000
FXUS61 KRNK 111154
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
654 AM EST THU MAR 11 2010

.SYNOPSIS...
A LARGE LOW PRESSURE SYSTEM WILL MOVE SLOWLY EAST FROM THE MID
MISSISSIPPI VALLEY INTO THE MID ATLANTIC REGION BY SATURDAY.
IMPULSES ROTATING AROUND THIS SYSTEM THIS WILL PRODUCE PERIODIC
SHOWERS AND PERHAPS HEAVIER RAINFALL INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
LIGHT SHOWERS THAT MOVED THROUGH THE SOUTHEAST COUNTY WARNING AREA
DURING WEDNESDAY EVENING ARE ALMOST OUT OF BUCKINGHAM COUNTY.
THEN THERE WILL BE A BREAK IN THE CHANCE OF RAIN UNTIL THE NEXT
SHORT WAVE APPROACHES FROM THE SOUTHWEST. HAVE SIGNIFICANTLY
TRIMMED PROBABILITY OF RAIN THIS MORNING. MODELS...INCLUDING THE
LOCAL WRF HAVE RAIN MOVING BACK INTO THE AREA AROUND 18Z IN
NORTHWEST NORTH CAROLINA AND REACHING ROUTE 460 BY 23Z. ALSO KEPT
THE ISOLATED THUNDERSTORMS IN THE FAR SOUTH AND SOUTHWEST THIS
AFTERNOON. HAVE RAISED TEMPERATURES THIS AFTERNOON SINCE RAINFALL
WILL BE DELAYED. DEEPER VALLEYS IN THE WEST WITH A CLEAR SKY THIS
MORNING HAVE DROPPED INTO THE MID TO UPPER 30S BUT AS MIXING
STARTS THIS MORNING AND SURFACE DEW POINTS RISE THROUGH THE 40S
TEMPERATURES WILL CLIMB QUICKLY.

TONIGHT LOW LEVEL WINDS GRADUALLY BECOME MORE SOUTHEAST TO EAST AS
MORE SURFACE REFLECTION OF THE SOUTHEAST SHORT WAVES DEVELOPS
ALONG THE COAST. KEPT LOW TEMPERATURES ON THE WARM SIDE OF
GUIDANCE WITH ALL THE CLOUD COVER AND SURFACE DEW POINTS POSSIBLY
IN THE LOWER TO MID 50S EAST OF THE BLUE RIDGE.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
ON FRIDAY...GUIDANCE IS TRENDING TOWARDS A SOLUTION THAT RESEMBLES A
PSEUDO-DAMMING SITUATION AS EASTERLY FLOW INCREASES...AND SURFACE
PRESSURE FIELDS HINT AT A WEAK INVERTED RIDGE ON THE EAST SIDE OF
THE APPALACHIANS. THE NAM IS THE MOST ROBUST WITH THIS SOLUTION WITH
THE INVERTED RIDGE BEING AMPLIFIED BY THE PRESENCE OF DEEPENING LOW
ALONG THE OUTER BANKS OF NORTH CAROLINA. THE 00Z GFS...GEM AND ECMWF
ARE FARTHER SOUTH WITH THIS LOW AND HAVE IT MORE OF A WEAK TROUGH.
WHILE THIS IS OCCURRING...WE STILL HAVE THE BROAD...CLOSED OFF UPPER
LOW ACROSS THE MID MISSISSIPPI VALLEY INCHING OUR WAY. DEEP
CONVECTION IN ADVANCE OF THIS SYSTEM IS EXPECTED TO REMAIN WEST OF
THE AREA UNTIL FRIDAY NIGHT...BUT SOME SCATTERED THUNDERSTORMS
CANNOT BE RULED OUT IN THE WESTERN PART OF THE REGION. THE PRESENCE
OF THE RIDGE IN THE EAST SHOULD HELP THAT AREA TO REMAIN RELATIVELY
STABLE...BUT WITH GOOD CLOUD COVER...SHOWERS...AND A TREND TOWARDS
LOWER HIGH TEMPERATURES THAN PREVIOUSLY FORECAST. HAVE NOT GONE AS
COOL AS THE LATEST GUIDANCE...BUT HAVE TRENDED LOWER.

