RSS FeedsIssued 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 250214 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 814 PM CST TUE NOV 24 2009 .DISCUSSION... 752 PM CST MAIN CONCERN FOR THE NEAR TERM THROUGH THE OVERNIGHT HOURS IS BROAD AREA OF PRECIP THAT IS CURRENTLY MOVING THROUGH THE CWA. THIS AREA OF PRECIP HAS BEEN RIDING OUT AHEAD OF UPPER LEVEL CLOSED LOW...AND ATTENDANT SURFACE LOW. AS THIS LOW HAS SLOWLY PROGRESSED TO THE EAST...IT HAS DRAWN A FAIR AMOUNT OF MOISTURE NORTH INTO THE REGION WHICH HAS BEEN EVIDENT ON SATELLITE IMAGERY ALONG WITH THE UPPER 40S/LOW 50S SURFACE DEW POINTS REPORTED THROUGHOUT THE CWA TODAY. THIS HAS HELP PROVIDE DECENT RAINFALL TOTALS OF UP TO HALF AN INCH...INCLUDED IN AREAS WHERE LIGHT TO MODERATE RAIN IS STILL BEING REPORTED. EXPECT AN ADDITIONAL QUARTER TO HALF AN INCH OF RAINFALL ACROSS PORTIONS OF NORTHERN ILLINOIS AND NORTHWEST INDIANA OVER THE NEXT COUPLE OF HOURS BEFORE THIS MAIN PRECIP SHIELD LIFTS TO THE NORTHEAST. A LACK OF ANY LIGHTNING STRIKES OVER THE LAST COUPLE OF HOURS ASSOCIATED WITH THIS PRECIP SHIELD GIVES PRUDENCE TO CURRENT RUC ANALYSIS WHICH HAS SHOWN A DOWNWARD TREND FOR ANY ELEVATED INSTABILITY. MODEL GUIDANCE CONTINUES WITH THIS TREND WITH VERY WEAK INSTABILITY THROUGH TONIGHT. WITH THESE TRENDS IN MIND...HAVE DECIDED TO PULL ANY MENTION OF THUNDER IN THE FORECAST. RODRIGUEZ && .PREV DISCUSSION... 228 PM CST PRESENT VORTEX ALONG THE IOWA AND MISSOURI BORDER SOUTH OF DES MOINES IS THE FOCUS OF THE UPCOMING RAIN EVENT THIS EVENING. MAIN CONVERGENCE ZONE AHEAD OF THIS SYSTEM EXTENDS FROM LOWER THRU MID MS VLY. HEAVIER RAINS IN THIS ZONE HAD DEVELOPED THUNDER EARLIER TODAY. MAY STILL BE A RUMBLE OR TWO OF THUNDER AS THIS BAND SWINGS NE FROM WRN IL INTO NRN IL THIS EVENING. PCPN BECOMES MORE SHOWERY BY MRNG WITH UPR LOW PASSAGE. BUT TEMPS STILL TOO WARM TO CHANGEOVER OR EVEN MIX WITH SNOW YET. THIS COMES LATER. MODELS UNFOLDING SIMILAR TO YDA WITH GFS AND ECMWF TAKING MAIN UPR VORTEX OF FIRST MAJOR TROF SOUTH OF CHICAGO LATE TONIGHT INTO TOMORROW MRNG AND NAM NORTH OF THE WISCONSIN BORDER. ALL TEND TO FILL THIS UPR TROF RAPIDLY OVER LOWER MICHIGAN AS WEAK UPR RIDGING SLIPS EAST ACROSS NRN IL ON WEDNESDAY. ITS THE SECOND VORTEX THAT WILL MAKE THE BIGGEST IMPACT. DEEPENING AS IT DIVES SE FROM CANADA AND DOWN ACROSS THE UPR MS VLY...THIS SECOND VORTEX WILL BRING THE COLDER AIR DOWN FROM CANADA AND BEGIN TO MIX AND EVENTUALLY CHANGE OVER TO SNOW LATE WED NGT THRU THURSDAY AFTER MOVING ACROSS CENTRAL IL WED NGT AND EARLY THURSDAY. GROUND TEMPS AND AIR TEMPS WILL NOT BE CONDUCIVE TO ACCUMULATIONS OVER MOST OF THE FORECAST AREA. THE COLDEST AIR PLUNGING INTO NORTHWEST ILLINOIS MAY ALLOW A HALF INCH ACCUMULATION ON NON-PAVEMENT SURFACES IN PARTS OF NORTH CENTRAL IL SUCH AS WESTERN OGLE AND LEE COUNTIES ON THURSDAY. THIS SECOND VORTEX CONTINUES TO DEEPEN AS IT WORKS ACROSS CENTRAL INDIANA MIDDAY THURSDAY TO CENTRAL OHIO BY THURSDAY EVENING. DRYING MOVES IN WITH THE COLD AIR ADVECTION BEHIND THIS MAJOR TROF...PUTTING AN END TO THE SNOW SHOWERS THURSDAY EVENING. UPR RIDGING WORKS EAST ACROSS THE MS VLY AND INTO THE FORECAST AREA FRIDAY...CLEARING SKIES AND BRINGING A BIT OF A WARMUP BACK TO ILLINOIS FOR SATURDAY. TEMPS MAY APPROACH 50 SATURDAY BUT THESE WILL PROBABLY NOT BE WIDESPREAD. IN THE LONG TERM...ANOTHER DEEPENING UPR TROF INTO THE PLAINS AND UPR MS VLY SAT NIGHT AND SUNDAY MAY BRING ANOTHER CHANCE OF RAIN ON SUNDAY...COOLING AS IT DRIES A BIT LATE SUNDAY NIGHT INTO TUESDAY. GFS SHOWING SOME MINOR WAVES MOVING SE DOWN THE PERSISTENT NORTHWESTERLY FLOW ALOFT IN THE POST TROF ENVIRONMENT. THIS SUGGESTS THAT A TOTALLY DRY FORECAST IS NOT THE WAY TO GO EARLY NEXT WEEK. SO LEAVING IN A SLIGHT RISK FOR RAIN AND SNOW AFTER SUNDAY. RLB && .AVIATION... 