080  
FXUS61 KPBZ 290522 AAC  
AFDPBZ  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE PITTSBURGH PA  
122 AM EDT THU JUN 29 2017  
   
SYNOPSIS
 
 
TEMPERATURES WILL CONTINUE TO WARM INTO THE WEEKEND, AND  
HUMIDITY LEVELS WILL ALSO INCREASE. THIS WILL RETURN THE RISK  
FOR SHOWERS AND STORMS, MAINLY FRIDAY AND SATURDAY.  
 

 
   
NEAR TERM /THROUGH TODAY/
 
 
NO CHANGES TO THE OVERNIGHT PERIOD.  
 
UPPER LEVEL HEIGHTS WILL SLOWLY INCREASE THIS MORNING, IN  
RESPONSE TO A WEAK SHORTWAVE TROUGH WHICH WILL SWING THROUGH THE  
LOWER GREAT LAKES. THIS SHORTWAVE WILL REACH NW PA BY THIS  
AFTERNOON. MODELS ARE INDICATING THAT MOST OF THE ENERGY FROM  
THE WAVE WILL BE USED TO FLATTEN THE RIDGE. IN ADDITION, WARM  
AIR ADVECTION WILL BE WELL UNDERWAY IN THE LOWER AND MID-LEVELS,  
WHICH WILL WORK TO PROVIDE A NICE CAP IN THE ATMOSPHERE.  
LOOKING AT FORECAST SOUNDINGS ACROSS THE AREA, THE TEMPERATURE  
PROFILE WILL BECOME DRY ADIABATIC THIS MORNING, CAUSING AN  
INCREASE IN LOW-LEVEL LAPSE RATES, AND MIXING HEIGHTS WILL ALSO  
QUICKLY RISE. MODEL DIFFERENCE WITH TEMPERATURES ALOFT BECOME  
IMPORTANT THIS AFTERNOON. THE NAM WANTS TO CUTOFF THE WARMING AT  
700MB LATE THIS AFTERNOON, WHILE THE GFS DOES NOT. THUS, THE  
GFS SHOWS THE CAP HOLDING THROUGH THE DAY, WHILE THE NAM  
DISSOLVES IT. SO WILL FIND A COMPROMISE BETWEEN THE MODELS AND  
FOCUS ON THE AREA OF SHORTWAVE INDUCED ASCENT. WITH STRONG LOW-  
LEVEL LAPSE RATES AND INCREASING SURFACE INSTABILITY, WILL  
INCLUDE POPS ACROSS THE NORTH THIS AFTERNOON. I BELIEVE THE  
ACTIVITY WILL INITIALLY BE SCATTERED AND WOULD DEVELOP ON THE  
EASTERN EDGE OF THE AFTERNOON SHORTWAVE. SPEED SHEAR DOES  
INCREASE THIS AFTERNOON, ESPECIALLY OVER NORTHERN COUNTIES, SO  
ITS NOT OUT OF THE QUESTION THAT UPDRAFTS COULD INTENSIFY AND  
ALLOW FOR CONVECTION TO BECOME MORE ORGANIZED. ANOTHER POINT TO  
KEEP IN MIND, IF ANY CONVECTION DOES INTENSIFY, THERE WILL ALSO  
BE OUTFLOW BOUNDARIES. THESE BOUNDARIES WOULD LEAD TO FURTHER  
DEVELOPMENT, WHICH COULD EXPAND THE RISK FOR STORMS. THIS WILL  
NEED TO BE WATCHED AS THE DAY PROGRESSES.  
 
ALSO EXPECT TO SEE SOME GUSTY SOUTH-SOUTHWESTERLY WINDS DEVELOP  
LATE THIS MORNING AND THROUGH THE AFTERNOON DUE TO A  
STRENGTHENING WIND PROFILE ALOFT AND RISING MIXING HEIGHTS.  
A CU FIELD SHOULD DEVELOP WITH DAYTIME HEATING, AS PARCELS WILL  
HAVE NO TROUBLE RISING TO THE CAP.  
 
THE INCREASING CLOUD COVER COULD HOLD TEMPS DOWN JUST A BIT, BUT  
THINK THAT WE WILL STILL SEE ABOVE NORMAL READINGS WITH THE  
STRONG WARM AIR ADVECTION AND WELL MIXED ATMOSPHERE.  
 

