[LeArc] Forecast Discussion : MLI@ 11/24/02 3:08:49 AM

[learc@mailman.qth.net]

The following weather message is provided by McDonough County E.S.D.A.


FXUS63 KDVN 240921
AFDMLI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
315 AM CST SUN NOV 24 2002

SD VORT...SEEN ON W/V IMAGERY...WILL SHEAR DOWN ACRS WEST IA THROUGH
18Z TODAY...CREATING NICE SURGE OF CVA FURTHER TO THE EAST ACRS THE
DVN CWA THIS AFTERNOON. CVA TO BECOME CHANNELED AND THUS A NON
FACTOR AFTER 02Z MON OR SO...BUT SNOW/LIGHT SNOW EVENT TO TAKE
PLACE BEFORE THEN. ABOVE MENTIONED FEATURE WILL OVERRIDE INCOMING
LLVL BAROCLINICITY ON EDGE OF ARCTIC COLD SURGE TODAY...AND INHERENT
LIFT...AUGMENTED BY STRONG UPPER LEVEL DIFFLUENCE OFF RIGHT REAR OF
120 KT GRT LKS STREAKING H3 JET...WILL PROVIDE DEEP BUT RELATIVELY
SHORT LIVED UVV SURGE FROM WEST TO EAST...MAINLY FROM 18Z SUN-00Z
MON. MUCH OF INITIAL LIFT OF COURSE...TO GO INTO LOW TO MID LEVEL
SATURATION THIS MORNING...WITH DEEPER LEVEL RH'S AND POS OMEGA
SURGE NOT COINCIDING TIL THIS AFTERNOON. LATEST VORT/CVA
EXTRAPOLATION ACRS THE CWA...AND LOOKING AT BOTH GFS AND ETA 290 K
COND P-DEFS LOWERING TO PRECIP-TO-SFC VALUES...BEGINS MAIN SNOW
SHOW IN WESTERN ZONES JUST AFTER 18Z...AND EAST OF THE MS RVR
PROBABLY NOT TIL LATE AFTERNOON. FLURRIES MAY GET SQUEEZED OUT OF
MID DECK ACRS THE WEST BY MID MORNING...BUT MAY NOT BE WORTH
MENTIONING.

ISENTROPIC LIFT...LOOKING AT 290 K SFCS...WEAK AND NEAR PARALLEL
ON BOTH THE GFS AND ETA FOR A RATHER SHORT PERIOD OF TIME(4-6 HRS)...
THUS NOT TOO IMPRESSIVE. MOISTURE AVAILABILITY FOR LIFT TO WORK
WITH...AFTER DEEP COLUMN SATURATION...AT QUESTION AS WELL AND WILL
BE RATHER SHORT LIVED AS NORTH-NORTHWEST FLOW DEEPENS FROM SFC ON UP
BY THIS EVENING. GETTING TO THE POINT...AFTER LOOKING AT OTHER SNOW
PRODUCING PARAMETERS FROM THE THREE SHORT RANGE MODELS SUCH AS
LIFTING AND FORCING MECHANISMS/LMRH'S/UVVS/THICKNESSES...SUGGEST IN
GENERAL NORTHERN THIRD OF DVN CWA TO RECEIVE UP TO AN INCH BY EARLY
THIS EVENING...CENTRAL THIRD 1-2 INCHES...AND FAR SOUTHERN TWO TIER
OF COUNTIES 1-1.5 INCHES. AGREE WITH ILX THAT FAR SOUTH SNOW AMOUNTS
WILL BE SOMEWHAT LIMITED DUE TO STILL RATHER WARM GROUND EATING AT
INITIAL SNOW IMPACT ON SFC...AS WELL AS SOME MIX POTENTIAL AT PRECIP
ONSET BEFORE EVAPORATIVE AND DYNAMIC COOLING HAVE THEIR EFFECT. AM
BIT CONCERNED THAT IF PVA ADVECTION BY H7-H4 THERMAL WIND CLOSE OR
JUST SURPASSES WHAT THE ETA/META SUGGESTS...COULD BE NARROW RIBBON
OF 3 INCH POTENTIAL FROM JUST SOUTHWEST OF MUSCATINE...TO PRINCETON
IL. LACK OF MORE WIDESPREAD 2-3 INCH POTENTIAL HAS MADE ME SHY AWAY
FROM WINTER WX ADVISORY HEADLINES FOR THE CENTRAL CWA...ALTHOUGH
FIRST REAL SNOW EVENT OF SEASON HAS ITS REASONS FOR AN ADVISORY AS
WELL EVEN WITH LIGHT AMOUNTS. MAIN ACCUMULATING SNOWS SHOULD END
WEST OF THE MS RIVER BY 00Z...AND EAST OF THE RIVER BY 02-03Z.

QUICK LOOK AT LATER PERIODS SHOW THAT GFS AND ETA HAVE THEIR TIMING
AND PLACEMENT DIFFERENCES ON NEXT DIGGING VORT INTO CENTRAL PLAINS
MONDAY NIGHT...WITH BULK OF LIFT AND SATURATION NOW KEEPING PRECIP
WEST OF THE CWA UNTIL TUE...EVEN ON FURTHEST EAST MODEL(ETA). WILL
TONE DOWN MONDAY NIGHT SNOW CHANCES...AND MAY REMOVE FROM EASTERN
ZONE GROUPS.

COORDINATED WITH ILX...DMX...THANX!


.DVN...
IA...NONE.
IL...NONE.
MO...NONE.

12