Area Forecast Discussion
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000
FXUS63 KLOT 251426
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
926 AM CDT WED MAR 25 2015

.SHORT TERM...
309 AM CDT

THROUGH TONIGHT...
EARLY THIS MORNING RAIN HAD OVERSPREAD THE FORECAST AREA AND WILL
CONTINUE UNTIL PRIOR TO DAYBREAK. THE SFC LOW WAS LIFTING
NORTHEAST ACROSS THE SOUTHERN CWFA...AND GUIDANCE CONTINUES TO
SLIDE THE LOW ACROSS GARY AROUND 12Z AND FURTHER NORTHEAST BY MID-
MORNING. AS THE LOW LIFTS OVERHEAD...WINDS WILL BRIEFLY DIMINISH.
THEN WINDS ARE PROGGED TO VEER SOUTHWESTERLY AND THE GRADIENT WILL
STEADILY INCREASE. BY LATE MORNING WINDS WILL CONTINUE TO TURN
WEST...THEN SLOWLY DIMINISH AS THE GRADIENT SLACKENS LATE THIS
AFTERNOON.

SURFACE TEMPS WILL SLOWLY CLIMB THIS MORNING...AND TEMPS THIS
AFTERNOON MAY BE A CHALLENGE. GUIDANCE HAS CONTINUED TO POINT
TOWARDS A WARM THERMAL RIDGE ARRIVING MIDDAY AND PUSHING SFC TEMPS
INTO THE LOW/MID 50S TO ARND 60 IN THE FAR SOUTH. THIS WILL HINGE
UPON CLOUD COVER...WHICH COULD LINGER LONGER AS A RESULT OF THE LACK
OF MIXING IN THE LOW LEVELS. THIS WOULD RESULT IN COOLER TEMPS.

TEH MID-LVL FLOW REMAINS PROGRESSIVE THIS AFTERNOON/EVENING...AS YET
ANOTHER SFC WAVE ACROSS THE SOUTHERN PLAINS BEGINS TO DEVELOP. THIS
SECOND LOW WILL FUNNEL A CHANNEL OF MOISTURE NORTHEAST ALONG A
FRONTAL BOUNDARY...WITH SOME LIFT DEVELOPING WITHIN THE BOUNDARY.
THIS MAY BE ABLE TO DEVELOP SOME LIGHT PRECIP LATE THIS AFTN/EVE FOR
THE CENTRAL/SOUTHERN CWFA. AT THIS TIME FEEL THIS WILL LIKELY HOLD
OFF UNTIL CLOSER TO 00Z. THE 500MB TROUGH AXIS WILL BEGIN TO PIVOT
EAST THIS EVENING...ALLOWING THE SOUTHERN SFC LOW TO LIFT NORTHEAST
INTO THE TENN VALLEY LATE TONIGHT. GUIDANCE CONTINUES TO PAINT A
SLUG OF PRECIP ACROSS THE SOUTHERN CWFA WITH THE FRONTAL
BOUNDARY...AND HAVE MAINTAINED POPS IN THIS AREA TONIGHT.

BY DAYBREAK THUR THE PRECIP SHUD BE PUSHING EAST OF THE FORECAST
AREA...WITH ANTI-CYCLONIC FLOW BEGINNING TO DRY THE WESTERN FORECAST
AREA AS COLDER AIR RETURNS. OVERNIGHT LOWS WILL LIKELY REMAIN IN THE
LOW/MID 30S...HOWEVER IF THE FRONTAL BOUNDARY FORWARD SPEED
INCREASES TEMPS MAY BE ABLE TO QUICKLY COOL INTO THE UPR 20S.

BEACHLER

&&

.LONG TERM...
354 AM CDT

THURSDAY THROUGH TUESDAY...

UPPER LEVEL RIDGING IS EXPECTED TO BUILD SIGNIFICANTLY
ACROSS THE WESTERN CONUS TODAY THROUGH THURSDAY IN RESPONSE TO
SIGNIFICANT DISTURBANCE ACROSS THE THE NORTHERN PACIFIC.  ULTIMATELY
THIS WILL SET THE STAGE FOR WELL BELOW AVERAGE HEIGHTS AND A DEEPER
COLD AIRMASS TO TAKE CONTROL OF THE EASTERN HALF OF THE COUNTRY FOR
A FEW DAYS INTO THE WEEKEND. THEREFORE...THE MAIN WEATHER STORY
DURING THE PERIOD WILL BE THE TRANSITION BACK TO A MUCH BELOW
AVERAGE WEATHER PATTERN THROUGH AT LEAST THE FIRST HALF OF THE
WEEKEND.

