Area Forecast Discussion
Issued by NWS Chicago, IL

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
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
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS63 KLOT 252311 AFDLOT AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 611 PM CDT SAT OCT 25 2014 .DISCUSSION... 237 PM CDT //SHORT TERM// REST OF TODAY THROUGH SUNDAY... QUIET WEATHER REMAINS ON TAP FOR THE REMAINDER OF THE WEEKEND AS UPPER LEVEL RIDGE TRANSLATES EAST ACROSS THE AREA THROUGH THE PERIOD. SURFACE RIDGE IN PLACE FROM THE NORTHERN PLAINS INTO THE LOWER MISSISSIPPI VALLEY THIS AFTERNOON WILL ALSO TRANSLATE EAST ACROSS THE AREA...BECOMING CENTERED OVER NORTH CENTRAL ILLINOIS BY THE EARLY MORNING HOURS SUNDAY. WITH DEWPOINTS MIXING OUT INTO THE LOW/MID 30S ACROSS PORTIONS OF THE OUTLOOK AREA TODAY...ALONG WITH LIGHT WINDS AND MOSTLY CLEAR SKIES IN PLACE TONIGHT...THE STAGE WILL BE SET FOR STRONG RADIATIONAL COOLING OVERNIGHT. BLENDED OVERNIGHT LOWS HEAVILY TOWARDS THE GEMNM/GEMNMBC WHICH APPEARS TO CAPTURE SOME OF THE TYPICAL COOL SPOTS WEST OF THE FOX RIVER VALLEY WELL...AND VERIFIES WELL UNDER THIS SYNOPTIC SITUATION. JET STREAM BEGINS TO BUCKLE IN THE WEST AS A WAVE MOVES ONSHORE OVER THE PAC NW AND CARVES OUT A TROUGH OVER THE GREAT BASIN BY SUNDAY EVENING. MEANWHILE...AT THE SURFACE...BROAD LOW PRESSURE WILL DEVELOP OVER THE FRONT RANGE OF THE ROCKIES WITH SOUTHWEST FLOW ALOFT DEVELOPING SUNDAY EVENING. LOCALLY...DAYTIME HOURS WILL BE DRY SUNDAY UNDER THE INFLUENCE OF THE DEPARTING SURFACE RIDGE BUT EXPECT AN INCREASE IN CLOUD COVER FROM MIDDAY ON AS MID LEVEL WARM ADVECTION STARTS TO OVERSPREAD THE REGION. SUNDAY NIGHT THROUGH TUESDAY... SURFACE LOW REMAINS UNORGANIZED SUNDAY NIGHT AS BROAD TROUGHING MOVES EAST INTO THE UPPER MIDWEST...HOWEVER MODELS CONTINUE TO ADVERTISE A 40-50 KT LOW LEVEL JET DEVELOPING ACROSS THE MID MISSISSIPPI VALLEY WITH A DECENT PUSH OF MOISTURE INTO THE REGION WITH PWATS OF AROUND 1.1 INCHES ADVECTING INTO THE AREA. ON THE NOSE OF THE LOW LEVEL JET EXPECT THE POSSIBILITY OF SOME SHOWERS AND THUNDERSTORMS TO DEVELOP WHERE THERE IS SOME MODEST ELEVATED INSTABILITY PRESENT. THE CORRIDOR WHERE THE BETTER INSTABILITY AND FORCING LINE UP STILL FAVORS AREAS NORTH OF THE CWA...HOWEVER CANNOT RULE OUT PRECIP BUILDING DOWN INTO THE NORTHERN COUPLE TIERS OF COUNTIES IN ILLINOIS. THE SURFACE LOW BEGINS TO DEEPEN AND BECOME BETTER ORGANIZED MONDAY INTO MONDAY NIGHT AS THE UPPER LEVEL TROUGH PUSHES INTO THE UPPER MIDWEST. LOW LEVEL CONVERGENCE STRENGTHENS ALONG THE COLD FRONT AT THIS TIME...AND THE CHANCES FOR SHOWERS AND THUNDERSTORMS