🚀 go-pugleaf

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1138 AM CST TUE FEB 19 2013

DISCUSSION...
926 AM CST

FOR MORNING UPDATE...

MINOR TWEAKS TO GRIDS/TEXT FORECASTS THIS MORNING...MAINLY WITH
RESPECT TO TEMP TRENDS THROUGH THE DAY AND SNOW SHOWERS THIS MORNING.

LOW PRESSURE WAS ANALYZED OVER THE EASTERN UPPER PENINSULA OF
MICHIGAN AT 15Z THIS MORNING...WITH THE COLD FRONT WHICH PUSHED
ACROSS OUR AREA LAST EVENING NOW EXTENDING FROM THE EASTERN GREAT
LAKES TO THE GULF COAST. STRONG WEST-NORTHWEST WINDS WERE PROVIDING
ADVECTION OF VERY COLD/DRY ARCTIC AIR INTO THE REGION...WITH TEMPS
FALLING THROUGH THE TEENS IN MOST AREAS. A DEEP UPPER LEVEL
TROUGH/LOW WAS OVER THE NORTHERN LAKES...WITH A SHORT WAVE FEATURE
ROTATING EASTWARD ACROSS LAKE MI/IL/IN. THE COMBINATION OF DEEPER
MOISTURE AND LIFT ASSOCIATED WITH THIS SHORT WAVE WAS PRODUCING SNOW
SHOWERS ACROSS MUCH OF THE NORTHERN 2/3 OR SO OF THE CWA.

NEAR TERM GUIDANCE CONTINUES TO INDICATE THE SHORT WAVE TROUGH OVER
THE AREA CURRENTLY WILL SHIFT OFF TO THE EAST BY MIDDAY...WITH
DECREASING LIFT AND MOISTURE BECOMING MORE SHALLOW OVER THE NEXT
SEVERAL HOURS. THIS SHOULD RESULT IN A DECREASE OF THE STRONGER SNOW
SHOWERS...WHICH HAVE BEEN REDUCING VISIBILITY TO LESS THAN 2SM IN
SOME SPOTS AND PRODUCING SOME MINOR ACCUMS OF 0.1-0.2 INCHES. WHILE
SNOW SHOWERS WILL DIMINISH...A FEW SCATTERED FLURRIES WILL LIKELY
LINGER INTO THE AFTERNOON HOWEVER GIVEN PRESENCE OF UPPER TROUGH AND
CYCLONIC FLOW WITH MOISTURE TRAPPED BELOW INVERSION NOTED AROUND 900
MB ON DVN 12Z SOUNDING. COLD TEMPS BELOW -10 C IN THE BOUNDARY LAYER
SHOULD ALLOW FOR CONTINUED ICE NUCLEATION AND THUS A FEW FLURRIES
FROM LINGERING STRATOCU CLOUD DECK. DESPITE CYCLONIC FLOW...VERY DRY
NATURE OF ADVANCING ARCTIC AIR /SUB-ZERO SFC DEW POINT TEMPS JUST
UPSTREAM/ WILL LIKELY RESULT IN SOME BREAKS IN THE CLOUD COVER THIS
AFTERNOON. CONTINUED STRONG COLD ADVECTION WILL LIKELY LIMIT TEMP
RISE TO ONLY A FEW DEGREES EVEN WITH SOME SUN.

GIVEN ABOVE...HAVE LOWERED MAX TEMPS A LITTLE AND HAVE INDICATED A
RATHER FLAT HOURLY TEMP CURVE THROUGH TODAY. ALSO TWEAKED POPS TO
MORE CLOSELY REFLECT AREAS OF SNOW SHOWERS THIS MORNING. GRIDS/ZFP
ALREADY AVAILABLE.

RATZER

//PREV DISCUSSION...
405 AM CST

THE VERY ACTIVE WEATHER PATTERN WILL CONTINUE OVER THE AREA FOR THE
NEXT SEVERAL DAYS WITH A RATHER HIGH AMPLITUDE/VERY PROGRESSIVE FLOW
PATTERN OVER NORTH AMERICA.

