Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 070912
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
312 AM CST SUN FEB 7 2016

.SHORT TERM...
231 PM CST

TONIGHT THROUGH SUNDAY...

MAIN NEAR TERM CONCERNS ARE PRIMARILY CLOUDY COVER TONIGHT AND
SUNDAY...AND RELATIVELY MILD TEMPERATURES FOR THE REMAINDER OF THE
WEEKEND BEFORE WE SLIDE BACK INTO MORE TYPICAL MID-WINTER
CANDIDNESS FOR THE COMING WEEK.

LOW PRESSURE WAS PASSING NORTH OF THE GREAT LAKES REGION THIS
AFTERNOON...WITH A TRAILING COLD FRONT WHICH WILL BECOME NEARLY
STATIONARY ACROSS UPPER MICHIGAN TONIGHT. MODEST LOW LEVEL
SOUTHWEST WINDS WERE IN PLACE ACROSS THE MIDWEST...WITH
CONSIDERABLE SUNSHINE AND MILD TEMPERATURES IN THE UPPER 30S TO
MID 40S OVER THE WFO LOT FORECAST AREA. EXTENSIVE LOW CLOUD COVER
WAS IN PLACE IMMEDIATELY NORTH AND NORTHWEST OF THE CWA...THOUGH
GUIDANCE TRENDS INDICATE THAT INCREASING SOUTH-SOUTHWEST WINDS
OVERNIGHT INTO SUNDAY WILL KEEP THE BULK OF THE LOW CLOUD COVER
OUT OF THE FORECAST AREA WITH FAR NORTH CENTRAL IL MORE LIKELY TO
BE ALONG THE EDGE OF THE LOW CLOUDS. MOSTLY CLEAR OR PARTLY CLOUDY
SKIES THIS EVENING WILL ALLOW TEMPS TO FALL BACK INTO THE UPPER
20S TO AROUND 30...WINDS INCREASING TO 10-15 MPH OVERNIGHT WILL
LIKELY HOLD TEMPS STEADY AFTER MIDNIGHT OR EVEN COME UP A DEGREE
OR TWO IN SOME PLACES. PATCHY MID/HIGH CLOUD COVER IS EXPECTED TO
INCREASE LATE TONIGHT AS WELL...IN PERSISTENT WARM ADVECTION
REGIME.

STRONG MID-LEVEL SHORT WAVE TROUGH SEEN IN WATER VAPOR IMAGERY
THIS AFTERNOON OVER THE NORTHERN HIGH PLAINS AND SOUTHERN CANADIAN
PRAIRIES WILL PROPAGATE SOUTHEAST ACROSS THE UPPER MIDWEST BY
SUNDAY MORNING...WITH A DIGGING JET STREAK AMPLIFYING THE UPPER
TROUGH ACROSS THE REGION LATE IN THE DAY. DESPITE STRONG HEIGHT
FALLS DEVELOPING DURING THE DAY...FORECAST SOUNDINGS AND TIME-
SECTIONS DEPICT DRY LOW LEVELS WITH MOISTURE MAINLY CONFIDENCE TO
THE MID AND UPPER LEVELS THROUGH THE AFTERNOON. THE RESULT IS
MINIMAL/NO PRECIPITATION POTENTIAL PRIOR TO SUNDAY EVENING.
SUNDAY LOOKS TO BE THE WARMEST DAY FOR AT LEAST THE NEXT
WEEK...WITH 925 MB T FIELDS SUPPORTING HIGHS IN THE LOW-MID 40S
ACROSS THE FORECAST AREA. BLEND OF DOMESTIC GUIDANCE LOOKS PRETTY
REASONABLE. IT WILL BE BREEZY AS WELL WITH WEST-SOUTHWEST WINDS
EXPECTED TO GUST 25-30 MPH...AND POTENTIALLY HIGHER IF WE MIX
DEEPER PER GFS SOUNDINGS.

RATZER

&&

.LONG TERM...
229 PM CST

SUNDAY NIGHT THROUGH SATURDAY...