INCREASE MONDAY EVENING AND NIGHT AS THE COLD FRONT SWEEPS ACROSS THE AREA. BOTH THE GFS AND NAM NOW ADVERTISE SOME PREFRONTAL ACTIVITY DURING THE DAY MONDAY...HOWEVER SOUNDINGS SHOW FAIRLY NEGLIGIBLE INSTABILITY AND DRY LOW/MID LEVELS. NOT SURE HOW MUCH PRECIP WOULD BE POSSIBLE GIVEN THE SOUNDINGS SO WILL CAP ANY POPS AT 20 BEFORE 00Z. TAKING A STEP BACK AND LOOKING A TEMPS MONDAY...GUIDANCE CONTINUES TO ADVERTISE AN ANONYMOUSLY WARM THERMAL RIDGE THOUGH HAS ACCELERATED THE TIMING OF THE RIDGE SOME FROM PREVIOUS RUNS. NUDGED TEMPS SLIGHTLY TOWARDS THE LATEST BIAS CORRECTED ECMWF/GEMNH BUT DIDNT MAKE ANY BIG CHANGES...STILL CALLING FOR MID TO UPPER 70S NORTH OF I-80 AND UPPER 70S WITH POSSIBLY A FEW 80S TO THE SOUTH. BEHIND THE COLD FRONT ON TUESDAY...THE H85 ZERO DEGREE ISOTHERM WILL APPROACH THE AREA. WHILE TUESDAY SHOULD BE DRY BEHIND THE COLD FRONT...BREEZY AND COOLER CONDITIONS ARE EXPECTED WITH AFTERNOON HIGHS ONLY IN THE LOW TO MID 60S. //LONG TERM// WEDNESDAY THROUGH SATURDAY MODELS CONTINUE TO ADVERTISE A HIGH AMPLITUDE PATTERN DEVELOPING BY LATE IN THE WEEK WITH A SHOT OF ARCTIC AIR PUSHING TOWARDS THE AREA...MORE AGGRESSIVELY NOW THAN COMPARED TO GUIDANCE 24 HOURS AGO. THE LOW PRESSURE SYSTEM THAT IMPACTS OUR AREA EARLY THIS WEEK WILL CONTINUE TO DEEPEN AS IT LIFTS ACROSS JAMES BAY WEDNESDAY WITH COLD AIR STARTING TO WRAP AROUND INTO THE NORTHERN GREAT LAKES. STRONG HIGH PRESSURE THEN BUILDS DOWN OVER THE CANADIAN PRAIRIES AND SINKS SOUTHEAST TOWARDS THE UPPER MIDWEST. THE AIRMASS IS QUITE COLD WITH GUIDANCE NOW SHOWING -10C TEMPS AT H85 SINKING INTO NORTHERN ILLINOIS BY FRIDAY. DID NOT DEVIATE FROM A GENERAL MODEL CONSENSUS BLEND GIVEN IT IS STILL A WAYS OUT...BUT THESE TEMPS MIGHT BE TOO WARM IF CURRENT MODEL TRENDS HOLD. DEUBELBEISS && .AVIATION...
-- Changed Discussion --
//ORD AND MDW CONCERNS...UPDATED 00Z... * NW WINDS OF 30-35KT AROUND 700 FT AGL TONIGHT. * CHANCE FOR AN EASTERLY SURFACE WIND SHIFT WITH A LAKE BREEZE SUNDAY AFTERNOON. //DISCUSSION...UPDATED 00Z... NORTHWEST WIND SPEEDS WILL CONTINUE TO SLOWLY EASE THIS EVE AS THE ATMOSPHERE DECOUPLES. WINDS WILL REMAIN STOUT ALOFT JUST ABOVE THE BOUNDARY LAYER THAT WILL BE REALLY SHALLOW TONIGHT. THE 30-35 KT FLOW THAT IS SAMPLED ON RADAR PROFILES AND AMDAR DATA IS EXPECTED TO CONTINUE JUST ABOVE THIS LAYER. THE SURFACE RIDGE AXIS WILL MOVE ATOP THE AREA SUNDAY MORNING AND EARLY AFTERNOON. THIS COMBINED WITH THE MILD TEMPERATURES OVER LAND SHOULD ALLOW FOR LAKE BREEZE DEVELOPMENT. THIS SHOULD NOT RACE INLAND DUE TO A LIMITED TEMPERATURE DISCONTINUITY...BUT IT MAY BE ENOUGH FOR A 9-10 KT EASTERLY PUSH AT