252  
FXUS61 KPBZ 200102  
AFDPBZ  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE PITTSBURGH PA  
902 PM EDT MON APR 19 2021  
   
SYNOPSIS
 
 
MOSTLY DRY WEATHER CONTINUES THROUGH TUESDAY. MIDWEEK LOW PRESSURE  
WILL PROVIDE RAIN/SNOW MIX TUESDAY NIGHT AND WEDNESDAY. SHOWERS AND  
CHILLY TEMPERATURES WILL LINGER INTO THURSDAY.  
 

 
   
NEAR TERM /UNTIL 6 AM TUESDAY MORNING/
 
 
UPDATED POPS TO REFLECT RADAR TRENDS WITH AN AREA OF PRE-FRONTAL  
SHOWERS. HOWEVER, VERY DRY AIR REMAINS NEAR THE SURFACE SUCH THAT ANY  
PRECIPITATION OVER THE NEXT FEW HOURS WILL BE LIGHT.  
 
PREVIOUS...  
DRY, SEASONABLE WEATHER PREVAILS THIS EVENING OWING TO WEAK RIDGING  
AHEAD OF A DIGGING TROUGH ACROSS THE GREAT LAKES.  
 
ASSOCIATED COLD FRONT WILL ENCROACH THE FORECAST AREA LATER TONIGHT,  
THOUGH MUCH OF THE MID- AND UPPER- LEVEL SUPPORT IN THE FORM OF  
VORTICITY ADVECTION AND MID-LEVEL FRONTOGENESIS/DEFORMATION ONLY  
SKIRT THE CWA NORTH OF I-80. WILL KEEP SLIGHT CHANCE POPS FOR THE  
POSSIBILITY OF LIGHT RAIN IN THIS AREA AFTER MIDNIGHT, WITH ONLY A  
MODEST CLOUD INCREASE TO THE SOUTH. TEMPERATURES WILL REMAIN  
GENERALLY SEASONABLE.  
 

 
   
SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/
 
 
THE SURFACE COLD FRONT WILL STALL OUT OVER THE NORTHERN PORTION OF  
THE REGION OR LIFT SLOWLY NORTH ON TUESDAY, WHILE WHATEVER MID-LEVEL  
FORCING THERE IS DISSIPATING OR LIFTING NORTH AS THE UPPER LOW MOVES  
INTO QUEBEC. THE RESULT WILL BE A MOSTLY DRY DAY TUESDAY. THERE  
WILL BE A DECENT NORTH-TO-SOUTH TEMPERATURE GRADIENT DUE TO THE  
COOLER AIR MASS BEHIND THE FRONT, RANGING FROM AROUND 50 NORTH OF I-0  
TO THE MID 60S NEAR THE MASON-DIXON LINE.  
 
A NEW TROUGH WILL DIG ACROSS THE NORTHERN PLAINS ON TUESDAY, INDUCING  
SURFACE CYCLOGENESIS OVER THE MISSISSIPPI VALLEY DURING THE DAY. THE  
DEEPENING LOW WILL LIFT OVER THE OHIO VALLEY AND INTO CENTRAL PA BY  
WEDNESDAY MORNING. WITH BETTER VORTICITY ADVECTION AND LAYERED  
FRONTOGENESIS, CATEGORICAL POPS ARE JUSTIFIED LATE TUESDAY NIGHT INTO  
WEDNESDAY.  
 
