AREA FORECAST DISCUSSION
NWS CHICAGO IL
1150 AM CST THU DEC 6 2007
.DISCUSSION...
427 AM CST
VERY ACTIVE PATTERN CONTINUES. SOUTHERN EXTENT OF THE UPPER TROUGH
OVER EASTERN NOAM TO WEAKEN TODAY AND PATTERN TRANSITIONING TO
MORE ZONAL ACROSS THE U.S. AS 170KT JET MAX PER AIRCRAFT REPORTS
BLASTS ACROSS THE PAC NW AND CENTRAL ROCKIES AND PLAINS. AHEAD OF
THIS FAST FLOW IS A SHARP SHORT WAVE MOVING E OUT OVER THE CENTRAL
HI PLAINS WITH WAA PRECIP SPREADING WELL E AHEAD OF IT ACROSS NEB
AND KS. A SHORT WAVE IS ALSO DROPPING ACROSS THE DAKOTAS AHEAD OF
AN UPPER LOW MOVING SE FROM NORTHERN ALBERTA INTO CENTRAL
SASKATCHEWAN.
THE SHORT WAVES BEGIN TO PHASE LATER TODAY AS THEY CROSS THE UPPER
AND MID MS VALLEY. MODELS STILL DO NOT INDICATE ANY LOW LEVEL
CIRCULATION DEVELOPMENT THOUGH STRONG LOW AND MID LEVEL FORCING
INDICATED TO SPREAD E WITH THE WAA PATTERN AHEAD OF THE PLAINS
SHORT WAVE. INITIALLY DRY AIR OVER THE FA EXPECTED TO MOISTEN
QUICKLY AS THE STRONG ISENTROPIC LIFT SHIFTS E ACROSS THE MS
RIVER DURING THE LATER AFTERNOON. H8 WINDS HAVE BACKED AND
STRENGTHENED TO 30-40KTS OK TO SOUTHERN NEB AND THIS STRONG
THERMAL FORCING TO ARRIVE INTO SE IA AND W CENTRAL IL BY LATE
AFTERNOON. EXPECT A BURST OF MODERATE SNOWFALL INTO N CENTRAL IL
BY SUNDOWN AND SPREADING QUICKLY ACROSS NE IL AND NW IND DURING
THE EARLY EVENING AS LOW LEVEL FORCING IS ENHANCED BY DIVERGENCE
AT LEFT EXIT OF JET MAX THEN TAPERING OFF FOR OVERNIGHT AS STRONG
FROTOGENETIC FORCING MOVES E ACROSS THE MIDWEST AND SOUTHERN
LAKES WITH SHORT WAVE TROUGH REACHING WI AND NORTHERN IL BY 06Z.
AMOUNTS WILL BE LIMITED BY DURATION BUT GIVEN EXPECTED HIGHER RATE
OF FALL FOR A COUPLE HOURS DURING THE LATE AFTERNOON AND EARLY
EVENING WILL HEADLINE A SNOW ADVISORY. EXPECTED RANGE 2-5 INCHES
WITH AVERAGE 3-4 IN ACROSS FA.
WEEKEND STILL LOOKS MESSY AS UPPER PATTERN BECOMES SOUTHWESTERLY
WITH STRONG JET DIGGING DOWN THE CA COAST AND POS TILT TROUGH
EXTENDING FROM BAJA CA INTO THE NORTHERN PLAINS. THIS ALLOWS
FURTHER NORTHWARD PENETRATION OF MILD AIR INTO THE REGION WHILE
NORTHERN BRANCH MAINTAINS A READY SUPPLY OF COLD AIR ACROSS THE
NORTHERN PLAINS...UPPER MIDWEST...NORTHERN GREAT LAKES.
DETAILS STILL QUITE UNCERTAIN ON HOW WILL EXACTLY PLAY OUT BUT
MODELS SUGGEST AN IMPULSE TO EJECT FROM THE WESTERN TROUGH ACROSS
THE PLAINS SAT AND INTO THE OH VALLEY SAT NIGHT. WHILE SURFACE
BOUNDARY TO BE WELL S NEAR THE OH RIVER...MILD AIR SPREADS WELL N
INTO NORTHERN IL ALOFT. LATEST THINKING IS FOR ALL/MOSTLY SNOW
ALONG THE WI BORDER WITH MIXED PRECIP/FREEZING RAIN/RAIN IN
SOUTHERN PORTION OF FA.