FOR THE REMAINDER OF THE NIGHT AND INTO THE MORNING HOURS...THE MAIN
CONCERN WILL BE STRONG GUSTY WINDS AND SOME ADDITIONAL LIGHT SNOW.
THE STRONG COLD FRONT BLASTED ACROSS AREA LAST EVENING...WITH RAIN
QUICKLY TRANSITIONING OVER TO SNOW AND TEMPERATURES QUICKLY DROPPING
FROM THE MIDDLE TO UPPER 40S DOWN INTO THE MIDDLE TEENS TO LOWER 20S
BY 3AM.  STRONG COLD ADVECTION WILL CONTINUE THROUGH THE REMAINDER
OF THE NIGHT AND INTO TOMORROW WITH TEMPS EXPECTED TO BOTTOM OUT TO
AROUND 12 DEGREES IN THE ROCKFORD AREA TO AROUND 20 IN NWRN
INDIANA.  WITH WINDS AROUND 25 MPH AND GUSTS TO 35 MPH...THE MINIMUM
WIND CHILL READING THIS MORNING WILL RANGE FROM 10 BELOW ZERO OVER
THE ROCKFORD METRO AREA TO NEAR OR SLIGHTLY ABOVE ZERO OVER THE
REMAINDER OF THE CWA.  THE PERSISTENT COLD ADVECTION WILL ALLOW FOR
LITTLE DIURNAL TEMPERATURE VARIATION...WITH TEMPERATURES ONLY RISING
PERHAPS 5 DEGREES THROUGH THE DAY.  ALSO...WITH STRONG BROAD SCALE
CYCLONIC CURVATURE ALOFT AND A MODEST VORT MAX TRACKING OVER NRN IL
AT THE CURRENT TIME PER LATEST WV IMAGERY...LIGHT SNOW SHOULD LIKELY
CONTINUE THROUGH THE MORNING HOURS.  THE SNOW MAY BE SCATTERED AT
TIMES...AND WITH THE STRONG WINDS WILL LIKELY BE DIFFICULT TO GET
ANY REALISTIC MEASURABLE AMOUNTS...BUT HAVE BUMPED UP POPS TO 60%
FOR THE REMAINDER OF THE MORNING HOURS TO ACCOUNT FOR WHAT IS A HIGH
POP...LOW QPF SITUATION.  BY THIS AFTERNOON...THE UPPER TROUGH AXIS
AND EMBEDDED VORT MAX SHOULD BE WELL EAST OF THE CWA...BUT RESIDUAL
CYCLONIC CURVATURE AND WHAT LITTLE DAYTIME SFC WARMING WILL OCCUR
SHOULD BE SUFFICIENT TO GENERATE SOME SCT FLURRIES...BIT NO
ADDITIONAL ACCUMULATION IS EXPECTED...FOR NOW.

WEDNESDAY SHOULD BE MUCH QUIETER...WITH RESPECT TO WIND AND
PCPN...BUT THE CLEARING SKIES AND LIGHTER WINDS WILL ALLOW FOR
ENOUGH RADIATIVE COOLING TO DROP TEMPERATURES ACROSS THE CWA INTO
THE SINGLE DIGITS.  AND WHILE WINDS WILL NOT BE NEARLY AS STRONG AS
THIS MORNING...THE EXPECTED 10 TO 15 MPH WINDS WILL BE SUFFICIENT TO
DRIVE WIND CHILL VALUES DOWN TO 10 TO 15 DEGREES BELOW ZERO. WITH
THE COLD ADVECTIVE PATTERN CONTINUING INTO WEDNESDAY...THERE WILL BE
LITTLE CHANGE IN MAX TEMPS...WHICH WILL RANGE FROM THE UPPER TEENS
TO THE MIDDLE 20S.

