RSS FeedsIssued by NWS Quad Cities, IA IL
000 FXUS63 KDVN 242115 AFDDVN AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE QUAD CITIES IA IL 315 PM CST TUE NOV 24 2009 .SYNOPSIS... VERY...VERY COMPLICATED WEATHER SCENE ACROSS THE AREA THIS AFTERNOON. A FAIRLY STRONG SURFACE LOW HAS MADE ITS WAY TO SOUTHERN IOWA THIS AFTERNOON FROM NORTHEAST KANSAS EARLY THIS MORNING. PRESSURE FALL TRENDS INDICATE IT SHOULD CONTINUE THE EAST-NORTHEAST TRACK. A WARM FRONT EXTENDED EAST-SOUTHEAST FROM THE LOW ACROSS THE SOUTHERN PORTIONS OF THE FORECAST AREA...AND DOWN INTO ILLINOIS. NORTH OF THE BOUNDARY IS WHERE MOST OF OUR PRECIPITATION IS...ALONG WITH SOME POTENT LITTLE THUNDERSTORMS ALONG THE BOUNDARY IN SOUTHEAST IOWA. AT UPPER LEVELS...THE 500MB SYSTEM IS NEARLY STACKED RIGHT OVER THE TOP OF THE SURFACE LOW...WITH GOOD FALLS ALOFT INDICATING CONTINUED EAST MOVEMENT. OF NOTE...THERE IS A SIGNIFICANT SHORTWAVE DROPPING DOWN FROM CANADA INTO THE DAKOTAS...WITH A SIGNIFICANT AMOUNT OF COLD AIR ASSOCIATED WITH IT. A NICE PLUME OF MOISTURE IS INDICATED EXTENDING TOWARDS EASTERN IOWA ON THE 850MB ANALYSIS...WHICH IS LIKELY FEEDING THE VERY SIGNIFICANT RAIN BAND CURRENTLY AFFECTING THE EASTERN HALF OF THE FORECAST AREA. ...LE... && .SHORT TERM...TONIGHT AND WEDNESDAY...TONIGHT THIS RAIN BAND WILL CONTINUE TO ROTATE NORTHEAST ACROSS THE FORECAST AREA...AS IS BEST DEPICTED BY THE GFS THIS EVENING. IT ALSO APPEARS THAT OUR BEST RAINFALL AMOUNTS SHOULD BE FALLING THIS AFTERNOON AND EVENING...WITH AMOUNTS AROUND ONE INCH DURING THIS 12 HOUR PERIOD. THE GFS SEEMS TO HAVE INITIALIZED THE BEST TODAY...SO HAVE FOLLOWED IT FOR TONIGHT...AND HAVE BLENDED TOWARDS THE NAM A LITTLE FOR WEDNESDAY FOR ITS BETTER HANDLING OF THE MID LEVEL TEMPERATURES. ESSENTIALLY THIS EVENING IS THE BEST LIFT...WITH FRONTOGENESIS...STRONG WARM AIR ADVECTION LIFT...AND EVEN A WEAK TROWAL APPARENT DURING THE EVENING HOURS BEFORE THESE FEATURES WEAKEN OVERNIGHT. LATE OVERNIGHT AND WEDNESDAY MORNING WE SHOULD BE IN A LULL PERIOD...WITH THE BEST DYNAMICS NOW FORMING UP WITH THE NEW SHORTWAVE DUE TO PUNCH IN HERE WEDNESDAY NIGHT. THIS WAVE BEGINS TO GET IN HERE DURING THE AFTERNOON. HAVE KEPT POPS THE SAME THROUGHOUT THE DAY...BUT THEY SHOULD BE MORE IN THE EARLY MORNING AND THEN LATE AFTERNOON HOURS. THERE IS A SIGNIFICANT AMOUNT OF COLD AIR PUNCHING INTO THE AREA WITH THIS SECOND WAVE...AND IT IS LIKELY TO CAUSE THE RAINFALL TO MIX WITH SNOW BY LATE AFTERNOON IN THE FAR NORTHWESTERN COUNTIES. THE COLD AIR ARRIVES VERY LATE INDEED...AND WE MAY NOT SEE THE MIX DEVELOP UNTIL LATE AFTERNOON. THE GROUND TEMPERATURES ARE STILL PRETTY WARM...AND DO NOT ANTICIPATE SIGNIFICANT ACCUMULATIONS DURING THE DAYTIME...BUT HAVE INCLUDED A TENTH IN THE GRIDS IN CASE THE PRECIPITATION RATES ARE RAPID ENOUGH TO OVERWHELM THE WARM GROUND. ...LE... .LONG TERM...WEDNESDAY NIGHT THROUGH NEXT TUESDAY PRIMARY FOCUS IS THE POTENTIAL FIRST WIDESPREAD MEASURABLE SNOWFALL OF THE SEASON THAT IS TIMED TO DEVELOP DURING THE CRITICAL PRE-THANKSGIVING PEAK TRAVEL PERIOD. IN SHORT...THE POTENTIAL STILL LOOKS LIKELY FOR UP TO A FEW INCHES OF WET SNOW...PRIMARILY ON ELEVATED AND GRASS COVERED SURFACES...WED EVENING INTO EARLY THU MORNING. THE AREA OF GREATEST LIKELIHOOD HAS SHIFTED EAST SOME...INTO FAR EASTERN IA AND NW IL...ROUGHLY N OF HIGHWAY 30. WITH STILL SOME UNCERTAINTY ABOUT