TRS
&&
.AVIATION...
1150 AM CST
FOR THE 18Z TAFS...GENRLLY CI STREAMING OUT AHEAD OF NEXT WX MAKER
IN THE PLAINS. REGIONAL RADAR INDICATING THAT LEADING EDGE OF SNOW
MAKER HAS ADVANCED INTO CNTRL IA AND MO. CIGS DROPPING DOWN TO
BKN-OVC AC THIS AFTN AND LOWERING BLO 5K BY SUNSET TO MVFR AT ONSET
OF SNOW ABOUT MID EVENING. CONTD SATURATION WITH HEAVIER SNOW BY
MIDNIGHT LIKELY TO LOWER CIGS AND VSBY TO IFR THRU THE PREDAWN HOURS
AFTER MIDNIGHT AND LIFTING TO HIGH MVFR OR EVEN VFR A FEW HOURS AFT
SUNUP. WINDS SHUD BE RUNNING SOUTH TO SW ARND 10 KTS THRU THE NEXT
24 HOURS...STARTING TO VEER MORE TO THE WEST NEAR 18Z TMRW. SHUD
WIND UP WITH A COUPLE OF INCHES AT LEAST WITH HIER AMOUNTS SOUTH OF
THE TERMINALS.
RLB
&&
.MARINE...
309 AM CST
A LARGE HIGH OVER ILLINOIS WILL MOVE O VIRGINIA BY THIS
AFTERNOON. A TROUGH EXTENDS FROM NORTHERN COLORADO TO HUDSON BAY
CANADA. COLD AIR WILL MOVE SOUTHEAST FROM SASKATCHEWAN INTO THE
NORTHERN PLAINS FRIDAY. WITH THE COLD AIR PRESENT THE TROUGH WILL
TAKE ON THE CHARACTER OF A COLD FRONT. THIS FRONT WILL MOVE ACROSS
THE GREAT LAKES FRIDAY NIGHT. A LARGE HIGH OVER SOUTHERN
SASKATCHEWAN WILL SPREAD SOUTHEAST TO NORTHERN ILLINOIS EARLY
SATURDAY. THIS WILL BRING COLDER AIR INTO LAKE MICHIGAN BY SUNDAY.
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...SNOW ADVISORY FROM 4 PM THIS AFTERNOON TO 6 AM CST FRIDAY FOR
ILZ003-004-008-010-011-019.
SNOW ADVISORY FROM 6 PM THIS EVENING TO 6 AM CST FRIDAY FOR
ILZ005-006-012>014-020>023-032-033-039.
IN...SNOW ADVISORY FROM 6 PM CST /7 PM EST/ THIS EVENING TO 6 AM CST
/7 AM EST/ FRIDAY FOR INZ001-002-010-011-019.
LM...NONE.
&&
$$
WFO LOT
AREA FORECAST DISCUSSION
NWS ST LOUIS MO
731 PM CST THU DEC 6 2007
.UPDATE...
FCST SNDGS...AND ACARS SNDG DATA FROM FLIGHTS IN AND OUT OF
STL...SHOW WRMST TEMPS NR .5C CNTRD NR 85H. TYPICAL P-TYPE RULES
SUGGEST THAT SOUNDINGS SUCH AS THIS WULD PRIMARILY SUPPORT SNOW
OR SLEET...BUT APPARENTLY THE LAYER NR 0C IS DEEP ENUF AND THE
LATENT HEAT RELEASE IS STG ENUF TO CHG PCPN NR STL TO PRIMARILY FRZG
RAIN. HWVR...HIER REFLECTIVITY ELEMENTS SHOWING UP ON 88D BTWN
STL AND COU ARE POCKETS OF HVY SNOW...AND PROB SOME SLEET. THIS IS
GOING TO CAUSE SNOW AMOUNTS TO BE ALL OVER THE PLACE...BUT
ADDITIONAL ACCUMULATIONS SHOULD CERTAINLY BE HIGHEST FROM NR TROY
TO N OF LITCHFIELD...WITH 2-3 INCHES IN THIS BAND BTWN NOW AND
MIDN. BASED ON 88D RETURNS...IT WULD ALSO APPEAR THAT THE HEAVIEST
SNOWFALL FOR THE REST OF THIS EVENING WILL GENERALLY BE ALG...AND
ESP E...OF A MONROE CITY...QUINCY LINE.