530 PM CST 1800 UTC TAFS...A VERY MESSY PERIOD EXPECTED FOR AVIATION WEATHER CONCERNS. A VERTICALLY STACKED LOW PRESSURE SYSTEM HAS MOVED OVER SERN IOWA. THE MAIN LOW CENTER WILL MOVE NORTHEAST ACROSS NCNTRL ILLINOIS BY 06Z AND WILL CONTINUE TO CNTRL LAKE MICHIGAN BY 12Z. PCPN ASSOCIATED WITH THE SYSTEM HAS SPREAD OVER ALL OF THE TERMINALS AT ISSUANCE TIME...WITH GENERALLY MVFR CIGS...AND SPOTTY IFR CIGS...ACROSS THE REGION...VIS VISIBILITY IN THE 2-3SM RANGE. THE INITIAL CONCERNS WILL BE TIMING OF CIGS DROPPING TO IFR AND HOW LOW CIGS WILL DROP THROUGH THE NIGHT. AT THIS POINT...EXPECT CIGS TO LOWER TO IFR BY 02Z...WHICH WILL COINCIDE WITH THE TIMING OF THE HEAVIER RAIN MOVING OUT OF THE AREA...AND THE PCPN TRANSITIONING OVER TO DRIZZLE. WITH THE LATEST MODEL GUIDANCE TAKING THE CENTER OF THE LOW RIGHT OVER RFD AND JUST NORTH OF THE OTHER TERMINALS...THE CORE OF THE COLD AIR ALOFT WILL BE RIGHT OVERHEAD AND EXPECT THAT THERE SHOULD BE PERIODS OF CIGS DROPPING TO LIFR. SO...HAVE INTRODUCED A TEMPO GROUP FOR LIFR CIGS IN DEFERENCE TO SOME UNCERTAINTY AS TO THE EXACT TIMING THAT THE LOW WILL BE OVERHEAD. AT THIS POINT...THE MOST LIKELY TIME FOR CIGS TO DROP TO LIFR WILL BE DURG THE PRE-DAWN HOURS. FOR PCPN...HAVE GONE WITH DRIZZLE FOR THE PERIOD AFTER MIDNIGHT AS THE SATELLITE IMAGERY INDICATES A MID LEVEL DRY SLOT MOVING ACROSS THE MIDDLE MISSISSIPPI VALLEY AND INTO WEST CENTRAL ILLINOIS. THE SHORT RANGE MODEL GUIDANCE IS WELL INITIALIZED WITH THIS FEATURE...WITH RH TIME SECTIONS SHOWING THE LAYER BELOW 700MB SATURATED AND WITH SIGNIFICANTLY DRIER AIR ABOVE. HOWEVER...WILL KEEP THE IDEA OF MORE SHOWERY RAIN WITH THE FRONTAL PASSAGE AS THERE WILL BE BETTER UPPER DYNAMICS AND SFC FORCING. THE GENERAL TREND FOR THE PERIOD WILL BE FOR CIGS TO DROP TO IFR THIS EVENING...AND REMAINING IFR UNTIL THE FRONTAL PASSAGE. HOWEVER...WITH THE LOW PRESSURE SYSTEM MOVING RIGHT OVER THE REGION...THERE WILL BE PERIODS OF LIFR CIGS DURG THE EARLY MORNING HOURS. WINDS WILL REMAIN SELY UNTIL THE FRONTAL PASSAGE AND THEN ABRUPTLY SHIFT WSWLY AS THE FRONT SWEEPS ACROSS THE AREA. VISIBILITY WILL BE A CONCERN AS WELL...AND IS THE BIGGEST QUESTION MARK AT THIS TIME. VISIBILITY WILL LIKELY REMAIN IN THE 3-5SM RANGE...THOUGH PERIODS OF IFR VIS ARE QUITE POSSIBLE...PARTICULARLY WHEN THE PCPN TRANSITIONS OVER TO DRIZZLE. KREIN && .MARINE... 137 PM CST WINDS WILL BE ON THE INCREASE ACROSS THE LAKE TONIGHT AS A LOW PRESSURE SYSTEM CURRENTLY IN SOUTHERN IOWA LIFTS NORTHEAST TOWARD THE SOUTHERN HALF OF THE LAKE. THIS LOW WILL THEN TAKE A JAUNT NORTH AND HEAD TOWARD FAR EASTERN LAKE SUPERIOR. THE STRONGEST WINDS WILL COME IN ACROSS THE LAKE ON THURSDAY AS A SECONDARY COLD FRONT DROPS DOWN THROUGH THE GREAT LAKES. WINDS WILL BE GUSTING UP TO 30 KT GIVEN THE STRONG COLD AIR ADVECTION AND WARM LAKE WATERS. LOOKS A BIT MARGINAL FOR GALES AT THIS POINT...SO WILL HOLD OFF ON ISSUING ANY GALE HEADLINES...BUT WILL HAVE TO MONITOR ON WEDNESDAY/THURSDAY. SMALL CRAFT CONDITIONS WILL LIKELY BE MET TOMORROW AFTERNOON AND THURSDAY AFTERNOON INTO FRIDAY MORNING. HALBACH && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...NONE. && $$
