FXUS63 KEAX 210602 AFDEAX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO 100 AM CDT SAT AUG 21 2004 .DISCUSSION... EARLY MORNING SATELLITE IMAGERY AND UPPER AIR ANALYSIS SHOW UNSEASONABLY STRONG UPPER LOW OVER HUDSON BAY WITH MEAN TROUGH EXTENDING SOUTHWARD ACROSS GREAT LAKES INTO MID MS VALLEY AND OZARKS REGION. 04Z SUBJECTIVE SURFACE ANALYSIS INDICATES COLD FRONT EXTENDING ACROSS OH VALLEY BACK INTO EASTERN TX SUPPRESSING GULF MOISTURE SOUTH OF REGION...WHILE SECONDARY COLD FRONT ACROSS SOUTHERN IA INTO CENTRAL NE MARKS THE LEADING EDGE OF UNSEASONABLY COOL AND DRY AIR...WITH DEW POINTS IN EASTERN SD/WESTERN MN IN THE 30S. AHEAD OF THIS FRONT LIGHT WINDS COMBINED WITH A MOIST GROUND FROM THURSDAY NIGHT'S RAINFALL WILL ALLOW FAVORABLE SETUP FOR DENSE FOG OVERNIGHT ACROSS SOUTHERN TWO THIRDS OF CWA. WILL LIKELY ISSUE DENSE FOG ADVISORY FOR AREAS ALONG/SOUTH OF HIGHWAY 36 THROUGH MID MORNING. MEANWHILE FURTHER WEST STRONG BELT OF WESTERLIES HAS UNDERCUT WESTERN RIDGE...RESULTING IN DEVELOPMENT OF REX BLOCK ACROSS AK/GULF OF AK...AND FALLING HEIGHTS ACROSS PACIFIC NORTHWEST. THIS IS THE ONSET OF A LONGWAVE PATTERN CHANGE WHICH WILL ALLOW SUMMER-LIKE WEATHER TO RETURN TO THE REGION EARLY NEXT WEEK...AS SOUTHWESTERLY FLOW DEVELOPS ACROSS THE CENTRAL CONUS. GOING FORECAST HANDLES WARM-UP WELL...WITH TEMPERATURES RETURNING TO NEAR 90 ACROSS PORTIONS OF THE CWA BY MONDAY...WITH DEW POINTS LIKELY RISING BACK INTO THE 70S. AS THIS WARMER AIR RETURNS TO THE REGION...MAY SEE A CHANCE OF ELEVATED SHOWERS/THUNDERSTORMS LATE SUNDAY NIGHT/EARLY MONDAY MORNING. ETA INDICATES DECENT PRESSURE ADVECTION ALONG 310K SURFACE ACROSS NORTHERN CWA ALONG WITH AREA OF ELEVATED INSTABILITY AHEAD OF WEAK SHORTWAVE DEPICTED BY BOTH ETA AND GFS. FOR NOW HAVE INCLUDED SLIGHT CHANCE POPS FOR THIS TIME PERIOD. SEAMAN && .PREV DISCUSSION... THE MID AFTERNOON SURFACE ANALYSIS DEPICTS TWO DISTINCT COLD FRONTS OVER THE CENTRAL UNITED STATES. THE FIRST IS PUSHING THROUGH SOUTHERN MISSOURI AND IS ASSOCIATED WITH THE WAVE THAT BROUGHT WIDESPREAD SHOWERS AND THUNDERSTORMS TO THE REGION LAST NIGHT. THE SECOND COLD FRONT IS MAKING ITS WAY INTO NORTHERN IOWA, AND IS REMARKABLY CHILLY FOR THIS TIME OF YEAR. TEMPERATURES BEHIND THE FRONT IN NORTHERN MINNESOTA ARE ONLY 60 DEGREES WITH FULL SUNSHINE! THIS SUMMER CONTINUES TO BE ONE OF THE COOLEST IN MANY YEARS FOR THE CENTRAL UNITED STATES. THE PATTERN IS BREAKING HOWEVER, AND A THERE IS CLEAR EVIDENCE OF THIS ON WATER VAPOR IMAGERY TODAY. THE WEST COAST RIDGE THAT HAS BEEN PERSISTENT NEARLY ALL SUMMER HAS BEEN SQUEEZED OFF. UNUSUALLY STRONG WESTERLIES OVER THE NORTHERN PACIFIC BASHED THE NORTHERN PERIPHERY OF THE HOT RIDGE DOWN THIS MORNING, AND THIS WILL FORCE THE UPPER LOW OVER CENTRAL CANADA TO MOVE EAST THIS WEEKEND. SO DESPITE THE VERY COLD AIRMASS OVER THE NORTHERN PLAINS THIS AFTERNOON, THE RAPID PROGRESSION OF THE POLAR VORTEX EAST THIS WEEKEND WILL ONLY PROVIDE MISSOURI WITH A GLANCING BRUSH WITH THE COLD AIR. BEFORE THE BIG WARM UP EARLY NEXT WEEK, SURFACE HIGH PRESSURE WILL BRING VERY PLEASANT CONDITIONS TO THE REGION