SHIFT OF THE MIX PCPN TYPE FORCED US TO CHG HEADLINES...AND NOW WINTER
WX ADVSRY IS IN EFFECT ALG AND S OF A MEXICO...BOWLING
GREEN..LITCHFIELD LN. SNOW ADVISORY CONTS N OF THIS LINE.
HOPEFULLY...LATEST ZONE/GRID UPDATE WILL HOLD FOR A FEW HRS...
TRUETT
&&
.DISCUSSION...
STORM SYSTEM HAS MOVED INTO REGION WITH SNOW BEING REPORTED OVER FAR
WESTERN HALF OF CWA. UPDATED ADVISORY FOR AREA...ADDING FAR SOUTHERN
8 COUNTIES INTO THE WINTER WX ADVISORY THROUGH 06Z TONIGHT. SYSTEM
IS FURTHER SOUTH...WITH THE SOUTHERN SECTIONS EXPECTED TO GET A MIX
OF SNOW AND SLEET. WILL KEEP REMAINING ADVISORY AREAS GOING AS WELL
WITH 3 TO 5 INCHES EXPECTED IN THE FAR NORTH...UP TO 3 OVER CENTRAL
MO...AND LESS AMOUNTS TO THE SOUTH AND EAST.
FRONTAL BOUNDARY SOUTH OF CWA TO SLIDE SLOWLY TO THE NORTH CLOSER TO
THE AREA ON FRIDAY WITH LOW CHANCE OF RAIN/SNOW. NAM AND GFS HAVE
SIMILAR SOLUTIONS FOR FRIDAY AND FRIDAY NIGHT...WHICH KEEPS THE
FRONTAL BOUNDARY JUST SOUTH OF CWA THROUGH FRIDAY NIGHT. WILL BEGIN
TO SEE MORE OF A FREEZING RAIN THREAT ON FRIDAY NIGHT AS MID LEVEL
WAA PICKS UP AND OVERRIDES FRONTAL BOUNDARY. ICE AMOUNTS WILL BE ON
THE LIGHT SIDE.
FORECAST CONTINUES TO BE TRICKY WITH BIG DIFFERENCES BETWEEN THE
ECMWF AND GFS...ESPECIALLY FOR SUNDAY THROUGH MONDAY. THE FRONT WILL
WAVER BACK AND FORTH OVER THE FORECAST AREA THROUGH EARLY NEXT WEEK
WITH SEVERAL ROUNDS OF PRECIPITATION EXPECTED. APPEARS THAT COLDER
AIR WILL MOVE IN AT THE SURFACE...WITH PERIODS OF FREEZING RAIN OR
SLEET FOR NORTHERN THIRD OF CWA THROUGHOUT THE EVENT. SINCE MODELS
HAVE BEEN HAVING PROBLEMS HANDLING THIS SYSTEM...FOR NOW WILL GO
WITH A COMPROMISE BETWEEN THEM AND WILL NOT ISSUE ANY WATCHES YET.
WILL WORD HWO ACCORDINGLY TO EMPHASIZE THE THREAT OF ICY WEATHER
LATER IN THE FORECAST PERIOD.
BYRD
&&
.AVIATION...
FOR THE 00Z TAFS...
WINTRY MIX OF PRECIPITATION WILL CONTINUE WEST OF THE MISSISSIPPI
AT LEAST THROUGH 04Z...AND THROUGH 06-07Z EAST OF THE MISSISSIPPI.
IFR FLIGHT CONDITIONS SEEM TO BE CONFINED TO THE NORTHERN 1/3 OF
THE CWFA WHILE THE REMAINDER OF THE CWFA IS PRIMARILY MVFR...AND
EVEN SOME VFR IN -FZRA AT KFAM. PRECIP TYPE HAS CHANGED AT LEAST 3
TIMES SINCE I TOOK OVER AT 400 PM...AND IT LOOKS LIKE IT COULD
CONTINUE TO SWITCH A FEW MORE TIMES BEFORE IT ENDS AS KCOU HAS
SWITCHED FROM SN TO FZRA TO UP AND BACK TO FZRA AGAIN IN THE PAST
COUPLE OF HOURS.
BASICALLY...THE WEATHER IS MESSY...AND IS GOING TO STAY MESSY FOR
THE NEXT 4-6 HOURS. THINK IFR CONDITIONS WILL CONTINUE TO STAY
PRIMARILY OVER NORTHERN MISSOURI/WEST CENTRAL IL...BUT POCKETS OF
IFR CIGS/VSBYS WILL BE POSSIBLE WHERE PL AND FZRA TURN TO SNOW.
