339
FXUS63 KLOT 042309
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
609 PM CDT SAT APR 4 2020
SHORT TERM
239 PM CDT
THROUGH SUNDAY NIGHT...
HIGH PRESSURE HAS BECOME ESTABLISHED ACROSS THE UPPER MIDWEST
THIS AFTERNOON, WITH INCREASING SURFACE PRESSURE AND DRY ADVECTION
SLOWLY WORKING TO ERODE STRATUS CLOUDS FROM THE NORTHWEST. AREAS
IN THE CLEAR HAVE BEEN ABLE TO SNEAK INTO THE 50S, WHILE IT
REMAINS A SLOW CLIMB ELSEWHERE. EXPECT MOST AREAS TO EXPERIENCE
SOME CLEARING, THOUGH IN NORTHWEST INDIANA IT MAY BE A RACE
BEFORE SUNDOWN.
THE SURFACE HIGH WILL SHIFT OVER THE GREAT LAKES TONIGHT INTO
SUNDAY AND RESULT IN QUIET AND SLIGHTLY WARMER CONDITIONS ACROSS
THE AREA AS MORE SUNSHINE WILL BE THE RULE. WE WILL HAVE SOME
MID-LEVEL CLOUDS OVERNIGHT AND INTO EARLY SUNDAY AS A WEAK
VORTICITY MAXIMUM ALONG THE IOWA/MISSOURI BORDER WILL SLIDE
THROUGH THE LOCAL AREA. OTHERWISE WITH MORE SUN THAN CLOUDS
TEMPERATURES WILL REBOUND TO THE 50S AWAY FROM THE LAKESHORE IN
THE ONSHORE FLOW REGIME.
KMD
LONG TERM
320 PM CDT
MONDAY THROUGH SATURDAY...
THE MAIN CONCERN IS THE OCCASIONAL THREAT FOR THUNDERSTORMS MONDAY
PM THROUGH TUESDAY EVENING AND POSSIBLY AGAIN WEDNESDAY AFTERNOON
AND EVENING. THIS INCLUDES A RISK FOR STRONG TO SEVERE
THUNDERSTORMS MID TO LATE TUESDAY AFTERNOON INTO TUESDAY EVENING.
A WARM FRONT WILL BE LOCATED WELL SOUTH OF THE CWA ON MONDAY
MORNING, ACROSS DOWNSTATE ILLINOIS. TEMPERATURES LOOK TO REACH THE
60S FOR MANY AREAS, EXCEPT THE ILLINOIS SHORE, WHICH WILL HOLD
ONTO ONSHORE FLOW UNTIL LATE AFTERNOON. ON MONDAY AFTERNOON AND
EVENING, LOW AMPLITUDE MID AND UPPER RIDGING OVER THE MIDWEST MAY
BE TOPPED BY A LEAD SHORT- WAVE IN WEST- NORTHWEST FLOW ALOFT. THE
GUIDANCE CONTINUES TO INDICATE THAT A PLUME OF VERY STEEP MID-
LEVEL LAPSE RATES (8+ C/KM IN 700-500 MB LAYER) WILL BE ADVECTED
EASTWARD, WHICH SHOULD YIELD SUFFICIENT MUCAPE FOR A THREAT FOR
SCATTERED EMBEDDED THUNDERSTORMS OVER THE REGION, PERHAPS IN A
LOOSELY ORGANIZED MCS.
ON THAT NOTE, THERE IS VARIANCE IN THE MAGNITUDE OF MUCAPE
REALIZED OVER THE CWA. WITH THE EXTREMELY STEEP MID-LEVEL LAPSE
RATES BUT POSSIBLY MORE LIMITED MOISTURE ALOFT WITH
EAST/NORTHEASTWARD EXTENT, THERE MAY BE A SHARP MUCAPE GRADIENT
ACROSS THE CWA. WILL NEED TO WATCH FOR POTENTIAL THAT THE
CONVECTION RIDES THIS GRADIENT, WITH BEST CHANCE FOR STORMS IN
WEST/SOUTHWEST CWA AND POINTS SOUTHWEST, ROUGHLY AS DEPICTED ON
12Z ECMWF. GIVEN THE UNCERTAINTY, DID CARRY CHANCE THUNDER MENTION
ACROSS THE CWA, AND LIKELY POPS FROM THE NBM. IF HIGHER MUCAPE
WITH LITTLE/NO MUCIN ARE REALIZED OVER PORTIONS OF THE CWA,
EFFECTIVE DEEP LAYER SHEAR COULD TICK UP TO 30-40 KT, WHICH MAY
SUPPORT AN ISOLATED SEVERE HAIL RISK IN STRONGEST STORMS.
LOOKING AHEAD TO TUESDAY, SURFACE WARM FRONT WILL BE LIFTING
NORTH, CARRYING DEW POINTS INTO THE LOWER 60S FOR MANY AREAS BY
MID DAY. ANY EARLY MORNING ELEVATED CONVECTION SHOULD HAVE EXITED
OFF TO THE EAST AND SOUTHEAST. A VERY STRONG EML WITH MID-LEVEL
LAPSE RATES AT OR ABOVE 8C/KM WILL STILL BE IN PLACE OVER THE
AREA, WHICH WOULD LIKELY PRESENT A CAP TO THUNDERSTORM DEVELOPMENT
FOR PART OF THE DAYTIME AS THINGS STAND NOW. A SURFACE LOW
PRESSURE SYSTEM WILL TRACK FROM THE NORTHERN PLAINS TO THE
CENTRAL LAKES, TIED TO A MID-LEVEL SHORT-WAVE AND SPEED MAX. THIS
WAVE WOULD THEN POTENTIALLY APPROACH TOWARD EARLY EVENING,
PROVIDING HEIGHT FALLS AND COOLING ALOFT TO ERODE THE CAP, WITH
LOW LEVEL CONVERGENCE FROM SURFACE COLD FRONT. ASSUMING WE ARE
CAPPED AND DRY OUT FOR A PORTION OF THE DAY WITH SOME SUN, TEMPS
WILL LIKELY WARM WELL INTO THE 70S PER 850 MB TEMPS IN THE MID
TEENS CELSIUS.
