Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
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 200755
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
255 AM CDT MON APR 20 2015

.SHORT TERM...
228 AM CDT

THROUGH TUESDAY...
COVERAGE OF RAIN CONTINUES TO DIMINISH EARLY THIS MORNING...WITH
THE LOW PRESSURE POSITIONED OVER SOUTHWEST LOWER MICHIGAN. THE
PRESSURE GRADIENT IS MINIMAL...ALLOWING PATCHY FOG AND LOW CLOUD
BASES TO DEVELOP. FORTUNATELY THIS WILL ONLY BE TEMPORARY...AS
JUST WEST OF THE FORECAST AREA THE GRADIENT QUICKLY INCREASES.
WINDS UPSTREAM ACROSS MN/IA HAVE BEEN GUSTING FROM THE NORTHWEST
BETWEEN 25 AND 35 MPH. AS THE LOW CONTINUES TO LIFT NORTHEAST THIS
MORNING...THE WRAP AROUND MOISTURE OVER NORTHEAST IA WILL PIVOT
EAST AND CLIP THE NORTHERN PORTIONS OF THE FORECAST AREA BEFORE
LIFTING NORTHEAST. DRY AIR REMAINS WELL NORTHWEST OF THE FORECAST
AREA...SO IT LOOKS LIKE THE BULK OF THE MORNING WILL FEATURE
ABUNDANT SOLAR SHIELDING. COLD AIR WILL STEADILY ADVECT SOUTHEAST
ACROSS THE REGION...WITH TEMPS STRUGGLING TO WARM MUCH FROM THE
EARLY MORNING LOWS OF THE MID 50S. ENOUGH DRY AIR SHUD FINALLY
ARRIVE ARND SUNSET TO START THINNING THE CLOUD SHIELD...WHICH WILL
ONLY ALLOW OVERNIGHT LOWS OF THE UPR 30S TO ARND 40.

500MB VORT WILL SLOWLY PUSH EAST ACROSS THE WESTERN GREAT
LAKES...REACHING LOWER MICHIGAN TUE MORNING. THE WEAK RIDGING ACROSS
THE NORTH ATLANTIC WILL SLOW THE DEPARTURE OF THE 500MB TROUGH
AXIS...WHICH WILL MAINTAIN A STEADY NORTHWEST FLOW ACROSS THE
FORECAST AREA. A WEAK EMBEDDED VORT WILL ROTATE SOUTHEAST ACROSS THE
UPPER MIDWEST TOWARDS SOUTHERN WISC...WHICH COULD BRING ANOTHER
PERIOD OF LIGHT SHOWERS TUE AFTN. THE SFC MAY WARM A TOUCH WITH THE
THIN CLOUD COVER...ENOUGH TO CREATE SOME INSTABILITY SHOWERS AS THE
LAPSE RATES SHUD STEEPEN MARGINALLY. HOWEVER AT THIS TIME IT DOES
NOT APPEAR TO BE UNSTABLE ENOUGHT TO WARRANT ANY MENTION OF THUNDER.
HIGHS WILL ONCE AGAIN REMAIN UNSEASONABLY COOL IN THE LOW/MID 50S.

BEACHLER

&&

.LONG TERM...
228 AM CDT

WEDNESDAY THROUGH SUNDAY...
THE PATTERN HAS CHANGED BACK INTO A NORTHWEST FLOW...AS A HIGH
LATITUDE BLOCK DEVELOPS AND MAINTAINS THE 500MB VORT OVER THE
GREAT LAKES/ONTARIO/QUEBEC THRU FRI. ENSEMBLES MAINTAIN MINIMAL
SPREAD AMONGST SOLUTIONS THRU FRI...INDICATING MODEST WEAKENING TO
THE INTENSITY OF THE TROUGH. BY THE WEEKEND THE TROUGH WILL BE
SHIFTING TO THE EAST COAST...WHICH WILL ALLOW A SLIGHTLY LESS
AMPLIFIED FLOW FOR THE GREAT LAKES.

SFC RIDGING IS POISED TO SLIP SOUTHEAST FROM CENTRAL CANADA
WED...AND BRING DRY/COOL WEATHER WED-SUN. THE SOUTHERN STREAM SHUD
REMAIN WELL SOUTH. OVER THE UPCOMING WEEKEND SOLUTIONS INDICATE THE
SOUTHERN STREAM MAY BUCKLE AND LIFT PRECIP NORTH INTO THE OHIO
VALLEY...HOWEVER THIS APPEARS TO BE A LOW CONFIDENCE SCENARIO AT
THIS TIME. DESPITE THE UNSEASONABLY COOL WEATHER FOR MID-WEEK...THE
LESS AMPLIFIED FLOW FOR THE WEEKEND SHUD ALLOW TEMPS TO APPROACH
SEASONAL CONDS ARND 60.

