FXUS63 KDMX 240543 AAB
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1145 PM CST WED DEC 23 2009
...UPDATED AVIATION FORECAST...
.SHORT TERM.../REST OF TODAY THROUGH TONIGHT/
FIRST PUSH OF WARM AIR ADVECTION IS HEADING OVER THE NORTHERN
PORTIONS OF THE STATE WITH MIXTURE OF FREEZING RAIN AND
SNOW...TRANSITIONING TO RAIN AS IT THE WARMER CONDITIONS BUILD
NORTH. TEMPERATURES GENERALLY ABOVE FREEZING NOW SOUTH. NEXT
UPSTREAM WAVE ALREADY IMPACTING EASTERN KS WITH CONVECTION WHICH IS
WEAKENING WITH TIME...BUT WILL STILL MAKE IT ACROSS THE SOUTHERN
COUNTIES THIS EVENING AND WILL CONTINUE THUNDER CHANCES THERE. FAR
NORTH LOOKS MAINLY TO CONTINUE AS SNOW WITH SEVERAL INCHES OF ACCUMS
TNT ALONG WITH A STRIP OF FREEZING RAIN AGAIN ALONG HIGHWAY 20 AFTER
06Z. HAVE UPDATED AUDUBON AND GUTHRIE COUNTIES TO WINTER STORM
WARNING WITH OTHER COUNTIES TO THE NORTH DUE TO FREEZING RAIN ACCUMS
AND NOW SEEING SOME POWER ISSUES WITH OUTAGES IN THE AREA. ROAD
CONDITIONS NOT BEING IMPACTED TOO MUCH BUT POWER OUTAGES AND SOME
FALLING TREES HAVE RAISED THE DANGER IN THESE COUNTIES FOR NOW.
OTHERWISE AS THE NEXT WAVE ARRIVES WITH ANOTHER ROUND OF STRONG
MOISTURE TRANSPORT...WILL BE LOOKING AT PRECIP CHANGES ACROSS THE
NORTH THROUGH MORNING AS WARM AIR ATTEMPTS TO SCOUR THE COLD SFC
AIR. TEMPERATURES WILL HOLD STEADY OR RISE SLOWLY WITH TIME.
.LONG TERM /THURSDAY THROUGH WEDNESDAY/...
FORECAST MODELS CONTINUE TO HAVE PROBLEMS PREDICTING THE INTERACTION
BETWEEN THE LARGE MID/UPPER CYCLONES TRAVELING THROUGH THE NORTHERN
AND SOUTHERN STREAMS. THEY HAVE SHIFTED SUBSTANTIALLY SINCE
YESTERDAY MORNING...WHEN THERE WAS NEARLY UNANIMOUS AGREEMENT IN THE
SOUTHERN VORTEX BEING THE MORE ENERGETIC AND SWINGING
NORTHEASTWARD...WITH THE ASSIMILATION OF THE NORTHERN VORTEX
DRAGGING THE THEN CONSOLIDATED GYRE FURTHER NORTHWEST INTO
SOUTHWESTERN IOWA. NOW THERE IS NEARLY UNANIMOUS AGREEMENT IN THE
NORTHERN VORTEX BEING THE MORE ENERGETIC...WITH THE SOUTHERN VORTEX
SWINGING MUCH WIDER IN ITS ARC AROUND THE SOUTHEASTERN PERIPHERY OF
THE CONUS-SCALE TROUGH...AND ASSIMILATING THE SOUTHERN VORTEX LATER
RESULTING IN A MORE NORTHWESTERLY TRACK OF THE CONSOLIDATED GYRE. IN
OTHER WORDS...THINGS ARE TRENDING COLDER /THAT IS...PRECIP SWITCHING
TO SNOW SOONER ACROSS OUR CENTRAL AREAS/ WITH PRECIP LINGERING
LONGER.
HAVE MAINTAINED NEAR 100 POPS FOR THE FIRST SEVERAL DAYS OF THE LONG
TERM FORECAST...TAPERING OFF SATURDAY AND SATURDAY NIGHT. BEYOND
THAT ECMWF CONTINUES TO TRY TO GENERATE ANOTHER STORM APPROACHING
FROM OUR SOUTHWEST...BUT KEPT THE FORECAST DRY AS THERE IS WAY TOO
MUCH UNCERTAINTY WITH THIS SYSTEM FIRST.
