Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KLOT 271950
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
250 PM CDT THU AUG 27 2015

.SHORT TERM...
246 PM CDT

THROUGH FRIDAY NIGHT...

TONIGHT...
VISIBLE IMAGERY THIS AFTERNOON SHOWS SOME FAIR WEATHER CUMULUS
CLOUDS ACROSS NORTHERN IL/NORTHWEST IN...WITH A CIRRUS SHIELD
ARRIVING OVERHEAD. THIS CIRRUS SHIELD WAS FROM THE AREA OF
SHOWERS/THUNDERSTORMS OVER THE CENTRAL PLAINS. WITH HIGH PRESSURE
CENTERED OVER THE REGION...THE EASTERN PROGRESSION OF PRECIP AND THE
LOW OVER THE CENTRAL PLAINS WILL BE SLOW TO MOVE. THIS WILL ALLOW
QUIET CONDITIONS TO LINGER TONIGHT...SO HAVE MAINTAIN A DRY
FORECAST. SKIES WILL STEADILY THICKEN OVERNIGHT AS THE LOW DRIFTS
EAST. EXPECT OVERNIGHT LOWS TO FALL INTO THE MID/UPR 50S ACROSS THE
BULK OF THE FORECAST AREA...WITH SOME AREAS CLOSER TO LAKE MICHIGAN
SEEING A LIGHT ONSHORE FLOW AND KEEPING TEMPS IN THE LOW 60S.

FRIDAY THROUGH FRIDAY NIGHT... DIFFERENCES AMONGST OPERATIONAL
SOLUTIONS LINGERS INTO FRI MORNING...WITH SOME OF THE HI-RES
SIMULATIONS ANTICIPATING AN AREA OF STORMS/RAIN TO PUSH EAST INTO
EASTERN IOWA THEN QUICKLY DECAY SHORTLY AFTER DAYBREAK FRI. GIVEN A
RATHER STABLE ENVIRONMENT OVER NORTHERN IL/NORTHWEST IN WITH
CONSIDERABLE CLOUD COVER...THIS APPEARS FAVORABLE TO OCCUR.
INSTABILITY DOES NOT LOOK TO EXPAND MUCH DURING THE LATE
MORNING/AFTERNOON HOURS...HOWEVER WITH SOME BETTER FORCING ARRIVING
IN THE MID-LVLS LATE MORNING/AFTERNOON...THIS MAY ALLOW FOR SOME
EMBEDDED THUNDER TO DEVELOP WITH THE SHORTWAVE AS IT APPROACHES THE
REGION. HAVE ONLY MADE MINOR ADJUSTMENTS TO THE PRECIP COVERAGE AND
TIMING.

ONE ITEM THAT MAY NEED FURTHER ADJUSTMENTS WILL BE HIGH TEMPS FOR
FRI...GIVEN THE THICKENING SOLAR SHIELDING. HAVE NUDGED TEMPS DOWN A
DEGREES INTO THE LOW/MID 70S FOR CENTRAL/NORTH AND UPR 70S ACROSS
THE FAR SOUTH. THERE MAY BE ENOUGH CLOUD COVER TO LIMIT
HEATING...AND KEEP TEMPS SEVERAL DEGREES COOLER IN THE UPR 60S TO
LOWER 70S.

PRECIP CHANCES WILL CONTINUE THRU FRI NIGHT...BUT WITH THE SHORTWAVE
LIFTING NORTHEAST ACROSS WISC...THE BEST PROBS FOR PRECIP WILL BE
FOCUSED TO OUR NORTH. HAVE REFLECTED THIS WITHIN THE CURRENT PRECIP
FORECAST WITH LOWER POPS FURTHER SOUTH. TEMPS FRI NIGHT WILL LIKELY
REMAIN MILD GIVEN THE THICK CLOUD COVER...WITH LOWS IN THE MID 60S.

BEACHLER

&&

.LONG TERM...
225 AM CDT

SATURDAY THROUGH WEDNESDAY...