OVERNIGHT LOWS WILL ALSO BECOME A CONCERN...ESPECIALLY WED NGT AND
THUR NGT. GUIDANCE CONTINUES TO SUGGEST LOWS MAY DIP INTO THE LOW
30S. WITH LIGHT WINDS DEVELOPING...PATCHY FROST MAY DEVELOP AND A
FEW LOCATIONS COULD SEE FREEZING CONDITIONS AS WELL.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* WINDS BACKING NORTHWEST LATE THIS EVENING.

* A PERIOD OF SHOWERS MONDAY MORNING.

* LIFR CIGS LASTING INTO OVERNIGHT WITH SLOW IMPROVEMENT DURING
  THE DAYBREAK TIME.

* MVFR VISIBILITY THROUGH THE EARLY MORNING HOURS.

* GUSTY WEST WINDS DEVELOPING MONDAY MORNING WITH MAX GUSTS ARND
  30 KT LATE MONDAY MORNING AND AFTERNOON.

KMD

//DISCUSSION...UPDATED 06Z...

IFR/LIFR CIGS ARE COMMON ACROSS THE AREA ON THE BACK SIDE OF THE
STRENGTHENING SURFACE LOW. VSBYS HAVE NOT DIPPED TOO FAR...HOLDING
AT 3-4SM AND LARGELY BETTER THAN THAT IN MOST AREAS THE LOW
CONTINUES NORTHEAST...EXPECT WINDS TO VEER TO SW. NOT EXPECTING
VSBYS TO DROP MUCH FURTHER AS WINDS STAY UP TONIGHT...THOUGH IFR
VSBYS ARE SLIGHTLY POSIBLE...BUT CIGS ARE EXPECTED TO HOLD IN THE
LIFR/IFR CATEGORY DUE TO A LOW LEVEL MOIST AXIS EXTENDING ACROSS
INTO IOWA.

A COLD FRONT WILL ADVANCE EAST TOWARD THE TERMINALS MONDAY
MORNING. TIME HEIGHTS SUGGSEST A GRADUAL LIFT IN CIGS BACK INTO
MVFR AFTER DAYBREAK...BUT A DIMINISHING TREND IN THE TRACKING OF
SHOWERS ACROSS THE TERMINALS THIS MORNING HAS BEEN SEEN IN LATEST
HI-RES MODEL RUNS. SO THE PERIOD OF -SHRA MENTIONED IN THE TAFS
MAY BE A BIT OVERDONE IN THE LENGTH OF TIME. OF MORE CONCERN ARE
THE WESTERLY WINDS THAT WILL GUSTS INTO THE 20S AND POSSIBLY NEAR
30 KT BEHIND THE COLD FRONT THAT WILL MOVE THROUGH DURING THE
LATTER HALF OF MORNING PUSH.

KMD

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN WIND DIRECTION THROUGH THE TAF. MEDIUM-HIGH IN SPEED.

* HIGH IN RAIN INITIAL TIMING THOUGH LOW IN DURATION.

* HIGH IN CIGS AND DURATION. MEDIUM IN CIGS ONLY DROPPING AS FAR
  AS 400-500FT.

* MEDIUM IN VISIBILITY TRENDS AND VISIBILITY DROPPING NO MORE THAN
  TO 3SM.

* MEDIUM IN CIGS/VISBYS AND SHRA DURING THE MORNING RUSH ON
  MONDAY.

KMD

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

TUESDAY...SLIGHT CHANCE OF SHRA AND MVFR. GUSTY WEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY-SATURDAY...VFR. WINDS BECOMING NORTHEAST.

MTF

&&

.MARINE...
247 AM CDT

DEEP LOW PRESSURE ALONG THE EAST SIDE LAKE MICHIGAN WILL CONTINUE
NORTH INTO SOUTHWEST ONTARIO TODAY. BEHIND THE LOW...A TRAILING
TROUGH AXIS AND COLD FRONT WILL MOVE OVER THE LAKE BRINGING A
PERIOD OF WEST WINDS TO 30 KT FOR THE NEARSHORE WATERS. ANOTHER
SECONDARY LOW ON THE BACK SIDE OF THIS SYSTEM WILL CREATE A
SIMILAR SETUP FOR TUESDAY. WINDS MAY BE A TOUCH STRONGER WITH THIS
LOW AS IT BRINGS A REINFORCING SHOT OF COLD AIR. RIGHT NOW
CONFIDENCE IS LOW ON GALES...THOUGH WINDS TO 30 KT SEEM A DECENT
BET FOR MUCH OF THE LAKE. HIGH PRESSURE IN THE CANADIAN PRAIRIES
AND EXTENDING SOUTH INTO THE UPPER MIDWEST WITH LOW PRESSURE IN SE
CANADA WILL CREATE A PERIOD OF WNW WINDS ACROSS THE LAKE.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM MONDAY TO 9 PM MONDAY.

&&

$$

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.