AFOREMENTIONED SET-UP WITH TEMPS IN 70S AND AROUND 60/LOWER 60S
DEW POINTS COULD YIELD MODERATE INSTABILITY OF 1000-2000 J/KG
MLCAPE. THIS IS CONCERNING AS STRENGTHENING NORTHWEST FLOW ALOFT
WITH APPROACHING WAVE LATER IN THE DAY/EARLY EVENING MAY SUPPORT
40-50+ KT OF DEEP LAYER BULK SHEAR AND A STRONGLY VEERING PROFILE.
THIS PERIOD WILL BE ONE TO WATCH FOR NORTHWEST FLOW STRONG TO
SEVERE THUNDERSTORM RISK TUESDAY PM. THE ABOVE DESCRIBED WIND
PROFILES WOULD POTENTIALLY BE SUPPORTIVE OF SUPERCELLS WITH A
LARGE TO VERY LARGE HAIL RISK GIVEN STEEP LAPSE RATES AND LARGE
CAPE IN HAIL GROWTH ZONE. STEEP LOW LEVEL LAPSE RATES MAY ALSO
DEVELOP, POSING A THREAT FOR DAMAGING DOWNBURST WINDS. LOOMING
UNCERTAINTY WITH THIS THREAT PERTAINS TO THE POTENTIAL FOR EML
CAPPING TO HOLD IF THERE IS LESS INSOLATION AND/OR FORCING AND
FRONTAL CONVERGENCE IS NOT ENOUGH TO ERODE THE MLCINH. ECMWF HAS
BEEN MOST CONSISTENT IN FAVORING CONVECTIVE INITIATION, WITH GFS
MORE CAPPED, THOUGH ECMWF DOES HAVE SOLID ENSEMBLE SUPPORT
INCLUDING FROM GEFS. CAPPED POPS IN MID TO HIGH CHANCE RANGE DUE
TO UNCERTAINTY, AND DID ADD SOME 3-HOURLY TEMPORAL DETAIL TO POPS
TUESDAY AFTERNOON.
INITIAL COLD FRONT WILL KNOCK TEMPS DOWN ONLY SLIGHTLY FOR
WEDNESDAY INTO THE 60S TO AROUND 70. A SECONDARY COLD FRONT
WEDNESDAY EVENING/NIGHT WILL BRING A HEALTHIER SURGE OF COOLER
AIR. THE MODELS AND ENSEMBLES HAVE TRENDED TOWARD A STRONGER
SIGNAL FOR RAIN SHOWERS WITH THIS SECONDARY FRONT, SO HAVE
INCREASED POPS INTO CHANCE RANGE. CAN'T RULE OUT ISOLATED
THUNDERSTORMS WITH THIS ACTIVITY, BUT HAVE REFRAINED FROM MENTION
IN THE GRIDS. THURSDAY WILL HAVE BREEZY-WEST NORTHWEST WINDS AND
TEMPS ONLY IN IN THE UPPER 40S TO AROUND 50, FOLLOWED BY YET
ANOTHER REINFORCING SHOT OF COOL AIR FOR FRIDAY, WHICH MAY STAY IN
THE 40S CWA WIDE ALONG WITH CONTINUED BREEZY NORTHWEST WINDS.
AFTER A LIKELY UNSEASONABLY CHILLY FRIDAY NIGHT, TEMPERATURES ON
SATURDAY WILL MODERATE BACK TO THE 50S.
CASTRO
AVIATION
FOR THE 00Z TAFS...
MVFR CIGS CONTINUE TO PUSH SOUTH OF THE REGION, BUT ANTICIPATE A
QUICKLY-ADVANCING MID-LEVEL (VFR) DECK WILL OVERSPREAD THE
TERMINALS THROUGH THE MID TO LATE EVENING HOURS. VERY DRY AIR IN
THE LOWEST 10 KFT SHOULD PRECLUDE ANY PRECIPITATION WITH THIS
INCOMING DISTURBANCE. THERE ARE SOME SIGNS OF SOME PATCHY BR
DEVELOPMENT LATE THIS EVENING AND OVERNIGHT, BUT THE CURRENT
THINKING IS THAT THE EXPANSIVE DECK OF MID-LEVEL CLOUD COVER WILL
CURTAIL THIS POTENTIAL WITH NO FORMAL MENTION IN THE TAFS AT THIS
TIME. RFD MAY CLEAR OUT A BIT QUICKER LATE TONIGHT, SO WE MAY NEED
KEEP AN EYE ON VISIBILITY TRENDS THERE.
OTHERWISE, NORTHEAST WINDS SHOULD BECOME A BIT MORE NORTHERLY OR
EVEN NORTH-NORTHWESTERLY TONIGHT AT ORD/MDW, BUT SPEEDS ARE
EXPECTED TO REMAIN UNDER 5 KTS. SYNOPTIC HIGH PRESSURE BUILDING
DOWN THE LAKE ON SUNDAY WILL ENHANCE A LAKE BREEZE PUSH THROUGH
THE MID-LATE MORNING HOURS WITH A REINFORCEMENT OF NORTHEASTERLY
WINDS.
CARLAW
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
VISIT US AT WEATHER.GOV/CHICAGO
FOLLOW US ON FACEBOOK, TWITTER, AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page