534  
FXUS61 KCTP 141155  
AFDCTP  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE STATE COLLEGE PA  
755 AM EDT TUE AUG 14 2018  
   
SYNOPSIS
 
 
A SLOW MOVING UPPER LEVEL LOW PRESSURE SYSTEM LOCATED OVER  
CENTRAL PENNSYLVANIA THIS MORNING WILL DRIFT NORTHEASTWARD  
TO NEAR BOSTON BY DAYBREAK WEDNESDAY. THIS WEATHER FEATURE  
WILL BRING FAIRLY NUMEROUS MODERATE, TO OCCASIONALLY HEAVY  
SHOWERS AND ISOLATED THUNDERSTORMS ACROSS PENNSYLVANIA TODAY  
THROUGH EARLY TONIGHT. LOCALIZED FLASH FLOODING IS POSSIBLE  
WHERE HEAVY SHOWERS AND THUNDERSTORMS TRAIN, OR REMAIN  
STATIONARY OVER THE SAME LOCATIONS. A RIDGE OF HIGH  
PRESSURE WILL MOVE EAST FROM THE OHIO VALLEY AND CREST OVER  
THE REGION WEDNESDAY INTO THURSDAY MORNING, ACCOMPANIED BY  
DRY WEATHER, LIGHT WIND, AND TEMPERATURES ABOUT 5 DEGREES ABOVE  
NORMAL BOTH WEDNESDAY AND THURSDAY. A WEAK COLD FRONT WILL  
ARRIVE LATE IN THE WEEK.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
FLOODING CONCERNS RE-IGNITING ACROSS PORTIONS OF THE CENTRAL  
AND NORTH- CENTRAL MTNS OF PA EARLY TODAY AS A COMPACT, THOUGH  
RATHER POTENT SPOKE OF MID/UPPER LEVEL VORTICITY PIVOTS WEST AND  
SW AROUND THE CENTER OF A SLOW-MOVING UPPER LOW LOCATED ACROSS  
THE MID/LOWER SUSQ VALLEY.  
 
GOES EAST, MID AND UPPER LEVEL WATER VAPOR CHANNELS SHOW SOME  
DRYING ALOFT AND SUBSEQUENT CLOUD-TOP COOLING WITH OCCASIONAL  
IC FLASHES AND CGS NEAR AND TO THE SW OF KUNV OVER THE PAST  
HOUR.  
 
QPE TO FFG HAS INCREASED TO 70-80 PERCENT IN A FEW OF THE  
HEAVIER SLOW-MOVING SHOWERS/TSRA BETWEEN KUNV AND KJST, WITH  
HYDROPHOBIC UNIT STREAMFLOW VALUES ALSO EXPANDING/INCREASING TO  
BETWEEN 3.5-7.5 M3*SEC-1*KM-2. THESE VALUES ARE SUFFICIENT TO  
BEGIN POOR DRAINAGE FLOODING AND BANKFULL CONDITIONS ON SMALL  
STREAMS IN THAT AREA, AND PROMPTED THE EXPANSION OF THE FLASH  
FLOOD WATCH THAT RUNS THROUGH 02Z WED.  
 
LAST SEVERAL RUNS OF THE HRRR HAVE BEEN ERRATIC, WITH RUNS FROM  
AROUND 04Z SHOWING A CONCENTRATION OF CONVECTION AND 2+ INCH  
RAINFALL BETWEEN KIPT AND KSEG, WHILE THE LAST FEW RUNS OF THIS  
CAMS GUIDANCE QUICKLY DISSOLVE THE CURRENT AND MOST INTENSE  
CONVECTION NEAR AND TO THE SOUTH OF KUNV AND SHIFT THE  
CONCENTRATION TO THE MID SUSQ VALLEY AND POINTS NORTH WHERE WPC  
HAS ITS HIGHEST RISK OF EXCESSIVE RAIN THIS MORNING.  
 
COMPACT AREA OF CONVECTION IS INTENSIFYING BETWEEN KSEG AND  
KAVP AND THIS IS WHERE THE EARLIER RUNS OF THE HRRR SHOWED THE  
HIGHEST QPF. ANOTHER AREA TO MONITOR CLOSELY OVER THE NEXT  
SEVERAL HOURS.  
 
EXPECT THE CURRENT AND AFOREMENTIONED COMPACT VORT LOBE TO  
MAINTAIN BETTER AREAL COVERAGE AND INTENSITY OF THE CONVECTION  
OVER CENTRAL AND SCENT PA THAN THE HRRR DEPICTS, BEFORE THE  
BRUNT OF THE SHOWERS/ISOLATED TSRA SHIFT PRIMARILY TO THE NORTH  
AND EAST OF A KBFD TO KUNV TO KSEG LINE THIS AFTERNOON AND  
EVENING AS THE UPPER LOW LIFTS ACROSS NEPA.  
 
