FXUS63 KDMX 070923
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
323 AM CST MON DEC 7 2009
...DANGEROUS WINTER STORM STILL ON TRACK FOR TUESDAY AND WEDNESDAY...
.SHORT TERM /TONIGHT THROUGH MONDAY/...
FIRST ROUND OF WINTER WX IS ON THE WANE ACROSS OUR CWA. WSR-88D
REFLECTIVITY AND SURFACE OBS INDICATE THE -SN HAS DECREASING IN
INTENSITY AND COVERAGE...WITH SURFACE VSBYS ACROSS THE NORTHWEST
3/4THS OF THE CWA AOB 6SM. WENT AHEAD AND CANCELED THE WINTER WX
ADVISORY EARLY DUE TO THIS FACT. ALTHOUGH THE -SN IS WINDING
DOWN...PAVEMENT AND WALKING SURFACES WILL REMAIN SLICK FOR AT LEAST
THE NEXT FEW HOURS...THOUGH...SO THE MORNING COMMUTE WILL BE SLOWER
THAN NORMAL IN SOME AREAS.
NORTHERLY TO NORTHWESTERLY WINDS WILL PREVAIL TODAY AS THE SURFACE
WX SYSTEM DEPARTS OUR REGION...AND A SURFACE PRESSURE RIDGE BUILDS
IN. DECREASE IN CLOUDS WILL BE MINIMAL THOUGH...AS CLOUDINESS FROM
THE NEXT WX SYSTEM SPREADS IN THIS AFTERNOON.
.LONG TERM /TONIGHT THROUGH SUNDAY/...
ALL EYES WILL BE ON INTENSE WINTER STORM SET TO AFFECT MUCH OF THE
REGION LATE TONIGHT INTO WEDNESDAY. WILL SEE WAA BEGIN TONIGHT IN
RESPONSE TO THE DEEPENING WESTERN SYSTEM. ISENTROPIC LIFT INCREASES
DURING THE OVERNIGHT ALONG WITH SOME WEAK QG FORCING. MAY BEGIN TO
SEE A FEW FLAKES BEFORE MIDNIGHT IN OUR SOUTHWEST WHERE EARLIEST
SATURATION OCCURS. AS FORCING CONTINUES THROUGH THE NIGHT...WL SEE
SNOW SPREAD ACROSS THE SOUTHERN HALF TO TWO-THIRDS OF THE STATE BY
DAYBREAK TUESDAY. HAVE INCREASED POPS TO CATEGORICAL IN THE SOUTH
WITH UP TO AN INCH OF NEW SNOWFALL SOUTH OF I80 BY TUESDAY MORNING.
THE LIGHTER SNOW PERSIST INTO TUESDAY MORNING AND SPREADS NORTHWARD
ACRS THE ENTIRE CWA AS ISENTROPIC LIFT PERSISTS. HOWEVER...MUCH
STRONG Q-G FORCING ARRIVES ON TUESDAY AFTERNOON AS SFC LOW RACES
ACRS SOUTHERN KS. SNOWFALL RATES ARE FORECAST TO INTENSIFY THROUGH
THE AFTERNOON WITH MODERATE TO HEAVY SNOW...ESPECIALLY SOUTH OF
HIGHWAY 20 WITH GOOD DENDRITIC GROWTH. THE STRONG FORCING AND HEAVIER
PCPN WILL CONTINUE INTO TUESDAY EVENING BEFORE THE BULK OF FORCING
SHIFTS TO THE EAST BY WEDNESDAY MORNING. THEREFORE...CONDITIONS ARE
EXPECTED TO DETERIORATE RAPIDLY BY TUESDAY AFTERNOON AND EVENING DUE
TO HEAVY SNOWFALL AND FAST ACCUMULATIONS. TOTAL ACCUMULATIONS BY
WEDNESDAY MORNING ARE GENERALLY 9 TO 12 INCHES ACROSS ALMOST THE
ENTIRE FORECAST AREA AND THERE WILL LIKELY BE AREAS WHICH RECEIVE
