720  
FXUS61 KRNK 271556  
AFDRNK  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BLACKSBURG VA  
1156 AM EDT THU APR 27 2017  
   
SYNOPSIS
 
 
CHANCES OF SHOWERS AND THUNDERSTORMS BEGIN THIS AFTERNOON AS A  
LOW PRESSURE SYSTEM PASSES TO THE NORTH. HIGH PRESSURE WILL  
BUILD OFF THE SOUTHEAST COAST DURING THE NEXT FEW DAYS TO BRING  
WELL ABOVE NORMAL TEMPERATURES.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
AS OF 1155 AM EDT THURSDAY...  
 
A LOW PRESSURE SYSTEM CENTERED JUST NORTH OF THE GREAT LAKES IS  
STRETCHING A COLD FRONT SOUTHWARD TOWARD THE OHIO RIVER VALLEY.  
AN OUTFLOW BOUNDARY FROM CONVECTION THE PREVIOUS DAY IN THIS  
AREA SHOULD MOVE AHEAD TOWARD THE APPALACHIAN MOUNTAINS BY THE  
AFTERNOON. THE LATEST HIGH RESOLUTION MODELS SHOW SCATTERED  
SHOWERS AND THUNDERSTORMS DEVELOPING OVER THE TENNESSEE RIVER  
VALLEY AND SPREADING EASTWARD TOWARD LOCATIONS WEST OF THE BLUE  
RIDGE, BUT THE TIMING HAS SLOWED DOWN BY A COUPLE HOURS AND IS  
REFLECTED IN THIS LATEST UPDATE.  
 
THE STORM PREDICTION CENTER HAS THE ENTIRE CWA OUTLOOKED FOR A  
MARGINAL RISK OF SEVERE THUNDERSTORMS TODAY. MODEL CAPE IS  
FORECAST INTO THE 1000-1500 J/KG RANGE THIS AFTERNOON, BUT  
DIURNAL GAINS IN BUOYANCY MAY BE MUTED BY INCREASING CLOUD  
COVERAGE AHEAD OF THE COLD FRONT. IF SUFFICIENT SOLAR HEATING  
OCCURS, LOW TO MID LEVEL FLOW WILL ENCOURAGE MOMENTUM TRANSPORT  
CAPABLE OF SUPPORTING LOCALLY DAMAGING WIND GUSTS.  
 
LOSS OF DAYTIME HEATING WILL RESULT IN A DEMISE OF THE SHOWER  
AND THUNDERSTORM ACTIVITY BEFORE MIDNIGHT. THE ACTUAL SURFACE  
FRONT SHOULD DISSIPATE OVERHEAD AS THE BUILDING UPPER RIDGE OF  
HIGH PRESSURE ACTS AS A ROAD BLOCK TO PREVENT ANY SORT OF CHANGE  
IN AIR MASS TO THE FORECAST AREA.  
 

 
   
SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/
 
 
AS OF 400 AM EDT THURSDAY...  
 
A BROAD AND STRONG H5 RIDGE WILL BE CENTERED OVER THE SOUTHEASTERN  
U.S. IN THIS PERIOD WITH 588 DM HEIGHTS OVER FLORIDA BUILDING TO  
591+ DM JUST OFF THE CAROLINA COAST BY SATURDAY. THIS WILL PROVIDE A  
VERY WARM AND FAIRLY HUMID AIR MASS ACROSS THE SOUTHERN APPALACHIAN  
REGION, ESPECIALLY FOR LATE APRIL. HIGH TEMPERATURES WILL RUN 10 TO  
15F ABOVE NORMAL BOTH FRIDAY AND SATURDAY WITH HIGHS IN THE UPPER  
70S TO LOW/MID 80S FRIDAY TO MID/HIGH 80S SATURDAY. NOT REALLY  
THREATENING RECORDS BUT STILL UNSEASONABLY WARM. PRECIPITATION-WISE  
DO NOT EXPECT TO SEE MUCH, IF ANY. A STRONG UPPER TROUGH WILL BE  
DIGGING SOUTHWARD INTO THE SOUTHERN HIGH PLAINS FRIDAY/SATURDAY  
SETTING THE STAGE FOR A HEAVY RAINFALL EVENT WELL TO OUR WEST,  
ACROSS PARTS OF THE SOUTHERN AND CENTRAL MISSISSIPPI VALLEY. FORCING  
FOR PRECIPITATION IN OUR AREA WILL BE WEAK WITH ONLY A CHANCE FOR  
DIURNALLY DRIVEN CONVECTION WHICH WILL BE WIDELY SCATTERED AND NOT  
HYDROLOGICALLY SIGNIFICANT. THIS WILL ALLOW THE LAST OF OUR FLOODED  
RIVERS TO CONTINUE RECEDING. MODELS INDICATE DECENT ML CAPE OF 1-2K  
SATURDAY AFTERNOON BUT ONLY MODEST SHEAR BUT COULD ALLOW A FEW  
STRONG TO NEAR-SEVERE PULSE THUNDERSTORMS IN THE AFTERNOON.  
 

