MESOSCALE PRECIPITATION DISCUSSION 0707
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
950 PM EST SAT DEC 26 2015
 
AREAS AFFECTED...SOUTHERN/CENTRAL MO...SOUTHERN IL...SOUTHWEST IN 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 270245Z - 270845Z
 
SUMMARY...SIGNIFICANT FLASH FLOODING WILL BE LIKELY OVERNIGHT AS
VERY HEAVY RAINS CONTINUE TO REPEAT OVER THE SAME AREA.

DISCUSSION...AN EXTENSIVE AXIS OF HEAVY SHOWERS AND THUNDERSTORMS
CONTINUES TO FOCUS ALONG A STATIONARY FRONT OVER THE MID MS VALLEY
AND INTO THE LOWER OH VALLEY OUT AHEAD OF AN AMPLIFYING
TROUGH/CLOSED UPPER LOW OVER THE SOUTHERN HIGH PLAINS.

VERY MOIST AND STRONG DEEP LAYER SOUTH/SOUTHWESTERLY FLOW
CONTINUES TO SURGE ACROSS THE ENTIRE LOWER/MID MS VALLEY REGION
AND INTO THE OH VALLEY FROM THE GULF OF MEXICO AND INTO THE
FRONTAL ZONE. THE SLOWLY APPROACHING UPPER TROUGH/CLOSED LOW IS
CREATING A VERY DIVERGENT FLOW PATTERN ALOFT THROUGHOUT THE REGION
WHERE DEEP CONVECTION IS ONGOING...AND THERE ARE ROBUST H25
RIGHT-ENTRANCE REGION JET DYNAMICS THAT ARE WORKING IN TANDEM WITH
THE STRONG MOISTURE TRANSPORT AND AT LEAST A MODEST DEGREE OF
INSTABILITY.

AREA VWPS SHOW A 40 TO 50 KT LOW LEVEL JET SURGING NORTH INTO THE
FRONT...AND THE GLOBAL MODELS SUSTAIN THIS THROUGHOUT THE NIGHT.
PWATS ARE ALREADY CLOSE TO 1.5 INCHES AND THIS IS 3 TO 4 STD DEV
ABOVE NORMAL FOR THIS TIME OF THE YEAR. THEREFORE...THE
EXPECTATION IS FOR THE CONVECTION TO FOSTER INTENSE RAINFALL
RATES...WHICH WILL APPROACH 2 INCHES/HR LOCALLY.

VERY HEAVY RAINS OF 3 TO 5 INCHES HAVE ALREADY OCCURRED OVER PARTS
OF CENTRAL AND SOUTHWEST MO INTO SOUTH-CENTRAL IL...AND ADDITIONAL
HEAVY RAINS WILL OCCUR OVERNIGHT WITH A VERY GRADUAL EASTWARD
SHIFT IN THE CONVECTIVE AXIS THAT WILL ALSO INCLUDE SOUTHWEST IN.

THE LATEST HRRR SUGGESTS AN AXIS OF 2 TO 3 INCH RAINFALL AMOUNTS
THROUGH 08Z FROM SOUTHWEST MO NORTHEAST INTO SOUTHERN IN AND
GENERALLY RIGHT ALONG THE STATIONARY FRONT WHERE FORCING WILL BE
MAXIMIZED. LOCALLY HEAVIER AMOUNTS OF 4 TO 5 INCHES CANNOT BE
RULED OUT GIVEN SUCH ANOMALOUS MOISTURE TRANSPORT AND STRONG DEEP
LAYER ASCENT.

EXPECT LOCALLY SIGNIFICANT FLASH FLOODING OVERNIGHT GIVEN WET
ANTECEDENT CONDITIONS AND THE EXPECTATION OF CONVECTION TO TEND TO
TRAIN OVER THE SAME AREA.

ORRISON

ATTN...WFO...ILX...IND...LSX...PAH...SGF...

ATTN...RFC...ABRFC...LMRFC...MBRFC...NCRFC...OHRFC...

LAT...LON   40118728 39828611 39098578 38578709 37918944 
            37139114 36579218 36529376 36969451 37729393 
            38849204 39649001 40018877