THE HEART OF THIS COLD AIRMASS IS SET TO BEGIN TO SHIFT SOUTHWARD
OVER THE AREA THURSDAY NIGHT INTO FRIDAY AS ANOTHER COLD FRONT
SHIFTS DOWN THE WESTERN GREAT LAKES. IT STILL APPEARS THAT THERE
COULD BE SOME SNOW SHOWERS ACROSS PORTIONS OF THE REGION THURSDAY
NIGHT INTO EARLY FRIDAY MORNING AS THIS COLD AIR SPILLS OVER THE
AREA. LOW LEVEL LAPSE RATES LOOK TO STEEPEN CONSIDERABLY WITH THE
COLD AIRMASS...AND THIS COMBINED WITH THE APPROACH OF A ANOTHER
UPPER LEVEL DISTURBANCE DIGGING INTO THE BASE OF THE LARGER SCALE
TROUGH OVER THE EASTERN HALF OF THE COUNTRY...COULD RESULT IN SOME
MINOR ACCUMULATIONS OF SNOW OVER PORTIONS OF NORTHEASTERN
ILLINOIS/NORTHWESTERN INDIANA. OTHERWISE...WITH 925 MB TEMPERATURES
PROGGED TO ONLY BE -8 TO -10 DEGREES CELSIUS OVER THE
AREA...AFTERNOON HIGHS WILL LIKELY REMAIN IN THE LOW TO MID 30S AT
BEST...WITH SOME AREAS LIKELY NOT TO BREAK THE FREEZING POINT.

LATE FRIDAY NIGHT INTO SATURDAY MORNING THE CENTER OF A COLD 1030 MB
SURFACE HIGH IS SET TO MOVE OVERHEAD. LIGHT WINDS AND CLEAR SKIES
UNDER THIS HIGH WILL LIKELY ALLOW TEMPERATURES TO DROP INTO THE
TEENS...WITH LOWER TEENS POSSIBLE IN THE USUAL COLD SPOTS OF
NORTHERN ILLINOIS. SATURDAY LOOKS TO BE SUNNY ACROSS THE
REGION...BUT WITH THE COLD AIRMASS STILL IN PLACE SURFACE
TEMPERATURES ONLY LOOK TO GET INTO THE UPPER 30S...TO POSSIBLY NEAR
40 IN MY FAR WEST.

A SIGNIFICANT NORTHERN PACIFIC WAVE IS FORECAST TO SHIFT EASTWARD
ONSHORE ACROSS THE PACIFIC NORTHWEST BY SATURDAY MORNING...THEN
CONTINUE EASTWARD...WEAKENING THE AMPLITUDE OF THE WESTERN CONUS
RIDGE AS IS MOVES ACROSS THE NORTHERN ROCKIES LATE SATURDAY. THIS
WAVE IS FORECAST TO MOVE TOWARDS THE WESTERN GREATS LAKES REGION BY
SUNDAY EVENING. AN ASSOCIATED SURFACE LOW LOOKS TO TRACK EASTWARD
ACROSS FAR SOUTHERN CANADA THROUGH SUNDAY. THIS SYSTEM COULD RESULT
IN SOME STRONG GUSTY SOUTHWESTERLY WINDS SUNDAY AS THE SURFACE
GRADIENT STRENGTHENS BETWEEN THIS LOW AND THE EXITING SURFACE RIDGE
MOVING OVER THE SOUTHEASTERN CONUS. WARM AIR ADVECTION SHOULD SET
UP WITH THIS PATTERN...SO WARMING CONDITIONS ARE EXPECTED.
HOWEVER...THIS ALSO COULD RESULT IN SOME PRECIPITATION OVER THE AREA
SUNDAY...ESPECIALLY IF THE MAIN MID LEVEL PV ANOMALY TRACKS OVER
NORTHERN ILLINOIS AND WISCONSIN. THE MODEL GUIDANCE HAS COME IN A
BIT COOLER...SO IT STILL LOOKS AS THOUGH TEMPERATURES SUNDAY COULD
REMAIN AT LEAST A FEW DEGREES BELOW AVERAGE.

WARMER CONDITIONS LOOK TO RETURN NEXT WEEK AS THE STORM TRACK LOOKS
TO FAVOR SYSTEMS TRACKING EASTWARD ACROSS THE NORTHERN CONUS.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* LOW END MVFR CIGS THRU 19Z. CIGS SHUD APPROACH VFR CONDS LATE
  THIS AFTERNOON.

* SOUTHWEST/WEST WINDS 12-15KT WITH GUSTS TO 23 KT TODAY.

* POSSIBLE LGT RAIN SHOWER THIS EVENING.

KMD

//DISCUSSION...UPDATED 12Z...

