AREA FORECAST DISCUSSION
NWS CHICAGO IL
AFDCHI 925 PM CST SUN FEB 22 2004
UPDATE TO GRIDS/PUBLIC FCSTS...GREATEST WAA GRADIENT MOVG ENE ACROSS
NRN IL...WITH N-S BACK EDGE OF MAIN AREA OF RA MOVG THRU N CNTRL IL.
EXPECT CONTINUOUS RA TO END IN NERN IL AROUND 06Z. CHC OF -SHRA
BEHIND THIS AREA LATE EVE AND OVRNGT AS MID LVL TROF OVR MN AND WRN
IA CONTS E TO MS RIVER.
TRS
525 PM CST SUN FEB 22 2004
UPDATE TO GRIDS/PUBLIC FCSTS...HAVE UPDATED TO GO ALL RA
TONIGHT...WITH ONLY A CHC OF MIXED -SN ACROSS NRN TIER OF IL
COUNTIES. APPEARS WAA ENUF TO COUNTER COOLING DUE TO LIFT AND
EVAPORATION OVER ALL BUT FAR NRN PART OF FA. DEW PTS INTO MID 30S
INTO SW WI WITH DBQ GOING FM -RA TO MIX BACK TO -RA BTWN 21Z AND
23Z. DEW PTS IN N CNTRL IL ALREADT IN MID 30S WITH THOSE IN FAR NERN
IL EXPECTED TO ALSO RISE INTO MID 30S NEXT COUPLE HRS.
TRS
245 PM CST SUN FEB 22 2004
.PUBLIC DISCUSSION FOR EVENING ZONES...
SKIES ARE FINALLY CLOUDY AND RAIN APPROACHING NRN IL. MANY DEWPTS
ARE AT OR ABOVE 32 AND SEE LITTLE OPPORTUNITY FOR EVAP COOLING OF
THE DEWPTS TO ALLOW MUCH CHC OF SNOW. HOWEVER BASED ON 850 TEMPS...
HAVE ORIENTED OCNL RAIN THIS EVE FROM LASALLE ON SOUTHEAST TO
IROQUOIS AND RAIN OR SNOW NORTH OF THERE. DID NOT MOVE PCPN INTO
NWRN INDY UNTIL 03Z. THEN MOVED OCNL RAIN LINE NORTH A BIT TO AROUND
I-80 BY 03Z AND LEFT IT THERE THRU 15Z MONDAY. HAVE NOWHERE A
CHANCE OF JUST SNOW ALONE UNTIL FROPA TOMORROW...AFT 15Z...IN THE
FAR NORTH AND NORTHWEST...THEN CHANGING TO SNOW BEFORE ENDING AS
COLD AIR ADVECTS SOUTHEAST THRU METRO AREA ARND NOONTIME. SNOW
AMOUNTS OVERNIGHT WITH THE WARM TEMPS HAVE BEEN BACKED OFF TO LESS
THAN AN INCH ALONG THAT NORTHERN TIER OF ILLINOIS COUNTIES. THESE
MAY BE QUITE SLUSHY. HAVE TAKEN PCPN OUT ALTOGETHER BY 00Z AS DRY
INTRUSION BEHIND SFC LOW INVADES AREA FROM THE WEST.
AM STILL CONFIDENT WITH ETA THIS RUN WHICH STRIVES TO DEEPEN AN
UPPER TROF IN NRN WI BY MONDAY. THIS IS FURTHER NORTH THAN YDA'S RUN
AND WUD ACCOUNT FOR THE WARMER TEMPS AND SUBSEQUENT EMPHASIS OF MORE
RAIN THAN SNOW. SFC TROF ASSOC WITH THIS UPR FEATURE IS WELL
REPRESENTED BY ETA. THIS INVERTED TROF POKES THRU WRN IA NOW AND IS
PROGGED TO DEEPEN TO A CLOSED LOW FEATURE IN NRN MO BY MDNGT TNGT...
WITH A VERY STRONG LOW LVL JET PUSHING WARM AIR FROM MO INTO NRN IL.
