FXUS63 KDMX 231225
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
625 AM CST WED DEC 23 2009
...PRODIGIOUS WINTER STORM TO HAVE PROLONGED EFFECT ON IOWA...
.SHORT TERM.../TODAY AND TONIGHT/
ALTHOUGH PRIMARY SYSTEM SHORT WAVES ARE STILL ROTATING THROUGH THE
BASE OF THE TROUGH INTO AZ AND NM...AND ALSO DIVING DOWN BACK SIDE
OF TROUGH FROM ALBERTA INTO MT...BEGINNING AREA OF PRECIP IS ALREADY
LIFTING ACROSS KS...MO AND IL WITH INITIAL SHORT WAVE LOBE. PRECIP
IS ASSOCIATED WITH DEEP KINEMATIC AND THERMODYNAMIC FORCING
INCLUDING THUNDER WITH SEVERAL HUNDRED MUCAPES PUSHING INTO KS AND
MO. MOST MODELS...INCLUDING 4KM NMM WRF...HAVE THIS PRECIP DEPICTED
QUITE WELL LIFTING INTO CENTRAL IA BY MIDDAY AND NRN IA DURING THE
AFTERNOON. THIS UVM IS REFLECTED QUITE WELL BY 290-300K ISENT
LAYERS AND SUGGESTS MODERATE PRECIP SHOULD CONTINUE THROUGH AT LEAST
MIDNIGHT WITH STEADY STREAM OF MOISTURE TRANSPORT AND LIFT.
VARIOUS P-TYPE TECHNIQUES SUGGEST FREEZING DRIZZLE THIS MORNING WITH
MORE SHALLOW MOISTURE UNTIL UPSTREAM CONVECTION ARRIVES...FOLLOWED
BY TRANSITION TO WINTRY MIX AND THEN JUST PLAIN OLE RAIN AND
POSSIBLY THUNDER SOUTH DURING THE LATE AFTERNOON AND EARLY EVENING
HOURS. HAVE SWITCHED FREEZING RAIN ADVY TO WINTER WX ADVY TO
ACCOUNT FOR MIXED PRECIP TYPES AND ALSO BLEND BETTER INTO ADJACENT
WFOS. SNOW RATIOS SHOULD BE FAIRLY TYPICAL 10-13 TO 1 BUT WITH NRN
IA GOING ALL SNOW FOR AROUND SIX HOURS...SNOW AMOUNTS MAY REACH 3-5
INCHES BY 12Z THU. ICE ACCUMS MAY BE SEVERAL TENTHS AS WELL...WITH
MORE SIGNIFICANT ACCUMS ALONG HIGHWAY 20/HIGHWAY 30 CORRIDOR.
ALTHOUGH IT MAY NOT TECHNICALLY REACH WARNING CRITERIA BY
TONIGHT...FELT IT BEST TO TRY AND KEEP IT SIMPLE STARTING PROLONGED
WINTER STORM WARNING IN NRN PORTIONS WHICH WILL RECEIVE THE BRUNT OF
THE ENTIRE STORM.
BLEND OF ALL AVAILABLE FORECAST SOUNDINGS WORKED WELL
YESTERDAY...AND SIMILAR CLUSTER SUGGESTS WARMING TO NEAR GFS MOS
TODAY...AND THEN STEADY OR SLOWLY RISING OVERNIGHT WITH MINS A
CATEGORY OR TWO ABOVE EVEN THE WARMEST GUIDANCE.
.LONG TERM /THURSDAY THROUGH SUNDAY/...FORECAST REMAINS FOCUSED ON
MAJOR WINTER STORM THROUGH SATURDAY. MODELS HAVE BEEN IN DECENT
AGREEMENT WITH HOW THIS SYSTEM WANTS TO PLAY OUT...BUT STILL SOME
DISCREPANCIES WITH THERMAL PROFILES AND PRECIPITATION TYPE MAKING FOR
A COMPLEX FORECAST THROUGH CHRISTMAS EVE. MODELS IN AGREEMENT WITH
THE CHANGE OVER TO ALL SNOW BY 12Z FRIDAY. WENT WITH A BLEND OF THE
GFS/NAM/SREF THROUGH THURSDAY NIGHT...THEN GFS/NAM FOR FRIDAY.
UPPER LOW DEVELOPING OVER THE FAR SOUTHERN ROCKIES WITH PUSH ACROSS
THE SOUTHERN PLAINS INTO MISSOURI BY THURSDAY NIGHT...THEN MERGES
WITH A SECOND UPPER LOW MOVING IN FROM CANADA BY FRIDAY. THE LOW
BECOMES VERTICALLY STACKED BY FRIDAY AND STALLS ACROSS THE CENTRAL
PORTION OF THE STATE. THE LOW SLOWLY SHIFTS EAST FRIDAY NIGHT INTO
SATURDAY AND FINALLY PUSHES INTO THE GREAT LAKES REGION BY
SATURDAY NIGHT.