A BROAD AREA OF INCREASED SUBTROPICAL MOISTURE IS SEEN ON MORNING
WATER VAPOR IMAGERY OVER THE INTERMOUNTAIN WEST AND WESTERN
PLAINS. WITHIN THIS ARE A FEW EMBEDDED SHORT WAVES...WITH TWO KEY
ONES ACCORDING TO NUMERICAL MODEL GUIDANCE BEING OVER NORTHERN
WYOMING AND SOUTHWEST COLORADO AS OF 230 AM. MODEL SOLUTIONS ARE
SPLIT ON WHICH OF THESE...IF EITHER...BECOME MORE DOMINANT ON
FRIDAY AS THEY TRACK EAST. A DEEPENING OF A LOW AMPLITUDE
SHORTWAVE TROUGH FROM THESE WAVES IS EXPECTED...WHICH SHOULD HELP
RAIN COVERAGE AND FOCUS WITHIN THE UPPER MIDWEST BY FRIDAY
EVENING. THE QUESTION IS AT WHAT LATITUDE WILL THIS BE AND THE
FURTHER SOUTH THE GREATER LIKELIHOOD FOR SHOWER POTENTIAL AND
DURATION IN THE CWA.

AT THIS TIME HAVE LEANED TOWARD A SLIGHTLY NORTH OF A MEAN
SOLUTION...CLOSER TO THE NAM AND EC. SUCH AN EVOLUTION WOULD STILL
APPEAR CLOSE ENOUGH FOR LIKELY RAIN SHOWERS WITHIN QG FORCING
FIELDS...ESPECIALLY NORTH OF INTERSTATE 80...FOR A PERIOD SOMETIME
FRIDAY NIGHT INTO SATURDAY MORNING. A 27.03 SREF MEAN FOR
ROCKFORD PROVIDES AROUND 0.40 OF AN INCH OF RAIN WITH AMOUNTS
DROPPING SOUTH AND EAST...ALTHOUGH QUITE A BIT OF SPREAD. HAVE
LEANED CLOSE TO A COLLABORATED WPC QPF WITH NO SIGNS OF ANY STRONG
MESOSCALE FORCING.

GUIDANCE ALSO DISAGREES ON HOW QUICKLY THE SURFACE TROUGH ASSOCIATED
WITH THIS SYSTEM MOVES EASTWARD. SOME MODELS SUCH AS THE EC HAVE IT
EAST OF THE AREA SATURDAY NIGHT...WHILE OTHER GLOBAL GUIDANCE LIKE
THE GFS AND GEM WEAKEN THE TROUGH JUST WEST OR OVER THE AREA GOING
INTO SUNDAY. BASICALLY CONTINUE TO GRADUALLY SHIFT RAIN CHANCES
EASTWARD THROUGH SATURDAY AFTERNOON AND NIGHT. MARGINAL INSTABILITY
MAY BE ENOUGH FOR ISOLATED TO SCATTERED THUNDER IN THE REGION
LATE FRIDAY NIGHT INTO SATURDAY...BUT SEVERE WEATHER IS UNLIKELY
BASED ON THE INSTABILITY AND MOISTURE SPECTRUM FORECAST.

WITH THE WEAKENING OF THE SURFACE LOW...LOOKS LIKE LINGERING CLOUDS
FROM THIS SYSTEM COULD BE A PROBLEM...ESPECIALLY IF A SLOWER
SOLUTION PANS OUT. CONCEIVABLY CLOUDS COULD LAST INTO THE DAY SUNDAY
AND LIMIT WARMTH. FOR NOW...HAVE KEPT SATURDAY HIGHS SEVERAL DEGREES
BELOW A SMART GUIDANCE BLEND.

INTO NEXT WEEK THE PATTERN CONTINUES TO LOOK SLOW-MOVING WITH THE
PRIMARY JET STREAM WELL NORTH INTO CANADA AND UPPER/MID-LEVEL
HEIGHTS ABOVE NORMAL ON THE SUITE OF LONG RANGE GUIDANCE. THE
PATTERN IS ONE THAT LOOKS MAINLY SUNNY FROM MONDAY ONWARD. THE EC
HAS QUICKER WARMING IN THE LOW-LEVELS THAN THE GFS...WITH 850MB
TEMPERATURES AT 19-20C BY MONDAY NIGHT INTO TUESDAY. HAVE GONE
WITH THE GUIDANCE BLEND AND A LITTLE WARMER BY WEDNESDAY. FLOW
STRENGTH LOOKS LIGHT ENOUGH THAT LAKE BREEZES COULD DEVELOP AND
WILL HAVE TO REFINE THOSE DETAILS IN TIME.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* SOUTHEAST WINDS JUST UNDER 10KTS THIS AFTERNOON.
* POSSIBLE LAKE BREEZE AND EASTERLY WINDS FRIDAY AFTERNOON. CMS