SFC LOW GENERALLY MOVES EAST ACROSS NRN IL DURING DAY MONDAY TAKING
FROPA THRU CHI AREA AROUND 18Z AND THRU NWRN INDY BY 00Z. IN THAT
PERIOD BOTH SFC AND UPR FEATURES TEND TO WEAKEN AND LITTLE OR NO
WRAPAROUND CLOUDINESS AND PCPN IS ADVECTED INTO NRN IL.
SYSTEM TENDS TO REFIRE EAST OF FCST AREA BUT BECOMES LITTLE CONCERN
AS HIGH PRESSURE BUILDS INTO AREA FROM MN MONDAY NGT. THIS CURVES
FLOW OFF OF LAKE MICHIGAN BUT TEMPS NOT COLD ENUF FOR LAKE EFFECT
CLDS OR PCPN THIS TIME AROUND. THIS RIDGE TENDS TO MEANDER IN THE
UPR MS VLY THRU WED WITH DRY CONDITIONS EXPECTED AND TEMPS NEAR
NORMAL.
RIDGE PASSES OVER LAKES THURSDAY BUT STILL MAINTAINS RELATIVELY
CLEAR SKIES THRU FRIDAY. A MAJOR UPR TROF COMES RIDING ACROSS THE
ROCKIES FRIDAY AND MAY SPREAD SOME WAA HIGH CLOUDINESS INTO THE AREA
SATURDAY...BUT LITTLE PCPN CONCERN TIL AFTER THEN. TEMPS MIGHT EVEN
SEE 50 BY THAT TIME.
RLB
&&
.AVIATION DISCUSSION FOR 00Z TAFS...
NRN STRM S/WV DIGGING THROUGH UPR MS VLY LATE AFTN WITH LLVL WAA
DVLPG AHEAD ACRS FCST AREA. ACARS AND FCST SOUNDINGS SHOWING SIG
WARM AIR IN LLVLS...WITH SFC DEWPOINTS INTO THE MID 30S ARCS MUCH OF
FCST AREA...SO ALTHOUGH HAS BEEN A LITTLE WET SNW MIXED IN AT ONSET
OF PCPN FROM KDBQ-KMSN...EXPECT PCPN TO BE ALL RA AT TAF SITES TNGT.
RADAR SHOWS AREA OF RA ACRS ERN IA/NRN IL WHICH HAS MOVED INTO KRFD
AND WILL MOVE INTO CHI AREA TERMINALS NEXT COUPLE OF HRS...WITH
VIS/CIGS INTO MVFR CAT IN HEAVIER RA. MAIN FORECAST QUESTION IS WHAT
HAPPENS LATER TONIGHT AT TAIL END OF WAA RAIN EPISODE. META FCST
SOUNDINGS IN BUFKIT SUGGEST CIGS RAISING BACK TO VFR AS DRY SLOT
CURRENTLY ACRS WRN IA MOVES IN...THOUGH MODEL MOS ALL PAINTING
PICTURE OF LINGERING LOWER CLDS WITH GRADUAL LOWERING TO IFR 08-09Z.
TRENDS ACROSS IA ATTM WOULD SUGGEST FIRST SCENARIO...THOUGH LIGHT
SERLY FLOW IN LLVLS UNDER INVERSION AND PCPN FALLING INTO
SUB-INVERSION LAYER WOULD SUGGEST CONTD MOISTENING AND FOR THIS
REASON HESITATE TO CHG MUCH FROM 18Z ISSUANCE.
PCPN ENDS EARLY MON AM AS MID LVL DRY SLOT MOVES ACRS
REGION...THOUGH AGAIN LLVL INVERSION AND TRAPPED MOISTURE LIKELY TO
KEEP IFR-MVFR CIG AND VIS CONDITIONS AT SFC. WK SFC LOW PASSES NORTH
OF FCST AREA IN WI...WITH TROUGH AXIS AND WNDSHFT OCCURRING AROUND
16Z AT KRFD AND AROUND 20Z KORD/KMDW. SHOULD SEE DIURNAL RISE IN
CIG/VIS BY MID MORN AND AGAIN WITH SOME DRYING WITH WIND SHIFT TO
280-290 DEG BEHIND TROUGH...THOUGH MODEL SOUNDINGS AND TIME SECTIONS
SUGGEST IFR CONDITIONS LATE MON AS THEY SIGNIFICANTLY INCREASE RH IN
LLVLS BY 00Z IN KRFD AND JUST AFT 00Z IN CHICAGO.
