FXUS63 KDMX 081745 AAB
AFDDMX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
1145 AM CST TUE DEC 8 2009
...EXTREMELY DANGEROUS WINTER STORM STILL ON TRACK FOR TODAY THROUGH
WEDNESDAY...
.SHORT TERM /TODAY/...
BROAD AREA OF WAA SNOWS HAVE SPREAD ACRS THE ALMOST THE ENTIRE CWA
EARLY THIS MORNING WITH VIGOROUS SHORTWAVE JUST ROUNDING BASE OF
TROF IN WESTERN ARIZONA. MODELS HAVE BEEN INDICATING THIS FIRST
AREA OF SNOWFALL WILL DIMINISH SOME IN INTENSITY THROUGH MID
MORNING. HOWEVER...FORCING ASSOCIATED WITH MAIN UPPER SYSTEM WILL
FOLLOW QUICKLY ON THE HEALS OF THIS INITIAL SNOW AND EXPECT THE SNOW
TO REINTENSIFY STARTING MIDDAY IN FAR SOUTHWEST AREA AND SPREADING
NORTHEAST DURING THE AFTERNOON. Q-G CONVERGENCE BECOMES QUITE
IMPRESSIVE BY LATE IN THE PERIOD...ESPECIALLY IN WESTERN IA AND WL
LIKELY SEE SNOWFALL RATES OF 1 TO 2 INCHES PER HOUR BY LATE
AFTERNOON/EARLY EVENING IN MUCH OF THE SOUTHERN HALF/TWO-THIRDS OF
THE CWA. ANY CONVECTIVE SNOWFALL WOULD APPEAR TOWARD THE END OF THE
PERIOD POSSIBLY IN THE FAR SOUTH. AT THIS POINT...WINDS WILL NOT BE
A BIG PLAYER IN TODAYS PERIOD ALTHOUGH A GENERAL INCREASE WILL BE
SEEN THROUGH THE DAY AS PRESSURE GRADIENT GRADUALLY TIGHTENS.
HEAVIEST SNOWFALL WILL BE IN THE SOUTHWEST WHERE A NEW 5 TO 7 INCHES
MAY BE SEEN BY SUNSET. EVENING RUSH WILL BE QUITE DIFFICULT AS
INCREASING SNOW INTENSITIES IN CENTRAL IOWA WILL COINCIDE WITH THOSE
LATE AFTERNOON HOURS.
.LONG TERM /TONIGHT THROUGH MONDAY/...
MODELS ARE IN VERY GOOD AGREEMENT ON MOST OF THE FEATURES FOR
TONIGHT THROUGH WEDNESDAY. MAIN EVENT NOW OVER NORTHERN CALIFORNIA
AND NEVADA WILL BE HEADING EAST AND HELP TO RAPIDLY DEEPEN THE SFC
LOW OVER EASTERN COLORADO. WITH RAPID DEEPENING OF LOW...FAVORED
H850 CLOSED LOW TRACKING OVER EXTREME SOUTHEAST IA THIS EVENING...
ALL FACTORS POINTING AT BLIZZARD CONDITIONS TO DEVELOP LATE TNT AND
MOST OF WEDNESDAY MORNING FOR A GOOD SHARE OF THE AREA. WITH SNOW
ONGOING THIS EVENING AND EXPECTED TO REALLY PICK UP IN INTENSITY
BETWEEN 00Z AND 09Z TNT OVER THE EAST HALF OF THE FORECAST AREA.
DYNAMICS IMPRESSIVE WITH STRONG MOISTURE TRANSPORT INTO A RATHER
STRONG AND DISTINCT H700 FRONTAL ZONE WHICH STRENGTHENS THIS EVENING
ALONG A LINE FROM NEAR OSKALOOSA NORTHEAST TOWARD WATERLOO/DUBUQUE
DURING THE OVERNIGHT HOURS. 650-600MB QVECTOR CONVERGENCE IS VERY
STRONG TNT AND WILL CONTINUE ALL NIGHT FROM SW TO NORTHEAST. EPV
ANALYSIS AT 650-600MB SHOWS AN AREA OF NEGATIVE EPV DEVELOPING BY
EARLY EVENING SOUTHEAST AND EXTENDING OVER THE EASTERN COUNTIES
THROUGH MIDNIGHT IN THE SAME AREA. HAVE ADDED ISO THUNDER ACROSS
THIS AREA AND RAISED SNOWFALL TOTALS TO 14 TO 16 INCHES OVER THIS
AREA WHICH INCLUDES MOST OF THE FORECAST AREA EAST OF INTERSTATE 80.
