000
FXUS63 KLOT 271954
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
154 PM CST MON DEC 27 2010
.DISCUSSION...
1200 PM CST
HAVE UPDATED SKY GRIDS. STRATUS HAS COVERED MUCH OF THE FORECAST
AREA WITH NOTABLE HOLES IN NW INDIANA AND NW IL. MAY SEE SOME HOLES
AND THIN SPOTS THROUGH THE AFTERNOON BUT INVERSION WILL STRENGTHEN
AS LOW LEVEL WAA GETS UNDERWAY TONIGHT. EXPECT STRATUS AND FOG TO
FILL BACK IN OVERNIGHT AND CLOUDS MAY STAY THROUGH THE END OF THE
WEEK. AS A RESULT NOT MUCH IMPROVEMENT EXPECTED IN TEMPERATURES THIS
AFTERNOON...AND NOT EXPECTING IT TO GET TOO COLD TONIGHT EITHER.
UPDATED ZFP FOR MOSTLY CLOUDY SKIES THROUGH TUESDAY.
ALLSOPP
PREVIOUS DISCUSSION...
259 AM CST
THE MAIN FORECAST CONCERN WILL BE WITH REGARDS TO THE STORM SYSTEM
EXPECTED IMPACT A LARGE PORTION OF THE CENTRAL CONUS LATER IN THE
FORECAST PERIOD. THIS SYSTEM PROMISES TO PRODUCE A LATE DECEMBER
THAW...ALONG WITH RAIN AND POSSIBLY EVEN SOME THUNDERSTORMS BY THE
END OF THE WEEK. THE MODELS GUIDANCE IS SHOWING BELOW AVERAGE
DIFFERENCES WITH THE EVOLUTION OF THE LARGE SCALE PATTERN ACROSS
NORTH AMERICA. THERE ARE ONLY DIFFERENCES WITH THE FINER DETAILS
OF THE SYSTEM...SUCH AS THE LESS PREDICTABLE SMALLER SCALE
DISTURBANCES EMBEDDED IN THE MAIN FLOW. THEREFORE...I HAVE CHOSEN A
BLEND OF THE LATEST 00 UTC GFS AND ECMWF.
CURRENTLY HIGH PRESSURE IS IN CONTROL AND IS CENTERED ACROSS MO THIS
MORNING. IN SPITE OF THIS...AREAS OF LOW CLOUDS PERSIST...WHILE
OTHER AREAS HAVE CLEARED OUT. IN THE CLEARED AREAS TEMPERATURES HAVE
DROPPED INTO THE SINGLE DIGITS TO LOW TEENS...WHILE CLOUDY AREAS
REMAIN IN THE 20S. THESE CLOUDS SHOULD CLEAR THE WHOLE AREA BY MID
TO LATE MORNING AS THE RIDGE OF HIGH PRESSURE BUILDS EASTWARD. LARGE
SCALE DESCENT AND A WESTERLY WIND COMPONENT SHOULD DRY OUT THE
COLUMN.
THE NEXT PROBLEM WILL BE WITH TEMPERATURES. IN SPITE OF MID-LEVEL
WARM ADVECTION TODAY. THE WESTERLY WINDS NEAR THE SURFACE WILL BE
BLOWING OVER EXTENSIVE SNOW PACK...SO HIGHS TODAY WILL BE COLDER
THAN THEY WERE ON SUNDAY. NORTHWEST INDIANA IS STILL DEALING WITH
SOME LAKE EFFECT CLOUDS AND SNOW SHOWERS EARLY THIS MORNING. THIS
HAS KEEP TEMPERATURES IN THE MID 20S. I BELIEVE TEMPERATURES HERE
WILL EITHER DROP OR STAY NEARLY STEADY THROUGHOUT THE DAY ONCE THE
WINDS OFF THE LAKE TURN OUT TO THE WEST.
WATER VAPOR IMAGERY DEPICTS A MID-LEVEL RIDGE BUILDING IN ACROSS THE
WESTERN GREAT LAKES THIS MORNING. FARTHER WEST ACROSS SOUTHERN CA...
A SHORT WAVE TROUGH IS MOVING ONSHORE. THIS IS IN RESPONSE TO A
BUILDING RIDGE ACROSS THE EASTERN PACIFIC. AS THIS RIDGE CONTINUES
TO BUILD...IT WILL EJECT ENERGY ASSOCIATED WITH AN UPPER LOW ACROSS
THE NORTHEASTERN PACIFIC EASTWARD ACROSS THE PACIFIC NORTHWEST. THIS
TROUGH WILL RAPIDLY DEEPEN AS IT DIGS ACROSS THE WESTERN CONUS BY
MID TO LATE WEEK.
