Issued by NWS Green Bay, WI
000 FXUS63 KGRB 242032 AFDGRB AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREEN BAY WI 232 PM CST TUE NOV 24 2009 .SHORT TERM...TNGT AND WED. MAIN FCST FOCUS TO BE ON EXTENT OF PCPN ASSOCIATED WITH THE FIRST SYSTEM TNGT INTO WED MORNING. THE 19Z MSAS SFC ANALYSIS SHOWED AN AREA OF LOW PRES LOCATED JUST SOUTH OF DSM WITH A CDFNT EXTENDED SEWD THRU ERN MO. AN OCCLUDED FNT STRETCHED NWD FROM THE LOW PRES ALONG THE MN/WI BORDER. VSBL SATL IMAGERY INDICATED A GOOD DEAL OF CLDS ASSOCIATED WITH THE SYSTEM WITH A FEW BREAKS IN THE OVERCAST OVR CNTRL WI. RADAR MOSAIC SHOWED A SLUG OF MSTR APPROACHING THE WI/IL BORDER AHD OF THE CDFNT MAKING A MOV TO THE NORTH. MDLS ARE VERY CONSISTENT WITH EACH OTHER IN BRINGING THE SFC LOW NEWD ACROSS NW IL AT MIDNGT AND THEN JUST NE OF MKE BY 12Z WED. COMBINATION OF OCCLUDED FNTL PASSAGE AT THE SFC...STG MID-LVL FORCING (BOTH Q-G AND FRONTOGENETICAL) AND LEFT EXIT RGN OF THE UPR JET ALL POINT TO A RAINY NGT OVR NE WI. BASED ON THE PROJECTED PATH OF THE SFC LOW AND LOCATION OF THE STRONGEST FORCING...HAVE PLACED HIGHEST POPS OVR E-CNTRL WI AND TIERED DOWN TO BARELY LIKELY POPS OVR N-CNTRL WI. E-CNTRL WI SHOULD SEE PCPN AMTS IN THE 0.25-0.50" RANGE OVRNGT. DO NOT SEE TEMPS DROPPING TOO FAR TNGT WITH PLENTY OF CLDS/PCPN EXPECTED...THUS HAVE ESSENTIALLY PLAYED PERSISTENCE WITH MINS COMPARABLE TO TUE MORNING. THIS INITIAL SYSTEM BEGINS TO ACCELERATE NEWD TOWARD NRN SECTIONS OF THE GREAT LKS ON WED IN RESPONSE TO A POWERFUL LOOKING UPSTREAM KICKER DROPPING SEWD INTO THE MIDWEST. BEST FORCING AND LIFT WITH THIS SECOND SYSTEM IS FCST TO REMAIN TO OUR SOUTH AND WEST ON WED... LEAVING NE WI WITH DIMINISHED FORCING IN THE MID-LVLS AND NOT MUCH AT THE SFC OR ALOFT. CURRENT THINKING IS TO SEE PCPN WIND DOWN IN THE MORNING AND THEN PICK BACK UP LTR IN THE AFTERNOON...ESP OVR CNTRL WI. DECIDED TO NOT GET TOO FANCY WITH THE TIMING AND JUST KEPT THE LIKELY WORDING GOING FOR NOW. MILD START TO THE DAY SHOULD ALLOW TEMPS TO RISE 5 TO 10 DEGS FROM MORNING LOWS...THUS HAVE ADDED A COUPLE OF DEGS TO THE PREV FCST. .LONG TERM...WEDNESDAY NIGHT THROUGH NEXT TUESDAY. INITIAL FOCUS ON THE MID WEEK SYSTEM TRACKING OVER THE GREAT LAKES REGION AND THEN DEALING WITH ANOTHER SYSTEM FOR LATE NEXT WEEKEND OR THE START OF THE NEW WEEK. LATEST MODELS RUNS EARLY TODAY IN GOOD AGREEMENT WITH TRENDING THE BETTER DYNAMICS OF THE SYSTEM TO THE SOUTH WEDNESDAY NIGHT INTO THURSDAY AND SIGNIFICANTLY FASTER. PCPN TYPE CHALLENGE REMAINS WITH THIS FORECAST...BUT BASED ON FORECAST SOUNDINGS...EXPECT RAIN TO INITIALLY DOMINATE WEDNESDAY NIGHT. AS BROAD UPPER LOW DEEPENS LATER WED NIGHT AND TEMPS ALOFT COOL ALONG WITH THE INJECTION OF THE SECONDARY COLD SHORTWAVE...EXPECT A TRANSITION FROM RAIN TO A MIX FROM WEST TO EAST. THIS SECONDARY SHORT WAVE IS PROGGED TO TARGET SRN WI WED NIGHT INTO EARLY THURSDAY...WHERE THE BEST POTENTIAL OF SNOW ACCUMULATION IS NOW ANTICIPATED. BUT STILL EXPECT SNOW TO BECOME MIXED WITH RAIN OR CHANGE TO SNOW LATER WED NIGHT AS TEMPS ALOFT COOL...BUT BY THE TIME THE COMPLETE CHANGEOVER TO SNOW OCCURS...SYSTEM IS ALREADY PROGGED TO BE PULLING OUT TO THE EAST TO DIMINISH THE PCPN FROM WEST TO EAST LATER THURSDAY MORNING. ECMWF RUN DOES HANG BACK A BIT MORE PCPN OVER EC WI INTO THURSDAY FOR THE OUTLIER WHILE THE GFS AND NAM FURTHER SOUTH. IF THE ECMWF VERIFIES...A FEW INCHES OF SNOW POSSIBLE OVER THE FOX CITIES AREA. DUE TO THE FASTER CONSENSUS THURSDAY...WILL MENTION A DIMINISHING PCPN TREND FOR THURSDAY. THE ONLY EXCEPTION WOULD BE LES SNOW SHOWERS OVER FAR NC WI CONTINUING INTO THURSDAY NIGHT. RETURN FLOW WITH THE UPPER RIDGE ALREADY SETTING UP FRIDAY TO END ANY LES ACTIVITY. TEMPERATURES WILL BE BACK TO NEAR OR SLIGHTLY NORMAL BY SATURDAY. MDM RANGE PROGS NOT IN AGREEMENT WITH THE SUNDAY INTO MONDAY SYSTEM WITH RESPECT TO LOCATION AND TIMING OF MAIN UPPER SUPPORT. IN ADDITION H8/H7 GUID TEMPS FOR THIS PERIOD SUGGEST A MIX OVER MOST LOCATIONS WITH MAINLY RAIN SUNDAY OVER THE SOUTHERN PORTION OF THE FORECAST AREA BEFORE SWITCHING TO A LIGHT MIX AS THE SYSTEM SHIFTS EAST. && .AVIATION...KIND OF A MISH-MASH OF CIGS THIS AFTERNOON RANGING FROM VFR TO IFR WHILE MVFR VSBYS HOLDING FOR THE MOST PART. AS THE RAIN MOVS INTO THIS EVENING...LOOK FOR BOTH CIGS AND VSBYS TO SETTLE INTO THE IFR RANGE FOR THE OVRNGT HRS. AS THE FIRST SYSTEM DEPARTS WED MORNING...EXPECT TO SEE BOTH CIGS AND VSBYS RISE INTO THE MVFR RANGE FOR THE REMAINDER OF THE DAY. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ AK/TDH
