Hopefully we can get this stubborn Low to move on and give Texas and especially Louisiana a break!!!
EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
355 AM EST THU MAR 10 2016
...LOWER MISSISSIPPI VALLEY / WESTERN GULF COAST UP THROUGH
WESTERN TN/KY...
A BROAD MODERATE RISK OF EXCESSIVE RAINFALL IS FORECAST FROM
BEAUMONT TEXAS ACROSS MUCH OF LOUISIANA AND INTO PORTIONS OF
WESTERN MISSISSIPPI AND TENNESSEE...AND EASTERN ARKANSAS. A SLIGHT
RISK SURROUNDS THE MODERATE RISK AND EXTENDS FARTHER NORTH TO
LOUISVILLE KENTUCKY. A SYNOPTICALLY EVIDENT FLASH FLOOD EVENT HAD
PRODUCED SEVERE IMPACTS ACROSS PORTIONS OF THIS REGION ON
WEDNESDAY. ADDITIONAL WIDESPREAD RAIN AND SOME VERY HEAVY RAIN IS
FORECAST TODAY...AND ALTHOUGH THE AXIS OF GREATEST NEW RAINFALL
AMOUNTS WILL BE SLIGHTLY FARTHER EAST...THERE WILL BE SOME OVERLAP
OF MODERATE RAINS BACK INTO AREAS THAT WERE HIT HARD YESTERDAY.
NO SINGLE MODEL QPF WAS HANDLING ALL OF THE DETAILS PARTICULARLY
WELL...ALTHOUGH ON THE LARGE SCALE THERE WAS GOOD AGREEMENT AMONG
THE GFS/ECMWF/UKMET/GEM REGIONAL. THERE WAS A SOMEWHAT SURPRISING
AMOUNT OF SPREAD WITH RESPECT TO DETAILS AMONG THE HI-RES MODELS.
WE FAVORED THE GEM REGIONAL...ESPECIALLY THE 18Z RUN...AS WELL AS
THE 00Z NSSL
WRF. THE 00Z WRF-ARW ALSO HINTED AT THE MORE EXTREME NATURE OF THE
RAIN RATES OVER LOUISIANA...BUT MAY ACTUALLY BE OVERDONE GIVEN
MORE FORWARD PROPAGATION TODAY.
THE BROAD CORRIDOR OF 1.50 TO NEAR 2.00 INCH PW FEEDING OFF
MOISTURE FROM THE CARIBBEAN AND TROPICAL PACIFIC WAS VERY
ANOMALOUS...AS GULF COAST ANOMALIES RARELY PUSH HIGHER THAN THE
2.5 TO 3 STANDARD DEVIATIONS NOW BEING OBSERVED BASED ON THE
ALREADY HUMID CLIMATE IN THAT REGION. THIS GIVES US REASON TO
CONTINUE PUSHING FORECAST AMOUNTS TOWARD THE HIGH SIDE OF THE
MODEL GUIDANCE...DESPITE THE FACT THAT EVENTS ON THURSDAY SHOULD
NOT BE QUITE SO FOCUSED AS THEY WERE WHEN 10 TO 16 INCHES OF RAIN
FELL YESTERDAY.
THIS MORNING A CONFLUENT LOW LEVEL FLOW REGIME WILL PERSIST FROM
NORTHWEST MISSISSIPPI THROUGH CENTRAL KENTUCKY...IN THE ENTRANCE
REGION OF A NORTHERN STREAM JET STREAK. THIS AREA WAS DOWNWIND OF
THE INSTABILITY AXIS NEAR THE GULF COAST...WITH SOME DEEP
CONVECTION NOTED OVER NORTHWEST MS AT 06Z...BUT WITH LITTLE
CONVECTIVE ENHANCEMENT TO THE PRECIPITATION FARTHER NORTH. THE
FORCING SUPPORTING THIS NARROW QPF AXIS SHOULD PERSIST THROUGH MID
AFTERNOON BEFORE TENDING TO RELAX OVER THE TENNESSEE VALLEY AND
ADJACENT REGIONS AS A NORTHERN STREAM WAVE MAKES PROGRESS TOWARD
THE UPPER OHIO VALLEY AND NEW ENGLAND...SPURRING AN INCREASE OF
PRECIPITATION IN THAT CORRIDOR.
BACK TOWARD THE GULF COAST...SOME DEGREE OF MID LEVEL DRY AIR WAS
WRAPPING AROUND THE DEEP LOW CENTER IN MEXICO...YIELDING
THUNDERSTORMS WITH A LITTLE MORE OUTFLOW AND FORWARD PROPAGATION
ACROSS SOUTHEAST TEXAS THIS MORNING. SUCH BEHAVIOR IS GENERALLY
EXPECTED TODAY...ESPECIALLY AS LOW LEVEL WIND SPEEDS ARE FORECAST
TO DROP OFF ONCE THE NORTHERN STREAM WAVE AND ASSOCIATED JET
STREAK START TO MOVE ON...AND RELAX THE SYNOPTIC GRADIENTS A BIT.
THE DIP IN LOW LEVEL WINDS WILL RESULT IN LESS RESISTANCE TO
EASTWARD MOVEMENT BY THIS AFTERNOON/EVENING...BUT PRECIPITATION
SHOULD NONETHELESS BE WIDESPREAD AND VERY EFFICIENT AT DUMPING
HEAVY AMOUNTS GIVEN THE COMBINATION OF HIGH PW AND MODERATE CAPE
OVER PARTS OF SOUTHERN LOUISIANA AND MISSISSIPPI. THE GREATEST
OVERLAP OF SLIGHT HEIGHT FALLS / Q-VECTOR CONVERGENCE WITH THE
AXIS OF DEEPEST MOISTURE SHOULD OCCUR DURING THE MORNING HOURS
OVER THE UPPER TX COAST AND SOUTHWEST LOUISIANA...YIELDING
EXPANSION OF ANOTHER MCS...AND SENDING IT ON A SLOW EASTWARD
MARCH. STRATIFORM PRECIPITATION BACK TO THE NORTH AND WEST MAY
DELIVER ANOTHER 1-2 INCHES OF RAIN ON AVERAGE TO NORTHWEST
LOUISIANA...WHILE THE STRONGER STORMS AT THE LEADING EDGE WILL
LIKELY PRODUCE RAIN RATES 2.5 INCHES PER HOUR.
THE FORECAST TODAY WAS NOT AS CLEAR CUT...NOR AS FOCUSED...TO
SUPPORT A HIGH RISK AREA...AND THE HEAVIEST RAIN WILL FALL IN
AREAS OF HIGHER FLASH FLOOD GUIDANCE. SO WE HAVE A BROAD MODERATE
RISK INSTEAD.