803 AM CST
FIRED OFF A QUICK ZFP UPDATE TO HIT SNOW A BIT HARDER IN THE GRIDS
TODAY. VIGOROUS VORT OVER WISCONSIN CONTINUES TO PIVOT
SOUTHEASTWARD WITH REGIONAL WSR-88D MOSAIC ALREADY SHOWING SOME
BANDS OF SCT SNOW SHOWERS ACROSS WISCONSIN INTO EXTREME NE IL.
RADAR REFLECTIVITY VALUES ARE OCCASIONALLY POKING OVER 30DBZ WITH
SFC OBS OF VSBY FALLING BELOW 2SM IN -SN...SO HAVE OPTED TO GO
WITH MORE OF AN UNQUALIFIED MENTION OF SCATTERED SNOW SHOWERS
TODAY.
THIS MORNINGS SOUNDINGS OUT OF MPX AND DVN SHOW FAIRLY STEEP LOW
AND MID LEVEL LAPSE RATES WITH COLUMN FAIRLY MOIST BELOW ABOUT 500
OR 600 MB. WOULD ANTICIPATE COVERAGE AND INTENSITY OF SNOW SHOWERS
TO RAMP UP A BIT AS WE GET SOME HEATING THAT WILL FURTHER STEEPEN
THE LOW LEVEL LAPSE RATES ALLOWING US TO GROW MORE CONVECTIVELY
UNSTABLE.
VERY SHALLOW ABOVE FREEZING LAYER NEAR THE SURFACE WITH WET BULB
ZERO HEIGHTS NEAR OR BELOW 1500 FT AGL WOULD OFFER LITTLE
OPPORTUNITY FOR RAIN TO MIX WITH SNOW...SO HAVE REMOVED THE
MIXTURE WORDING FOR THIS AFTERNOON. GIVEN THE CONVECTIVE NATURE OF
THE PRECIP ITS PLAUSIBLE THAT WOULD SEE SOME GRAUPLE MIX IN WITH
THE SNOW SHOWERS.
WITH SURFACE TEMPS ABOVE FREEZING NOT ANTICIPATING ANY ACTUAL
ACCUMS...BUT SNOW COULD FALL RATHER HEAVILY AT TIMES IN BRIEF
BURST TODAY...ESPECIALLY NORTHERN HALF TO TWO THIRDS OF THE CWA.
IZZI
//PREV DISCUSSION...
341 AM CST
IR IMAGERY EARLY THIS MORNING SHOWS A NARROW CHANNEL OF CLEAR SKIES
THAT STRETCHES FROM MISSOURI NORTHEAST THROUGH NORTHERN ILLINOIS
INTO EASTERN WISCONSIN. TEMPERATURES HAVE BEEN ABLE TO RADIATE INTO
THE LOWER TO MIDDLE 30S THIS MORNING...AND IN SOME LOCATIONS ACROSS
FAR NORTHWEST ILLINOIS TEMPS WILL BE IN THE UPPER 20S TO START THE
DAY. WRAP AROUND MOISTURE WAS BEGINNING TO SLIDE SOUTHEAST AS
WELL...CURRENTLY LOCATED OVER EASTERN IOWA STRETCHING NORTHEAST
THROUGH WESTERN WISCONSIN. BASED ON THE CURRENT PATH AND LATEST
TRENDS OF THIS LINE...EXPECT CLOUDS TO PUSH OVER THE CENTRAL
PORTIONS OF THE CWFA AROUND DAYBREAK. THEN THIS LINE SHOULD CONTINUE
TO PUSH EAST.
ONCE CLOUDS ARRIVE THIS MORNING...CHANCES OF SEEING A WARM-UP A VERY
MINIMAL. THE COMBINATION OF STRONG COLD AIR ADVECTION...CONSIDERABLE
SOLAR FILTERING...AND AN 850MB THERMAL TROUGH OF -6 TO -9 DEG C
OVERHEAD SHOULD RESULT IN TEMPS REMAINING IN THE UPPER 30S FOR MANY
LOCATIONS. THE EXCEPTION WOULD BE LOCATIONS CLOSER TO CENTRAL
ILLINOIS...WHICH MAY ONLY SEE PARTLY CLOUDY SKIES TODAY.
