549  
FXUS61 KRNK 242355  
AFDRNK  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BLACKSBURG VA  
755 PM EDT WED MAY 24 2017  
   
SYNOPSIS
 
 
A WARM FRONT OVER SOUTHWEST VIRGINIA WILL LIFT NORTH TONIGHT,  
FOLLOWED BY A COLD FRONT MOVING FROM WEST TO EAST. BY THURSDAY  
MORNING LOW PRESSURE WILL BE OVER THE OHIO VALLEY WITH THE COLD  
FRONT TRAILING ACROSS FAR EASTERN VIRGINIA AND NORTH CAROLINA.  
FRIDAY WILL BE A DRY DAY WITH THE LOW WELL INTO NEW ENGLAND.  
 

 
   
NEAR TERM /THROUGH THURSDAY/
 
 
AS OF 745 PM EDT WEDNESDAY...  
 
DEEP SYNOPTIC SCALE LONG WAVE TROF WAS OVER THE EASTERN UNITED  
STATES WITH TWO UPPER LOW WITHIN THE TROF. THE TROF CROSSES THE  
OHIO VALLEY ON THURSDAY WITH THE MAIN TROF AXIS MOVING TOWARD  
THE EAST COAST ON TUESDAY AFTERNOON.  
 
HAVE TRIMMED THE TORNADO WATCH AND EXPANDED THE FLASH FLOOD  
WATCH BASED ON CURRENT RADAR TRENDS AND DISCUSSION WITH BOTH SPC  
AND WPC.  
 
THE THREAT FOR FLASH FLOODING WILL CONTINUE UNTIL THE COLD  
FRONT PASSES. EXPECTING RAINFALL RATES TYPICAL IN CONVECTIVE  
STORMS. PRECIPITABLE WATER VALUES INCREASE TO AROUND 1.5 INCHES  
IN THE PIEDMONT OF VIRGINIA AND NORTH CAROLINA TONIGHT. RATES OF  
1.0 TO 1.5 INCHES PER HOUR WOULD EXCEED WHAT IS NEEDED FOR  
FLASH FLOODING IN PARTS OF SOUTHWEST VIRGINIA AND NORTHWEST  
NORTH CAROLINA. THE FLASH FLOOD WATCH WILL BE EXPANDED TO  
INCLUDE ANOTHER TIER OF COUNTIES FROM PULASKI TO HALIFAX.  
 
COLD POOL ALOFT WITH THE SOUTHERN OF THE TWO UPPER LOWS PASSES OVER  
THE CAROLINAS BUT 500MB TEMPERATURES STILL LOWER ENOUGH TO  
PRODUCE LARGE LAPSE RATES OVER SOUTHEAST WEST VIRGINIA,  
SOUTHWEST VIRGINIA, AND NORTHWEST NORTH CAROLINA ON THURSDAY.  
CAPES ARE FORECAST AROUND 800 J/KG IN THE PIEDMONT THURSDAY  
AFTERNOON. LOW LEVEL MOISTURE WILL ERODE EAST OF THE BLUE RIDGE  
THURSDAY BUT WILL INCREASE WITH THE INCREASING WEST WIND ON THE  
WEST SIDE OF THE CENTRAL APPALACHIANS.  
 
AS THE WARM FRONT MOVES NORTH TEMPERATURES WILL TEMPORARILY GO UP  
THEN THEY WILL COOL OFF AGAIN BEHIND THE COLD FRONT. DEFINITELY  
A NON-DIURNAL TREND. EXPECTING ENOUGH BREAKS IN THE CLOUDS EAST  
OF THE BLUE RIDGE ON THURSDAY FOR SOME SUN AND TEMPERATURES  
WARMER THAN WEDNESDAY. BLEND OF MET/MAV GUIDANCE LOOKS  
REASONABLE FOR MAXIMUM TEMPERATURES ON THURSDAY.  
 

 
   
SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/
 
 
AS OF 245 PM EDT WEDNESDAY...  
 
THURSDAY NIGHT INTO FRIDAY, THE CENTER OF THE UPPER LOW RESPONSIBLE  
FOR THE WET WEATHER ON THURSDAY WILL TRANSLATE FROM NEAR THE MASON-  
DIXON LINE TO OFF THE COAST OF CAPE COD. THIS TRANSITION WILL PLACE  
THE REGION ON THE BACKSIDE OF THE DEPARTING SYSTEM WITHIN A  
TIGHTENING PRESSURE GRADIENT. LOOK FOR WINDS TO BECOME GUSTY FROM  
THE NORTHWEST AS 850MB FLOW IS PROGGED TO PEAK AROUND 40KTS IN THE  
EVENING. RIDGETOP GUSTS IN THE 30 TO 40 MPH RANGE WILL BE COMMON  
WITH THE HIGHEST PEAKS EXPERIENCING A FEW MPH ABOUT THAT. MOUNTAIN  
VALLEYS WILL EXPERIENCE GUSTS MORE IN THE 20 TO 30 MPH RANGE. GUSTS  
OF ANY SUBSTANTIAL NATURE ARE NOT EXPECTED DOWNSTREAM OF THE CREST  
OF THE BLUE RIDGE.  
 