PRECIPITATION WILL BEGIN AS RAIN, BUT A MIX WITH/CHANGE TO RAIN IS  
EXPECTED NORTHWEST OF PITTSBURGH BY 12Z WEDNESDAY AS THE 850MB FRONT  
ARRIVES AND COLD ADVECTION STARTS TO RAMP UP. MUCH OF THE STEADY  
PRECIPITATION DEPARTS BY MIDDAY WEDNESDAY AS THE LOW LIFTS OUT.  
HOWEVER, ISOLATED/SCATTERED RAIN AND SNOW SHOWERS WILL CONTINUE INTO  
THURSDAY IN THE FOLLOWING NORTHWEST FLOW PATTERN. LAKE  
ENHANCEMENT/LAKE EFFECT IS EVEN POSSIBLE, GIVEN LAKE ERIE  
TEMPERATURES OF 6-8C AND 850MB TEMPERATURES DROPPING TO AROUND -10C.  
OVERALL SNOW TOTALS WILL BE HELD IN CHECK BY THE RELATIVELY WARM  
GROUND/LATE APRIL SUN ANGLE, WITH ROAD TEMPERATURES LIKELY NOT  
DIPPING TO FREEZING IN MOST CASES. MUCH OF THE OBSERVED ACCUMULATION  
WILL OCCUR ON ELEVATED/GRASSY SURFACES. AREAS NORTH OF I-80 AND ON  
THE HIGHER RIDGES HAVE THE BEST CHANCE OF SEEING ANY ACCUMULATION OF  
MORE THAN A HALF INCH OVERALL.  
 
THE OTHER CONCERN WITH THIS ANOMALOUSLY COLD LATE APRIL AIR MASS WILL  
BE THE SUBFREEZING TEMPERATURES EXPECTED THURSDAY MORNING, AND  
PERHAPS FRIDAY MORNING DEPENDING ON THE SPEED OF CLOUD CLEARING. AN  
HWO MENTION FOR EXPECTED FROST/FREEZE HEADLINES WAS SENT FOR AREAS  
WHERE THE GROWING SEASON IS UNDERWAY.  
 

 
   
LONG TERM /THURSDAY THROUGH MONDAY/
 
 
DRY WEATHER RETURNS THURSDAY NIGHT THROUGH FRIDAY NIGHT AS  
FLATTENING RIDGING BUILDS INTO THE REGION. FRIDAY MORNING WILL ALSO  
SEE FROST/FREEZE CONCERNS AS THE SKY CLEARS, BUT TEMPERATURES WILL  
MODERATE FOR FRIDAY/FRIDAY NIGHT AS SOUTHWEST LOW-LEVEL FLOW  
DEVELOPS.  
 
TROUGHING DEVELOPS OVER THE LOWER OHIO VALLEY ON SATURDAY, AND THE  
ASSOCIATED MOISTURE INCREASE AND FRONTAL APPROACH/PASSAGE WILL BRING  
PRECIPITATION CHANCES TO THE REGION OVER THE WEEKEND. STRENGTH AND  
TIMING DIFFERENCES REMAIN IN THE MODELS, ALTHOUGH MOST AGREE THAT AN  
ALL-RAIN SYSTEM IS LIKELY. DRY WEATHER RETURNS MONDAY WITH THE  
ARRIVAL OF THE NEXT SURFACE HIGH.  
 

 
   
AVIATION /01Z TUESDAY THROUGH SATURDAY/
 
 
VFR SHOULD PREVAIL UNDER AN ERODING SHORTWAVE RIDGE BEFORE  
INTERRUPTION BY AN ENCROACHING COLD FRONT LATE TONIGHT. WITH LIMITED  
MOISTURE AND FORCING FOR ASCENT DISPLACED NORTH OF THE FORECAST  
AREA, PORTS FM PIT NWD SHOULD ONLY OBSERVE A SFC WIND SHIFT TO THE  
WNW IN CONJUNCTION WITH AN INCREASING CLOUD DECK AND LOWERING BASES  
TO MVFR.  
 
A STRATOCU DECK SHOULD THEN PERSIST THROUGH THE REMAINDER OF THE TAF  
PERIOD, WITH GRADUAL IMPROVEMENT FROM MVFR TO VFR AS WARM ADVECTION  
AND DIURNAL MIXING ENSUES.  
   
OUTLOOK
 
 
RESTRICTIONS AND RAIN RETURN TUESDAY NIGHT AND WEDNESDAY WITH THE  
PASSAGE OF THE CDFNT.  
 

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

 
 

 
 
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