Forecast Discussions mentioning ACARS, received at FSL on 02/08/01

MAIN FORECAST CONCERNS CONTINUE TO REVOLVE AROUND DEVELOPMENT OF SOUTHWESTERN U.S. UPPER TROF...AND RESULTING PRECIP AND TEMPERATURE ISSUES AS IT LIFTS NORTHEAST INTO THE GREAT LAKES REGION THROUGH FRIDAY. AVN/ETA/NGM FAIRLY SIMILAR WITH THIS PROGRESSION THROUGH ABOUT 30 HOURS...THEN SIGNIFICANT TIMING DIFFERENCES ARISE WITH ETA/NGM FASTER WITH UPPER AND SURFACE SYSTEMS WHILE AVN LAGS BEHIND. THIS MAY NOT RESULT IN BIG SENSIBLE WEATHER DIFFERENCES OTHER THAN TIMING OF PRECIP ENDING AND COLD AIR ARRIVING ON FRIDAY.

IN THE SHORT TERM...SURFACE WARM FRONT INTO SOUTHERN MISSOURI AND WESTERN KENTUCKY AT 20Z...MOVING NORTHWARD WITH 4 MB PRESSURE FALLS TO THE NORTH. FORECAST SOUNDINGS AND ACARS AIRCRAFT SOUNDINGS SHOW ENTIRE COLUMN BELOW FREEZING INITITIALY THIS AFTERNOON...SO EXPECT PRECIPITATION TO BEGIN AS A MIX OF LIGHT SNOW...SLEET AND FREEZING RAIN. BY 06Z FORECAST SOUNDINGS WELL ABOVE FREEZING IN THE LOWER LAYERS...SO SHOULD SEE QUICK CHANGE OVER TO ALL RAIN DURING THE EVENING. CONCERN INTITIALLY ABOUT SURFACE TEMPS OVER NORTH CENTRAL ILLINOIS...AS LOW CLOUDS HAVE KEPT TEMPS IN THE 20S THIS AFTERNOON. THUS FREEZING RAIN MAY BE A PROBLEM IN THOSE AREAS UNTIL TEMPS RISE ABOVE FREEZING DURING THE NIGHT.

ETA AND AVN BOTH BRING THE WARM FRONT THROUGH THE WFO CHICAGO FORECAST AREA BY MORNING...AND INTO SOUTHERN WISCONSIN ON THURSDAY. AVN PUSHES IT A BIT FARTHER NORTH THAN DOES THE ETA...BUT NORTHERN IL AND NORTHWEST IND SHOULD MAKE IT INTO THE WARM SECTOR EVEN IN ETA SCENARIO. SHORT WAVE LIFTING NORTHEAST WITH WARMFRONT TONIGHT SHOULD RESULT IN A BATCH OF RAIN LATE TONIGHT...WITH MORE SHOWERY OR SCATTERED RAIN CONTINUING THURSDAY INTO THURSDAY NIGHT. SURFACE SYSTEM AND COLD FRONT TO MOVE ACROSS THE AREA FRIDAY MORNING...WHICH SHOULD PRODUCE ANOTHER IMPRESSIVE ROUND OF PRECIPITATION. COMBINATION OF MELTING OF CURRENT SNOWPACK...NEW RAINFALL TOTALS IN THE 1.5 TO 2 INCH RANGE...AND FROZEN GROUND MAY CAUSE RISES ON AREA STREAMS AND RIVERS. FLOOD OUTLOOK POTENTIAL WILL BE UPDATED AND ISSUED AROUND 330 PM.

SYSTEM DEPARTS RAPIDLY LATE FRIDAY...WITH A BRIEF CHANGE BACK TO LIGHT SNOW BEFORE ENDING. COLDER BUT DRY SAT.