MDW AND POSSIBLY ORD...ALTHOUGH GIVEN THE LATE AFTERNOON TIME OF ARRIVAL IF IT OCCURS IT SHOULD NOT LAST LONG /1-3 HOURS/. LATER SUNDAY EVE SOUTHEAST WINDS SHOULD CONTINUE TO INCREASE AS LOW PRESSURE EVOLVES ACROSS THE PLAINS STATES. //ORD AND MDW CONFIDENCE...UPDATED 00Z... * HIGH IN SURFACE WINDS THROUGH EARLY SUNDAY AFTERNOON. MEDIUM AFTER. //OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z... MONDAY...SHRA LIKELY MAINLY DURING THE EVE WITH A CHANCE OF TSRA. SW WINDS. TUESDAY...CHANCE OF SHRA DURING THE MORNING WITH A SLIGHT CHANCE OF TSRA. W WINDS. WEDNESDAY...VFR. W WINDS. THURSDAY...CHANCE OF SHRA. W WINDS TURNING N. FRIDAY...SLIGHT CHANCE OF SHRA. NE WINDS. MTF
-- End Changed Discussion --
&& .MARINE... 251 PM CDT LOW PRESSURE CROSSING JAMES BAY THIS AFTERNOON WILL CONTINUE EASTWARD WHILE WEAKENING AS IT MOVES INTO SOUTHERN QUEBEC TONIGHT AND SUNDAY. HIGH PRESSURE ACROSS THE NORTHERN PLAINS AND UPPER MISSISSIPPI RIVER VALLEY WILL SLIDE SOUTHEASTWARD TONIGHT WHICH WILL ALLOW THE PRESSURE GRADIENT ACROSS MUCH OF LAKE MICHIGAN TO TIGHTEN LEADING TO AN INCREASE IN WEST TO NORTHWEST WINDS TONIGHT. WINDS HAVE UNDER PERFORMED THROUGH EARLY AFTERNOON ACROSS MUCH OF THE REGION BUT ARE STARTING TO COME UP INTO SMALL CRAFT ADVISORY RANGE ACROSS THE ILLINOIS NEARSHORE WATERS SO WILL MAINTAIN THE CURRENT SMALL CRAFT. WILL ALSO KEEP THE SMALL CRAFT FOR THE INDIANA WATERS THROUGH SUNDAY MORNING WITH WINDS TURNING NORTHWESTERLY AND INCREASING LEADING TO AN INCREASE IN WAVES. WILL EVALUATE STARTING THE ADVISORY A FEW HOURS LATER CLOSER TO NEARSHORE ISSUANCE TIME. WINDS SETTLE DOWN SUNDAY AS RIDGING PASSES OVERHEAD BUT LOW PRESSURE WILL BE DEVELOPING ACROSS THE CENTRAL AND NORTHERN PLAINS AND WORK INTO THE UPPER GREAT LAKES LATER MONDAY. SOUTHEAST WINDS WILL PICK UP MONDAY AHEAD OF THE LOW THEN SHIFT WESTERLY WITH THE PASSAGE OF A COLD FRONT MONDAY NIGHT. THE LOW WILL CONTINUE NORTHEAST AND DEEPEN WHILE CONSOLIDATING ACROSS CENTRAL AND SOUTHERN ONTARIO. A SECOND FRONT WILL TURN WINDS MORE NORTHWESTERLY TUESDAY NIGHT. SOUTHERLY WIND GUSTS SHOULD BE TEMPERED AHEAD OF THE FIRST FRONT WITH A VERY WARM AIRMASS LIMITING MIXING. GUSTS WILL INCREASE BEHIND THE FRONT WITH COLDER AIR SPREADING IN. NOT A CLEAR SIGNAL FOR GALES RIGHT NOW WITH THE LOW FAIRLY BROAD BUT SIMILAR SYSTEMS HAVE PRODUCED A SHORT PERIOD OF STRONGER UNDERFORECAST WINDS SEVERAL TIMES THIS SEASON SO WILL NEED TO MONITOR THIS CLOSELY IN THE NEXT DAY OR SO. HIGH PRESSURE WILL THEN BUILD IN WEDNESDAY. MDB && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 10 AM SUNDAY. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.