TOMORROW. PER MY EARLIER DISCUSSION SHALLOW GROUND FOG IS LIKELY TONIGHT. THE SHORTWAVE RESPONSIBLE FOR THE CLOUD COVER THIS AFTERNOON IS PROGRESSING TO THE EAST, AND SKIES SHOULD CLEAR OUT EARLY THIS EVENING OVER NORTHERN MISSOURI. WEAK LOW LEVEL FLOW, MOIST GROUND FROM LAST NIGHT'S RAIN, AND GOOD RADIATIONAL COOLING POINT TOWARD SOME LOCALLY DENSE FOG IN FAVORED AREAS. CLOUD COVER THIS AFTERNOON HAS KEPT THE MAJORITY OF MISSOURI COOL AND MOIST TODAY, SO SATURATION CAN BE EXPECTED EARLY TONIGHT. AFTER THE FOG BURNS OFF TOMORROW MORNING, QUIET CONDITIONS ARE EXPECTED THROUGH THE REST OF THE WEEKEND. ZONAL FLOW ACROSS THE ROCKIES WILL INDUCE LEE SIDE TROUGHING OVER THE HIGH PLAINS AND SOUTHERLY WINDS WILL BRING HIGHER DEWPOINTS BACK TO THE REGION ON SUNDAY. THEY MAY REACH 70 DEGREES BY SUNDAY AFTERNOON SINCE LOW LEVEL MOISTURE HAS BUILT UP OVER TEXAS AND LOUISIANAN DURING THE LAST COUPLE OF DAYS. THIS AIRMASS IS HEADED OUR WAY. NEXT WEEK WILL PROBABLY FEEL LIKE SUMMER, AND SINCE THE LONGWAVE PATTERN HAS BROKEN IT MAY STICK AROUND FOR A WHILE. KOCH THE MEDIUM RANGE MODELS HAVE BEGUN TO CONVERGE TOWARD A SOLUTION FOR NEXT WEEK...WITH THE 00Z GFS COMING MORE IN LINE WITH THE ECMWF AND ENSEMBLE MEAN. THE ANTICIPATED PATTERN CHANGE WITH AN UPPER TROUGH ENTERING THE NORTHWEST CONUS WHILE THE RIDGE SLIDES EAST...WILL PLACE THIS REGION UNDER SOUTHWEST FLOW ALOFT. A PREDOMINANT SOUTHERLY FLOW AT THE SURFACE WILL ALLOW FOR AN INCREASE IN TEMPERATURES AND MOISTURE FOR NEXT WEEK. WITH A BIT MORE CONFIDENCE IN THE MODEL SOLUTIONS...ALBEIT STILL RATHER LOW...HAVE TRIED TO NARROW DOWN PRECIPITATION CHANCES. A SHORTWAVE IS FORECAST TO MOVE ACROSS THE CENTRAL PLAINS ON MONDAY. HAVE RETAINED SLIGHT PRECIPITATION CHANCES ACROSS EAST CENTRAL KANSAS AND CENTRAL MISSOURI WHERE MORE FAVORABLE FORCING AND MOISTURE WILL BE. A SURFACE FRONT IS EXPECTED TO STALL FROM MINNESOTA INTO WESTERN KANSAS THE MIDDLE OF NEXT WEEK. A PORTION OF THE UPPER TROUGH IS TO ADVANCE EAST AND DISLODGE THE FRONT TOWARD THE FORECAST AREA ON FRIDAY...WITH PRECIPITATION CHANCES INCREASING ACCORDINGLY. STOFLET && .PREV DISCUSSION... 1130 AM... TEMPERATURES HAVE GONE NO WHERE THIS MORNING AND THICK CLOUD COVER WILL PLAGUE MISSOURI AND EASTERN KANSAS FOR MUCH OF THE DAY SOUTH OF INTERSTATE 70. I HAVE LOWERED TEMPERATURES FOR MUCH OF THE REGION. SEDALIA, CLINTON, WARRENSBURG, AND SEDALIA WILL STRUGGLE TO REACH 70. FOG STILL LOOKS LIKE A GOOD BET TONIGHT. DEWPOINTS WILL NOT DROP MUCH TODAY GIVEN THE VERY WEAK LOW LEVEL FLOW. CLOUD TRENDS WILL BE MONITORED THIS AFTERNOON AND EVENING, BUT I EXPECT A GRADUAL CLEARING FROM NORTH TO SOUTH. MODEL SOUNDINGS SUGGEST DRY AIR ABOVE A SHALLOW MOIST LAYER WHICH IS AN IDEAL SET UP FOR RADIATION FOG. THERE IS ALMOST NO FLOW FORECAST IN THE LOWEST 150MB EITHER, SO MIXING SHOULD NOT BE A PROBLEM. I'VE UPDATED THE GRIDS ACCORDINGLY, AND ALL BUT EXTREME NORTHERN MISSOURI MAY BE DEALING WITH DENSE FOG TOMORROW MORNING. (SLIGHTLY LOWER DEWPOINTS ARE EXPECTED ALONG THE IOWA BORDER TONIGHT.) KOCH && .EAX WATCHES/WARNINGS/ADVISORIES... KS...NONE. MO...NONE. $$ WFO EAX