IT APPEARS SEVERAL WAVES OF ENERGY WILL EJECT OUT ACROSS THE PLAINS
BEFORE THE MAIN TROUGH MOVES EASTWARD LATE THIS WEEK. CYCLOGENESIS
IS LIKELY TO OCCUR ACROSS THE FRONT RANGE OF THE COLORADO ROCKIES
LATE WEDNESDAY AND WEDNESDAY NIGHT. THIS WILL LIKELY INDUCE AN
IMPRESSIVE 40+ KT LOW LEVEL JET ACROSS THE CENTRAL CONUS...AND
TRANSPORT IMPRESSIVE AMOUNTS OF WARM GULF MOISTURE NORTHWARD ACROSS
IL. IN FACT...PRECIPITABLE WATER VALUES MAY APPROACH ONE
INCH...WHICH FOR LATE DECEMBER/EARLY JANUARY IS NEAR THE 99
PERCENTILE FOR THE AREA. CONSIDERING THIS...ALONG WITH THE FACT
THAT THIS WILL BE A VERY DYNAMIC STORM...I WOULD NOT BE SURPRISED TO
SEE SOME THUNDERSTORMS AND A PERIOD OF HEAVY RAIN AS THE COLD FRONT
PUSHES ACROSS THE AREA LATE FRIDAY. THERE COULD EVEN BE SOME STRONG
STORMS. HOWEVER...IT IS STILL TO EARLY TO TELL IF ENOUGH INSTABILITY
WILL REACH THIS FAR NORTH FOR A SEVERE WEATHER EVENT. BUT GIVEN THAT
DEEP LAYER SHEAR WILL BE STRONG...WE MAY NOT NEED A WHOLE LOT OF
INSTABILITY TO GET SOMETHING GOING.
THE OTHER FINAL CONCERN WITH THIS STORM WILL BE THE POSSIBILITY FOR
INCREASED RUNOFF DUE TO THE FROZEN GROUND AND THE FACT THAT MUCH
OF MY CWA HAS A SNOW PACK OF 6 TO 12 INCHES WITH ABOUT AN INCH TO
A INCH AND A HALF OF WATER IN IT. THIS DEFINITELY IS SOMETHING TO
KEEP IN MIND AS WE GET CLOSER TO THIS EVENT.
FOLLOWING THE COLD FRONT...THINGS WILL GET COLD AGAIN...AS
TEMPERATURES WILL LIKELY DROP BACK BELOW AVERAGE.
KJB
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 18Z...
* BASES AND DURATION OF THE STRATUS DECK THROUGH THE PERIOD.
* POSSIBILITY OF REDUCED VISIBILITY IN BR/HZ THIS AFTERNOON AND
TONIGHT.
KREIN.
//DISCUSSION...UPDATED 18Z...
THE AXIS OF A WEAK RIDGE OF HIGH PRESSURE IS CROSSING THE
MISSISSIPPI RIVER INTO ILLINOIS AND WISCONSIN. THE CENTER OF THE
HIGH PRESSURE IS MOVING SOUTH OF THE TERMINALS INTO SOUTHERN
ILLINOIS. LATEST SATELLITE AND METARS INDICATE A THIN LAYER OF
STRATUS OVER THE AREA WITH THE LEADING EDGE MOVING OVER ORD AT
1715Z. THE STRATUS SHOULD REACH MDW SHORTLY THEREAFTER. MODEL AND
OBSERVED TEMPERATURE PROFILES INDICATE A STRONG SURFACE BASED
INVERSION OVER THE REGION WHICH IS FORECAST TO REMAIN IN PLACE
INTO TUESDAY EVENING. SO...WILL MAKE A SIGNIFICANT CHANGE TO THE
GOING TAFS AND ADD A BKN010 TO THE FORECAST THROUGH THE PERIOD.
THE SATELLITE IMAGERY DOES SHOW SOME BREAKS AND SMALL HOLES IN THE
STRATUS...SO SHORT PERIODS OF IMPROVED CIGS WILL BE LIKELY AT THE
TERMINALS. HOWEVER...EXPECT THAT THE DURATION OF THE PERIODS OF
IMPROVED CEILINGS WILL BE BRIEF AND NOT LONG ENOUGH TO REALLY
CONSIDER A TEMPO GROUP IN THE TAF.
THE OTHER CONCERN IS WITH VISIBILITY. CURRENTLY...THERE IS
EXTENSIVE IFR VISIBILITY IN BR/SN ALONG AND WEST OF THE
MISSISSIPPI RIVER. SOME SLIGHTLY MOISTER AIR HAS BEEN ABLE TO MOVE
INTO THIS REGION AS WINDS ARE MORE SOUTHERLY ON THE WESTERN SIDE
OF THE SURFACE RIDGE. WITH THE CENTER OF THE HIGH PRESSURE MOVING
SOUTHEASTERLY INTO SOUTHERN ILLINOIS THIS AFTERNOON CONTINUING
SOUTHEAST THIS EVENING AND TONIGHT...WINDS WILL SHIFT FROM WLY TO
SWLY AND NEVER GET SOUTHERLY. THIS WILL LIMIT THE INFLUX OF LOW
LEVEL MOISTURE. SO FEEL THAT THERE WILL LIKELY BE SOME VISBY
RESTRICTION TO MVFR LEVELS TONIGHT...BUT THE CHANCES FOR IFR VIS
REACHING THE TERMINALS IS SMALL. THE MOST LIKELY EXCEPTION WOULD BE
RFD AS THEY ARE IN CLOSEST PROXIMITY TO THE CURRENT LOW VISIBILITY
COVERAGE.