SO FOR THE BIG STORM THE BIGGEST ISSUE REMAINS P-TYPES...THEIR
TRANSITIONS...AND RESULTING EFFECTS ON ACCUMULATIONS ACROSS THE
AREA. WITH THE THINKING NOW BEING A SOONER TRANSITION TO SNOW ACROSS
MOST OF OUR AREA THE RESULTING FORECAST SNOW ACCUMULATIONS ARE
HIGHER THAN ON PREVIOUS SHIFTS...EXCEPT IN THE NORTHWEST WHERE
THINKING HAS NOT CHANGED MUCH. OUTGOING STORM TOTAL SNOWFALLS NOW
RANGE FROM AROUND 6 INCHES IN THE SOUTHEAST...TO 9 TO 13 INCHES
CENTRAL...AND 14 TO 17 INCHES IN OUR FAR WESTERN AND NORTHWESTERN
COUNTIES. AT FIRST BLUSH THESE AMOUNTS APPEAR A BIT HIGH BUT ONE
MUST REMEMBER THAT THEY ARE 84-PLUS HOUR TOTAL ACCUMULATIONS. THERE
REMAINS SOME QUESTION AS TO WHETHER ANY OF THE CENTRAL AREAS WILL BE
ABLE TO GET 6 INCH SNOW ACCUMULATIONS IN ANY 12 HOUR WINDOW THUS
MEETING WARNING CRITERIA. THERE ARE ALSO QUESTIONS OF WHETHER OR NOT
BLIZZARD CONDITIONS WILL MAKE AN APPEARANCE IN OUR CWA. HOWEVER...IT
APPEARS THAT THE CONSOLIDATED SURFACE LOW WILL STALL SOMEWHERE OVER
OUR AREA FOR MANY HOURS FROM FRIDAY THROUGH SATURDAY WHICH MAY
RESULT IN WEAKER WINDS OVER MUCH OF THE AREA.
FOR NOW...THE WINTER STORM WATCH WILL BE LEFT AS IS BEGINNING AT 18Z
THURSDAY. THERE IS SOME CONCERN THAT FZRA ACCUMULATIONS MAY BE HIGH
ENOUGH TO WARRANT A WARNING A BIT SOONER IN THE SOUTHWEST TOMORROW
MORNING...BUT CONFIDENCE IS NOT HIGH ENOUGH TO TAKE THE
WATCHES/WARNINGS THAT WAY AT THIS TIME.
&&
.HYDROLOGY...
SIGNALS ARE BECOMING STRONGER OF A MODERATE TO HEAVY RAINFALL EVENT
ACROSS OUR SOUTHERN AND SOUTHEASTERN CWA THROUGH THURSDAY NIGHT.
CONFIDENCE IS AT OR ABOVE THE 50 PERCENT THRESHOLD FOR FLOODING IN
THIS AREA...THUS HAVE DECIDED ON A FLOOD WATCH THERE.
PRECIP TYPE WILL BE A MAJOR DRIVING FORCE BEHIND THE HYDROLOGIC
RESPONSE. WITH PRIMARILY LIQUID PRECIP EXPECTED THROUGH THURSDAY
NIGHT IN THE ABOVE AREA OF CONCERN...HYDRO ISSUES ARE DEFINITELY A
CONCERN. RIVER FLOODING MAY RESULT FROM THE SHEER VOLUME OF
RUNOFF...ALONG WITH SNOW MELT. ANY WATER THAT MAKES ITS WAY INTO
STREAMS WOULD IMPART ENOUGH ENERGY TO BEGIN THE PROCESS OF BREAKING
UP RIVER ICE. SINCE THE RIVER ICE IS RELATIVELY THIN...THOUGH...WE
EXPECT ANY FLOODING FROM ICE JAMS TO BE LOCALIZED AND LESS SEVERE
THAN WOULD TYPICALLY OCCUR LATE IN THE WINTER.
IN ADDITION...FLOODING MAY OCCUR IN OTHER AREAS...SUCH AS TOWNS AND
CITIES...WHOSE NORMAL DRAINAGE SYSTEMS WOULD HAVE LOWER THAN NORMAL
CONVEYANCE DUE TO SNOW AND ICE OBSTRUCTED INTAKES.
ANY RISES THAT OUR STREAMS DO EXPERIENCE SHOULD BE QUICKLY REDUCED
AS COLDER TEMPERATURES WORK THEIR WAY IN TO OUR REGION ON FRIDAY.
&&
.AVIATION...
24/06Z...TEMPS TO REMAIN ABOVE FREEZING FROM KAIO-KALO THROUGH 12Z
ON THURSDAY. HOWEVER...COLDER AIR WILL ARRIVE IN WESTERN IA AND
PROGRESS EASTWARD DURING THE DAY WITH BELOW FREEZING TEMPERATURES
EXPANDING ACRS THE FORECAST AREA. WL SEE FZRA AND SN AFFECTING KFOD
AND KMCW TONIGHT WITH TRANSITION TO ALL SNOW DURING THE DAY ON
THURSDAY. RAIN WILL OCCUR ELSEWHERE WITH TRANSITION TO FROZEN PCPN
DURING THURSDAY AS WELL. IFR/LIFR CONDITIONS WILL BE WIDESPREAD FOR
THE ENTIRE FORECAST PERIOD WITH PERIODS OF PCPN.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
WINTER WX ADVY KAMW/KMIW/KALO AREAS TIL 12Z
WINTER STORM WARNING ALONG AND N OF KAUD/KEBS/KOLZ LINE TIL 06Z SAT
WINTER STORM WATCH SWRN IA...THROUGH CENTRAL IA...TO NERN IA 18Z
THU TO 06Z SAT
FLOOD WATCH ALONG AND SE OF ALO...TO DSM...TO LWD LINE FROM 12Z THU
TO 12Z FRI
$$
SHORT TERM...REV
AVIATION...COGIL
HYDROLOGY...ZOGG
LONG TERM...LEE