A HIGHLY AMPLIFIED UPPER LEVEL PATTERN WILL CONTINUE INTO THE LONGER
TERM FORECAST PERIOD WITH A STRONG NORTHERN STREAM SHORTWAVE
DROPPING FROM THE UPPER MISSISSIPPI VALLEY SUNDAY NIGHT ACROSS LAKE
MICHIGAN AND INTO LOWER MICHIGAN MONDAY.  AN ASSOCIATED COLD FRONT
WILL PUSH ACROSS THE REGION LATE SUNDAY NIGHT INTO MONDAY WITH
BLUSTERY CONDITIONS DEVELOPING THROUGH THE DAY WITH NWLY WINDS
GUSTING TO 25 TO 30MPH AT TIMES.  STRONG COLD ADVECTION SHOULD BEGIN
IN EARNEST MONDAY NIGHT AS THE UPPER LOW MOVES SLOWLY TOWARD THE ERN
GREAT LAKES AND UPPER RIDGING BUILDS OVER THE PAC NORTHWEST.  THE
UPPER FLOW PATTERN SHOULD CONTINUE TO INCREASE IN AMPLITUDE INTO
MIDWEEK WHILE SHOWING LITTLE PROGRESSION.  THIS WILL SET UP THE NEXT
ROUND OF COLDER CONDITIONS FOR THE REGION AS A PERSISTENT FETCH OF
COLD AIR OUT OF THE ARCTIC WILL OVERSPREAD THE REGION.  BY
TUESDAY...HIGH TEMPS SHOULD ONLY BE IN THE UPPER TEENS TO MIDDLE
20S.  OVERNIGHT LOWS WEDNESDAY AND THURSDAY MORNING SHOULD GENERALLY
BE IN THE SINGLE DIGITS ACROSS THE AREA...WITH TEMPS ARND 10-12F
OVER THE SERN PORTIONS OF THE CWA AND DOWNTOWN CHICAGO.  WIND CHILL
READINGS SHOULD BE LOWEST WEDNESDAY MORNING AS WINDS ARND 10 MPH
PERSIST OVERNIGHT...DRIVING WIND CHILLS DOWN TO -10 TO -15F.  BY
THURSDAY...THE PATTERN IS EXPECTED TO BREAK DOWN A BIT WITH THE
UPPER RIDGE OVER THE WRN CONUS FLATTENING IN RESPONSE TO A DEEP
UPPER LOW DROPPING SOUTH OF HUDSON BAY WHICH WILL ALSO HELP THE
UPPER TROUGH TO SHIFT TO THE EAST.  SO...BY LATE IN THE
PERIOD...CONDITIONS SHOULD TREND A LITTLE WARMER...BUT TEMPERATURES
SHOULD STILL BE WELL BELOW NORMAL.

THE GREATEST CHANCE FOR PCPN WILL BE SUNDAY NIGHT INTO TUESDAY AS A
SERIES OF SHORTWAVES DROP SEWD THROUGH THE FAST NWLY FLOW SETTING UP
ACROSS THE REGION.  THE MAY END UP BEING A PERIOD OF RELATIVELY HIGH
POPS AND LOW QPF AS THERE SHOULD BE LITTLE IN THE WAY OF DEEP LAYER
MOISTURE FOR THE SHORTWAVES TO WORK WITH. BY MONDAY AFTERNOON INTO
TUESDAY...PCPN MAY ALSO JUST BE SCT SNOW SHOWERS UNDER CYCLONIC FLOW
ALOFT.  THERE WILL LIKELY BE SOME ACCUMULATION FOR THE PERIOD FROM
SUNDAY NIGHT THROUGH TUESDAY WITH CURRENT INDICATORS SUGGESTING 1 TO
3 INCHES OF SNOW OVER THE 48 HOUR PERIOD.  FROM WEDNESDAY THROUGH
SATURDAY...EXPECT THAT PCPN CHANCES WILL SHUT OFF AS UPPER FLOW
TRENDS TOWARD A BROAD UPPER TROUGH OVER PORTIONS OF THE CONUS EAST
OF THE ROCKIES AND WEAK RIDGING ALONG THE ROCKIES.  SOME LAKE EFFECT
SNOW SHOWERS COULD IMPACT THE ERN SHORES OF LAKE MICHIGAN...BUT THE
LOCAL AREA SHOULD TREND DRY.