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

MAIN FORECAST CONCERN AND CHALLENGE WILL BE WIND DIRECTIONS THRU
THE PERIOD. WINDS ARE GENERALLY LIGHT SOUTHEASTERLY ACROSS THE
AREA EARLY THIS AFTERNOON WITH SPEEDS UNDER 10KTS THOUGH THERE IS
SOME VARIABILITY TO THE WIND DIRECTIONS. A LAKE BREEZE HAS FORMED
ACROSS FAR NORTHEAST IL. THIS LAKE BREEZE MAY TURN WINDS A BIT
MORE EASTERLY...IF IT MAKES IT TO ORD/MDW...BUT SPEEDS SHOULD
REMAIN UNDER 10KTS. SPEEDS WILL DIMINISH A BIT THIS EVENING WITH
SOUTHERLY WINDS EXPECTED FRIDAY MORNING. LOW PRESSURE OVER THE
PLAINS WILL MOVE TO NORTHEAST IA BY FRIDAY EVENING. THE GRADIENT
WILL TIGHTEN FRIDAY AFTERNOON WITH SOUTH/SOUTHEASTERLY WINDS
AROUND 10KTS FRIDAY AFTERNOON. ITS POSSIBLE A LAKE BREEZE WILL
REACH ORD/MDW MID/LATE FRIDAY AFTERNOON TURNING WINDS MORE TO THE
EAST/SOUTHEAST WITH THE POTENTIAL FOR 10KTS WITH THIS LAKE BREEZE.

ANY PRECIPITATION FROM THE APPROACHING LOW PRESSURE SHOULD BE
AFTER THE 30 HR ORD TAF AND PERHAPS EVEN AFTER 00Z AT RFD. SOME
LIGHT/SHALLOW GROUND FOG IS POSSIBLE OVERNIGHT INTO FRIDAY
MORNING. NOT EXPECTING ANYTHING TOO WIDESPREAD AND CONFIDENCE IS
LOW SO NO MENTION WITH THIS FORECAST.

CU/STRATOCU MAY BE SLOW TO SCATTER OUT ACROSS FAR NORTHEAST IL AND
NORTHWEST INDIANA THIS AFTERNOON BUT CIGS SHOULD REMAIN AT OR JUST
ABOVE 3KFT. CMS.

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM FOR WINDS THRU THE PERIOD. CMS

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

FRIDAY NIGHT...SHRA AND CHC TSRA. MAINLY VFR. SOUTHEAST WINDS.

SATURDAY...SHRA AND SCHC TSRA. MVFR OR LOWER PSBL. SOUTH WINDS
BCMG NORTHWEST OVERNIGHT.

SUNDAY...VFR. NORTH WINDS BCMG SOUTH OVERNIGHT.

MONDAY AND TUESDAY...VFR. SOUTH WINDS.

WEDNESDAY...VFR. SOUTHEAST WINDS.

JEE

&&

.MARINE...
225 AM CDT

HIGH PRESSURE IS OVER THE LAKE THIS MORNING AND IT WILL SLOWLY DRIFT
EAST THROUGH FRIDAY AFTERNOON.  VARIABLE WIND DIRECTIONS ACROSS THE
LAKE WILL BECOME MAINLY SOUTH BY THIS EVENING AS THE HIGH SHIFTS
EAST.  THE NEXT LOW IS OVER THE CENTRAL PLAINS...AND WHILE GUIDANCE
STILL DIFFERS ON THE EXACT PATH OF THIS LOW...SIDING WITH THE
MAJORITY OF GUIDANCE MEMBERS THAT TAKE THE LOW OVER THE CENTRAL
PORTION OF THE LAKE SATURDAY.  SOUTHEAST WINDS INCREASE TO 20 KT
OVER THE SOUTHERN TWO THIRDS OF THE LAKE FRIDAY NIGHT AND SPREAD TO
THE WHOLE LAKE BY SATURDAY MORNING. AS THE LOW MOVES OVER THE
LAKE...WIND DIRECTION WILL VARY FROM EAST OVER THE NORTHERN END TO
WEST OVER THE SOUTHERN END.  THE LOW DISSIPATES OVER THE EASTERN
GREAT LAKES SUNDAY WITH A BROAD HIGH PRESSURE SYSTEM REMAINING OVER
THE LAKE THROUGH NEXT WEEK. LIGHT WINDS BECOME SOUTH MONDAY THROUGH
AT LEAST MID WEEK.

JEE

&&

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

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.