THE OTHER CONCERN FOR TODAY WILL BE THE UNSTABLE NATURE OF THE
ATMOSPHERE...AND THE MID-LVL TROUGH AXIS. DEEP MOISTURE REMAINS
TODAY WITH SOME LIFT EXPECTED. DEW PT WILL REMAIN
SUB-FREEZING...THUS EXPECT ANY PRECIP THIS MORNING TO OCCUR WOULD
REMAIN IN A DENDRITIC FORM. BY MIDDAY WITH SOME HEATING ALOFT COULD
AID IN ENHANCING THE PRECIP...WITH DEEP MOISTURE LINGERING AROUND.
THERMAL PROFILES SUGGEST A SHARP DECLINE. THUS NOT ANTICIPATING ANY
ICE PELLETS OR GRAUPEL...ALTHOUGH THE THREAT OF THIS IS NOT ZERO.
CONFIDENCE IS VERY LOW...THUS GOING TO RIDE WITH A RASN MIX. EVEN
THIS COULD END UP BEING ALL SN. NOT ANTICIPATING ANY ACCUMS TODAY
EITHER...WITH POSSIBLY JUST TRACE AMOUNTS.
WITH HEIGHTS BEGINNING TO BUILD IN FROM THE SOUTHWEST AND DEEP
MOISTURE BEGINNING TO PEEL TO THE EAST...ALONG WITH DECOUPLED
WINDS...AND SFC TEMPS WILL STEADILY RADIATE INTO THE 20S. EXPECT
OVERNIGHT LOWS TO END UP FALLING INTO THE MID 20S ACROSS MOST OF THE
CWFA. THE EXCEPTION WILL BE CLOSER TO THE MARINE ENVIRONMENT...WHERE
TEMPS MAY HOLD IN THE UPPER 20S TO LOWER 30S. THERMAL DIFFERENTIAL
WILL REMAIN OVER THE LAKE...THUS LAKE EFFECT CLOUDS AND PRECIP WILL
PERSIST.
FRIDAY...
500MB TROUGH AXIS CONTINUES TO PIVOT EAST AWAY FROM THE GREAT LAKES
REGION...AS THE THERMAL TROUGH AT 850MB BEGINS TO WARM AS WELL. THIS
SHOULD BRING A GRADUAL END TO THE LAKE EFFECT
CLOUDS/PRECIP...HOWEVER IT MAY TAKE UNTIL SAT FOR THIS TO OCCUR.
MEANWHILE THE LARGER STORY WILL BE THE POTENT SYSTEM POISED TO MOVE
ONSHORE NEAR SOUTHERN CALIFORNIA LATE IN THE WEEK. ENSEMBLES HAVE
CONTINUED TO SLOW THIS ARRIVAL...HOWEVER THE POTENCY REMAINS THE
SAME AT -3 TO -4 SIGMA AT 500MB. ANTI-CYCLONIC FLOW WILL BE PRESSING
EAST INTO THE GULF STATES...INFLUENCING THE WEATHER AS FAR NORTH AS
THE GREAT LAKES REGION. THIS SHOULD PROVIDE ENOUGH SUBSIDENCE TO
ERODE MOST CLOUDS DURING THE DAY ACROSS THE CWFA WITH TEMPS
REBOUNDING INTO THE UPPER 40S TO LOWER 50S. IT IS POSSIBLE WITH
WINDS SHIFTING TO THE SOUTHWEST ENOUGH WARM AIR ADVECTION COULD
OCCUR THAT TEMPS COULD BE A FEW DEGREES WARMER YET. AT THIS TIME
HAVE ADJUSTED TEMPS WARMER A DEGREE OR TWO. HAVE ALSO MAINTAINED A
DRY FORECAST...WITH THE EXCEPTION BEING OVER LAKE MICHIGAN DURING
THE DAY.
OVERNIGHT SKIES WILL SEE MINIMAL CLOUD COVER...AND WINDS SHOULD
DECOUPLE. THIS WILL ALLOW TEMPS TO RADIATE EFFICIENTLY INTO THE
30S.
SATURDAY THROUGH WEDNESDAY...