 
   
SHORT TERM /TONIGHT THROUGH SATURDAY/
 
 
ANY CONVECTION WILL DISSIPATE TONIGHT WITH SUNSET AND THE  
ABSENCE OF LARGE SCALE ASCENT. WEAK RIDING ALOFT IS EXPECTED AS  
WELL. MODELS ARE TRYING TO SQUEEZE OUT SOME QPF TONIGHT, LIKELY  
DUE TO THE PASSING SHORTWAVE TROUGH AND BRIEF LOWERING OF 500MB  
HEIGHTS, BUT AT THIS POINT, NOT SURE IF THAT IS REALISTIC.  
TEMPERATURES ALOFT BEGIN TO WARM AGAIN WITH THE PASSAGE OF THE  
WAVE AND DEEP MOISTURE IS NOT AVAILABLE. FOR NOW WILL KEEP MOST  
OF THE TONIGHT PERIOD DRY, BUT THIS WILL NEED TO BE REEVALUATED  
IN FUTURE MODEL RUNS.  
 
FRIDAY LOOKS SIMILAR TO TODAY, BUT WITH EVEN GREATER WARMING  
ALOFT AND RISING HEIGHTS IN THE MORNING. THIS WOULD MEAN THE  
ATMOSPHERE WOULD AGAIN BE CAPPED. SURFACE INSTABILITY WILL BE  
INCREASING DUE TO A RISE IN SURFACE DEWPOINTS, BUT AGAIN, THIS  
IS DEPENDENT ON WHICH MODEL HITS THOSE NUMBERS CORRECTLY. IF  
ANYTHING, FRIDAY LOOKS LIKE MORE POPUP SUMMER TIME CONVECTION,  
SO WILL JUST GO WITH LOW CHANCE POPS FOR THE ENTIRE AREA. TEMPS  
FRIDAY WILL BE ABOVE NORMAL AND HUMIDITY LEVELS WILL BE MUCH  
MORE NOTICEABLE.  
 

 
   
LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/
 
 
THE MIDWESTERN UPPER TROUGH IS PROGGED TO ADVANCE E SATURDAY  
DRIVING A COLD FRONT ACROSS THE AREA. DRY WEATHER IS EXPECTED TO  
RETURN SUN/MON AS SURFACE RIDGING BUILDS UNDERNEATH THE UPPER  
TROUGH. ANOTHER TROUGH IS PROGGED TO ADVANCE E FROM THE MIDWEST  
AND PLAINS REGIONS TUE, THOUGH WITH UNCERTAINTY IN TIMING AND  
LOCATION LIMITED POPS TO THE CHANCE CATEGORY FOR NOW ON THE 4TH  
OF JULY.  
 

 
   
AVIATION /06Z THURSDAY THROUGH MONDAY/
 
 
MAINLY VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD.  
MID/HIGH CLOUDS SHOULD CONTINUE STREAMING E FROM WEAKENING  
THUNDERSTORMS TO THE W.  
 
CU RULE/MODEL SOUNDINGS SHOW SCT TO BKN CU BY LATE MORNING,  
THOUGH BASES SHOULD STILL BE VFR. A SHORTWAVE TROUGH IS PROGGED  
TO MOVE ACROSS SRN ONTARIO/NW PA BY AFTERNOON WITH SCT  
SHOWERS/TSTMS EXPECTED. MENTIONED A VCTS FOR FKL/DUJ, THOUGH  
CAPPING WARMTH ALOFT SHOULD LIMIT TSTM POTENTIAL ELSEWHERE. A  
TIGHTENING PRESSURE GRADIENT AND MIXING SHOULD ALSO RESULT IN  
GUSTY SW WINDS TODAY.  
   
OUTLOOK
 
 
RESTRICTION CHANCES WILL INCREASE FRI AND SAT WITH THE APPROACH  
AND PASSAGE OF A COLD FRONT.  
 

 
   
PBZ WATCHES/WARNINGS/ADVISORIES
 
 
MD...NONE.  
OH...NONE.  
PA...NONE.  
WV...NONE.  
 

 
 

 
 
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