SWOMCD
SPC MCD 241155
MTZ000-241630-
MESOSCALE DISCUSSION 0144
NWS STORM PREDICTION CENTER NORMAN OK
0555 AM CST TUE FEB 24 2009
AREAS AFFECTED...PORTIONS CENTRAL/ERN MT.
CONCERNING...FREEZING RAIN
VALID 241155Z - 241630Z
PATCHY AREAS OF FREEZING RAIN...CONTAINING LOCALIZED RATES AROUND
.05 INCH/HOUR...MAY SHIFT GENERALLY W-E ACROSS THIS AREA THROUGH
MID-MORNING LOCAL TIME...OR ABOUT 15-16Z.
UPPER LOW -- HAVING MOVED ONSHORE WA COAST DURING PAST FEW HOURS --
IS FCST TO DEAMPLIFY INTO OPEN-WAVE TROUGH AND PIVOT ENEWD-EWD
ACROSS ID PANHANDLE REGION THROUGH 18Z. AT SFC...11Z ANALYSIS SHOWS
LOW OVER CENTRAL MT VICINITY LWT...WHICH IS FCST TO PROPAGATE SEWD
ALONG WAVY/QUASISTATIONARY FRONTAL ZONE THAT EXTENDS SEWD ACROSS
CARTER COUNTY. FREEZING LINE WAS ANALYZED JUST N OF THAT
FRONT...AND SHOULD MOVE ONLY IN LOCALIZED/WAVY FASHION AS WAA AND
WET BULB EFFECTS FROM PRECIP ACT AS THERMAL COUNTERBALANCES. FCST
SOUNDINGS SUGGEST SUFFICIENTLY DEEP WARM LAYER -- ABOVE SHALLOW AIR
MASS N OF WARM FRONT -- TO SUPPORT MELTING OF PRECIP GENERATED AS
SNOW ALOFT. FREEZING RAIN SHOULD TRANSITION TO LIGHT SNOW INVOF NRN
FRINGES OF DISCUSSION AREA WHERE WARM LAYER BECOMES WEAKER AND
SHALLOWER TO NONEXISTENT.
PRIND PRECIP COVERAGE WILL INCREASE WITH TIME N OF FREEZING LINE AS
STRENGTHENING LARGE SCALE ASCENT/DESTABILIZATION OCCURS IN ADVANCE
OF UPPER TROUGH. THIS INCLUDES BOTH DPVA ALOFT...AND ISENTROPIC
ASCENT IN 297-300K LAYER ACCOMPANYING ELEVATED LOW LEVEL WAA REGIME.
ASSOCIATED STEEPENING OF LAPSE RATES MAY SUPPORT
EMBEDDED/CONVECTIVE PRECIP THAT COULD BOOST RATES ON VERY
SHORT-LIVED/LOCALIZED BASIS TO AROUND .1 INCH/HOUR. WHILE
BRIEF/ISOLATED THUNDER CANNOT BE RULED OUT...PER DAY-1 CONVECTIVE
OUTLOOK...MOST AREAS APPEAR MRGL FOR AOA .05 INCH/HOUR RATES AND
OVERALL THUNDER PROBABILITIES ARE VERY SMALL. MAIN FACTOR
PREVENTING HEAVIER RATES WILL BE LACK OF MORE ROBUST MOISTURE ABOVE
SFC...IN LEE OF NRN ROCKIES.
..EDWARDS.. 02/24/2009
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
...NOTICE...
SPC WINTER WEATHER MESOSCALE DISCUSSIONS WILL BE ISSUED ON A
SCHEDULED BASIS FROM DECEMBER 1 THROUGH FEBRUARY 28...FOUR
TIMES A DAY...AROUND 00 UTC...06 UTC...12 UTC...AND 18 UTC
FOR SIGNIFICANT SHORT RANGE WINTER WEATHER EVENTS.
ATTN...WFO...BYZ...GGW...TFX...
LAT...LON 46510553 46410591 46520845 47460897 47610937 47151027
47171121 47531139 47851112 48550966 48580819 48410708
48070542 47740477 47290424 46610454 46510553
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