 
   
LONG TERM /SUNDAY THROUGH WEDNESDAY/
 
 
AS OF 400 AM EDT THURSDAY...  
 
VERY WARM AND HUMID CONDITIONS CONTINUE SUNDAY WITH THE CHANCE FOR  
SHOWERS AND THUNDERSTORMS, ESPECIALLY ALONG THE BLUE RIDGE. BY  
MONDAY, THE VERTICALLY STACKED UPPER CLOSED LOW OVER THE MIDWEST  
WILL MOVE INTO THE GREAT LAKES REGION. THIS WILL PUSH A VIGOROUS  
COLD FRONT INTO THE AREA FROM THE WEST WITH A GOOD CHANCE OF SHOWERS  
AND THUNDERSTORMS THROUGH MONDAY AFTERNOON INTO MONDAY NIGHT. HIGH  
PRESSURE WILL THEN BUILD ON FOR TUESDAY WITH COOLER WEATHER AND  
WINDY CONDITIONS. MOISTURE INCREASES ON WEDNESDAY, WITH BETTER  
CHANCES OF RAIN WEDNESDAY NIGHT INTO THURSDAY.  
 

 
   
AVIATION /16Z THURSDAY THROUGH MONDAY/
 
 
AS OF 745 AM EDT THURSDAY...  
 
VFR CONDITIONS AT ALL SITES THROUGH 18Z/2PM TODAY BEFORE  
FRONTAL SHOWERS AND A FEW STORMS ARRIVE ALONG THE WESTERN SLOPES  
OF THE APPALACHIANS. INCREASING CLOUDS/SHOWERS ARE THE RESULT  
OF AN APPROACHING COLD FRONT. ONGOING LINE OF DEEP CONVECTION  
OVER THE TN VALLEY IS FORECAST TO WEAKEN THIS MORNING BEFORE  
REDEVELOPING ALONG THE OUTFLOW BOUNDARY AS IT MOVES INTO THE  
WESTERN APPALACHIANS THIS AFTERNOON. STORM COVERAGE THE  
AFTERNOON IS EXPECTED TO BE SCATTERED IN NATURE...THUNDERSTORM  
CLUSTERS AS OPPOSED TO A SOLID LINE. SOUTHERLY WINDS WILL BECOME  
A BIT GUSTY FROM MID MORNING ON PER 35 TO 40 KNOT LLJ AHEAD OF  
THE APPROACHING FRONT.  
 
SHOWERS/STORMS ARE FORECAST TO LINGER UNTIL LOSS OF DAYTIME  
HEATING. THE ACTUAL SURFACE FRONT IS EXPECTED TO WASH OUT AND  
DISSIPATE AS IT CROSSES THE MOUNTAINS, SO IN SPITE OF A WIND  
SHIFT AS IT CROSSES THE MOUNTAINS THIS EVENING, VERY LITTLE IF  
ANY WIND SHIFT IS EXPECTED OVER THE PIEDMONT EAST OF THE  
MOUNTAINS WHERE THE WINDS WILL REMAIN PREDOMINANTLY OUT OF THE  
SOUTH OR SOUTHWEST.  
 
EXTENDED AVIATION DISCUSSION...  
 
MAINLY VFR FLYING WEATHER IS EXPECTED FOR FRIDAY AND INTO THE  
WEEKEND AS HIGH PRESSURE BUILDS OVER THE SOUTHEAST STATES  
PROMOTING TEMPERATURES WHICH WILL BE MUCH ABOVE NORMAL. WARMING  
SURFACE TEMPERATURES ALSO MEANS INCREASING ATMOSPHERIC  
INSTABILITY. AS SUCH, POTENTIAL WILL EXIST FOR CLOUD BUILD-UPS  
AND THE RISK FOR ISOLATED TO SCATTERED THUNDERSTORMS ALONG THE  
SPINE OF THE APPALACHIANS DURING THE PEAK HEATING HOURS EACH  
AFTERNOON.  
 

 
   
RNK WATCHES/WARNINGS/ADVISORIES
 
 
VA...NONE.  
NC...NONE.  
WV...NONE.  
 

 
 

 
SYNOPSIS...PW  
NEAR TERM...PM/PW  
SHORT TERM...PC  
LONG TERM...KK/NONE  
AVIATION...PM  
 
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