PRECIPITATION WILL LINGER THROUGH THE OVERNIGHT HOURS IN THE FORM OF  
UPSLOPE SCATTERED SHOWERS. THE BEST COVERAGE WILL BE ACROSS  
SOUTHEAST WEST VIRGINIA WITH DECREASING POTENTIAL HEADING EASTWARD  
TO ROUGHLY THE INTERSTATE-81 CORRIDOR.  
 
ON FRIDAY, WE WILL GRADUALLY LOSE THE UPSLOPE SCATTERED SHOWERS, AND  
ASSOCIATED CLOUD COVER, AS LOW LEVEL WINDS START TO BACK MORE  
WESTERLY THROUGH THE DAY WITH THE APPROACH OF AN UPPER LEVEL  
SHORTWAVE RIDGE. THE ARRIVAL OF DRIER AIR WILL ALSO YIELD A  
DECREASING TREND IN COVERAGE. THE BEST COVERAGE WILL STILL BE OVER  
PARTS OF SOUTHEAST WEST VIRGINIA, MAINLY DURING THE MORNING HOURS.  
THE VAST MAJORITY OF THE FORECAST AREA WILL EXPERIENCE LIMITED CLOUD  
COVER AND WEAK WINDS.  
 
OUR PERIOD OF DRIER WEATHER WILL BE SHORT LIVED. FRIDAY NIGHT INTO  
SATURDAY WE WILL BE WATCHING A COLD FRONT APPROACH AND THEN ENTER  
THE REGION. ISOLATED SHOWERS MAY ON THE RADAR SCREEN BY SUNRISE  
SATURDAY IN THE WESTERN PORTIONS OF THE AREA, BUT THE BETTER CHANCES  
WILL BE DURING THE DAY SATURDAY WITH THE ARRIVAL OF THE FRONT  
COMBINED WITH DAYTIME HEATING.  
 
GUIDANCE VARIES ON WHAT EXTENT THE FRONT MAKES IT THROUGH THE REGION  
BEFORE STALLING. MODEL ARE LEANING TOWARDS A THUNDERSTORM COMPLEX  
POTENTIALLY RIDING ALONG THIS STALLED FRONT LATE SATURDAY NIGHT AND  
ENTERING THE AREA BY SUNDAY MORNING.  
 
TEMPERATURES DURING THIS PORTION OF THE FORECAST WILL START NEAR  
NORMAL, BUT TREND TO A LITTLE OVER FIVE DEGREES ABOVE NORMAL BY  
SATURDAY.  
 

 
   
LONG TERM /SUNDAY THROUGH WEDNESDAY/
 
 
AS OF 205 PM EDT WEDNESDAY...  
 
DURING THIS PART OF THE FORECAST, A BROAD, SLOW MOVING UPPER LOW  
WILL TRANSITION FROM THE GREAT LAKES REGION TO OVER SOUTHEAST  
CANADA. THIS WILL KEEP OUR REGION IN A PATTERN DOMINATED BY A  
PERSISTENT TROUGH OF LOW PRESSURE ACROSS THE EASTERN PORTION OF THE  
U.S. WITHIN THIS TROUGH PATTERN A SERIES OF COLD FRONTS ARE  
EXPECTED TO ENTER, AND THEN MOVE THROUGH THE FORECAST REGION.  
GUIDANCE OFFERS THE FIRST OF THESE TWO TO HAVE A SUNDAY NIGHT INTO  
MONDAY TIME FRAME, WITH A SECOND DURING LATE TUESDAY NIGHT INTO  
WEDNESDAY. BOTH OF THESE TIME FRAMES WILL BE PERIODS WITH A GREATER  
POTENTIAL FOR SHOWERS AND STORMS, WITH THE FIRST BEING MORE ROBUST  
THAN THE SECOND. HOWEVER, WHILE THE AREA IS WITHIN THE OVERALL  
TROUGH PATTERN, DAYTIME HEATING WILL BE ENOUGH TO PRODUCE AT LEAST  
ISOLATED SHOWERS DURING OTHER PARTS OF THIS TIME PERIOD.  
 