COORDINATION WITH MKX AND DVN. THANKS. .CHI...NONE

RATZER



.OVERVIEW... COMPOSITE IMAGERY AND GLOBAL MODELS SHOW A LONG WAVE RIDGE NEAR 150W AND A TROUGH IN THE INTERMOUNTAIN W. SHORT WAVE FEATURES MOVING THROUGH THE 150W RIDGE ARE DRIVING SE AS THEY APPROACH THE W COAST. THE FIRST FEATURE IS A NEARLY CLOSED 996 MB LOW 51N/147W AT 03Z. THIS LOW IS FORECAST BY THE 00Z MESOETA TO MOVE INTO THE N OREGON COAST FRI WITH THE AVN A LITTLE FARTHER S AND OFFSHORE ON ITS TRACK AND THE NGM BRINGING THE LOW INTO THE OLYMPICS. WILL USE THE COMPROMISE MESOETA TONIGHT. IN THE LONGER RANGE A DEEPER SUB 1000 MB LOW MOVES SE ALONG THE BC COAST AND JUST OFF THE WA COAST SAT FOR A REPEAT PERFORMANCE. IN THIS NW FLOW WITH MAINLY OFFSHORE PRESSURE GRADIENTS AND TEMPERATURES NEAR THAT CRITICAL RAIN/SNOW TRANSITION VALUE... EXPECT LOW CONFIDENCE IN FORECAST DETAILS OF PCPN AMOUNTS AND TYPE THRU THE WEEKEND.

.SHORT TERM... TEMPERATURES ARE NEAR FREEZING TONIGHT...BUT DEWPOINTS ARE IN THE LOWER TO MID 20S WITH 850 MB TEMPERATURES NEAR M7C PER ACARS SOUNDINGS...AND FLOW IS OFFSHORE. ALSO PER ONE ACARS SOUNDING THAT HAD DEWPOINT THIS EVENING OUT OF KBFI THE AMS TO 10KFT IS QUITE DRY. SO ANY PCPN TONIGHT OR THU MORNING WILL BE IN THE FORM OF SN IN THE INTR. BASED ON RADAR EXPECT FLURRIES TO LIGHT SNOW NOW FROM VICTORIA NE TO POWELL RIVER BC TO SPREAD SE INTO THE AREA DURING THE EARLY MORNING HOURS. ACCEPT NEW MESO GUIDANCE THAT BRINGS 0.1 TO 0.3 INCHES PCPN TO THE INTERIOR BY 18Z. THEN TEMPERATURES BECOME SUFFICIENTLY WARM TO BRING THE NEAR SEA-LEVEL PCPN TYPE TO MAINLY RA. BASED ON MESOETA WOULD EXPECT A TRACE UP TO 1 INCH BY LATE MORNING MOST INTERIOR LOWLAND LOCATIONS WITH 1-3 INCH ACCUMULATIONS POSSIBLE OVER THE KITSAP PENINSULA AND HOOD CANAL AREA. SNOW LEVELS WILL LIKELY REMAIN NEAR 1000 FEET THRU FRI MORNING AS MARINE AIR NEVER REALLY MAKES IT IN. WILL ADJUST THE 1ST/2ND PERIOD FORECAST WORDING AND ISSUE A SNOW ADVISORY FOR THE KITSAP/HOOD CANAL AREA THRU THU MORNING.

.EXTENDED...THE 00Z AVN AND LAST NIGHTS MRF...AS WELL AS TONIGHTS MESOETA SHOW ANOTHER STRONG/COLD SHORT WAVE TROUGH DIGGING JUST OFFSHORE SAT/SUN...THEN DRIER NLY FLOW FOR MON/TUE FOLLOWED BY UNDERCUTTING OF THE OFFSHORE RIDGE/BLOCK ON WED FOR AN INCREASING CHANCE OF PRECIPITATION. NO CHANGES FOR NOW.

UIL 6++5 SEA 3775 OLM 3886 ALBRECHT

.SEW...GALE WARNING FOR W ENTRANCE OF STRAIT. .SMALL CRAFT ADVISORY COAST. .SNOW ADVISORY LATE TONIGHT AND THU MORNING KITSAP/HOOD CANAL AREA.

.KATX...VCP31/CSR31...OPERATIONAL.