THE NEXT SIGNIFICANT WEATHER SYSTEM IS STILL TAKING SHAPE OFF THE
PACIFIC NORTHWEST COAST AND SHOULD MAKE LANDFALL INTO NRN CALIFORNIA
BY THIS AFTERNOON.  THE GENERAL TREND OF THE SYSTEM UP TO THIS POINT
HAS BEEN RATHER CONSISTENT IN TRACKING IT INTO THE FOUR CORNERS
REGION BY THURSDAY NIGHT.  HOWEVER...THE LATEST MODEL RUNS ARE
TRACKING IT A LITTLE SLOW AND A LITTLE FARTHER TO THE SOUTH...AT
LEAST THOUGH 06Z THURSDAY.  THROUGH THE DAY THURSDAY...UPPER RIDGING
WILL STEADILY BUILD ACROSS THE MISSISSIPPI VALLEY WHILE INCREASING
IN AMPLITUDE.  IT IS THIS STRONG RIDGING THAT WILL FORCE THE SYSTEM
INTO AN ALMOST NORTHERLY TRACK THROUGH THE DAY.  SO...AS FAR AS THE
SENSIBLE WEATHER IS CONCERNED...WHAT THE REGION CAN EXPECT IS AN
EXTENDED PERIOD OF WARM ADVECTION SNOW.  WITH THE SLOWER EASTWARD
PROGRESSION OF THE SYSTEM THAN PREVIOUSLY ANTICIPATED...HAVE DELAYED
BRINGING THE SNOW INTO THE SWRN PORTIONS OF THE CWA...INCLUDING THE
PONTIAC METRO AREA...UNTIL AROUND NOON.  THE SNOW SHOULD THEN
QUICKLY OVERSPREAD THE AREA THOUGH THE AFTERNOON AND INTO THE EARLY
EVENING...LIKELY MAKING THE EVENING RUSH HOURS QUITE A MESS.  THE
MODEL GUIDANCE HAS ALSO BEEN VERY CONSISTENT IN DRY-SLOTTING THE
AREA THURSDAY NIGHT AS THE SFC SYSTEM GOES THROUGH THE OCCLUSION
PROCESS.  THIS PUNCH OF MUCH DRIER AIR ALOFT WILL OVERRUN THE MUCH
MOISTER LOWER LEVELS AND SHUT OFF THE SNOW POTENTIAL AS THERE WILL
BE INSUFFICIENT MOISTURE IN THE DENDRITIC GROWTH ZONE.  SO...THE
SNOW SHOULD TRANSITION OVER TO A PERIOD OF LIGHT FREEZING DRIZZLE JUST
AFTER MIDNIGHT THURSDAY NIGHT INTO FRIDAY MORNING.  AT THIS
POINT...THE TOTAL SNOWFALL EXPECTED OVER THE AREA IF FORECAST TO
RANGE FROM AROUND 5 INCHES OVER NORTH CENTRAL ILLINOIS...INCLUDING
THE ROCKFORD METRO AREA...TO 3 TO 4 INCHES IN A BAND FROM CHICAGO TO
PONTIAC...DROPPING OFF TO 2 TO 3 INCHES OVER NWRN INDIANA. AS
USUAL...SNOW FORECASTS ARE ALWAYS A BIT TRICKY AND ARE HIGHLY
DEPENDENT ON THE EXACT TRACK OF THE SYSTEM...SO THESE NUMBERS ARE
SUBJECT TO CHANGE WITH SUCCESSIVE FORECAST UPDATES.

THE SYSTEM IS EXPECTED TO WEAKEN CONSIDERABLY THROUGH THE DAY FRIDAY
AS IT BEGINS TO MEANDER AROUND THE UPPER MISSISSIPPI VALLEY.  THERE
IS SOME CONCERN THAT THE LIGHT FREEZING DRIZZLE COULD LINGER INTO
FRIDAY UNTIL THE UPPER LOW FINALLY LIFTS OFF TO THE NORTHEAST AND
HIGH PRESSURE BUILDS IN AT THE SURFACE FRIDAY EVENING.  FROM A QPF
PERSPECTIVE...THE EXPECTED PERIOD OF FREEZING DRIZZLE POTENTIAL MAY
NOT AMOUNT TO MUCH IN THE WAY OF MEASURABLE PCPN...BUT IT COULD HAVE
A GREATER IMPACT FOR TRAVEL ON UNTREATED ROAD SURFACES.

THE WEATHER ROLLER COASTER WILL TAKE ANOTHER DIP OVER THE WEEKEND
INTO EARLY NEXT WEEK WITH TEMPERATURES REBOUNDING INTO THE LOWER TO
MIDDLE 30S ON SATURDAY...THE UPPER 30S TO LOWER 40S ON SUNDAY...AND
THE LOWER TO MIDDLE 40S BY MONDAY.  THE NEXT ROUND OF PCPN IS NOT
EXPECTED UNTIL LATE MONDAY OR TUESDAY IN THE FORM OF ANOTHER SYSTEM
DROPPING OUT OF THE GULF OF ALASKA...THROUGH THE FOUR CORNERS REGION
AND THEN LIFTING INTO THE CENTRAL PLAINS.  THIS IS A VERY SIMILAR
SCENARIO AS THE SYSTEM TO IMPACT THE REGION ON THURSDAY...SO IT IS
POSSIBLE THAT MORE SNOW MAY BE ON THE WAY.

KREIN

&&

AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* STRONG WEST WINDS WITH GUSTS UP TO 35 KT AT TIMES THROUGH THE
  DAY.

* OCCASIONAL FLURRIES AND BLOWING SNOW POSSIBLY LASTING THROUGH
  THE AFTERNOON.

PAW

//DISCUSSION...UPDATED 18Z...

A STRONG LOW PRESSURE SYSTEM WELL TO THE NORTHEAST OF THE
TERMINALS IS MOVING FURTHER AWAY THIS AFTERNOON. THE SNOW
ASSOCIATED WITH THIS SYSTEM HAS TAPERED OFF TO OCCASIONAL FLURRIES
AND BLSN. WINDS WILL GRADUALLY DECREASE THIS EVENING AND THROUGH
THE OVERNIGHT HOURS IN THE WAKE OF THE SYSTEM. AS THE WINDS
DECREASE THERE WILL BE FEWER VISIBILITY RESTRICTIONS DUE TO BLSN
AND RESIDUAL FLURRIES...WITH MOST VISIBILITIES BETTER THAN 6SM BY
01Z. THEN THERE IS A BREAK BETWEEN SYSTEMS ON WEDNESDAY...WITH VFR
CONDITIONS EXPECTED.

