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000
FXUS63 KLOT 051730
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1130 AM CST THU MAR 5 2015

.SHORT TERM...
356 AM CST

TODAY THROUGH FRIDAY...

HIGH PRESSURE WAS CENTERED TO OUR WEST OVER THE MID-MISSOURI VALLEY
EARLY THIS MORNING...AND WILL SPREAD SOUTHEAST ACROSS CENTRAL
ILLINOIS THIS AFTERNOON IN THE WAKE OF A POSITIVE-TILT UPPER TROUGH
PROPAGATING ACROSS THE AREA THIS MORNING. ARCTIC AIR HAS OOZED INTO
THE REGION OVER THE PAST 24 HOURS...THOUGH HIGH CLOUD COVER
ASSOCIATED WITH THE UPPER JET STREAK AHEAD OF THE TROUGH AXIS HAS
HELPED TO KEEP READINGS FROM BOTTOMING OUT TOO HARD OVERNIGHT. 3 AM
SURFACE MAP SHOWS ONLY ROCHELLE AT -1...WITH TEMPERATURES OTHERWISE
IN THE POSITIVE SINGLE DIGITS ACROSS THE FORECAST AREA OUTSIDE OF A
FEW LOWER TEENS IN THE CORE OF THE CHICAGO URBAN HEAT ISLAND. MAY
SEE A FEW MORE SUB-ZERO TEMPS THROUGH SUNRISE ESPECIALLY ACROSS
NORTH CENTRAL ILLINOIS ALONG THE NORTHWEST PERIPHERY OF THE HIGH
CLOUD COVER...WITH LIGHT NORTH WINDS PRODUCING WIND CHILLS FROM -5
TO -15 F.

THE HIGH CLOUDS WILL SHIFT OFF TO THE EAST TODAY WITH THE UPPER
TROUGH...WITH MAINLY SUNNY SKIES EXPECTED. ONLY SHALLOW MIXING IS
ANTICIPATED WITH THE NORTHERN EXTENT OF THE SURFACE HIGH PASSING
ACROSS THE AREA...THOUGH STRENGTHENING MARCH SUNSHINE SHOULD HELP
CHILLY MORNING TEMPERATURES RECOVER INTO THE 15-20 DEGREE RANGE BY
AFTERNOON. HAVE MAINTAINED FORECAST HIGHS A FEW DEGREES ABOVE THE
WARMER END OF THE GUIDANCE SPECTRUM. THE HIGH WILL SHIFT SOUTHEAST
OF THE AREA TONIGHT...ALLOWING SOUTHERLY WINDS TO DEVELOP AND WARM
ADVECTION TO DEVELOP ALOFT. WINDS WILL BE LIGHT INITIALLY...WHICH
COMBINED WITH MAINLY CLEAR SKIES SHOULD ALLOW TEMPS TO FALL QUICKLY
THIS EVENING...THEN BECOME STEADY OR SLOWLY RISE A FEW DEGREES LATER
IN THE NIGHT AS THOSE SOUTH WINDS INCREASE JUST A BIT. SOUTH WINDS
WILL BECOME GUSTY FRIDAY AS A MID-LEVEL WAVE AND ASSOCIATED SURFACE
LOW PRESSURE PASS NORTH OF THE LAKES ACROSS ONTARIO...NEARING 25 MPH
AT TIMES DURING THE DAY. WHILE TEMPERATURES MODERATE INTO THE MID
20S TO AROUND 30 ON FRIDAY...THE GUSTY WINDS WILL KEEP WIND CHILLS
IN THE TEENS THROUGH THE AFTERNOON MAKING FOR A RAW FEEL TO THE DAY.

RATZER

&&

.LONG TERM...
356 AM CST

SATURDAY THROUGH WEDNESDAY...

THE EASTERN NORTH AMERICAN UPPER TROUGH BROADENS AND DEAMPLIFIES
DURING THE PERIOD...WHILE THE PERSISTENT STRONG WEST COAST UPPER
RIDGE LOSES STRENGTH. THIS WILL PROVIDE MODERATING TEMPERATURES AS
LOW LEVEL FLOW BECOMES MORE PERSISTENTLY WEST-SOUTHWEST...AND
NORTHWEST FLOW ALOFT BECOMES MORE ZONAL ESPECIALLY INTO NEXT WEEK.