SNOWFALL RATES SHOULD REACH 1 TO 2 INCHES PER HOUR FOR SEVERAL HOURS
OVER THE EAST THIS EVENING. TIME HEIGHT CROSS SECTION AT KOTM SHOWS
A NEARLY 200MB DEEP DENDRITIC LAYER AT THE HEIGHT OF THE EVENT FROM
18Z TODAY THROUGH NEARLY 06Z TNT. PHENOMENAL. AS PROGGED FOR SEVERAL
DAYS NOW... WINDS WILL BE INCREASING DRAMATICALLY AFTER 06Z FROM
WEST TO EAST DURING THE NIGHT. QUICKLY BETWEEN 06 AND 12Z WINDS WILL
REACH 30 TO 35 MPH WITH GUSTS TO 45 TO 50 MPH BY 12Z. BUFKIT
SOUNDING SHOW A SHALLOW INVERSION WITH NEAR ADIABATIC SOUNDING INTO
THE MORNING HOURS...WITH TOP OF BOUNDARY LAYER WINDS TO 45KT. WINDS
WILL BE GUSTING TO 40 MPH WEST BY MIDNIGHT...37 TO 45 MPH WEST OF
I80 BY 3 AM CDT...AND 45 TO 50 MPH OVER MUCH OF THE AREA FROM 6AM
CDT THROUGH NOON. TROWAL ALSO LINGERS ACROSS THE EAST FOR WEDNESDAY
MORNING THOUGH THE LIFT WILL BE ON THE DECREASE DURING THE MORNING
HOURS. PRECIP WILL BE ON THE DECLINE BUT LIGHT SNOW OR FLURRIES
SHOULD CONTINUE WELL INTO THE AFTERNOON HOURS WED. THE ZONE OF VERY
WORST CONDITIONS AGAIN LOOKS TO BE ALONG AND EAST OF INTERSTATE 80
AND ALONG AND NORTH OF HIGHWAY 34...BUT FOR ALL PRACTICAL PURPOSES
ALL AREAS WILL BE LOOKING AT EXTREMELY DANGEROUS CONDITIONS. SINCE
THE BLIZZARD CONDITIONS WILL BEGIN TO DEVELOP BETWEEN 9PM AND
MIDNIGHT TNT WEST AND RAPIDLY INCREASE EAST...WE PLAN ON LEAVING THE
BLIZZARD WATCH AS IS FOR NOW AND WHEN NECESSARY UPGRADE LATER. THIS
WILL BETTER MATCH THE ONGOING CONDITIONS AND SEVERITY AT THE TIME.
ALONG WITH THE SNOW...WIND...WILL COME COLD TEMPERATURES. TNTS
SUBJECTIVE SFC ANALYSIS SHOWS SUB-ZERO READINGS OVER THE DAKOTAS
ALREADY TNT. THIS COLD AIR WILL BE QUICKLY PULLED INTO THE REGION
AND BEHIND THE LOW...WHICH THE 06Z RUN OF THE NAM NOW HAS DEEPENING
TO 979MB BY 12Z WED NEAR KMKE...VS THE EURO WHICH HAS IT DOWN TO
982MB BY 12Z JUST EAST OF KMKE. IN ANY CASE...WINDS WILL HAVE NO
PROBLEM PULLING COLD AIR ACROSS THE STATE WITH STEADY TO SLOWLY
FALLING TEMPERATURES DURING THE AFTERNOON HOURS WED. WIND CHILL
VALUES WILL DROP BELOW -20 OVER THE NORTH HALF FOR WED NIGHT AND AN
ADVISORY FOR WIND CHILLS WILL MORE THAN LIKELY BE NEEDED FOR THAT
REGION AS OVERNIGHT LOWS DROP BELOW ZERO OVER MOST OF THE FORECAST
AREA. NO REAL GOOD NEWS GOING FORWARD AS COLD TEMPERATURES WILL
CONTINUE INTO THE END OF THE WEEK. THOUGH DOWNWARD ADJUSTMENTS HAVE
ALREADY BEEN MADE...DEEP SNOW PACK AND LIGHT WINDS FRIDAY NIGHT MAY
REQUIRE EVEN COLDER LOWS THAN CURRENTLY PROGGED. LITTLE WX GOING
INTO THE WEEKEND WITH SOME MODERATION IN TEMPS.
&&
.AVIATION...
08/18Z...LIFR CONDITIONS THROUGHOUT MUCH OF THE TAF PERIOD WITH THE
CURRENT SNOWFALL AND ANTICIPATED STRONG NORTH TO NORTHWEST WINDS
DEVELOPING TONIGHT. BLIZZARD CONDITIONS ARE EXPECTED TO AFFECT MUCH
OF THE TAF FORECAST AREA OVERNIGHT TONIGHT THROUGH THE END OF THE
TAF PERIOD. WIND SHIFT FROM THE EAST TO NORTHEAST THROUGH THE FIRST
6-10 HOURS OF THE TAF FORECAST...THEN WILL ABRUPTLY SHIFT TO THE
NORTH NORTHWEST PAST 03Z WED BEGINNING AT THE NORTHERN TAF SITES
FIRST. CONDITIONS NOT EXPECTED TO IMPROVE AT ALL DURING THE TAF
FORECAST PERIOD.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING THROUGH 9 PM CST TUESDAY...BLIZZARD WARNING
FROM 9 PM TUESDAY TO 6 PM CST WEDNESDAY FOR ENTIRE FORECAST AREA.
&&
$$
SHORT TERM...COGIL
AVIATION...PODRAZIK
LONG TERM...REV
