Oak Ridge Weather

000
FXUS61 KPBZ 132104
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
404 PM EST MON FEB 13 2012

.SYNOPSIS...
LOW PRESSURE, COMING EAST FROM KANSAS, WILL BRING A MIX OF SNOW
AND RAIN SHOWERS TUESDAY. HIGH PRESSURE WILL FOLLOW WITH DRY
CONDITIONS WEDNESDAY. A SECOND LOW PRESSURE SYSTEM, ALSO COMING
EAST FROM THE PLAINS, WILL BRING A MIX OF RAIN AND SNOW SHOWERS
THURSDAY.

&&

.NEAR TERM /THROUGH TUESDAY NIGHT/...
RECENT SREF MODEL OUTPUT CONTINUES TO SHOW A LOW PRESSURE SYSTEM,
COMING EAST FROM KANSAS, WILL PROVIDE INCREASING CLOUDS TONIGHT
AND SHOWERS TUESDAY AND TUESDAY NIGHT.

NAM MODEL PROFILES SHOW A WET ADIABATIC LAPSE RATE, SO THE
TRANSITION FROM SNOW TO RAIN AND BACK TO SNOW WILL NOT INCLUDE
ANY FREEZING RAIN OR SLEET.

SURFACE LAYER TEMPERATURES WILL BE KEY TO PRECIPITATION TYPE.
FORECASTED SURFACE TEMPERATURES CLOSER TO COLDER THAN NAM MODEL
OUTPUT THAN WARMER GFS. THIS YIELDED THE INITIAL PRECIPITATION TYPE
AS SNOW TUESDAY MORNING. HOWEVER, PREFRONTAL SOUTHERLY WINDS MAY
PUSH ENOUGH SURFACE LAYER WARMTH TO PROMOTE A CHANGE TO RAIN
SHOWERS BY TUESDAY AFTERNOON AS FAR NORTH AS THE U.S. 422
CORRIDOR NORTH OF PITTSBURGH.

FORTUNATELY PRECIPITATION AMOUNTS WILL BE LIGHT, AS SNOW AMOUNTS
IN THESE CASES CAN BE CHALLENGING. AT THIS JUNCTURE, HAVE
CONTINUED A FORECAST OF UP TO AN INCH GENERALLY, AND UP TO 2 INCHES ACROSS
THE I-80 CORRIDOR AND HIGHER MOUNTAINS.

DUE TO A ZONAL JETSTREAM ALOFT, POST FRONTAL COOLING WILL BE
WEAK, SO CORRESPONDING POST FRONTAL SNOW SHOWERS TUESDAY NIGHT WILL
LIKEWISE BE WEAK AND SHORT-LIVED, AND LIKELY NOT YIELD MORE THAN
AN ADDED INCH OF SNOWFALL.


&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
SREF MODEL OUTPUT CONTINUES TO SHOW ENSUING HIGH PRESSURE
PROVIDING A DRY BREAK WEDNESDAY INTO WEDNESDAY EVENING. THEN A
SECOND LOW PRESSURE SYSTEM, MORE DEVELOPED THAN TUESDAY`S SYSTEM,
WILL COME NORTHEASTWARD FROM KANSAS, AND PROVIDE ANOTHER BOUT OF
SHOWERS OF SNOW AND RAIN LATE WEDNESDAY NIGHT AND THURSDAY.

ALTHOUGH THE TEMPERATURE FORECAST WAS BASED MORE ON COLDER NAM
MOS, TEMPERATURES WITH THIS SYSTEM SHOULD BE MILDER, SO EXPECT
MORE OF THE PRECIPITATION TO BE IN THE FORM OF RAIN.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
AN UPPER TROUGH AND ASSOCIATED SURFACE LOW WILL MOVE NORTHEAST INTO
EASTERN CANADA BY FRIDAY. SCATTERED RAIN AND SNOW SHOWERS SHOULD
BEGIN TO TAPER OFF BY FRIDAY MORNING. LINGERING MOISTURE AND
NORTHWEST FLOW SHOULD MAINTAIN A FEW SHOWERS OVER THE FORECAST AREA
ESPECIALLY NORTH OF I-80 FRIDAY AFTERNOON. WEAK SYSTEMS PASSING TO
OUR NORTH COUPLED WITH MOIST NORTHWEST FLOW WILL MAINTAIN CLOUDS AND
ISOLATED SHOWERS OVER THE REGION DURING THE WEEKEND.

SURFACE HIGH PRESSURE WITH DRIER AIR SHOULD PROVIDE MORE SUNSHINE
ON MONDAY.

TEMPERATURES ARE FORECAST TO BE A FEW DEGREES ABOVE NORMAL DURING
THE EXTENDED PERIOD.
&&

.AVIATION /21Z MONDAY THROUGH SATURDAY/...
VFR CONDITIONS WILL CONTINUE THROUGH TONIGHT AS A SURFACE RIDGE
SLIDES OFF THE SOUTHEAST COAST. CIRRUS CLOUDS WILL BE ON THE
INCREASE THIS AFTERNOON...FOLLOWED BY BROKEN MID CLOUDS TONIGHT AS A
SHORT WAVE TROUGH APPROACHES FROM THE WEST. HAVE HIGH CONFIDENCE
THAT CONDITIONS WILL QUICKLY LOWER TO MVFR AND THEN IFR FROM WEST TO
EAST AFTER 09Z TUESDAY AS AREAS OF SNOW SPREAD EASTWARD INTO THE
REGION. WARMING BOUNDARY LAYER TEMPERATURES WILL LIKELY CAUSE SNOW
CHANGE TO RAIN MAINLY SOUTH OF A KPHD-KBVI-KLBE LINE BY 18Z TUESDAY.

OUTLOOK...TUESDAY NIGHT THROUGH SATURDAY...
MIX OF SNOW AND RAIN SHOWERS WITH MAINLY MVFR RESTRICTIONS WILL
LIKELY PERSIST TUESDAY NIGHT WITH LOW PRESSURE SYSTEM PASSAGE.
ENSUING HIGH PRESSURE WILL BRING VFR WEDNESDAY. RESTRICTIONS ARE
LIKELY AGAIN THURSDAY INTO FRIDAY DUE TO A MIX OF RAIN AND SNOW
SHOWERS ASSOCIATED WITH THE PASSAGE OF A STRONGER LOW PRESSURE
SYSTEM TRACKING NORTHEAST FROM THE PLAINS.

MOIST NORTHWEST FLOW BEHIND THE DEPARTING LOW PRESSURE SYSTEM MAY
MAINTAIN AREAS OF MVFR CEILINGS OVER THE TERMINALS SATURDAY.


&&

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

&&

$$

NWS PBZ Office Area Forecast Discussion