KREIN.
//ORD AND MDW CONFIDENCE...UPDATED 18Z...
MODERATE CONFIDENCE IN AT LEAST MVFR CIGS TO PERSIST THROUGH THE
PERIOD. THERE IS A CHANCE THAT CIGS COULD DROP TO 800-900FT AT
TIMES. THESE IS ALSO A CHANCE THAT CIGS COULD IMPROVE TO VFR FOR
BRIEF PERIODS.
MODERATE CONFIDENCE IN VISIBILITY DROPPING TO MVFR OVERNIGHT
TONIGHT.
KREIN.
//OUTLOOK FOR ORD/MDW FOR 06Z WEDNESDAY-12Z MONDAY...UPDATED 18Z...
TUESDAY NIGHT...MVFR CIGS/VIS IN BR.
WEDNESDAY...MVFR CIGS THRU THE DAY. IFR CIGS/VIS WITH RA/FZRA/FG
DEVELOPING IN THE EVENING.
THURSDAY...IFR CIGS/VIS IN FG/RA.
FRIDAY...IFR CIGS/VIS IN FG/RA.
SATURDAY...IFR BECMG MVFR CIGS/VIS IN BR/RA/SN...ENDING OVERNIGHT.
SUNDAY...VFR.
KREIN
&&
.MARINE...
154 PM...SEVERAL FORECAST CONCERNS THIS PERIOD WITH GALES POSSIBLE
SATURDAY AND SATURDAY NIGHT.
A COMPLEX PRESSURE GRADIENT WILL PERSIST INTO MID WEEK WITH DEEP
LOW PRESSURE OFF THE COAST OF MAINE SLOWLY MOVING NORTH ACROSS THE
CANADIAN MARITIMES THROUGH WEDNESDAY AS IT SLOWLY WEAKENS. A LARGE
AREA OF HIGH PRESSURE EXTENDING FROM THE WESTERN LAKES SOUTH TO
THE GULF OF MEXICO THIS AFTERNOON...WILL MOVE SOUTHEAST AND BE
CENTERED OVER FLORIDA BY WEDNESDAY MORNING...THEN MOVE BACK NORTH
TO THE MID ATLANTIC STATES BY THURSDAY MORNING. LOW PRESSURE WILL
MOVE NORTHEAST ACROSS MANITOBA TONIGHT INTO TUESDAY EVENTUALLY
BECOMING STATIONARY OVER WESTERN HUDSON BAY WEDNESDAY. THIS WILL
SET UP A TIGHTENING WESTERLY GRADIENT ACROSS THE LAKE TONIGHT WITH
30 KTS QUITE REASONABLE OVER NORTHERN LAKE MICHIGAN TONIGHT INTO
TUESDAY MORNING. AS THE MANITOBA LOW MOVES NORTH...THE GRADIENT
WILL WEAKEN SOME WITH WINDS DIMINISHING TUESDAY NIGHT.
A LARGE TROUGH OF LOW PRESSURE IS EXPECTED TO DEVELOP OVER THE
WESTERN PLAINS WEDNESDAY AND WEDNESDAY NIGHT. WITH THE HIGH MOVING
NORTH ACROSS THE EAST COAST DURING THIS TIME...SOUTHERLY FLOW WILL
INCREASE ACROSS THE WESTERN LAKES WITH WINDS BACK TO 15-25 KTS
WEDNESDAY NIGHT INTO THURSDAY. THE WESTERN TROUGH KICKS OUT ONE
WEAKER AREA OF LOW PRESSURE THURSDAY THAT MOVES ACROSS WESTERN
LAKE SUPERIOR THURSDAY EVENING. THIS MAY BRIEFLY ALLOW WINDS TO
INCREASE TO 30 KTS OVER PARTS OF LAKE MICHIGAN. THIS SOUTHERLY
FLOW WILL BRING WARMER TEMPERATURES AND LOW LEVEL MOISTURE THAT
WILL LIKELY RESULT IN QUITE A BIT OF FOG...AND THE POSSIBILITY OF
DENSE FOG.
THE MAIN TROUGH FORMS A LOW OVER THE CENTRAL PLAINS FRIDAY...
WHICH LIFTS NORTH AS IT DEEPENS OVER ONTARIO FRIDAY NIGHT INTO
SATURDAY. IN ADDITION TO THE LOW DEEPENING AND A TIGHTENING
PRESSURE GRADIENT...MUCH COLDER AIR WILL SPREAD ACROSS THE LAKES
REGION AND WEST/SOUTHWEST GALES LOOK QUITE REASONABLE DURING THIS
TIME PERIOD. THE LOW WILL CONTINUE NORTH ACROSS HUDSON BAY
SUNDAY...WITH WINDS SLOWLY DIMINISHING. CMS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 PM MONDAY.
&&
$$