ANOMALOUSLY STRONG 500MB TROUGH CONTINUES TO SLIDE EAST INTO THE
SOUTHWEST CONUS REGION EARLY IN THE WEEKEND. DOWNSTREAM OF THIS
FEATURE ENSEMBLES CONTINUE TO DEMONSTRATE A STEADY INCREASE IN
CONFIDENCE IN A MID-LVL TROUGH SLIDING SOUTHEAST FROM THE CANADIAN
ROCKIES INTO THE CENTRAL PLAINS MON. MEANWHILE ENSEMBLE MEMBERS HAVE
ALSO DEMONSTRATING OVER THE PAST FEW CYCLES OF INCREASING THE
STRENGTH OF THE RIDGE OVER THE FAR SOUTHEAST CONUS.
OPERATIONAL SOLUTIONS CONTINUE TO HINT THAT A SHORTWAVE WILL BE
PUSHING EAST THROUGH THE CENTRAL PLAINS EARLY SUN AND ARRIVING
ACROSS THE WESTERN GREAT LAKES REGION LATE SUN EARLY MON. WHILE THE
PRECISE ARRIVAL TIME WILL CONTINUE TO FLUCTUATE...THE PATTERN PRIOR
TO THIS ARRIVAL IS FOR MUCH OF THE OHIO VALLEY WILL SEE WARM AIR
ADVECTION. THE PRESSURE GRADIENT BETWEEN THE DOWNSTREAM RIDGE AND
THE ARRIVING TROUGH STEADILY TIGHTENS SUN...THUS EXPECT IF MINIMAL
CLOUD COVER CAN OCCUR TEMPS WILL EASILY PUSH INTO THE UPPER 50S SUN
AND POSSIBLY LOWER 60S IN SOME LOCATIONS. WITH A TIGHT PRESSURE
GRADIENT SUN...EXPECT VERY BREEZY CONDITIONS.
IT APPEARS ONCE THE FRONT PUSHES THROUGH EARLY IN THE WEEK...TEMPS
WILL COOL. ALTHOUGH WITH A RELATIVELY FLAT 850MB THERMAL TROUGH...IT
DOES NOT APPEAR TEMPS WILL FALL OFF DRAMATICALLY AT THIS TIME. A FEW
ENSEMBLE MEMBERS SUGGEST A REINFORCING SHOT OF COOLER AIR ARRIVES
TOWARDS THE MIDDLE OF THE WEEK...WHICH COULD AID IN FURTHER COOLING
OF THE SENSIBLE WEATHER.
PRECIPITATION CHANCES WILL BE GREATEST IN THE SUN/MON
TIME FRAME...HOWEVER RELATIVELY LOW CHANCES EXIST THROUGHOUT THE
REMAINDER OF THE EXTENDED. A FEW ENSEMBLE MEMBERS ALSO SUGGEST A
SYSTEM WILL DEVELOP IN THE SOUTHERN PLAINS AND LIFT NORTHEAST INTO
THE TENNESSEE VALLEY LATE TUE. WITH THE EXPECTED PATTERN...AND THE
LOCATION IN WHICH THESE SOLUTIONS ARE PRODUCING THIS SYSTEM...ONE
COULD IMAGINE A FURTHER NORTHWEST TRACK OVER THE GREAT LAKES REGION
TUE NGT/WED.
BEACHLER
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 20Z...
* SCT'D SNOW SHOWERS THIS AFTERNOON
* WESTERLY WINDS GUSTING TO AROUND 20 KT UNTIL AROUND SUNSET
* OCNL MVFR CIGS THROUGH EARLY EVENING
IZZI
//DISCUSSION...UPDATED 20Z...
ONLY CHANGE TO GOING TAFS WAS TO INTRODUCE SOME GRAUPLE INTO THE
TEMPO. HAVE BEEN GETTING NUMEROUS REPORTS OF GRAUPLE IN ADDITION
TO SNOW WITH THESE SHOWER...INCLUDING A COUPLE REPORTS OF FAIRLY
HEAVY GRAUPLE. OTHERWISE NO CHANGES MADE TO 18Z TAFS.
IZZI
UPDATED 18Z...