MORE THAN A FOOT. HOWEVER...THIS SNOW IS JUST THE FIRST PART OF THE
SYSTEM. AS THE STORMS PULLS TO THE EAST THE DEEPENING UPPER SYSTEM
BECOMES NEGATIVELY TILTED. SFC LOW PRES OF 980MB IS REACHED BY 12Z
ON WEDNESDAY NEAR THE SOUTHERN END OF LAKE MICHIGAN. THE PRESSURE
GRADIENT TIGHTENS QUICKLY AFTER 06Z WEDNESDAY WITH EURO STILL
INDICATING 50KTS+ AT 925MB WITH NAM/GFS SLIGHTLY WEAKER. MIXED
LAYER WINDS ON THE GFS ARE AROUND 40-45KTS BY 12Z WEDNESDAY AND IT
APPEARS SFC WIND GUSTS TO 45 MPH WILL BE POSSIBLE. CERTAINLY WITH
THE AMOUNT OF SNOW ON THE GROUND AVAILABLE FOR TRANSPORT...BLOWING
AND DRIFTING SNOW WILL BECOME PROBLEMATIC. NEAR WHITEOUT CONDITIONS
ARE LIKELY BY DAYBREAK WEDNESDAY WITH TRAVEL DIFFICULT IF NOT NEAR
IMPOSSIBLE BY THEN. THE WINDS WILL BE STRONGEST THROUGH WEDNESDAY
MORNING BUT SHOULD SLOWLY SUBSIDE DURING THE AFTERNOON AS THE SYSTEM
PULLS RAPIDLY INTO THE UPPER GREAT LAKES REGION. AS FOR
HEADLINES...WL LEAVE THE WINTER STORM WATCH IN PLACE AS IT CURRENTLY
STANDS. WL LIKELY SEE A WARNING BY THIS AFTERNOON AND POSSIBLY A
BLIZZARD WATCH ISSUED FOR LATE TUESDAY NIGHT INTO WEDNESDAY FOR THE
WINDY PORTION OF THE STORM. HAVE DONE LITTLE IF ANY MODIFICATION TO
THE FORECAST BEYOND WEDNESDAY NIGHT.
&&
.AVIATION...
07/06Z...BASED ON OBS IT LOOKS AS THOUGH THE WORST IS OVER. VSBYS
DOWNSTREAM IN THE 2-3SM RANGE AND HIGHER REFLECTIVITIES ON RADAR ARE
NOW SHRINKING. NEW MODEL GUIDANCE STILL SHOWING OMEGA QUICKLY ON
THE DECLINE OVER THE NEXT HOUR OR SO AND CLOUD TOPS ARE WARMING THUS
THE SNOW SHOULD BE TAPERING OFF FM W TO E. MVFR/LCL IFR CIGS SHOULD
PREVAIL OVERNIGHT AND THERE MAY BE SOME AREAS OF FOG AFTER THE SNOW
WHICH MAY LOWER VSBYS SOME. AFTER 08/00Z CLOUDS LOWER AHEAD OF THE
BIG SYSTEM BUT PRECIP SHOULD HOLD OFF UNTIL AFTER THE VALID PERIOD
OF THIS SET OF TAFS. SFC FLOW THROUGH 08/00Z WILL BE NRLY AT
10-20KTS.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM LATE MONDAY NIGHT THROUGH WEDNESDAY
AFTERNOON FOR ADAIR-ADAMS-APPANOOSE-AUDUBON-BLACK HAWK-BOONE-BREMER-
BUTLER-CALHOUN-CARROLL-CASS-CERRO GORDO-CLARKE-CRAWFORD-DALLAS-
DAVIS-DECATUR-EMMET-FRANKLIN-GREENE-GRUNDY-GUTHRIE-HAMILTON-
HANCOCK-HARDIN-HUMBOLDT-JASPER-KOSSUTH-LUCAS-MADISON-MAHASKA-
MARION-MARSHALL-MONROE-PALO ALTO-POCAHONTAS-POLK-POWESHIEK-
RINGGOLD-SAC-STORY-TAMA-TAYLOR-UNION-WAPELLO-WARREN-WAYNE-
WEBSTER-WINNEBAGO-WORTH-WRIGHT.
&&
$$
SHORT TERM...ZOGG
AVIATION...FAB
LONG TERM...COGIL