AFTER THE PRECIP CLEARS THE AREA THINK WE`LL PRIMARILY SEE MVFR
CIGS/VSBYS...BUT WITH SOME IFR FOG DEVELOPING OVER NE MO/WEST
CENTRAL IL LATE.
CARNEY
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...WINTER WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR AUDRAIN-
BOONE-CALLAWAY-COLE-CRAWFORD-FRANKLIN-GASCONADE-IRON-
JEFFERSON-LINCOLN-MADISON-MONITEAU-MONTGOMERY-OSAGE-PIKE-
REYNOLDS-ST. CHARLES-ST. FRANCOIS-ST. LOUIS-ST. LOUIS CITY-
STE. GENEVIEVE-WARREN-WASHINGTON.
SNOW ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR KNOX-LEWIS-MARION-
MONROE-RALLS-SHELBY.
IL...WINTER WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR BOND IL-
CALHOUN IL-CLINTON IL-FAYETTE IL-GREENE IL-JERSEY IL-
MACOUPIN IL-MADISON IL-MARION IL-MONROE IL-MONTGOMERY IL-
RANDOLPH IL-ST. CLAIR IL-WASHINGTON IL.
SNOW ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR ADAMS IL-BROWN IL-
PIKE IL.
&&
$$
WFO LSX
AREA FORECAST DISCUSSION
NWS SEATTLE WA
845 PM PST TUE DEC 4 2007
.SYNOPSIS...WESTERLY FLOW ALOFT OFF THE PACIFIC WILL CONTINUE TO
MAINTAIN THE THREAT OF SHOWERS INTO WEDNESDAY. DRY AND COOLER
NORTHERLY FLOW WILL BECOME ESTABLISHED OVER THE REGION THURSDAY
THROUGH SATURDAY. THE NEXT THREAT OF PRECIPITATION APPEARS TO EARLY
NEXT.
&&
.SHORT TERM...WESTERLY FLOW ALOFT IS CONTINUING TO MOVE A MOIST
UNSETTLED AIR MASS ONSHORE FOR SHOWERS. IT APPEARS THE OLYMPICS ARE
SHADOWING THE CENTRAL AND NORTH PUGET SOUND AREA AT THIS TIME. AS
THE FLOW VEERS TO MORE NW BY WED..EXPECT THAT SHADOW TO SLIP
SOUTHWARD. THIS PATTERN WILL ALSO FAVOR DEVELOPMENT OF A PUGET SOUND
CONVERGENCE ZONE IN THE N KITSAP/SOUTHERN SNOHOMISH/NORTHERN KING
COUNTY REGION.
BY LATE WED..THE THREAT OF SHOWERS SHOULD BECOME MAINLY CONFINED TO
THE CASCADES ALTHOUGH THE CONVERGENCE ZONE COULD HANG ON INTO THE
EVENING.
GRADIENTS CONTINUE TO EASE. HAVE DROPPED THE REMAINING GALE WARNINGS
ALONG THE COAST AND WEST ENTRANCE. RIVERS CONTINUE TO RECEDE WITH
THE EXCEPTION OF THE LONG-STEM STREAMS LIKE THE CHEHALIS AS WATER
CONTINUES TO MOVE DOWNSTREAM. SEE THE LATEST FLOOD STATEMENTS.
00Z PROGS IN THUS FAR CONTINUE TO BUILD AN UPPER RIDGE NEAR 145W OR
SO BEGINNING WED THROUGH THU AND FRI. FLOW ALOFT TURNS MORE NW THEN
N AND SURFACE GRADIENTS TURN OFFSHORE WITH COOLER DRIER AIR MOVING
OVER THE REGION. DAYTIME AND NIGHTTIME TEMPS SHOULD FALL BACK BELOW
NORMAL DUE TO CLEARING SKIES AND COLD AIR ADVECTION.
AND FINALLY..NEWS ON THE KUIL UPPER AIR SITE. THE POWER OUTAGE THERE
APPARENTLY RESULTED IN NEED FOR SERVICE OF THE SYSTEM. A TECH IS
ENROUTE BUT MAY NOT GET THERE UNTIL WED AS FALLEN TREES ARE CLEARED
ALONG THE WAY. A RAOB MAY BE AVAILABLE BY WED AFTERNOON. BUEHNER
.LONG TERM...FROM PREVIOUS DISCUSSION.