CRITICAL THERMAL FIELDS CONSIDERING THE RATHER COMPLEX SYSTEM...WILL HOLD OFF ON AN ADVISORY FOR NOW. 12Z UPPER AIR ANALYSIS INDICATED 110 M HT FALLS AHEAD OF THE STRONG SHORTWAVE IN SOUTHERN MANITOBA...SEEN THIS AFTERNOON ON WV IMAGERY DROPPING SE FROM FAR SRN SASK INTO NW ND. THIS DEEPENING IS LIKELY IN RESPONSE TO ENERGY FROM A 130KT H3 JET TOPPING THE PACIFIC NW UPPER RIDGE...WHICH IS PROGGED BY SHORT TERM MODELS TO CARVE THIS SHORTWAVE THIS INTO ANOTHER IMPRESSIVE H5 LOW OVERHEAD BY WED EVENING. THIS 535 DM LOW WOULD BE EVEN DEEPER THAN THE CURRENT SYSTEM THAT IS JUST EXITING THE EASTERN GREAT LAKES BY THIS TIME. AT THE SURFACE...THIS SLOWS THE DEPARTING LOW OVER THE GREAT LAKES AND DEVELOPS A TROUGH THAT ROTATES AROUND THE WEST SIDE OF THE LOW THROUGH THE AREA THU NIGHT. MODELS SHOW IMPRESSIVE MID LEVEL OMEGA AND A TROWAL LIKE FEATURE ACCOMPANYING THIS PROCESS WITH GREATEST LIFT OVER THE N CENTRAL AND NE CWFA LATE WED EVENING. IN ADDITION... THE STRENGTH OF THE UPPER LOW RESULTS IN STEEP MID LEVEL LAPSE RATES THAT COULD ALLOW SOME CONVECTIVE ENHANCEMENT. THE MOST SIGNIFICANT MODEL DIFFERENCE IS IN LOW LEVEL THERMAL FIELDS...WHERE THE GFS IS A COUPLE DEGREES C WARMER AT H8...OR SLOWER WITH COLD AIR ADVECTION WRAPPING SW BEHIND THE UPPER LOW... AND ALSO WARMER WITH THE LOW LEVEL TEMPERATURES IN THE TROUGH EXTENDING OUT OF THE GREAT LAKES. THE WRF/NAM AND ECMWF ARE SOMEWHAT COLDER AND SUPPORTIVE OF A FASTER CHANGEOVER TO SNOW. WITH THE STRENGTH OF FORCING AND OMEGA IN FAVORABLE TEMPERATURES ALOFT FOR SNOW GROWTH...WILL LEAN TOWARD A FASTER CHANGE OVER FROM RAIN TO SNOW WED EVENING. INITIALLY WARM PAVEMENT AND SOIL TEMPERATURES WILL REQUIRE AT LEAST MODERATE SNOWFALL RATES TO ALLOW ACCUMULATION... WHICH LOOKS LIKELY GIVEN THE FORCING. CONSIDERING THE LOW CONFIDENCE IN THE CRITICAL LOW LEVEL THERMAL FIELDS...THE PREVIOUS FORECAST OF 1 TO 2 INCHES STILL LOOKS VALID. HAVE ADJUSTED THIS AREA TO ROUGHLY NE OF A LINE FROM ABOUT VINTON...THROUGH CID...MLI TO PRINCETON IL. BEST POTENTIAL FOR ACCUMULATIONS ON PAVEMENT AND AMOUNTS CLOSER TO 2 INCHES WILL BE ALONG HIGHWAY 20 CORRIDOR FROM DBQ TO FREEPORT. ON THU...HAVE ADJUSTED TIMING SOME TO HAVE BULK OF SNOW OR FLURRIES EXITING THE AREA EARLY IN THE MORNING. WARM ADVECTION THEN KICKS IN BY EVENING...BUT NOT IN TIME TO ALLOW SIGNIFICANT WARMING AND KEPT HIGHS LIMITED TO THE UPPER 30S TO AROUND 40. BEYOND...FRI AND SAT WILL HAVE MODERATING TEMPERATURES BEFORE NEXT WEAKER WAVE IN A SPLIT FLOW PATTERN PUSHES THROUGH AND BRINGS RAIN OR POSSIBLY RAIN SNOW MIX SUN NIGHT INTO MON. TUE WILL LIKELY BE BETWEEN SYSTEMS WITH NEAR NORMAL TEMPERATURES. ..SHEETS.. && .AVIATION... CONDITIONS TO REMAIN IN THE SOUP THROUGH AT LEAST EARLY WEDNESDAY MORNING AS THE LOW PRESSURE SYSTEM ROTATES ACROSS THE AREA TODAY AND TONIGHT...WITH IMPROVING CONDITIONS AFTER 10Z WEDNESDAY MORNING. KDBQ WILL HAVE MAINLY LIFR CIGS AND VSBYS THROUGH THE PERIOD. KCID AND KMLI WILL LIFT BRIEFLY INTO MVFR CIGS AND VSBYS THIS AFTERNOON BEFORE LOWERING BACK DOWN INTO LIFR LATE BY TONIGHT. KBRL IS ALREADY UP TO MVFR...BUT SHOULD LOWER DOWN TO IFR LATE THIS AFTERNOON OR EARLY THIS EVENING. TOMORROW MORNING ALL BUT KDBQ SHOULD RISE UP INTO IFR BEFORE DROPPING AGAIN IN THE AFTERNOON AS THE NEXT SYSTEM MOVES IN. ...LE... && .DVN WATCHES/WARNINGS/ADVISORIES... IA...NONE. IL...NONE. MO...NONE. && $$ LE/SHEETS