FRIDAY NIGHT...EXPECTING A SIGNIFICANT BAND OF MODERATE TO HEAVY RAIN
SHOWERS TO MOVE THROUGH THE REGION IN ASSOCIATION WITH A SURFACE
TROUGH LIFTING NORTHEAST ACROSS THE AREA. FOR THE FIRST HALF OF THE
NIGHT...CONVECTIVE PARAMETERS STILL SUGGEST THE POTENTIAL OF
THUNDERSTORMS. AFTER MIDNIGHT...MODERATE TO HEAVY RAIN SHOWERS ARE
EXPECTED WITH THE BEST COVERAGE IN THE EAST.

BY SATURDAY...THE MAIN UPPER LOW IS PROGGED TO MOVE OVER THE AREA.
SHOWERS WILL CONTINUE THANKS TO STEEP LAPSE RATES IN ASSOCIATION
WITH THE LOW. COVERAGE OF SHOWERS WILL BE GREATEST IN THE NORTH
WHERE FRIDAY NIGHTS TROUGH IS EXPECTED TO PIVOT TO ALONG A NW-SE
ORIENTATION ACROSS NORTHERN VIRGINIA.

SATURDAY NIGHT INTO SUNDAY NIGHT...THE CENTER OF THE UPPER LOW IS
EXPECTED TO SHIFT EAST OF THE AREA...AND THE GENERAL FLOW ACROSS THE
AREA WILL BECOME MORE NORTHWEST. THIS DEVELOPING NORTHWEST FLOW WILL
ALLOW FOR PRECIPITATION TO BECOME MORE OF THE UPSLOPE FLOW TYPE WITH
PRECIPITATION MAXIMIZED OVER THE MOUNTAINS OF SE WV WITH LESSER
AMOUNTS THE FARTHER EAST ONE IS. COLDER AIR WILL ALSO START TO WORK
ITS WAY INTO THE AREA. STILL EXPECTING THE VAST MAJORITY OF THE
PRECIPITATION TO BE IN THE FORM OF RAIN SHOWERS...HOWEVER A FEW
ISOLATED SPOTS AT THE HIGHER ELEVATIONS OF SOUTHEAST WEST
VIRGINIA...FAR SOUTHWEST VIRGINIA AND THE NORTHERN MOUNTAINS OF
NORTH CAROLINA MAY SEE SOME SNOW FLAKES LATE SUNDAY NIGHT.

&&

.LONG TERM /MONDAY THROUGH WEDNESDAY/...
THE MAIN UPPER LOW WILL MOVE EAST ACROSS OUR REGION SUNDAY.
AS WE TRANSITION TO BEING ON THE BACKSIDE OF THE DEPARTING SYSTEM
BY SUNDAY NIGHT...AND GRADUALLY EXPERIENCE MORE UPSLOPE
PRECIPITATION IN THE WEST. THE THREAT OF UPSLOPE RAIN/SNOW SHOWERS
WILL PERSIST INTO MONDAY AS THE LOW OFF THE MID ATLANTIC COAST
DEEPENS AND SHIFTS NORTHEAST TOWARD THE CANADIAN MARITIMES MONDAY
WITH MAIN 5H AXIS OF TROUGH OVER EAST COAST. WITH NORTHWEST FLOW
KEPT LIGHT POPS IN THE WEST ON TUESDAY SIMILAR TO HPCGUIDE. HIGH
PRESSURE WILL BUILD ACROSS OUR AREA FROM THE OHIO VALLEY TUESDAY
NIGHT INTO WEDNESDAY. IN GENERAL KEPT TEMPERATURES ON THE COOLER
SIDE EARLY NEXT WEEK THEN MODERATE A LITTLE BY MID WEEK.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
LOW CLOUDS WITH IFR CEILINGS WERE SPREADING NORTH EAST OF THE BLUE
RIDGE EARLY THIS MORNING. EXPECT CEILINGS TO LIFT TO VFR THIS
MORNING AT ROA AND LYH. IMPROVEMENT AT DAN WILL TAKE LONGER.

