860172/htdocs/usaextremes.php on line 55

Warning: implode(): Invalid arguments passed in /homepages/6/d330860172/htdocs/usaextremes.php on line 55
Day 1 Outlook Day 2 Outlook Day 3 Outlook Days 4-8 Outlook

Day 1 Outlook Convective Tornado
Hail Wind
Categorical Day1 1200Z Outlook
  
Images courtesy of the NWS Storm Prediction Center
 Forecast Discussion

  
000
ACUS01 KWNS 180601
SWODY1
SPC AC 180559

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1259 AM CDT Fri Aug 18 2017

Valid 181200Z - 191200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE LOWER
HUDSON VALLEY SOUTH INTO CENTRAL VIRGINIA...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR THE MIDDLE
ATLANTIC STATES INTO CONNECTICUT AND NEW YORK...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MIDDLE
AND LOWER MISSOURI VALLEYS INTO KANSAS AND OKLAHOMA...

...SUMMARY...
Scattered strong to localized severe gusts capable of wind damage
are forecast from the Chesapeake Bay vicinity northward into
southern New York.  Isolated severe thunderstorms are possible
across portions of the middle to lower Missouri Valley southward
into Kansas and Oklahoma.

...Synopsis...
A broad area of cyclonic mid-level flow aloft will extend from the
northern Plains into the Northeast.  A lead shortwave trough will
move from the Upper Great Lakes across the Northeast with surface
low over eastern Ontario by 00Z.  A well-defined surface trough east
of the Appalachians will focus shower/thunderstorm development in
advance of a cool front forecast near the Appalachian spine by early
evening.  

Farther west, an amplifying shortwave trough will move from the
eastern Dakotas into the southern Great Lakes during the period.  A
weaker surface boundary will extend from western MN southward across
KS and trailing west across the OK/TX Panhandles. 

...Middle Atlantic states northward into NY/CT...
Scattered early-day cloud cover, associated with a plume of
mid-level moisture from the TN Valley into the Mid-Atlantic states,
will give way to strong heating from PA/NJ southward.  A
moisture-rich airmass sampled by Thursday evening RAOBS (reference
the Dulles sounding) will become moderately to strongly unstable by
mid afternoon from the Mid-Atlantic to southern NY.  Models show the
strongest mid-level flow will generally remain north of central VA
with effective shear increasing from 25-40 kt with northward extent.
 
The combination of weak ascent associated with a mid-level vorticity
maximum (forecast to move from IN to PA during the day), and a weak
cap and strong heating in the lee of the higher terrain, will favor
scattered to numerous storms developing during the afternoon from
central VA northward into the lower Hudson Valley.  Forecast
soundings show MLCAPE 1500-3000 J/kg and 70s degrees F boundary
layer dewpoints.  A mixed mode of multicells and perhaps a couple of
supercells will favor isolated gusts around 60 mph---conducive for
scattered wind damage.  A marginal risk for a tornado is possible
from the Chesapeake Bay vicinity north into the lower Hudson Valley.
 Forecast hodographs are largest over the Delaware River Valley
north into southeast NY during the late afternoon/early evening.  A
gradual weakening in storm intensity is expected by the early-mid
evening as the activity moves towards the coast. 

...Middle to lower MO Valley into KS/OK...
A more conditional severe risk will likely exist across portions of
this region during the afternoon/evening.  It seems to reason the
greatest risk for thunderstorms and isolated severe will focus near
1) a residual frontal zone forecast to advance northward through the
Ozarks and into the lower MO Valley by early evening and/or 2) in
the vicinity of the northeastern portion of a central plains cool
front.  With that stated, mesoscale dependencies related to
overnight thunderstorm clusters across the central Plains lend
relatively large uncertainty on the initiation and subsequent
development of concentrated thunderstorm areas.  However, the
eastward advection of a steep 700-500 mb lapse rate plume into
OK/KS/western MO and sufficient 500-mb northwesterly flow will
result in an environment supportive of organized severe storms. 
Will reevaluate for a possible inclusion of higher severe
probabilities in later outlook(s).

..Smith/Gleason.. 08/18/2017

$$