TEMPERATURES DURING THIS PORTION OF THE FORECAST WILL START THE  
PERIOD ABOUT TEN DEGREES ABOVE NORMAL. BY WEDNESDAY, READINGS WITHIN  
A DEGREE OR TWO OF NORMAL ARE FORECAST.  
 

 
   
AVIATION /00Z THURSDAY THROUGH MONDAY/
 
 
AS OF 740 PM EDT WEDNESDAY...  
 
WEDGE AT 8PM EXTENDED FROM BATH COUNTY VIRGINIA INTO WATAUGA  
COUNTY NORTH CAROLINA WITH EACH SIDE OF THE MORE STABLE AIR  
ERODING, ESPECIALLY IN THE PIEDMONT OF VIRGINIA AND NORTH  
CAROLINA. CEILINGS WERE IFR TO LIFR IN THE WEDGE. MODERATE TO  
HEAVY SHOWERS AND ISOLATED THUNDERSTORMS WERE REDUCING  
VISIBILITIES INTO THE MVFR RANGE. HIGH CONFIDENCE IN TIMING OF  
THE MODELS BRINGING THE COLD FRONT THROUGH THE REGION AFTER  
MIDNIGHT. ONCE THE RAIN BEGINS TO MOVE NORTHEAST OUT OF THE  
AREA, MEDIUM TO HIGH CONFIDENCE THAT FOG WILL FORM FOR A LEAST A  
FEW HOURS BEFORE WEST WINDS INCREASE.  
 
DOWNSLOPE WINDS ON THE EAST SIDE OF THE BLUE RIDGE WILL ERODE  
CLOUDS AND FOG ONCE MIXING BEGINS THURSDAY MORNING. LOW LEVEL  
MOISTURE AND VFR STRATOCUMULUS WILL REMAIN OVER THE MOUNTAINS.  
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL DEVELOP IN THE  
AFTERNOON. SOME OF THE STRONGER THUNDERSTORMS MAY HAVE SMALL  
HAIL AND MVFR VISIBILITIES.  
 
EXTENDED AVIATION DISCUSSION...  
 
FRIDAY WILL BE DRIER WITH A BETTER CHANCE OF VFR CEILINGS AND  
VISIBILITIES. ANOTHER FRONT REACHES THE AREA FOR SATURDAY WITH  
MORE SHOWERS AND THUNDERSTORMS INCLUDING SUB-VFR CONDITIONS  
INTO MONDAY.  
 

 
   
HYDROLOGY
 
 
AS OF 730 PM EDT WEDNESDAY...  
 
FLASH FLOOD WATCH EXPANDED INTO SOUTHEAST WEST VIRGINIA. UPPER  
DIFFLUENCE AND SYNOPTIC LIFT WILL LEAD TO HEAVY RAIN POTENTIAL.  
RAINFALL RATES MAY NOT BE EXCESSIVELY LARGE, HOWEVER, FLASH  
FLOOD GUIDANCE ACROSS MUCH OF THE MOUNTAINS WAS LOW, BELOW 1.7  
INCHES IN 3 HOURS.  
 
THE RIVER FORECAST FOR THE DAN AND ROANOKE RIVERS WILL BE  
UPDATED AGAIN AFTER 8PM BASED ON RAINFALL THROUGH THAT TIME AND  
EXPECTED RAINFALL FOR OVERNIGHT. MINOR FLOODING IS EXPECTED TO  
CONTINUE ON THE DAN RIVER AT SOUTH BOSTON AND IS FORECAST ON THE  
DAN RIVER AT PACES AND ON THE ROANOKE RIVER AT RANDOLPH.  
 

 
   
RNK WATCHES/WARNINGS/ADVISORIES
 
 
VA...FLASH FLOOD WATCH UNTIL MIDNIGHT EDT TONIGHT FOR VAZ007-  
009>018-022-032-033-043-044-058.  
NC...FLASH FLOOD WATCH UNTIL MIDNIGHT EDT TONIGHT FOR NCZ001>006-  
018>020.  
WV...FLASH FLOOD WATCH UNTIL MIDNIGHT EDT TONIGHT FOR WVZ042>044-  
507-508.  
 

 
 

 
SYNOPSIS...AMS  
NEAR TERM...AMS  
SHORT TERM...DS  
LONG TERM...DS  
AVIATION...AMS/JH  
HYDROLOGY...AMS  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab VA Page
The Nexlab WV Page
The Nexlab NC Page Main Text Page