000
FOUS11 KWBC 200837
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
436 AM EDT SAT MAR 20 2010
VALID 12Z SAT MAR 20 2010 - 12Z TUE MAR 23 2010
DAY 1...
...CNTRL/SRN PLAINS INTO THE MID MS VLY...
A SIGNIFICANT WINTER STORM WILL BE EVOLVE OUT OVER THE CNTRL U.S.
THIS PD AS SHRTWV ENERGY NOW EJECTING OUT OF THE SRN ROCKIES WILL
BE AMPLIFYING INTO A STG CLSD LOW OVER N TX BY LATE SAT BEFORE
REACHING EWD TO THE LWR MS VLY EARLY SUN. THIS WILL BE FOSTER SFC
LOW PRESSURE DEVELOPMENT NEAR THE ARKLATEX REGION WHICH SHOULD
SLOWLY TRACK ENEWD INTO CNTRL/ERN AR BY SUN MORNING. THE LATEST
MODELS ARE IN BETTER AGREEMENT ABOUT A SOLN A LITTLE MORE
SUPPRESSED THAN PREV FORECAST CYCLES...WITH THE GENERAL PREFERENCE
TWD A NON-GFS CONSENSUS LED BY THE NAM/ECMWF SOLNS. IN ANY
EVENT...RAPIDLY COOLING THERMAL COLUMNS ASSOC WITH THE HEIGHT
FALLS COUPLED WITH STG POST-FRONTAL LOW LVL COLD AIR ADVECTION
WILL SET THE STAGE FOR A HVY SNOWFALL EVENT BEGINNING EARLY
SAT...AND CONTINUING INTO SAT NIGHT AND EARLY SUN ALONG A CORRIDOR
FROM CNTRL/ERN OK NEWD INTO SERN KS AND WRN MO AS THE STORM
INTENSIFIES COMING OUT OF THE ARKLATEX REGION. INCREASING MOISTURE
TRANSPORT FROM THE GULF OF MEXICO AND STG DYNAMIC COOLING WITHIN
THE DEVELOPING COMMA-HEAD IS EXPECTED TO GENERATE AN AXIS OF
LOCALLY VERY HVY SNOWFALL RATES. WARM GROUND CONDITIONS ACROSS THE
PLAINS/MIDWEST WILL INITIALLY RESULT IN SUBSTANTIAL MELTING...BUT
HVY SNOWFALL RATES AND SUFFICIENT LOW LVL COLD AIR ADVECTION NW OF
THE SFC LOW TRACK SHOULD SUPPORT SIGNIFICANT ACCUMS. A BROAD AXIS
OF 4 TO 8 INCH SNOWFALL AMTS IS EXPECTED...BUT LOCALIZED SNOWFALL
AMTS IN EXCESS OF 1 FOOT ARE POSSIBLE INVOF THE COMMA-HEAD. THE
SNOW SHOULD EXTEND AS FAR SOUTH AS NRN/NERN TX INVOF THE RED RIVER
VLY AS THE UPPER LOW PASSES OVER THE AREA LATE SAT. ANOTHER
POTENTIAL CONCERN...WITH LIMITED CONFIDENCE...IS THE THREAT OF
ICING SAT NIGHT OVER THE HIGHER TERRAIN OF THE OZARKS AND ADJACENT
FOOTHILLS INVOLVING SWRN MO...WHERE MDL THERMAL PROFILES INSIST ON
SFC TEMPS DROPPING SEVERAL DEGREES BELOW FREEZING AS A WARM LAYER
ALOFT WRAPS NWD AROUND THE DEEPENING LOW CENTER. EXPECTING A
NARROW AXIS OF SLEET/FREEZING RAIN INVOLVING THIS REGION...WITH
ANY SIGNIFICANT ICING EXPECTED TO BE ON ELEVATED SURFACES OFF THE
WARMER GROUND AND ESP OVER AREAS OF HIGHER TERRAIN.
DAYS 2 AND 3...
...ERN OK/SWRN MO/NWRN AR...
THE PROXIMITY EARLY SUN OF THE SLOWLY DEPARTING MID/UPR LVL CLSD
LOW CENTER ADVANCING ACRS THE LWR MS VLY WILL SUPPORT A LINGERING
DEFORMATION ZONE/COMMA-HEAD ACROSS MUCH OF ERN OK/NRN AR AND SRN
MO. MDT TO HVY PCPN...IS LIKELY ON SUN BEFORE IT TAPERS OFF...BUT
THE QUESTION IS HOW MUCH COLD AIR WILL STILL BE ASSOC WITH THIS
STORM SYS. THE LATEST GLOBAL MDLS SUGGEST A STEADILY MODERATING
BNDRY LAYER BEGINNING EARLY SUN AND CONTINUING THROUGHOUT THE
DAY...AND WITH NOT NEARLY AS MUCH DYNAMIC COOLING ALOFT. THIS
WOULD SUPPORT MANY AREAS THAT WERE SEEING SNOW TO SEE A MIX WITH
OR CHANGEOVER BACK TO RAIN. MUCH OF THE ACCUM SNOWFALL THREAT IS
EXPECTED TO BE EARLY SUN...WITH SOME POTENTIAL FOR A FEW MORE
INCHES LOCALLY IN THE COMMA-HEAD ALONG THE OK/AR BORDER AND NEAR
THE OZARKS WHERE ELEVATION WILL BE OF NOTE.
...PAC NW/NRN ROCKIES...
A PACIFIC UPPER TROUGH AND AN ASSOC COLD FRONT WILL PUSH STEADILY
INTO THE NWRN U.S. SUN NIGHT...REACHING THE NRN ROCKIES BY MONDAY
BEFORE GRADUALLY DIGGING SEWD TWD THE CNTRL ROCKIES BY EARLY TUE.
POST-FRONTAL UPSLOPE FLOW AND AN INFLUX OF PAC MOISTURE SHOULD
RESULT IN NUMEROUS SNOW SHOWERS FROM THE HIGHER TERRAIN FROM THE
WA/OR CASCADES TO THE MTNS OF ID AND NWRN MT...AND SPILLING INTO
NWRN WY BY EARLY TUE. LOW TO MDT RISKS FOR 4 INCH PLUS AMTS ARE
INDICATED ATTM.
THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.
ORRISON
$$