KREIN

&&

.AVIATION...

UPDATE...
FOR THE 09Z TAFS...

WILL BE CLOSE TO LOW-LEVEL WIND SHEAR CRITERIA THROUGH ABOUT 14Z
THIS MORNING WITH SOUTHWEST WINDS IN THE 1000-2000 FT LAYER AT
40-45 KT AND POSSIBLY 50 KT. THERE HAS NOT BEEN ANY ACARS DATA TO
DIRECTLY ASSESS AT THIS POINT BUT MODELS GENERALLY AGREE AND A
PATTERN IS IN PLACE THAT CAN SUPPORT LLWS. THE ONE THING IS
SURFACE AND LIKELY NEAR-SURFACE WINDS ARE ON THE INCREASE TOO THIS
MORNING...LESSING THE ABRUPTNESS OF THE SPEED INCREASE WITH
HEIGHT. SO HAVE ONLY INCLUDED FOR RFD AT THIS TIME.

MTF

FOR THE 06Z TAFS...

VFR CONDITIONS THROUGH THE PERIOD. LIGHT SOUTHERLY WINDS WILL
GRADUALLY INCREASE OVERNIGHT AND BECOME MORE SOUTHWESTERLY.
SOUTHWEST WINDS WILL ALSO BECOME INCREASINGLY GUSTY SUNDAY MORNING
WITH GUSTINESS CONTINUING INTO THE AFTERNOON. COLD FRONT AND UPPER
LEVEL DISTURBANCE SHOULD RESULT IN AN INCREASING THREAT OF SNOW
SHOWERS LATE SUNDAY NIGHT...WITH SOME POTENTIAL FOR SOME BRIEF
HEAVIER SNOW SHOWERS.

IZZI

&&

.MARINE...
148 AM CST

THE LAKE MICHIGAN WEATHER FROM TODAY THROUGH WEDNESDAY WILL BE
ENTIRELY INFLUENCED BY A STRONG LOW PRESSURE DIVING IN FROM CANADA
LATER TODAY THAT WILL THEN DRIFT EAST OVER THE GREAT LAKES. THE
SOUTHWEST WINDS AHEAD OF THIS WILL BE AROUND OR A TAD ABOVE 30 KT
THIS MORNING OVER THE OPEN WATER...AND SOME 22-25 KT GUSTS IN THE
ILLINOIS AND INDIANA NEARSHORE. AT THIS TIME AM LEANING ON NOT
HAVING A SMALL CRAFT ADVISORY TODAY DUE TO LACK OF DURATION OF
THESE WINDS AND THE CONFIDENCE IN DEGREE OF MIXING BEING LOWER
THAN TYPICAL FOR A FORECAST ONLY 6 TO 12 HOURS FROM NOW. WILL
ASSESS TRENDS THROUGH DAYBREAK THOUGH AND IF THEY ARE OUTPACING
THE FORECAST THEN WILL ISSUE AN ADVISORY.

AS THE NORTHWEST FLOW ON THE BACKSIDE OF THE LOW BEGINS TO WRAP IN
ON MONDAY...SMALL CRAFT CRITERIA IS VERY LIKELY TO BE SEEN IN THE
NEARSHORE. AS FOR THE OPEN WATER...THE POTENTIAL FOR GALES
DEFINITELY EXITS FOR AT LEAST TIMES IN THE MONDAY NIGHT THROUGH
TUESDAY NIGHT WINDOW. THE LOW IS FORECAST TO SLOW DUE TO A VERY DEEP
LOW LIFTING NORTHWARD OFF THE EASTERN U.S. SEABOARD. SO THIS THROWS
CONTINUED UNCERTAINTY ON HOW FAST THE LOW WILL MOVE EASTWARD AND
THUS THE DEGREE OF PRESSURE GRADIENT AND COLD ADVECTION COUPLED OVER
THE OPEN WATERS FOR GALES. WILL NOTE SOME GALES IN THE GLF AND
CONTINUED LIGHT FREEZING SPRAY CHANCES.

MTF

&&

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

$$

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