NEXT BAND OF SHOWERS WILL ARRIVE FROM THE SOUTHWEST THIS
AFTERNOON. HIGH CONFIDENCE IN TIMING WITH ALL THE MODELS HOLDING
OFF ON ANY PRECIPITATION AT THE TAF SITES UNTIL AFTER 18Z.

ONCE THE PRECIPITATION BEGINS...CONDITIONS WILL DETERIORATE BACK
TO IFR OR MVFR. AFTER 06Z THE SHORT WAVE LIFTS TO THE NORTHEAST
AND RAINFALL SHOULD END. CONFIDENCE IS LOW ON WHAT CEILING HEIGHTS
WILL BE FOLLOWING THE SHOWERS.

THE LARGE AND SLOW-MOVING UPPER LOW OVER THE MIDWEST WILL BRING
INCREASINGLY POOR FLYING CONDITIONS THROUGH THE END OF THE WEEK. THERE
IS HIGH CONFIDENCE OF SCATTERED CONVECTIVE STORMS FRIDAY
AFTERNOON INTO FRIDAY NIGHT. CEILINGS AND VISIBILITIES WILL FALL
BACK INTO THE LOW MVFR TO IFR RANGE LATE FRIDAY...AND LAST MUCH OF
THE EXTENDED FORECAST PERIOD AS AN AREA OF UPPER LEVEL LOW
PRESSURE DRIFTS ACROSS THE REGION.

&&

.HYDROLOGY...
CONTINUING TO MONITOR THE POSSIBILITY OF FLOODING DUE TO COMBINED
SNOW MELT/HEAVY RAINFALL SCENARIO LATE THIS WEEK. NCEP AND MODEL
QPF BY EARLY SUNDAY COULD RANGE FROM 1 TO 3 INCHES IN SOME RIVER
BASINS. THE ESTIMATES OF SNOW WATER EQUIVALENT (SWE) IN PORTIONS
OF THE WESTERN MOUNTAINS..MAINLY THE GREENBRIER BASIN ARE STILL
OVER 2 INCHES WITH ISOLATED AMOUNTS OVER 5 INCHES.

CURRENT THINKING IS THAT MOST IF NOT ALL OF THIS SNOW WILL MELT
UNDER THE ONSLAUGHT OF RAINFALL AND HIGHER DEWPOINT AIR. DEWPOINTS
MAINLY REMAIN IN THE UPPER 40S IN THE WEST BUT COULD REACH LOW 50S
WHICH IS VERY EFFECTIVE IN MELTING SNOW ESPECIALLY IF COMBINED
WITH STRONG WINDS. THERE IS SUBSTANTIALLY LESS SWE IN THE UPPER
JAMES AND NEW RIVER BASINS...HENCE THE POTENTIAL FOR RIVER
FLOODING IS LESS...BUT 2 TO 3 INCHES OF RAINFALL ON TOP OF
BASICALLY SATURATED GROUND MIGHT STILL BE ENOUGH IN THOSE BASINS
TO CAUSE AT LEAST MINOR RIVER FLOODING BY LATE IN THE WEEK OR THE
WEEKEND. THE POSSIBILITY OF MORE RAPID RUNOFF AND FLASH FLOODING
ALSO EXISTS ON FRIDAY AS CONVECTIVE ELEMENTS WITH LOCALLY HEAVY
RAINFALL MAY DEVELOP AND TRACK ACROSS THE PARTS OF THE AREA.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...NONE.
NC...NONE.
WV...FLOOD WATCH FROM 6 PM EST THIS EVENING THROUGH SATURDAY
     AFTERNOON FOR WVZ043>045.

&&

$$
SYNOPSIS...AMS
NEAR TERM...AMS
SHORT TERM...DS
LONG TERM...KK
AVIATION...AMS
HYDROLOGY...

NWS RNK Office Area Forecast Discussion