DRY..NLY FLOW AND CONTINUED COLD AIR ADVECTION WILL KEEP TEMPS BELOW
CLIMO ON SATURDAY. A LOW PRES SYSTEM DROPPING OUT OF THE GULF OF AK
IS EXPECTED TO BRING PRECIP TO THE AREA ON SUNDAY. THE MODELS HAVE
NOT BEEN CONSISTENT WITH THE STRENGTH AND TIMING OF THIS SYSTEM BUT
IT BEARS WATCHING. THE AIR MASS WILL BE COLD ENOUGH TO SUPPORT SOME
LOWLAND SNOW BUT IT IS TOO EARLY TO TELL EXACTLY WHERE AND HOW MUCH.
IT APPEARS THAT AN UNSETTLED AND COOL WEATHER REGIME WILL BECOME
ESTABLISHED NEXT WEEK...WITH SYSTEMS DIVING DOWN FROM THE GULF OF AK
ACROSS THE PAC NW.
&&
.AVIATION...SURFACE WINDS FINALLY STARTING TO SHOW A NOTABLE
DECREASE OVER THE PAST THREE HOURS. STRONG LOW LEVEL WINDS BELOW
5000 FEET EARLIER HAVE ALSO WEAKENED AS EVIDENCED BY KSEW SOUNDER
SHOWING ABOUT 30 KNOTS NEAR 3000 FEET...DOWN FROM 55 KNOTS THIS
MORNING. SOUNDER DATA SEEMS TO MATCH RECENT ACARS DATA PRETTY WELL.
WOULD EXPECT A MIX OF MVFR AND VFR CONDITIONS THROUGH THE NIGHT AS
SCATTERED SHOWERS CONTINUE TO PUSH ONSHORE. MESOSCALE MODELS DEVELOP
A CONVERGENCE ZONE WEDNESDAY MORNING...BUT SUGGEST ACTIVITY SHOULD
REMAIN NORTH OF THE SEATTLE METRO AREA TERMINALS.
.KSEA...HIT OR MISS SHOWERS WILL PASS THROUGH THE AREA OVERNIGHT
WITH TEMPO MVFR CEILINGS AT TIMES. WINDS BELOW 10K FEET BEGINNING TO
WEAKEN CONSIDERABLY...SHOULD BE GENERALLY 30 KNOTS OR LESS BY
DAYBREAK. SURFACE GRADIENTS ALSO COMING DOWN. SOUTH WIND 12 KT
OCCASIONALLY GUSTING 20 KT THIS EVENING EASING TO SOUTH 7 TO 10 KT
BY 12Z OR SO. 27
&&
.MARINE...MANY BUOYS REPORTING SEAS BELOW 20 FEET...THOUGH ONE BUOY
NEAR 50N 127W HAD 21 FEET. DECIDED TO ERR ON THE SIDE OF CAUTION AND
WILL PROBABLY ALLOW CURRENT HIGH SURFACE ADVISORY TO EXPIRE AT 12Z.
ELSEWHERE...WILL KEEP SMALL CRAFT ADVISORIES GOING ACROSS MOST
WATERS THROUGH 12Z AS WELL. GRADIENTS COMING DOWN ACROSS REGION.
MUCH DESERVED TRANQUIL PATTERN DEVELOPING FOR THE LATER HALF OF THE
WEEK. WAVE WATCH MODEL GRADUALLY BRINGS COASTAL SEAS DOWN DURING THE
DAY WEDNESDAY...THEN BELOW 10 FT BY EARLY THURSDAY. OFFSHORE
GRADIENTS SETTING UP LATE IN THE WEEK AS SURFACE RIDGE BUILDS OVER
BC WITH WEAK TROUGH OFFSHORE HEADED FOR SOUTHERN OREGON OR NORTHERN
CAL. 27
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
.HIGH SURF ADVISORY NORTH AND CENTRAL COAST.
.SMALL CRAFT ADVISORIES ALL WATERS EXCEPT NORTHERN INLAND AND
ADMIRALTY INLET.
.SMALL CRAFT ADVISORY GRAYS HARBOR BAR FOR ROUGH BAR CONDITIONS
$$
WEATHER.GOV/SEATTLE
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