RATZER
&&
.LOT...WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LK MI...NONE.
&&
AREA FORECAST DISCUSSION
NWS CHICAGO IL
AFDCHI 554 PM CST SUN FEB 22 2004
.AVIATION DISCUSSION FOR 00Z TAFS...
NRN STRM S/WV DIGGING THROUGH UPR MS VLY LATE AFTN WITH LLVL WAA
DVLPG AHEAD ACRS FCST AREA. ACARS AND FCST SOUNDINGS SHOWING SIG
WARM AIR IN LLVLS...WITH SFC DEWPOINTS INTO THE MID 30S ARCS MUCH OF
FCST AREA...SO ALTHOUGH HAS BEEN A LITTLE WET SNW MIXED IN AT ONSET
OF PCPN FROM KDBQ-KMSN...EXPECT PCPN TO BE ALL RA AT TAF SITES TNGT.
RADAR SHOWS AREA OF RA ACRS ERN IA/NRN IL WHICH HAS MOVED INTO KRFD
AND WILL MOVE INTO CHI AREA TERMINALS NEXT COUPLE OF HRS...WITH
VIS/CIGS INTO MVFR CAT IN HEAVIER RA. MAIN FORECAST QUESTION IS WHAT
HAPPENS LATER TONIGHT AT TAIL END OF WAA RAIN EPISODE. META FCST
SOUNDINGS IN BUFKIT SUGGEST CIGS RAISING BACK TO VFR AS DRY SLOT
CURRENTLY ACRS WRN IA MOVES IN...THOUGH MODEL MOS ALL PAINTING
PICTURE OF LINGERING LOWER CLDS WITH GRADUAL LOWERING TO IFR 08-09Z.
TRENDS ACROSS IA ATTM WOULD SUGGEST FIRST SCENARIO...THOUGH LIGHT
SERLY FLOW IN LLVLS UNDER INVERSION AND PCPN FALLING INTO
SUB-INVERSION LAYER WOULD SUGGEST CONTD MOISTENING AND FOR THIS
REASON HESITATE TO CHG MUCH FROM 18Z ISSUANCE.
PCPN ENDS EARLY MON AM AS MID LVL DRY SLOT MOVES ACRS
REGION...THOUGH AGAIN LLVL INVERSION AND TRAPPED MOISTURE LIKELY TO
KEEP IFR-MVFR CIG AND VIS CONDITIONS AT SFC. WK SFC LOW PASSES NORTH
OF FCST AREA IN WI...WITH TROUGH AXIS AND WNDSHFT OCCURRING AROUND
16Z AT KRFD AND AROUND 20Z KORD/KMDW. SHOULD SEE DIURNAL RISE IN
CIG/VIS BY MID MORN AND AGAIN WITH SOME DRYING WITH WIND SHIFT TO
280-290 DEG BEHIND TROUGH...THOUGH MODEL SOUNDINGS AND TIME SECTIONS
SUGGEST IFR CONDITIONS LATE MON AS THEY SIGNIFICANTLY INCREASE RH IN
LLVLS BY 00Z IN KRFD AND JUST AFT 00Z IN CHICAGO.
RATZER
&&
.PUBLIC DISCUSSION FOR EVENING ZONES...
UPDATE TO GRIDS/PUBLIC FCSTS...HAVE UPDATED TO GO ALL RA
TONIGHT...WITH ONLY A CHC OF MIXED -SN ACROSS NRN TIER OF IL
COUNTIES. APPEARS WAA ENUF TO COUNTER COOLING DUE TO LIFT AND
EVAPORATION OVER ALL BUT FAR NRN PART OF FA. DEW PTS INTO MID 30S
INTO SW WI WITH DBQ GOING FM -RA TO MIX BACK TO -RA BTWN 21Z AND
23Z. DEW PTS IN N CNTRL IL ALREADT IN MID 30S WITH THOSE IN FAR NERN
IL EXPECTED TO ALSO RISE INTO MID 30S NEXT COUPLE HRS.