PAW

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN WIND TREND.

* MEDIUM CONFIDENCE IN FLURRIES AND BLOWING SNOW TIMING AND
  DETAILS.

PAW

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

WEDNESDAY NIGHT...VFR.

THURSDAY...SNOW DEVELOPING IN THE LATE AFTERNOON/EARLY EVENING
WITH FZDZ POSSIBLE LATER IN THE NIGHT. IFR CONDITIONS LIKELY BY
EVENING. STRONG EAST WINDS LIKELY.

FRIDAY...IFR/LIFR POSSIBLE WITH DZ/FZDZ.

SATURDAY...MVFR CIGS POSSIBLE.

SUNDAY...VFR.

MONDAY...SLIGHT CHANCE OF RAIN OR SNOW. MVFR POSSIBLE.

KJB

&&

MARINE...
221 AM CST

A STRONG COLD FRONT HAS JUST PUSHED ACROSS THE SOUTHERN PORTION OF
THE LAKE EARLY THIS MORNING. THE SURFACE LOW CURRENTLY RESIDES
ACROSS THE NORTHERN PORTION OF THE LAKE...AND WILL MOVE NORTHEAST
INTO FAR SOUTHEASTERN ONTARIO TODAY. ONCE THIS LOW CLEARS THE
LAKE...THE WINDS WILL INCREASE OUT OF THE WEST NORTHWEST UP TO 40 TO
45 KT LATER THIS MORNING AND THIS AFTERNOON AS STRONG PRESSURE RISES
AND COLD AIR ADVECTION SETS UP ALONG THE BACK SIDE OF THE DEPARTING
AREA OF LOW PRESSURE. A VERY STRONG AREA OF HIGH PRESSURE...IN
EXCESS OF 1040 MB...WILL BUILD IN ACROSS ONTARIO AND THE UPPER GREAT
LAKES REGION IN THE WAKE OF THE LOW. THE COMBINATION OF THESE TWO
STRONG PRESSURE SYSTEMS...WILL CONTINUE TO PRODUCE A STRONG PRESSURE
GRADIENT THROUGH WEDNESDAY...ESPECIALLY ACROSS THE NORTHERN HALF OF
THE LAKE. THEREFORE...GALES OF 35 TO 40 KT WILL LIKELY CONTINUE INTO
AT LEAST WEDNESDAY MORNING. HOWEVER...IT IS POSSIBLE THAT SOME LOW
END GALES COULD CONTINUE THROUGH THE DAY ON WEDNESDAY...ESPECIALLY
NORTH. THE CURRENT GALE GOES THROUGH THE MORNING ON WEDNESDAY FOR
THE NORTH HALF OF THE LAKE. THIS MAY NEED TO BE EXTENDED.
HOWEVER...I OPTED TO HOLD OFF ON EXTENDING THE WARNING AT THIS TIME.

THE GALE WARNING FOR THE NEAR SHORES AND SOUTHERN OPEN WATER ZONES
REMAINS IN EFFECT THROUGH THIS EVENING. IT APPEARS WESTERLY GALES UP
TO 40 KT WILL OCCUR THROUGH THIS TIME...AND ALTHOUGH A FEW GALES MAY
PERSIST PAST THE CURRENT EXPIRATION TIME ON THE SOUTHERN END OF THE
LAKE...I ALSO OPTED TO HOLD ON TO THE CURRENT ENDING TIME.

THESE STRONG WINDS AND COLD AIR TEMPERATURES WILL ALSO ADD A HIGH
RISK FOR SIGNIFICANT FREEZING SPRAY THIS AFTERNOON THROUGH WEDNESDAY
MORNING. NO CHANGES HAVE BEEN MADE TO THE HEAVY FREEZING SPRAY
HEADLINES.

KJB

&&

LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ870-LMZ872-
     LMZ874-LMZ876-LMZ878 UNTIL 9 PM TUESDAY.

     HEAVY FREEZING SPRAY WARNING...LMZ080-LMZ261-LMZ362-LMZ364-
     LMZ366-LMZ563-LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-
     LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878
     UNTIL NOON WEDNESDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ868 UNTIL 9 AM WEDNESDAY.

     HEAVY FREEZING SPRAY WARNING...LMZ740-LMZ741-LMZ742-LMZ743-
     NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 4 AM WEDNESDAY.

&&

$$