COMBINATION OF COLD AIR ALOFT AND AN UPPER LEVEL DISTURBANCE
MOVING THROUGH THE REGION WILL LEAD TO FLURRIES WITH SOME OCNL
HEAVIER SNOW SHOWERS THIS AFTERNOON. HEAVIER BURSTS OF SNOW SHOULD
BE RELATIVELY BRIEF IN NATURE BUT COULD STILL RESULT IN VSBYS
DROPPING TO IFR. THERE IS A LOW END THREAT OF SOME GRAUPLE (GS)
WITH THE MORE INTENSE CONVECTIVE CELLS...BUT THAT THREAT IS TOO
LOW FOR INCLUDING IN TAFS.
CIGS WILL HAVE A TENDENCY THIS AFTERNOON TO TREND DOWN TO
MVFR...BUT GIVEN UPSTREAM OBS EXCEPT BASES TO BE RAGGED AND CIGS
SOMEWHAT VARIABLE THIS AFTERNOON. LOWER CIGS SHOULD CLEAR OUT THIS
EVENING THOUGH MID AND HIGH LEVEL CLOUDS WILL INCREASE AHEAD OF
NEXT SYSTEM PROGGED TO PASS NORTH OF THE AREA FRIDAY. MAIN EFFECT
FROM THIS SYSTEM WILL BE TO CAUSE WINDS TO BACK TO SOUTHERLY
FRIDAY MORNING AND INCREASE AGAIN FRIDAY WITH GUSTS OVER 20KT
ONCE AGAIN LIKELY DURING THE AFTERNOON.
IZZI
//ORD AND MDW CONFIDENCE...UPDATED 20Z...
* MEDIUM CONFIDENCE ON SHSN TODAY AND MVFR CIGS THRU EVENING
* HIGH CONFIDENCE ON ALL OTHER ASPECTS OF THE FORECAST
IZZI
//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...
FRI NIGHT...VFR...WX NIL.
SAT...VFR...WX NIL.
SUN...VFR...CHANCE SHOWERS MVFR.
MON...VFR...CHANCE SHOWERS.
TUE...VFR...SLIGHT CHANCE SHOWERS.
WEDNESDAY...VFR...WX NIL.
TRS
&&
.MARINE...
223 PM CST
UPCOMING PERIODS OF POTENTIAL GALES WILL BE THE PRIMARY CONCERN IN
THE OPEN WATER FORECASTS. WHILE THE STRONG LOW PRESSURE THAT MOVED
OVER THE AREA ON WEDNESDAY IS FAR NORTH OF THE AREA OVER ST JAMES
BAY...IT CONTINUES TO HAVE INFLUENCE WITH WEST NORTHWEST WINDS OVER
THE LAKE INTO THIS EVENING. THESE WILL SLOWLY DIMINISH AS A
QUICK-PACED WEATHER PATTERN RESUMES OVER THE REGION. AFTER A RIDGE
PASSES OVERNIGHT INTO FRIDAY MORNING...A CLIPPER SYSTEM WILL MOVE
RAPIDLY EAST TO THE IMMEDIATE NORTH OF THE LAKES. THE INFLUENCE OF
THIS WILL CAUSE SOUTHWEST WINDS TO COME UP QUICKLY FRIDAY
AFTERNOON...WITH POTENTIAL GALE FORCE GUSTS OVER THE NORTHERN LAKE
DUE TO THE RAPID PRESSURE FALLS AND MIXING POTENTIAL OVER THE LAKE.
ANOTHER POTENTIAL ROUND OF GALES IS SET FOR LATE SATURDAY NIGHT
THROUGH SUNDAY ACROSS MUCH OF THE LAKE DUE TO A DEEPER LOW PRESSURE
PASSING AGAIN JUST NORTH OF THE LAKES. BECAUSE OF THE LONGER
DURATION INFLUENCE...CONFIDENCE IN THIS EVENT IS ACTUALLY SLIGHTLY
HIGHER. ALSO...THE LIKELIHOOD OF NEEDING SMALL CRAFT ADVISORIES
FOR THE IL AND IN NEARSHORE ZONES FOR AT LEAST A PORTION OF THAT
TIME IS PROBABLE.
MTF
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 3 AM FRIDAY.
SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 9 PM THURSDAY.
&&
$$