THE 600MB EQUIVALENT POTENTIAL TEMPERATURE SHOWING THREE SEPARATE
OCCASIONS OF A TROWAL DEVELOPING AND MOVING ACROSS THE AREA FROM
THIS AFTERNOON THROUGH FRIDAY. ONE TODAY...THEN A SECOND TROWAL
ANTICIPATED BY EARLY THURSDAY MORNING WITH A MORE SIGNIFICANT
FINAL TROWAL OVERNIGHT THURSDAY NIGHT INTO FRIDAY MORNING...WHICH
EXTENDS AS FAR NORTH AS THE CANADIAN BORDER. THIS WILL PLAY A ROLE
IN THE TEMPERATURES ACROSS THE STATE...WITH WARMER TEMPERATURES TO
THE NORTHEAST AND COOLER TO THE SOUTHWEST. THE ALO AREA LOOKS TO
BE PRIMED FOR SIGNIFICANT ICE EVENT WITH THE BUFR SOUNDINGS
WOBBLING BACK AND FORTH FROM SNOW...SLEET...AND FZRA THURSDAY
MORNING INTO EARLY FRIDAY MORNING. THESE TROWAL FEATURES MATCH UP
VERY WELL WITH THE STRONGEST ISENTROPIC LIFT AND DEEP COLUMN OF
MOISTURE AND THETA-E ADVECTION.
THE BUFKIT SOUNDINGS/CROSS SECTIONS OVER THE WESTERN AND NORTHERN
PORTIONS OF THE CWA ARE DEPICTING SNOW LASTING THROUGH SATURDAY
MORNING...WITH THREE SEPARATE TIME FRAMES MENTIONED ABOVE...THE
MAX OMEGA WITHIN THE DENDRITIC LAYER IS PROLIFIC. FN VECTOR
DIVERGENCE AND 2D FRONTOGENESIS INTENSIFY BY 12Z FRIDAY AND
CONTINUE TO STRENGTHEN THROUGHOUT THE DAY FRIDAY INTO FRIDAY
EVENING. WITH THE NORTHWEST LOOKING TO BE ALL SNOW THROUGH MUCH OF
THE EVENT...WITH A MIX EXPECTED TONIGHT INTO THURSDAY MORNING...IS
LIKELY TO SEE A SIGNIFICANT AMOUNT OF SNOWFALL. INCREASED TOTALS
TO NEARLY A FOOT AND HALF BY EST...AND AROUND A FOOT ALONG AND
NORTHWEST OF A LINE FROM MCW TO CRL/DNS. THE 00Z NAM CRL BUFKIT
SOUNDING SHOWED OVER 30 INCHES OF TOTAL SNOWFALL USING THE ZONE
OMEGA SNOW RATIO TECHNIQUE. THOUGHT THIS WAS A LITTLE TOO
EXCESSIVE WITH THE AMOUNT OF WARM AIR BEING ADVECTED IN THE MID
LEVELS TONIGHT INTO TOMORROW MORNING LEADING TO THE SLEET/SNOW
MIX. BOTH THE NAM/GFS COBB OUTPUT HAVE BEEN FAIRLY CONSISTENT
THE PAST COUPLE OF MODEL RUNS WITH THE AMOUNT OF SNOW ACROSS THE
WEST AND NORTH.
BY FRIDAY...THE STRONG UPPER LOW TIGHTENS RAPIDLY AND SLOWLY
SHIFTS TO THE EAST. WINDS ARE GOING TO CAUSE SOME LOW
VISIBILITY...EVEN NEAR BLIZZARD CONDITIONS WITH THE SNOW RATIOS
INCREASING THROUGHOUT THE DAY. THIS WILL BE ESPECIALLY DANGEROUS
ACROSS THE WESTERN AND NORTHERN PORTIONS OF THE CWA. CONFIDENCE
IS LOW WITH THE REST OF THE CWA RECEIVING BLIZZARDS CONDITIONS AS
UNCERTAIN HOW FAR EAST THE LOW WILL TRACK ON FRIDAY.
&&
.AVIATION...
23/12Z...HAVE HIGH CONFIDENCE THAT IFR/LIFR CONDITIONS WILL REMAIN
SOCKED INTO ALL TAFS SITES THROUGH DURATION OF THE VALID PERIOD.
FOD/MCW/ALO WILL SEE FREEZING OR FROZEN PRECIP TODAY AND TONIGHT...
AND COULD SEE AT LEAST MODERATE ICE AND SNOW ACCUMULATIONS LATER
THIS AFTERNOON AND EVENING. HOWEVER KDSM/KOTM SHOULD TRANSITION TO
ALL LIQUID BY THIS AFTERNOON. THUNDER IS PRESENTLY OCCURRING OVER
PARTS OF KS AND MO...AND COULD VERY WELL REACH THESE TAF SITES.
TIMING AND DURATION CONFIDENCE LOW HOWEVER...SO FOR THE TIME BEING
HAVE ONLY MENTIONED CB AT KOTM.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER WX ADVY TIL 21Z ALL BUT FAR SRN COUNTIES
WINTER WX ADVY KAIO/KADU/KDSM/KAMW/KMIW/KALO AREAS 21Z TIL 06Z
WINTER STORM WARNING ALONG AND N OF KCIN/KEBS/KOLZ LINE 21Z TIL 06Z SAT
WINTER STORM WATCH SWRN IA...THROUGH CENTRAL IA...TO NERN IA 18Z THU
TO 06Z SAT
&&
$$
SHORT TERM...SMALL
AVIATION...SMALL
LONG TERM...PODRAZIK
