693  
ACUS01 KWNS 191248  
SWODY1  
SPC AC 191246  
 
DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK  
0746 AM CDT THU APR 19 2018  
 
VALID 191300Z - 201200Z  
 
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF  
CENTRAL AND SOUTHERN NEW MEXICO AND FAR WEST TEXAS...  
   
..SUMMARY
 
 
ISOLATED SEVERE THUNDERSTORMS MAY IMPACT PARTS OF CENTRAL AND  
SOUTHERN NEW MEXICO AND FAR WEST TEXAS LATE THIS AFTERNOON AND  
EVENING WITH A RISK FOR DOWNBURST WINDS AND HAIL.  
   
..SYNOPSIS
 
 
IN MID/UPPER LEVELS, A COMPLEX CYCLONE WILL SHIFT EASTWARD ACROSS  
THE NORTHEAST AND CANADIAN MARITIMES THROUGH THE PERIOD, WHILE A  
PROGRESSIVE/SPLIT-FLOW PATTERN WILL DOMINATE THE WESTERN U.S. A  
LARGE CYCLONE -- NOW APPARENT IN MOISTURE-CHANNEL IMAGERY OVER MUCH  
OF CA/NV -- WILL MOVE EASTWARD TO UT/AZ AND WESTERN PARTS OF CO/NM  
BY THE END OF THE PERIOD, WITH THE 500-MB LOW OVER UT AT 12Z.  
 
AT THE SURFACE, A LARGE, CONTINENTAL/POLAR ANTICYCLONE WILL SPREAD  
ACROSS MUCH OF THE CENTRAL/EASTERN U.S. IN THE WAKE OF A LOW-LEVEL  
COLD FRONT RELATED TO THE DEPARTING NORTHEASTERN CYCLONE ALOFT.  
THIS WILL PRECLUDE SUBSTANTIAL MOISTURE RETURN OR DESTABILIZATION  
EXCEPT FOR A NARROW CORRIDOR OVER AND NEAR THE MOUNTAINS OF NORTHERN  
MEXICO, AROUND THE WESTERN PART OF THE RESIDUAL FRONTAL ZONE NOW  
STALLED ACROSS NORTHERN PORTIONS OF COAHUILA AND CHIHUAHUA.  
   
..CENTRAL/SOUTHERN NM, FAR WEST TX
 
 
WIDELY SCATTERED THUNDERSTORMS ARE EXPECTED TO DEVELOP OVER NORTHERN  
CHIHUAHUA AND THEN SOUTHERN NM THIS AFTERNOON INTO EARLY EVENING,  
SHIFTING EASTWARD TO NORTHEASTWARD OVER THE OUTLOOK AREA. WHILE  
STORMS ARE SURFACE-BASED OR VERY NEARLY SO, ISOLATED SEVERE GUSTS OR  
LARGE HAIL MAY OCCUR.  
 
THE AFOREMENTIONED RIBBON OF CONVECTIVELY FAVORABLE MOISTURE RETURN  
THROUGH NORTHERN MX SHOULD EXTEND NORTHWARD OVER THE MARGINAL-SEVERE  
OUTLOOK AREA THIS AFTERNOON AND EVENING, JUXTAPOSED WITH SURFACE  
HEATING OF THE DESERT VALLEYS AND HIGHER TERRAIN. THE AIR MASS OVER  
THE REGION IS QUITE DRY AT THIS TIME; HOWEVER, SOME LOWER-ELEVATION  
SURFACE DEW POINTS IN THE 30S TO LOW 40S F SHOULD RESULT FROM MOIST  
ADVECTION BY MID/LATE AFTERNOON. THIS PROCESS WILL START SOONER IN  
NORTHERN CHIHUAHUA THIS AFTERNOON, WHERE STRONGER HEATING AND  
SOMEWHAT HIGHER PW WILL COMBINE WITH LOW-LEVEL CONVERGENCE AND  
OROGRAPHIC FORCING TO ERODE MLCINH AND BOOST MLCAPE TO NEAR 1000  
J/KG. BUOYANCY SHOULD DIMINISH GRADUALLY NORTHWARD ACROSS SOUTHERN  
NM, WHILE BECOMING LESS SURFACE-BASED EASTWARD OVER THE TRANS-PECOS  
AND BIG BEND REGIONS.  
 
STORMS WILL HAVE LITTLE ROOM TO ACCESS FAVORABLE BOUNDARY-LAYER  
PARCELS BEFORE MOVING ATOP A MORE STABLE/LOWER-THETA-E AIR MASS THIS  
EVENING, EVEN THOUGH A GENERAL THUNDER RISK MAY PERSIST EASTWARD  
TOWARD THE PECOS VALLEY. WITHIN THE NARROW ZONE OF FAVORABLE  
MLCAPE, HOWEVER, WELL-MIXED SUBCLOUD LAYERS BENEATH THAT BUOYANCY  
WILL SUPPORT MAINTENANCE OF ANY HAIL TO THE SURFACE, AS WELL AS SOME  
DOWNBURST POTENTIAL. DEEP SHEAR SHOULD BE INCREASINGLY FAVORABLE,  
WITH THE JUXTAPOSITION OF SURFACE SOUTHEASTERLIES UNDER  
STRENGTHENING MID/UPPER GRADIENT WINDS AHEAD OF THE CYCLONE.  
FORECAST SOUNDINGS SHOW EFFECTIVE-SHEAR MAGNITUDES 45-55 KT, ALONG  
WITH SUFFICIENTLY STRAIGHT HODOGRAPHS TO SUPPORT SPLITTING CELLS  
WITH BOTH RIGHT- AND LEFT-MOVING OFFSPRING.  
 
..EDWARDS/GOSS.. 04/19/2018  
 

 
 
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