Issued by NWS Chicago, IL
Versions: 1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
000 FXUS63 KLOT 061028 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 528 AM CDT WED MAY 6 2009 .DISCUSSION... 300 AM CDT MAIN FORECAST CONCERN FOR THE SHORT TERM FORECAST PERIOD WILL FOCUS ON A SERIES OF NORTHERN STREAM SHORT WAVES AND THEIR IMPACT ON THE LOCAL WEATHER PICTURE. THE FIRST OF THESE IS A WEAK EMBEDDED WAVE MOVING THROUGH SWRN WI WITH ASSD SHRA/ISOL TS EXTENDING BACK INTO NERN IA. THIS SYSTEM IS EXPECTED TO CONTINUE TO LIFT NEWD. HAVE MAINTAINED SLIGHT CHANCE POPS FOR THIS MORNING OVER THE FAR NWRN CORNER OF THE CWA...BUT THE BETTER FORCING WILL CONTINUE TO LIFT TO THE NORTHEAST...AND CHANCES OF THIS AREA SEEING ANY WETTING PCPN ARE LOW. THE NEXT WAVE IS DEVELOPING OVER SOUTH DAKOTA/NRN NEBRASKA AND IS EXPECTED TO CONTINUE TO DIVE ESELY ACROSS THE MIDDLE MISSISSIPPI VALLEY THIS AFTERNOON AND ACROSS CNTRL IL/IN. THIS WAVE SEPARATED FROM THE MAIN NRN STREAM WESTERLIES AND IS A LITTLE SLOWER IN IT/S PROGRESSION. THUS HAVE MAINTAINED A MORE EXTENDED PERIOD OF POPS ACROSS THE AREA. THE SYSTEM MOVING THROUGH THE LOWER MISSISSIPPI VALLEY HAS ROBBED THE AREA OF ANY SIGNIFICANT MOISTURE INFLUX...SO WHILE THE WAVE AND AN ASSOCIATED WEAK COLD FRONT WILL PROVIDE ENOUGH OF A TRIGGER FOR SHOWERS AND SCT THUNDERSTORMS...PCPN AMOUNTS SHOULD BE ON THE LIGHTER SIDE...WITH 6-HOURLY QPF AMOUNTS ON THE ORDER OF A TENTH OF AN INCH OR LESS. THE SHORT RANGE MODELS HAVE SIMILAR SOLUTIONS FOR THE SYNOPTIC SCALE PATTERN...AND HAVE GENERALLY FOLLOWED THE MAV GUIDANCE WITH RESPECT TO TEMPERATURES/DEWPOINTS. THE MAV GUIDANCE SEEMS TO BE HANDLING THE LOWER SURFACE DEWPOINTS OBSERVED OVER THE AREA AT ISSUANCE TIME AND MAINTAINS A BETTER TREND ON KEEPING DEWPOINTS FROM GETTING TOO HIGH AS THE MODELS HAVE RECENTLY EXHIBITED A STRONG MOIST BIAS RECENTLY. ONE AREA THAT DEVIATES A BIT FROM GUIDANCE IS THE LAKE FRONT. A WEAK GRADIENT WILL BE IN PLACE FOR TODAY AND TOMORROW...SO EXPECT LAKE BREEZE DEVELOPMENT. SO...HAVE ADJUSTED MAX TEMPS NEAR THE LAKE DOWN A FEW DEGREES. OTHERWISE...EXPECT TEMPS TO CONTINUE A SLIGHT WARMING TREND AND REACH INTO THE LOW TO...POSSIBLY...MIDDLE 70S TODAY AND TOMORROW. UNFORTUNATELY...THE AFOREMENTIONED COLD FRONT WILL FINALLY SWEEP THROUGH THE AREA BRINGING A COOLING TREND FOR FRIDAY AND INTO THE WEEKEND. KREIN && .AVIATION... 1200 UTC TAFS...A SOMEWHAT ZONAL WEST TO EAST UPPER LEVEL FLOW ACROSS THE CONUS DISPLAYS FREQUENT MINOR RIPPLES MEANDERING THRU THIS FLOW AND CREATING AREAS OF LIFT ACROSS THE MIDWEST. THE LATEST RIPPLE OVER ERN IA TO CENTRAL WI COINCIDES WITH A STREAM OF LOW LVL MOISTURE CONVERGENCE FEEDING UP THRU THE PLAINS FROM THE GULF. CURRENT UPPER LEVEL PATTERNS INDICATE THAT THIS AREA OF SHOWERS SHUD CONTINUE TO MOVE EAST NORTHEAST ACROSS WISCONSIN. HOWEVER A DIVING POLAR JET THRU THE HIGH PLAINS IS DEEPENING THIS LATEST RIPPLE OVER THE MS VLY AND FORCING THE ZONAL FLOW INTO A MORE NW TO SE PATTERN FROM THE PLAINS THRU THE MIDWEST THIS AFTN AND TNGT. COOLING THRU THESE UPPER LAYERS WILL HELP DESTABILIZE THE AREA WHILE THIS ZONE OF LOW LVL MSTR CONVERGENCE WORKS ACROSS THE MS VLY WITH THIS LATEST PUSH TO THE SOUTHEAST. RAPID DESTABILIZATION AND TROF DEEPENING IS PROGGED ON THE MODELS TO THE EAST OF ILLINOIS LATE THIS AFTN AND TONIGHT WHILE MINOR WAVES STILL PLAGUE THE MS VLY AND MIDWEST. DYNAMICS STILL REMAIN LIMITED FOR ANY WIDESPREAD OUTBREAK IN TSTMS BUT TIMING OF PCPN CHANCES APPEAR BEST WITH AFTN HEATING AND AGAIN AFTER MIDNIGHT TONIGHT AS A RATHER WEAK COLD FRONT APPROACHES. DUE TO THE TIME OF DAY AFTER MIDNGT...THUNDER IS LESS LIKELY IN THE OVERNIGHT HOURS...SO LEAVING IT AS SHOWERS. SFC WINDS SHUD HOVER AROUND 10 KTS OR LESS FROM THE SOUTH TODAY AND VEERING A LITTLE TO THE SW THIS AFTN AS UPPER LEVELS STEEPEN TO MORE NW...THEN EVENTUALLY START VEERING TO THE WEST WITH APPROACH OF THE WEAK FRONT EMBEDDED IN A RATHER BROAD SFC TROF. WITH MORE DISTINCT SW FLOW THIS AFTN...NOT LOOKING FOR A LAKE BREEZE. CIGS SHUD REMAIN VFR TODAY AND TNGT...PSBLY DROPPING NEAR MVFR TONIGHT WITH THE OVERNIGHT SHOWERS. RLB && .MARINE... 418 AM CDT LOW PRESSURE OVER SOUTHERN MANITOBA WILL MOVE SLOWLY EAST TO JUST NORTH OF LAKE SUPERIOR IN ONTARIO THURSDAY MORNING...THEN INTO SOUTHWEST QUEBEC FRIDAY MORNING. A WEAK COLD FRONT EXTENDING SOUTH FROM THIS LOW WILL PUSH ACROSS LAKE MICHIGAN THIS EVENING. HOWEVER A SECONDARY COLD FRONT WILL TRAIL ACROSS THE LAKES FRIDAY AFTERNOON. HIGH PRESSURE WILL THEN BUILD FROM THE NORTHERN PLAINS TO THE WESTERN LAKES OVER THE WEEKEND. RLB && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$