INITIALLY...A COUPLE OF SMALL AMPLITUDE SHORT WAVES WILL RIPPLE
SOUTHEAST ACROSS THE GREAT LAKES REGION OVER THE WEEKEND...ONE ON
SATURDAY AND ANOTHER LATER IN THE DAY SUNDAY. WEAK SURFACE COLD
FRONTS WILL GLANCE THE AREA WITH THESE TWO DISTURBANCES...TEMPERING
THE WARM-UP JUST A BIT. STILL...WITH WARMING ALOFT AND
SOUTH-SOUTHWEST FLOW AT THE SURFACE AHEAD OF EACH OF THESE WEAK
FRONTS TEMPS SHOULD REACH THE 35-40 DEGREE RANGE BOTH SATURDAY AND
SUNDAY. SOME OF THE ENSEMBLE GUIDANCE TRIES TO PAINT A LITTLE LIGHT
PRECIPITATION AHEAD OF THESE BOUNDARIES AS WELL...THOUGH FORECAST
TIME/HEIGHT SECTIONS AND SOUNDINGS SHOW A LACK OF DEEP MOISTURE AND
IT APPEARS THAT THE THREAT OF ANY MORE SIGNIFICANT PRECIPITATION
WILL REMAIN NORTH OF THE CWA.

MORE ROBUST WARMING LOOMS JUST PAST THE WEEKEND AS UPPER FLOW
BECOMES MORE ZONAL...AND ANOTHER DEEPER LOW MOVES EAST ACROSS
CANADA. ECMWF WARMS OUR 850 MB TEMPS TO +2 C BY TUESDAY AND TO +6 C
BY WEDNESDAY...WITH BOTH GFS/ECMWF GUIDANCE BOOSTING SFC TEMPS INTO
THE LOW-MID 40S TO START THE WEEK...AND INTO THE 50-55 DEGREE RANGE
TUESDAY AND WEDNESDAY. SURFACE HIGH PRESSURE RIDGE REMAINS TO OUR
SOUTH FROM TEXAS TO SOUTHERN NEW ENGLAND DURING THE PERIOD...
MINIMIZING THE RETURN OF DEEP MOISTURE AND KEEPING PRECIPITATION
CHANCES LOW THROUGH THE EXTENDED.

RATZER

&&

.AVIATION...

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

* NWLY WINDS OCNLLY GUSTING TO 18-20 KT THIS AFTERNOON.

KREIN

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

HIGH PRESSURE IS CENTERED OVER THE MIDDLE MISSISSIPPI VALLEY WILL
CONTINUE TO SAG SOUTHEAST TO THE OHIO VALLEY BY THIS EVENING. NWLY
WINDS OCNL GUSTING TO 18-20KT WILL SLOWLY BACK TO WLY THIS EVENING
WHILE DIMINISHING TO 5-7KT. AS THE HIGH CONTINUES TO SAG TO THE
UPPER OHIO VALLEY TO LOWER MISSISSIPPI VALLEY TOMORROW AS WEAK
TROUGHING DEVELOPS OVER THE NRN PLAINS. WINDS WILL THE BECOME SWLY
TOMORROW...BUT WITH A STRENGTHENING PRESSURE GRADIENT AND AMPLE
SUNSHINE FOR DEEP LAYER MIXING...GUSTING TO 20-25KT IS EXPECTED
FROM LATE MORNING THROUGH THE AFTERNOON. VFR CONDITIONS WILL
PREVAIL THROUGH THE PERIOD AS HIGH PRESSURE REMAINS THE DOMINANT
FEATURE OVER THE REGION.

KREIN

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

* MEDIUM-HIGH CONFIDENCE IN WIND TRENDS.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

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

FRIDAY NIGHT THROUGH WEDNESDAY...PRIMARILY VFR.

BMD

&&

.MARINE...
318 AM CST

HIGH PRESSURE IS OVER THE UPPER MIDWEST EARLY THIS MORNING AND WILL
DRIFT ACROSS THE OHIO VALLEY THIS EVENING...THEN SETTLE ACROSS THE
SOUTHEASTERN STATES THROUGH THE WEEKEND. AS THE HIGH DRIFTS ACROSS
THE MIDWEST...WINDS WILL BACK TO THE WEST THIS EVENING...THEN
SOUTHWEST TONIGHT. A SERIES OF LOWS WILL MOVE ACROSS ONTARIO AND THE
NORTHERN LAKES REGION THIS WEEKEND AND EARLY NEXT WEEK. WINDS WILL
GENERALLY STAY OUT OF THE WEST AND SOUTHWEST THROUGH THIS
PERIOD...FRESHENING UP AT TIMES IN ADVANCE OF THE LOWS.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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