PRECIP HAS ENDED ACROSS NORTHEAST IL AIRFIELDS AND LIFTED WELL
NORTH OF THE TAF SITES...UNFORTUNATELY PATCHY FOG HAS DEVELOPED.
THE LOW PRESSURE SYSTEM WAS SLOW TO PUSH NORTHEAST ACROSS THE
REGION. ONCE THE LOW LIFTS NORTHEAST OF THE TAF SITES WINDS WILL
QUICKLY INCREASE FROM THE WEST. GUSTS WILL ACCOMPANY THE
INCREASING WINDS...NEARING 20-25KT BY MID-MORNING. THE FOG SHOULD
QUICKLY LIFT ONCE WINDS BEGIN TO INCREASE...AS WELL AS THE
IFR/LIFR CIGS. CIGS MAY LINGER AT IFR HOWEVER THROUGH
MIDDAY...UNTIL DRIER AIR BEGINS TO FEED NORTHEAST ACROSS THE
REGION. A FRONTAL BOUNDARY WILL APPROACH FROM THE WEST THIS
EVENING...AND GUIDANCE HAS CONTINUED TO INDICATE SOME LIGHT PRECIP
FEEDING ALONG THE COLD FRONT. CURRENTLY FEEL THAT THE BULK OF THE
PRECIP WILL BE WELL SOUTH OF THE TAF SITES THIS EVENING. AS A
RESULT HAVE OPTED TO ONLY MENTION A VCSH IN THE CURRENT TAF. WINDS
WILL STEADILY TURN NORTHWEST OVERNIGHT...WITH GUSTS RETURNING
AFTER DAYBREAK THUR.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* HIGH CONFIDENCE IN WIND DIR/SPEED/GUSTS. MEDIUM CONFIDENCE IN
  END TIMING OF GUSTS.

* MEDIUM CONFIDENCE IN CIGS REMAIN AT OR ABOVE 1000 FT THIS
  MORNING.

* MEDIUM/HIGH CONFIDENCE IN CIGS NEARING VFR CONDS BY 23Z.

* HIGH CONFIDENCE IN PRECIP REMAINING OUT OF TAF SITES THRU
  00Z...MEDIUM CONFIDENCE PRECIP THIS EVENING WILL STAY SOUTH OF
  ORD/MDW.

KMD

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...CHANCE OF SNOW SHOWERS. PATCHY MVFR CIGS AND
POSSIBLE VSBY REDUCTION.

FRIDAY...VFR.

SATURDAY...VFR.

SUNDAY...CHANCE RAIN THROUGH THE DAY...POSSIBLY MIXING WITH SNOW
EARLY. MVFR CIGS/VIS POSSIBLE.

MONDAY...VFR.

TUESDAY...VFR.

BEACHLER

&&

.MARINE...
411 AM CDT

A SURFACE LOW...NOW OVER PORTIONS OF NORTHERN ILLINOIS...WILL SHIFT
NORTHEASTWARD ACROSS SOUTHERN LAKE MICHIGAN IN THE NEXT FEW
HOURS...THEN CONTINUE NORTHEASTWARD TOWARDS SOUTHEASTERN ONTARIO.
THE WINDS WILL BECOME SOUTHWESTERLY FLOWING THE PASSAGE OF THIS
SYSTEM THIS MORNING...BUT WIND SPEEDS DO NOT LOOK AS THOUGH
THEY WILL BE AS STRONG AS WHAT THEY APPEARED YESTERDAY.

A SECOND SURFACE LOW WILL SHIFT EASTWARD OVER NORTHERN MINNESOTA
TODAY...THEN MERGE WITH THE REMNANTS OF THE FIRST LOW BY THIS
EVENING. COLDER AIR WILL THEN BEGIN TO SHIFT SOUTHWARD OVER THE LAKE
ON THURSDAY AS A COLD FRONT MOVES SOUTHWARD AND RESULTS IN
INCREASING NORTHERLY FLOW DOWN LAKE MICHIGAN. IT APPEARS THAT
NORTHERLY WINDS OF 30 KT WILL DEVELOP LATER THURSDAY IN THE WAKE OF
THIS FRONT AND CONTINUE THROUGH FRIDAY MORNING AS A SURFACE RIDGE OF
HIGH PRESSURE SHIFTS SOUTHEASTWARD FROM CANADA TO THE UPPER MIDWEST.
THIS WILL LEAD TO LARGE WAVES AND HAZARDOUS CONDITIONS SUPPORTIVE OF
ANOTHER SMALL CRAFT ADVISORY FOR THE ILLINOIS AND INDIANA NEAR SHORE
WATERS DURING THIS PERIOD.

THE SURFACE HIGH LOOKS TO SHIFT SOUTHEAST OF LAKE MICHIGAN BY
SATURDAY NIGHT AND SUNDAY AS ANOTHER POTENT SURFACE LOW TRACKS
EASTWARD ACROSS SOUTH CENTRAL CANADA. THESE TWO PRESSURE PATTERNS
LOOK TO SET UP AN OPTIMAL SURFACE PRESSURE GRADIENT PATTERN TO
SUPPORT A PERIOD OF SOUTHERLY GALES OVER THE OPEN WATERS OF LAKE
MICHIGAN ON SUNDAY.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM WEDNESDAY.

&&

$$

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