245 PM CST SUN FEB 22 2004
SKIES ARE FINALLY CLOUDY AND RAIN APPROACHING NRN IL. MANY DEWPTS
ARE AT OR ABOVE 32 AND SEE LITTLE OPPORTUNITY FOR EVAP COOLING OF
THE DEWPTS TO ALLOW MUCH CHC OF SNOW. HOWEVER BASED ON 850 TEMPS...
HAVE ORIENTED OCNL RAIN THIS EVE FROM LASALLE ON SOUTHEAST TO
IROQUOIS AND RAIN OR SNOW NORTH OF THERE. DID NOT MOVE PCPN INTO
NWRN INDY UNTIL 03Z. THEN MOVED OCNL RAIN LINE NORTH A BIT TO AROUND
I-80 BY 03Z AND LEFT IT THERE THRU 15Z MONDAY. HAVE NOWHERE A
CHANCE OF JUST SNOW ALONE UNTIL FROPA TOMORROW...AFT 15Z...IN THE
FAR NORTH AND NORTHWEST...THEN CHANGING TO SNOW BEFORE ENDING AS
COLD AIR ADVECTS SOUTHEAST THRU METRO AREA ARND NOONTIME. SNOW
AMOUNTS OVERNIGHT WITH THE WARM TEMPS HAVE BEEN BACKED OFF TO LESS
THAN AN INCH ALONG THAT NORTHERN TIER OF ILLINOIS COUNTIES. THESE
MAY BE QUITE SLUSHY. HAVE TAKEN PCPN OUT ALTOGETHER BY 00Z AS DRY
INTRUSION BEHIND SFC LOW INVADES AREA FROM THE WEST.
AM STILL CONFIDENT WITH ETA THIS RUN WHICH STRIVES TO DEEPEN AN
UPPER TROF IN NRN WI BY MONDAY. THIS IS FURTHER NORTH THAN YDA'S RUN
AND WUD ACCOUNT FOR THE WARMER TEMPS AND SUBSEQUENT EMPHASIS OF MORE
RAIN THAN SNOW. SFC TROF ASSOC WITH THIS UPR FEATURE IS WELL
REPRESENTED BY ETA. THIS INVERTED TROF POKES THRU WRN IA NOW AND IS
PROGGED TO DEEPEN TO A CLOSED LOW FEATURE IN NRN MO BY MDNGT TNGT...
WITH A VERY STRONG LOW LVL JET PUSHING WARM AIR FROM MO INTO NRN IL.
SFC LOW GENERALLY MOVES EAST ACROSS NRN IL DURING DAY MONDAY TAKING
FROPA THRU CHI AREA AROUND 18Z AND THRU NWRN INDY BY 00Z. IN THAT
PERIOD BOTH SFC AND UPR FEATURES TEND TO WEAKEN AND LITTLE OR NO
WRAPAROUND CLOUDINESS AND PCPN IS ADVECTED INTO NRN IL.
SYSTEM TENDS TO REFIRE EAST OF FCST AREA BUT BECOMES LITTLE CONCERN
AS HIGH PRESSURE BUILDS INTO AREA FROM MN MONDAY NGT. THIS CURVES
FLOW OFF OF LAKE MICHIGAN BUT TEMPS NOT COLD ENUF FOR LAKE EFFECT
CLDS OR PCPN THIS TIME AROUND. THIS RIDGE TENDS TO MEANDER IN THE
UPR MS VLY THRU WED WITH DRY CONDITIONS EXPECTED AND TEMPS NEAR
NORMAL.
RIDGE PASSES OVER LAKES THURSDAY BUT STILL MAINTAINS RELATIVELY
CLEAR SKIES THRU FRIDAY. A MAJOR UPR TROF COMES RIDING ACROSS THE
ROCKIES FRIDAY AND MAY SPREAD SOME WAA HIGH CLOUDINESS INTO THE AREA
SATURDAY...BUT LITTLE PCPN CONCERN TIL AFTER THEN. TEMPS MIGHT EVEN
SEE 50 BY THAT TIME.
RLB
&&
.LOT...WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LK MI...NONE.
&&