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 110931 CCA AFDLOT AREA FORECAST DISCUSSION...CORRECTED NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 422 AM CDT MON MAY 11 2009 .DISCUSSION... 324 AM CDT DRY WEATHER WILL OCCUR TODAY THROUGH TUESDAY. THUNDERSTORMS ARE LIKELY THURSDAY. TODAY THROUGH TUESDAY...DRY WEATHER WILL CONTINUE AS A HIGH MOVES ACROSS ILLINOIS AND INDIANA. WE USED THE MOS GUIDANCE FOR THE HIGH AND LOW TEMPERATURE FORECASTS. THE MOS GUIDANCE HAD THE LOWEST AVERAGE BIAS FOR THE LAST 10 DAYS. SINCE MOST OF THE MODELS WERE RUNNING A COOL BIAS WE RAISED THE TEMPERATURE VALUES UP A LITTLE. THE LOCAL WRF AND MOS GUIDANCE WERE USED IN THE DEWPOINT FORECASTS. THE GFS MODEL WAS USED FOR FORECAST MOVEMENT OF UPPER AIR AND SURFACE FEATURES. THE MODEL HAS BEEN CONSISTENT WITH WEATHER PATTERNS SEEN ON IR SATELLITE IMAGERY. THE SYNOPTIC WIND WILL BE LIGHT ACROSS NORTHEAST ILLINOIS TODAY. BOTH THE NAM AND OUR LOCAL WRF MODELS SHOW A LAKE BREEZE THIS AFTERNOON. WE WILL FORECAST A LOWER HIGH TEMPERATURE ALONG LAKE MICHIGAN TODAY. TUESDAY NIGHT THROUGH THURSDAY MORNING... THE HIGH MOVES EAST AND GULF MOISTURE RETURNS. A WAVE TROUGH MOVES INTO IOWA NORTH TO WESTERN ONTARIO BY 00 UTC THURSDAY. THIS TROUGH HAS A LARGE HEIGHT GRADIENT AND THERE IS A LOT VORTICITY FORECAST WITH THIS TROUGH. THIS WILL GIVE A STRONG SOUTH LOW LEVEL WIND INTO NORTHEAST ILLINOIS AND NORTHWEST INDIANA. ON THE SURFACE WE EXPECT A STRONG COLD FRONT. THERE WILL BE THUNDERSTORMS WEDNESDAY THROUGH EARLY THURSDAY MORNING. SOME OF THE THUNDERSTORMS COULD BE VERY STRONG. THURSDAY MORNING THROUGH MONDAY...HIGH PRESSURE WILL MOVE INTO ILLINOIS AND INDIANA. THE TEMPERATURES WILL BE A LITTLE LOWER WITH THE HIGH TEMPERATURE IN MIDDLE TO UPPER 60S ON THURSDAY AND IN THE LOWER 70S FRIDAY. ANOTHER LOW WILL MOVE THROUGH WISCONSIN FRIDAY NIGHT THROUGH SATURDAY. THIS WILL BRING A CHANCE OF SHOWERS AND THUNDERSTORMS FOR THE WEEKEND. && .AVIATION... 0600 UTC TAFS...GLOB OF SC OVER SRN WI HAS BEEN ERODING SLOWLY ALTHO SOME SWD PROGRESS HAS BEEN EVIDENT VIA SATL PIX. THIS SWD ADVANCE BEING OFFSET BY DISSIPATING NEAR THE WI BORDER. WILL LEAVE MENTION OF 5K SC AT RFD BUT NOT TAKE IT INTO A CEILING. THIS STILL A POSSIBILITY HOWEVER. OTHERWISE...WEST TO EAST STREAMING AC/CI IN UPPER LVL CONVERGENCE ZONE FROM THE CENTRAL PLAINS THROUGH ILLINOIS WILL SLOWLY DROP SOUTH OVERNIGHT AND LEAVE CLEAR SKIES AT TERMINALS BY MORNING. LOOKS LIKE ANTICYCLONIC FLOW PREVAILS UNDER SFC HIGH PRESSURE ON MONDAY. MAY BE A FEW CU NEAR 5K CONSIDERING A CONVECTIVE TEMP OF 60 WHILE FORECASTING HIGHS IN THE LOW TO MID 60S. WITH LIGHT NORTHERLY WIND FIELD ON MONDAY...CAN EXPECT ANOTHER EARLY TO MID AFTN LAKE BREEZE TO KICK IN AND SHIFT WINDS TO THE EAST. AGAIN THESE WILL DROP OFF NEAR SUNSET TO LIGHT AND VARIABLE. HAS BEEN DRYING LAST COUPLE OF DAYS AND SEE NO PROSPECT FOR DENSE FOG FORMATION TONIGHT OR MONDAY NIGHT. BUT SINCE IT WILL BE RADIATING VERY WELL OVERNIGHT...WOULD NOT BE SURPRISED TO SEE SOME MORNING GROUND FOG IN FIELDS THAT LIFT BRIEFLY TO LOWER MORNING VSBY DOWN TO 4 OR 5 MILES. RLB && .MARINE... 343 AM CDT LIGHT VARIABLE WINDS ON LAKE MI THE FIRST PART OF TODAY WITH BROAD HIGH PRESSURE EXTENDING FROM THE PLAINS TO THE CENTRAL GREAT LAKES SYNOPTIC FLOW FAVORS A SOUTH TO SOUTHEAST DIRECTION LATER TODAY AS THE ANTICYCLONE WILL BE CENTERED OVER THE SOUTHERN GREAT LAKES AND OHIO VALLEY TONIGHT BY LOCAL INFLUENCES AND LAKE BREEZES WILL LIKELY OBSCURE THIS WEAK SYNOPTIC FLOW. WITH THE HIGH MOVING EAST OVER NEW ENGLAND TUESDAY AND TUESDAY NIGHT AND LOW PRESSURE DEEPENS AS IT MOVES EAST SOUTHEAST TO FAR SOUTHERN MANITOBA BY WEDNESDAY MORNING WINDS OVER THE WESTERN GREAT LAKES WILL FRESHEN OUT OF THE SOUTHEAST AND SOUTH THOUGH VERY STRONG WARM AIR ADVECTION TO BE TAKING PLACE WITH 30 TO 40 KT SOUTH WINDS PROGGED AT 1K FT ABOVE THE SURFACE BY 00Z WED...STRENGTHENING FURTHER TO 35 TO 45 KTS BY WED MORNING. HOWEVER...STRONG INVERSION DUE TO THE COLD WATER WILL SEVERELY LIMIT MOMENTUM TRANSFER DOWN TO THE NEAR THE WATER SURFACE. MODELS DEPICT THE LOW TURNING TO THE NORTHEAST DURING WED AND AS IT APPROACHES JAMES BAY LATE IN THE DAY A STRONG COLD FRONT TRAILING SOUTHWESTWARD FROM THIS LOW BACK INTO THE PLAINS WILL PUSH EAST ACROSS THE UPPER MIDWEST...AND INTO THE WESTERN GREAT LAKES WEDNESDAY EVENING. BY THE TIME LOW LEVEL AIR COLD ENOUGH REMOVE THE INVERSION ARRIVES OVER LAKE MICHIGAN DURING THE DAY THURSDAY...THE CENTER OF THE LOW IS FAR REMOVED HAVING MOVED TO NORTHERN QUEBEC BY THEN. THE RESULT IS A MUCH RELAXED PRESSURE GRADIENT OVER THE WESTERN LAKES BY MIDDAY AND THUS ONLY MODERATE WEST WINDS OF 20 KTS AND DECREASING WITH TIME EXPECTED THU. TRS && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$