ALTHOUGH THE FLASH FLOOD THREAT IS NOT AS GREAT AS MONDAY,  
VERY WET GROUND COULD LEAVE THE EASTERN COUNTIES SUSCEPTIBLE TO  
ADDITIONAL FLOODING ISSUES THROUGH THIS AFTERNOON/EARLY  
EVENING.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/
 
 
UPPER LOW CONTINUES TO SLOWLY LIFT NEWD TO THE HUDSON VALLEY  
LATER TONIGHT. THIS WILL LEAD TO STEADILY DECREASING AREAL  
COVERAGE AND INTENSITY OF SHOWERS AS THE HREF SHOWS VERY LITTLE  
QPF TO THE WEST OF A KELM TO KSEG LINE AND PWAT VALUES ON THE  
GEFS DROP FROM ABOUT 40MM AT 00Z WED TO UNDER 25 MM BY 12 WED  
ACROSS MOST OF THE CWA.  
 
ANY PARTIAL CLEARING WILL COMBINE WITH THE MOIST GROUND AND NEAR  
CALM AIR TO PRODUCE AREAS OF DENSE VALLEY FOG LATE  
TONIGHT/EARLY WED MORNING. MIN TEMPS WILL STILL BE NEAR TO  
SLIGHTLY ABOVE NORMAL FOR TONIGHT - IN THE UPPER 50S NW TO LOW  
AND MID 60S ELSEWHERE.  
 

 
   
LONG TERM /WEDNESDAY THROUGH MONDAY/
 
 
MODELS AGREE IN THE CURRENT UPPER LOW LIFTING OUT ACROSS THE NEW  
ENGLAND STATES AND WEAKENING WEDNESDAY, BRINGING A SHORT PERIOD  
OF DRY WEATHER FOR A CHANGE FOR MIDWEEK AS A FLATTENING RIDGE  
ALOFT SLIDES EAST ACROSS PA.  
 
THE RESPITE IN THE RAIN WILL BE SHORT LIVED AS A NEW UPPER  
TROUGH/WEAK COLD FRONT IS SLATED TO APPROACH THE AREA THURSDAY  
AND FRIDAY. IN FACT THE MODELS HAVE A PAIR OF UPPER SHORTWAVES  
THAT TRANSLATE INTO SEVERAL MORE DAYS OF AT LEAST SCATTERED  
SHOWERS AND THUNDERSTORMS, MAINLY FROM LATER THURSDAY THROUGH  
SATURDAY.  
 
DRIER WEATHER SHOULD ARRIVE FOR SUNDAY, BUT THE OVERALL PATTERN  
LOOKS TO REMAIN UNSETTLED AS THE MEDIUM RANGE GUIDANCE FAVORS  
AND EASTERN TROUGH AND WESTERN RIDGE PATTERN THROUGH AT LEAST  
THE MIDDLE OF NEXT WEEK.  
 

 
   
AVIATION /12Z TUESDAY THROUGH SATURDAY/
 
 
UPPER LOW CONTINUES TO BRING IMPACTS TO FLYING CONDITIONS OVER  
CENTRAL PA. CONDITIONS VARIABLE THIS MORNING, WITH RESTRICTIONS  
GENERALLY CONFINED TO THE NW HALF. BUT SHOWERS/ISOLATED  
THUNDERSTORMS BRINGING LOCAL REDUCTIONS AND BRIEF HEAVY RAINFALL  
AS THEY DRIFT SOUTHWARD.  
 
CONVECTION SHOULD RETREAT TO JUST THE NE COUNTIES BY LATE  
MORNING AS CONDITIONS GRADUALLY IMPROVE TO VFR, BUT SCATTERED  
SHOWERS/TSTMS RETURN THIS AFTERNOON WITH LOCAL IMPACTS.  
 
BREAK IN THE PRECIP STARTS TONIGHT BUT ANTICIPATE CEILING  
RESTRICTIONS TO DEVELOP OVER THE WESTERN HIGHER TERRAIN AND  
(WITH VERY WET GROUND) A GOOD AMOUNT OF VALLEY FOG AREAWIDE.  
   
OUTLOOK
 
 
 
WED...AM FOG. OTHERWISE NO SIX WX.  
 
THU-SAT...AM FOG. OTHERWISE, SCATTERED SHOWERS/TSTMS WILL BRING  
LOCAL RESTRICTIONS.  
 

 
   
CTP WATCHES/WARNINGS/ADVISORIES
 
 
FLASH FLOOD WATCH THROUGH THIS EVENING FOR PAZ012-018-019-  
024>028-037-041-042-045-046-049>053-058.  
 

 
 

 
SYNOPSIS...LAMBERT  
NEAR TERM...LAMBERT  
SHORT TERM...FITZGERALD/LAMBERT/TYBURSKI  
LONG TERM...LA CORTE/LAMBERT  
AVIATION...MARTIN/RXR  
 
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